Arborists are trained in seminars and texts that rot in trees is bad. Wood decay can constitute a “hazardous condition” which when accompanied by the tree being in a place that has a target and the tree is large, can create a “hazardous tree”. The notion of hazardous trees is a uniquely human construct that has little to do with the ecology of trees, the variety of organisms that utilizes large declining trees, and does not consider what the various defects in trees may be contributing to the environment or forest around that tree in terms of organism habitat. Humans require that trees living near them must perform appropriately otherwise get out the chain saw and make them comply. In the last decade tree care for birds and wildlife has become a popular training subject for arborists in the western United States. In Europe researchers have been popularizing the notion that large trees can become centers of biodiversity because they have many microhabitats that support numerous organisms not found on younger trees. This concept is abbreviated TreM or Tree related Microhabitat.
As trees mature and then decline, they accumulate deadwood, cavities, epiphytic organisms, excrescences, exudates, fungal decay organisms, and even accumulates of soil or pockets of water in branch crotches. Arboriculture practice tends to regard tree defects as having no value, thus we remove dead wood, cut down trees with cavities and condemn trees with wood decay sporophores. It is now accepted that the more “defects” a tree accumulates the quantity and diversity of organisms associated with that individual tree also increases. In this sense old trees become centers of biodiversity within both managed and unmanaged forests.
The health of a forest is not measured only by the quality of the wood it can produce or the number of board feet it can supply, but also by its connections to other organisms that ensure its health over time. Forests are ecosystems and require connections between organisms and diversity of organisms in order to be resilient. These organisms utilize not only living but also dying and declining trees. Ancient trees are often rich in defects and have many TreM’s.
Tree injuries such as storm damaged branches, lightning scars, frost cracks, branch failures and and other damage are all considered TreM’s. While these are functional habitat in forests they may be quickly removed from the urban forest even if they do not pose a hazard. Now that they have apparent value, perhaps we can rethink their removal where and when appropriate.
The TreM concept is derived from trees growing in forests not those in cities. TreM’s may not become a management tool for urban forestry, however there are many lessons to be learned from the TreM concept. The greater the number of microhabitats, the more organisms and connections between organisms there will be. This provides resilience even to urban ecosystems. There is strong evidence that TreM’s serve as a reservoir of organisms in forests helping to maintain their health. Using the TreM concept for non-forest trees will not change how trees are managed for many situations. Risk tolerance often trumps ecosystem services. Greater understanding of TreM’s will perhaps allow us to save trees that do not pose hazards where they would otherwise be disposed of. Some tree managers have tried to create defects in trees to enhance habitat for wildlife. This is not based in science and I do not advocate creating TreM’s for the sake of having them in trees. Fungi and other organisms find their way into trees all too easily. Until we have some science based evidence for the creation of TreM’s, I recommend against it. It’s the whole do no harm thing we have going as plant pathologists. Being aware of TreM’s and evaluating their usefulness in the urban forest is a new area of study.
In their field guide, Butler et al., 2020 describe 47 TreM’s that they further break down into 15 groups and 7 types. The field guide is available on line if you want to find out more about TreM’s. The research on TreM’s is nascent, and restricted mainly to Europe and Canada. This fall we will collect data in the Chiricahua Mountains to add to that body of research as part of the South Western Research Station’s Trees Course to be held the last week of September into early October.
References
Butler, R., T. Lachat, F. Krumm, D. Kraus, and L. Larrieu. 2020. Field guide to Tree-related Microhabitats. Descritpions and size limits for their inventory. Birmensdorf, Swiss Federal Insitute for Forest, Snow and Landscape Research WSL. 59 p. www.wsl.ch/fg-trems
Larrieu, L., Paillet, Y., Winter, S., Butler, R., Kraus, D., Krumm, F., Lachat, T., Michel, A.K., Regenery, B., and Vanderkerkhove, K. 2018 Tree related microhabitats in temperate and Mediterranean European forests: a hierarchical typology fr inventory standardization. Ecologial Indicators, 84: 194-207
In the last week, I’ve driven all the way from western Virginia, where the redbuds are blooming, to Tallahassee, FL, where red clover is everywhere. As I drove through the mountains north of Charlotte NC, I noticed some signs indicating that strong gap winds may blow down the valleys when atmospheric pressure patterns align to produce strong pressure gradients that drive the wind. I have discussed wind before in previous posts (“Who has seen the wind?” and “Does wind chill affect plants?”) so you can find the basics of what causes wind and some of the different kinds of local winds by going to those posts. In today’s article I want to share some different local names for winds and other local weather and invite you to share your own local weather names. Note that this is not a complete list, but I will provide links at the end that prove a bigger sample of all the names that are used around the world to denote different kinds of weather, especially wind.
Local weather names based on topography
Local mountains and valleys can cause a big variety in the types of winds we observe. Generally, these winds can be classified as katabatic winds blowing downhill and anabatic winds blowing uphill. The direction depends on the time of day due to heating but also to large-scale weather patterns that direct the flow of air. Local winds can also occur due to changes in the heights of the ridges so that where the ridges are low, air can spill over the mountains in the gaps between peaks. Winds blowing downslope can also accelerate as they move to lower elevations, increasing their strength. Those winds can be very strong because of the funneling effect of the terrain leading to warnings like the ones I saw on Interstate 77 in the northern North Carolina Mountains. Some of these local winds in other parts of the world are called the Viento Zonda (or Zonda wind) in Argentina, the Williwaw in the Alaskan Panhandle, Karaburan in Central Asia, Chinook wind along the Front Range of the Rocky Mountains in the USA, Mistral in France, and the Warm Braw in the Schouten Islands north of New Guinea. You can read more about each of these by looking online at Wikipedia or other sites (link below). Winds which are affected by topography can provide good sources of steady wind for wind farms.
One of the most interesting large-scale topography-driven winds is the Tehuantepecer in southern Mexico which begins in the Gulf of Mexico (after coming south across North America) as a north wind that crosses the Mexican isthmus and blows through the gap between the Mexican and Guatamalan Mountains. It is so strong that it can be felt as much as 100 miles out to sea. This happens several times a year, especially in winter when the wind is more often from the north, and is amazing to see on https://earth.nullschool.net/ when it happens. In fact, as I am writing this on Thursday (March 28, 2024) it is happening today! How cool is that?
Local weather names based on changes of air mass
Some winds are named for abrupt shifts in atmospheric temperature and humidity when air from a different source region moves in. They can be small-scale changes due to outflows from individual thunderstorms like gust fronts or can be larger-scale changes due to wind blowing an air mass with colder, hotter, or drier characteristics into the area.
Some of the winds associated with drier and dustier conditions occur near desert locations as the wind shifts to bring in air from the desert regions to replace the air that was already there. One of the most common terms for one of these is haboob, which originated in Sudan but is now used in the western U. S. (Haboob basically means “dust storm” in Arabic but sounds a lot more exotic). A haboob is associated with a wall of hot, dusty air that moves into the region from the desert, bringing low visibilities to the region (often resulting in car accidents as drivers caught unawares can be blinded by the sudden change in conditions). Other dry winds include the Khamsin in Egypt and the Red Sea region, the Scirocco in North Africa and the Mediterranean, and the Harmattan in West Africa.
Cold winds include the Blue Norther, a fast-moving cold front that moves in from the north that can send temperature plummeting by 20-30 degrees in a few minutes, the Bora in the Adriatic region, the Khazri in the north Caspian Sea, the Montreal Express in New England, and the Norte in Mexico. In the Southeast US, we have what we call the Wedge, which is a shallow layer of cold air that moves south along the eastern slope of the Appalachian Mountains under northeast flow, bringing clouds, cold weather, and the chance of ice storms to the region in spring. The Wedge is partly due to topography as well, since the cold air is so shallow that it can’t move west over the Appalachian Mountains and thus is forced down to us in parts of the Carolinas and Georgia. Hot dry winds include the Brickfielder in southern Australia, the Leveche in southern Spain, and the Diablo and Santa Ana winds in California, which are also affected by air moving down from the mountains into coastal areas of the state when high pressure dominates the Southwest.
Local winds are associated with thunderstorms
In addition to the wind names associated with topography and change of air quality there are also some names that are tied to smaller weather events like hurricanes and thunderstorms. Those include the Kalbaishakhi in India and Bangladesh, the Bayamo on Cuba’s southern coast, the Pampero in Argentina and Uruguay, the Cordonazo on the west coast of Mexico, and the Borasco in the Mediterranean. Strong winds associated with thunderstorms can cause tremendous damage to gardens, trees, and buildings and can cause problems with flights and road transportation. Since it is spring and we are entering severe weather season for a lot of the US, it’s a good reminder that it does not need to be a tornado to cause significant damage—straight-line winds can be just as severe.
Knowing your local climate is important for gardeners
Anyone who lives for a long time at a location will start to recognize the local weather and climate patterns that govern your local garden conditions. If you are really dedicated, you can even measure these variations. If you know that in certain seasons, you are more likely to experience very dry dusty air, you might consider plants that can survive those conditions with less care. If you live in an area that is subject to frequent strong local winds, you will need to plan your garden to place more wind-resistant plants where the air flow is the strongest or else construct a wind shelter to keep more sensitive plants safe. Buildings can also affect the wind flow and can cause “wind tunnels” where the air is constricted and blows faster in the narrow passage.
Note: For those of you who wonder about the title of this post, Maria (sometimes listed as Mariah) is a fictional wind popularized in “Paint Your Wagon” (Lerner and Lowe, 1951) and by the Kingston Trio (1959). The name may have originated with the 1941 book “Storm” by George R. Stewart according to my colleague Jan Null of Golden Gate Weather Services.
Sources of more local wind information
Here are some websites that have listings of additional
local winds, although none of them is a complete list, I am sure.
Wherever
whitetail deer occur they present a challenge for gardeners. The internet
offers abundant advice on this, but too often it is simplistic gardening myth
such as scattering human hair or planting garlic.
Historically
in deer control literature there have been occasional observations that deer
hesitate to enter an area which looks too small or constrained for rapid
escape. Finally, it came time to acknowledge and test this theory.
Green Island
Preserve and the University of Minnesota Extension set about investigating this
possibility through their Regional Sustainable Development Partnership (RSDP)
program which provides support to community-benefit projects in partnership
with private citizens and organizations. The test site was a 60 acre rewilded
forest inside a small northern city. Deer pressure was heavy with resident herd
numbers varying from 16-30 animals during the trial.
The first issue was defining a “small space” for testing the theory. In all the literature only one other trial of this concept could be found. It was conducted in Wisconsin with traditionally fenced spaces ranging from 15 ft by 15 ft to 21 ft by 21 ft feet during part of one summer. The Minnesota Green Island Preserve and RSDP trial chose 16 feet by 16 feet based upon the dimensions of manufactured, ridged cattle panels. These panels are 50 inches in height and 16 ft long and tend to be readily available at Fleet or Home stores even in suburban areas. If successful, their advantage would be very easy set-up and portability at a reasonable cost.
What was the
result? Over 2 years of trial, this test demonstrated 95% success. Six
micro-exclosures were established and planted within forested and forest edge
locations in a zone of heavy deer pressure. During an observation period of 730
days, only one instance of deer browse occurred inside a micro-exclosure.
This success
rate is more impressive because these fences are not a physical barrier
to deer entry. They are strictly a psychological deterrent. This places them in
much the same class as flashing lights, sound cannon, water spray, etc., but
according to this study’s data, they’re actually more effective. All
psychological deterrents have a failure rate dependent on application,
monitoring, seasonality, rainfall, and more. But micro-exclosures show a low
failure rate, without maintenance. If a deer breach does occur, the solution is
simply to make the exclosure appear even smaller. This can be done by
stretching rope across the center holding noticeable flagging. It can be lifted
off when tending plants.
This is a highly promising discovery which merits further controlled testing by universities and professionals. The Minnesota Green Island Preserve and RSDP trial was specifically targeted to white tail deer predation while other ungulates present browse problems in other geographies. Rabbits were not addressed. However, until further and definitive research is conducted, citizen-scientist gardeners can contribute by testing versions of this method for themselves and adding their data to the general deer-control knowledge base. In using and testing micro-exclosures, gardeners will fare infinitely better than by spreading human hair, interplanting garlic, or buying “ultrasonic” gizmos.
This post was provided by Kent Scheer. Kent is a career sculptor with a side mission for reforestation and environmental compassion. He is the editor of three handbooks on sustainable agriculture resources and owner/ manager of a rewilded pine forest in northern Minnesota created for environmental education and awareness. You can contact Kent at kentscheer@outlook.com.
Continuing
with the theme of Underrated Beneficial Arthropods that I brought up in my
December post about Underrated Pollinators– I will be focusing on the next
category of what I consider the trio of beneficial arthropods (which includes
pollinators, natural enemies, and nutrient cyclers).
Natural
Enemies
Natural enemies are comprised of predatory and parasitic arthropods, in which one or more life stages of the arthropod feed on other organisms, such as garden pests, thereby killing them. Many gardeners are familiar with this group which includes some of our most ‘famous’ predatory arthropods such as mantids, lady beetles, lacewings, etc. This category, however, contains a plethora of beneficials that you may not always think about because most of what they do often occurs behind the scenes.
This is also a very broad category so this post will not be a comprehensive collection of all the natural enemies out there (because there are literally countless) but will have a variety of some of the most abundant, important, and unique. Like the last post it will be grouped by order or major category of Arthropod, where I will go into examples of the rockstars within that category. I will also include several resources at the end which I used to compile this information and encourage those of you who want to dig deeper into the world of natural enemies to take a look.
Flies
Flies (order: Diptera) are an incredibly diverse group of insects which provide a wide variety of different ecosystem services. They undergo complete metamorphosis (which basically means that they have 4 growth stages starting as an egg, and a major transition from their larval form of maggots that turn into pupae, and then into the adults that we recognize as flies). As such, flies also inhabit countless different ecosystems (including terrestrial and aquatic) and can be found on every continent including Antarctica. We learned about pollinating flies in the Underrated Pollinators blog post but, like many of the arthropods that we are going to cover, flies span all 3 of the major categories of beneficial arthropods. We will discuss them a bit more in-depth in the nutrient cycler category, but for this post I wanted to highlight some examples of the cool predatory and parasitic flies that we can find in our yards and gardens.
Tachinid flies [Tachinidae] are dark-colored medium-sized flies that are recognized by the dark bristles covering the body of the adults (which look similar to house flies). This family contains over 8000 described species and can be found on nearly every continent. The cool thing about this group is that every single species of Tachinids has a parasitic larval stage and many are continually utilized as natural enemies of many common pest species. As such, these flies have also been intentionally imported into various locations for biocontrol purposes. The targets of tachinids include a variety of different arthropods including caterpillars, sawflies, grubs, adult beetles, and many more! To learn more about this awesome group of parasitic flies, check out this excellent article on Tachinids written by Susan Mahr of University of Wisconsin-Madison.
Hover flies
[Syrphidae] also known as flower flies or ‘Syrphids’ are another awesome group
(you might recognize them from their shout-out as pollinators in their
bee-resembling adult stage). Larval syrphids can be terrestrial or aquatic. You
may recognize the term “rat-tailed maggots” which refers to the aquatic larval
syrphids that have a breathing tube resembling a ‘tail’ at the end of their
body. They are used in biocontrol of a variety of soft-bodied arthropods
including aphids, mealybugs, thrips, mites, and more. To learn more about hover
flies, check out this excellent resource about their use as
a biocontrol agent from
Cornell University.
True Bugs
True bugs
(Hemiptera and Homoptera) contain a variety of easily recognizable garden
inhabitants that can be characterized by their piercing/sucking mouthparts.
Although there are many plant feeders and common pests in this category
(including aphids, cicadas, mealybugs, leafhoppers, scale insects, stink bugs,
etc.) there are also some excellent natural enemies that don’t always get the
spotlight. Often referred to as ‘Predatory Bugs’, this fierce category of
insects includes assassin bugs [Reduviidae], big-eyed bugs [Geocoridae], minute
pirate bugs [Anthocoridae], damsel bugs [Nabidae], and predatory stink bugs
[Pentatomidae]. They vary in shape and size, but feed in the same way: by
piercing their prey with their mouthparts and sucking out the fluids. Many are,
therefore, excellent biocontrol agents in our yard and garden landscapes. Some
are even commercially available for use in greenhouses and hoop houses/high
tunnels to suppress populations of common soft bodied insect and mite pests. To
learn more about them, check out this great article on Predatory Bugs from Colorado State University.
Wasps
Wasps (order: Hymenoptera) often strike fear in many people who are unaware of the sheer diversity and complexity of this group of insects. You learned about the pollinating wasps in my last Blog post, but there are also several groups of predatory and parasitoid wasps that are commonly found in our landscapes. Predatory wasps include many different species including the commonly known social wasp species (such as yellow jackets, hornets, and paper wasps) but also include countless other predatory species. One group of these common predators includes the striking family of thread-waisted wasps [Sphecidae]. This family includes spider-hunting wasps, cricket-hunter wasps, and katydid wasps. Another common family includes the cicada-killers [Crabronidae] which are a large and intimidating-looking wasp species that are actually harmless to humans. Both of these groups of solitary wasps work similarly by paralyzing their prey (often characterized by their common names) and then bringing their live bodies back to their underground nests for their larvae to feed on.
Parasitoid
wasps are an incredibly large group of wasps which include many species varying
greatly in size and shape. If you’ve seen the movie ‘Alien’ you have an idea of
what the life cycle of these wasps is like. The mother lays her eggs in a
living host (which spans countless species of insects), and her larvae feed on
the host from within, until they emerge as adults. This includes groups such as
braconid wasps [Braconidae], ichneumon wasps [Ichneumonidae], and families such
as Aphelinidae, Scelionidae, Eulophidae, and Trichogrammatidae. Each species of
parasitoid wasp needs another species of host insect in which to complete its
life cycle, and entomologists estimate that there may be hundreds of thousands
of species of these incredible organisms! Many parasitoid
wasp species are important biocontrol agents for some very famous insect
pests (including the Emerald Ash Borer, which those of us in North America are
very familiar with). You can even purchase some commercially available species
of these parasitoids to manage certain pests in your gardens and greenhouses. There
are even hyperparasitoids
which are parasitoid wasps that specifically use other parasitic wasps as
hosts. To learn more about the incredible world of wasps, check out this great
article by Marissa Schuh from University of Minnesota.
Beetles
Beetles
(order: Coleoptera) are one of the most diverse groups of insects and include groups
that fall into each of the three categories of beneficial arthropods. Although
some are pests in their larval and/or adult stages (example: Japanese beetles)
and feed on a variety of different plant structures including leaves, stems/trunks,
fruit, flowers, seeds, and roots. We are also familiar with some of these
predatory beetles (with many shining a spotlight on the easily recognizable and
lovable lady beetles). That being said, there are countless other groups of
predatory and parasitic beetles that can have a significant beneficial impact
on our landscapes.
One example of a large group of these are the predatory ground beetles [Carabidae]. This dark and iridescent family of beetles can vary in size and shape. They have distinct and powerful chewing mouthparts (mandibles) which enable them to be excellent generalist predators and scavengers. The more than 40,000 species (spanning every continent except Antarctica) are common garden-inhabitants and perform invaluable services of biocontrol in agricultural, horticultural, and home garden settings.
In addition to feeding on many insect and mollusc pests, certain host-specific groups of plant-feeding beetles are also used in the biological control of weed species (including many noxious weeds) and reared by insectaries for distribution.
Neuroptera
Neuroptera (derived
from the Greek words meaning “nerve” and “wing”) is an entire order consisting
only of predatory insects! The most famous of this group are the lacewings [Chrysopidae]
(which many gardeners recognize as an awesome predator of many soft-bodied
garden pests). This order also includes other incredible species such as
antlions or “doodle-bugs” [Myrmeleontidae], dobsonflies [Corydalidae],
mantidflies or mantid lacewings [Mantispidae], snakeflies [Raphidiidae], and
more.
Mites
Mites (subclass: Acari) are another often misunderstood group of arthropods. These are arachnids (characterized by 4 pairs of legs and two body segments). Mites feed on countless living and decaying organisms including plants, animals, fungi, yeasts, algae, mosses, and even bacteria. They range in size, though most are tiny and many are even microscopic soil-dwelling organisms. The sheer diversity of mite species (due to their very broad range of ecological roles) indicates that there may be over a million species that have yet to be described.
Many
gardeners recognize some common mite pests (such as the two-spotted spider
mite), but there are countless predatory mite species as well. Predatory
mites [Phytoseiidae] are slightly larger than spider mites, and excellent predators
of spider mites and eriophyid mites which are common plant-gall causing mites.
There are several species used in biocontrol of soft-bodied insect and mite
pests as well as commercially available ones that you can purchase.
Spiders
I am sure that no one reading this post would be surprised to find these amazing arachnids on this list. Although some species are dangerous to humans, most species of spiders will leave you alone, and are incredible predators of lots of indoor and outdoor insect pests. Many humans dislike these 8-legged organisms, though most are still understanding of the important role that they play. Spiders can be strikingly beautiful, colorful, and variable in size and shape. Although some build webs to capture prey, others are active hunters or trappers that capture other organisms on which to feed. Some are even kept as pests (I had 4 tarantulas of my own at one point, and I thoroughly enjoyed observing them daily, and handling the more mild-mannered ones). There is so much that can be said about the incredible role of spiders in our homes, gardens, and natural ecosystems that it would be difficult to condense into a short summary (and may therefore be a separate Blog post in the future since this one is getting pretty lengthy).
Centipedes
Centipedes
span 4 different orders including soil centipedes [Geophiulomorpha], garden/rock
centipedes [Lithobiomorpha], giant centipedes [Scolopendromorpha], and house
centipedes [Scutigeromorpha] all of which are carnivorous. This group of
arthropods is characterized by many body segments, venomous fangs, and 1 pair
of legs per segment. Although many people are creeped out by these ferocious many-legged
beasts, they stay out of the way and eat many common pests in home and garden
landscapes.
I hope that
you enjoyed reading about some of your gardening companions, and if nothing
else: I hope that it broadened your perspective of all the different critters
that share your landscape with you. Stay tuned for my next post in June, which
will cover the third and final category of beneficial arthropods: the nutrient
cyclers.
In the quarter century that I’ve been researching, publishing, and educating on the topic of landscape mulches, one thing has become clear: cardboard should never be used as a mulch. This viewpoint has been of great interest to gardeners; in fact, my earlier post has been the most frequently viewed post since it was published in 2015. I occasionally appended new information to the original post as needed, but the topic deserves an update.
Landscape mulching with cardboard is wildly popular but has no published research to support it.Photo courtesy of Chris Martin on Flickr.
Rather than rehashing what’s been written earlier (which can be found here, here, here, here, and here in addition to the link above), I’m providing information in a Q&A format that might be helpful:
Q: Is there research on using cardboard mulch in home landscapes?
A: Not much. To date, the only peer-reviewed research relevant to landscape soil conditions is our own work published in 2019. The abstract explains the importance of the results to landscape soil health as stated in the abstract (below):
“The orders of magnitude differences in diffusion
coefficients among the mulch materials, however, could negatively impact a
diverse soil environment such as those found in biologically rich landscapes
with higher oxygen demands. Among the mulches tested, wood chips are a
preferred method of mulching in terms of providing best gas permeability,
particularly in landscape conditions.”
This chart (derived from our 2019 study results) demonstrates the increased impairment of gas movement by different mulch types.
Q: Cardboard has been used as a mulch in agricultural production. Why doesn’t that research support using it in landscapes?
Sheet mulches, including black plastic, is frequently used in agricultural production where weed control and maximzing plant yield are the most important concerns. Photo courtesy of Wyoming BLM.
A: The goal in agricultural production is to maximize yield of an annual crop. In contrast, the goal in caring for a permanent landscape is to maintain a healthy soil ecosystem that will support plant life long term. The table below explains these differences in more detail.
Comparative criteria for intensive agricultural production, home vegetable gardens, and managed landscapes
Q: Okay, I understand that science doesn’t support using cardboard as a landscape mulch, but what about my vegetable garden? Isn’t the research on agricultural crops relevant there?
A: The research on agricultural production mulches is more relevant if maximizing yield is your most important goal. But your goals may include maintaining a healthy soil ecosystem, reducing the use of pesticides and fertilizers, and other criteria. Are you concerned about the established negative impacts that cardboard and other sheet mulches have on soil life? If so, then sheet mulches are not a good choice compared to chunky, three-dimensional mulches.
Typical agricultural soil (photo courtesy of Soil Science on Flickr)
Healthy landscape soil (photo courtesy of Jim Downer)
Agricultural soils are devoid of the structure provided by soil organisms such as fungi and roots found in well-maintained landscape soils.
Q: I like reusing cardboard packaging as part of organic weed control. Isn’t that a good enough reason to use cardboard?
A: In addition to interfering with water and gas movement into the soil environment, corrugated cardboard has chemical contaminants that you really don’t want in your soil or even your compost pile. Corrugated cardboard contains environmental contaminants including dioxin and PFAs or “forever chemicals.” No gardener should want to introduce more of these widespread contaminants into their landscape or garden soils.
Recent peer-reviewed publication looking at hazardous chemicals contained in cardboard and other recycled materials.
Table from Fernandes et al. (2023). Compare the levels of contaminants between shredded cardboard and untreated wood shavings.
As I’ve been recommending for nearly a quarter century now, the very best mulch to use for treed landscapes is arborist wood chips. There is robust, peer-reviewed science establishing the benefits of arborist chip mulches in controlling weeds, enhancing growth and establishment of landscape plants, and maintaining a functional soil ecosystem. In contrast, sheet mulches such as plastic, weed fabric, and cardboard have demonstrated negative impacts on the long-term health of landscape soils. Any resource that says otherwise is not paying attention to the research-based facts.
Arborist wood chips protect exposed soil and suppress weeds while supporting desired landscape plants
In this blog I’ve talked several times about El Niño and La Niña and how they affect climate across the Northern Hemisphere as well as their impacts on the rest of the world. We are currently in a strong El Niño with sea surface temperatures in the Eastern Pacific Ocean (EPO) that are much warmer than the long-term average. But underneath the surface the ocean currents are starting to change and the El Niño is expected to swing quickly into the opposite phase, La Niña. That will affect us in North America but also other parts of the world since both El Niño and La Niña are linked to global atmospheric patterns. Since a La Niña Watch was just issued by NOAA this week I will be talking about the changes we can expect to see over the next few months and how those changes will affect gardens and gardeners.
Daffodil crop ready, Andrew Wood , Commons Wikimedia
Review—What are El Niño and La Niña?
El
Niño
and La Niña
are opposite phases of a large-scale atmosphere/ocean pattern that is driven by
temperatures in the EPO. The pattern affects climate in many places around the
globe. It is the biggest driver of seasonal climate in the Southeast and
Pacific Northwest as well as in some other countries, especially in Northern
Hemisphere (NH) winter when it is usually the strongest.
In September 2023 I discussed the
likely impacts of the El Niño that was growing at that time and how
it would affect your winter gardens. The conditions I expected have mostly been
observed, although there are some local differences that are not surprising
considering that each event is unique. Northern states have been incredibly warm
with little snow, while in the Southeast we have had a lot of rain and cooler
(although not frigid) temperatures due to wet soils and a lot of clouds
blocking the sun. California is getting hit by one atmospheric river event
after another, so they are also very wet and are even seeing a lake
in Death Valley. I imagine they will have quite a bloom of spring flowers
when it gets warmer because of the ample moisture. What have you experienced in
your area? Did my earlier column get it right?
How is this season different than a typical El Niño winter?
Even though we have had the swings of El Niño and La Niña (collectively called El Nino Southern Oscillation or ENSO) for thousands of years as evidenced by layers in ice sheets in Peru and ocean sediments, there are other changes that are not cyclical. The rise in global temperature over time is showing up as a warming trend in all seasons but especially in winter. That does not mean we don’t see other swings in climate over time because ENSO and other atmospheric cycles are still occurring, but they are superimposed on the slowly rising temperature associated with increases in greenhouse gases so the cold outbreaks aren’t quite as severe and the warm spells last longer.
Sea surface temperature departure from normal for 2024-2-12.
Plum blossoms starting to bloom, John Morgan, Commons Wikimedia.
In addition, in spite of one cold big outbreak this winter across the eastern United States, most areas have been warmer than normal resulting in an early spring that has brought honeysuckle leaves to my yard more than a week early. You can follow the “green wave” north and see when it gets to your area or verify that it’s already there at the National Phenology Network site. I am concerned about the possibility of having another late frost like 2023 that could impact the peach and blueberry growers in the Southeast since our average last spring frost date is early to mid-March for most of the commercial peach region. There has been enough cold weather for most of the fruit-producing plants to have reached their required number of chill hours, which means the warm weather is making them ready to bloom. While I don’t see another cold outbreak on the horizon for the next few weeks, we have had frosts in the Southeast into April before so we are not out of the woods yet.
ENSO probabilities for 2024 as of mid-February.
When will La Niña begin?
Climatologists predict that El Niño will weaken through spring and we will swing back into neutral conditions by the April through June period. From there most models predict we will move into a La Niña by the June through August period. By NH fall (September through November) there is a 77% chance we will be in La Niña conditions. This has implications for the summer and especially for the Atlantic tropical season since in neutral and La Niña years the number of tropical storms that occur in the Gulf and Atlantic is higher than in El Niño years. Last year despite El Niño we had 20 named storms, much more than the average of 14 events. This was in part due to the unusually warm water. Most of those stayed over the Atlantic Ocean rather than make landfall due to the presence of a strong jet stream high in the atmosphere which disrupted the development of storms farther to the west and prevented a lot of damage to us in the United States. In spite of that, we still had Hurricane Idalia and Tropical Storm Ophelia, both of which caused a lot of damage to infrastructure and agriculture.
With La Niña fully in place by fall, there will be little to stop the development of tropical storms in the Gulf and Atlantic Ocean except for Saharan dust and unfavorable weather patterns in the United States that could at least shunt any storms away from land. Some early unofficial predictions are for 25 or more named storms to occur this year, although the official predictions are still a few weeks away.
Next winter, we can expect La Niña to control a lot of our climate. That means warmer and drier conditions across the southern part of the United States while cold and wet conditions return to the northern states. Here in the Southeast, that means soil could be pretty dry in spring 2025 leading to issues with planting although it will be easier to drive heavy equipment into the fields than I expect will happen this year.
Field with daffodils, Txllxt TxllxT , Commons Wikimedia
What does all of this mean for gardeners in the United
States?
Because of the recent warm conditions associated with rising
temperatures and enhanced by El Niño in northern parts
of the country, spring is coming early to many places. That can be a good thing
if you like flowers and don’t like snow, but it does mean that your early
flowers will still be susceptible to frost damage if we get another cold
outbreak later in March or even into April or May for northern states. So you
will need to be prepared to protect the tender plants if a frost or freeze
occurs.
The end of El Niño and the eventual rise of La Niña also has implications for areas that are affected by tropical systems. This includes the Gulf and East Coasts and areas downwind of those locations but can also include parts of California and the Southwest which can see impacts from tropical systems in the EPO west of Mexico. Rainfall could be hit or miss in the late summer depending on where the storms go. You should prepare well in advance of June 1, the official start of the season, because the warm ocean water could allow tropical storms to develop in May ahead of the “official” start. That means making sure you remove damaged limbs or other objects that could become wind-borne debris, make sure you have adequate drainage for heavy rain, and keep an inventory of your belongings that could be washed or blown away in a storm. Have a family plan to keep in touch and evacuate if you need to, including pets and livestock. You can find a lot of good information on preparing for and recovering from natural disasters in this University of Georgia handbook, even if you are not in Georgia or the Southeast.
While the current warm weather makes gardeners eager to get out in their plots and get started, it’s probably too early to start in most of the country except the most southern areas. But you can dream and start planning for the warmer weather soon to come!
Over the course of this winter there have been several days when the temperature plummeted after the passage of an Arctic front as strong winds blew frigid air into parts of the United States. It can happen in other parts of the world, too. When this happens, the National Weather Service (NWS) often issues Wind Chill Warnings urging people to bundle up before they head outside into the dangerously cold weather. From time to time I am asked if plants also experience wind chill. This week let’s explore how wind does and does not affect plants.
Birch trees in heavy wind and snow in Hemsedal, Norway, Havardtl, Commons Wikimedia.
What is wind chill?
The Oxford Dictionary defines wind chill as “the cooling effect of wind blowing on a
surface”. That is partially correct as a general statement of how the wind
makes you feel, but it is lacking as a scientific definition. A better one is “a quantity expressing the
effective lowering of the air temperature caused by the wind, especially as
affecting the rate of heat loss from an object or human body or as perceived by
an exposed person.” The wind-chill index is a calculated index that tries to
quantify how a strong wind can remove heat from a human or animal body. A low
wind chill indicates that heat is being rapidly removed from the body,
potentially resulting in the lowering of internal temperature and the chance of
frostbite to extremities like fingers, toes, and noses if directly exposed to
the frigid wind.
“Wind chill” is used by the NWS as a way to provide a warning message to people who might be working or playing outside to make sure they are well protected from direct contact with the wind. As a calculated index wind chill cannot be measured directly although there have been some lab experiments in temperature-controlled laboratories that have tried. The formula for calculating wind chill has been changed in the past as science has improved our understanding heat transfer by wind.
When wind blows across a surface, it causes a transfer of energy between the wind, which is at one temperature, to or from the surface which is most likely at a different temperature. If the temperature of the wind is lower than the surface, then heat (which is just a measure of the energy of the molecules at the surface) is stripped from the surface and transferred to the wind. That lowers the energy of the surface and cools it off (note that this is different than evaporative cooling, which is cooling due to evaporation of water from a surface). The faster the wind blows, the quicker the energy is stripped away. In summer, when the ambient air temperature is high, this cooling effect from a breeze off a cooler water body like the ocean may feel pretty good. But in winter, when temperatures are already icy, it may cool off the surface (and by connection, the body beneath the surface) to dangerous levels resulting in frozen cells that are the hallmark of frostbite or hypothermia if the core body temperature is affected.
Plants do not generate internal heat and so are generally the same temperature as the air. Because of this, there is no transfer of heat energy between the air and the plants and so the plants would not experience “wind chill.” However, anything that has an internal source of energy, including humans, animals or running engines, could experience a chilling effect as heat is stripped away from the surface by the wind especially if the warm surface is exposed directly to the cold wind. That is why it is important to wear layers to provide protection from the wind when the wind chill is expected to be extreme since it keeps heat from being removed from the skin. Ranchers help protect their livestock in blizzards by creating wind breaks that reduce the wind speed and so limit the impacts of wind chill on their cattle. Newborn calves may be especially susceptible to wind chill on their ears and may be outfitted with earmuffs to protect them from frostbite.
A calf wears adjustable ear muffs called Moo Muffs to protect its ears from frostbite. (WPR Photo courtesy of Holly Poad), published in the Superior Telegram on January 23, 2020.
What
other impacts does wind have on plants?
Even though plants do not experience wind chill, that does not mean that there are no impacts from the wind. In addition to transferring heat, wind can also transfer moisture from the plant to the air, desiccating the plants if the humidity of the air is low. This can happen at any temperature as long as there is not much water vapor in the air, but we generally think of it happening at high temperatures because the difference between the water content of the plants is much higher than the water vapor in the air. The difference in humidity, like the difference in temperatures, leads to transfer of water out of the plant and into the air blowing over it. It’s not all bad, though–wind blowing through the plant canopy can be a good thing if it keeps humidity levels near the plant low enough to prevent the development of fungal diseases that thrive on very moist conditions, so gardeners should consider wind conditions in their garden when they determine where to place their plants and what to grow.
Winds
can also cause damage to
trees and garden plants. I recently read an article that indicated nearly all
tree trunks break at the same wind speed of around 90 mph (42 m/s),
regardless of species or size. According to the authors, “In
a strong wind, a tree may break through one of three mechanisms. Uprooting can
occur in rain-moistened ground, or if the tree’s roots are rotten. Alternatively,
if the roots can hold, then it becomes the tree trunk that is at risk from
breakage – either through torsion or, more commonly, bending.” Of
course, damage to tree limbs can cause breakage at weak spots as well at lower
wind speeds.
Bent over with the wind (Isle of Wight), Ronald Saunders from Warrington, UK, Commons Wikimedia.
Wind also has beneficial impacts on plants. The gusty nature
of wind causes variable forces on tree trunks and plant stems that increase their
strength by forcing them to resist the wind. That is one reason why you
might not want to stake young trees too tightly, because they need to be
able to move
in the wind to form strong tapered trunks. Wind that blows all the time in the
same direction causes trees and plants to grow in distorted (and sometimes
beautiful) ways as their shapes are formed by those constant winds. Wind also
provides a way to spread pollen from one tree to another, helping to spread
genetic material through a wide area for reproduction.
Pine (Pinus sylvestris) releasing pollen into the wind in Tuntorp, Brastad, Lysekil Municipality, Sweden.
Part of this “candelabra” tree crown failed in a windstorm
The proximity of this tree to a school makes it a high risk
Sometimes trees need to be drastically pruned or removed to prevent damage to property and injury to people.
I’ve been a gardening mythbuster for almost a quarter century. You’d think the quality of information would slowly be improving, given the increased sophistication of many gardeners regarding their information source. But every day my news feed connects me with articles that I’m sure some AI entity thinks will be enlightening. One recent story getting lots of eyeballs is entitled “The Benefits of Girdling a Tree Vs. Cutting It Down.” It makes for a good application of the CRAP analysis. While the link to the publication I’ve provided will go into more detail on CRAP analysis, all you need to know for this post is we’re going to assess Credibility, Relevance, Accuracy, and Purpose of the information.
Urban trees whose roots have been severely pruned should be removed to minimize the risk of failure.
First, let’s consider the Credibility of the source. According to HouseDigest.com, the author is “a plant mom…intrigued by nature and plant life which she exhibits by caring for and doting on her succulents.” Her college degree was in applied biochemistry, which has no substantial connection to applied plant and soil sciences. Bottom line, the author is not an expert in the science of tree care.
Let’s look at Accuracy next (we’ll get to relevance later). The author’s premise that girdling is “another great option” for tree management is grossly inaccurate. The article contains no links to any published research supporting her opinions, and demonstrates a lack of understanding woody plant physiology. The author states that girdling “would prevent erosion from occurring” in contrast to cutting the tree down which apparently removes “the tree roots acting as a protective cover for the soil.” Cutting a tree down removes its crown, but leaves the root system undisturbed. The roots stop transporting water aboveground (there’s no demand for it any longer) thought they can continue to grow as long as they have stored resources. Eventually they will die and their woody structure slowly decomposes.
Erosion’s going to happen any time you have unprotected soil: roots aren’t a “protective covering” (but mulch is)
Girdling the tree, on the other hand, does not prevent root uptake and transport of water through the xylem to the crown of the tree. It does prevent phloem movement of sugars and other resources from the crown to the roots. In other words, roots remain active in transporting water and nutrients but slowly starve to death without phloem-transported sugars and other resources. A good article on the topic of tree girdling goes into more physiological detail on the process that causes trees to decline “before entering an irreversible state of desiccation caused by definitive root death.”
Pine in the center is failing due to girdling from neglected staking. The dying root system is losing its ability to transport water to the crown.
Another possibility is that the girdled tree might send up new shoots below the girdling, leading to the formation of a new crown. Without constant vigilance in removing these new branches, the tree will survive and presumably continue to cause whatever problems that led to the original mismanagement.
Vigorous branch growth occurs beneath girdling. In this case, the girdling was unintentional (neglected staking) but the physiological response is the same.
The author also suggests that girdling is useful in preventing disease spread: “A sick tree would need to be killed in order to prevent the disease from spreading out to other trees and vegetation.” Or, if your trees “are hoarders by nature,” girdling renders them “incapable of taking in nutrients and being a burden to the environment.” Neither of these statements is accurate.
Trees on farmland provide a number of benefits, and the risk to people and property is far lower compared to residential areas.
While the information in this article is somewhat Relevant to homeowners, it does wander into agricultural advice. We’re advised if we have “a danger tree or one that is resting on arable farmland with crops on it, it’s strongly advised that you chop it down and not girdle it. You don’t want an unpredictable girdled tree falling on your harvest, house, or worse — on someone — out of nowhere.”
This Garry oak was killed by lightning about 10 years ago. We kept the snag as a wildlife tree because there was little risk to people or property. It finally came down in the spring of 2023.
At this point it’s worth noting that deliberately killing a tree by girdling also opens the property owner up to legal action should the tree fall and damage property or injure someone. This alone should be enough to dissuade property owners from taking advice from this article. And given the number of years it can take for a girdled tree to die (and eventually fall), is this really a useful process if you need to have a tree removed for some reason?
There are many potential risks associated with trees in populated areas; self-proclaimed experts are poor sources of information for making decisions about tree risk potential.
Finally, what is the Purpose of this article? It’s hard to know exactly why the author promotes girdling, and the language she uses in describing tree care is odd. Statements such as “sometimes circumstances call for trees to be put down and killed” and “trees need to be put down for all kinds of reasons” seem to equate trees with stray animals or dangerous wildlife. It creates an antagonistic situation where none exists.
Tree management, especially when it come to discussions about removal, needs to involve a certified arborist who can assess potential risks associated with leaving, as well as removing, any tree.
Like it or not, the use of AI (Artificial Intelligence) has
become a part of our daily lives. While you might not use AI directly (or you
don’t know that you do) it is now a common part of society, especially in the
online world. Many people, sites, can companies use it to create content. It is
part of the “smart” gadgets that we use at home. Map software (like Google Maps),
search engines, ride share apps, and even the spam filter on your email all use
AI. You’re even more likely to encounter AI on social media and even standard media
these days, with it being used to write articles and text, create ads, and
images.
We know that there’s no getting around it these days. You’ve
probably heard stories about how AI provides incorrect information, steals
content, or might help the robots overthrow humanity today. While it seems to
be the wild, wild west, there are a few (voluntary) safeguards in place now to
prevent the overthrow of humanity (I hope).
Where the real damage is right now is the use of AI to mislead people
outright. There’s also some danger from just lazy use of AI where whoever is
using it to create content just copies and pastes it verbatim without checking
what it actually says.
Gardening misinformation on the internet is nothing new. Gardening misinformation before the internet is nothing new either. But the risk that AI poses is the amplification and multiplication of that information. It is now easier than ever for someone to create online content at the click of a button. And the way that AI works is it scours the internet for existing information to learn how to respond. This new(ish) generation of AI is generative, meaning that it can actually put together information to form something new. Previously, if you did an internet search you would just get a list of websites to read for information. Now AI can use those sites as source material and write the information in a new way – however you prompt it to do. Search engines like Microsoft’s Bing (the much-loathed replacement for the archaic Internet “Exploder”) now have AI built in as a feature. AI is only as smart as what it can learn on the internet, and we all know that while there is good information on the web it is also full of a lot of manure.
Identifying Artificial Gardening Information
First, how can you tell if it is AI generated? At first glance you might not be able to
tell. It is just like any writing. There are tools you can use to try to figure
it out, but you’ll often find that writing from AI doesn’t have personality. It
is often very dry. You can tell it to add humor or any other style to its
writing, but it often misses the mark. When I asked ChatGPT (one of the common
AI platforms) to add humor to something it sounded like I was trying to be
cutesy, like an employee at the famous park in the swamps of Orlando run by a
mouse and not my usual wit, sarcasm, and cynicism. AI often fails to see context
and answers are often very black and white. Which doesn’t work in dynamic systems
like gardening and the environment. AI therefore sticks a lot with generalities
and doesn’t often provide a lot of specific information unless you ask for it.
As an example, I prompted ChatGPT to write “three sentences
about seed starting”. Here’s what it spit out:
Nothing alarming there, but it is pretty dry and isn’t very
informative. It isn’t what I would write. Now, I prompted it to rewrite those
sentences, but to add “humor and wit”. This is what it vomited out:
Vomit, indeed. Though still nothing too alarming. Definitely
too cute and not enough snark.
Where AI generated text falls short is that it incorporates some of that incorrect manure from the web in answers. It doesn’t know that information on the web is incorrect. A few times it told me to put rocks in the bottom of pots for drainage (something we’ve fiercely disproven time and time again).
It told me to practice companion planting (another fallacy we’ve taken on) but it never gave me a lot of details about how to do it.
I did ask it directly about biodynamic gardening, which is the pinnacle of garden misinformation. It gave an amazingly nuanced and diplomatic response, which is much closer to what I’d actually say and much nicer than what GP founder Dr. Linda Chalker-Scott would say. (Don’t tell her I said that).
So, nothing too earth shattering in text, but where I think the real risk lies is in AI generated images and videos. It is easier than ever to create images of things that aren’t possible or incorrect and pass them off as real. People often do this to drive traffic – by making wild claims that people must check out or by “rage baiting” people who just have to respond to tell people how wrong something is (it still drives engagement and earns money).
Fake images are nothing new in the gardening world. I can’t tell you how many ads I’ve seen for magical rainbow-colored rose seeds, trees that grow 10 kinds of fruits, and more all before the advent of AI. But now it is easier than ever to create those images at the click of a button.
For an example, I turned to DALL-E, which is a common AI Image generator. I tried to think of things that wouldn’t be possible. My first prompt was “monarch butterfly on a snow-covered flower”. Something that isn’t possible, but that someone might create to make a social media post about something amazing or miraculous that people have to see to believe.
The results look realistic(is) enough, though improbable. But you’d have to know that to not believe it.
Image generated using DALL-E with prompt: monarch butterfly on a snow covered flower
The second test, not so much: “realistic looking tree that has 15 different types of fruits and veggies growing on it”. I had to add the “realistic” because the first results were cartoon-y. It didn’t help much. So, I guess my magical 15 fruit and veggie tree won’t be coming to an online scam shop any time soon.
Image generated using DALL-E with prompt: realistic looking tree that has 15 different types of fruits and veggies growing on it
So, I moved on and created “a grape vine covered with scary
looking bugs”.
Image generated with DALL-E with prompt: a grape vine covered with scary looking bugs
At first glance, the result can look terrifying. But if you
inspect it closely, you’ll see that those bugs have all kinds of legs coming
from all over their bodies. Scary, yes, but realistic – no. But could someone
do something like this to scare people about an invading insect? Absolutely!
Cutting through the Artificial CRAP
GP Founder Dr. Linda C-S has written about using the CRAP test to identify if a source of information is trustworthy. She used it to talk about Jerry Baker, the self-appointed “America’s Master Gardener” who peddled misinformation and garden snake-oil for decades through books and tv shows to earn big bucks. The same principles can be applied now to digital content created by AI to help figure out if the information is reliable. Here are the steps:
C = credibility. What are the credentials of the person or
organization presenting the information? Are they actual experts? Or is it a
random account that doesn’t have ties to a credible source? Does the source
have academic training, or even practical knowledge?
R = relevant. Is the information relevant for home
gardeners? Or does it try to use information other than home gardening, like
production agriculture, to answer the questions. For AI, especially images, I could
also say that R= realistic. Is it something that could actually be true, or is
it a monarch butterfly covered in snow?
A = accuracy. This could lend itself to the realistic assertion, but I see this as more in accuracy of the source of information. Does it site sources, like journal articles, extension publications, USDA reports, etc.? And does the information follow along with trusted information from other sources?
P = purpose. Why is someone presenting this information? In the Jerry Baker example, he was raking in money with books, TV shows, and product promotions. But what benefit does someone get from posting incorrect info on the web? Also, money. Whether you give them a dime, most social media sites and websites generate income by the number of clicks or viewers they have. How do you think people get rich and famous from TikTok? People aren’t paying them to watch them, but they generate income from engagement and interaction. So, creating content that is fanciful to get people to check it out, or even wrong for people to interact with it to rail against it, creates income.
Is all AI bad?
Not necessarily. I mean, the technology is applied in so many ways to solve so many problems. Sure, there is a risk and people do misuse it. But AI can be a powerful and useful tool when used appropriately, when information is checked, and when it isn’t copied and pasted directly. For example. Over most of 2023 I wrote a series of GP articles about plant diseases. No, I didn’t have AI write the article. That would have been wrong. But I did ask my friend ChatGPT to create lists of common diseases for each type of disease to write about. Instead of me having to dig through social media to see what people were asking about, the platform searched to see what the most common diseases that people talked or asked about were, or which ones were most likely to show up on websites. But I took that list, added to it, subtracted from it, and then wrote the article myself. But the more unethical (and lazy) users of AI just copy what it says verbatim without even reading or editing for accuracy. Or even have automated systems that just crank out AI-generated content with no oversight.
In the end, AI isn’t going away. So as savvy gardeners we
just have to know what to look for to “spot the bot”. And always be ready with a shovel to scoop
away the CRAP.
January is here with its resolutions, cold long nights and not that warm days. Winter is a season of rest and survival. The cats and horses have long furry coats, the resident song birds eagerly clean out the feeder every day and the garden beckons. For me Winter is a special season when I can do a lot of fruit tree pruning, especially enjoyed with my daughter. Father-daughter pruning bonding is not to be missed if it’s an option for you. Gardens are tuned to winter as period of rest but the promise of longer days that will initiate the changes that happen in Spring will soon be upon us. In this post I’ll reflect on how plants survive winter and what we can do to help them.
Winter is actually a very dry time of the year in many places and the winter cold that freezes soil leads to dehydration. Plants installed just before winter will not emerge in spring alive w/o moisture in their systems. Mulch is an essential and natural part of winterization for many North American temperate plants. Protecting the root ball of a newly planted perennial is a must do for winter survival. In nature this is accommodated by the deciduous habit of many trees and shrubs, falling leaves are a big part of winterization. In our gardens we can do this with mulch.
Deciduosity
I know deciduosity is not often used but I like to use unusual words so here we go. The deciduous habits of many north American temperate trees enable them and other plants to survive cold, dry, freezing winters. Environmental cues (photoperiod and cooling temperatures) signal trees to drop their leaves (Fadon et al., 2020). Cold temperatures are also required by temperate perennials to invigorate buds and make starch into soluble sugars for strong spring growth. Deciduosity also leads to abundant mulch on the forest (or garden) floor. This protects soil and surface root systems, seeds, perennial herbaceous plants and bulbs and provides an insulating layer under snow, if snow is a thing where you are. When warm temps arrive in Spring the leaves quickly break down as growth under them emerges.
Leaf fall covers the forest floor protecting roots and increasing arthropod diversity in the litter layer.
Solutes
Deciduosity brings certain challenges to woody perennials that donate their canopy to the soil each year. Trees in spring have no photosynthetic organs to supply the energy of growth. That energy has to be stored in the wood and roots as carbohydrates, mostly as starch, at the end of the growing season and before leaf fall. In spring at the end of dormancy when buds grow, these stored carbohydrates convert to soluble sugars and fuel the rebirth of a a new canopy. Having all that stored sugar in cells throughout the plant also reduces the freezing point of water in the cells so that subzero temperatures do not lead to ice crystal formation (and cell death) of the dormant plant.
Seeds
Another way plants survive Winter is by forming seeds. The strategy of annual plants is to “go to sleep” as seeds and “wake up” by germinating. To ensure that seeds don’t germinate too early, they often have inhibitors that need to be washed away by water (Spring thaw), burned by fire (usually summer time), or by scarification (tumbling in the creek etc). Many seeds germinate better after a cold winter than if they were sown without cold chilling. Not all seeds will germinate at the same time as inhibitors delay germination. This ensures that conditions will be right for some of the seeds and thus the species will survive, even thrive in the right place.
Roots
While the above ground part of gardens can be in a dormant state in January, the situation underground is different. Roots respire (break down sugars to get energy for growth) during winter and may grow continuously depending on climate, depth and soil coverage conditions. Roots, just like buds, utilize stored carbohydrates to fuel their growth. If temperatures remain more moderate under the soil they can continue to respire well into winter months. Soils freeze when they lack snow cover or mulch, Reinmann and Templer (2016) propose that roots in frozen soils are less active. Leaf mulches help protect soils from hard freezes.
Snow cover protect soils from freezing and leads to more live roots during spring emergence from dormancy
Am I crazy or What?
I know that a leaf dump on the garden every year is not what many gardeners want to deal with. That is what leaf blowers are for right? Some municipalities even have line items in their budget for disposing of fallen leaves which are some of the most disposed of green waste. Leaves that accumulate on hardscape can be a pollution source accounting for up to 80% of phosphorus pollution in one study (Bratt et al., 2017). It’s best to utilize leaves around perennials and keep them away from streets, gutters and sidewalks. Trees evolved to drop their leaves on the ground and for them to stay there. Finding ways to accommodate this in gardens will lead to a healthier garden and less waste in landfills. Leaves can be mown on turf areas and the biomass will be incorporated into the turf sward (Nektarios et al., 1999) without loss of turfgrass quality. In gardens they can become part of the surface mulch. If you are really crazy, you can grind them in a shredder to make really high quality micro mulch to be used around certain plants or vegetables (we do this with coast live oak leaves of which we have an abundance in California). Stavi, (2020) encourages us to think of fallen leaves as a resource not a waste product. Your garden will benefit.
For more information on leaves please see the other blogs at this site:
A. R. Bratt, J.C. Finlay, S. E. Hobbie, B. D. Janke, A. C. Worm, and K.L. Kemmitt 2017. Contribution of Leaf Litter to Nutrient Export during Winter Months in an Urban Residential Watershed. Environ. Sci. & Technol. 6: 3138-3147 https://pubmed.ncbi.nlm.nih.gov/28215078/
Fadon, E. E. Fernandez, H. Behn, and E. Luedeling. 2020. A conceptual Framework for Winter Dormancy in Deciduous trees. Agronomy10(2), 241; https://doi.org/10.3390/agronomy10020241
P. Nektarios, A.M. Petrovic and D. Sender 1999. Tree Leaf Deposition Effects on Kentucky Bluegrass (Poa pratenses L.), J. of Turfgrass Man., 3:(1) 69-74. DOI: 10.1300/J099v03n01_06
Reinmann AB, Templer PH. 2016. Reduced winter snowpack and greater soil frost reduce live root biomass and stimulate radial growth and stem respiration of red maple (Acer rubrum) trees in a mixed-hardwood forest. Ecosystems. 19:129- 141. https://www.jstor.org/stable/48719251
Stavi, I. 2020. On-Site Use of Plant Litter and Yard Waste as Mulch in Gardening and Landscaping Systems. Sustainability 12(18), 7521; https://doi.org/10.3390/su12187521