Is local always better?

As those that have followed the blog for awhile are aware, among my pet peeves are some of the naïve statements that are repeated ad nauseam by proponents of native plants for landscaping. You know the usual litany: natives don’t need water, don’t need fertilizer, resistant to insects, resistant to diseases, yada, yada… According to the dogma, native plants possess these traits because they’ve evolved here and they belong here. I hasten to point out; I have nothing against natives and think we ought to plant more of them whenever they are an appropriate choice.  The problem, of course, with the typical native company line is that these statements are so obviously nonsensical they undermine the credibility of native plant advocates. Adaptations to resist environmental stress, for example, are a function natural selection and evolution. There are lots of droughty environments in the world; why should we assume that only local plants will be adapted to drought? Then there is the obvious problem of disturbed environments. Why should we assume that trees that have evolved in native woodlands will be good street trees?  In fact, often they’re not.


Torryea taxifolia

But a new and potentially contentious argument is emerging in the ‘Is native better?’ discussion:  Assisted migration.   The basic premise of assisted migration (also referred to as assisted colonization) is that climate is changing faster than many organisms, especially long-lived organisms like trees, can evolve.  Therefore to prevent species extinctions we should pro-actively move species (typically northward in the Northern hemisphere) so they will be in a better place as the world gets warmer.  Sound far-fetched?  Some of this is already occurring.  In Florida a group called the Torreya Guardians has already taken it upon themselves to establish populations of a threatened conifer, Torreya taxifolia, in the southern Appalachians, outside of its native range in the panhandle of Florida.  In British Columbia, the provincial forest service is beginning to incorporate climate change scenarios into its tree improvement and development plans; trying to identify seed sources and species adapted to climates predicted throughout the 21st century.


Is local better?  Foresters often see significant growth gains by moving seed sources northward.  Will climate change increase this effect?

Clearly assisted migration is a controversial topic fraught with all kinds of uncertainties.  Is climate really changing?  How fast will it change?  What about unintended consequences?  Could the assisted species out-compete a local species that would’ve been OK otherwise?  And then there are those who might wonder aloud about the hypocrisy of embracing species movements when they’re done by conservation biologists but not by horticulturists.

Cake and Cultivars

I was working on something entirely different, but thought better of it. I’d like to continue Bert’s (now Dr. Mister Smartypants) really intriguing discussion.

Because when I read it, I felt a pang of…guilt? Confusion?

I’d describe my usual perspective on the “native” topic as ultra-liberal, highly plant-introduction-centric. New plant? Gimme!!! (“Native” shall appear in this post surrounded by quotes throughout, as a safety measure.)

Commenter Wes perceptively noted “part of the gardening public is becoming so enamored with the concept
of natives that I think they are grasping at straws to to assuage their
belief in ecological principal. In my opinion, many want to have their
cake and eat it too.”  As a card-carrying member of the gardening public, yes, I do like using “native” plants, there is some portion of “feel good” to it, and I adore it when a hot new cultivar is also a “native”. And many breeders, propagators, growers, and garden centers would like to assist me with this.

A good example:  the “American Beauties Native Plants” program from a large propagation nursery in Pennsylvania. Some straight species, lots of cultivars, all with marketing materials to match (tags, pots, banners).
Has “Big Plant Introduction and Branding” (really, not that big or scary an entity) co-opted “native”?  Discuss.

Finally, some advice, please:  in our campus garden, we’ve nearly an acre of new plantings in a meadow style that consists of lots of cultivars and some interspecific hybrids; all of “native” plants (even the freakin’ buffalo grass is a cultivar). How in the heck should I refer to these plants, let alone the entire concept, in our educational/interpretive materials?  Any and all suggestions will be considered.

Can cultivars be considered native plants?

One of the questions that arise in discussing native plants is the question of whether ornamental cultivars (e.g., ‘October golory’ red maple) can or should be considered ‘native’.  In short, my answer is ‘No.’

Here’s my rationale on this.  First, when we think about natives we need to put political boundaries out of minds and think about ecosystems. Political boundaries – a ‘Michigan native’ or ‘an Oregon native’ – are meaningless in a biological context.  What’s important is what ecosystem the plant occurs in naturally.  In addition to taking an ecological approach to defining natives we also need to consider its seed source or geographic origin.  Why is it important to consider seed origin or ‘provenance’?  Species that occur over broad geographic areas or even across relatively small areas with diverse environments can show tremendous amounts of intra-species variation.   Sticking with red maple as an example, we know that red maples from the southern end of the range are different from the northern end of the range.   How are they different? Lots of ways; growth rate, frost hardiness, drought tolerance, date of bud break and bud set.  Provenances can even vary in insect and disease resistance.


Native range of red maple

If we’re dealing with an ornamental cultivar, do we know the original seed source or provenance?   Sometimes yes, sometimes no, sometimes maybe.  Think for a minute how most ornamental cultivars come to be.  Some are developed through intentional crosses in breeding programs.  The breeder may or may not know the geographic origins of the plants with which they are working.  Or they may produce interspecfic hybrids of species that would not cross in nature.  Some cultivars are identified by chance selection; an alert plantsperson finds a tree with an interesting trait (great fall color) in the woods or at an arboretum.  They collect scion wood, propagate the trees and try them out to see if they are true to type.  If the original find was in a native woodlot and the plantsperson kept some records, we may know the seed source.  If the tree was discovered in a secondary location, such as an arboretum, it may not be possible to know the origin.


So, if a breeder works with trees of known origin or a plantsperson develops a cultivar from a chance find in a known location AND the plants are planted back in a similar ecosystem in that geographic area, we can consider them native, right?  As Lee Corso would say, “Not so fast, my friend.”  We still need to consider that matter of propagation.  Most tree and shrub cultivars are partly or entirely clonal.  Cultivars that are produced from rooting cuttings; for example, many arborvitae, are entirely clonal.  Cultivars that are produced by grafting, like most shade trees, are clonal from the graft union up.  The absolute genetic uniformity that comes from clonal material is great for maintaining the ornamental trait of interest but does next to nothing to promote genetic diversity within the species.  From my ultra-conservative, highly forestry-centric perspective, the only way to consider a plant truly native, it needs to be propagated from seed and planted in an ecosystem in the geographic region from which it evolved.  Few, if any, cultivars can meet that test.

Why do nurseries sell this plant?

I wish I were more like Holly…wandering around nurseries finding pretty and unusual annuals and perennials to get excited about.  Instead, I seem to gravitate to plants that annoy me.

Today while looking for some trellises (for those containerized Clematis vines that I’ve been torturing) I saw pots of the Equisetum hyemale (“a tall, evergreen, spreading, reed-like grass”) for sale:


As readers of this blog surely know, Equisetum spp. – or horsetails – are not grasses but primitive relatives of ferns.  That taxonomic blunder aside, the thought of deliberately planting any Equisetum species in a landscape sends shivers down my spine.

Now E. hyemale is not as weedy as E. arvense, but in nearly every seminar I give on controlling weeds with mulch someone asks about getting rid of horsetails.  Short answer – you pull.  And pull and pull.  There’s no good herbicide for them, nothing seems to eat them, and they spread aggressively.

And speaking of eating, did you know that horsetails are poisonous?  They contain an enzyme (thiaminase) that deactivates thiamin (vitamin B1) in the unfortunate consumer’s body.  The most common victims of horsetail poisoning, ironically, are horses.  Horsetails are considered noxious weeds in pastures used for grazing – and yes, they are native to the United States.

Sure, horsetails are interesting looking plants.  But do you really want something in your garden that the production nursery describes as having “indefinite spread?”  And how does keeping them in a pot, as one production nursery recommends, keep them from spreading spores?  Especially if you plant them “in or around ponds and streams?”

I just think this is such a bad idea for home landscapes.  Even if it is a native species.

Visiting Professor guest post: Native wildflowers

Recently I have been fascinated by the native wildflower field I planted last fall.  Although I seeded it with the same mixture of seeds (mixed with sand to spread them evenly), you can see that we have clumps of different flowers throughout the area.

Figure 1. Descanso Gardens, California

The area where the wildflowers were planted had several 1-2 foot raised mounds; some were in the shape of keyholes.  These were built with silty sand from a nearby seasonal stream that had some erosion problems in a rainy year.

Small differences between the temperature, moisture, light and soil on the different parts of each mound have favored different species of wildflowers.  In one of the keyholes, I even found some miner’s lettuce (Claytonia perfoliata), a species I had not seeded that favors wetter areas.  If I sampled for insects, I bet I might find a similar patchy distribution as well.

As an ecologist/biologist, I am really fascinated by the way that species diversity can be affected by topography, climate, moisture, and soils.  As a gardener, I like that I could create conditions that favor different plants just by moving soil around.  Plus I think that the waves of color are lovely as well.

Rachel Young is the head of the California Garden at Descanso Gardens, just outside Los Angeles.  She has an MS degree in Ecology and Evolutionary biology from UCLA and lectures on various garden and horticulture related topics.

Surviving the desert with beauty and efficiency

I’m away this week for an out-of-state seminar and a little annual leave.   Some of my favorite places to visit this time of year are the high deserts of California.  Today we hiked to Horse Thief Creek, a relatively easy trail in the Santa Rosa Wilderness.  It’s the perfect time of year to see the high desert in bloom, especially with last winter’s substantial rainfall.

In graduate school I became interested in environmental stress physiology, and I still am entranced by the plant kingdom’s ability to overcome nearly every environmental extreme on earth.  Desert ecosystems are particularly harsh, as rainfall is limited to a short period of time, often in the winter or spring.  While many perennials are able to tolerate the subsequent dry season, annual species cannot.  In essence, they escape drought stress altogether by existing only in seed form for most of the year.  Seeds contain relatively little water anyway, and are so protected against environmental extremes that they can remain viable for decades or even centuries.

But back to our desert.  After the rainy season, seeds of annual plants go into overdrive, germinating, growing, setting seed, and dying back all the span of a few weeks.  Thus, the lucky hiker can find an abundance of tiny, brilliant desert annuals when seasons and vacation schedules coincide.

Tomorrow it’s the Salton Sea.  Not sure what we’ll see in terms of plant life, but we’re hoping to catch some of the migratory waterfowl on their journey north.





I’m Saving Myself for Pollination

Let’s take a very brief respite from the socio-religious implications of science, soil testing, and compost tea to ponder a more lighthearted topic. I need a bit of a morale-boost.

You: “O.K. Holly, Spring’s allegedly coming…how about a closer look at some wildflowers?”

Me: “Done!” (fingers snapping)

For a short time in March, forest floors across Eastern North America can be absolutely littered with a multitude of sparkling white flowers.  This very cool little plant, Sanguinaria canadensis, is one of the first wildflowers to emerge in the spring and colonizes deciduous and mixed woodlands.

Flock of bloodroots, open for business at the fabulous Mt. Cuba Center.

A member of the Poppy family, Sanguinaria is a monotypic genus; that is, there’s only one species.  Commonly known as Bloodroot –  mostly.  However, S. canadensis is also known as (and I quote):   Bloodroot, Red Puccoon, King Root, Red Root, Red Indian Paint, Ochoon, Coonroot, Cornroot, Panson, Pauson, Snakebite, Sweet Slumber, Tetterwort. Large Leaved Sandwort, Large Leaved Bloodwort, plus whatever else Aunt Minnie “knowed it by”.

As one of the first wildflowers out of the ground, it’s still darn cold when the Bloodroot flower appears, and they’re quite protective of their private parts. The one leaf emerges at the same time and cups around the flower, helping to protect the fragile blossom from wind, rain, and snow. The petals also close up at night to save the pollen,since in most locations it’s so cold that few insects, save the occasional fly or beetle, are out and about. And as a last resort, they can just “do it themselves”, better described as self-pollination.

I have been pollinated! Victory is mine!

If you break off a stem or piece of the root, out will ooze a reddish-orange juice, hence the common name.  It’s been prescribed for myriad conditions by Native Americans and herbal practitioners.  One of the more interesting properties is that the sap is an escharotic – it kills tissue. Ironically, according to herbal lore, to draw love to you, wear or carry a piece of the rhizome. If attempting this bit of magic, maybe it’s best not carried in one’s pants pocket.

Native vs. introduced species – the discussion continues

I was asked earlier today to comment on the Garden Rant blog regarding the issue of nonnative plants and insect survival, specifically in reference to Dr. Tallamy’s research.  Though I haven’t read his popular book (Bringing Nature Home), I did read one of his most recent papers (DW Tallamy and KJ Shropshire, 2009.  Ranking lepidopteran use of native versus introduced plants, Conservation Biology 23(4): 941-947).  The authors argue that lepidopterans prefer native to alien species for egg laying.  A serious problem I see in this paper is that the authors are literally comparing apples to oranges.  They do not compare effects among species in the same genus (the reasoning is there aren’t enough publications to look at), but among genera.  Thus, they lump at least 179 “alien” woody species into “native” woody genera and compare those to woody genera that are completely alien.  There are only 112 species in the latter.

I would bet that if he separated out these 179 woody species and added them to the alien genera list his findings would be quite different.


Baptisia: Beyond the Blue

The Perennial Plant Association recently released the identity of the PPA Plant of the Year – for 2010 it is Baptisia australis (False Blue Indigo).  Various blogs have noted this (including Garden Professor fave Garden Rant) and I’ve read some interesting comments, both pro and con.

True story: I asked for Baptisia at a small rural garden center years ago; the owner said “Don’t have any; but I think I have a Methodist running around here somewheres…”  Badda-bump.

Me? I think it is a truly wonderful native perennial. I’ve had great success with it in both Zone 7b and 6a and teach it as a “bread and butter” component plant for the mixed border. As a PPA member, it certainly got my vote on the last ballot (beats the hell out of last year’s Hakonechloa macra ‘Aureola’ – hard to say and even harder to grow in the Southeast).

The great thing about the PPA “Plant of the Year” program is not just in the promotion of that particular species, but that it opens the door for other cultivars and hybrids.  Two of my favorites:  Baptisia x ‘Twilite Prairieblues’ [sic] and B. x ‘Solar Flare’. Both were bred and/or selected by that delightful genius Dr.Jim Ault, of the Chicago Botanic Garden, and introduced through the Chicagoland Grows program.  Pictured are plants that are have only one full year of growth after purchase and planting (nice full gallons to start with; from Saunders Brothers nursery, located in the greater metropolitan area of Piney River, Virginia).

x ‘Twilite Prairieblues’ is a cross between B. australis (our PPA winner) and B. sphaerocarpa – a shrubby, tough little guy with yellow flowers. This fortuitous romance yielded quite a jaw-dropping color combination of dusky violet with a yellow keel petal. These puppies are in our campus horticulture garden.

Now take a gander at B. ‘Solar Flare’ – a “complex hybrid, probably open-pollinated” of B. alba (white-flowered), B. tinctoria (yellow-flowered), and B. australis. This is what can happen when a whole bunch of species and hybrids are planted close together (cocktails and/or bees are usually involved). From my own garden:

Buttercup-yellow fades to warm apricot, then to plum – the thing absolutely glows in the late afternoon sunshine.  Gosh, I miss summer…


Are natives the answer?

Last week Jeff kicked off a lively discussion about invasive plants.  Let me state up front that no one on this blog is promoting invasive plants.  But the issues surrounding invasive plants are extremely complex and have profound implications for many groups with whom we work in landscape horticulture and urban and community forestry.  It is essential in these discussions that we separate fact from hyperbole.  In some quarters, lines have been blurred and people fail to make key distinctions and lump exotic, alien, or non-native species together with invasives.  According to the Federal Executive Order on Invasive species “Invasive species” means an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.  All invasives are alien but only a small fraction of alien species are invasive (all humans are mammals but not all mammals are humans).  Nevertheless, there is a temptation to ‘hedge all bets’ and promote only native species for horticultural planting since native plants, by definition, cannot be invasive.  In addition, there is a ‘feel good’ aura that surrounds native plants – if they’re native they must be good – that clouds some of the logic in the argument.

Some examples:

Natives are more stress tolerant and better adapted than exotics.
Really.  If native plants are always better adapted, why do we have invasives?  Shouldn’t the “better adapted” natives out-compete them? Stress tolerance and adaption are a function of natural selection pressures of the environment in which a species or population evolves.  The world is full of stressful environments and, therefore, lots of stress tolerant species.  There is no a priori reason, for example, to believe that a native species needs less water than an exotic.  The ability to withstand drought depends on the particular species in question.  I’ve done a lot of research on stress physiology of Scots pine – few, if any, native species here in Michigan can match it for drought and cold hardiness.  Moreover, as Jeff pointed out, most of our urban and suburban environments no longer reflect native conditions.  Urban heat islands can result in temperatures 10-20 deg. F warmer than the native countryside.  In our research on heat island effects in downtown Lincoln, NE we logged temperatures in tree canopies in excess of 125 deg. F.  These temperatures were coupled that with the usual urban conditions of impervious surfaces and compacted soils – what tree species is native to that ecosystem?

Native restoration?  This nurse-log ecosystem is typical of forests in western Oregon & Washington.  Trying to keep it alive in downtown Portland requires constant mist irrigation..

Native plants are more pest resistant than exotics.  This would be true if native pests were all we had to contend with.  But the exotic pest train has already left the station.  Emerald ash borer, Dutch elm disease, white pine blister rust, chestnut blight, Asian long horned beetle, and sirex wood wasp are here and here to stay.  And their friends are coming.  The continued expansion of global trade will almost undoubtedly mean that exotic pests, for which native trees have not evolved resistance, will become more, not less, of a problem in the future.   Relying exclusively on native trees means more, not fewer, catastrophic tree failures.  Heavy planting of green and white ash, which are both native in Michigan, has resulted in the loss of 30% or more of the urban tree canopy to EAB in some Michigan communities.

Natives increase diversity  This presupposes that exotic species do not or cannot fill niches occupied by natives.  Exotics can certainly add structural diversity and age class diversity to an urban and community forest.  I would also argue that they add to species biodiversity as well.  If we consider an urban community such as Lansing or Detroit, there are maybe six or seven native tree species that we could expect to have reasonable longevity as street trees.  If we expand our choices to include non-natives we can expand the list to twenty or so.  Not a huge number to be sure, but still a better hedge against catastrophic urban tree loss that the ‘native only’ policy.

Where to go from here?  We cannot ignore that fact the invasive plants are a huge economic and environmental issue.  Presently we do not have models that will accurately predict which exotics will become invasive and which ones won’t.  Trees that are demonstrated to be invasive in a given environment need to be dropped from planting programs.  Except for the desert Southwest and parts of the Plains, every region of the country has great native trees that can. and should, be an integral part of their urban and community forests.  While it’s tempting to play it safe and promote natives only, this policy has significant shortcomings.  Urban and community forests provide enormous economic, environmental, and societal benefits.  In order for our urban forests to provide these functions over the long term we need as broad an array of trees species as possible, including appropriate exotics.