Ecosystem services: Am I going to get a bill?

Spent last Friday in a departmental faculty retreat – you know, the “vision thing”  – S.W.O.T. analysis, where are we going to be in five years, etc.  But we actually got some things accomplished. One of the more interesting aspects was discussing trends in horticulture, both popular and practical, and how we could respond. One of the reoccurring themes throughout the day, especially related to urban agricultural/horticulture, was ecosystems services. I’ve heard the term mostly from environmental science and urban forestry folks.  But also seems fairly appropriate for us horticulturists, who are constantly trying to explain what, exactly, we do.

The definition offered by the American Institute of Biological Sciences (“Bringing biology to informed decision making”) is pretty good:

Ecosystem Services are the processes by which the
environment produces resources that we often take for granted such as
clean water, timber, and habitat for fisheries, and pollination of
native and agricultural plants. Whether we find ourselves in the city or
a rural area, the ecosystems in which humans live provide goods and
services that are very familiar to us. [They include:]

  • moderate weather extremes and their impacts
  • disperse seeds
  • mitigate drought and floods
  • protect people from the sun’s harmful ultraviolet rays
  • cycle and move nutrients
  • protect stream and river channels and coastal shores from erosion
  • detoxify and decompose wastes
  • control agricultural pests
  • maintain biodiversity
  • generate and preserve soils and renew their fertility
  • contribute to climate stability
  • purify the air and water
  • regulate disease carrying organisms
  • pollinate crops and natural vegetation”

Horticulture, as a discipline, touches on so many of these areas.

My question to our readers: does the term ecosystem services mean much to you? Or do you consider it jargon, best kept to grant proposals and impact reports?

Striking a Balance

About two weeks ago a reader (Julie) e-mailed me about some young gardeners/farmers and how they believed in a natural balance.  The e-mail read: “Would you mind devoting a blog or two to the philosophy that nature is perfectly balanced and will find a solution to whatever ails it and therefore we do not need to use any chemicals or poisons to fight pests and disease?”

I thought this was a good question, and here’s my quick answer (followed, naturally, by a more long and drawn out answer).  Yes, I do believe that nature will strike its own balance.  Unfortunately this balance won’t always be great for humans.

The more in-depth explanation…..Organisms like diseases, plants and animals do what they have evolved to do.  The plants grow, the insects feed on them, the insect poo goes back into the ground.  The insects get eaten by an animal and then that animal’s poo goes back into the ground – the tree uses the poo as fertilizer — it’s all a big cycle and it works.  If any particular plant or insect gets out of hand then invariably something that eats it will eventually show up and go gangbusters — and all of it goes back to the ground.

For humans who “live off the land” this balance works fine.  They’re not looking for huge yields of food per acre, and they’re willing to forgo certain foods if that food happens to be in short stock in a particular forest in a particular year because of an insect or disease or whatever.  And so insect or disease losses will usually leave them plenty of food to eat.  But modern agriculture is based on large yields per unit area.  That means that the whole balance thing goes out the window.  Likewise, because humans prefer non-blemished food, the whole balance thing gets screwed up too.  So, in the end, we usually end up doing something to get rid of pests.

And then there’s fertility to consider — When we grow crops on a piece of land we take whatever is produced and then eat it or sell it – but rarely do we put our waste back on that land.  What that means is that we’re fighting the balance.  By not recycling our waste we’re taking from the land without returning what we took from it back to it.  So, after a few years, we end up having to fertilize because the land just can’t make up for what we’ve taken and not returned.

Balance is great – I just think that it’s tough to strike a balance with modern agriculture and still feed ourselves.

So, there you have it – my two cents on balance.

In defense of weeds?

Blog reader Shawn sent this link to me yesterday. It’s a pretty short take on a complex topic, but even so I was troubled by the perception that all nuisance weed species are our own fault.

Sure, it’s true that humans have moved plants or plant parts around with them for centuries. Sometimes it’s been deliberate, and sometimes it’s been accidental. But other animals also move plants around, especially seeds. When we draw this kind of distinction between what we do and what other animals do, philosophically we are removing ourselves from the natural world. True, we have technology and all kinds of other human inventions, but as a species we are still part of the biosphere.

Ivy’s little dispersal units – spread by birds

Philosophical issues aside, there’s another part of this blithe acceptance of weedy species that concerns me. Though plants take advantage of animals as a means of dispersal, the rate at which nonnative, weedy species are spreading and colonizing new environments is unprecedented (this is where technology comes in). Ecosystems can adapt to new species and other environmental challenges – but when the rate is accelerated, the adaptive process is impaired. Thus, some native species go extinct when the rate of change is too great.

Ivy left to its own devices in a natural area

These are basic ecological concepts – and we ignore them at our own peril.

Does native matter?

We’ve had lots of lively discussion on my post regarding the Mark Davis et al. comment in Nature on natives and exotics. I have been traveling and otherwise occupied and have not had a chance to comment so I feel a little like the kid that kicked the anthill and then ran away. Fortunately, Holly was gracious enough to forego her post today (I promise to return the favor, Holly!) so I can chime back in.

Obviously there are lots of layers to the debate but one of the main items in the discussion is whether there is an inherent ecological advantage in planting natives over exotics.  At this point the focus always seems to shift to herbivory and the question of whether native insects will eat non-native plants.  There are certainly examples each way; some insects are generalists while others are highly specific.  More importantly, however, plants fill many other roles in the environment beyond serving as food for insects.   Moreover, species composition is just one aspect of diversity.  The ecological function of landscape is also determined by how we manage other factors such as structural diversity and age class distributions.  In his book “Bringing Nature Home” Doug Tallamy shows a picture of a bland, sprawling suburban landscape ( p. 24) and notes “this highly simplified community is made up of a few species of alien ornamental plants that provide neither food nor shelter for wildlife.”  OK, I’ll buy that.  But would the situation change if the blue grass was changed to a native grass kept mowed to 2” and the two widely spaced shade trees were changed to natives?  Doubtful.   The structural complexity; that is, the number and arrangement of grasses, annuals, shrubs, and trees, is likely a bigger driver of ecosystem function than whether the plants are native or exotic.

In his thoughtful comments on the blog post Vincent Vizachero sums up, “I stand by my view that the general heuristic of favoring native plants over alien plants is better than the alternative of not caring about origin at all.”   I can buy that as well, but with the caveat that other factors are equal.  The rub, of course, is that other factors are rarely equal.  And I suppose this is where the pragmatic approach discussed by Davis et al.  resonates with me.  In my position I do a lot of programming on trees for urban and community forests.  I go through a list of criteria to consider for tree selection.  Here are some of the key factors I usually discuss:

Adaptation There is no argument that there are well-documented environmental, economic and social benefits to trees in urban and suburban areas.   But in order to fulfill these roles trees must be able to survive where they are planted.  This means being adapted to abiotic and biotic environmental conditions which are often adverse.  In this region of the country there are some native trees that fit the ‘tough trees for tough places’ bill, such as swamp white oak, bur oak, and honey locust.  Many other natives, especially understory species, are much more difficult to site.

This street planting in Lansing alternated green ash and Norway maple.  

Available space This seems like a no-brainer, but it’s amazing how often this gets overlooked and we end up with too much tree and too little space.  Again, we have some great small native trees; Carpinus, redbud, striped maple.  But these can be limited in their site adaptability.

Ash stumps

Diversity  In Michigan some communities have lost 30% of their tree cover to the emerald ash borer.  Have we learned our lesson about improving species diversity?  Not really.  But we need to keep trying.  Exotic pests are here and here to stay.  Does anyone believe that global trade will decrease in the near future?  Does anyone believe that there will be quantum leap in our ability to detect and intercept hitch-hiking pests?  In order to continue to accrue the benefits of urban and community forests we need to continue to diversify our portfolio; this includes a mix of natives and exotics.  I doubt there will ever be sufficient data to prove one way other, but it seems reasonable to me that an urban and community forest balanced among 20-25 native and exotic species will be better able to withstand the slings and arrows of weather and pests better than one made up of 8-10 natives.

Excerpt from Davis et al. letter to Nature on natives vs aliens

In yesterday’s post I linked to a letter in Nature by Mark Davis and a number of other ecologists on the role and native and alien plants.  Unfortunately the journal requires a subscription.   Copyright laws prevent me from re-printing the entire article, however, below is an excerpt from the conclusion, which I think captures most of their message.

“Most human and natural communities now consist both of long-term residents and of new arrivals, and ecosystems are emerging that never existed before. It is impractical to try to restore ecosystems to some ‘rightful’ historical state. For example, of the 30 planned plant eradication efforts undertaken in the Galapagos Islands since 1996, only 4 have been successful. We must embrace the fact of ‘novel ecosystems’ and incorporate many alien species into management plans, rather than try to achieve the often impossible goal of eradicating them or drastically reducing their abundance. Indeed, many of the species that people think of as native are actually alien. For instance, in the United States, the ring-necked pheasant, the state bird of South Dakota, is not native to the great plains of North America but was introduced from Asia as a game bird in the latter half of the nineteenth century.

“Specifically, policy and management decisions must take into account the positive effects of many invaders. During the 1990s, the US Department of Agriculture (USDA) declared several species of introduced honeysuckles to be alien (harmful), and banned their sale in more than 25 states. Ironically, from the 1960s to the 1980s, the USDA had introduced many of these same species in land reclamation projects, and to improve bird habitats. Recent data suggest that the agency’s initial instincts may have been appropriate. In Pennsylvania, more non-native honeysuckles mean more native bird species. Also the seed dispersal of native berry-producing plants is higher in places where non-native honeysuckles are most abundant (Gleditsch, J. M. & Carlo, T. J. Diversity Distrib. 17, 244-253 (2010).

“Clearly, natural-resource agencies and organizations should base their management plans on sound empirical evidence and not on unfounded claims of harm caused by non-natives. Another valuable step would be for scientists and professionals in conservation to convey to the public that many alien species are useful.

“We are not suggesting that conservationists abandon their efforts to mitigate serious problems caused by some introduced species, or that governments should stop trying to prevent potentially harmful species from entering their countries. But we urge conservationists and land managers to organize priorities around whether species are producing benefits or harm to biodiversity, human health, ecological services and economies. Nearly two centuries on from the introduction of the concept of nativeness, it is time for conservationists to focus much more on the functions of species, and much less on where they originated.”