From "Eradicating Invasives" to Managing ecosystems: social ideas need to have a better match with ecological systems.

The city has just released a management plan to deal with "invasive species", the Invasive Species Management Plan, not yet completely formalized but pretty much there.  It got me thinking about two related issues:

1) "Invasive" is a matter of terminology as much as anything else.  in common usage the word usually means "a newer arrival I don't like" or "a newer arrival that is screwing up something about our present ecosystem."  For example, Ligustrum is "taking over" riparian areas near greenbelts and parks;  the stuff represents over half of the biomass of Blunn Creek Preserve today, displacing possible growth of natives.  The preserve begins to look like an Asian forest rather than a Hill Country forest.  We dont like that esthetically, and it does cause ecological problems (less water retention in soils, etc.).  But the problem with this view of "invasive" is:

            a. almost everything in any ecosystem was an "invasive" at one point.

            b. it can lead to automatic assumption about the "evil" nature of an "invasive".  For example:  soils need leaves to decompose and replenish the nutrients in the soil, as well as hold more water.  It may be that some "invasives" will do that better than "natives" in some areas.  

            c. sometimes a "native" species disrupts things as much or more than an "invasive".  For example, biologist Mark Davis notes in an article in the journal Nature that "the insect currently suspected to be killing more trees than any other in North America is the native mountain pine beetle Dendroctonus ponderosae".  The insect occurs naturally in the forests, but cold weather normally kills off enough of them to keep the population in check.  Global warming is causing less cold that kill them off in the winter, thus they overpopulate and kill more trees than they "naturally" would.  My understanding is that Cedar trees, which are "native", took over land denuded by cattle farming in our area.  Many people claim they are a nuisance, and want to eradicate them, but they "invaded" lands by taking over lands that were otherwise denuded by human use.  Human action allowed them to "invade" oak forests.

            d.  the concept of "invasion" is a human concept, not a biological term.  It was first coined in England in the 1830's to describe non-native plants introduced to that island.  The word "invasive" connotes "threat" and militaristic understandings of natural processes, which in turn suggest militaristic solutions such as "eradication".

            e.  biologists use the term in a more precise way, to indicate a species that has some impact on a local ecosystem that harms the others species in that ecosystem.  Thus some "invasive" species are defined as big problems - for example birds introduced by humans to Hawaii when Europeans conquered it brought germs that killed off about half of the native birds.

            f. on the other hand, some introduced species are not defined as "invasives": wheat, for example, or soybeans - which are grown in the USA for human consumption - were introduced and "invaded" the local ecosystems.  Yet we are not interested in "eradicating" them.  They have a specific use (food) so we do not socially define them as "invasive" (we define them as "agriculture").

            2. We have to deal with an unpleasant fact caused by global warming.  Fellow Sierran and Ex-Com member Bruce Melton points out that  "We are currently smack-dab in the middle of a great forest die-off in the American southwest that extends from the western fringes of the piney woods all the way to the Pacific coast and from the mountains of Central Mexico all the way to the jack pine forest of the boreal region. What replaces these ecotypes will in all cases be invasives because by definition, "invasive plants" deals with plants that are not a part of an original ecosystem. The original ecosystem will of course, disappear as the original climate (continues to) disappears. For example (and this is just conjecture on my part): As our Central Texas forest continues to die from successive droughts, the holes in the canopy will often be filled by existing species that are more drought tolerant like mesquite, huisache, or another of the great invasives in our region; Chinaberry."

            Thus, we have to look further than just the term  "invasive" before we decide to spend time and resources to eradicate something.  We need to look at any plant or animal in terms of the way it functions in a particular ecosystem, and balance our time and resources accordingly.  For example, several groups in town are spending lots of labor time trying to cut out ligustrum. Most biologists I have talked to say on the whole ligustrum is worse for our soils than natives, because it has a net effect of decreasing moisture in the soils relative to native grasses and shrubs.  So far so good, but does the effort to eradicate it stand a chance of actually getting it out of the creekbeds and greenbelts?  Sadly, no.  We do not have the volunteer manpower, or financial ability to hire workers, to do that.

            Think of it this way: even if we got rid of every single "invasive" plant along the Barton Creek greenbelt this year, they would re-appear in the next few, as birds and wind brought seedlings back in from yards outside the greenbelt.  Ironically, the drought we are living through might do a better jot of eradicating "invasives" than volunteer organizations do.  As I walk through the greenbelt today I see almost half the ligustrum and nandina dying from thirst. Another year of this and 90% of it might be gone, "naturally", while most oaks and cedars and pecans that are drought resistant will make it another year.  In that strange universe, drought becomes an eradication tool (though certainly not the one I would choose if I were a "native" tree!). 

            Changing the concept from "eradicating"  "invasives" to managing total biomass for a more healthy ecosystem is thus a better way to conceive what we do with plants here (and the reason to prioritize cutting Ligustrum in Blunn Creek, for example).  Here is a great link to a blog post that lays this out.  It is by Peter Kareiva, chief scientist for Nature Conservancy  http://blog.nature.org/2011/06/invasive-species-fight-mark-davis-peter-kareiva/

            This is a big thought, and we need to start thinking about it more:  as global warming wipes out a range of our current tree and plant species ( we can not know at this point how much will die, because we do not know at this point how bad it will actually get), what might replace them?  How might newer plants function in creating the new ecosystem that might emerge?  Are some "invasives" more drought resistant, for example, and thus more able to live into the next century and play some part in the more desert ecosystem  that will emerge?  What "invasives"  (chinaberry, etc) might replace natives as we become more of a desert?  And which will disappear as it gets drier?

            This is a difficult set of questions, because it points out that dealing with "invasives" is not as simple as it may sound. It points towards management of biomass; with our existing resources rather than just eradication, and with an uncertain future of climate change ahead.  Luckily, the new city proposal heads in that direction; the title itself is Management, not Eradication, of invasives.  It has been crafted with management in mind.

            The plan overall deserves support as presented, though keeping in mind prioritizing efforts to control various "invasives".

            And now we need to get people in Austin to start thinking about ecological factors when they think of  "invasives".  Is eradication actually possible?  Is it cost effective, or would the same money and time and effort be better spent in the long term by planning and acting for a different kind of ecosystem (which will come, in some form, from global warming)?  There are times to attempt eradication, but other times not to.  Just assuming we have to eradicate "invasives" is not necessarilythe best path to take in all situation, nor even the most workable.

Swearingen is a member of the Austin Sierra Club Conservation Committee, and teaches environmental classes at St Edward's University

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