Tom's Blog

Thursday, May 10, 2018

Invasive plants: Complete eradication is important!

How important is it to eradicate "all" the bad guys? I posted on this some years ago, but it deserves repeating.

One important part of restoration work is planning brush and weed removal. The question often arises: how important is it to get rid of "all" of the invasives? Eradication is expensive; do we really need to eliminate every last sweet clover sprig or buckthorn stem?

If one is thinking of the long term, the answer to this question is "Yes". The reason? Because annual stewardship cannot be assured. All sorts of reasons might arise that would prevent continued restoration on a preserve. Money problems first come to mind, but passing on or moving away of key personnel may be more important. What happens if work is stopped on a site before it is completely cleared of bad stuff? In a few years, bad plants will start to appear, and in a few more years there will be more.

At first these "stragglers" may seem acceptable, but this is just what microbiologists call the "lag" phase. Eventually the "log" phase is reached, and the site will suddenly "explode" with invasive plants. With exponential growth, it is the last doubling that turns the site from tolerable to hopeless. One year the site may look more or less OK and the next year it is ruined. That final point where everything suddenly becomes ruined is sometimes called the “tipping point”.

However, if the bad stuff has been completely eradicated, then the site should be able to stand some neglect, with perhaps just an annual or biennial prescribed burn. (But don't count on burns to get rid of new invaders! This won't happen.)

Even more important: if all invaders have been eradicated, it becomes a very inexpensive process to remove the few new ones that move in from outside. One or two passes through this blissful preserve may be all that is necessary each year.

Thinking of the budgetary and personnel problems, which is more important? A smaller area completely restored, or a larger area partly restored? The answer to this interesting question may depend to a great extent on the goals.

For instance, if the goal is to provide habitat for grassland birds, then large open areas are critical, but they may not need to be completely weed free. Indeed, some grassland bird species seem to be reasonably happy with a field of Queen Anne’s lace or even an alfalfa field, as long as it isn’t mowed too early.

But if the goal is preservation of plant diversity, then smaller sites with high botanical quality will be more important.

The ideal time to canvas a fully restored site for new invaders is mid-October, when the native vegetation has senesced. Exotic invaders such as buckthorn and honeysuckle keep their green leaves longer, and the occasional straggler (or new invader) really stands out. Carry a backpack sprayer filled with aqueous Garlon 3A or glyphosate (foliar spray concentration) and spray the green leaves. The senesced native vegetation will not be hurt, and the invader will be killed.

Honeysuckle green among the senesced native vegetation. Perfect time to spray.

Even a single buckthorn plant can be found hidden among the native vegetation!


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