Threats to Forests - Weeds

Weeds

Weeds aren’t dramatic, they are even hard to define, but, “non-native, invasive plants” works as a definition.  Non-native, that’s obvious, a way to think about that is the way the Native American people probably viewed the first  settlers from across the oceans.  Invasive, the metaphor holds, the “invaders” seem harmless at first, maybe even desirable, but as their population explodes they will change everything.

The natives we want to save

Ok, but really, what’s so bad about a few weeds?  Fair question, let’s look at weeds in crop land first.  Any weed in a crop field is competing with the corn, wheat, soy beans, alfalfa, or whatever for soil moisture, nutrients, and growing space above ground and in the soil, so any weed is taking away from what the crop plants could be producing.  Too many weeds in a field will reduce the crop yield a lot. Lower yields mean less food produced and higher prices at the grocery store.  That’s real and that a good reason to control weeds.  Next, weeds in wild lands where there are no cultivated crops.  Wildlife don’t eat most weeds.  Wild animals evolved through thousands of years eating a diet of native plants in the area where they live.  When weeds come in fast and thick, the available forage for wildlife is significantly reduced.  In a heavy winter with a lot of snow on the traditional wildlife winter range that has been taken over by weeds the wild animals are out of alternatives, they starve to death.  It is not only the wild animals that suffer, the native plants can be outcompeted by weeds and just go away.   This can increase soil erosion as the fibrous roots of native grasses are replaced by tap roots of weeds, tap roots don’t do as much to hold soil together.  So, whether you are a people, a domestic animal, a wild animal, a plant or even a particle of soil, weeds can be a problem, especially where they become epidemic.   

  

There are lots of non-native, invasive plants in and around the woods today.  A plant that is non-native, but is not invasive can be tolerated by native plants, animals and people.  It is the invasive part that gets serious and will change the color, character and productivity of the landscape from what it has been for thousands of years and it can happen in a matter of a few years.

What to do?  There are biologists who, for years, have studied non-native invasive plants that threaten native ecosystems.  The research is mostly financed by government, no one else would pay for it because the consequences of weeds are so subtle, indirect and happen over time.  When an invasive weed is discovered in an ecosystem there are three things that can be done to prevent the weed from taking over and crowding out the natives: we can pull the weeds, we can spray the weeds, or we can get mother nature’s help.  All three are expensive and in most cases all three are used.  Pulling is obvious, spraying is obvious and comes with side-effects, getting nature’s help - very complicated. 

Here is how getting nature’s help goes.   Scientists determine where this invasive weed is native, it is probably on some distant continent.  Where the weed is native it is probably not invasive, it may not even be a weed, maybe its plant neighbors, the animals and people like it there.  The biologists study the invasive plant’s native environment to determine what keeps it from running wild.  The studies look for something that just loves to chew on the plant where it is native, but the chewer doesn’t exist in the plant’s new neighborhood, America.  The “chewer” may be a bug, a worm, a fungus, a virus, or some fuzzy critter. Whatever it is, the chewer, or chewers (there are usually several types) keep the plant population in check in its natural environment.  Learning what the natural enemies are, the scientists bring home several of these.  The chewer immigrants can’t just be turned lose, they might do damage to plants we like.  A long period of testing and retesting must be done to determine if the new agents will only attack the targeted weed and not damage other plants. Biological controls works best if there are at least three different bugs or diseases that will attack the invasive plant.   From dozens of agents tested there will be only a few that are safe and effective to release.  The agents that make the cut will have to be produced by the millions and distributed into the environment where they can attack the invasive plants. Biological control is a very long, complicated and expensive process, but it has been working for years and is one of the important tools against invasive weeds. 

You can do your part by learning about invasive weeds in your area and pulling them, also, pay your taxes that support the scientists doing this work. 

Mariposa Lilly -  A Native