Tuesday, December 18, 2007

Native Plants Do It Better

It's rare that a new (to me) ecological concept related to gardening and wildlife hits me upside the head, but I treasure it when it does. Reading Douglas W. Tallamy's new book, Bringing Nature Home, brought me just such a moment.

For years I have believed that gardening with natives was important, but I have allowed myself to become less single-minded about that belief, especially in recent years. I couldn't answer people's questions about why, for example, a native berry-producing shrub was better than an exotic berry-producing shrub if the birds liked to eat both types of berries equally. Instinctively I felt the native was better, but I couldn't produce the underlying logic to share with others.

Tallamy nails my missing logic in this book.

Every time a plant is described as "pest free", the nurseryman is saying that leaf-eating insects (and often other herbivores) won't eat it, usually because they truly can't eat it due to its chemical makeup. This means that the particular plant in question - almost always an exotic introduced from another country or from a different area of this country - is taking space, using nutrients from the soil, capturing sunlight...and adding little or nothing to the local food chains. In essence, it is a sterile placeholder, taking the place of other, native plants that can and do support diverse, healthy populations of native animals. Because the exotic plant is not getting eaten or controlled in any way, it can easily outcompete the locally palatable native vegetation, so when the exotic escapes into the wild, there is nothing holding back its takeover of local habitats and sterilizing them.

So right now I can practically hear the question going through your head, "Why would I possibly WANT insects to eat my plants? Won't that kill them?"

The simple answer is, "No, it won't kill them. Native plants evolved along with native herbivores so that both balance each other. Then, too, having native predators feeding on the native herbivores further keeps that balance in place."

Insects are one of the primary ways that the energy captured by plants gets moved up the food chain. They are the primary herbivores of many, probably most, plants; then they become the food for primary predators, from other insects to amphibians to birds.

If you love to attract birds to your yard, it's important to know that the energy and nutrients for bird reproduction are almost entirely based upon insect food. Berries in the fall won't do birds any good if there haven't been any birds produced earlier in the year because there were no insects available to provide the food and energy for eggs and young.

I can hear another question, "Japanese beetles are eating my roses to stubs. How can you say that insects won't kill my plants?"

Japanese beetles aren't native insects, and they are not acting "naturally" for our native ecosystems. Many major pest outbreaks are actually caused by alien insects or diseases introduced accidentally into our country. Like the alien plants they often come in on, these alien pests have no natural enemies and ravage unchecked throughout the countryside. Chestnut blight, Dutch elm disease and now sudden oak wilt are all examples of alien disease organisms; (Asian) azalea lace bug, soybean aphid and Japanese beetles are examples of devastating alien insects.

I've just hit the highlights of Tallamy's book here. He describes the concepts in much greater depth than I have here, plus he provides lots of interesting examples. He has also included a wonderful section about the different types of insects, including some fascinating and fun insect life histories. If you love to garden, especially if you love to attract wildlife to your yard, I highly recommend that you read this book.

3 comments:

Anonymous said...

Can you tell me more about the oak wilt? We noticed many pin oaks in the KC, MO area that had lost most, if not all, of their leaves last July. Later in the summer we noticed that one of our pin oaks ( east of Holton) had many leaves that were turning bown and dropping. We couldn't find evidence of any pest. We're feeling decidedly uneasy since we've lost nearly all of our Scotch and Austrian pines to blight.

Gaia gardener said...

To my knowledge, sudden oak death (which is what I meant to say when I wrote "sudden oak wilt") is still basically confined to the west coast. It is a relatively new disease, caused by a specific fungus, that acts on oaks, rhododendrons, viburnums and multiple other species, but I don't think pines are among its target species.

There are apparently several other diseases and stressors in oaks that can mimic sudden oak death, including oak wilt, oak decline, red oak borer, herbicide injury, and freeze damage, to name just a few. Not knowing more about the situation in K.C., I can't really even hazard a guess as to what's going on there. Contacting the Extension office in the area would probably be the best bet.

As for your specific pin oak in late summer in Holton, my first reaction is that it's probably suffering from stress due to drought. Here in the Wichita area, I know we had lots of trees turning brown and losing leaves early last fall. If it was drought, the tree should be fine this spring, assuming fairly normal weather conditions.

Other possibilities certainly would have to include oak wilt (different from sudden oak death), possibly introduced through ice storm damage or warm season pruning, or accidental herbicide injury. It's easy to forget that trees and shrubs are broad-leaved plants that will be damaged by herbicides applied to control (broad-leaved) weeds in grass, corn, etc.

Here are a couple web sites on oak diseases that might be worth visiting for more information: http://www.na.fs.fed.us/spfo/pubs/pest_al/sodeast/sodeast.htm and http://www.anr.msu.edu/robertsd/oakwilt/index.html

I'm not sure what the soil pHs are in K.C. or on your property, but the other thing to remember is that pin oaks don't tolerate high pH soil well and will often get chlorotic and simply not do well in limestone based soils. They've been taken off the recommended plant list here in Wichita because of those problems.

Hopefully both your pin oak and the ones in K.C. were/are suffering from unusual weather conditions and will recover without issue as weather returns to more normal patterns.

Anonymous said...

Thank you for your insights and information. We'll keep our fingers crossed and hope that all is well come spring. We have several majestic pin oaks that have been with us for nearly 35 years They, unlike the maples in our yard, survived the recent ice with very few broken limbs. I don't want the heartbreak of watching these old friends succumb to some disease. Again, thank you.