|Tallamy's study included sawfly larvae in with caterpillars.|
Douglas Tallamy of University of Delaware makes an interesting case that not all trees contribute the same amount to the resilience of an ecosystem. Tallamy and his team investigated the hypothesis at the genus level. That is, they did not care what species of oak they were looking at, they were looking at the fact that it was in the "Oak" genus. Genus is the next step up in coarseness from species when looking at how life is categorized.
Key Point: A node's contribution to a system's resilience is related to the number of links to other nodes. A Swiss Army Knife adds more resilience than an ice-pick.
Their premise is that caterpillars are the largest primary consumers of green plants in the ecosystem and are very well documented. They created a sub-set of 83 counties that provided a diagonal slice through the United States and provided representation of different climates. They dredged up academic studies and totaled up the number of butterfly species that made use of a given genus within each county.
They found that the data looked much like a Pareto distribution. Some genus like Oak, Willow and Prunus were favored by a broad spectrum of butterfly species in nearly every county. The vast number of other plant genus were consumed by zero, one or two species.
They used their methodology to create a defensible quantification of HOW MUCH a given genus member contributes to the resilience of a given ecosystem.
- Cherries and Plums
- Aspen and Cottonwood
- Blueberries, Cranberries
- Hickory and Pecan
- Raspberries and Blackberries (Brambles)
- Chestnut and Chinquipin
- Douglas Fir
How might this be useful?
Suppose you inherited a piece of property that floods and was completely filled with Silver Maple. Properties like that is not uncommon in this part of the world.
While Maple is in the middle of the list it would not be hard to add Willows, Hawthorn, Brambles and Viburnum. All four of those would be likely to spontaneously occur if a large enough of a patch of maple was harvested to ensure the sun hit the forest floor and that there was a gradient from very wet-to-damp.
With a little bit of work and money, even more genus could be folded into the mix. The majority of the forest might still be Silver Maple but the insect food-base for bird species would be vastly more "buffered" against catastrophe AND one would expect a large increase in both numbers of bird species nesting and their reproductive success.
Or consider if you were harvesting firewood from a woodlot. You would diminish the resilience of the woodlot less if you removed the last Hackberry or Honeylocust than if you removed the last oak tree.
Weaknesses of the study
The term "primary grazers" is a bit misleading. The majority of vegetation does not get grazed. Rather, it falls to the ground and is either decayed or directly consumed by worms, beetles, etc. Even the material that decays are subject to consumption by beetles/worms as fungi.
Hat-tip to Lucas Machias for calling this article to my attention.