Friday, December 18, 2020

Creating resilient ecosystems through strategic choices in Genus


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.

The list:

  1. Oak
  2. Willow
  3. Cherries and Plums
  4. Pine
  5. Aspen and Cottonwood
  6. Birch
  7. Blueberries, Cranberries 
  8. Maples
  9. Hickory and Pecan
  10. Apple
  11. Elm
  12. Alder
  13. Basswood
  14. Hawthorn
  15. Raspberries and Blackberries (Brambles)
  16. Chestnut and Chinquipin
  17. Spruce
  18. Douglas Fir
  19. Ash
  20. Viburnum

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.


  1. On our little acre or so, our cabin is surrounded by mostly Pines, with Oaks coming in second. Also interspersed are some Cherry, Hickory and Red or Southern Sugar Maple. We also have some Black Berry. Basically a mixed lot... or as we call them around here... the forest, ha.

    I guess it depends on what you want to accomplish with your wood lot. If you want it for biodiversity, you let nature take it's course and let it be. But if you want to harvest the lot for lumber, you would want to divest the property of any pests that would devalue the particular crop you're trying to produce.

    For instance, Oaks are susceptible to Boring Beetles and certain Moth larvae that develop under the bark and eventually killing the tree, as well as destroying the marketability of the lumber. Also, keeping the undergrowth cut down will help, brambles, Saw Briars, Fox Grapes, ect. as well as woody bushes that suck up soil nutrients.

    There are several pests that will destroy a pine forest. Christmas trees are big business just north of me, Fraser Firs, mostly, and pest control is big business and occupies as much time as mowing, pruning the trees for shape and fertilizing the fields.

    Decisions, decisions...biodiversity or money making crop.

    1. With all due respect, most people don't own enough acreage to make pure economics the sole reason to make management decisions. Should I live long enough I might benefit from maximizing the timber value growing on my property. However, I can enjoy tracks in the snow all this winter if I make SOME concessions to promote wildlife.

      There are also some shortcomings in letting nature take its course. There is a nature area west of Lansing called Woldumar Nature Center. They followed "Let nature take its course" and much of the acreage is now an impenetrable mass of multi-flora rose, Japanese honeysuckle, privet, poison ivy and box elder. Not so good for wildlife or for humans trying to enjoy it.

    2. I get your point. I guess I was trying to explain how some people in my area of operation view land ownership and use. Even Christmas tree growers leave stands of trees around the edges and sometimes in the middle of their fields for wildlife habitat. But they also have to be cognizant of the types of pests that will harm their crop.

      On our acre or so of mixed woods, letting nature take it's course, the only undergrowth we have are Saw Briars, Fox Grape vines and maybe a little poison ivy. I think in our woods, there's not enough sunlight for Privet or Multi-Flora Rose?

      We do have Mountain Laurel and Rhododendren thickets in the higher elevations, though, which are a beyotch to climb through and around when trying to layout a house site for a potential rich home buyer.

  2. Interesting premise...The question in my mind, is how LONG will it take to establish that equilibrium in the wood lot?

    1. It is never quite an equilibrium.

      But since the caterpillars graze leaves, it does not require that the trees or bushes be sexually mature.

      The only real complication is that leaves that are close to the ground expose birds to snakes and feral cats.

  3. I’ve got a lot of ash in woods that once served as hayfields. Cutting out the ash results in a prickly ash thicket, so it’s a puzzler. I’ve been leaving the ash, EAB is just starting, and planting a mix of stuff to eventually replace it.

    I do have some local sources of burr oak and shag bark hickory from trees that are very cold hardy, developed, or found, by a local guy years back. I’ve planted most of my hickory nuts but have a half dozen I could send you if you want to experiment. I could send you a big bag next fall if you have a use. Tim

    1. Thank-you for your generous offer.

      The great ash die-off is an opportunity to bring in some tree species that are currently not in Michigan. I am planting much persimmon, some Cherrybark and Nuttall oak and Bald Cypress. Oh, and Northern Pecans.

      Most years I have a good local supply of acorns and the hickory nut crop is variable.

      Again, thanks for the very generous offer. I might take you up on it next year. We will have to see how it goes.

    2. When I collect nuts next year I will contact you to see if you need any.

  4. Note...I planted some of the nuts and acorns u see controlled conditions so I could see the germination rate. I was surprised at the 80-90% I got,


    Not as easy as we would like.