Killer trees via Colby
   Nov 26, 2003 15:08 PST 


   Colby's given us another jewel. It is reproduced below for your perusal. The Grand Ent has added another perspective of young vs old woods and what competition spawns.



We've got a variety of useful discussions going, but this has some relevance to our combined index.

Killer trees? Yes, it's another of my rather hypothetical observations. Now, I certainly don't suggest that trees think, but some, like walnuts, make it pretty clear that they're programmed to make things miserable for the competition. Some trees survive, some don't. Lots of trees die from lack of sunlight, or are subject to windthrow. Often it's dumb luck, but in some cases it appears that the survivors were not only stronger themselves, but survived by putting their nearest competitors at a disadvantage. Where it appears that the survivor actually influenced the demise of its neighbors, I've applied the term "killer tree," just to see how that might affect my understanding of changes in forest structure.

After two hurricanes and a variety of local storms, parts of my woods look like a war zone. The fallen trees are mostly second growth, two to three feet thick. Here and there trees remain standing. They are usually the more shapely specimens, with large crowns supplying sufficient nutrients to build a strong root system. They had competition, but those trees were more slender, with smaller crowns, often deflected sideways. Of course, trees having trunks both tall and of critical mass were most vulnerable to windthrow or breakage in a severe storm.

A new forest will fill in the openings, and will compete with the older specimens, but those younger trees will be at a structural disadvantage, so that the old specimen will hasten their demise also. So it is, that over several hundred years, older specimens will continue to be "killer trees."

Of course, tuliptrees, by their unusual height, are subject to such thinning, but some massive specimens will survive, their numbers increasingly affected by lightning. So it is that tuliptree becomes only an occasional massive fixture, but offering its seeds to the wind to the broadest possible area, in the slim chance that some opening may give rise to a successor.

Oaks and other species also become "killer trees," hastening the fall of taller, unstable competitors. The survivors are not so tall, but compete successfully by their broad crowns. Certainly, their strong wood gives them that spreading capability, and it follows that capabilities persist because they are utilized. Having no winged seed, there is no reason for an oak to grow taller than necessary.

So, in an old woods, we see killer trees and upstarts. Sometimes the killer trees are numerous, and form continuous open woodlands. Sometimes the upstarts form groves where examples of great height are produced, as in second growth, but eventually, killer trees destabilize the grove. Beech trees, by their shade tolerance, may skew the ascent of other species. Beeches and sour gums can have much influence in parts of a woodland, their crowns persisting despite breakage and eventual dieback.

So, the structure of an old woods can follow rules different and more complex than the simplistic verticality of second growth. With less clear trunk to be maintained, more energies are available for other structural development. An interesting question is how a second growth woodland gets back to such a structure. Tall slender trees can't become rugged stocky ones. Windthrow openings would seem to produce more tall spindly stuff. So, maybe we need to add another influence, and I wondered about killer trees.

Killer trees aren't as tall as second growth, and their trunks aren't as large as field grown specimens. Still, overall, they can be massive structures. That's where our combined index comes in. Of course, we could weight either of the two factors, but the index seems to work as is. Some specimens, like the Seneca Pine or numerous unnamed deciduous examples, aren't the tallest or thickest of their species, but they have an influence on our perception of the forest.

I suspect that frequent exposure to severe storms is a greater factor locally than at CFSP, MTSF, or GSMNP. Killer trees may be more numerous at Carter's Grove, Corcoran Woods, and Cedar Park, where huge trunks and broad crowns impose an unmistakable influence of compact dominating biomass. Renewal is often dramatic, but on a longer cycle than in more fragile second growth.

So, let's see what the combined index tells us about different sites and "killer trees."