Jenny/Ed- I agree with Ed. One of the few criteria for defining old-growth forest ecosystems that in my mind has held up the best is a summarization of one of Jerry Franklin's criteria. Which is to say that a forest ecosystem over time will respond to cycles of disturbance regimes, and eventually develop a "vertical and horizontal heterogeneity of forest structure and composition".
The vertical element here is analogous to your question of tree heights...heterogeneity here refers to the natural variability of heights that develop over time in response to disturbance regimes...the array of species and their spacing would be analogous to the horizontal diversity (or heterogeneity) that would develop in response to disturbance cycles. This natural variation in species spacing and composition is also often referred to as a spatial mosaic. Here in the West, that mosaic may often be the response to a wildfire pattern (they seldom are a continuous wall of fire consuming everything in their path, although sadly enough the more catastrophic fires these days are approaching that at times). It may be elsewhere a response to a forest pathogens, or cyclic wind events, etc. -Don From: [email protected] To: [email protected] Subject: [ENTS] Re: Forest densities Date: Sun, 15 Mar 2009 10:31:59 -0400 Jenny, What is the average distance between mature trees in the forest? You write: "I know it depends on the kind of forest and what kind of disturbance there has been," But that is the entire point. The answer is dependant on a variety of factors, so that a single answer is not possible. We have had similar discussions on the average height of trees. Look at how the trees grow. Initially a patch of seedlings grow very close together with several seedling per square foot. Over time, some of the seedlings die out and the average spacing increases between the stems. The spacing is greater in saplings. It increases on maturity. As trees begin to die in a mature forest the spacing between the stems continues to increase. It increases through time for a particular species. Beyond the initial rapid thinning phase in which there are many trees already growing to fill the space lost by a dead tree, there is a point at which the loss of a tree will open up a space in the canopy and forest floor that will be filled by new growth. This is where the period of disturbance comes into play. The shorter the period of small disturbance the more common these denser new growth patches will be in the forest. The size of the disturbance likewise plays a role in determining the size of the openings and the size of the denser new growth patches. There is the size of the species in the mix. Some trees simply grow bigger than others. Those species that grow larger, will support a larger canopy, and have a greater trunk spacing than small species in areas that are relatively undisturbed. A patchwork of mixed species may have a denser packing than those of a single or limited number of species. The species present will also impact the number and type of trees in the understory. So there may be measurements made of the spacing in a particular forest, but that does not really answer the question. It is a snapshot in time. It tells you what the density of stems is in this particular forest, at this particular point in time, with this particular mix of species, and this particular disturbance history. Numbers can be generated, but are they meaningful? A density measurement taken earlier in time, or later in time will give you different results. The measurement is dynamic and changes with time, so that a simple answer that can be applied broadly can't really be found. What I suggest doing is to try to reconsider what exactly you are trying to determine, what are you trying to accomplish, and find a different way to approach the problem. Ed Frank _________________________________________________________________ Hotmail® is up to 70% faster. Now good news travels really fast. http://windowslive.com/online/hotmail?ocid=TXT_TAGLM_WL_HM_70faster_032009 --~--~---------~--~----~------------~-------~--~----~ Eastern Native Tree Society http://www.nativetreesociety.org Send email to [email protected] Visit this group at http://groups.google.com/group/entstrees?hl=en To unsubscribe send email to [email protected] -~----------~----~----~----~------~----~------~--~---
