Post
by gnmcmartin » Tue Sep 18, 2018 9:02 pm
Bob:
No real insights or specific knowledge. But, I do know that while the sites for east coast species are virtually always rated at a base age of 50 years, thus a very good white pine site will be rated as 100, meaning the best dominant trees in an acre will be 100 feet tall at 50 years. Because west coast species grow much larger, and sustain their growth over longer periods, they are sometimes rated at a base age of 50 years, but also commonly at 100 years.
Next, growth curves have been calculated and plotted for many, if not most west coast conifers, usually with reference to a specific site in a specific location. I have seen a few of these, but have not studied them carefully, and can't make any large generalizations. But, my guess is that species such as redwood will show the best sustained height growth. Douglas fir should be outstanding also. These growth curves far "outstrip" those of our eastern conifers. A web search can turn up a lot of these.
Now to the "nitty gritty" of foresters decisions on when to harvest. There are all kinds of harvesting methods/schedules, but much of the short rotations we hate to see in our eastern forests are based on a careful calculation of growth and yield. If, the goal is the maximum production of wood, as measured in cubic feet, then a determination is made of what is called "mean annual increment." Annual increment is the growth per year at any given age, mean annual increment (MAI) is the total growth at any given age divided by the age of the stand. When the MAI reaches the point of "culmination" (CMAI), the average annual increase in volume of a stand begins to decline. On this basis, if the objective is attaining the maximum yield from a site, say as measured in cubic feet volume, the stand should be harvested, and a "new" one initiated. I think we in NTS should understand the basis on which these relatively short rotations are used--it is very strict, harsh economics.
Different species of trees on different sites have the CMAI occur at different ages. I believe that this CMAI occurs at later ages for west coast conifers. Of the eastern conifers frequently grown in plantations, such as red pine, white pine, and Norway spruce, CMAI for white pine--I am not sure I remember, but I think it occurs by age 50 or a bit sooner--for Norway spruce, it is sometime after age 60. This is according to studies done at SUNY Syracuse on sites in central NY.
But, if the goal is high quality lumber, knot free, etc., then a completely different management regimen and harvesting schedule is needed. Forest managers decide how to manage a stand, and for what products, based on the markets for those products, the prices they bring, and the cost of management and harvesting. It is all "hard-nosed" economics. We can complain all we want to, but to no avail.
In some very special circumstances, hard-nosed economics is not the determining factor, and one branch of forestry, relatively new, is forest aesthetics.
Now we must understand that growth and yield of individual trees, rather than the total of growth for a full acre of trees, is a totally different thing. An individual tree, as it grows larger and larger, can continue to produce a lot of wood, and if a CMAI was calculated for individual trees, I would guess it would come at a much later time than the total for a stand of trees. As a stand grows older, the number of trees an acre can support declines.
Ultimately what happens with an old growth stand is that not only is the stand CMAI long past, but eventually the annual production of wood of the very old trees will decline, trees will occasionally die, and the MAI if calculated on a recent period of ten years or so, it could be essentially zero, or perhaps show a decline, depending on the species mix and the reproduction. At this point, the "carbon sink" value of a stand will involve some very complex calculations based on a number of assumptions, including some about the soil. The amount of carbon stored in the wood of the standing trees may approximate an equilibrium. But, the carbon "sequestration" of the stand can continue to increase, depending on factors such as the climate, the condition of the soil, and the "biota."
You have done valuable research on the continued growth of older white pine trees, and I hope you continue. As for the wood production of very, very old and large trees, a number of years ago I read that according to one calculation, the General Sherman tree in Sequoia National Park was determined to be at its very great age, the fastest growing tree on earth. I don't know how the calculations were done, or what the basic assumptions were, but if that were true, I would not be totally surprised. I would guess that in terms of total wood production, some of the large old white pines you are studying would prove to be very fast growing also.
--Gaines
