One could ask same thing about any ecosystem -- why does preservation matter? There are many reasons, of course, including:

1. Utilitarian perspectives. Ecosystems support unique mixtures of species, and some of these may be important to humans as sources of new medicines, foods, and so forth. A relatively recent example comes from the PNW, in which a previously "ignored" small tree species, Taxus brevifolia, was found to contain taxol, a compound that is tremendously successful against ovarian and other cancers. This utilitarian perspective follows the adage of Aldo Leopold, that the first rule of intelligent tinkering is to save all the pieces. You never know which small, seemingly unimportant piece may turn out to be much more important than anticipated.

2. Ethical perspectives. These are numerous, but essentially argue that living things (and, by implication, the environments necessary to support them) have fundamental rights to exist.

3. Aesthetic perspectives. The lives of many people are enriched aesthetically by having untrammeled places in which to spend time, think, observe, and seek spiritual connections with being.

4. Perspectives based on our reliance on ecosystem services (and the reliance of other living things on these); functions such as nutrient cycling, energy flow, hydrological stability, regulation over gases in the atmosphere (as we discussed at the very beginning of this term). In fact, the maintenance of forest productivity over the long term depends on these.

5. There are many lessons to learn about wise land management by observing the function of natural systems. We can then try to incorporate knowledge from these lessons in our management of land, so we have something more than a plantation -- and so that we have long term sustainability and stability of these systems.

That is, what are its essential features, and can we try to accommodate them in our management of younger, commercial forests? Or, from an ecosystem perspective, what are the consequences of conversion from old growth to managed second growth forests? Are there things that foresters can do in their management of forests that perpetuate some of the old growth features in second growth forests? Things that would maintain important ecosystem attributes -- attributes that are important both ecologically and commercially

TO ANSWER THIS, WE NEED TO KNOW WHAT WE MEAN BY "OLD-GROWTH FOREST"

What are the essential features of old growth, and how does it function? We'll answer this with reference to Douglas-fir/western hemlock forests in western OR and WA. Definitions vary -- some focus on age, some on size, some on other features. However, ecologists and land managers are now coming into agreement that an old-growth forest is much more than a collection of large old trees. I'm skipping the quantitative details here, because they don't matter as much as do the concepts. The operational definition being used by the US Forest Service and BLM refers to sizes of trees (a certain number per acre must be greater than 30 - 32 inches in diameter) or to age, with a certain number of trees per acre being over 200 years old. There should be a certain number of snags (standing dead trees) per acre of a certain size, and there should be a specified tonnage of down logs ("coarse woody debris"), and a certain number of these logs should be of certain sizes. The forest canopy is supposed to be deep and multilayered (that is, there are not only big old trees, but also regeneration under them), and there should be at least two tree species in a wide variety of age and size classes.

It generally takes 350 - 750 years to develop all of these features, but some forests, depending on their disturbance history, attain old growth features by 200 years - and some may even acquire many of these features even younger than 200 years, if management is wise. That is, it is difficult to define a lower age limit for old-growth forests. The transition from mature to old growth is gradual and occurs at different rates on different sites and with different histories.

In general, for the Douglas-fir region of the PNW, forests up to about 75 - 100 years old are ecologically young. This is the period during which the most rapid growth occurs (adolescence). "Mature" forests are usually considered to be 100 - 200 years old. These are in the period between the culmination of maximum growth (peak of growth curve) and the development of old growth characteristics.

THESE DEFINITIONS EMPHASIZE TWO IMPORTANT ATTRIBUTES OF FOREST ECOSYSTEMS:

1) Their composition -- what species are found there and in what proportions, and
2) Their structure.

Note that age itself is less important in these definitions than are structural and compositional features of these forests.

Functional attributes are also important. Old-growth forests support a great number of tightly interconnected species -- an extensive array of symbiotic relationships. We'll discuss these more in the following section of these notes. Old-growth forests are also characterized as being nutrient retentive - few nutrients are lost from the system, as erosion rates are very low, nutrients are slowly released by decomposition, and there are abundant plants there to take up the nutrients as they are released. Gross production is high in old-growth forests, but rates of respiration are also high, so net production is not very great compared to younger forests. Further, rates of mortality are fairly high, so there is little or no increase in living biomass in old-growth forests. However, total organic matter in these forests does still increase (living + dead); primarily because of coarse woody debris, which accumulates faster than it decomposes.

CAN YOUNGER FORESTS ALSO PROVIDE SOME OF THESE ATTRIBUTES, IF MANAGED DIFFERENTLY THAN BY CONVENTIONAL, TIMBER-ORIENTED APPROACHES?

Old growth forests differ from younger forests - especially from traditionally managed second growth forests -- in some aspects of each of these structural, compositional, and functional attributes. An important question is, can we adjust our management of commercial forests so as to retain some of the features of old growth that are valuable in terms of biological diversity, influences on nutrient and soil dynamics, sustainable production, influence on stream ecosystems and so forth?

Adjusting forest management in this way is important for two main reasons:

1. It would have effects on the sustainability of the forestry systems -- on timber production itself. The inherent productivity of our forests -- their sustainability - is conferred by ecosystem services, such as nutrient retention and uptake, nutrient cycling, pest control, pollination, nitrogen fixation, water capture and retention., etc.

2. It has been said that even if we were to immediately preserve everything that there is left to preserve in the PNW, and that was our only strategy towards preservation of biological diversity, the battle would be lost. There is simply not enough intact old-growth forest left to preserve - the remnants are too fragmented, too small. The same case can be made for many other ecosystems. If we rely on "preservation" as our only strategy, we'll lose. Not only are preserves too fragmented and small, but they are also too vulnerable to change -- climate change, political and social change. Preserves are important, of course, but preserves alone are not sufficient!! We need to broaden the battle for protection of biological diversity to include commodity lands, incorporating a more ecologically-based approach to their management.

(Another section of notes, under development, will discuss changes in forest management now being implemented that pay attention to the entire ecosystem, rather than focusing on the trees (timber) or one or two species of particular concern (such as the Northern Spotted Owl.)

Click "structural features" to move to the next section of notes, which focuses on the structural features that characterize old growth and their connections to forest composition and function. "Deforestation" takes you to the list of topics included in this area, while the contents box, below, takes you to the master table of contents for this BI 301 web site. Navigate gives reminders on how to move about within and among these pages.

Page maintained by Patricia S. Muir. Last updated November 19, 2002.