Long-term Ecosystem Studies
RESEARCH BRIEF No. 2 Catamount Biological Field Station
Long-term Ecosystem Studies
There is a growing consensus among forest researchers today that present forest stocking, primarily the result of diligent and long-standing fire suppression practice, is both unnatural and undesirable. Accordingly, plans are in the offing to conduct large-scale commercial thinning operations on forested lands throughout the west. We support efforts to restore our forests to pre-settlement conditions (as best we understand them), but remain sensitive to the need for continuing research to avoid creating additional, unanticipated problems. Our knowledge of forest community dynamics is incomplete at best, and the many landscape changes that have occurred in the west over the last century, including the spread of aggressive, non-native plant and animal species, present new ecological challenges of largely unknown dimension. With this in mind, we have launched a research program at CBFS to assess the present condition of our montane forest ecosystems and project the long-term effects of different management strategies on the health of forest communities throughout the Front Range.
Changes in the structure of a forest canopy, whether initiated by natural processes or purposeful manipulation, set into motion a series of reactions that may profoundly affect the entire forest community. Opening the forest canopy admits more light to the forest floor, resulting in warmer soil temperatures. Warmer soil accelerates microbial activity and subsequent mineralization of organic matter. Increased nutrient availability (plus sunlight) then stimulates more understory growth, raising the level of resources available to consumers (herbivores and their predators) at all trophic levels. Energy flow is increased and nutrient cycling is accelerated (figure 1). But there are potential complications with this simple scenario: Nutrients may be leached from soils and lost before new ground cover is established, or, alternatively, tree regeneration, stimulated by release from overhead competition, may quickly sequester nutrients into long-lived tissues. The effects of opening the understory to more light are further confounded by the potential negative feedback (particularly on nutrient cycles) of increasing evapotranspiration and reducing soil moisture. Acting in concert, these changes may shift competitive balances, possibly in favor of alien species that could have a lasting impact on native plant and animal communities.
While a return of our forests to more natural conditions may be desirable, the simplified scheme presented above highlights just a few of the unknowns that can plague well-intentioned management plans. Given our present understanding of complex montane forest ecosystems, we cannot be sure that the outcome of wide-scale forest thinning will be exactly as we anticipate.
A natural experiment
At Catamount we have a natural experiment already in place for testing some of these unknowns. Extensive logging activity in the 1980′s has left a legacy of thinned stands in both spruce-fir and limber pine forests. Several of these stands are situated adjacent to unlogged areas of similar slope and aspect, providing us with controls against which the results of 20 years of ecosystem response can be measured.
Toward that end, 5 permanent study plots have been established to date, with several more planned for the future. Extensive sampling is underway to reconstruct stand histories and quantify differences in plant and animal communities in each. The two plots presently being evaluated encompass both logged and unlogged areas on moderate to steep northeast and northwest facing slopes. Each is permanently staked in a 10 x 10 meter grid pattern to facilitate precise and replicable sampling over a period of many years. In addition to characterizing differences in forest overstory within control and thinned plots, we are measuring factors such as the number of standing dead trees, herbaceous and shrub groundcover, and the amount of woody debris on the forest floor, as these affect the faunal community. We will also be studying nutrient cycling processes, particularly nitrogen mineralization and its subsequent effect on tree vigor and stand development. In addition, we will be evaluating the specific impact of overstory thinning on bird, mammal, and insect populations, measuring, for example, the effects of different stand densities on tree-roosting bats or on the incidence of songbird nest parasitism by cowbirds.
It is our hope that by fully assessing the impact of past management practices on the entire forest ecosystem, we can better anticipate the consequences of management plans currently being developed. Our best glimpse into the future of our forests may come from looking back.
Figure 1. Hypothesized ecosystem response to changes in forest overstory. Bold type indicates areas of emphasis in current studies. Internal cycles and system inputs/outputs are omitted for simplicity.