Ecological Knowledge and Environmental Problem-Solving Concepts and Case Studies (1986) / Chapter Skim
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23. Ecological Effects of Forest Clearcutting
23. Ecological Effects of Forest Clearcutting
Pages 345-357
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From page 345... ...
Not only are trees longlived, but differences between sites make it difficult to extrapolate results from one location to another. This case study reviews the ways in which these problems have been approached and assesses the current state of prediction of the amounts and significance of nutrient losses from forests after clearcutting.
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From page 346... ...
The first studies of nutrient loss due to clearcutting were concerned primarily with only parts of the nutrient budget of an ecosystem, for example, leaching losses. Improved understanding of ecosystem functioning made it apparent that useful interpretation of nutrient losses due to clearcutting required an analysis of both the nutrient stocks in the ecosystem and the nutrient inputs and losses.
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From page 347... ...
However, forest growth decreased, particularly in already poor sites, and Ebermayer attributed this to the export of plant nutrients (Tamm, 19791. Interest in the role of nutrients in forest growth continued throughout the early part of the twentieth century, but only within the last several decades have scientists begun to quantify total forest-ecosystem nutrient budgets and changes in budgets due to various logging practices.
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From page 348... ...
APPROACHES TO EVALUATING LOSSES Leaching arid Erosion Nutrient leaching losses often increase as a result of clearcutting. After removal of trees, evapotranspiration on the site decreases, so the amount of water percolating through the soil increases; the result is an increase in leaching potential.
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From page 349... ...
Studies of nutrient dynamics in conifer forests of the Pacific Northwest also showed an increase in loss rates after clearcut harvesting and slash burning (Feller and Kimmins, 1984; Gessel and Cole, 1965; Miller and Newton, 19834. An important study of nutrient loss after clearcutting was carried out in northern hardwoods at the Hubbard Brook watershed site in New Hampshire (Bormann and Likens, 1970; Borrnann et al., 1968; Likens et al., 1970~.
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From page 350... ...
Other clearcutting studies in the Hubbard Brook region showed that nutrient losses are less if herbicides are not used after clearcutting, but can still be important because the soils in the region are shallow (Pierce et al., 19721; harvesting removes a larger proportion of the total nutrient pool there than in areas with deeper soils. Because of the importance of nutrient uptake by vegetation, alternating contour strip cuts with undisturbed forest on a mountainside should decrease nutrient leaching.
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From page 351... ...
Estimates of the quantities of nutrients remaining in the site and of the rates at which they are replenished are also needed. Scientists attempting to predict the effect of nutrient loss on site productivity must determine nutrient stocks remaining in the soil and the fractions of those stocks available to growing trees (Johnson et al., 19821.
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From page 352... ...
Budgets arid Sensit~vi~ Analysis Nutrient budgets of ecosystems have proved extremely difficult to measure precisely, because of high variability in both space and time. In addition, such important quantities as the proportions of nutrients available to plants and the rate of mineral weathering are often hard to measure; errors in their measurement could result in large errors in estimates of total ecosystem nutrient budgets.
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From page 353... ...
A model like the nitrogen model of Swank and Waide (1980) , which predicts yield under various management strategies on the basis of nitrogen dynamics in the treated ecosystems, can be used to assess the effect of an error of a given magnitude on the overall conclusion and can aid in a decision as to whether more accurate measurements are necessary.
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From page 354... ...
1984. Effects of clearcutting and slash burning on streamwater chemistry and watershed nutrient budgets in southwestern British Columbia.
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From page 355... ...
1970. Effects of forest cutting and herbicide treatment on nutrient budgets in the Hubbard Brook watershed-ecosystem.
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From page 356... ...
Committee Comment As illustrated by this case study, methods of analyzing nutrient budgets of ecosystems have developed slowly as scientists gradually have recognized the need to perform a complete accounting of nutrient stocks and fluxes if the significance of changes in flux rates induced by clearcutting is to be understood. This represents discovery of methods that were already well known in the business world, and it might be asked whether ecologists would have progressed more rapidly if they had been better versed in budget analyses as practiced in various disciplines.
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From page 357... ...
Sensitivity analysis helps to avoid consequential errors errors that could lead to inappropriate management decisions. The natural inclination of most scientists to measure all quantities as accurately as possible might actually lead to poorer predictive abilities, given the investment of comparable resources, than an approach designed to obtain accurate measurements only for the quantities identified as critical.
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