LITTER AND DEAD WOOD DYNAMICS IN PONDEROSA PINE FORESTS ALONG A 160-YEAR CHRONOSEQUENCE

Authors

  • S. A. Hall,

    1. Graduate Degree Program in Ecology, Department of Forest, Rangeland and Watershed Stewardship, Colorado State University. Fort Collins, Colorado 80523-1472 USA
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    • 3 Present address: The Nature Conservancy, North Central Washington Field Office, 6 Yakima Street, Suite 1A, Wenatchee, Washington 98801 USA. E-mail: shall@tnc.org

  • I. C. Burke,

    1. Graduate Degree Program in Ecology, Department of Forest, Rangeland and Watershed Stewardship, Colorado State University. Fort Collins, Colorado 80523-1472 USA
    2. Natural Resources Ecology Laboratory, Colorado State University. Fort Collins, Colorado 80523-1499 USA
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  • N. T. Hobbs

    1. Graduate Degree Program in Ecology, Department of Forest, Rangeland and Watershed Stewardship, Colorado State University. Fort Collins, Colorado 80523-1472 USA
    2. Natural Resources Ecology Laboratory, Colorado State University. Fort Collins, Colorado 80523-1499 USA
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  • Corresponding Editor: J. Gulledge.

Abstract

Disturbances such as fire play a key role in controlling ecosystem structure. In fire-prone forests, organic detritus comprises a large pool of carbon and can control the frequency and intensity of fire. The ponderosa pine forests of the Colorado Front Range, USA, where fire has been suppressed for a century, provide an ideal system for studying the long-term dynamics of detrital pools. Our objectives were (1) to quantify the long-term temporal dynamics of detrital pools; and (2) to determine to what extent present stand structure, topography, and soils constrain these dynamics. We collected data on downed dead wood, litter, duff (partially decomposed litter on the forest floor), stand structure, topographic position, and soils for 31 sites along a 160-year chronosequence. We developed a compartment model and parameterized it to describe the temporal trends in the detrital pools. We then developed four sets of statistical models, quantifying the hypothesized relationship between pool size and (1) stand structure, (2) topography, (3) soils variables, and (4) time since fire. We contrasted how much support each hypothesis had in the data using Akaike's Information Criterion (AIC).

Time since fire explained 39–80% of the variability in dead wood of different size classes. Pool size increased to a peak as material killed by the fire fell, then decomposed rapidly to a minimum (61–85 years after fire for the different pools). It then increased, presumably as new detritus was produced by the regenerating stand. Litter was most strongly related to canopy cover (r2 = 77%), suggesting that litter fall, rather than decomposition, controls its dynamics. The temporal dynamics of duff were the hardest to predict. Detrital pool sizes were more strongly related to time since fire than to environmental variables. Woody debris peak-to-minimum time was 46–67 years, overlapping the range of historical fire return intervals (1 to >100 years). Fires may therefore have burned under a wide range of fuel conditions, supporting the hypothesis that this region's fire regime was mixed severity.

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