SILVA: a model for forecasting the effects of SO/sub 2/ pollution on growth and succession in a western coniferous forest

Technical Report · Thu Feb 26 04:00:00 EST 1981

OSTI ID:6529437

Kercher, J R; Axelrod, M C

A forest succession simulator, SILVA, has been developed for the mixed conifer forest type of the Sierra Nevada, California (seven major species), to simulate the effects of SO/sub 2/ on forest dynamics. SILVA was developed by extensively modifying a northeastern US simulator. The model simulates growth and includes the development in time of tree diameter, tree height, leaf area index, and available light for each tree. Recruitment and mortality are modeled stochastically. Modifications include the introduction of fire ecology and the use of temporal seed-crop patterns and seedling survival factors unique to Sierra Nevada forests. Probability of mortality is determined by height of crown scorch (which is a function of fire intensity), dbh, and bark thickness. Pollutant impacts are modeled as an effect on tree growth. Dose-response functions relating change in tree growth to increases in pollutant loads were developed using published data. The model simulates community dynamical and structural response to many factors quite well. For 500-year simulations from clearcut, the ratios of the time-averaged basal area fraction of Pinus ponderosa to Abies concolor were 5.2:1 and 1:16 for elevations of 1524 m and 1829 m, respectively. At 1524 m, the ratio of P. ponderosa to A. concolor decreased 59% with the introduction of fire suppression. To investigate effects of low-level chronic SO/sub 2/ fumigation in sample runs, the pollutant level is set to cause these annual reductions in growth: P. ponderosa, 10%; Pseudotsuga menziesii, 18%; and SO/sub 2/-tolerant species such as A. concolor, 1 to 2%. Time-averaged P. ponderosa basal area fraction decreased 28% and A. concolor (SO/sub 2/ tolerant) increased by 260% at 1524 m elevation. Three scenarios of pollutant time histories are investigated: rising levels, constant levels, and rising and falling levels. We also calculate the sensitivities of the model parameters to determine relative importance for model behavior.

• Research Organization: Lawrence Livermore National Lab., CA (USA)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 6529437
• Report Number(s): UCRL-53109
• Country of Publication: United States
• Language: English

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