Abstract:
For management purposes, it would be useful to be able to predict streamflow
response to forest practices in small, unmonitored basins. The primary objective of this
study is to investigate the influence of early successional vegetation on summer
streamflow levels. The long-term data records from watershed 1 at the H.J. Andrews
Experimental Forest provide a case study of vegetation dynamics and streamflow
changes during the first three decades following clear-cut harvest. This study
documents the vegetation dynamics in watershed 1, based on long-term vegetation plot
data and aerial photos. Hypotheses about the mechanisms by which vegetation
influences streamflow levels are presented and explored using a spatially explicit
watershed model, MAPSS-W (Daly, 1994).
in order to test these hypotheses of vegetation - hydrology interaction, spatially
distributed climate, soils and vegetation datasets were developed for MAPSS-W.
MAPSS-W was calibrated and evaluated for use in watersheds 1 & 2 at the H.J.
Andrews Experimental Forest. Following calibration and evaluation of MAPSS-W,
experimental simulations were run to explore the hypotheses of vegetation - hydrology
interaction.
These analyses of long-term vegetation data and results from watershed simulations
indicate that changes in summer streamflow levels in watershed I are related to shifts in
the dominant vegetation in the watershed. Rapid growth of herbaceous vegetation
appears to influence summer streamflow during the first 5-10 years following harvest.
Summer streamflow deficits appear to be related to the dominance of deciduous
broadleaf vegetation in the watershed during the second decade following harvest.
Conifers appear to begin to play a significant hydrologic role during the third decade
following harvest.
