The effects of prescribed fire on riparian groundwater

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Montana State University - Bozeman, College of Agriculture


The hypothesis of this study is that the use of prescribed fire to reduce trees and tree canopy, on a watershed scale, will decrease depth to riparian groundwater, increase riparian plant species diversity, and increase riparian biomass production. To test these hypotheses two watersheds, primarily managed for cattle grazing, located in Fergus (Dry Armells watershed) and Jefferson (Little Whitetail watershed) Counties, Montana, were chosen. Both watersheds were densely dominated with coniferous tree species. Average preburn tree density was 1,276 trees/ha and 350 trees/ha for both the Dry Armells and Little Whitetail sites respectively. Ten riparian drainages were selected for treatment and analysis within the two watersheds. Six of these drainages were burned and four were used as unburned comparisons. Prescribed fires took place in the spring of 2001 at Dry Armells and in the fall of 2005 and spring of 2006 at Little Whitetail. At Dry Armells 18 to 20% of the watershed area was burned. At the Little Whitetail site only 3 to 15% of the watershed area was burned.
At Dry Armells, average depth to riparian groundwater significantly decreased from 122 cm below grade to 79 cm below grade after one year, and monitoring continues to show an average annual decrease. Riparian groundwater at Little Whitetail has yet to respond. Plant species diversity did not significantly increase in the post burned riparian areas at either of the sites. Plant species diversity did increase, post burn, in the Dry Armells uplands. However, there was no increase in species diversity, post burn, in the Little Whitetail uplands. In the riparian areas (Dry Armells) that had the strongest response in groundwater, 14% more biomass was produced in 2005 as compared to their unburned counterparts. Benefits of this prescribed fire are enhanced riparian zone process and function, increased biodiversity, and possibly, restoration of perennial streamflow in systems that were previously ephemeral. Management implications based on these benefits could take the form of using fire to increase groundwater and stream discharge, or at the other extreme, using prescribed fire for total ecosystem rehabilitation.




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