Responses of soil and water chemistry to mountain pine beetle induced tree mortality in Grand County, Colorado, USA

Background/Question/Methods

Pine forests in northern Colorado and southern Wyoming, USA, recently experienced the most severe mountain pine beetle epidemic in recorded history, and possible degradation of drinking-water quality is a major concern.  The objective of this study was to investigate possible changes in soil and water chemistry in Grand County, Colorado in response to the epidemic, and to identify major controlling influences on stream-water nutrients and carbon in areas affected by the mountain pine beetle. 

Results/Conclusions

Soil moisture and soil nitrogen increased in soils beneath trees killed by the mountain pine beetle, reflecting reduced evapotranspiration and litter accumulation and decay.  No significant changes in stream-water nitrate (NO₃^-) or dissolved organic carbon (DOC) were observed during 2001-2009; however, total nitrogen and total phosphorus increased, possibly due to litter breakdown or increased productivity related to warming air temperatures.  Multiple-regression analyses indicated that % of the basins affected by mountain pine beetles had minimal influence on stream-water NO₃^- and DOC; instead, other basin characteristics, such as average slope, precipitation, and percent of the basin covered by forest, were much more important.