Document: CRI-3-59-37

The effect of windthrow disturbance and salvage logging on nitrogen cycling in a coniferous forest ecosystem.

RUMBAITIS-DEL RIO, C.* and C.A.WESSMAN

CIRES/University of Colorado, Boulder, CO, 80309, USA. ¹

Abstract:
The biogeochemical effects of windthrow disturbance have been studied in tropical and temperate deciduous forests, but have not been studied in temperate coniferous forests. Furthermore, previous studies have produced somewhat conflicting results. This study examines the short-term effects of windthrow disturbance and subsequent salvage logging activities on soil physical and chemical properties and on nitrogen mineralization in a coniferous forest. The study location is Routt National Forest, which sustained a large(> 8,000 hectares)windthrow disturbance in October 1997. Experimental plots were installed in August 1999 in areas of intact forest, areas of blowdown forest and in recently salvage-logged areas. Soil physical and chemical properties were measured in these three treatment types, and nitrogen mineralization rates were calculated using the in-situ buried bag method for August through November. The first-year results of this three-year study established that soil physical and chemical properties do not differ significantly between areas of intact forest and areas of blowdown forest. Control and blowdown treatment values for percent soil organic matter were 35 5%, and 25 10%, respectively and depth of the organic horizon was 4 0.5 cm and 4 0.6 cm, respectively. Soil moisture did differ between the control and blowdown treatments (123 7g of H₂O/g of dry soil for control plots and 107 5g of H₂O/g of dry soil for blowdown plots). However, recently logged sites were significantly drier, and were nearly uniformly lacking an organic horizon. Consequently, there were significant differences in the percent soil organic matter (4 0.5%), depth of the organic horizon (0 cm), and soil moisture (39 3g of H₂O/g of dry soil) between logged areas relative to blowdown and intact forest areas. Differences in nitrogen mineralization rates, and C: N ratios were also observed. These results indicate that in the short-term, alterations to soil properties and nitrogen mineralization rates are more pronounced as a result of salvage logging activities than from large-scale windthrow disturbance.

Keywords: Disturbance, Biogeochemistry, Windthrow, Blowdown, Logging, N mineralization

This abstract is being presented at: 2:00 PM in session:
Oral Session #51: Disturbance Ecology: Harvesting, Grazing and Roads.