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Understorey vegetation response following restoration of ingrown ponderosa pine and Douglas-fir stands in the East Kootenay region

Author(s) or contact(s): R.F. Newman, J. Parminter, and B.M. Wallace
Source: Southern Interior Forest Region
Subject: Fire Ecology, Plant Ecology, Thinning and Spacing
Series: Technical Report
Other details:  Published 2012.
 

Abstract

The response of understorey vegetation was monitored over a 7-year period following restoration of ingrown stands of ponderosa pine (Pinus ponderosa) and interior Douglas-fir (Pseudotsuga menziesii var. glauca) in the East Kootenay region of British Columbia. The restoration was based on a prescription of partial cutting and slashing in 1999 and 2000. The ponderosa pine site was also subjected to a prescribed fire in April 2004. At the ponderosa pine site, total herbaceous biomass doubled over a 6-year period on areas where treatments increased understorey light by 32-44%. Most of the forage increase was due to grass biomass, including pinegrass (Calamagrostis rubescens) and bunchgrasses. The forage response developed over time after an initial lag of 2-4 years and was most evident by years 5 and 6 following treatment. A regression model derived from 2006 herbaceous biomass/light relationships at the ponderosa pine site predicted that 80% canopy removal is required to achieve 50% of the forage potential for the site. Despite an increase in herbaceous biomass, the frequency of most plant species was not different on more open canopy areas compared to those with a relatively more closed canopy. This indicates that little colonization of unvegetated areas occurred during the study period. In fact, increases in the frequency of exposed mineral soil, especially following the prescribed fire, indicate that more unvegetated areas were created. The prescribed fire increased the frequency of exposed mineral soil by 40% and initially reduced the frequency of five important understorey plant species. At the Douglas-fir site, restoration treatments that created an average of 32% more understorey light increased total herbaceous biomass by 70% after 7 years. Most of the forage increase was due to forb biomass. The total forage response developed steadily over time after an initial lag of 2-4 years. The same lag in response was noted at the ponderosa pine site and was likely due to the same reasons (i.e., mechanical damage due to harvesting, and drought). It is evident at both sites that desirable plant species such as rough fescue (Festuca campestris) have not yet been able to reproduce substantially with the treatments employed and under the environmental conditions experienced over the study period.

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Updated August 14, 2012