Abstract
Methods of analysis are needed that quantitatively characterize the response of organisms to anthropogenic disturbance. Herein a method is presented that characterizes bryophyte morphological variability in response to timber harvest treatments (clearcut and partial cut). Samples (n = 6196) of the semi-aquatic bryophyte Brachythecium frigidum were collected from clearcut, partial cut and full forest stream reaches between August 2003 and October 2005 and analyzed to obtain mass to stem length ratios (M:SL). Results show that relative to a full forest (i.e. full canopy cover condition), average M:SL ratios were reduced approximately 18% in the partial cut and 37% in the clearcut, indicating a decrease in biomass per unit stem length with increasing harvest intensities. Increased light intensities and higher air temperatures resulting from decreased canopy cover in the harvest treatments corresponded to lower M:SL ratios (0.31 and 0.24 for the partial cut and clearcut, respectively). Results quantify the morphological response of B. frigidum to habitat perturbation, thereby validating the method as a useful assessment of anthropogenic disturbance in post-timber harvest environments. Additional work should be conducted to test the method in other physiographic regions and to isolate bryophyte response to alterations of distinct environmental variables.
Highlights
Multiple authors have identified the need for studies that investigate bryophyte response to post-timber harvest environments [1,2,3,4,5,6]
Average ambient air temperatures in the riparian zone (Ta Riparian) were 4.94 ̊C, 4.43 ̊C and 4.36 ̊C in the clearcut, partial cut and full forest, respectively. These results show that average air temperatures in the riparian zones were 1.66 ̊C, 1.66 ̊C, and 1.76 ̊C less than air temperatures at mid-slope climate stations in the clearcut, partial cut, and full forest, respectively
Air temperatures measured in the riparian zone displayed a narrower range of variation than air temperatures measured at the mid-slope climate stations (Figure 4)
Summary
Multiple authors have identified the need for studies that investigate bryophyte response to post-timber harvest environments [1,2,3,4,5,6]. Bryophytes are widely distributed among terrestrial and aquatic environments [7,8] and serve a number of important roles in forested ecosystems by contributing greatly to net primary productivity, nutrient retention, and by providing habitat and a food base for invertebrates [1,3,9]. Timber harvest effects that may prove detrimental to bryophyte health include increased erosion and sediment, altered stream flow regimes, microclimate (including light availability and air and stream temperature) and nutrient regimes [11,12,13,14,15,16,17,18,19,20,21]. Given bryophyte sensitivity to disturbance, forest management including clearcutting or thinning (i.e. partial cutting) may result in nearly immediate changes to bryophyte health
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