Forest Investment Account

Abstract of FIA Project 6065002 and 6067002

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Weyerhaeuser BC variable retention adaptive management program habitat monitoring 1999 to 2002: summary

Author(s): Huggard, David
Imprint: Kamloops, B.C. : The Author, 2003
Subject: Forest Investment Account (FIA), Variable retention harvesting
Series: Forest Investment Account (FIA) - Land Base Investment Program


From 1999 to 2002, Weyerhaeuser conducted surveys to monitor retained habitat structure in 158 VR blocks, 42 benchmark unharvested sites (including pre-harvest experimental sites), 19 blocks with old remnant patches and 12 riparian reserves. Measured habitat attributes included live trees (species, dbh, height), snags (species, dbh, height, decay class), coarse woody debris (CWD; species, diameter, decay class), cover layers (canopy, small tree, shrub, herb, moss, litter, mineral soil), dominant shrub and herb species, and site series. Summaries are provided for major types of these attributes and for some important specific structures (e.g., large cedar snags, large well-decayed CWD, etc.), with measurements of edge effects, comparisons of VR types, comparisons of VR to benchmark sites and riparian reserves, and progress from 1999 to 2001. (Operational VR was not sampled in 2002). Habitat variables in this initial post-harvest monitoring showed no substantial edge effects into VR patches or into the harvested opening, even within 10m of the edge. In a few cases, habitat variables did show differences 25-50m into the VR patches, because of wetlands or rocky outcrops used to anchor some patches. The lack of edge effects suggest that several small VR patches would retain the same attribute levels as one or a few large patches of the same total area. However, edge effects are expected to develop with time. Dispersed VR retained substantially lower levels of many habitat elements than group VR (assuming 15% patch retention in group VR), except in the CWHvm/vh BEC group where the 2 types were more similar. Snag retention was particularly low in dispersed VR, although large trees and large snags had relatively better retention levels in dispersed blocks. However, the importance of the distribution of habitat elements across the block and the need for a variety of stand types suggests not neglecting dispersed VR. Retention patches in mixed and group VR were very similar. The additional retention in the mixed VR matrix would favour that system if the percentage in patches is the same for both types. Benchmark sites in several BEC variants had higher levels of several habitat attributes than VR patches, particularly large trees and snags, and overall basal areas. This probably reflects poor representation of large trees and higher productivity sites in VR patches, although it may also be that some benchmark sites are protected from harvesting because they have exceptional habitat attributes. Comparisons of pre- versus post-harvest experimental sites will help resolve this issue in the coming years. Riparian areas also differed in some attributes from VR patches, providing opportunities to retain some elements that were at lower levels in VR patches compared to benchmarks. Riparian areas should be included in future monitoring of operational VR practices. Most habitat attributes were at similar levels in 2001 blocks as in 2000, which were generally improvements over 1999. However, retention of a few important elements declined from 2000 to 2001, including deciduous trees, some snag types and small understory trees. These changes may be simply due to chance in sampling, but continued monitoring of progress over 5 to 10 years is encouraged. A comparison of models for combining BEC variants for summary suggests that the current groupings (CDF, CWHxm, CWHmm/dm, CWHvm/vh, CWHwh and MH) represent a reasonable trade-off between pooling to improve sample sizes, and separating ecosystems with distinct habitat structures. With future sampling of benchmarks in CWHmm, this variant should be treated separately from CWHdm. Expected precision for estimates of habitat elements from the 1999 pilot study corresponded well to the actual precision obtained in monitoring of benchmarks in 2001. Based on these results, current effort of about 10 benchmark sites per BEC group will demonstrate moderate differences in main habitat elements and larger deviations for more specific elements at moderate densities.

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Updated August 02, 2006 

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