Forest Investment Account (FIA) - Land Base Investment Program
FIA Project 4295005

    Species-level test of ecological representation in the Arrow TSA: distribution and density of birds in Spring and Winter
Project lead: Slocan Forest Products Ltd.
Contributing Authors: Herbers, Jim; Serrouya, Robert; Maxcy, Katherine; Martin, Kathy
Imprint: Telkwa, BC : Cairn Ecological Research and Management, 2004
Subject: Forest Investment Account (FIA), Birds, British Columbia, Habitat
Series: Forest Investment Account (FIA) - Land Base Investment Program
Over the past 4 years, the Arrow Innovative Forestry Practices Agreement (IFPA) has been developing a framework for maintaining biological diversity in the Arrow timber supply area (TSA). One of the main components of this framework is the development of a coarse-filter strategy of ecological representation. Ecological representation is about representing ecosystems in an unmanaged state and, as such, is an important first step towards maintaining biodiversity because it helps to account for species that are too poorly known or numerous to manage individually. To date, research conducted by the Arrow IFPA has largely focused on quantifying how well the non-harvestable landbase represents ecosystem types and key habitat elements in the harvestable landbase. The first stages of this work revealed that the overall level of unmanaged area in the Arrow TSA was high (43%), and that all 15 ecosystem types in the TSA were equitably represented in non-harvestable areas. However, sampling habitat attributes in the 5 largest ecosystems revealed several important differences between the harvestable and non-harvestable landbase. Key among these differences was lower deadwood resources (snags and coarse-woody debris) and less productivity in non-harvestable forests, particularly in the ESSF. These differences were not as pronounced in the ICH, but well-decayed snags were at very low levels in the non-harvestable portion of the ICH. Recently, the Arrow IFPA began examining if the structural differences between landbase types are biologically meaningful to the organisms that depend on this structure. During winter 2003, a species-level test of ecological representation in the Arrow TSA was initiated in the harvestable and non-harvestable landbases of the 3 largest ecosystems (Serrouya et al. 2003). Serrouya et al. concluded that non-migratory birds were generally well 'represented' in the non-harvestable landbase of ESSF ecosystems. However, they found 45% fewer birds in the ICH non-harvestable landbase despite similar levels of forest structure. This raised concern that the ICH non-harvestable landbase may not be doing a good job representing the avian community found in the ICH harvestable landbase. In this study we built upon previous research by examining spring breeding bird diversity and density in the harvestable and non-harvestable landbases of the 3 largest ecosystems. We also followed up on the results from the non-migratory bird project conducted during winter 2003 by re-surveying harvestable, non-harvestable and partially harvested stands in the ICH ecosystem. We chose to re-survey the ICH because of differences noted the previous winter. Our overall objectives were: 1) to examine breeding birds in the 3 largest ecosystems in the Arrow TSA, 2) to examine breeding birds between the harvestable and non-harvestable landbases in the 3 largest ecosystems, 3) to examine winter birds between the harvestable and non-harvestable landbases in the ICH ecosystem, and 4) to examine winter birds in 2 commonly implemented partial harvesting treatments. We used the point transect method to measure bird community composition and density. Point counts were systematically spaced at 200-m intervals within each stand and were a minimum 100 m from stand boundaries. During the breeding season 8 stands were sampled 2 times each in the harvestable and non-harvestable landbases of the three largest ecosystems. The 8 sampled stands were a random subset of the 12 stands sampled within each ecosystem and landbase during winter 2003 and winter 2004. Only mature unharvested stands between 101-140 years were sampled and sampling was conducted from mid May to mid July, 2003. We found that the ICH ecosystem had an average 27% higher number of species relative to the ESSF, but that the ESSF ecosystems had a 15% higher density of breeding birds. Community similarity, bird diversity, and bird density were similar between ESSF ecosystems and ESSF landbase types. In addition, we found few systematic differences in bird diversity or density between the harvestable and non-harvestable landbase. Results from the ESSF ecosystems further increase confidence that the non-harvestable landbase is doing a good job ‘representing the harvestable landbase. In contrast, several species showed significant differences in density between the harvestable and non-harvestable ICH. These differences suggest that the harvestable ICH landbases might be a good candidate for medium and fine-filter strategies for maintaining biological diversity. The medium-filter is the management of stand-level attributes upon which many groups of organisms depend, such as snags and coarse-woody debris and the fine-filter is the management of individual species or unique ecosystems. Medium and fine-filter strategies might be efficiently implemented using partial harvesting strategies in the partially constrained ICH landbase. From early February to early March, 2004 we re-sampled 12 stands in each of the ICH harvestable and non-harvestable landbases and re-sampled 10 stands in the dispersed and aggregated partially harvested treatments. Stands in the harvestable and non-harvestable ICH were between 101-140 years old. Results from the ICH harvestable/non-harvestable comparison show that bird diversity was similar in both 2003 and 2004. However, in contrast to winter 2003, results from the ICH comparison show little difference in the density of birds during winter 2004. In 2003, the harvestable landbase had 45% more birds than the non-harvestable landbase; in 2004 this difference declined to 19%. These results suggest the non-harvestable landbase may better 'represent' the avian biodiversity of the harvestable landbase in some years but not others. As a result, we suggest that the ICH non-harvestable landbase should not be counted on to completely 'represent' the ICH harvestable landbase. Again, partially constrained areas in harvestable ICH can provide a mechanism for increasing mature stand characteristics in this landbase type through the use of longer rotations or partial retention logging. Partial harvesting is common in the Arrow TSA because 25% of the TSA is in designated visual quality zones. We compared the diversity and density of non-migratory birds in stands that were partially harvested using two different harvesting patterns: dispersed or aggregated live tree retention. Stands in the partially harvested treatments were harvested between 1989 and 1997 with an average 13% basal area was retained. In both 2003 and 2004, species diversity and bird density was highest in mature unharvested stands and lowest in the aggregated retention treatment. The density of individual species showed the same pattern. Partial harvesting treatments were likely serving at least one intended function – ensuring the continued use of harvested stands by forest-dependent species. Generally, our results support the position that non-harvestable areas represent a substantial component of biological diversity in the Arrow TSA. Differences between landbase types were not consistent and did not correspond well to the observed systematic differences in habitat attributes. Given the lower abundance of some bird species in non-harvestable ICH areas, stand-level retention in the timber-harvesting landbase should not be abandoned. Additional sampling using a design that surveyed a broader range of organisms (e.g., different species or species groups) would help to confirm some of the conclusions from this study.


Final Technical Report (0.3Mb)

To view PDF documents you need Adobe Acrobat Reader, available free from the Adobe Web Site.

Updated August 16, 2010 

Search for other  FIA reports or other Ministry of Forests and Range publications.

Please direct questions or comments regarding publications to