Forest Investment Account

Abstract of FIA Project 4281009

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Habitat supply modelling for the Cranbrook and Invermere TSAs: preliminary estimates for large snags and down wood

Author(s): Wilson, Steven F.
Subject: British Columbia, Biodiversity
Series: Forest Investment Account (FIA) - Land Base Investment Program - Innovative


Monitoring and forecasting the abundance of key habitat elements in managed forests is an important aspect of evaluating the ecological state of a land base. The supply of habitat elements can be used to predict the current and future availability of habitat for wildlife species and guilds.
We developed a stand structure classification and habitat supply models for the Cranbrook and Invermere Timber Supply Areas to project the density of large snags (>20 cm DBH) and down wood volumes associated with the harvesting scenarios modelled under the Kootenay-Boundary Higher Level Plan Order spatial timber supply analysis.
The stand structure classification system was intended to provide an essential link between strategic and operational forest planning, and to provide the basis for more accurate projections of important habitat elements.
A workshop was held 18 November 2003 to review and revise a draft stand structure classification to ensure that it could accurately track stand structure through multiple entries. A second purpose of the workshop was to capture current forest practices for the purpose of improving future strategic modelling. The results of the workshop were a stand structure classification that tracked overstorey and understorey structure separately, and a series of tables that linked current retention strategies directly to the stand structure classification and to stand types. The classification and tables can be used in the future to refine habitat supply models, based on operational practices.
Habitat supply models were based on available data and on conceptual models of stand dynamics inferred from the scientific and management literature. Different models were developed for the major stand types occurring on the Cranbrook and Invermere TSAs. Models were linked to the output of timber supply analyses to predict the current and future abundance and distribution of large snags and down wood, based on various harvesting scenarios.
The projected abundance of large snags and down wood on the crown forest land base as a whole was very dependent on the disturbance routines applied to the non-harvestable land base. A rapid decline in snags over the first 80 years of the projection in the timber harvesting land base was largely balanced by recruitment in the non-harvestable land base. A similar trend occurred for down wood, although it was not as strong. This general pattern has been observed in results of other habitat supply modelling exercises, despite different parameters and modelling approaches.
Partial retention outside wildlife tree patches was not modelled by the timber supply analyses, nor were retention data available for existing managed stands; as a result, the abundance of snags and down wood was underestimated in projections. The impact of future partial retention was estimated by applying the tables of current forest practices developed at the November workshop to the base case harvest scenarios. Projections suggested that partial retention will result in an additional >6000 ha of habitat (mostly in the medium and large tree diameter classes) in the Cranbrook TSA and nearly 3500 ha in the Invermere TSA.
Future work should focus on defining future desired conditions in the forest, particularly with respect to the abundance and distribution of habitat elements on the timber harvesting portion of the land base, and identifying the key parameters responsible for those future conditions. Timber supply analyses should also be adapted to better accommodate habitat supply modelling. This can be achieved by explicitly incorporating stand structure classes as both modelling inputs and outputs, and by grouping stands into analysis units that are more biologically relevant.
The stand structure classification should be used to inventory the structural characteristics of existing and future managed stands. These data can be used to inform timber supply analyses in order to generate more accurate projections of the future abundance of habitat elements.

For further information, please contact Steven F. Wilson, EcoLogic Research (

Updated September 08, 2005 

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