Abstract
Old growth is an important issue in forest management. It has been the subject of review papers and strategy development. The Old-Growth Task Force of British Columbia recommended that older forests should be inventoried; typical, rare, and rapidly decreasing old-growth types should be identified; and the maps and associated database should be used as input for local planning processes. The Protected Areas Strategy (PAS) includes old-growth as a conservation issue to be addressed. Identification and mapping of older age classes was undertaken as part of PAS. The focus has been on ecological units with rare, limited, or under-represented old growth.
A regional forest cover map was generated by combining existing electronic versions for timber supply areas (TSA) with paper map and remote sensing information from federal parks, provincial parks, and tree farm licences (TFL). Private land was not included. A geographical information system (GIS) was used to combine ecosection (1:600 000), biogeoclimatic (1:250 000), and forest cover (1:20 000) maps for the Kootenay-Boundary Region. For each ecosection, the database was summarized by forest cover within each biogeoclimatic subzone/variant. The following fields were extracted from the database: total area for all cover classes, area of age class 7 (121 - 140 yr), area of age classes 8 + 9 (>140 yr), and area of productive forest land. Area of age classes 8+9 as a percent of productive forest land was calculated. The GIS generated a 1:250 000 product map that identified older age classes and included biogeoclimatic and ecosection boundaries. The GIS also produced 1:50 000 scale maps and a database for areas within TSA boundaries.
Ecological units with forests >140 yr covering 10% or less of the productive forest land base were examined. These units were considered potential old-growth areas. Twenty-two units were identified as of concern to land managers because of relatively limited amounts of forests >140 yr. Units were also examined that had <1 000 ha of>140 yr old forests although the percent of the productive forest land base covered was> 10%. Ten units were identified as of concern because the low area of these units makes them vulnerable to significant reduction or loss. For units with low percent or low actual area of older forests, it is recommended that map notations be placed to warn potential users that old-growth may be limited in these areas. It is also recommended that these units, where possible, be incorporated in special management areas such as old-growth reserves, ecosystem networks, or riparian zones.
A critical minimum level of old-growth is difficult to specify. Levels for age classes 8+9 are even more difficult to specify as these areas indicate potential old-growth, are not inventoried for ecological function, and mapping errors exist. Many natural and human factors affect the quantity of old-growth in an area. The quantity is decreased by timber harvesting and probably increased by fire suppression. Natural factors include stand-replacing fires, disease, insects, and geological processes. Low-intensity fire is needed for drier areas to maintain old-growth structures in these forests. These include snags and large, down logs used by wildlife species. These structures also provide aesthetic appeal for many people. Fire-maintained old-growth is a characteristic of stands with ponderosa pine and western larch.
Future work on old-growth should include stand verification and development of old-growth criteria Landscape work should include guidelines on minimal area per ecological unit, range of patch sizes for older forests, and distribution of these stands across the landscape. Fire management prescriptions should be developed to maintain desired old-growth features in stands with natural low-intensity fires.
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Updated April 12, 2007
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