Effects of Operational Brushing on Conifers and Plant Communities in the Southern Interior of British Columbia Results from PROBE 1991–2000 PRotocol for Operational Brushing Evaluations

Description of the Dry Alder Complex Sitka alder (Alnus viridis ssp. sinuata) is the dominant species of the Dry Alder Complex, and willow (Salix spp.) is also present on some sites (Figure ). Characteristic understorey species are fireweed (Epilobium angustifolium) on sites mesic and wetter, and pinegrass (Calamagrostis rubescens) on sites drier than mesic (Kimmins and Comeau ). Thimbleberry (Rubus parviflorus) may also be prominent in the understorey on some sites. The Dry Alder Complex is most common in the MS zone, where it occurs in all subzones. It is also found in the ICH and SBS zones, and at upper elevations of the IDF zone and lower elevations of the ESSF zone. The Dry Alder community also occurs in the BWBS zone of northeastern British Columbia. The Dry Alder Complex occurs on a range of soils and parent materials, but is most common on moderately wellto well-drained, coarse to loamy textured Brunisols and Luvisols (Boateng and Comeau f). It occurs predominantly on north and east aspects. The complex develops mainly on submesic to subhygric sites, and does not become abundant on either very wet sites with a high water table, or on subxeric or drier sites sites that are prone to drought. Sitka alder lacks the physiological adaptations needed to prevent moisture loss from the foliage, and is thus poorly adapted to drought (Haeussler et al. ). Development of the Dry Alder Complex Sitka alder is often present under mature lodgepole pine forests in the southern interior of British Columbia, but because it is only moderately shade tolerant (Krajina et al. ), it tends to remain suppressed until light is increased following logging. Ground disturbance during logging, mechanical site preparation, and burning enhance alder and willow abundance by providing a favourable seedbed and by damaging the root crowns of existing plants, thereby stimulating sprout growth. Clean-cut and shattered stumps are reported to sprout equally well (Haeussler et al. ). Mechanical site preparation of established alder communities (e.g., backlog sites) stimulates sprouting and simply results in renewal of the complex. Practices that hinder development of the complex include severe fire or mechanical disturbances that destroy roots, and incomplete removal of the overstorey canopy. Wind-borne seed from alder and willow plants in the vicinity of logged areas contributes to development of the Dry Alder Complex. Germination of both species is favoured by seedbeds that are burned or have exposed mineral soil, and receive sunlight. Alder is a nitrogen-fixing pioneer species that can establish on sites that have been severely disturbed with little organic matter remaining. Alder produces good seed crops every year from plants that are – years old and bumper crops every – years, while willow produces prolific quantities of seed annually. Alder seeds disperse during late fall and winter and germinate the