Mixedwood stands are composed mainly of aspen (Populus tremuloides [Michx.]) and white spruce (Picea glauca [Moench] Voss) and comprise the top two harvested species by volume in the Peace Forest District (PFD), however, because of under-utilization of this resource, the timber supply area (TSA) is at risk of losing up to 10% of the mixedwood or hardwood contribution to the annual allowable cut (AAC) (1). Current British Columbia (BC) policy guidelines discourage adaptive management when it comes to managing mixedwood stands (2). Research suggests however, that complex species mixtures have greater productive potential than single species stands (3, 4, 5). The focus of this long-term study is the complex interactions between intimate mixtures of conifer and deciduous species that make up a highly significant portion of the northern and central interior of BC. The trial is comprised of two sites, the first, Woodlot 1217 and the second, the Rice Property, which now forms part of Tree Farm License 48. The approach has been to reduce aspen density in a linear fashion and monitor responses of residual aspen, underplanted white spruce (TFL 48), released white spruce (WL 1217), understory vegetation, and soil nitrogen (N) mineralization. This includes changes in plant communities, soil N dynamics, growth and yield of valuable timber resources, and changes in productive potential. Although the response has been delayed, by 2004, aspen are beginning to show a response to the thinning treatments. Differences in spruce growth between treatments are not yet evident. Changes in understory vegetation were not found to vary between treatment and year. There are changes in soil mineralization and soil moisture between spring and fall and from 2001 to 2004. Growth and yield projections and subsequent economic analyses require the development or modification of an existing model that will reflect the growth of the underplanted spruce.
Hawkins, Chris D.B.. 2005. Managing for Intimate Species Mixtures in BC's Boreal Forest. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report