Extended density-dependent mortality in mature conifer forests: causes and implications for ecosystem management.

Understanding processes driving mortality in forests is important for comprehension of natural stand dynamics and for informing natural disturbance-based ecosystem management. There has been considerable study of mortality in forests during the self-thinning phase but we know much less about processes driving mortality in stands at later successional stages. We addressed this through study of five 1-ha spatially explicit permanent plots in mature (111-186 yr old in 2012) Pinus contorta stands in the Canadian Rocky Mountains using data from repeated measurements over a 45-yr period, dendrochronological information, and point pattern analysis. We tested the hypothesis that these stands had completed the self-thinning/density-dependent mortality stage of succession. Contrary to our expectations, the self-thinning phase can persist for more than 140 yr following stand establishment. Our findings suggest this was attributable to prolonged post-fire establishment periods due to surface fires in three of the plots while in the other two plots moist conditions and slow growth most likely delayed the onset of competition. Several pieces of evidence indicated the importance of density-dependent mortality in these stands over the study period: (1) The diameter distribution of individuals changed from initially right-skewed toward normality as a result of mortality of smaller-diameter stems. (2) Individuals of lower canopy positions were proportionally more affected by mortality. (3) When compared to the pre-mortality pattern, surviving stems in all stands had an increasingly uniform spatial distribution. In two of the plots, recent windthrow and/or ingrowth initially hindered our ability to detect density-dependent mortality but our dendrochronological sampling and permanent plot data allowed us to untangle the different processes at play; in doing so we demonstrate for the first time how density-independent processes can mask underlying density-dependent mortality processes in older stands. Mortality of larger dominant canopy trees increased over the study period and mortality of dominant stems was a random process in all stands suggesting these stands were approaching the end of the self-thinning stage and that density-independent processes might soon become more important. Our results provide an improved understanding of mortality processes that can be applied to natural disturbance-based ecosystem management.

Alberta biodiversity monitoring program - monitoring effectiveness of sustainable forest management planning.

A conceptual model of sustainable forest management is described based on three connected and necessary components: Policy/Strategic Planning, Operational Planning, and Effectiveness Monitoring/Science. Alberta's proposed Forest Management Planning Standard is described as an example of operational planning. The standard utilizes coarse and fine filter approaches to conserving biodiversity and sets requirements for implementation monitoring. The Alberta Biodiversity Monitoring Program (ABMP) is described as an example of effectiveness monitoring supporting Operational Planning. The ABMP is a rigorous science-based initiative that is being developed to monitor and report on biodiversity status and trends throughout the province of Alberta, Canada. The basic survey design consists of 1656 sites, 20 km apart, evenly spaced on a grid pattern across Alberta. Sites will be sampled over a five-year period at a rate of 350 sites/year. Standardized sampling protocols will be used to cover a broad range of species and habitat elements within terrestrial and aquatic environments, as well as broader landscape-level features. Trends and associations detected by ABMP products will be validated through cause-effect research. ABMP focuses research on critical issues and informs both operational planning and the development of policy and strategic-level plans. The Alberta Forest Management Planning Standard and the ABMP are described as key components to implementing resource planning based on ecosystem management principles.