Spatial and temporal stand dynamics of mature lodgepole pine forests of the Canadian Rocky Mountains

Abstract

In forest ecosystems, structure and species composition change over time as a function of ageing and minor disturbances and it is important to understand these changes for predicting forest productivity and habitat suitability for other plant and animal biota. Disturbances play a major role in controlling these changes and in many forest ecosystems disturbance regimes have recently changed due to either the influence of climate or human management. The reduced fire frequency and recent mountain pine beetle (MPB) outbreak in lodgepole pine forests of Alberta are a good example of such changes. These forests were historically characterized by relatively frequent stand-initiating disturbance but previous studies have recognized a variety of post-fire successional pathways. We have a limited understanding of the pattern and underlying processes of stand dynamics of these forests, particularly in mature forests as they proceed towards the canopy breakup stage. To better understand the dynamics of both the understory and overstory communities of mature lodgepole pine forest I used data from spatially explicit long term permanent plots in the Rocky Mountains of Alberta, Canada to determine the mechanisms or processes responsible for the observed patterns in community composition and structure as well as how these patterns changed in time. I also used dendrochronology to reconstruct the timing of establishment and disturbance history to assess how they influenced stand dynamics. I first assessed whether canopy closure led to the homogenization and convergence of understory communities and if the processes spatially structuring these communities changed during stand development. I also assessed what was driving mortality of lodgepole pine trees and if mortality in different canopy positions was affected by different processes. Finally I assessed which factors were influencing the establishment and survival of regeneration throughout stand development.