Fires are generally confined by topography to the mountain valley in which they ignited. Large areas of forest can burn in one valley during a bad fire year while a nearby valley remains unburned, even with similar fuel loadings and fire weather conditions. When forest stands are not burned and the trees are able to grow old, they often become more susceptible to attack by insects or disease, and uneven-age stand structures develop as individuals or groups of trees are killed. Periodically, outbreaks of bark beetles or other insects cause

widespread tree mortality (Safranyik et al., 2004). Trametinib In order to restore ecological integrity to forests that have been affected by fire suppression, Parks Canada has recently begun prescribed burning in many of its national parks including Kootenay and Yoho but these have been limited to small areas and were not considered in this study. The size of the forested valleys in our study area is relatively small, and our study period is relatively short within the context of the natural history and life-cycle of disturbance

and regeneration in these forests. The forests in one valley could have been younger than those in a neighbouring check details valley 100 years ago (before park establishment) simply as a result of random chance (e.g., lightning happened to ignite fires in one valley but not the other). The C dynamics of the forests we see today are strongly influenced by the legacy effects Etomidate of past disturbances, even as long as 100 years ago. The disturbance history of each mountain valley is unique, and therefore no two valleys have identical forests, even when they share common ecological characteristics and natural history. In our study, we compared forests under different management histories (conservation versus no conservation) and similar ecology and natural history, but our design cannot fully control for disturbance history because of the stochastic nature and spatial scale of forest disturbance in our study area, where two different forest areas can be subject to the same disturbance

regime, yet have different disturbance histories. The study consisted of two components – (i) characterizing and comparing the forest stand age structure and disturbance regimes inside and outside of parks, and (ii) assessing and comparing the carbon stocks and fluxes, impacted by these disturbances, inside and outside of parks. To make comparisons inside and outside of the national parks, each park’s forests were compared with the managed forests in its immediate surroundings, which we termed ‘reference areas’ (Table 1 and Fig. 2). Some surrounding areas were adjacent to more than one park and thus contributed to more than one reference area. We did not account for C dynamics of non-forest ecosystems; only forested lands in the parks and their reference areas were considered.