Temporal patterns of age-class distributions on foothills landscapes in Alberta

The strategy of managing for "natural" patterns towards ecological sustainability of forests is currently limited to simple spatial attributes of landscapes. Yet, there is general agreement that landscapes are highly dynamic entities suggesting that temporal patterns may also be important. This study used historical estimates of 20-yr disturbance rates, and a spatially explicit, stochastic landscape model to create multiple possible landscape mosaic scenes for three different landscapes in the foothills of Alberta. The results were summarized as frequency distributions by age-class, and the distributions compared to the percentage of area in the current, and the pre-commercial landscapes. Results indicated that aside from one age-class in one of the landscapes, both current and pre-commercial age-class distributions were well within the historical ranges suggested by the simulations. More generally, the simulations indicated relatively high, but landscape specific, levels of historical temporal variability. This implies that there are patterns to temporal variability which may be captured, quantified. and emulated as alternatives to single age-class management targets. The research also demonstrates a method of assessing age-class distributions within the context of historical ranges of distributions.