Understanding forest dynamics incorporating both local and regional ecological processes

Classifying tree species as early-, mid-, and late-successional is often based on their characteristics, e.g. age, height growth rates. Chapter Two examines the validity of these classifications by comparing the age and height growth of upland boreal tree species in Saskatchewan. Age classifications were examined by comparing the age of individuals as determined by coring trees and by locating the root collar and missing rings. Root collar ages show all species recruit within ten years after fire. Height growth classifications were examined by comparing the mean time each species takes to grow to each one-metre. Species classified as early-successional have relatively higher growth rates in the first metre; however, above one metre there are few species differences. Consequently, age and height growth rates cannot be used to classify tree species.; Forest succession has been studied using static (e.g. static diameter distribution, static age distribution, chronosequence) and dynamic methods (e.g. reconstructed age distribution). Chapter Three examines the assumptions and limitations of these methods. Results show that the assumptions of static approaches are not met; diameter is not correlated with age, age as determined by coring a tree does not reflect the date of recruitment, and changes in species composition and abundance over decreasing size or age classes within a stand, or across stands, are not the same changes one sees if the stand is followed through time. In twelve stands sampled there is no evidence for succession, i.e. replacement of species over time.; Chapter Four examines the relative importance to forest dynamics of local population processes (i.e. seed production, germination, recruitment, mortality, height growth) and regional processes (i.e. disturbance, seed dispersal, and geomorphology). For all tree species rapid recruitment after fire is important to their regional persistence because only early recruiting species form the canopy and produce seed for the next generation. Local processes are relatively more important to the persistence of sprouting and serotinous species because local seed and sprouts are available after fire. However, regional processes are relatively more important to the persistence of wind-dispersed species because seed dispersal is required for re-colonization after fire.