Natural disturbance and structure in two primary boreal forests of western Newfoundland

It was long assumed that small-scale gap disturbance did not figure predominantly in boreal forests. Attention has focused, instead, on the role of stand-replacing fire and insect outbreaks in structuring the boreal forest landscape. Recent work, however, beginning principally in Scandinavian boreal forests, has highlighted the primary role of small-scale canopy gap disturbance in old-growth boreal forests.; To examine the role of gap dynamics in boreal forests of western Newfoundland, two primary forest landscapes were compared: (1) a 225 km2 Main River study area located at the southern base of the Great Northern Peninsula, and (2) a 106 km2 Little Grand Lake study area in western Newfoundland, Canada. It was hypothesized that the size and age structure, on both the stand- and landscape-level, were determined by distinctly different disturbance regimes, namely, fungal-mediated gap dynamics in the Main River forests and insect-mediated patch dynamics in the Little Grand Lake forests. The contrast between the cool, short-growing season of the Main River watershed and the warmer, longer-growing season of the Little Grand Lake area probably determine the different disturbance regimes.; The hypothesis was tested by comparing the size and age structure of two primary forests and inferring disturbance process from stand and landscape patterns. In the Little Grand Lake study area, a chronosequence of naturally regenerated stands also permitted the examination of post-disturbance stand development.; Results confirmed that the structure of both forest landscapes is determined by radically different disturbance regimes. The Main River landscape is a natural disturbance type (NDT) 1 ecosystem in which stand-initiating disturbance is rare. The Little Grand Lake landscape, however, is an NDT 3 ecosystem in which stand-initiating disturbances are frequent.; The old-growth stage of stand development dominates the Main River landscape. Stands are structurally complex with well-developed rotated sigmoidal diameter distributions (semi-logarithm), heterogeneous canopies, and reverse-J age class distribution with trees at maximal known ages. The seedling bank is old (up to 100+ years) and characterized as well by a reverse-J size and age distribution. Stand and landscape structure are reflective of a disturbance regime dominated by small-scale (<100 to 200 m2) canopy disturbance mediated by fungal root and butt rots.; The Little Grand Lake forests are a fine patch mosaic composed of approximately 0.5 to 150 ha even-aged or irregular stands comprising all age classes from 0--20 to 120 + years. All stages of stand development (stand initiation to transition/true old-growth) are present and form a well-developed chronosequence. Stands and seedling banks are generally modal or near modal in terms of tree diameter at breast height (dbh), height, and age distributions. Stands of edaphic or stochastic old-growth further complexify the mosaic landscape. Stand and landscape structure are reflective of a disturbance regime dominated by large-scale patch mortality and partial mortality mediated by recurrent hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) and spruce budworm (Choristoneura fumiferana (Clem.)) herbivory.; Sustainable forest management of these forest landscapes is called to develop appropriate strategies, goals and objectives that are congruent with differences in disturbance regime and stand and forest structure.