Relative competitiveness of nine early-successional boreal forest species associated with planted jack pine and black spruce seedlings

Differences in yield-density models derived from an additive experimental d esign were used to compare the relative competitiveness of nine early-succe ssional boreal forest plants (aster, grass, fireweed, fern, raspberry, will ow, alder, birch, and aspen) on jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill.) BSP). A randomized complete block split-spli t-plot design with three replications blocked on soil type was used. Initia l density gradients were 0-4 plants/m(2) for woody and 0-8 plants/m(2) for herbaceous species. An a priori analytical approach that compared a full mo del (using Linear regression analysis of 4th-year stem diameter of conifers under increasing cover and height of competitors) to various reduced model s was used to assess competition. Increasing cover and (or) height of all c ompetitors (except fern) significantly (P < 0.05) decreased conifer stem di ameter. The final regression model (based on visual estimates of cover and differences in initial conifer size) accounted for 89% of the variation in stem diameter. During the years studied, both conifers responded similarly to competition, and herbaceous species were on average 28.9% mon competitiv e than woody species. Under different growing conditions (e.g., a natural f orest) the relative competitiveness of herbaceous and woody species may var y from these results.