Reproductive ecology and allometry of red pine (Pinus resinosa) at the northwestern limit of its distribution range in Manitoba, Canada

Abstract

Red pine (Pinus resinosa Ait.) has been described as a poor seed producer at its distribution range limit; however, few studies have verified this claim or have examined the factors influencing the reproduction of the species. In 2000, data were collected from 60 trees growing in Manitoba at the extreme northwest limit of the natural distribution range for this species. Cones per tree were counted and samples weighed and measured. Likewise, seeds per cone were counted, measured, weighed, and tested for germination. Correlation and regression analyses compared measured characteristics among cones, among individual trees, and among portions of tree crowns (north, west, south, and east portions). Cone abundance among individual trees was significantly and positively correlated with stem diameter and with basal area increment from 1 to 4 years preceding cone maturation. Cone size and fresh mass and seed abundance, mass, and germination were not significantly correlated with individual trees or crown portions; however, seed number per cone and seed size were found to be significantly and positively correlated with cone size. Germination success in red pine increased with seed mass to a certain threshold value, beyond which more than 80% of the seeds germinated no matter what their mass. Our data for 2000 and field observations for 1999 and 2001 showed that red pine at its northwest limit of distribution range produced numerous cones and viable seeds.Key words: red pine, Pinus resinosa, distribution limit, seeds, germination, cones.