by Gordon Fox
American Journal of Botany 99: 1-6
• Premise of the study: Reproductive output varies considerably among individuals within plant populations, and this... more
• Premise of the study: Reproductive output varies considerably among individuals within plant populations, and this is especially
so in cone production of conifers. While this variation can have substantial effects on populations, little is known about
its magnitude or causes.
• Methods: We studied variation in cone production for 2 years within a population of Pinus palustris Mill. (longleaf pine;
Pinaceae). Using hurdle models, we evaluated the importance of burn treatments, tree size (dbh), canopy status (open, dominant,
subordinate), and number of conspecifi c neighbors within 4 m (N 4 ).
• Key results: Cone production of individuals — even after accounting for other variables — was strongly correlated between
years. Trees in plots burned every 1, 2, or 5 years produced more cones than those burned every 7 years, or unburned. Larger
trees tend to produce more cones, but the large effects of the other factors studied caused substantial scatter in the dbh-cone
number relationship. Among trees in the open, dbh had little explanatory power. Subordinate trees with three neighbors produced
no cones.
• Conclusions: Tree size alone was a weak predictor of cone production. Interactions with neighbors play an important role in
generating reproductive heterogeneity, and must be accounted for when relating cone production to size. The strong betweenyear
correlation, together with the large variance in cone production among trees without neighbors, suggests that still more of
the variance may be explainable, but requires factors outside of our study.
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