Conifer samara structure diverges across the height of the tree crown

Abstract

Samara morphology, including weight, size, and wing-to-seed ratios, is an important precursor to seed dispersal, and therefore a primary driver in large-scale alien conifer invasions. Prior studies have not reported morphological differences between samaras of different cones within a tree possibly because cone position at differing crown heights has not been examined. This preliminary study investigated whether cones from different crown heights of three lodgepole pine (Pinus contorta Douglas) trees differ in the morphological characteristics of their samaras. Samaras from the lower tree crown were 17% heavier on average than those from the upper crown, without any significant differences in wing loading. Cones in the upper crown produced more seeds than in the lower crown, although this was inconsistent across the small sample size. These results suggest the effects on primary seed-dispersal are negligible, but further research is needed to determine the effect on secondary seed-dispersal. Larger seeds from the lower crown are better adapted to survive in a competitive environment near other trees, while cones in the upper crown may produce more, but smaller, seeds which could infer a bet-hedging strategy when dispersing into heterogeneous environments. These results suggest canopy-height should be considered when accounting for inter-cone variation in conifers.