Reproductive traits variation in the herb layer of a submediterranean deciduous forest landscape

In submediterranean ecosystems macro-environmental stress gradients (winter cold stress and summer drought stress linked to elevation, slope aspect, and angle) affect forest distribution and composition. We hypothesized that in the herb layer of submediterranean deciduous woods (central Apennines), environmental stress gradients, jointly with overstory type, determine patterns of reproductive strategies, which are supported by different acquisitive/retentive traits. We used indicator species analysis, canonical redundancy analysis, and variance partitioning to identify the main gradients of trait variation, detect trait patterns, and assess the contribution of each environmental variable to the explanation of trait variability. Our results indicated that reproductive traits, related to resource acquisition and conservation strategies, showed a pattern mainly linked to the joint effect of altitude and overstory type and, second, to slope aspect. Species with both sexual and vegetative propagation, more abundant than those reproducing only sexually, did not show any trend. Below 1,000 m a.s.l. the long-lasting growing season favored traits aimed at efficient light and soil resource acquisition and space exploitation (e.g., persistent green leaves, runners, tap roots, medium sized seeds) that support a long reproductive cycle. Over 1,000 m a.s.l. the intense and long-lasting winter cold stress and the shorter growing period fostered traits aimed at fast growth and reproduction (e.g., self-pollination, low seed weight, spring and overwintering green leaves), and at stress tolerance (rhizomes, bulbils).