Sprouting extends the regeneration niche in temperate rain forests: The case of the long-lived tree Eucryphia cordifolia

Sprouting is a widespread trait of geographical, ecological and taxonomical scales that allows resource exploitation, space colonization, vegetative reproduction and post-disturbance persistence. It is considered that persistence is the most frequent functional role of sprouting in woody plants. Here we propose that niche differentiation between sprouts and saplings extends the regeneration niche to suboptimal conditions for sexual recruitment. To test this hypothesis, we sampled root suckers (sprouts) and saplings of the long-lived tree species Eucryphia cordifolia Cav. in an even-aged coastal temperate rain forest. Canopy openness was measured over each recruit as a proxy of regeneration niche. Sapling survival was checked after two years. The entire forest canopy openness range was used as an estimation of niche availability. Light and microclimatic conditions were recorded for different canopy openness. Sprouts and saplings occupied a narrow range of the canopy openness near to the closest extreme of the gradient (4.8-14.1%). The distribution of saplings was explained by the lower survival of small saplings under more open canopies, as a consequence of the interactive effect of higher evaporative demand and radiation load in more opened canopies. Although the niches of sexual and vegetative recruits slightly overlapped (31% of the interquartile range on average), sprouts inhabit the more opened sites. Therefore, sprouts extend the regeneration niche to suboptimal conditions for sapling establishment. Our results contribute toward explaining the high colonization ability of E. cordifolia in this kind of forest, whose composition is strongly driven by gap dynamics.