Nutrient availability predicts multiple stem frequency, an indicator of species resprouting capacity in tropical forests

Resprouting capacity is a key component of plant life history. While resprouting requires substantial nutrient reserves to support new growth, the influence of soil fertility on resprouting is largely unknown. We tested whether the frequency of multi-stemmed trees, a potential indicator of resprouting history, is associated with low soil fertility, reflecting selection for conservative life histories that enhance survival, or with high fertility, reflecting greater resource availability to support regrowth. Data from the Barro Colorado Island (BCI) 50-ha plot in Panama showed that multi-stemmed trees are more likely to resprout during their lifetime than single-stemmed trees, and that multiple stem frequency has a strong taxonomic signal for adult trees. To test how multiple stem frequency varies with demographic rates and nutrient allocation strategies, we compiled functional trait datasets for 71 species from lowland forest on BCI and 43 species from lower montane forest in western Panama. We also assessed environmental correlates of community-wide multiple stem frequency in thirty-seven 1-ha lowland plots in the Panama Canal watershed and twelve 1-ha montane plots in western Panama, spanning gradients of rainfall and soil fertility. Multiple stem frequency was not correlated with species demographic rates or wood density, suggesting that resprouting is unrelated to classical ‘persistence’ traits in neotropical tree species. Multiple stem frequency of tree species occurring on BCI was weakly but significantly positively correlated with regional soil phosphorus associations, but unrelated to foliar nutrient concentrations. Multiple stem frequency covaried strongly with soil and tissue nutrient status across fertility gradients. It was significantly positively correlated with nutrient allocation traits, including foliar phosphorus and wood nitrogen and phosphorus, among species sampled across soil habitats in western Panama. At the community level, the proportion of woody stems >10 cm DBH with at least one multiple stem increased with plant available soil phosphorus. Synthesis. These results suggest a novel mechanism by which soil phosphorus availability influences tree recruitment and forest dynamics by facilitating resprouting. Future experiments should seek to understand whether soil fertility mediates resprouting frequency through nutrient supply directly, or via the formation of enhanced wood nutrient reserves.