No abstract

In tropical forest communities, seedling recruitment can be limited by the number of fruit produced by adults. Fruit production tends to be highly unequal among trees of the same species, which may be due to environmental factors. We observed fruit production for ~2,000 trees of 17 species across 3 years in a wet tropical forest in Costa Rica. Fruit production was modeled as a function of tree size, nutrient availability, and neighborhood crowding. Following model selection, tree size and neighborhood crowding predicted both the probability of reproduction and the number of fruit produced. Nutrient availability only predicted only the probability of reproduction. In all species, larger trees were more likely to be reproductive and produce more fruit. In addition, number of fruit was strongly negatively related to presence of larger neighboring trees in 13 species; presence of all neighboring trees had a weak‐to‐moderate negative influence on reproductive status in 16 species. Among various metrics of soil nutrient availability, only sum of base cations was positively associated with reproductive status, and for only four species. Synthesis Overall, these results suggest that direct influences on fruit production tend to be mediated through tree size and crowding from neighboring trees, rather than soil nutrients. However, we found variation in the effects of neighbors and nutrients among species; mechanistic studies of allocation to fruit production are needed to explain these differences.

No abstract

Regional-scale tree die-off events driven by drought and warming and associated pests and pathogens have occurred recently on all forested continents and are projected to increase in frequency and extent with future warming. Within areas where tree mortality has occurred, ecological, hydrological and meteorological consequences are increasingly being documented. However, the potential for tree die-off to impact vegetation processes and related carbon dynamics in areas remote to where die-off occurs has rarely been systematically evaluated, particularly for multiple distinct regions within a given continent. Such remote impacts can occur when climate effects of local vegetation change are propagated by atmospheric circulation-the phenomena of 'ecoclimate teleconnections'. We simulated tree die-off events in the 13 most densely forested US regions (selected from the 20 US National Ecological Observatory Network [NEON] domains) and found that tree die-off even for smaller regions has potential to affect climate and hence Gross Primary Productivity (GPP) in disparate regions (NEON domains), either positively or negatively. Some regions exhibited strong teleconnections to several others, and some regions were relatively sensitive to tree loss regardless of what other region the tree loss occurred in. For the US as a whole, loss of trees in the Pacific Southwest-an area undergoing rapid tree die-off-had the largest negative impact on remote US GPP whereas loss of trees in the Mid-Atlantic had the largest positive impact. This research lays a foundation for hypotheses that identify how the effects of tree die-off (or other types of tree loss such as deforestation) can ricochet across regions by revealing hot-spots of forcing and response. Such modes of connectivity have direct applicability for improving models of climate change impacts and for developing more informed and coordinated carbon accounting across regions.

Summary Trees commonly reproduce via masting cycles, which involves synchronized inter‐annual variability in fruit crop size. A few individuals in a population will commonly produce much more fruit than others. If these trees produce fruit more frequently, as indicated by a lower inter‐annual variability in fruit production, they may dominate fruit production over time. By measuring fruit production of 1635 individuals of 10 temperate tree species across 4 years in northern lower Michigan, we estimated the inter‐annual variability and synchrony in each species. We compared fruit production estimates with measurements of tree size, soil nutrient availability and neighbourhood crowding to investigate the source of inter‐individual variation in number of fruit produced. We found that trees’ fruit production increased with tree size. The trees that accounted for the largest proportion of total fruit production had lower inter‐annual variability and higher synchrony in fruit production. These ‘super‐producer’ trees tended to have high nutrient availability and few neighbouring trees, but there were no effects of nutrient availability or neighbourhood crowding on fruit production in the population as a whole. Synthesis. Masting is a population‐level phenomenon, and is typically studied at this level. However, when we apply individual tree observations of fruit production to this phenomenon, it reveals super‐producers which produce fruit more consistently than the rest of the population. By reducing inter‐annual variability in fruit production, but increasing synchrony and making large numbers of fruit, super‐producers may be able to reap the benefits of masting while governing population fruit production over time.