In tropical forests, trees often have damage in the form of visible cavities. However, the impacts of these cavities on tropical tree growth and survival are unknown, despite potential implications for the global carbon cycle. Here, we integrate 10 years of forest dynamics data with a survey of cavity presence on 25,450 rainforest trees (> 5 cm in diameter) in the 20 ha Xishuangbanna plot in southern China. We found that cavities negatively impacted tree growth, but not survival, with the growth of smaller trees more negatively affected by cavities. Variation in the impact of cavities was not explained by functional traits related to species life history strategy (specific leaf area, wood density, seed mass, leaf %N, leaf %P). These results suggest that cavities may affect both the compositional and carbon dynamics of tropical forests, but further research is needed to determine what drives variation amongst tree species in cavity impact.

The composition, dynamics, and health of forest tree communities are governed by interactions with the abiotic and biotic environment. Fungi are critical biotic interactors that play an increasingly appreciated role in forest tree health, particularly with respect to mycorrhizal and pathogenic fungi. Heart rot fungi, while known to infect a large fraction of the individuals in managed stands, have been considerably understudied in tree community ecology. Heart rot has been predicted to form hotspots in the forest due to crown or bole damage and/or soil moisture gradients and is expected to vary across species due to life‐history differences. To address this knowledge gap, we quantified the incidence, magnitude, and spatial distribution of heart rot in 328 individual trees with diameters greater than or equal to 10 cm across the six most dominant tree species in a mixed broadleaf temperate forest dynamics plot. The results show that 71% of individuals display some degree of heart rot in this natural community. The incidence of heart rot did not significantly vary across species despite their life history strategy differences, but one species had a significantly higher magnitude of heart rot in infected individuals. Lastly, heart rot was spatially clustered across species, but heart rot incidence and magnitude were not related to soil moisture, indicating the importance of crown and bole breakage likely promoted by severe weather. The present study has conducted the first spatially explicit study of heart rot incidence and magnitude in a natural forest tree community. We demonstrate that over two‐thirds of the large trees in the forest studied have some degree of heart rot indicating their widespread, but underappreciated, incidence in tree communities. We demonstrate that heart rot is nonrandomly distributed in this community and that spatial clustering of heart rot in forests is most likely due to hotspots of individual tree damage and not gradients in soil moisture.

Summary: Forest health is critical for sustaining ecosystem services like carbon sequestration. Heart rot, a widespread disease in upland northern hardwood forests, may affect greenhouse gas (CO ₂ and CH ₄ ) fluxes, but its impacts remain poorly measured. Using non‐destructive tomography and direct gas flux measurements, we quantified the effects of heart rot on sugar maple ( Acer saccharum Marshall) stems and surrounding soils. Heart rot increased CH ₄ emissions from stems but did not affect CO ₂ fluxes from stems or soils, nor CH ₄ fluxes from soils. All stems emitted CO ₂ and CH ₄ , while soils absorbed CH ₄ and emitted CO ₂ . Stem CH ₄ fluxes strongly correlated with decay severity, but CO ₂ fluxes did not. CH ₄ was produced in the heartwood, CO ₂ in the sapwood, and methanogens were present in all stems. Severe heart rot often caused bark fractures, enhancing CH ₄ diffusion to the atmosphere and creating emission hotspots. These findings show that forest health influences carbon cycling. Capturing stem CH ₄ hotspots requires direct measurement, and fungal diseases like heart rot may shift forests from CH ₄ sinks to sources, with implications for atmospheric greenhouse gas dynamics.

1. Trees must functionally respond to dynamic abiotic and biotic challenges in their environment. Heart rot decay is a common disease in adult trees in forests, but the functional responses of individual trees to rot is rarely quantified. 2. Here we tested the hypothesis that heart rot should impact the water status, as measured by water use efficiency, and stress and defense responses, as measured using transcriptomics in the ecologically and economically important tree species Acer saccharum. 3. We found that 5536 genes are differentially expressed between trees that have no decay and those that do have rot, while leaf water use efficiency was not related to the level of heart rot. The genes that were differentially expressed were annotated to core physiological processes and stress, plant-pathogen interactions and transcription factors and demonstrate a widespread functional genomic response to heart rot. 4. Heart rot decay is relatively common in adult trees in natural stands and while the functional consequences of this disease can be difficult to detect with a measure of water use efficiency, there are genome-wide changes in expression that provided detailed insights into how trees provide an initial and often sustain response to rot.

1. The composition, dynamics and health of forest tree communities are governed by interactions with the abiotic and biotic environment. Fungi are critical biotic interactors that play and increasingly appreciated role in forest tree health particularly with respect to mycorrhizal and pathogenic fungi. Heart rot fungi, while known infect large fractions of the individuals in managed stands, have been considerably understudied in tree community ecology. Heart rot has been predicted to form hotspots in the forest due to crown or bole damage and/or soil moisture gradients and is expected to vary across species due to life history differences. 2. To address this knowledge gap, we quantified heart rot the incidence, magnitude and spatial distribution of heart rot in 328 individuals with diameters greater than or equal to 10 cm across the six most dominant tree species in a mixed broadleaf temperate forest dynamics plot. 3. The results show that 71% of individuals display some degree of heart rot in this natural community. The incidence of heart rot does not significantly vary across species despite their life history strategy differences, but one species had significantly more heart rot in infected individuals. Lastly, heart rot was spatially clustered across species, but heart rot incidence and magnitude were not related to soil moisture indicating the importance of crown and bole breakage likely promoted by severe weather. Summary The present study conducted the first spatially explicit study of heart rot incidence and magnitude in a natural forest tree community. We demonstrate that over two thirds of every large tree in the forest studied have some degree of heart rote indicating their widespread, but underappreciated, role in tree communities. We demonstrate that heart rot is non-randomly distributed in this community and that spatial clustering of heart rot in forests is most likely due hotspots of individual tree damage and not gradients in soil moisture.