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Forest carbon storage inherently depends on the frequency and severity of characteristic disturbances and long-term changes in climate. The tropical forest of Lanjenchi, Taiwan is affected by the northeast monsoon wind, resulting in a varying vegetation structure depending on wind exposure. However, the northeast monsoon winds have been decreasing due to the climate change. We used four censuses over 22 years (1997, 2005, 2013, and 2019) to examine how tree density and aboveground biomass change under different levels of wind stress. We assessed tree density, aboveground biomass, aboveground woody productivity, and aboveground woody mortality from trees with diameter at breast height (DBH) ≥ 1 cm across 5.28 ha subdivided into 10 × 10 m quadrats. We tested for differences in tree density and aboveground biomass among three habitat types (windward, intermediate, and leeward), among small-diameter (1 cm ≤ DBH < 10 cm), medium-diameter (10 cm ≤ DBH < 17.2 cm) and large-diameter trees (DBH ≥ 17.2 cm). The 49,481 trees (density 9,272 ± 3612 trees ha−1) of 140 species held 129.37 ± 51.95 Mg ha−1 of aboveground biomass. From 1997 to 2019, tree density decreased and aboveground biomass was stable in the whole forest. However, changes in density and aboveground biomass were apparent among different habitat types and among different diameter classes. Specifically, in the windward habitat, aboveground biomass of small-diameter trees declined over time (from 35.34 Mg ha−1 to 26.29 Mg ha−1), and that of large-diameter trees increased (from 48.62 Mg ha−1 to 57.78 Mg ha−1). In the leeward habitat, large-diameter trees exhibited both high biomass productivity (1.04 Mg ha−1 year−1) and mortality (1.43 Mg ha−1 year−1). Although the overall state of the forest appears to possess multi-decadal stability, differences in dynamics among diameter classes and habitats may lead to forest changes if trees in those habitats continue to respond differentially to shifting magnitudes of monsoon wind speed. [ABSTRACT FROM AUTHOR]

The reintroduction of fire to landscapes where it was once common is considered a priority to restore historical forest dynamics, including reducing tree density and decreasing levels of woody biomass on the forest floor. However, reintroducing fire causes tree mortality that can have unintended ecological outcomes related to woody biomass, with potential impacts to fuel accumulation, carbon sequestration, subsequent fire severity, and forest management. In this study, we examine the interplay between fire and carbon dynamics by asking how reintroduced fire impacts fuel accumulation, carbon sequestration, and subsequent fire severity potential. Beginning pre-fire, and continuing 6 years post-fire, we tracked all live, dead, and fallen trees ≥ 1 cm in diameter and mapped all pieces of deadwood (downed woody debris) originating from tree boles ≥ 10 cm diameter and ≥ 1 m in length in 25.6 ha of an Abies concolor/Pinus lambertiana forest in the central Sierra Nevada, California, USA. We also tracked surface fuels along 2240 m of planar transects pre-fire, immediately post-fire, and 6 years post-fire. Six years after moderate-severity fire, deadwood ≥ 10 cm diameter was 73 Mg ha−1, comprised of 32 Mg ha−1 that persisted through fire and 41 Mg ha−1 of newly fallen wood (compared to 72 Mg ha−1 pre-fire). Woody surface fuel loading was spatially heterogeneous, with mass varying almost four orders of magnitude at the scale of 20 m × 20 m quadrats (minimum, 0.1 Mg ha−1; mean, 73 Mg ha−1; maximum, 497 Mg ha−1). Wood from large-diameter trees (≥ 60 cm diameter) comprised 57% of surface fuel in 2019, but was 75% of snag biomass, indicating high contributions to current and future fuel loading. Reintroduction of fire does not consume all large-diameter fuel and generates high levels of surface fuels ≥ 10 cm diameter within 6 years. Repeated fires are needed to reduce surface fuel loading. [ABSTRACT FROM AUTHOR]

Questions: We examined the spatial patterns of dominant canopy species in a tropical forest to investigate: (a) what is the niche occupancy of canopy species with respect to topographic gradients; (b) what are the dominant ecological processes that explain their distribution; (c) what are the interactions among the most prevalent canopy species; and (d) what are the interactions between canopy species adults and juveniles trees? Location: Rabi permanent CTFS‐ForestGEO plot, Gabon. Methods: We selected the four most abundant canopy species and one timber species. We used Berman's test to determine the effect of three topographic variables on the distribution of each species and univariate analysis to model the spatial pattern of each species using either an inhomogeneous Poisson process or an inhomogeneous Cox process. We also used a bivariate form of the pair correlation function (PCF) to determine the spatial interaction between species and the correlation among conspecific adult and juvenile trees. Results: Four of the five species had aggregated spatial patterns while Lophira alata showed spatial randomness. Most of the variance in the local tree density was explained by within‐population dispersal processes rather than environmental factors. Bivariate PCF tests showed significant segregation between species associations. Two species exhibited aggregation at small distances between young and adult trees, while others showed either complete spatial randomness at small inter‐tree distances or segregation at large distances. Conclusions: This study showed that the spatial pattern in the majority of canopy species was aggregation. Seed dispersal limitation mainly explained the observed aggregation pattern. Habitat filtering, as evidenced by the influence of topographic variables on niche occupancy, marginally, yet significantly, explained this pattern. The different spatial patterns of the principal species permit their coexistence. Spatial segregation among adult and juvenile trees reveals a strong pattern of either species‐specific seed predation or pathogens. [ABSTRACT FROM AUTHOR]

Aim: To examine the contribution of large-diameter trees to biomass, stand structure, and species richness across forest biomes. Location: Global. Time period: Early 21st century. Major taxa studied: Woody plants. Methods: We examined the contribution of large trees to forest density, richness and biomass using a global network of 48 large (from 2 to 60 ha) forest plots representing 5,601,473 stems across 9,298 species and 210 plant families. This contribution was assessed using three metrics: the largest 1% of trees ≥ 1 cm diameter at breast height (DBH), all trees ≥ 60 cm DBH, and those rank-ordered largest trees that cumulatively comprise 50% of forest biomass. Results: Averaged across these 48 forest plots, the largest 1% of trees ≥ 1 cm DBH comprised 50% of aboveground live biomass, with hectare-scale standard deviation of 26%. Trees ≥ 60 cm DBH comprised 41% of aboveground live tree biomass. The size of the largest trees correlated with total forest biomass (r2=.62, p<.001). Large-diameter trees in high biomass forests represented far fewer species relative to overall forest richness (r2=.45, p<.001). Forests with more diverse large-diameter tree communities were comprised of smaller trees (r2=.33, p<.001). Lower largediameter richness was associated with large-diameter trees being individuals of more common species (r2=.17, p5.002). The concentration of biomass in the largest 1% of trees declined with increasing absolute latitude (r2=.46, p<.001), as did forest density (r2=.31, p<.001). Forest structural complexity increased with increasing absolute latitude (r2=.26, p<.001). Main conclusions: Because large-diameter trees constitute roughly half of the mature forest biomass worldwide, their dynamics and sensitivities to environmental change represent potentially large controls on global forest carbon cycling. We recommend managing forests for conservation of existing large-diameter trees or those that can soon reach large diameters as a simple way to conserve and potentially enhance ecosystem services. [ABSTRACT FROM AUTHOR]