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Management of tree cover, either to curb bush encroachment or to mitigate losses of woody cover to over-browsing, is a major concern in savanna ecosystems. Once established, trees are often “trapped” as saplings, since interactions among disturbance, plant competition, and precipitation delay sapling recruitment into adult size classes. Saplings can be directly suppressed by wildlife browsing and competition from adjacent plants, and indirectly facilitated by grazers, such as cattle, which feed on neighboring grasses. Yet few experimental studies have simultaneously quantified the effects of cattle and wildlife on sapling growth, particularly over long time scales. We used a series of replicated 4-ha herbivore-manipulation plots to investigate the net effects of wildlife and moderate cattle grazing on Acacia drepanolobium sapling growth over 10 years that encompassed extended wet and dry periods. We also simulated more intense cattle grazing using grass removal treatments (0.5-m radius around saplings), and we quantified the role of intraspecific tree competition using neighborhood tree surveys (trees within a 3-m radius). Wildlife, which included elephants, had a positive effect on sapling growth. Wildlife also reduced neighbor tree density during the 10-yr study, which likely caused the positive effect of wildlife on saplings. Although moderate cattle grazing did not affect sapling growth, grass removal treatments simulating heavy grazing increased sapling growth. Both grass removal and neighbor tree effects on saplings were strongest during above-average rainfall years following drought. This highlights that livestock-driven reductions in grass cover and catastrophic wildlife damage to trees during droughts present a need, or an opportunity, for targeted management of sapling growth and woody plant cover during ensuing wet periods.

Plant self‐thinning, which is density‐dependent mortality, has several observed characteristics, including a certain mathematical relationship between growth and density. The original equation that describes self‐thinning is logw¯=C−(3/2)×logdensity, w¯ = mean weight. The basic equation is supported by data from ecology and forestry, but there have been a number of reported slopes that differ from −3/2. This study proposed that change in plant density over time decreases exponentially and that plant growth (weight or volume) increases over time according to one of two models: either exponential growth or sigmoid growth. Exponential growth with a finite time limit, in conjunction with exponential decrease in density, led to the equation log w = C + α/γ × log density, where α/γ < 0, w is total weight, but did not imply any particular value for its slope. Sigmoid growth, in conjunction with exponential decrease in density, led to the equation log (w/(a1 + a2w)) (or v) = C + a1/γ × log density, where a1/γ < 0, w (or v) is a total, but did not imply any particular value for its slope. For the data examined, exponential density decrease was supported by all data sets. For eight data sets, exponential growth was supported and in 7 of 8, log w = C + β log density was a good fit with α/γ a good predictor of β. For 31 data sets, sigmoid growth was supported, and in 29 of 31, log (w/(a1 + a2w)) (or v) = C + β log density was a good fit with a1/γ a good predictor of β. The numerical value of β can be regarded as an index, and there was some indication that a wide range of values (or lack) is associated with a wide (or narrow) range of environments to which the species is adapted. For the larch data, the initial spatial distribution of trees was aggregated but changed toward a random distribution of individuals over time.

Plants adjust their size and reproductive effort in response to numerous selection pressures and constraints. The self‐thinning law describes a well‐known trade‐off between size and density. Plants also trade‐off investment into growth vs. sexual reproduction, as described by life‐history theory. We build on past work on plant allometry and life history by examining both self‐thinning and size‐dependent reproduction in a single plant species, the saltmarsh grass Spartina alterniflora, across a wide range of settings: three landscape positions, two habitats and eight sites, across sixteen years. Plants in different landscape positions and years varied tremendously in size and shoot density. However, all this variation could be explained by a single allometric relationship consistent with the self‐thinning law, but with a lower slope. Flowering was size‐dependent, and the size at which plants had a 50% probability of flowering varied among habitat, sites and years. Plants that were stressed reproduced at a smaller size than plants that were growing under good conditions, and this pattern was consistent among habitat, sites and years. Finally, reproductive biomass and the proportion of shoots flowering increased with increasing vegetative size (plant height or shoot biomass). Combining these two patterns, S. alterniflora plants growing high density are small and reproduce at a smaller size than large plants growing at low density. Although there is tremendous spatial and temporal variation in S. alterniflora growth and reproductive patterns, all this variation can be understood as resulting from two simple allometric trade‐offs. Because saltmarsh plants often occur in monospecific stands, they may serve as simple, model systems for studies of plant life history. A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article.

1. Tropical forest mortality is controlled by both biotic and abiotic processes, but how these processes interact to determine forest structure is not well understood. Using long-term demography data from permanent forest plots at the Paracou Tropical Forest Research Station in French Guiana, we analysed the relative influence of competition and climate on tree mortality. We found that self-thinning is evident at the stand level, and is associated with clumped mortality at smaller scales (<2 m) and regular spacing of living trees at intermediate (2.5-7.5 m) scales. A competition index (CI) based on spatial clustering of dead trees was used to build predictive mortality models, which also accounted for climate interactions. 2. The model that most closely fitted observations included both the CI and climatic variables, with climate-only and competition-only models less informative than the full model. There was strong evidence for U-shaped size-specific mortality, with highest mortality for small and very large trees, as well as sensitivity of trees to drought, especially when temperatures were high, and when soils were water saturated. The effect of the CI was more complex than expected a priori: a higher CI was associated with lower mortality odds, which we hypothesize is caused by gap-phase dynamics, but there was also evidence for competition-induced mortality at very high CI values. 3. The strong signature of competition as a control over mortality at the stand and individual scales confirms its important role in determining tropical forest structure. The complexity of the competition-mortality relationship and its interaction with climate indicates that a thorough consideration of the scale of analysis is needed when inferring the role of competition in tropical forests, but demonstrates that climate-only mortality models can be significantly improved by including competition effects, even when ignoring species-specific effects. 4. Synthesis. Empirical models such as the one developed here can help constrain and improve process-based vegetation models, serving both as a benchmark and as a means to disentangle mortality processes. Tropical vegetation dynamic models would benefit greatly from explicitly considering the role of competition in stand development and self-thinning while modelling demography, as well as its interaction with climate.

Density dependence (DD) controls community recovery following widespread mortality, yet this principle rarely has been applied to coral assemblages. The reefs of Mo’orea, French Polynesia, provide the opportunity to study DD of coral population growth, because coral assemblages in this location responded to declines in abundance with high recruitment and an increase in cover during which recruitment of pocilloporid corals was inversely associated with density. This study tests for DD in this system, first, by describing the context within which it operates: coral cover changed from 46% in 2005, to <1% in 2010 following an outbreak of a corallivorous sea star and a cyclone, and then increased to 74% by 2017, in large part through inverse density-associated pocilloporid recruitment. Second, a test for DD of recruitment was conducted by decreasing Pocillopora spp. cover from 33% to 19%: one year later, the density of Pocillopora spp. recruits was 1.65-fold higher in the low vs. high cover treatment. Finally, the effects of DD were investigated by comparing simulated and empirical distributions of pocilloporid colonies: as predicted by DD, small colonies were randomly distributed, while large colonies were uniformly distributed. Together these results demonstrate DD of population regulation for Pocillopora spp. corals, thus revealing the potential importance of this ecological principle in determining the resilience of coral assemblages.

The self‐thinning rule in forest stands is fundamental to the development of density management strategies, as it determines the maximum stand density achievable for a given tree size. Accurate modeling of the maximum density line is crucial, but selecting representative data points for this purpose remains a challenge. Using 18 years of data from five Cunninghamia lanceolata plantations with varying initial planting densities, this study investigated whether relationships between mean tree basal area (g) and height (H) can reveal forest developmental stages and identify when stands begin self‐thinning and reach maximum density. Our results showed a significant linear relationship (p < 0.05) between g and H after self‐thinning was established, supporting the presence of self‐regulatory growth mechanisms. These findings enabled the development of a novel sample selection method for constructing more accurate maximum density line models, outperforming traditional methods that rely on arbitrary thresholds. Additionally, we derived formulas to describe total stand basal area (G1.0) during different growth stages, revealing positive correlations with mean height during early growth and negative correlations with mean diameter during self‐thinning. This research advances the understanding of self‐thinning dynamics and provides practical tools for improving density management in plantation forestry. The mean basal area and height showed a significant linear relationship during two growth stages (from canopy closure to prethinning, anaphase self‐thinning). The forest may have a self‐regulatory mechanism that ensures a relative balance of mean basal area and height.

Questions: What are the prevailing types of intraspecific spatial distributions and interspecific association patterns at species and life stage levels of trees in a tropical rain forest? Which ecological processes could structure these patterns? Possible processes include dispersal limitation, self-thinning, facilitation and competition between species and life stages. Location: A tropical broad-leaved forest in north-central Vietnam. Methods: We used univariate and bivariate pair-correlation functions to investigate the spatial distribution and association patterns of 18 abundant tree species.To disentangle first-and second-order effects, we used a scale separation approach with the heterogeneous Poisson process as null model. Results: (1) Sixteen of 18 species had aggregated patterns at various scales and regardless of their abundance. (2) Significant and aggregated patterns were found in 64% of all specific life stages. (3) At scales up to 15 m, 12.4% species pairs showed significant associations, among that 71% were spatial attractions, 5% were spatial repulsions and 24% were non-essential interactions. (4) In different life stage associations, attractions (81%) predominated over repulsions (19%) at small scales of up to 15 m. Conclusions: Our findings provide evidence that dispersal limitation may regulate the spatial patterns of tree species. Moreover, positive spatial associations between tree species and life stages suggest the presence of species herd protection and/or facilitation in this forest stand, while the persistence of intraspecific aggregation through life stages suggests a very late onset or even absence of selfthinning.Habitat heterogeneity plays an important role for species distribution patterns, and the spatial segregation occurs at a scale around 15 m in this forest.

1. Forests are an important, yet poorly understood, component of the global carbon cycle. We develop a general integrative framework for modelling the influences of stand age, environmental conditions, climate change and disturbance on woody biomass production and carbon sequestration. We use this framework to explore drivers of carbon cycling in New Zealand mountain beech forests, using a 30‐year sequence of data from 246 permanent inventory plots. 2. A series of disturbance events (wind, snow storms, earthquakes and beetle outbreaks) had major effects on carbon fluxes: by killing large trees, they removed significant quantities of carbon from the woody biomass pool, and by creating canopy gaps, they reduced the crown area index (CAI) of stands (i.e. canopy area per unit ground area) and woody biomass production. A patch‐dynamics model, which we parameterized using permanent plot data, predicts that episodic disturbance events can create long‐term (c. 100‐year) oscillations in carbon stocks at the regional scale. 3. Productivity declined with stand age, as shown in many other studies, but the effect was hard to detect because of canopy disturbance. Individual trees can increase productivity by adjusting the positioning, nutrient content and angle of leaves within canopies. We show that such optimization is most effective when trees are large and suggest it reduces the impact of water and nutrient limitation in old stands. 4. We found no evidence that forests were responding to changing climatic conditions, although strong altitudinal trends in biomass production indicate that global warming could alter carbon fluxes in future. 5. Synthesis.Our study emphasizes the critical role of disturbance in driving forest carbon fluxes. Losses of biomass arising from tree death (particularly in older stands) exceeded gains arising from growth for most of the 30‐year study, moving 0.3 Mg C ha−1 year−1 from biomass to detritus and atmospheric pools. Large‐scale disturbance events are prevalent in many forests world‐wide, and these events are likely to be a driving factor in determining forest carbon sequestration patterns over the next century.

As climatic changes continue to drive increases in the frequency and severity of forest fires, it is critical to understand all of the factors influencing the risk of forest fire. Using a spatial dataset of areas burnt over a 65 year period in a 528 343 ha study area, we examined three possible drivers of flammability dynamics. These were: that forests became more flammable as fine biomass (fuel) returned following disturbance (H1), that disturbance increased flammability by initiating dense understorey growth that later self-thinned (H2), and that climatic effects were more important than either of these internal dynamics (H3). We found that forests were unlikely to burn for a short ‘young’ period (5–7 years) following fire, very likely to burn as the regrowing understorey became taller and denser (regrowth period), then after a total post-disturbance period of 43–56 years (young + regrowth periods), fire became unlikely and continued to decrease in likelihood (mature period). This trend did not change as the climate warmed, although increases in synoptic variability (mean changes in synoptic systems per season) had a pronounced effect on wildfire likelihood overall. Young forest and regrowth forest became increasingly likely to burn in years of greater synoptic variability and the time taken for forests to mature increased, but in years with the most severe synoptic variability, mature forests were the least likely to burn. Our findings offer an explanation for fire behaviour in numerous long-term studies in diverse forest types globally and indicate that, even in the face of a warming climate, ‘ecologically-cooperative’ approaches may be employed that reinforce rather than disrupt natural ecological controls on forest fire. These range from traditional indigenous fire knowledge, to modern targeting of suppression resources to capitalise on the benefits of self-thinning, and minimise the extent of dense regrowth in the landscape.

While enhanced tree growth over the last decades has been reported in forests across the globe, it remains unclear whether it drives persistent biomass increases of forest stands, particularly in mature forests. Enhanced tree growth and stand-level biomass are often linked with a simultaneous increase in density-driven mortality and a reduction in tree longevity. Identifying empirical evidence regarding the balance between these processes is challenging due to the confounding effects of stand history, management, and environmental changes. Here, we investigate the link between growth and biomass via the negative relationship between average tree size and stand density (tree number per area). We find increasing stand density for a given mean tree size in unmanaged closed-canopy forests in Switzerland over the past six decades and a positive relationship between tree growth and stand density across forest plots—qualitatively consistent with our simulations using a mechanistic, cohort-resolving ecosystem model (BiomeE). Model simulations show that, in the absence of other disturbances, enhanced tree growth persistently increases biomass stocks despite simultaneous decreases in carbon residence time and tree longevity. However, the magnitude of simulated biomass changes for a given growth enhancement critically depends on the shape of the mortality functions. Our analyses reconcile reports of growth-induced reductions of tree longevity with model predictions of persistent biomass increases, and with our finding of trends toward denser forests in response to growth—also in mature stands.