Chia-Hao Chang-Yang

Forest-associated Saccharomycotina occur at low relative abundance, limiting inference about their diversity and dynamics. We sampled leaf litter weekly for 47 weeks across a subtropical forest in northern Taiwan. Enrichment, isolation and ITS sequencing recovered 687 isolates, including 613 Saccharomycotina representing 56 described species and 77 putatively novel operational taxonomic units. Rarefaction indicated unsampled culturable diversity. Among litter traps, community dissimilarity was high and dominated by taxon replacement, but neither topography nor geographic distance was associated with composition, and turnover matched randomised expectations. Richness peaked during warm, wet periods and declined in winter, and minimum temperature showed the strongest statistical association. Composition was associated with maximum temperature, minimum relative humidity, precipitation and solar radiation. Selected isolates' thermal optima covaried with collection-week temperatures, and two October Magnusiomyces magnusii isolates had higher optima than four winter isolates. Together, these findings reveal substantial culturable diversity and seasonal community restructuring consistent with temperature-related filtering.

Background and Aims: Plant–soil feedback (PSF) shapes plant competition, yet classic PSF experiments often overlook the density dependence and temporal complexities of PSFs, especially after host death. We ask whether microbial effects vary after host death and mediate density dependence in seedling competition. Methods: We combined forest inventory data from a subtropical forest with a density-gradient greenhouse experiment to evaluate seedling competition among two tree species with different mycorrhizal associations (ectomycorrhizal versus arbuscular mycorrhizal). In 2023, we collected soil inocula from living and dead trees (died between 2014 and 2019) with unsterilized and sterilized treatments. We applied invasion analysis to infer seedling competitive outcomes and used bootstrapping to evaluate uncertainty. Results: Soil microbial communities shaped seedling competition, favoring the ectomycorrhizal species. Using soils collected from living versus dead hosts as live inocula, we found similar plant competitive outcomes, indicating that PSF persists for over 4–9 years following host death. In contrast, when using sterilized inoculum, we found shifts in competition after host death, suggesting underlying abiotic changes which might masked by microbial effects. Moreover, we found significant evidence that soil microbes can mediate nonlinear density dependence in seedling competition. Conclusion: We provide experimental evidence of persistent microbial legacies that benefit ectomycorrhizal tree species in a subtropical forest. Our study demonstrates how integrating field-based census data with density-gradient experiments and explicit uncertainty estimation can better capture the temporal dimensions, complexities of density dependence, and uncertainties of PSF.

The duration of tree seedling persistence in the understory varies greatly between forests and across environmental conditions within a forest ecosystem. To examine species‐level variation in understory persistence and passage to the sapling life stage, we followed 5236 seedlings in single‐tree canopy gaps and closed canopy conditions over three years and simulated seedling passage times and the number of seedlings required to produce one 1.5‐m tall sapling of five common tree species in a hemlock–hardwood forest of Massachusetts, USA. Averaged across species, it took 26 years in gaps and 31 years under closed canopies to go from a first‐year seedling to a 1.5‐m sapling. Across species, the average number of seedlings needed for one sapling was 294 in gaps and 2674 in closed canopy environments. We observed high interspecific variation in passage times and number required for one sapling. Betula congeners and Pinus strobus took less time and significantly fewer individuals than Acer rubrum and Tsuga canadensis, which are generally regarded as more tolerant of understory conditions. The largest intraspecific difference in gaps versus closed canopy environments was for Quercus rubra, where we estimated the number of seedlings required to produce one sapling in closed canopies to be 172 times higher than in gaps. Stem breakage also increased the number of seedlings needed per sapling, especially in closed canopy environments. We evaluated our estimates in the lab by aging cross‐sections obtained from seedlings in gap and closed canopy conditions. Compared to our empirical age‐to‐height relationships, most simulations tended to underpredict seedling age for a given height, suggesting that passage times may be even longer than our simulations indicated. Our study shows that trees can persist for decades in the seedling life stage, highlighting a need for better‐parameterized recruitment processes in demographic forecasting.

Questions: Maintaining forest species diversity, regenerative function and ecosystem resilience begins with successful seedling establishment. Despite their critical role, seedlings face the highest mortality risks among plant life‐history stages. Our research aims to answer the following questions: In a tropical forest disturbed by typhoons, what is the median survival time for seedlings, to what extent do light levels contribute to mortality risks and what are the crucial mortality risks across seedling age groups?Location: A tropical mountain zonal foothill evergreen broad‐leaved forest in Nanjenshan Nature Reserve, Taiwan, frequently visited by typhoons.Methods: We investigated woody seedlings in 75 quadrats (each 1 m × 1 m) every 3 months from October 2009 to January 2018, spanning 8.3 years with 34 censuses. We used the Kaplan–Meier method to estimate seedlings’ median survival time and Generalized Linear Models to identify mortality risk factors for all seedlings and those that persisted beyond the median survival time.Results: The median survival time for all seedlings was 0.5 years, ranging from 0.25 years for shade‐intolerant species to 1.25 years for shade‐tolerant species. Seedlings germinated in high‐light microhabitats and high conspecific seedling density exhibited higher mortality probabilities, regardless of age.Conclusions: This study reveals the short survival time and key mortality risks of seedlings in a typhoon‐disturbed forest. The negative impact of light levels on seedling survival highlights the potential consequences of increased light levels resulting from typhoon disturbances in the study region.

The fundamental trade‐off between current and future reproduction has long been considered to result in a tendency for species that can grow large to begin reproduction at a larger size. Due to the prolonged time required to reach maturity, estimates of tree maturation size remain very rare and we lack a global view on the generality and the shape of this trade‐off. Using seed production from five continents, we estimate tree maturation sizes for 486 tree species spanning tropical to boreal climates. Results show that a species' maturation size increases with maximum size, but in a non‐proportional way: the largest species begin reproduction at smaller sizes than would be expected if maturation were simply proportional to maximum size. Furthermore, the decrease in relative maturation size is steepest in cold climates. These findings on maturation size drivers are key to accurately represent forests' responses to disturbance and climate change.

The future trajectory of global forests is closely intertwined with tree demography, and a major fundamental goal in ecology is to understand the key mechanisms governing spatio‐temporal patterns in tree population dynamics. While previous research has made substantial progress in identifying the mechanisms individually, their relative importance among forests remains unclear mainly due to practical limitations. One approach to overcome these limitations is to group mechanisms according to their shared effects on the variability of tree vital rates and quantify patterns therein. We developed a conceptual and statistical framework (variance partitioning of Bayesian multilevel models) that attributes the variability in tree growth, mortality, and recruitment to variation in species, space, and time, and their interactions – categories we refer to as organising principles (OPs). We applied the framework to data from 21 forest plots covering more than 2.9 million trees of approximately 6500 species. We found that differences among species, the species OP, proved a major source of variability in tree vital rates, explaining 28–33% of demographic variance alone, and 14–17% in interaction with space , totalling 40–43%. Our results support the hypothesis that the range of vital rates is similar across global forests. However, the average variability among species declined with species richness, indicating that diverse forests featured smaller interspecific differences in vital rates. Moreover, decomposing the variance in vital rates into the proposed OPs showed the importance of unexplained variability, which includes individual variation, in tree demography. A focus on how demographic variance is organized in forests can facilitate the construction of more targeted models with clearer expectations of which covariates might drive a vital rate. This study therefore highlights the most promising avenues for future research, both in terms of understanding the relative contributions of groups of mechanisms to forest demography and diversity, and for improving projections of forest ecosystems.

Numerous studies have shown reduced performance in plants that are surrounded by neighbours of the same species^1,2, a phenomenon known as conspecific negative density dependence (CNDD)³. A long-held ecological hypothesis posits that CNDD is more pronounced in tropical than in temperate forests^4,5, which increases community stabilization, species coexistence and the diversity of local tree species^6,7. Previous analyses supporting such a latitudinal gradient in CNDD^8,9 have suffered from methodological limitations related to the use of static data^10–12. Here we present a comprehensive assessment of latitudinal CNDD patterns using dynamic mortality data to estimate species-site-specific CNDD across 23 sites. Averaged across species, we found that stabilizing CNDD was present at all except one site, but that average stabilizing CNDD was not stronger toward the tropics. However, in tropical tree communities, rare and intermediate abundant species experienced stronger stabilizing CNDD than did common species. This pattern was absent in temperate forests, which suggests that CNDD influences species abundances more strongly in tropical forests than it does in temperate ones¹³. We also found that interspecific variation in CNDD, which might attenuate its stabilizing effect on species diversity^14,15, was high but not significantly different across latitudes. Although the consequences of these patterns for latitudinal diversity gradients are difficult to evaluate, we speculate that a more effective regulation of population abundances could translate into greater stabilization of tropical tree communities and thus contribute to the high local diversity of tropical forests.

Background From passive acoustic monitoring (PAM) recordings, the vocal activity rate (VAR), vocalizations per unit of time, can be calculated and is essential for assessing bird population abundance. However, VAR is subject to influences from a range of factors, including species and environmental conditions. Identifying the optimal sampling design to obtain representative acoustic data for VAR estimation is crucial for research objectives. PAM commonly uses temporal sampling strategies to decrease the volume of recordings and the resources needed for audio data management. Yet, the comprehensive impact of this sampling approach on VAR estimation remains insufficiently explored. Methods In this study, we used vocalizations extracted from recordings of 12 bird species, taken at 14 PAM stations situated in subtropical montane forests over a four-month period, to assess the impact of temporal sampling on VAR across three distinct scales: short-term periodic, diel, and hourly. For short-term periodic sampling analysis, we employed hierarchical clustering analysis (HCA) and the coefficient of variation (CV). Generalized additive models (GAMs) were utilized for diel sampling analysis, and we determined the average difference in VAR values per minute for the hourly sampling analysis. Results We identified significant day and species-specific VAR fluctuations. The survey season was divided into five segments; the earliest two showed high variability and are best avoided for surveys. Data from days with heavy rain and strong winds showed reduced VAR values and should be excluded from analysis. Continuous recordings spanning at least seven days, extending to 14 days is optimal for minimizing sampling variance. Morning chorus recordings effectively capture the majority of bird vocalizations, and hourly sampling with frequent, shorter intervals aligns closely with continuous recording outcomes. Conclusions While our findings are context-specific, they highlight the significance of strategic sampling in avian monitoring, optimizing resource utilization and enhancing the breadth of monitoring efforts.

Understanding processes and mechanisms of how species assemble in a metacommunity is crucial for illuminating the factors that contribute to the maintenance of biodiversity and developing management decisions. Ecologists have proposed a number of analytical methods for identifying the effects of various ecological processes, but there is no consensus on the best approach. Our study extends the existing framework which synthesizes multiple analytical methods and incorporates community data across space and time to understand the underlying ecological processes. We extended this framework by 1) including null‐model‐based analytical methods; 2) defining metacommunity archetypes that illustrate extreme cases of metacommunities, to observe how well they can be distinguished by different summary statistics, 3) applying the extended framework to real‐world vegetation data from a subtropical forest and interpreting the results, and 4) discussing the potential advantages, limitations, and future directions of applying this framework. We used a process‐based metacommunity simulation model to generate a simulated community dataset and applied random forest (RF) approach to estimate the strength of ecological processes in the process‐based model by considering the summary statistics calculated by the analytical methods as predictors. We also quantified the performance of the trained RF and applied it to estimate the strength of ecological processes in Fushan Forest Dynamics Plot. Our results demonstrate the framework's flexibility in incorporating different analytical methods and its generality to be applied to different community systems. We highlight its theoretical values in evaluating the performance of different statistics or indices in identifying ecological processes and its practical values in assessing the strength of ecological processes underlying real‐world metacommunities. Future improvements should focus on synthesizing statistics that capture specific signals of ecological processes and evaluating the robustness of estimation against dataset complexity and incompleteness.