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1. The importance of regeneration processes on forest biodiversity in old-growth forests in the Pacific Northwest

   https://doi.org/10.1098/rstb.2023.0016  

   Luu, Hoang; Ris_Lambers, Janneke Hille; Lutz, James A; Metz, Margaret; Snell, Rebecca S (May 2024, Philosophical Transactions of the Royal Society B: Biological Sciences)

   Forest diversity is the outcome of multiple species-specific processes and tolerances, from regeneration, growth, competition and mortality of trees. Predicting diversity thus requires a comprehensive understanding of those processes. Regeneration processes have traditionally been overlooked, due to high stochasticity and assumptions that recruitment is not limiting for forests. Thus, we investigated the importance of seed production and seedling survival on forest diversity in the Pacific Northwest (PNW) using a forest gap model (ForClim). Equations for regeneration processes were fit to empirical data and added into the model, followed by simulations where regeneration processes and parameter values varied. Adding regeneration processes into ForClim improved the simulation of species composition, compared to Forest Inventory Analysis data. We also found that seed production was not as important as seedling survival, and the time it took for seedlings to grow into saplings was a critical recruitment parameter for accurately capturing tree species diversity in PNW forest stands. However, our simulations considered historical climate only. Due to the sensitivity of seed production and seedling survival to weather, future climate change may alter seed production or seedling survival and future climate change simulations should include these regeneration processes to predict future forest dynamics in the PNW. This article is part of the theme issue ‘Ecological novelty and planetary stewardship: biodiversity dynamics in a transforming biosphere’. 

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2. Physiological and Growth Responses of Tropical Dry Forest Tree Seedlings to Water and Nutrient Additions: Comparisons Between Nitrogen Fixers and Non‐Fixers

   https://doi.org/10.1111/btp.70075  

   Calderón‐Morales, Erick; Werden, Leland K; Smith‐Martin, Chris M; Waring, Bonnie G; Cordero‐Solorzano, Roberto; Powers, Jennifer S (September 2025, Biotropica)

   Harrison, Rhett (Ed.)

   ABSTRACT Belowground resources are key determinants of seedling growth and survival in tropical forests. Nutrients and light may limit plant growth the most in tropical wet forests, whereas water may limit plant growth more in tropical dry forests. Nitrogen (N)‐fixing species play an important role in the nitrogen and carbon cycles across tropical dry forests. However, studies investigating the joint effects of water and nutrients on the physiology and performance of N‐fixing species are scarce. We implemented a full factorial shade house experiment that manipulated water and nutrients (NPK 20:20:20 and complete micronutrients) using eight tree species representing N‐fixing and non‐fixing tree species in the tropical dry forest of Costa Rica to determine: (1) How plant responses to water and nutrient availability vary between N‐fixing and non‐fixing tree species?; and (2) How nutrient and/or water availability influences seedling water‐ and nutrient‐use traits? We found that growth and physiological responses to water and nutrient addition depended directly on the capacity of species to fix atmospheric N₂. N‐fixing species responded more strongly to nutrient addition, accumulating 67% more total biomass on average (approximately double that of non‐fixing taxa) and increasing average height growth rate by 41%. N‐fixing species accumulated more biomass without compromising water‐use efficiency, taking full advantage of the increased nutrient availability. Interestingly, results from our experiment show that increased water availability rarely influenced tropical dry forest seedling performance, whereas nutrient availability had a strong effect on biomass and growth. Overall, our results highlight the ability of N‐fixing seedlings to take advantage of local soil resource heterogeneity, which may help to explain the dominance of N‐fixing trees in tropical dry forests. 

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3. Leveraging Remote Sensing and Theory to Predict Tree Size Abundance Distributions Across Space

   https://doi.org/10.1111/geb.70085  

   Eichenwald, Adam J; Grady, John M; Knott, Jonathan A; Rodriguez, J Marcos; Weinstein, Ben; Orwig, David A; Record, Sydne (August 2025, Global Ecology and Biogeography)

   ABSTRACT BackgroundRemote sensing (RS) technologies provide unprecedented opportunities to assess forest structure at broad spatial scales. Light detection and ranging (LiDAR) is a powerful tool that offers detailed vertical information, but its consistent high‐resolution coverage can be limited across vast areas and quantifying understory vegetation remains challenging due to occlusion. Conversely, while high‐resolution RGB imagery is more accessible and valuable for large‐scale analyses, it comes with higher uncertainty and only captures canopy‐level information. Integrating RGB data with ecological theory and existing LiDAR‐derived products (e.g., canopy height models, CHM) allows us to enhance predictions and broaden the applicability of forest size structure mapping from the understory to the canopy, particularly through tree size–abundance relationships. TheoryTree size and abundance generally follow known distributions, where smaller trees are exponentially more common than larger trees. This pattern emerges from fundamental ecological constraints, including volume packing, metabolic scaling and light competition, which collectively govern forest self‐organisation across spatial scales. Proposed ApproachWe present a workflow that integrates size‐abundance scaling theory with RGB data and CHMs to improve predictions of forest structure. By estimating tree size distributions from RGB imagery, we extend the applicability of ecological scaling models to broader spatial scales and offer an approach that complements traditional methods. AssessmentWe apply this approach to forest monitoring networks, including NEON and ForestGEO, to assess its accuracy and generalisability across a range of forests (e.g., subtropical pine, boreal, low and dry, tall and dense) in North America. Our results show that RGB‐based estimates can successfully recover size‐abundance distributions from the understory to the canopy. Future DirectionsFurther refinement of our approach could enhance predictions by incorporating species classifications from hyperspectral data and using more spatially or taxonomically specific allometric equations. These additions would enable more precise scaling of tree diameter from remote sensing data. 

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4. Limits to reproduction and seed size-number trade-offs that shape forest dominance and future recovery

   https://doi.org/10.1038/s41467-022-30037-9  

   Qiu, Tong; Andrus, Robert; Aravena, Marie-Claire; Ascoli, Davide; Bergeron, Yves; Berretti, Roberta; Berveiller, Daniel; Bogdziewicz, Michal; Boivin, Thomas; Bonal, Raul; et al (December 2022, Nature Communications)

   Abstract The relationships that control seed production in trees are fundamental to understanding the evolution of forest species and their capacity to recover from increasing losses to drought, fire, and harvest. A synthesis of fecundity data from 714 species worldwide allowed us to examine hypotheses that are central to quantifying reproduction, a foundation for assessing fitness in forest trees. Four major findings emerged. First, seed production is not constrained by a strict trade-off between seed size and numbers. Instead, seed numbers vary over ten orders of magnitude, with species that invest in large seeds producing more seeds than expected from the 1:1 trade-off. Second, gymnosperms have lower seed production than angiosperms, potentially due to their extra investments in protective woody cones. Third, nutrient-demanding species, indicated by high foliar phosphorus concentrations, have low seed production. Finally, sensitivity of individual species to soil fertility varies widely, limiting the response of community seed production to fertility gradients. In combination, these findings can inform models of forest response that need to incorporate reproductive potential. 

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5. Rapid migration of Mongolian oak into the southern Asian boreal forest

   https://doi.org/10.1111/gcb.17002  

   Tang, Yang; Du, Enzai; Guo, Hongbo; Wang, Yang; Peñuelas, Josep; Reich, Peter B (January 2024, Global Change Biology)

   Abstract The migration of trees induced by climatic warming has been observed at many alpine treelines and boreal–tundra ecotones, but the migration of temperate trees into southern boreal forest remains less well documented. We conducted a field investigation across an ecotone of temperate and boreal forests in northern Greater Khingan Mountains of northeast China. Our analysis demonstrates that Mongolian oak (Quercus mongolica), an important temperate tree species, has migrated rapidly into southern boreal forest in synchrony with significant climatic warming over the past century. The average rate of migration is estimated to be 12.0 ± 1.0 km decade⁻¹, being slightly slower than the movement of isotherms (14.7 ± 6.4 km decade⁻¹). The migration rate of Mongolian oak is the highest observed among migratory temperate trees (average rate 4.0 ± 1.0 km decade⁻¹) and significantly higher than the rates of tree migration at boreal–tundra ecotones (0.9 ± 0.4 km decade⁻¹) and alpine treelines (0.004 ± 0.003 km decade⁻¹). Compared with the coexisting dominant boreal tree species, Dahurian larch (Larix gmelinii), temperate Mongolian oak is observed to have significantly lower capacity for light acquisition, comparable water‐use efficiency but stronger capacity to utilize nutrients especially the most limiting nutrient, nitrogen. In the context of climatic warming, and in addition to a high seed dispersal capacity and potential thermal niche differences, the advantage of nutrient utilization, reflected by foliar elementomes and stable nitrogen isotope ratios, is also likely a key mechanism for Mongolian oak to coexist with Dahurian larch and facilitate its migration toward boreal forest. These findings highlight a rapid deborealization of southern Asian boreal forest in response to climatic warming. 

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