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1. Flower and Seed Production, Seedling Dynamics, and Tree Life Cycles

   https://doi.org/10.5479/si.26882626  

   Wright, Joseph; Calderón, Osvaldo; Hernández, Andrés; Muller-Landau, Helene (November 2024, Smithsonian Institution Scholarly Press)

   We present highlights derived from 36 years of weekly observations of flower and seed production and 25 years of annual observations of seedling dynamics at Barro Colorado Island (BCI), Panama. Highlights concern levels and causes of spatial, temporal, and interspecific variation in flower production, seed production, seed dispersal, and seedling recruitment, growth, and survival as well as the consequences for plant regeneration and diversity. Full tree life cycles are assembled by combining seed production, seedling dynamics, and observations of larger plants from the 50-ha Forest Dynamics Plot and are used to evaluate the costs of dioecy, lifetime insights from functional traits, and interspecific variation in the impact of lianas among host tree species. A variety of results demonstrate the importance of long-term observations to understand forest dynamics and responses to rising atmospheric carbon dioxide concentrations and a changing climate. 

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2. Compound disease and wildfire disturbances alter opportunities for seedling regeneration in resprouter-dominated forests

   Simler-Williamson, A. B.; Metz, M.R.; Frangioso, K.M.; Meentemeyer, R.K.; Rizzo, D.M. (January 2019, Ecosphere)

   Human-altered disturbance regimes and changing climatic conditions can reduce seed availability and suitable microsites, limiting seedling regeneration in recovering forest systems. Thus, resprouting plants, which can persist in situ, are expected to expand in dominance in many disturbance-prone forests. However, resprouters may also be challenged by changing regimes, and the mechanisms determining facultative seedling recruitment by resprouting species, which will determine both the future spread and current persistence of these populations, are poorly understood. In the resprouter-dominated forests of coastal California, interactions between wildfire and an emerging disease, sudden oak death (SOD), alter disturbance severity and tree mortality, which may shift forest regeneration trajectories. We examine this set of compound disturbances to (1) assess the influence of seed limitation, biotic competition, and abiotic conditions on seedling regeneration in resprouting populations; (2) investigate whether disease-fire interactions alter postfire seedling regeneration, which have implications for future disease dynamics and shifts in forest composition. Following a wildfire that impacted a preexisting plot network in SOD-affected forests, we monitored seedling abundances and survival over eight years. With pre- and postfire data, we assessed relationships between regeneration dynamics and disturbance severity, biotic, and abiotic variables, using Bayesian generalized linear models and mixed models. Our results indicate that postfire seedling regeneration by resprouting species was shaped by contrasting mechanisms reflecting seed limitation and competitive release. Seedling abundances declined with decreasing postfire survival of mature, conspecific stems, while belowground survival of resprouting genets had no effect. However, where seed sources persisted, seedling abundances and survival generally increased with the prefire severity of disease impacts, suggesting that decreased competition with adults may enhance seedling recruitment in this resprouter-dominated system. Species’ regeneration responses varied with their relative susceptibility to SOD and suggest compositional shifts, which will determine future disease management and forest restoration actions. These results additionally highlight that mechanisms related to biotic competition, seed limitation, and opportunities for seedling recruitment beneath mature canopies may determine possible shifts in the occurrence of resprouting traits. This result has broad applications to other systems impacted by human-altered regimes where asexual persistence may be predicted to be a beneficial life history strategy. 

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3. Sugar maple seedling regeneration of a natural cohort across a latitudinal gradient in New Hampshire

   https://doi.org/10.1139/cjfr-2024-0314  

   Cleavitt, Natalie L; Deegan, Carrie; Thorne, Sarah; Suppé, Ana; Colson, Kimberly L; Rice, Wanda (June 2025, Canadian Journal of Forest Research)

   Sugar maple, an economically and ecologically important tree in the northern hardwood forest, has experienced regeneration failure that in the Northeast portion of the range has been variously attributed to soil acidification and resultant changes in soil chemistry, impacts of climate change, and effects of species composition. In a 5-year study spanning a latitudinal gradient in the state of New Hampshire, we examined evidence for these three hypotheses to explain sugar maple regeneration patterns. Overall, sugar maple seedling survival was highest in the two sites with lower sugar maple abundance. Alternatively, the two other sites with greater than 50% sugar maple relative dominance shared the following outcomes: higher seed production per area, greater foliar pest damage, lower seedling survival, lower sapling density, and higher canopy maple mortality, while the sites with lower dominance of maple had opposite outcomes. Based on field data and a common garden experiment, conspecific impacts on seedling survival were related to foliar pests and fungal pathogens rather than through soil feedbacks. These results lend support to other studies encouraging promotion of stand tree diversity and avoidance of monocultures. 

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4. Conifer Seedling Survival in Response to High Surface Temperature Events of Varying Intensity and Duration

   https://doi.org/10.3389/ffgc.2021.731267  

   Rank, Robin; Maneta, Marco; Higuera, Philip; Holden, Zachary; Dobrowski, Solomon (January 2022, Frontiers in Forests and Global Change)

   Forests face accelerating threats due to increases in the severity and frequency of drought and heat stress associated with climate change. In particular, changing patterns of forest regeneration after disturbance will be important in predicting future forest distribution across the western United States, where patterns of recurring fire and regrowth are important in establishing landscape dynamics. To predict shifting landscape patterns, it will be important to identify environmental boundaries for forest regeneration using environmental variables with clear consequences for seedling survival. Here, we explore soil surface temperature as an environmental variable with direct consequences for seedling survival and forest regeneration potential. We conducted a literature search to identify five previous laboratory experiments, spanning a period of 1924 to 1986, that exposed conifer seedlings to elevated soil surface temperatures for varying durations. We then synthesized the data from these studies to explore the survival of western U.S. conifer species in response to differing surface temperature levels. We found mortality thresholds consistent with previously reported measurements in field and lab studies, but found that as surface temperatures reach these lethal thresholds the duration of exposure matters greatly to survival outcomes. This work leverages an intuitive climate metric with clear consequences for seedling survival as an indicator of forest regeneration potential. 

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5. Lower‐intensity restoration interventions drive greater seedling establishment for later‐successional tree species

   https://doi.org/10.1111/1365-2664.70116  

   Joyce, Francis H; Zahawi, Rakan A; Holl, Karen D (September 2025, Journal of Applied Ecology)

   Abstract Recovery of tree community composition in restored tropical forests relies on successful recruitment of later‐successional species. However, the long‐term effects of different restoration interventions on establishment success of arriving seeds are poorly understood.We evaluated the effects of three restoration treatments on the seed‐to‐seedling transition for later‐successional tree species in a fragmented agricultural landscape in southern Costa Rica. Restoration plots (0.25 ha) were established in a block design nearly two decades prior and spanned a gradient of intervention intensity: natural regeneration (not planted), applied nucleation (planted tree clusters) and plantation (fully planted). We conducted seed addition experiments from 2021 to 2023 using eight species at seven replicate restoration sites and in four nearby remnant forests. We defined the seed‐to‐seedling transition as two stages: seedling emergence and post‐emergence survival.Seedling emergence was highest in natural regeneration (48%), intermediate in applied nucleation (37%) and lowest in plantation (25%) and remnant forests (27%), with high variability across species. First‐year survival of emerged seedlings was greater in applied nucleation than in plantation and was lower in remnant forest than in all restoration treatments. On average, seedlings grew slightly taller in natural regeneration compared to the other treatments.Despite seed mass spanning four orders of magnitude among the eight species, this trait did not explain variation in seedling emergence or survival.Synthesis and applications: Taken together, results suggest that after ~15 years, applied nucleation and natural regeneration plots may provide more favourable conditions for establishment of later‐successional trees than do plantation plots. When the seed‐to‐seedling transition is not a major barrier for the recruitment of later‐successional tree species in restoration plots, practitioners should focus on increasing seed arrival for these species. Seed addition could be a viable strategy to introduce later‐successional species that fail to colonize restoration sites, particularly in restoration sites with low intensity interventions (i.e. natural regeneration or applied nucleation). 

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