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1. Spring phenological escape is critical for the survival of temperate tree seedlings

   https://doi.org/10.1111/1365-2435.13821  

   Lee, Benjamin R. ; Ibáñez, Inés ( May 2021 , Functional Ecology)

   Understorey plants in deciduous forests often rely on access to ephemeral light availability before the canopy closes in spring and after the canopy reopens in fall, a strategy commonly referred to as phenological escape. Although there is evidence for a relationship between understorey plant phenology and demographic performance, a mechanistic link is still missing.

   In this study, we bridged this gap by estimating annual carbon assimilation as a function of foliar phenology and photosynthetic capacity for seedlings of two temperate tree species that commonly co‐occur across eastern North America. We then modelled the relationship between estimated carbon assimilation and observed seedling survival and growth.

   Our results indicate that seedlings of both species strongly depend on spring phenological escape to assimilate the majority of their annual carbon budget and that this mechanism significantly affects their likelihood of survival (but not growth). Foliar desiccation also played a strong role in driving patterns of seedling survival, suggesting that water availability will also help shape seedling recruitment dynamics. We found only weak associations between seedling senescence in fall and annual carbon assimilation, suggesting that phenological escape in fall plays a relatively minor role in seedling demographic performance.

   Our results indicate that spring phenological escape is critical for survival of these temperate tree species, and thus, any changes to this dynamic associated with climate change could strongly impact these species' recruitment.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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2. Long‐term dynamics of liana seedlings suggest decelerating increases in liana relative abundance over time

   https://doi.org/10.1111/1365-2745.13297  

   Umaña, María N. ; Manzané‐Pinzón, Eric ; Comita, Liza S. ; Zotz, ed., Gerhard ( October 2019 , Journal of Ecology)

   Over the past decades, tropical forests have experienced both compositional and structural changes. In the Neotropics, researchers at multiple sites have observed significant increases in the abundance and biomass of lianas (i.e. woody vines) relative to trees. However, the role of dynamics at early life stages in contributing to increasing liana abundance remains unclear.

   We took advantage of a unique dataset on seedling dynamics over 16 years in ~20 000 1‐m²plots in a tropical forest in Panama to examine temporal and spatial trends in liana and tree seedling abundance.

   We found that the relative abundance of liana seedlings increased across the study period, from 0.18 in 2001 to 0.24 in 2017. However, increases in liana seedling relative abundance appear to have levelled off in more recent years. The observed increases in liana relative abundance appear to be the result of both higher survival and higher recruitment rates of liana seedlings compared to tree seedlings.

   Increasing liana abundance in the seedling layer was not explained by annual variation in dry season length, total rainfall or the proportion of area occupied by canopy gaps. In addition, liana seedlings did not exhibit a demographic advantage (i.e. higher recruitment or survival) over tree seedlings in dry habitats.

   Synthesis.Our results reveal that seedling communities experienced important compositional changes in the past, but liana seedling relative abundance may have stabilized in recent years. Longer‐term monitoring is needed to determine whether tropical forests will continue to experience compositional changes that may alter forest structure and ecosystem function.

    

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3. Interactions with soil fungi alter density dependence and neighborhood effects in a locally abundant dipterocarp species

   https://doi.org/10.1002/ece3.8478  

   Segnitz, R. Max ; Russo, Sabrina E. ; Peay, Kabir G. ( January 2022 , Ecology and Evolution)

   Seedling recruitment can be strongly affected by the composition of nearby plant species. At the neighborhood scale (on the order of tens of meters), adult conspecifics can modify soil chemistry and the presence of host microbes (pathogens and mutualists) across their combined canopy area or rooting zones. At local or small spatial scales (on the order of one to few meters), conspecific seed or seedling density can influence the strength of intraspecific light and resource competition and also modify the density‐dependent spread of natural enemies such as pathogens or invertebrate predators. Intrinsic correlation between proximity to adult conspecifics (i.e., recruitment neighborhood) and local seedling density, arising from dispersal, makes it difficult to separate the independent and interactive factors that contribute to recruitment success. Here, we present a field experiment in which we manipulated both the recruitment neighborhood and seedling density to explore how they interact to influence the growth and survival ofDryobalanops aromatica, a dominant ectomycorrhizal tree species in a Bornean tropical rainforest. First, we found that both local seedling density and recruitment neighborhood had effects on performance ofD. aromaticaseedlings, though the nature of these impacts varied between growth and survival. Second, we did not find strong evidence that the effect of density on seedling survival is dependent on the presence of conspecific adult trees. However, accumulation of mutualistic fungi beneath conspecifics adults does facilitate establishment ofD. aromaticaseedlings. In total, our results suggest that recruitment near adult conspecifics was not associated with a performance cost and may have weakly benefitted recruiting seedlings. Positive effects of conspecifics may be a factor facilitating the regional hyperabundance of this species. Synthesis: Our results provide support for the idea that dominant species in diverse forests may escape the localized recruitment suppression that limits abundance in rarer species.

    

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4. Wildflower phenological escape differs by continent and spring temperature

   https://doi.org/10.1038/s41467-022-34936-9  

   Lee, Benjamin R. ; Miller, Tara K. ; Rosche, Christoph ; Yang, Yong ; Heberling, J. Mason ; Kuebbing, Sara E. ; Primack, Richard B. ( December 2022 , Nature Communications)

   Abstract Temperate understory plant species are at risk from climate change and anthropogenic threats that include increased deer herbivory, habitat loss, pollinator declines and mismatch, and nutrient pollution. Recent work suggests that spring ephemeral wildflowers may be at additional risk due to phenological mismatch with deciduous canopy trees. The study of this dynamic, commonly referred to as “phenological escape”, and its sensitivity to spring temperature is limited to eastern North America. Here, we use herbarium specimens to show that phenological sensitivity to spring temperature is remarkably conserved for understory wildflowers across North America, Europe, and Asia, but that canopy trees in North America are significantly more sensitive to spring temperature compared to in Asia and Europe. We predict that advancing tree phenology will lead to decreasing spring light windows in North America while spring light windows will be maintained or even increase in Asia and Europe in response to projected climate warming. 

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5. Seedbed not rescue effect buffer the role of extreme precipitation on temperate forest regeneration

   https://doi.org/10.1002/ecy.3926  

   Clark, Peter W. ; D'Amato, Anthony W. ( January 2023 , Ecology)

   Alterations in global climate via extreme precipitation will have broadscale implications on ecosystem functioning. The increased frequency of drought, coupled with heavy, episodic rainfall are likely to generate impacts on biotic and abiotic processes across aquatic and terrestrial ecosystems. Despite the demonstrated shifts in global precipitation, less is known how extreme precipitation interacts with biophysical factors to control future demographic processes, especially those sensitive to climate extremes such as organismal recruitment and survival. We utilized a field‐based precipitation manipulation experiment in 0.1 ha forest canopy openings to test future climate scenarios characterized by extreme precipitation on temperate tree seedling survival. The effects of planting seedbeds (undisturbed leaf litter/organic material vs. scarified, exposed mineral soils), seedling ontogeny, species, and functional traits were examined against four statistically defined precipitation scenarios. Results indicated that seedlings grown within precipitation treatments characterized by heavy, episodic rainfall preceded by prolonged drying responded similarly to drought treatments lacking episodic inputs. Moreover, among all treatment conditions tested, scarified seedbeds most strongly affected seedling survivorship (odds ratio 6.9). Compared with any precipitation treatment, the effect size (predicted probabilities) of the seedbed was more than twice as important in controlling seedling survivorship. However, the interaction between precipitation and seedbed resulted in a 27.9% improvement in survivorship for moisture‐sensitive species. Seedling sensitivity to moisture was variable among species, and most closely linked with functional traits such as seed mass. For instance, under dry moisture regimes, survivorship increased linearly with seed mass (log transformed; adjustedR² = 0.72,p < 0.001), yet no relationship was apparent under wet moisture regimes. Although precipitation influenced survival, extreme rainfall events were not enough to offset moisture deficits nor provide a rescue effect under drought conditions. The relationships reported here highlight the importance of plant seedbeds and species (e.g., functional traits) as edaphic and biotic controls that modify the influence of extreme future precipitation on seedling survival in temperate forests. Finally, we demonstrated the biophysical factors that were most influential to early forest development and that may override the negative effects of increasingly variable precipitation. This work contributes to refinements of species distribution models and can inform reforestation strategies intended to maintain biodiversity and ecosystem function under increasing climate extremes.

    

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