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1. Geographic variation in growth and reproduction trade‐offs: Implications for future tree performance

   https://doi.org/10.1002/ecs2.4863  

   Vincent, Chantalle; Ibáñez, Inés (June 2024, Ecosphere)

   Abstract Forests play a crucial role providing ecosystem services to humans, yet many aspects of forest dynamics remain unknown. One key area is how climate change might impact reproduction of tree species. While most studies have focused on predicting tree growth, understanding how reproduction may change will be vital to forecasting future forest communities. Of particular interest is the relationship between annual growth and reproductive output, which has often been hypothesized as a trade‐off between allocating resources to growth or to reproduction. Two proposed pathways of this trade‐off, resource accumulation, that is, storage of resources over time, and resource allocation, that is, same year allocation of resources to reproduction, have been widely explored in relation to masting events. It has also been proposed that there is no internal trade‐off between the two functions, but rather there exists one or more climate variables that are intrinsically linked to both, that is, the weather hypothesis. In this study, we use 15 years of dendrochronological data and seed rain collections from forest stands at two latitudes to determine whether one or more of these strategies are taking place in two commonly occurring tree species: red maple,Acer rubrum; and sugar maple,Acer saccharum. We found evidence of a trade‐off in both species. We also found a combination of strategies was the norm, and there appeared to be evidence to also support the weather hypothesis. However, in both species, the strategy which dictated the trade‐off switched between the northern and southern regions, indicating a degree of plasticity that could be beneficial under changing environmental conditions. By identifying the ways in which growth and reproduction are connected and how these connections vary between different populations, we can gain insights into how trees allocate resources in response to changing conditions. 

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2. Reconstructing 120 years of climate change impacts on Joshua tree flowering

   https://doi.org/10.1111/ele.14478  

   Yoder, Jeremy_B; Andrade, Ana_Karina; DeFalco, Lesley_A; Esque, Todd_C; Carlson, Colin_J; Shryock, Daniel_F; Yeager, Ray; Smith, Christopher_I (August 2024, Ecology Letters)

   Abstract Quantifying how global change impacts wild populations remains challenging, especially for species poorly represented by systematic datasets. Here, we infer climate change effects on masting by Joshua trees (Yucca brevifoliaandY. jaegeriana), keystone perennials of the Mojave Desert, from 15 years of crowdsourced observations. We annotated phenophase in 10,212 geo‐referenced images of Joshua trees on the iNaturalist crowdsourcing platform, and used them to train machine learning models predicting flowering from annual weather records. Hindcasting to 1900 with a trained model successfully recovers flowering events in independent historical records and reveals a slightly rising frequency of conditions supporting flowering since the early 20th Century. This reflects increased variation in annual precipitation, which drives masting events in wet years—but also increasing temperatures and drought stress, which may have net negative impacts on recruitment. Our findings reaffirm the value of crowdsourcing for understanding climate change impacts on biodiversity. 

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3. Climate teleconnections synchronize Picea glauca masting and fire disturbance: Evidence for a fire‐related form of environmental prediction

   https://doi.org/10.1111/1365-2745.13308  

   Ascoli, Davide; Hacket‐Pain, Andrew; LaMontagne, Jalene_M; Cardil, Adrián; Conedera, Marco; Maringer, Janet; Motta, Renzo; Pearse, Ian_S; Vacchiano, Giorgio; Bellingham, ed., Peter (November 2019, Journal of Ecology)

   Abstract Synchronous pulses of seed masting and natural disturbance have positive feedbacks on the reproduction of masting species in disturbance‐prone ecosystems. We test the hypotheses that disturbances and proximate causes of masting are correlated, and that their large‐scale synchrony is driven by similar climate teleconnection patterns at both inter‐annual and decadal time scales.Hypotheses were tested on white spruce (Picea glauca), a masting species which surprisingly persists in fire‐prone boreal forests while lacking clear fire adaptations. We built masting, drought and fire indices at regional (Alaska, Yukon, Alberta, Quebec) and sub‐continental scales (western North America) spanning the second half of the 20th century. Superposed Epoch Analysis tested the temporal associations between masting events, drought and burnt area at the regional scale. At the sub‐continental scale, Superposed Epoch Analysis tested whether El Niño‐Southern Oscillation (ENSO) and its coupled effects with the Atlantic Multidecadal Oscillation (AMO) in the positive phase (AMO+/ENSO+) synchronize drought, burnt area and masting. We additionally tested the consistency of our synchronization hypotheses on a decadal temporal scale to verify whether long‐term oscillations in AMO+/ENSO+ are coherent to decadal variation in drought, burnt area and masting.Analyses demonstrated synchronicity between drought, fire and masting. In all regions the year before a mast event was drier and more fire‐prone than usual. During AMO+/ENSO+ events sub‐continental indices of drought and burnt area experienced significant departures from mean values. The same was observed for large‐scale masting in the subsequent year, confirming 1‐year lag between fire and masting. Sub‐continental indices of burnt area and masting showed in‐phase decadal fluctuations led by the AMO+/ENSO+. Results support the ‘Environmental prediction hypothesis’ for mast seeding.Synthesis. We provide evidence of large‐scale synchronicity between seed masting inPicea glaucaand fire regimes in boreal forests of western North America at both inter‐annual and decadal time scales. We conclude that seed production in white spruce predicts changes in disturbance regimes by sharing the same large‐scale climate drivers with drought and fire. This gives new insides in a mechanism providing a fire‐sensitive species with higher than expected adaptability to changes in climate. 

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4. Masting, fire‐stimulated flowering, and the evolutionary ecology of synchronized reproduction

   https://doi.org/10.1002/ecy.4261  

   Beck, Jared J.; McKone, Mark J.; Wagenius, Stuart (February 2024, Ecology)

   Abstract Synchronized episodic reproduction among long‐lived plants shapes ecological interactions, ecosystem dynamics, and evolutionary processes worldwide. Two active scientific fields investigate the causes and consequences of such synchronized reproduction: the fields of masting and fire‐stimulated flowering. While parallels between masting and fire‐stimulated flowering have been previously noted, there has been little dialogue between these historically independent fields. We predict that the synthesis of these fields will facilitate new insight into the causes and consequences of synchronized reproduction. Here we briefly review parallels between masting and fire‐stimulated flowering, using two case studies and a database of 1870 plant species to facilitate methodological, conceptual, geographical, taxonomic, and phylogenetic comparisons. We identify avenues for future research and describe three key opportunities associated with synthesis. First, the taxonomic and geographic complementarity of empirical studies from these historically independent fields highlights the potential to derive more general inferences about global patterns and consequences of synchronized reproduction in perennial plants. Second, masting's well developed conceptual framework for evaluating adaptive hypotheses can help guide empirical studies of fire‐stimulated species and enable stronger inferences about the evolutionary ecology of fire‐stimulated flowering. Third, experimental manipulation of reproductive variation in fire‐stimulated species presents unique opportunities to empirically investigate foundational questions about ecological and evolutionary processes underlying synchronized reproduction. Synthesis of these fields and their complementary insights offers a unique opportunity to advance our understanding of the evolutionary ecology of synchronized reproduction in perennial plants. 

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5. Mast seeding promotes evolution of scatter-hoarding

   https://doi.org/10.1098/rstb.2020.0375  

   Zwolak, Rafał; Clement, Dale; Sih, Andrew; Schreiber, Sebastian J. (December 2021, Philosophical Transactions of the Royal Society B: Biological Sciences)

   Many plant species worldwide are dispersed by scatter-hoarding granivores: animals that hide seeds in numerous, small caches for future consumption. Yet, the evolution of scatter-hoarding is difficult to explain because undefended caches are at high risk of pilferage. Previous models have attempted to solve this problem by giving cache owners large advantages in cache recovery, by kin selection, or by introducing reciprocal pilferage of ‘shared’ seed resources. However, the role of environmental variability has been so far overlooked in this context. One important form of such variability is masting, which is displayed by many plant species dispersed by scatterhoarders. We use a mathematical model to investigate the influence of masting on the evolution of scatter-hoarding. The model accounts for periodically varying annual seed fall, caching and pilfering behaviour, and the demography of scatterhoarders. The parameter values are based mostly on research on European beech ( Fagus sylvatica ) and yellow-necked mice ( Apodemus flavicollis ). Starvation of scatterhoarders between mast years decreases the population density that enters masting events, which leads to reduced seed pilferage. Satiation of scatterhoarders during mast events lowers the reproductive cost of caching (i.e. the cost of caching for the future rather than using seeds for current reproduction). These reductions promote the evolution of scatter-hoarding behaviour especially when interannual variation in seed fall and the period between masting events are large. This article is part of the theme issue ‘The ecology and evolution of synchronized seed production in plants’. 

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