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  1. Abstract

    Predicted increases in extreme droughts will likely cause major shifts in carbon sequestration and forest composition. Although growth declines during drought are widely documented, an increasing number of studies have reported both positive and negative responses to the same drought. These divergent growth patterns may reflect thresholds (i.e., nonlinear responses) promoted by changes in the dominant climatic constraints on tree growth. Here we tested whether stemwood growth exhibited linear or nonlinear responses to temperature and precipitation and whether stemwood growth thresholds co‐occurred with multiple thresholds in source and sink processes that limit tree growth. We extracted 772 tree cores, 1398 needle length records, and 1075 stable isotope samples from 27 sites across whitebark pine's (Pinus albicaulisEngelm.) climatic niche in the Sierra Nevada. Our results indicated that a temperature threshold in stemwood growth occurred at 8.4°C (7.12–9.51°C; estimated using fall‐spring maximum temperature). This threshold was significantly correlated with thresholds in foliar growth, as well as carbon (δ13C) and nitrogen (δ15N) stable isotope ratios, that emerged during drought. These co‐occurring thresholds reflected the transition between energy‐ and water‐limited tree growth (i.e., the E–W limitation threshold). This transition likely mediated carbon and nutrient cycling, as well as important differences in growth‐defense trade‐offsmore »and drought adaptations. Furthermore, whitebark pine growing in energy‐limited regions may continue to experience elevated growth in response to climate change. The positive effect of warming, however, may be offset by growth declines in water‐limited regions, threatening the long‐term sustainability of the recently listed whitebark pine species in the Sierra Nevada.

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    Free, publicly-accessible full text available April 23, 2024
  2. Abstract

    Range shifts of infectious plant disease are expected under climate change. As plant diseases move, emergent abiotic-biotic interactions are predicted to modify their distributions, leading to unexpected changes in disease risk. Evidence of these complex range shifts due to climate change, however, remains largely speculative. Here, we combine a long-term study of the infectious tree disease, white pine blister rust, with a six-year field assessment of drought-disease interactions in the southern Sierra Nevada. We find that climate change between 1996 and 2016 moved the climate optimum of the disease into higher elevations. The nonlinear climate change-disease relationship contributed to an estimated 5.5 (4.4–6.6) percentage points (p.p.) decline in disease prevalence in arid regions and an estimated 6.8 (5.8–7.9) p.p. increase in colder regions. Though climate change likely expanded the suitable area for blister rust by 777.9 (1.0–1392.9) km2into previously inhospitable regions, the combination of host-pathogen and drought-disease interactions contributed to a substantial decrease (32.79%) in mean disease prevalence between surveys. Specifically, declining alternate host abundance suppressed infection probabilities at high elevations, even as climatic conditions became more suitable. Further, drought-disease interactions varied in strength and direction across an aridity gradient—likely decreasing infection risk at low elevations while simultaneously increasing infectionmore »risk at high elevations. These results highlight the critical role of aridity in modifying host-pathogen-drought interactions. Variation in aridity across topographic gradients can strongly mediate plant disease range shifts in response to climate change.

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  3. Abstract

    Long‐term environmental variation often drives local adaptation and leads to trait differentiation across populations. Additionally, when traits change in an environment‐dependent way through phenotypic plasticity, the genetic variation underlying plasticity will also be under selection. These processes could create a landscape of differentiation across populations in traits and their plasticity. Here, we performed a dry‐down experiment under controlled conditions to measure responses in seedlings of a shrub species from the Cape Floristic Region, the common sugarbush (Protea repens). We measured morphological and physiological traits, and sequenced whole transcriptomes of leaf tissues from eight populations that represent both the climatic and the geographical distribution of this species. We found that there is substantial variation in how populations respond to drought, but we also observed common patterns such as reduced leaf size and leaf thickness, and up‐regulation of stress‐related and down‐regulation of growth‐related gene groups. Both high environmental heterogeneity and milder source site climates were associated with higher plasticity in various traits and co‐expression gene networks. Associations between traits, trait plasticity, gene networks and the source site climate suggest that temperature may play a greater role in shaping these patterns when compared to precipitation, in line with recent changes in themore »region due to climate change. We also found that traits respond to climatic variation in an environment‐dependent manner: some associations between traits and climate were apparent only under certain growing conditions. Together, our results uncover common responses ofP. repenspopulations to drought, and climatic drivers of population differentiation in functional traits, gene expression and their plasticity.

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  4. Abstract

    Climate forecasts agree that increased variability and extremes will tend to reduce the availability of water in many terrestrial ecosystems. Increasingly severe droughts may be exacerbated both by warmer temperatures and by the relative unavailability of water that arrives in more sporadic and intense rainfall events. Using long‐term data and an experimental water manipulation, we examined the resilience of a heterogeneous annual grassland community to a prolonged series of dry winters that led to a decline in plant species richness (2000–2014), followed by a near‐record wet winter (2016–2017), a climatic sequence that broadly resembles the predicted future in its high variability. In our 80, 5‐m2observational plots, species richness did not recover in response to the wet winter, and the positive relationship of richness to annual winter rainfall thus showed a significant weakening trend over the 18‐year time period. In experiments on 100, 1‐m2plots, wintertime water supplementation increased and drought shelters decreased the seedling survival and final individual biomass of native annual forbs, the main functional group contributing to the observed long‐term decline in richness. Water supplementation also increased the total cover of native annual forbs, but only increased richness within nested subplots to which seeds were also added. Wemore »conclude that prolonged dry winters, by increasing seedling mortality and reducing growth of native forbs, may have diminished the seedbank and thus the recovery potential of diversity in this community. However, the wet winter and the watering treatment did cause recovery of the community mean values of a key functional trait (specific leaf area, an indicator of drought intolerance), suggesting that some aggregate community properties may be stabilized by functional redundancy among species.

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  5. Abstract Aim

    We may be able to buffer biodiversity against the effects of ongoing climate change by prioritizing the protection of habitat with diverse physical features (high geodiversity) associated with ecological and evolutionary mechanisms that maintain high biodiversity. Nonetheless, the relationships between biodiversity and habitat vary with spatial and biological context. In this study, we compare how well habitat geodiversity (spatial variation in abiotic processes and features) and climate explain biodiversity patterns of birds and trees. We also evaluate the consistency of biodiversity–geodiversity relationships across ecoregions.


    Contiguous USA.

    Time period


    Taxa studied

    Birds and trees.


    We quantified geodiversity with remotely sensed data and generated biodiversity maps from the Forest Inventory and Analysis and Breeding Bird Survey datasets. We fitted multivariate regressions to alpha, beta and gamma diversity, accounting for spatial autocorrelation among Nature Conservancy ecoregions and relationships among taxonomic, phylogenetic and functional biodiversity. We fitted models including climate alone (temperature and precipitation), geodiversity alone (topography, soil and geology) and climate plus geodiversity.


    A combination of geodiversity and climate predictor variables fitted most forms of bird and tree biodiversity with < 10% relative error. Models using geodiversity and climate performed better for local (alpha) and regional (gamma) diversity than for turnover‐based (beta) diversity. Amongmore »geodiversity predictors, variability of elevation fitted biodiversity best; interestingly, topographically diverse places tended to have higher tree diversity but lower bird diversity.

    Main conclusions

    Although climatic predictors tended to have larger individual effects than geodiversity, adding geodiversity improved climate‐only models of biodiversity. Geodiversity was correlated with biodiversity more consistently than with climate across ecoregions, but models tended to have a poor fit in ecoregions held out of the training dataset. Patterns of geodiversity could help to prioritize conservation efforts within ecoregions. However, we need to understand the underlying mechanisms more fully before we can build models transferable across ecoregions.

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  6. Abstract Issue

    Geodiversity (i.e., the variation in Earth's abiotic processes and features) has strong effects on biodiversity patterns. However, major gaps remain in our understanding of how relationships between biodiversity and geodiversity vary over space and time. Biodiversity data are globally sparse and concentrated in particular regions. In contrast, many forms of geodiversity can be measured continuously across the globe with satellite remote sensing. Satellite remote sensing directly measures environmental variables with grain sizes as small as tens of metres and can therefore elucidate biodiversity–geodiversity relationships across scales.


    We show how one important geodiversity variable, elevation, relates to alpha, beta and gamma taxonomic diversity of trees across spatial scales. We use elevation from NASA's Shuttle Radar Topography Mission (SRTM) andc. 16,000 Forest Inventory and Analysis plots to quantify spatial scaling relationships between biodiversity and geodiversity with generalized linear models (for alpha and gamma diversity) and beta regression (for beta diversity) across five spatial grains ranging from 5 to 100 km. We illustrate different relationships depending on the form of diversity; beta and gamma diversity show the strongest relationship with variation in elevation.


    With the onset of climate change, it is more important than ever to examine geodiversity for its potential to foster biodiversity.more »Widely available satellite remotely sensed geodiversity data offer an important and expanding suite of measurements for understanding and predicting changes in different forms of biodiversity across scales. Interdisciplinary research teams spanning biodiversity, geoscience and remote sensing are well poised to advance understanding of biodiversity–geodiversity relationships across scales and guide the conservation of nature.

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