Long‐term changes in flowering synchrony reflect climatic changes across an elevational gradient

Abstract

Synchrony defines an organism's overlap with potential resources and mates, essential for survival and reproduction. Flowering synchrony influences gene flow within species and patterns of interaction among plants and with other trophic levels, including pollinators. Climate-change driven shifts in plant phenology may disrupt plant-plant and plant-pollinator interactions, resulting in reshuffling of communities and altered ecosystem processes. We present a unique long-term metacommunity-wide study relating changes in flowering synchrony within and among species along an elevational gradient to changes in local climatic conditions. We apply a circular statistical method that estimates flowering phenology overlap between entire flowering distributions, overcoming limitations and biases of single indicators such as first and last flowering dates. We analyzed more than 300 000 flowering overlap estimates between 217 species in five plant communities across a 1267 m gradient over four decades in the southwestern USA. We show that co-flowering synchrony significantly decreased in all plant communities, with a maximum of 28.1% of synchrony lost at the lowest elevations. Decreased synchrony was significantly negatively correlated with increasing temperatures recorded across the gradient. Reduced precipitation had locally-dependent effects and, in combination with warmer temperatures, accelerated the decrease in synchrony, especially at the lowest elevations. Flowering synchrony within plant species occurring in multiple communities increased between most community pairs, with a maximum increase of 30.5%, and at accelerated rates in recent years. The exception, likely associated with differences in topography, was a 5.6% decrease in synchrony between the two highest-elevation communities. Overall, increased synchrony within species occurring at multiple elevations indicates homogenization of flowering phenology across the gradient. These results show significant reshaping of flowering synchrony within and between plant communities in response to changing climate. Because plant phenology influences many ecological processes, such fundamental changes may have far-reaching and negative effects on ecosystem stability.

Warmer springs increase potential for temporal reproductive isolation among habitat patches in subalpine flowering plants

“…To our knowledge, our study is unique in combining data on whole flowering distributions and long-term phenological monitoring to assess the effect of temperature on flowering synchrony within plant populations. Studies investigating the role of temperature or climate change on synchrony at larger spatial scales, along latitudinal or altitudinal gradients, have found contrasting trends: a decrease (Menzel et al, 2008;Rivest et al, 2021;Wang et al, 2015;Zohner et al, 2018), an increase (Fisogni et al, 2022;Prevéy et al, 2017;Rafferty et al, 2020) or no trend (Park et al, 2019) which could explain the discrepancy between our results and those of some studies conducted at larger spatial scales.…”

“…To our knowledge, our study is unique in combining data on whole flowering distributions and long‐term phenological monitoring to assess the effect of temperature on flowering synchrony within plant populations. Studies investigating the role of temperature or climate change on synchrony at larger spatial scales, along latitudinal or altitudinal gradients, have found contrasting trends: a decrease (Menzel et al, 2008; Rivest et al, 2021; Wang et al, 2015; Zohner et al, 2018), an increase (Fisogni et al, 2022; Prevéy et al, 2017; Rafferty et al, 2020) or no trend (Park et al, 2019) in synchrony with warmer years or over time. The effect of temperature on synchrony that we observed (a decrease in overlap of 2.5% per °C, if expressed relative to our average overlap value of 0.52) is comparable in magnitude to that reported among populations—although comparisons are made challenging by the different metrics of change used in different studies.…”

“…The effect of temperature on synchrony that we observed (a decrease in overlap of 2.5% per °C, if expressed relative to our average overlap value of 0.52) is comparable in magnitude to that reported among populations—although comparisons are made challenging by the different metrics of change used in different studies. For example, Fisogni et al (2022) studied a large elevational gradient over 33 years, and found an increase in overlap over the study period in 3 of 10 elevation pairs, with a change between adjacent pairs of 6.8%. Prevéy et al (2017) investigated variation in temperature sensitivity of flowering phenology among sites across the Canadian and European Arctic and found that cooler plots were more sensitive to warming—exhibiting a 0.35 day per °C greater sensitivity, per degree difference in summer temperature.…”

“…Considering the importance of flowering synchrony for populations' adaptive responses to environmental change, it is critical to understand the extent to which intraspecific flowering synchrony is affected by climate change. However, while populations have been shown to vary in their phenological sensitivity to temperature (Fisogni et al, 2022; Parmesan & Yohe, 2003; Pau et al, 2011; Prevéy et al, 2017; Primack et al, 2009; Rivest et al, 2021; Zohner et al, 2018), information about how flowering synchrony within populations is affected by climate warming is extremely limited. Indeed, most long‐term data on flowering phenology consider population‐level trends in mean, median or first flowering dates (e.g.…”

Microgeographic variation in early fitness traits of Pinus sylvestris from contrasting soils

“…Most available studies on microgeographic adaptation in forest trees have focused on steep temperature and precipitation gradients found along altitudinal clines, which have been shown to be associated with genetically determined phenological and growth differences among trees growing few hundreds of meters apart at different elevations (Ducousso et al, 1996; Green, 2005; Vitasse et al, 2009; Alberto et al, 2011; Bresson et al, 2011; Gauzere et al, 2020). Even if altitude induces flowering phenology asynchronies (Fisogni et al, 2022), they do not seem sufficient to prevent substantial pollination overlap and effective gene exchange across the range of altitudes over which adaptive genetic divergence has been observed (Schuster et al, 1989; Gauzere et al, 2020). These results suggest that fine‐scale adaptation along altitudinal gradients frequently occurs despite gene flow, which should be considered for management and conservation of forest genetic resources.…”