Abstract
Plant phenology will likely shift with climate change, but how temperature and/or moisture regimes will control phenological responses is not well understood. This is particularly true in Mediterranean climate ecosystems where the warmest temperatures and greatest moisture availability are seasonally asynchronous. We examined plant phenological responses at both the population and community levels to four climate treatments (control, warming, drought, and warming plus additional precipitation) embedded within three prairies across a 520 km latitudinal Mediterranean climate gradient within the Pacific Northwest, USA. At the population level, we monitored flowering and abundances in spring 2017 of eight range‐restricted focal species planted both within and north of their current ranges. At the community level, we used normalized difference vegetation index (NDVI) measured from fall 2016 to summer 2018 to estimate peak live biomass, senescence, seasonal patterns, and growing season length. We found that warming exerted a stronger control than our moisture manipulations on phenology at both the population and community levels. Warming advanced flowering regardless of whether a species was within or beyond its current range. Importantly, many of our focal species had low abundances, particularly in the south, suggesting that establishment, in addition to phenological shifts, may be a strong constraint on their future viability. At the community level, warming advanced the date of peak biomass regardless of site or year. The date of senescence advanced regardless of year for the southern and central sites but only in 2018 for the northern site. Growing season length contracted due to warming at the southern and central sites (~3 weeks) but was unaffected at the northern site. Our results emphasize that future temperature changes may exert strong influence on the timing of a variety of plant phenological events, especially those events that occur when temperature is most limiting, even in seasonally water‐limited Mediterranean ecosystems.
Highlights
Plant phenology, the timing of key events in plant life cycles, is shifting with climate change (Cleland, Chuine, Menzel, Mooney, & Schwartz, 2007; Menzel et al, 2006; Parmesan & Yohe, 2003)
We asked: (a) How will the phenology of individual species, as well as prairie plant communities, respond to climate change across a latitudinal gradient? (b) Will range‐restricted species’ phenological responses and flowering abundances differ in direction and/or magnitude when planted within versus beyond their current northern range limits? And, (c) will changes to soil temperature or moisture be more predictive of phenological responses?
20 circular plots (7.1 m2) were randomly assigned to one of four climate treatments with five replicates each: control, warming, warming with additional precipitation, and drought
Summary
The timing of key events in plant life cycles, is shifting with climate change (Cleland, Chuine, Menzel, Mooney, & Schwartz, 2007; Menzel et al, 2006; Parmesan & Yohe, 2003). Manipulative experiments designed to study climate change effects on phenology often impose extensions of the growing season via snow removal, temperature increases, or moisture manipulations (Bernal et al, 2011; Peñuelas et al, 2004; Rosa et al, 2015; Tielbörger et al, 2014; Whittington et al, 2015) but rarely are designed to manipulate both temperature and moisture, despite potentially confounding effects (Wolkovich et al, 2012) We manipulated both temperature and soil moisture in three prairies across a 520 km latitudinal Mediterranean climate gradient within the PNW to examine the responses of plant phenology at both the population and community levels. We asked: (a) How will the phenology of individual species, as well as prairie plant communities, respond to climate change across a latitudinal gradient? (b) Will range‐restricted species’ phenological responses and flowering abundances differ in direction and/or magnitude when planted within versus beyond their current northern range limits? And, (c) will changes to soil temperature or moisture be more predictive of phenological responses?
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