Nonnative old‐field species inhabit early season phenological niches and exhibit unique sensitivity to climate

Abstract

Native and nonnative plant species can exhibit differences in the timing of their reproductive phenology and their phenological sensitivity to climate. These contrasts may influence species' interactions and the invasion potential of nonnative species; however, a limited number of phenology studies expressly consider phenological mismatches among native and nonnative species over broad spatial or temporal scales. To fill this knowledge gap, we used two complementary approaches: First, we quantified the flowering phenology of native and nonnative plants at five old‐field sites across a spatially extensive range of eastern North America. Second, we used herbarium records to compare the sensitivity of flowering and fruiting phenology to climate across a 114‐yr time period in a subset of common old‐field species in southwestern Pennsylvania. Across the study region, nonnatives reproduced substantially earlier in the growing season than natives, suggesting that nonnatives occupy a unique phenological niche (0.55 months earlier flowering across the North American study sites; 50.1 d earlier flowering and 17.5 d earlier fruiting in southwestern Pennsylvania). Both natives and nonnatives advanced their reproductive phenology between 1900 and 2014 but exhibited contrasting phenological sensitivity to climate factors. During the flowering stage of phenology, nonnatives were more sensitive to changes in precipitation than natives and generally delayed flowering in wetter years. Nonnative plants had greater sensitivity and advanced fruiting when the month preceding fruiting was warmer, while native plants had greater sensitivity and advanced fruiting when the three‐month period preceding fruiting was warmer. Our findings suggest that nonnative old‐field species occupy an earlier phenological niche relative to native species, which may facilitate their invasion into old‐field communities. However, given the different sensitivities of native and nonnative plants to climate factors, present‐day patterns of phenology are likely to shift with future climate changes, potentially leading to novel species interactions that may influence the outcomes of invasion.

Plant phenological responses to experimental warming—A synthesis

“…First, if warming is inconsistent (i.e., a warm spring but cool summer) within a single season, the downstream effects on later phenophases may be more variable depending on the environmental conditions and responsiveness of the plant species to that variation. Second, later season phenology may be less sensitive to temperature and more sensitive to other environmental cues (e.g., precipitation or photoperiod) than are early‐season phenologies (Gallinat et al, 2015; Reeb et al, 2020), increasing the variation in their response. Finally, there is some evidence that plants that leaf out earlier in the spring in response to warming will also senesce earlier in the fall, potentially owing to limited supplies of nutrients or photosynthates, or other physiological constraints on the annual leaf or plant life span (Zani et al, 2020; Zohner & Renner, 2019).…”

Phenological displacement is uncommon among sympatric angiosperms

“…Less diverse, smaller floral displays may reduce pollinator visitation, whereas increased asynchrony in flowering can concentrate the chance of predation on a given species' reproductive organs (Rathcke, 1983;Feldman et al, 2004;Moeller, 2004;Ghazoul, 2006;Gurung et al, 2018). Phenological divergence can also create new reproductive niches, which may be conducive to invasion by nonnative species (Sherry et al, 2007;Wolkovich & Cleland, 2014;Reeb et al, 2020). Finally, changes in climate can directly modify selective pressures on flowering phenology and alter associated biotic interactions across trophic levels (Filchak et al, 2000;Forkner et al, 2008;Renner & Zohner, 2018).…”

Extirpated prairie species demonstrate more variable phenological responses to warming than extant congeners

“…While some species and populations exhibit little phenological plasticity (i.e., shift their phenology little in response to environmental variation), other species and populations respond strongly to temperature and precipitation (Visser and Both, 2005; Matthews and Mazer, 2016; Thackeray et al, 2016; Cremonense et al, 2017) and other environmental variables such as nutrient availability or competition (Smith et al, 2012; Xia and Wan, 2013; Du et al, 2019; Wang and Tang, 2019). Phenological plasticity may promote population growth (or limit population declines) in the face of climate change and has been associated with invasiveness and range size (Crawley et al, 1996; DeFalco et al, 2007; Willis et al, 2008, 2010; Cleland et al, 2012; Pearson et al, 2012; Wolkovich et al, 2013; Lustenhouwer et al, 2018; Zettlemoyer et al, 2019b; Reeb et al, 2020), suggesting that species that are less phenologically plastic may be more at risk of population declines and eventual extirpation (Møller et al, 2008; Willis et al, 2008; Forrest and Miller‐Rushing, 2010; Miller‐Rushing et al, 2010).…”