Climate change has resulted in increased temperature means across the globe. Many angiosperms flower earlier in response to rising temperature and the phenologies of these species are reasonably well predicted by models that account for spring (early growing season) and winter temperatures. Surprisingly, however, exceptions to the general pattern of precocious flowering are common. Many species either do not appear to respond or even delay flowering in, or following, warm growing seasons. Existing phenological models have not fully addressed such exceptions to the common association of advancing phenologies with warming temperatures. The phenological events that are typically recorded (e.g., onset of flowering) are but one phase in a complex developmental process that often begins one or more years previously, and flowering time may be strongly influenced by temperature over the entire multi-year course of flower development. We propose a series of models that explore effects of growing-season temperature increase on the multiple processes of flower development and how changes in development may impact the timing of anthesis. We focus on temperate forest trees, which are characterized by preformation, the initiation of flower primordia one or more years prior to anthesis. We then synthesize the literature on flower development to evaluate the models. Although fragmentary, the existing data suggest the potential for temperature to affect all aspects of flower development in woody perennials. But, even for relatively well studied taxa, the critical developmental responses that underlie phenological patterns are difficult to identify. Our proposed models explain the seemingly counter-intuitive observations that warmer growingseason temperatures delay flowering in many species. Future research might concentrate on taxa that do not appear to respond to temperature, or delay flowering in response to warm temperatures, to understand what processes contribute to this pattern.
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Extirpated prairie species demonstrate more variable phenological responses to warming than extant congeners
Shifting phenology in response to climate is one mechanism that can promote population persistence and geographic spread; therefore, species with limited ability to phenologically track changing environmental conditions may be more susceptible to population declines. Alternatively, apparently nonresponding species may demonstrate divergent responses to multiple environmental conditions experienced across seasons.
Capitalizing on herbarium records from across the midwestern United States and on detailed botanical surveys documenting local extinctions over the past century, we investigated whether extirpated and extant taxa differ in their phenological responses to temperature and precipitation during winter and spring (during flowering and the growing season before flowering) or in the magnitude of their flowering time shift over the past century.
Although warmer temperatures across seasons advanced flowering, extirpated and extant species differed in the magnitude of their phenological responses to winter and spring warming. Extirpated species demonstrated inconsistent phenological responses to warmer spring temperatures, whereas extant species consistently advanced flowering in response to warmer spring temperatures. In contrast, extirpated species advanced flowering more than extant species in response to warmer winter temperatures. Greater spring precipitation tended to delay flowering for both extirpated and extant taxa. Finally, both extirpated and extant taxa delayed flowering over time.
This study highlights the importance of understanding phenological responses to seasonal warming and indicates that extirpated species may demonstrate more variable phenological responses to temperature than extant congeners, a finding consistent with the hypothesis that appropriate phenological responses may reduce species’ likelihood of extinction.
- Award ID(s):
- 1757530
- PAR ID:
- 10450078
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- American Journal of Botany
- Volume:
- 108
- Issue:
- 6
- ISSN:
- 0002-9122
- Page Range / eLocation ID:
- p. 958-970
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Protea species. We also explore phylogenetic conservatism in flowering phenology.Results We show that herbarium data combined with our sliding window approach successfully captured independently reported flowering phenology patterns (
r = 0.93). Both warmer sites and warmer years were associated with earlier flowering of 3–5 days/°C, whereas precipitation variation had no significant effect on flowering phenology. Although species vary widely in phenological responsiveness, responses are phylogenetically conserved, with closely related species tending to shift flowering similarly with increasing temperature.Discussion Our results point to climate‐responsive phenology for this important plant genus and indicate that the subtropical, aseasonally flowering genus
Protea has temperature‐driven flowering responses that are remarkably similar to those of better‐studied northern temperate plant species, suggesting a generality across biomes that has not been described elsewhere. -
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Location Six headwater streams in the Lookout Creek basin, H.J. Andrews Experimental Forest, Oregon, USA.
Methods We collected emerging adults of four abundant insect species twice weekly throughout spring for 6 consecutive years. We fit Gaussian models to the empirical temporal distributions to characterize peak emergence timing (mean) and duration (days between 5th and 95th percentiles) for each species/stream/year combination. We then quantified relationships between degree‐day accumulation and phenological response.
Results Only one of the four species (a caddisfly) showed a simple response of earlier emergence timing in both warmer streams and years. One stonefly had lengthy emergence periods resulting in substantial phenological overlap between warmer and cooler streams/years. Interestingly, two species (a mayfly and a stonefly) responded strongly to temporal (interannual) temperature differences but minimally to spatial differences, indicating that emergence was nearly synchronous among streams, within years. These two species had among‐stream differences approaching 500 degree‐days from mid‐winter to peak emergence. Conversely, duration of emergence was more strongly associated with spatial than temporal differences, with longer duration in lower‐elevation (warmer) streams.
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