Phenology studies mostly focus on variation across time or landscapes. However, phenology can vary at fine spatial scales, and these differences may be as important as long-term change from climate warming. We used high-frequency “PhenoCam” data to examine phenology of Spartina alterniflora, a foundation species native to salt marshes on the US East and Gulf coasts, and a common colonizer elsewhere. We examined phenology across three microhabitats from 2013 to 2017 and used this information to create the first spring green-up model for S. alterniflora. We then compared modern spatial variation to that exhibited over a 60-year climate record. Marsh interior plants initiated spring growth 17 days earlier than channel edge plants and spent 35 days more in the green-up phenophase and 25 days less in the maturity phenophase. The start of green-up varied by 17 days among 3 years. The best spring green-up model was based on winter soil total growing degree days. Across microhabitats, spring green-up differences were caused by small elevation changes (15 cm) that drove soil temperature variation of 0.8°C. Preliminary evidence indicated that high winter belowground biomass depletion triggered early green-up. Long-term change was similar: winter soil temperatures warmed 1.7 ± 0.3°C since 1958, and green-up advanced 11 ± 6 days, whereas contemporary microhabitat differences were 17 ± 4 days. Incorporating local spatial variation into plant phenology models may provide an early warning of climate vulnerability and improve understanding of ecosystem-scale productivity. Microscale phenology variation likely exists in other systems and has been unappreciated.
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The Georgia Coastal Ecosystems LTER is supported by the National Science Foundation (OCE12-37140). We thank Wade Sheldon, Jacob Shalack and the National PhenoCam Network for managing and curating the GCE PhenoCam, and the GCE field crew for collecting belowground biomass data (particularly Caroline Reddy, Timothy Montgomery, Dontrece Smith, and Alyssa Peterson). We thank the editor and reviewers for helpful comments that improved the manuscript. This is contribution 1076 of the University of Georgia Marine Institute.
JLO designed the study, analyzed the data, wrote the paper; MA designed the study, contributed to the paper writing, provided funding for the study; SCP designed the study, contributed to the paper writing, provided funding for the study.
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O’Connell, J.L., Alber, M. & Pennings, S.C. Microspatial Differences in Soil Temperature Cause Phenology Change on Par with Long-Term Climate Warming in Salt Marshes. Ecosystems 23, 498–510 (2020). https://doi.org/10.1007/s10021-019-00418-1
- digital camera imagery
- global climate change
- coastal tidal marsh
- Georgia Coastal Ecosystems LTER
- Spartina alterniflora
- Sporobolus alterniflorus
- soil temperature gradient
- spring green-up