Climate change and plant phenology in Santa Cruz County, California

Background/Question/Methods

Plant phenological events are expected to shift in response to climate change. In this study, we used a long-term dataset along with climate data from the PRISM Climate Group to detect changes in flowering phenology from 1989-2013 in Santa Cruz County, California. We surveyed 2 habitats: 4 sandhill and 6 grassland (3 coastal and 3 inland) sites to assess both temporal and spatial patterns. We hypothesize that: 1) Maritime buffering is stronger at the coast than inland; compared to inland, coastal areas have a smaller temperature range, lower rainfall, and less change in temperature and precipitation over time. 2) Inland plants will bloom earlier in the year than coastal plants because inland sites warm earlier than coastal sites. 3) A higher proportion of species will have shifted flowering phenology over time at sites where temperature and precipitation have changed the most. We used regression to detect changes in climate over time, and ANOVA and ANCOVA for climatic differences between sites. We compared historic first flowering dates (FFDs), duration of flowering and last flowering dates collected from 1989-1998 to those observed in 2012-2013.

Results/Conclusions

Climate (1980-2013): Minimum temperatures increased significantly over time at 9 of 10 sites; sandhills had a significant site by year interaction. Maximum temperature declined at 2 coastal grassland sites and precipitation did not change anywhere.  Inland grassland sites had larger temperature ranges and more precipitation than coastal sites, though all climate variables vary within (e.g., coastal) and between climate zones.

Flowering phenology (based on 2012 data): Most species have similar FFDs at coast and inland grassland sites, though many bloom earlier at the coast than inland. At the 2 climatically similar coastal grassland sites most species had earlier FFDs than historically observed. At 2 climatically similar inland grassland sites most species did not change FFDs; if they did, most bloomed earlier than historically. This suggests that species bloom earlier in response to both minimum temperature increase and maximum temperature decrease. Most sandhill species had later FFDs than historically, though some did not change and only a few bloomed earlier, suggesting that sandhill species bloom later with increasing minimum temperature. Many species responded differently at each site within a climate zone, suggesting that site differences are also important.  For all sites, 2013 patterns are similar to 2012.