Climatic impacts on phenology of southern California native ecosystems using MODIS-derived time series

Abstract:

Phenology, the timing of seasonal activities of animals and plants, is a straightforward process used to track the response of ecology to climate change. Remote sensing can be utilized to track these responses and ecosystem functioning in Mediterranean-type ecosystems. This study elucidates these climate-phenology relations in native chaparral- and coastal sage scrub-dominated ecosystems in southern California. Whole ecosystem phenology is monitored for the period 2000-2014 using the Normalized Difference Vegetation Index (NDVI) derived from MODIS MOD13Q1. Changes in phenology are assessed through comparison of the time series with raw data and anomalies of temperature, precipitation, and Palmer Drought Indices (Modified Drought Index and Z Index) data to address the following questions: 1) Which climatic factors have the greatest impact on southern California whole ecosystem phenology? And 2) What are the differences between chaparral- and coastal sage scrub-dominated ecosystems? In addressing these questions, special consideration is given to late 2013/ 2014; a season of exceptional drought. We find that anomalous Palmer Drought Indices show highest correlations with vegetation NDVI. Each vegetation type displays a different response to short-term climate; with chaparral ecosystems having highest correlations with drought indices, and coastal sage scrub correlations highest with discrete precipitation events and temperature. Climate anomalies had little to no correlations with NDVI, indicating that the phenology of these native plants may be highly resilient to short-term changes in climate.