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Assessing the frequency and drivers of early-greening in broad-leaved woodlands along a latitudinal gradient in southern Africa.
- Source :
- Austral Ecology; May2017, Vol. 42 Issue 3, p341-353, 13p
- Publication Year :
- 2017
-
Abstract
- Savannas are the only deciduous system where new leaf flush pre-empts the onset of suitable conditions for growth, a phenological phenomenon known as early-greening. Limited understanding of the frequency and drivers of the occurrence of early-greening in southern African savanna trees exists. We aimed to estimate the frequency of early-greening events across southern Africa and investigated potential environmental drivers of green-up. We selected and compared seven broad-leaved woodland sites where Burkea africana was a dominant species using remotely sensed data along a latitudinal gradient from South Africa to Zambia. Normalized difference vegetation index ( NDVI) values were extracted from the Moderate Resolution Imaging Spectroradiometer ( MODIS) satellite imagery at each site from January 2002 to June 2014. Using an austral year (July 1st-June 30th), early-greening was recorded if the green-up start date occurred prior to the onset date of seasonal rainfall. A latitudinal gradient of early-green-up was detected across southern Africa ( R<superscript>2</superscript> = 0.74) with the two most northerly (Zambian) sites showing the earliest and most consistent green-up start dates (3 October ± 5.34 days). A strong latitudinal gradient was observed between the variability in the amount of rainfall in the first 6 months of green-up and the green-up start dates across southern Africa ( R<superscript>2</superscript> = 0.92). Photoperiod appeared to play a role in areas where the onset of rainfall commenced late into the austral year. Mean maximum temperatures recorded 10 days prior to green-up start dates suggested a potential threshold of about 35°C, which could drive early-greening in the absence of rainfall. Correlations between the proportion of early-greening years and the above mentioned environmental factors indicated that rainfall variability had the strongest influence over the observed phenological gradient ( R<superscript>2</superscript> = 0.96). Understanding early-greening in complex savanna systems is a vital step in furthering predictive phenological models under changing climatic conditions. [ABSTRACT FROM AUTHOR]
- Subjects :
- FORESTS & forestry
SAVANNAS
MODIS (Spectroradiometer)
RAINFALL
CLIMATE change
Subjects
Details
- Language :
- English
- ISSN :
- 14429985
- Volume :
- 42
- Issue :
- 3
- Database :
- Complementary Index
- Journal :
- Austral Ecology
- Publication Type :
- Academic Journal
- Accession number :
- 122539348
- Full Text :
- https://doi.org/10.1111/aec.12448