Header

UZH-Logo

Maintenance Infos

Primary productivity and its correlation with rainfall on Aldabra Atoll


Shekeine, John; Turnbull, Lindsay A; Cherubini, Paolo; de Jong, Rogier; Baxter, R; Hansen, Dennis; Bunbury, Nancy; Fleischer-Dogley, Frauke; Schaepman-Strub, Gabriela (2015). Primary productivity and its correlation with rainfall on Aldabra Atoll. Biogeosciences Discussions, 12(2):981-1013.

Abstract

Aldabra Atoll, a UNESCO World Heritage Site since 1982, hosts the world’s largest population of giant tortoises. In view of recent rainfall declines in the East African region, it is important to assess the implications of local rainfall trends on the atoll’s 5 ecosystem and evaluate potential threats to the food resources of the giant tortoises. However, building an accurate picture of the effects of climate change requires detailed context-specific case-studies, an approach often hindered by data deficiencies in remote areas. Here, we present and analyse a new historical rainfall record of Aldabra atoll together with two potential measures of primary productivity: (1) treering measurements of the deciduous tree species Ochna ciliata and, (2) satellite-derived NDVI (normalized difference vegetation index) data for the period 2001–2012. Rainfall declined by about 6 mm yr⁻¹ in the last four decades, in agreement with general regional declines, and this decline could mostly be attributed to changes in wet-season rainfall. We were unable to cross-date samples of O. ciliata with suffcient precision 15 to deduce long-term patterns of productivity. However, satellite data were used to derive Aldabra’s land surface phenology (LSP) for the period 2001–2012 which was then linked to rainfall seasonality. This relationship was strongest in the eastern parts of the atoll (with a time-lag of about six weeks between rainfall changes and LSP responses), an area dominated by deciduous grasses that supports high densities of 20 tortoises. While the seasonality in productivity, as reflected in the satellite record, is correlated with rainfall, we did not find any change in mean rainfall or productivity for the shorter period 2001–2012. The sensitivity of Aldabra’s vegetation to rainfall highlights the potential impact of increasing water stress in East Africa on the region’s endemic ecosystems.

Abstract

Aldabra Atoll, a UNESCO World Heritage Site since 1982, hosts the world’s largest population of giant tortoises. In view of recent rainfall declines in the East African region, it is important to assess the implications of local rainfall trends on the atoll’s 5 ecosystem and evaluate potential threats to the food resources of the giant tortoises. However, building an accurate picture of the effects of climate change requires detailed context-specific case-studies, an approach often hindered by data deficiencies in remote areas. Here, we present and analyse a new historical rainfall record of Aldabra atoll together with two potential measures of primary productivity: (1) treering measurements of the deciduous tree species Ochna ciliata and, (2) satellite-derived NDVI (normalized difference vegetation index) data for the period 2001–2012. Rainfall declined by about 6 mm yr⁻¹ in the last four decades, in agreement with general regional declines, and this decline could mostly be attributed to changes in wet-season rainfall. We were unable to cross-date samples of O. ciliata with suffcient precision 15 to deduce long-term patterns of productivity. However, satellite data were used to derive Aldabra’s land surface phenology (LSP) for the period 2001–2012 which was then linked to rainfall seasonality. This relationship was strongest in the eastern parts of the atoll (with a time-lag of about six weeks between rainfall changes and LSP responses), an area dominated by deciduous grasses that supports high densities of 20 tortoises. While the seasonality in productivity, as reflected in the satellite record, is correlated with rainfall, we did not find any change in mean rainfall or productivity for the shorter period 2001–2012. The sensitivity of Aldabra’s vegetation to rainfall highlights the potential impact of increasing water stress in East Africa on the region’s endemic ecosystems.

Statistics

Altmetrics

Downloads

21 downloads since deposited on 23 Dec 2015
13 downloads since 12 months
Detailed statistics

Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute of Geography
Dewey Decimal Classification:910 Geography & travel
Language:English
Date:2015
Deposited On:23 Dec 2015 09:58
Last Modified:08 Dec 2017 16:17
Publisher:Copernicus Publications
ISSN:1810-6285
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.5194/bgd-12-981-2015
Related URLs:http://www.biogeosciences-discuss.net/12/981/2015/ (Publisher)

Download

Download PDF  'Primary productivity and its correlation with rainfall on Aldabra Atoll'.
Preview
Content: Published Version
Language: English
Filetype: PDF
Size: 3MB
View at publisher
Licence: Creative Commons: Attribution 3.0 Unported (CC BY 3.0)