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2016 ; 371
(1703
): ä Nephropedia Template TP
gab.com Text
Twit Text FOAVip
Twit Text #
English Wikipedia
Woody encroachment over 70 years in South African savannahs: overgrazing, global
change or extinction aftershock?
#MMPMID27502384
Stevens N
; Erasmus BF
; Archibald S
; Bond WJ
Philos Trans R Soc Lond B Biol Sci
2016[Sep]; 371
(1703
): ä PMID27502384
show ga
Woody encroachment in 'open' biomes like grasslands and savannahs is occurring
globally. Both local and global drivers, including elevated CO2, have been
implicated in these increases. The relative importance of different processes is
unresolved as there are few multi-site, multi-land-use evaluations of woody plant
encroachment. We measured 70 years of woody cover changes over a 1020 km(2) area
covering four land uses (commercial ranching, conservation with elephants,
conservation without elephants and communal rangelands) across a rainfall
gradient in South African savannahs. Different directions of woody cover change
would be expected for each different land use, unless a global factor is causing
the increases. Woody cover change was measured between 1940 and 2010 using the
aerial photo record. Detection of woody cover from each aerial photograph was
automated using eCognitions' Object-based image analysis (OBIA). Woody cover
doubled in all land uses across the rainfall gradient, except in conservation
areas with elephants in low-rainfall savannahs. Woody cover in 2010 in
low-rainfall savannahs frequently exceeded the maximum woody cover threshold
predicted for African savannahs. The results indicate that a global factor, of
which elevated CO2 is the likely candidate, may be driving encroachment.
Elephants in low-rainfall savannahs prevent encroachment and localized megafaunal
extinction is a probable additional cause of encroachment.This article is part of
the themed issue 'Tropical grassy biomes: linking ecology, human use and
conservation'.