a systematic review of the impacts of woody encroachment
TRANSCRIPT
ContentsA systematic review of the impacts of woody encroachment on ecosystem services in African and North American
savannas and grasslands.
Felix V. Skhosana
PhD Candidate
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Woody encroachment (WE)
Photo By Vision2030 - Own work, CC BY-SA 4.0,
• WE – The directional increase of indigenous woody plants in savannas and the
‘invasion’ of the formerly grassland biomes by indigenous woody plants (O’Connor et al.
2014).
• Eg. WE at the Waterberg Plateau Park in Namibia
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Woody Encroachment (WE) across the world
Stevens et al. 2018
• WE occurs mostly in savannas and grasslands worldwide.
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Drivers of Woody encroachment (WE)
Luvuno et al. 2018
• Substantial knowledge on drivers and encroachers of WE.
• A combination of local and global drivers causing WE.
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Encroaching species
Photo By Vision2030 - Own work, CC BY-SA 4.0,
• Mostly N-fixing legumes to search and review.
S. melifera P. glandulosa
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Gap in literature
• Impacts of WE on ecosystem services (ES) and ecosystem
disservices (EDS) warrants a clear synthesis.
– AIM: Systematically reviewing the impacts of WE on ES & EDS.
– Objective: Use online databases to search and review literature.
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Ecosystem services (ES) and disservices (EDS)
• ES: Benefits and services humans obtain from ecosystems (MA, 2005).
– Provisioning, Regulating and Cultural
• EDS: goods and services that harm human well-being (Lyytimäki, 2014).
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Methods
• Searching electronic databases for literature
• Using MA, TEEB & CICES categories as guidelines.
Provisioning ES & EDS Regulating ES and EDS Cultural ES & EDS
Grass forage availability Carbon sequestration Tourism & view obstruction
Water availability Drought regulation Herding obstruction
Woody fuels Erosion regulation Cultural heritage
Woody materials Flood regulation Cultural standing
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Preliminary Results
• 313 published cases from 186 publications documented the impacts of WE on ES & EDS.
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Impacts on provisioning ESN
. Am
eric
aA
fric
a
Canada: Decline in grass cover from 50% to 0% from open to 80% shrub cover (Bork et al. 2009).
E.g. Decrease provisioning E.g. Increase provisioning
Namibia: 60% reduction in cattle carrying capacity (de
Klerk 2004); decline in cattle from 2,5milllion in 1958 to 800 000 in 2001 resulting to a 64% decline in meat production (Jones et al. 2009; Demas et al., 2012)
Namibia: Use 0.5mil to 1mil tons of firewood per yr. and exports 60 000 – 158 000 tons/yr. of charcoal (Rothauge
2014; Trede and Patt, 2015).
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Impacts on regulating ES
Eg. Increase regulation Eg. Decrease regulating Eg. EDS
RSA: Increase of 12100 kg/ha in AGC (Coetsee et al., 2013).
WE facilitates weed invasion (e.g. Chromolaena), causing bloating or even death (Solomon et al. 2007; Wigley
et al. 2009).
WE causing diseases (e.g. Trypansomiasis) in animals spread by Glossima fly (Bollig and Osterle
2008).
Afr
ica
Eg. Increase regulating Eg. Decrease regulating Eg. EDS
USA : Increase in AGC ranged from 1200 to 80958kg/ha (Collins et al. 1998; Asner et al.
2003; Campbell et al. 2012).
USA: Increase in SOC ranging from 300 to 61200 kg/ha (Hibbard et al., 2003; Liao et
al., 2006; Neff et al., 2009).
USA: Decrease in SOC ranging from -50 000 to -30kg/ha from grass-dominated to tree-dominated areas(McCulley and Jackson 2012; Shifa 2017).
N. A
me
rica
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Conclusion
• Review presents both the benefits and negative impacts of WE on ES.
• At local scale, whether benefits outweigh negative impacts depends on the type of
landuse and the ES of interest.
• At wider scale WE is largely a problem than a benefit.
– WE beneficial in C sequestration but huge negative impact on livestock production.
– 50% to 80% of savannas and grasslands are used as rangelands & > 70% of these rangelands are degraded due to WE (Lukomska et al., 2014; Belayneh a.nd Tessema, 2017; Stevens et
al. 2017).
– > 1bil. people earn their livelihood from livestock farming in these impacted areas (Lukomska et al., 2014; MA, 2005).
• Control measures are essential to reduce WE.
Acknowledgements
Graham von Maltitza, Malebajoa Anicia Maoelaa, Gregor T. Feigac and Guy Midgleyb
• aCouncil for Scientific and Industrial Research, Pretoria, South Africa
• bDepartment of Botany and Zoology, Stellenbosch University, Matieland, South Africa
• cDepartment of Geography, Geoinformatics and Meteorology, University of Pretoria, South Africa