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

2

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

3

Woody Encroachment (WE) across the world

Stevens et al. 2018

• WE occurs mostly in savannas and grasslands worldwide.

4

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.

5

Encroaching species

Photo By Vision2030 - Own work, CC BY-SA 4.0,

• Mostly N-fixing legumes to search and review.

S. melifera P. glandulosa

6

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.

7

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).

8

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

9

Preliminary Results

• 313 published cases from 186 publications documented the impacts of WE on ES & EDS.

10

Distribution of the studies

11

Impacts on provisioning ES

12

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).

13

Impacts on regulating ES

14

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

15

Impacts on cultural ES

16

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

Thank you