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Biomass Increases Go under Cover: Woody Vegetation Dynamics in South African Rangelands.

Mograbi PJ, Erasmus BF, Witkowski ET, Asner GP, Wessels KJ, Mathieu R, Knapp DE, Martin RE, Main R - PLoS ONE (2015)

Bottom Line: Loss of large trees and gain in subcanopy shrubs could result in a structurally simple landscape with reduced functional capacity.This research demonstrates that intensive harvesting can, paradoxically, increase biomass and this has implications for the sustainability of ecosystem service provision.The structural implications of biomass increases in communal rangelands could be misinterpreted as woodland recovery in the absence of three-dimensional, subcanopy information.

View Article: PubMed Central - PubMed

Affiliation: Restoration and Conservation Biology Research Group, School of Animal, Plant & Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa; Centre for African Ecology, School of Animal, Plant & Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa.

ABSTRACT
Woody biomass dynamics are an expression of ecosystem function, yet biomass estimates do not provide information on the spatial distribution of woody vegetation within the vertical vegetation subcanopy. We demonstrate the ability of airborne light detection and ranging (LiDAR) to measure aboveground biomass and subcanopy structure, as an explanatory tool to unravel vegetation dynamics in structurally heterogeneous landscapes. We sampled three communal rangelands in Bushbuckridge, South Africa, utilised by rural communities for fuelwood harvesting. Woody biomass estimates ranged between 9 Mg ha(-1) on gabbro geology sites to 27 Mg ha(-1) on granitic geology sites. Despite predictions of woodland depletion due to unsustainable fuelwood extraction in previous studies, biomass in all the communal rangelands increased between 2008 and 2012. Annual biomass productivity estimates (10-14% p.a.) were higher than previous estimates of 4% and likely a significant contributor to the previous underestimations of modelled biomass supply. We show that biomass increases are attributable to growth of vegetation <5 m in height, and that, in the high wood extraction rangeland, 79% of the changes in the vertical vegetation subcanopy are gains in the 1-3 m height class. The higher the wood extraction pressure on the rangelands, the greater the biomass increases in the low height classes within the subcanopy, likely a strong resprouting response to intensive harvesting. Yet, fuelwood shortages are still occurring, as evidenced by the losses in the tall tree height class in the high extraction rangeland. Loss of large trees and gain in subcanopy shrubs could result in a structurally simple landscape with reduced functional capacity. This research demonstrates that intensive harvesting can, paradoxically, increase biomass and this has implications for the sustainability of ecosystem service provision. The structural implications of biomass increases in communal rangelands could be misinterpreted as woodland recovery in the absence of three-dimensional, subcanopy information.

No MeSH data available.


Related in: MedlinePlus

Height-specific correlation (p < 0.001) between change in biomass (%) and subcanopy returns (%).Wood extraction levels for each rangeland are listed per column as high, intermediate and low.
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pone.0127093.g005: Height-specific correlation (p < 0.001) between change in biomass (%) and subcanopy returns (%).Wood extraction levels for each rangeland are listed per column as high, intermediate and low.

Mentions: There was a positive correlation between change in biomass and change in % subcanopy returns (Fig 5); particularly in the 1–3 m height class in the high extraction sites (high extraction: r = 0.22, p <0.0001; intermediate extraction: r = 0.58, p<0.0001) and the 3–5 m height class (high extraction: r = 0.62, p <0.0001; intermediate extraction: r = 0.64, p <0.0001; low extraction: r = 0.56, p <0.0001). Although this relationship was also present in the 5–10 m height class at all extraction levels (r >0.31), it degraded at heights >10 m (r < 0.10) (Fig 5). It is interesting to note that the strength of the relationship between change in biomass and change in % subcanopy returns across all height categories was strongest at the intermediate wood extraction site (Fig 5).


Biomass Increases Go under Cover: Woody Vegetation Dynamics in South African Rangelands.

Mograbi PJ, Erasmus BF, Witkowski ET, Asner GP, Wessels KJ, Mathieu R, Knapp DE, Martin RE, Main R - PLoS ONE (2015)

Height-specific correlation (p < 0.001) between change in biomass (%) and subcanopy returns (%).Wood extraction levels for each rangeland are listed per column as high, intermediate and low.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4430526&req=5

pone.0127093.g005: Height-specific correlation (p < 0.001) between change in biomass (%) and subcanopy returns (%).Wood extraction levels for each rangeland are listed per column as high, intermediate and low.
Mentions: There was a positive correlation between change in biomass and change in % subcanopy returns (Fig 5); particularly in the 1–3 m height class in the high extraction sites (high extraction: r = 0.22, p <0.0001; intermediate extraction: r = 0.58, p<0.0001) and the 3–5 m height class (high extraction: r = 0.62, p <0.0001; intermediate extraction: r = 0.64, p <0.0001; low extraction: r = 0.56, p <0.0001). Although this relationship was also present in the 5–10 m height class at all extraction levels (r >0.31), it degraded at heights >10 m (r < 0.10) (Fig 5). It is interesting to note that the strength of the relationship between change in biomass and change in % subcanopy returns across all height categories was strongest at the intermediate wood extraction site (Fig 5).

Bottom Line: Loss of large trees and gain in subcanopy shrubs could result in a structurally simple landscape with reduced functional capacity.This research demonstrates that intensive harvesting can, paradoxically, increase biomass and this has implications for the sustainability of ecosystem service provision.The structural implications of biomass increases in communal rangelands could be misinterpreted as woodland recovery in the absence of three-dimensional, subcanopy information.

View Article: PubMed Central - PubMed

Affiliation: Restoration and Conservation Biology Research Group, School of Animal, Plant & Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa; Centre for African Ecology, School of Animal, Plant & Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa.

ABSTRACT
Woody biomass dynamics are an expression of ecosystem function, yet biomass estimates do not provide information on the spatial distribution of woody vegetation within the vertical vegetation subcanopy. We demonstrate the ability of airborne light detection and ranging (LiDAR) to measure aboveground biomass and subcanopy structure, as an explanatory tool to unravel vegetation dynamics in structurally heterogeneous landscapes. We sampled three communal rangelands in Bushbuckridge, South Africa, utilised by rural communities for fuelwood harvesting. Woody biomass estimates ranged between 9 Mg ha(-1) on gabbro geology sites to 27 Mg ha(-1) on granitic geology sites. Despite predictions of woodland depletion due to unsustainable fuelwood extraction in previous studies, biomass in all the communal rangelands increased between 2008 and 2012. Annual biomass productivity estimates (10-14% p.a.) were higher than previous estimates of 4% and likely a significant contributor to the previous underestimations of modelled biomass supply. We show that biomass increases are attributable to growth of vegetation <5 m in height, and that, in the high wood extraction rangeland, 79% of the changes in the vertical vegetation subcanopy are gains in the 1-3 m height class. The higher the wood extraction pressure on the rangelands, the greater the biomass increases in the low height classes within the subcanopy, likely a strong resprouting response to intensive harvesting. Yet, fuelwood shortages are still occurring, as evidenced by the losses in the tall tree height class in the high extraction rangeland. Loss of large trees and gain in subcanopy shrubs could result in a structurally simple landscape with reduced functional capacity. This research demonstrates that intensive harvesting can, paradoxically, increase biomass and this has implications for the sustainability of ecosystem service provision. The structural implications of biomass increases in communal rangelands could be misinterpreted as woodland recovery in the absence of three-dimensional, subcanopy information.

No MeSH data available.


Related in: MedlinePlus