- Title
- Factors affecting effective ecological restoration of Portulacaria afra (spekboom)-rich subtropical thicket and aboveground carbon endpoint projections
- Creator
- Van der Vyver, Marius Lodewyk
- Subject
- Restoration ecology
- Subject
- Plant conservation -- South Africa Portulacaria afra -- South Africa Shrubs -- South Africa
- Date Issued
- 2018
- Date
- 2018
- Type
- Thesis
- Type
- Doctoral
- Type
- DPhil
- Identifier
- http://hdl.handle.net/10948/23250
- Identifier
- vital:30468
- Description
- Among the requirements to achieve effective ecological restoration on a landscape scale are a scientific underpinning, strong adaptive management and the setting of realistic endpoints. Efficacy and success depend on a complex interplay of factors of both local and regional influence. Biome-wide restoration experiments are rare, but valuable for evaluating efficacy of different protocols according to local context. The Thicket-wide Plot (TWP) experiment was initiated by the Subtropical Thicket Restoration Programme to inform landscape-scale ecological restoration of degraded Portulacaria afra (spekboom)-rich Subtropical Thicket. Thirteen different planting treatments of Portulacaria afra (spekboom) truncheons were planted as replicated rows on 0.25 ha fenced plots across the distribution range of spekboom-rich thicket habitat to better establish effective restoration protocols. I used a rule-based learning ensemble algorithm to evaluate 60 different predictors that potentially impact effective restoration, covering a range of climatic, topographic, edaphic, ecological and management related factors observed at 227 of these TWP plots. Percentage survivorship and aboveground biomass carbon sequestration rate (ABCsr) were taken as proxies for efficacy derived from subsequent monitoring data gathered 2 - 5 years after establishment, and a new allometric model I developed for spekboom. I found herbivory and identification of target habitat the two most important predictors of restoration efficacy, both well within the control of the practitioner. Highest survivorship and ABCsr were associated with larger truncheons planted deeper. The only exception to this pattern was found amongst the two smallest size truncheon categories. The application of external rooting hormone or watering treatment to truncheons were found of no significance to effective restoration, while all the pruned treatments were, in association with lesser planting depth, found to be significantly less effective than untreated truncheons planted deeper. When the restoration protocol is optimal (largest truncheons planted deepest in target habitats and protected from herbivory), my results show higher annual carbon sequestration rates (1.46 - 3.7 t C ha−1 yr−1 in aboveground biomass) than most older restoration sites that have been identified as benchmarks of success. In order to project ABC endpoints, I generated 40 new species-specific allometric models and used them to estimate biomass and carbon of intact and degraded stands on five sites spread out across the region. The highest AGC for stands in both intact and degraded states were estimated at 42.96 t Cha−1 and 12.98 t C ha−1 respectively, and the lowest at 26.32 t C ha−1 and 2.52 t C ha−1. Large canopy dominant (LCD) species contributed the largest AGC portion at three intact stands. The second largest portion was recorded for spekboom. The difference between paired stands on each sample site ranged between 23.8 and 32.8 t C ha−1, which provide a realistic target for biome-wide restoration that, when adopted together with current protocols, may be reached within three decades of inception.
- Format
- 168 leaves
- Format
- Publisher
- Nelson Mandela University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- Nelson Mandela University
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