Exploring the concept of applied nucleation as a restoration tool in a previously invaded Mediterranean climate vegetation type

Date
2022-04
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: There is a need to scale-up ecological restoration efforts. The urgency to restore degraded habitats means that we, as researchers, need to be at the forefront of new and innovative restoration techniques. Sometimes this means assessing the efficacy of techniques which are not commonly employed in the vegetation type in need of restoration. In the case of this study, it involved exploring the concept of applied nucleation as a restoration tool in Cape Flats Sand Fynbos (CFSF). Applied nucleation involves establishing clusters of vegetation (nuclei) either by sowing or planting, and these clusters then produce and set seed into the surrounding area, facilitating nucleation. Colonization is further facilitated when the clusters of vegetation establish and are able to capture seed from other species (Corbin & Holl, 2012). This thesis assessed whether applied nucleation would be an effective restoration method in a vegetation type where it has not been employed before. This was done by resurveying previously restored plots to assess whether sown species had begun to set seed and nucleate into the surrounding environment (Chapter 2), and by designing a simulation model to assess which invasion management regimes and Cape Flats Sand Fynbos Species would most effectively facilitate nucleation (Chapter 3). The management regimes were fell & stack whereby felled Acacia biomass was stacked into brushpiles and fell & burn involved burning the felled Acacia biomass. A resurvey of active restoration plots established in 2013 through sowing indigenous Cape Flats Sand Fynbos investigated which species had established and persisted, as well as determined which species had set seed outside the initial 10m x 5m sowed plot. Fourteen plots were resurveyed in 2019 by determining species presence and abundance. This information was then compared to survey data from 2014 and 2017 to assess how the restored plots were faring. Of the 30 species sown in 2013, only 11 were observed to still be persisting in 2019. By establishing a larger 20m x 20m plot around the initial sowing plot, young plants of the species inside in sowing plot were identified, and these species were assumed to be nucleating species. The size (volume) of these young plants as well as their distance to the sowing plot was measured. This was to determine whether there was a significant difference between plant size inside the plot as opposed to outside, as well as to determine the distribution of plants of different ages. Plant size was used as a surrogate for plant age. Four species were seen to have consistently set seed outside the initial sowing plots, and these were Anthospermum aethiopicum, Ifloga repens, Dimorphotheca pluvialis, and Pelargonium capitatum. A practical simulation model was designed to assess which management regimes and species would facilitate nucleation the most effectively. The model was designed using the principles of inverse modelling, which is a modelling technique commonly used when certain model parameters are not available, as it makes use of model outputs to infer the values of model parameters. Management regimes were simulated by arranging theoretical felled Acacia brush piles in different patterns and distances around the initial sowed plot as seed traps. Furthermore, the dispersal and colonization of the four nucleating species identified in Chapter 2 was simulated to determine which species possessed the highest colonization and nucleation potential by manipulating certain biological parameters. The models showed that a fell and stack management regime where brush piles were arranged in a radial pattern facilitated nucleation the best, as this obstacle arrangement initially allowed for long distance dispersal, whereafter seed was trapped when it reached the Acacia brushpiles. This resulted in new sources of seed to continue to facilitate nucleation. The Acacia reinvasion simulation resulted in the poorest nucleation, as seed was trapped nearby the sowing plot and not allowed to disperse further. The species which displayed the highest nucleation potential was Dimorphotheca pluvialis, as this species had a high dispersal distance and reproductive rate. By analysing and interpreting the results from this study, certain management recommendations and recommendations for future research are proposed to provide a more in-depth understanding of using applied nucleation as a restoration tool in Cape Flats Sand Fynbos. It was concluded that this technique shows promise, but that further research is needed, particularly on the nucleation potential of species that require fire for seed germination.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
Description
Thesis (MScConsEcol)--Stellenbosch University, 2022.
Keywords
Applied nucleation, Restoration ecology -- South Africa -- Western Cape, Cape Flats Sand Fynbos, Vegetation type, Mediterranean fynbos ecosystem, Fynbos -- Climatic factors -- South Africa -- Western Cape, Nucleation -- Environmental aspects, Climatic changes, UCTD
Citation