Exploring the concept of applied nucleation as a restoration tool in a previously invaded Mediterranean climate vegetation type
Date
2022-04
Authors
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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.
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