19 research outputs found
Vachellia erioloba dynamics over 38 years in the Kalahari Gemsbok National Park, South Africa
Vachellia erioloba is a keystone tree species in the southern Kalahari. This long-term study over nearly four decades tracks two populations in different landscapes (the interior sandy duneveld versus the clayey Nossob riverbed) of a large conservation area and offers valuable data on this species under natural soil moisture conditions and with limited anthropogenic influences. In 1978, 18 trees were permanently marked in a 1 ha plot in the interior duneveld of the Kalahari Gemsbok National Park (Dankbaar site). In the Nossob riverbed all trees in a 1 ha plot were surveyed in 1979 (Grootkolk site). At both sites, tree height and stem circumference were subsequently measured at irregular intervals until 2016 in order to investigate growth rates and population structure. Of the 18 marked trees at Dankbaar, six died and three showed coppice regrowth following substantial dieback after a fire. A mean height increase of 60 mm/year was recorded and the mean height of the remaining uncoppiced trees was 6.8 m in 2016. Stem diameter growth rate per year varied widely between trees and between years with a mean value of 2.5 mm/year over the 38-year period. Growth rate calculated for three 10-year intervals varied. Using the mean growth rate derived in the current study and stem size of the dead trees, the mean age of the trees when they died was estimated. At the Grootkolk site, the position of the centroid in relation to the midpoint of the diameter class range suggests that this population is gradually becoming a mature to old population with limited recruitment. This was supported by the size class distribution curves. However, no differences between slopes or intercepts of the stem diameter size class distributions were found.
Conservation implications: This study was conducted in a large conservation area, that is, a natural ecosystem excluding most of the anthropogenic threats that are present outside of the park. The study illustrated that in the duneveld the population studied was self-sustaining, with recruitment occurring and large individuals presumably dying of old age. Although fire caused a few individuals to coppice, no fire-related deaths were reported. In the Nossob riverbed, surveys started in a stand of predominantly young trees and the size class distribution at that stage already showed a lack of recruitment. This stand is ageing and will likely disappear at this site; however, new young stands are appearing at other sites in the Nossob riverbed. Under the current conditions with negligible anthropogenic influences, it therefore appears that some V. erioloba populations in the park are increasing in size while others are decreasing, but that overall the species will persist. The impact of global climate change on this species is, however, unknown
Floristic and phytogeographycal analysis of coastal and subcoastal vegetation in the Kouilou Department (Republic of Congo)
The zone of study is located north of Pointe noire town, in the Department of Kouilou, in Republic of Congo. In
order to better understand the floristic richness and chorology of the study site of interest, an analysis on a flora, of the
autoecological and phytogeographycal spectra of species was undertaken. This analysis is based on the floristic material from
different botanical surveys carried out in 2012, and deposited at the National Herbarium of the Congo (IEC). Over a study
area of 202’700 ha investigated through 243 phytosociological plots, a matrix of 580 specific and subspecific taxa, distributed
in 386 genus and 119 families, were inventoried. Seven species, of which one for the science, were new for the flora of
Republic of Congo. The families of Fabaceae, Poaceae, Rubiaceae, Euphorbiaceae, of Malavaceae and Annonaceae and are
the most diversified in species. The ecological spectrum highlights the strong preponderance of the phanerophytes,
sarcochores and mesophiles, thereby confirming the dominance of the forest biodiversity compared to grasslands. From a
phytogeographical perspective, the preponderance of the base element identified as well as three families and eleven genus
of endemic nature integrate the flora within the Guineo-Congolian centre of endemism.La zone d’étude est située au nord de Pointe noire, dans le Département du Kouilou, en République du Congo. Pour
mieux connaître la richesse floristique et la position chorologique du site d’intérêt, une analyse sur la flore, des spectres
autoécologiques et phytogéographiques des espèces a été entreprise. Cette analyse est basée sur le matériel floristique issu
de différentes prospections botaniques effectuées en 2012, et déposé à l’Herbier National du Congo (IEC). Sur une superficie
de 202.700 hectares prospectée, au travers de 243 relevés phytosociologiques, une matrice floristique de 580 espèces et
taxons infra spécifiques réparties en 386 genres et en 119 familles, a été retenue. Sept nouvelles espèces, dont une nouvelle
pour la science, sont des ajouts Ă la flore du Congo. Les familles des Fabaceae, des Poaceae, des Rubiaceae, des
Euphorbiaceae, des Malavaceae et des Annonaceae et sont les plus diversifiées en espèces. Les spectres écologiques mettent
en relief la forte représentativité des phanérophytes, des sarcochores et des mésophylles, confirmant de facto la
prépondérance de la biodiversité forestière par rapport aux formations herbacées. Sur le plan phytogéographique, la prépondérance de l’élément base décelé ainsi que la présence de trois familles et de onze genres endémiques, intègrent bien
cette flore au Centre d’endémisme guinéo-congolais.http://www.ijias.issr-journals.org/am2017Centre for Wildlife Managemen
Floristic composition, diversity and structure of the forest communities in the Kouilou DĂ©partement, Republic of Congo
The objectives of the study were to classify, describe and map the forest
communities in the study area and to investigate possible gradients in plant diversity. The
study area comprised approximately 166 000 ha in the Kouilou DĂ©partement, Republic of
Congo, a section of land targeted for extensive future development. In total 156 forest sample
sites were surveyed using the Braun-Blanquet method of phytosociology. Diversity of each plant
community was expressed in terms of species richness; Shannon-Wiener index; exponent of
Shannon-Wiener index; evenness; Fisher's alpha; Simpson’s index; and inverse Simpson index.
Eleven plant communities were described and mapped at a much finer scale than has been done
previously. The communities were arranged along two gradients: a degraded – relatively intact
gradient and a wet – dry gradient. The least degraded communities, and consequently those
with the highest conservation value, were the swamp forests and the okoumé forest. Overall,
the values reported for the diversity parameters in the current study were within the range
reported for other tropical forests in Central Africa. The study revealed a gradient between the
coast (west) and the Mayombe mountain range (east) in plant diversity linked to topography
and climate with plant diversity lowest at the coast. Furthermore, plant diversity was
negatively related to the distance to human infrastructure. The forest communities appear to be
fairly resilient to past anthropogenic disturbances, however, there is no historical analogue to
the more severe types of forest destruction associated with some of the future developments
anticipated, such as mechanized logging or mining.http://journals.cambridge.org/action/displayJournal?jid=TRO2017-06-30hb2017Centre for Wildlife ManagementPlant Scienc
Long-term vegetation dynamics (40 yr) in the succulent Karoo, South Africa : effects of rainfall and grazing
QUESTIONS : Vegetation change in arid regions with a coefficient of rainfall
exceeding 33% usually displays non-equilibrium dynamics, where abiotic factors
override internal biotic controls. Irreversible changes have nonetheless also
been described for arid regions. What are the contributions of internal/equilibriumvs
external/non-equilibriumfactors to vegetation dynamics and can degradation
due to overstocking be reversed after removal of livestock?
LOCATION : Goegap Nature Reserve, Namaqualand, South Africa.
METHODS : The descending point method was conducted annually from 1974 at
two transects. Vegetation change was assessed in terms of vegetation cover, species
composition, life-form composition, range condition, species richness and
diversity. Principal coordinates analysis was used to illustrate the trajectories in
floristic data, and the effects of stocking density and rainfall were examined with
redundancy analysis.
RESULTS : Vegetation cover, species richness and Shannon-Wiener index of
diversity showed an increase and range condition improved with time. These
positive changes could be related to the removal of high numbers of livestock
and low wildlife numbers in the first years of survey. A gradual decline in the
rate of increase in some of these parameters could be related to high grazing
pressure during the later monitored years. There was a notable increase in nonsucculent
chamaephytes, but the initial increase in succulent chamaephytes was
not sustained. The directional change evident in perennial species composition,
supports the equilibrium concept, whereby the negative changes induced by
heavy grazing were partially reversed. Within the directional change, four
quasi-stable states could be distinguished, which could be reconciled with the
state-and-transition model. The annual component showed no directional
change, but displayed event-driven, non-equilibrium dynamics by fluctuating
in reaction to the timing and quantity of rainfall.
CONCLUSIONS : The vegetation change displayed elements of both equilibrium
and non-equilibrium dynamics, and demonstrated that the effects of heavy grazing
in the Succulent Karoo were reversible. Overall, the recovery process proceeded
slowly and was primarily detected in the perennial component of the
vegetation. The increase in wildlife numbers in the later studied years and
decline in perennial vegetation cover stress the need for active management of
animal numbers to avoid vegetation degradation.University of Pretoria, the German Federal Ministry of Education and Research (BMBF)
through the BIOTA South Project and the National Research Foundation (Grant no. 61277).http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1654-109X2016-04-30hb201
Vegetation of the Hantam-Tanqua-Roggeveld subregion, South Africa Part 2: Succulent Karoo Biome related vegetation
The Hantam-Tanqua-Roggeveld subregion lies within the Succulent Karoo Hotspot that stretches along the western side of the Republic of South Africa and Namibia. This project, carried out to document the botanical diversity in the Hantam-Tanqua-Roggeveld subregion, was part of a project identified as a priority during the SKEP (Succulent Karoo Ecosystem Programme) initiative in this Hotspot. Botanical surveys were conducted in an area covering over three million hectares. Satellite images of the area and topocadastral, land type and geology maps were used to stratify the area into relatively homogeneous units. An analysis of the floristic data of 390 sample plots identified two major floristic units, i.e. the Fynbos Biome related vegetation and the Succulent Karoo Biome related vegetation. A description of the vegetation related to the Succulent Karoo Biome is presented in this article. Seven associations, 16 subassociations and several mosaic vegetation units, consisting of more than one vegetation unit, were identified and mapped. Various threats to the vegetation in the region were identified during the survey and are briefly discussed
Plant diversity and flowering displays on old fields in the arid Namaqua National Park, South Africa
National Park and to investigate whether the time since abandonment has impacted on the diversity and mass flowering displays. Sixty-two old field sample sites were surveyed using the Braun-Blanquet method. Floristic data were analysed to produce a hierarchical classification, while a principal coordinates analysis was used to establish whether the ordination supported the classification. Species richness (total number of taxa), as well as the Shannon-Wiener diversity index, was calculated per vegetation unit for the different life forms. Four old field communities were identified, each containing a unique complement of species, which differed in their potential to produce a mass flowering display. On the Skilpad section of the park, Ursinia cakilefolia dominated the spectacular mass floral displays for which the park has become well known. Old fields in other parts of the park did not produce the same spectacular displays. Although total and perennial species richness did not differ significantly with time since abandonment, the richness of annual species, in particular of the showy annual species, decreased with time since abandonment. The relative contribution of the perennial species to vegetation cover increased with time since abandonment, whereas the relative contribution made by showy annual species to vegetation cover declined with time since abandonment. Although species composition and the potential to produce mass flowering displays of the four communities differed, diversity parameters were similar. However, to maintain a flower display for tourists on the Skilpad section, a degree of disturbance is essential.
Conservation implication: Although deliberate disturbance is not desirable in a national park, we find that some disturbance is essential to maintain a spectacular flowering display. However, these intentionally disturbed old fields cover only a small proportion of the total area of the park. All other old fields in the park should not be disturbed, and should be allowed to recover naturally
Vegetation of the Hantam-Tanqua-Roggeveld subregion, South Africa. Part 1 : Fynbos Biome related vegetation
The Succulent Karoo Hotspot stretches along the western side of the Republic of South Africa and Namibia. A lack of botanical information on the Hantam-Tanqua-Roggeveld area of the Succulent Karoo Hotspot was identified during the SKEP (Succulent Karoo Ecosystem Plan) process. A grant from CEPF (Critical Ecosystem Partnership Fund) funded a study to produce a vegetation map of the
area to serve as baseline for ecosystem management. Vegetation surveys were conducted over an area of more than three million hectares from August to October 2004. Two major floristic units were identified, namely the Fynbos Biome related (Mountain Renosterveld) and Succulent Karoo Biome related units. An analysis of the floristic data of the predominantly Mountain Renosterveld vegetation unit is presented in this paper. Three associations were identified, which were subdivided into nine subassociations, one of which contains four variants. The vegetation units are described in terms of their species composition and their relationships with the physical environment. A vegetation map is provided depicting the geographical distribution of the different vegetation types. The main threat to the vegetation of the region identified by the farming community was a lack of infrastructure
Plant diversity and flowering displays on old fields in the arid Namaqua National Park, South Africa
Plant diversity of flowering displays on old fields in the arid Namaqua National Park, South Africa
The main aim of this study was to classify the vegetation on the abandoned fields in the Namaqua
National Park and to investigate whether the time since abandonment has impacted on the
diversity and mass flowering displays. Sixty-two old field sample sites were surveyed using the
Braun-Blanquet method. Floristic data were analysed to produce a hierarchical classification,
while a principal coordinates analysis was used to establish whether the ordination supported
the classification. Species richness (total number of taxa), as well as the Shannon-Wiener diversity
index, was calculated per vegetation unit for the different life forms. Four old field communities
were identified, each containing a unique complement of species, which differed in their potential
to produce a mass flowering display. On the Skilpad section of the park, Ursinia cakilefolia
dominated the spectacular mass floral displays for which the park has become well known. Old
fields in other parts of the park did not produce the same spectacular displays. Although total and
perennial species richness did not differ significantly with time since abandonment, the richness of
annual species, in particular of the showy annual species, decreased with time since abandonment.
The relative contribution of the perennial species to vegetation cover increased with time since
abandonment, whereas the relative contribution made by showy annual species to vegetation cover
declined with time since abandonment. Although species composition and the potential to produce
mass flowering displays of the four communities differed, diversity parameters were similar.
However, to maintain a flower display for tourists on the Skilpad section, a degree of disturbance
is essential.
Conservation implication: Although deliberate disturbance is not desirable in a national park, we
find that some disturbance is essential to maintain a spectacular flowering display. However, these
intentionally disturbed old fields cover only a small proportion of the total area of the park. All
other old fields in the park should not be disturbed, and should be allowed to recover naturally.Articlehttp://www.koedoe.co.z
Long-term vegetation change (>20 years) in the plains habitat on the Goegap Nature Reserve, Succulent Karoo, South Africa
Because vegetation change in arid ecosystems is slow, long-term data are essential to gain an understanding of how the vegetation responds to short-term, inter-annual variation in rainfall; long-term cyclic rainfall patterns; and grazing pressure. The point intercept method was conducted annually over a period of more than 20 years at five transects in the plains habitat on the Goegap Nature Reserve in the Northern Cape, South Africa. Vegetation change was assessed in terms of vegetation cover, species composition, species abundance, growth form composition, range condition and plant diversity. Non-metric multidimensional scaling was used to illustrate the trajectories in floristic data and to determine the strength of the correlations with rainfall and grazing variables. The effects of the high grazing pressure on the plains were apparent in the overall decrease in total plant cover and reductions in the cover of grazingsensitive species over the monitored period. Diversity parameters, of especially the annual component, were strongly related to rainfall. A directional change, which supports the equilibrium concept, was evident in changes in perennial species composition over time. The annual component, however, showed no directional change, but displayed eventdriven, non-equilibrium dynamics by fluctuating in reaction to the timing and quantity of rainfall.Keywords: diversity, equilibrium/non-equilibrium, rainfall, vegetation dynamics, wildlif