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(a) The 5 April 2012 SPOT image (RGB:321), and (b) sub-pixel classification of woody vegetation cover on the image.
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The proliferation of woody vegetation on open grass savannas constitutes degradation in rangeland quality. Historical high spatial resolution satellite imagery in archive provides possibilities for assessing increase in woody vegetation cover on the rangelands. This paper examines the quantification of woody vegetation in the field and on historica...
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Context 1
... correction, which applies when the signature is used in the same scene as that from which it was derived, was selected as opposed to the scene-to-scene option. On the 2012 image that had a small amount of cloud cover (Figure 3a), sample pixels representing cloud cover were specified at this stage. ...
Context 2
... general on all three historical images, the sub-pixel classification generally detected high woody cover for the lower woody cover fractions (<40%), which was in agreement with the field data in Table 2 that show the highest woody cover to have been about 40%. Sub-pixel classification also detected a general pattern of high woody cover in the valleys (Figures 3-5), which also was in agreement with the pattern from the field data as shown in Table 2. Table 2 Indicative woody canopy cover data illustrating the relationship between field data and sub-pixel classification of the images listed in Table 1 Study site (as on Figure 1c) The sub-pixel classification correctly assigned the woody cover at most of the field sample plots to their correct fraction of cover classes (Table 2). Using a contingency table, which is a simple cross-tabulation of the mapped class against that observed in the field (Foody, 2002), the overall classification accuracy was 83.3%. ...
Context 3
... demonstrated in this paper, using imagery that was acquired during a season when the herbaceous vegetation is in senescence but the woody vegetation is in leaf is critical. Season partly accounts for the differences in amount of woody cover that was mapped for the 2001 and 2012 images in this study (Figures 3, 4; Table 3). On the September 2001 image, the woody vegetation that was detected was mainly that in river valleys whereas way from the river valleys the woody canopies were still in early spring leaf. ...
Context 4
... the high spatial resolution of the aerial photographs that were used (Table 1), more woody cover should have been detected on the aerial photographs than was detected (Table 3). Although more woody cover detail was detected on the higher resolution aerial photographs than on the SPOT images (Figures 3-5), the amount of woody cover that was detected on the aerial photographs was lessened by the failure of the sub-pixel classifier to detect portions of woody canopies that were under shadow as being part of the respective canopies. Without such an error, the results from this study indicate that historical aerial photographs are quite useful in detecting woody encroachers using sub-pixel classification because of their high spatial resolution ( Figure 5). ...
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... The canopy diameter then gave a canopy radius (r) measurement (r ½ d). We modeled the shape covered by the canopy as circular and calculated the area covered by each canopy as area πr2 (Innocent and Munyati, 2014). Tree clearing and thinning practices were completed in February 2018 during the dry season. ...
... The sum of individuals per species was calculated and analyzed in terms of species/ woody/tree/sapling density ha −1 (Shankar, 2001;Tiwari et al., 2010). The total area covered by woody canopy within the plots is defined as the ratio of 1-ha area covered by woody canopies (Innocent and Munyati, 2014). The average monthly and annual rainfalls were calculated from the 2 years' amounts. ...
High bush density and cover have negative effects on the environment in general and on livestock production, in particular in savanna rangelands. The study examined the effects of bush control techniques on woody sapling recruitment in the low land savanna region. The study consisted of 21 plots located next to each other on an area of 5.3 ha encroached by Acacia mellifera and Acacia reficiens trees. Seven bush control treatments were assigned randomly to the plots and replicated three times. In the bush clearing plot, woody species were removed at ground level using a handsaw. In the tree thinning; thinning and grazing; thinning and browsing; thinning and fire, and thinning with fire-browsing treatments, trees were thinned to the equivalents of 60% of the density of that of the control plot. Positive changes in sapling densities were observed in the clearing, thinning, and thinning and grazing treatments. In contrast, the control, thinning and browsing, and thinning and fire treatments presented negative changes in densities. A change in sapling density was highest in the cleared plot, whereas it was lowest in the thinning, fire, and browsing treatment. The correlation between changes in sapling densities and new recruitments was highly (p < 0.001) significant in the clearing, thinning, and thinning and grazing treatments thus increased sapling recruitment with the proportion greater for the clearing treatment. The significant correlation induced average sapling recruitment in the control, and low in the thinning with browsing and thinning with fire treatments. The relationship was insignificant in the thinning, fire, and browsing combination treatment and resulted in the lowest rate of saplings’ recruitment. Postthinning techniques reduced woody tree recruitment and would sustain open savanna under the continuous management plan.
... Alguns autores (por ex.: LU & WENG, 2007; HUBERT-MOY et al., 2001) j? avaliaram comparativamente os referidos classifi cadores. Contudo, existem poucos trabalhos comparativos do desempenho dos algoritmos param?tricos na classifi ca??o de imagens multiespectrais de sat?lite de alta resolu??o espacial em paisagens heterog?neas com fi tofi sionomias de Savana (Cerrado) (SINTHUMULE & MUNYATI, 2014). O mapeamento de ?reas de Savana ? ...
RESUMO Esse trabalho teve como objetivo geral avaliar comparativamente a efi ciência dos quatros algoritmos paramétricos de classifi cação supervisionada por pixel mais utilizados no mapeamento da cobertura do solo, em uma área sob domí-nio do Cerrado que apresenta uma vegetação heterogênea, complexa e extremamente dinâmica, situada no Parque Municipal de Mucugê (12º59'18 " S e 41º20'22''W). Para isso foi utilizado uma imagem de alta resolução espacial (KOMPSAT-2). Os algoritmos escolhidos foram de máxima verossimilhança, paralelepípedo e a distância Euclidiana mínima e de Mahalanobis. Para comparar e verifi car qual foi o algoritmo paramétrico que teve o melhor desempenho foram calculadas duas medidas que foram discordância de quantidade e de alocação baseado em uma matriz de erro. Para avaliar se as classes produzidas pelo melhor classifi cador representavam bem a variação estrutural da vegetação da área de estudo foi realizada uma análise de variância (ANOVA) e o teste post-hoc de Tukey. De modo geral, o
... Sample plots measuring 100m x 100m (1 ha) were used during the field quantification. At each plot the fraction of cover (%) by woody canopies was quantified using a detailed field methodology [5], and the location of the plot determined using a 3m-accuracy GPS. ...
Esse trabalho teve como objetivo geral avaliar comparativamente a eï¬ciência dos quatros algoritmos paramétricos de classiï¬cação supervisionada por pixel mais utilizados no mapeamento da cobertura do solo, em uma área sob domínio do Cerrado que apresenta uma vegetação heterogênea, complexa e extremamente dinâmica, situada no Parque Municipal de Mucugê (12º59'18"S e 41º20'22''W). Para isso foi utilizado uma imagem de alta resolução espacial (KOMPSAT-2). Os algoritmos escolhidos foram de máxima verossimilhança, paralelepípedo e a distância Euclidiana mínima e de Mahalanobis. Para comparar e veriï¬car qual foi o algoritmo paramétrico que teve o melhor desempenho foram calculadas duas medidas que foram discordância de quantidade e de alocação baseado em uma matriz de erro. Para avaliar se as classes produzidas pelo melhor classiï¬cador representavam bem a variação estrutural da vegetação da área de estudo foi realizada uma análise de variância (ANOVA) e o teste post-hoc de Tukey. De modo geral, o algoritmo que apresentou melhor desempenho e que representou melhor a variação da estrutura da vegetação foi o de máxima verossimilhança. Considerando o resultado obtido conclui-se que o algoritmo de máxima verossimilhança é o mais adequado, dentre as possibilidades testadas nesse estudo para realizar mapeamentos de áreas de vegetação nativas naturalmente heterogêneas. Esse estudo pode ter grande utilidade para conservação, monitoramento e gestão de ambientes naturais.
Encroachment of woody plants has negative effects on grass species and seriously challenging livestock production and pastoral livelihood in semi-arid savanna. The effect of thinning and season on grass species composition and biomass was investigated in lowland grazing area for three seasons. The study consisted of 15 plots (each 50 m × 50 m), thinned to differing intensities. The plots were located next to each other on a homogeneous area of 3.8 ha. Five thinning intensities (0, 25, 50, 75, and 100%) were allocated randomly to the plots and replicated three times. The 0% plot was left unthinned referred to as the control plot. The remaining plots were thinned to the equivalents of 25, 50, 75, and 100% of the tree density of that of the control plot. A two-way analysis of variance and Tukey Honest Significant Differences tests were used to compare responses of grass species. Ordination of variables was carried out by multivariate technique using correspondence analysis to explore the similarity relationship of plots, seasons and species. The differences in species composition and biomass in the control and the thinned plots were significant (p < 0.05). Higher grass species composition and biomass were documented in thinned plots than in the control plot. Species abundance in thinned plots ranged from 11 to 12, while that of the 0% plot was six species. Grass biomass (Kg ha-1) varied from 2,688.4 ± 736.8 to 5,035.8 ± 743.9 across thinned plots, whereas in the control plot the yield was 885.8 ± 369.1. The result showed that grass species composition and biomass increased with the increasing intensity of thinning. Grass values appeared to be optimum at the heavy intensity of thinning woody plants. Seasons were also significant with the highest values recorded in the rainy season. Rainfall played an important role by interacting with thinning and influenced total grass values. Overall, thinning that combined improved soil moisture negatively influenced woody cover and enhanced grass species composition and biomass production. Thinning of bushes to the 75% of tree density would sustain the original savanna and maximize forage production for grazers.
Fish undertake migrations for a number of reasons including to spawn, feed and seek
refuge. These migrations are also essential to ensure the dispersal of species and
maintain genetic fitness within fish communities. Fishladders, also known as fishways
or fish passes, are structures placed on or around constructed barriers (such as dams
or weirs) to re-establish connectivity between critical habitats for migratory fish
species, thus mitigating the impacts of the blockage of migration routes. If this
management tool is to be meaningful for conserving fish species, it must provide a
fully permeable connection and ensure both up- and downstream movements.
Additionally, fishladders must be able to operate effectively over a wide range of river
flows, and cater for a broad range of fish sizes, varying swimming abilities and
behavioural preferences.
In 2011 a fishladder was constructed in the Letaba River at Engelhard Dam in Kruger
NP. The following year a study was initiated to: (1) determine whether migratory fish
and their offspring are able to swim upstream to the dam, and (2) evaluate the
selectivity of the fishladder in attracting different fish. The top
part of the ladder was closed, thereby restricting movement
downstream through the ladder and only allowing upward
movement. Samples of ichthyofauna were collected from the
21 buckets along the ladder using electronarcosis. The fish
were identified to species level and released. Two days later
the survey was repeated to determine if fish are able to swim
up the ladder. The occurrence (species number) and relative
abundance of fish in the buckets along the fishladder as well
as at various sites along the Letaba River were recorded. The
study was carried out during low flows in winter of 2012, 2013
and 2014.
Preliminary results indicate that fish are able to use the ladder as a migratory route,
that they are able to ascend the ladder at different times of the year, and that the
ladder caters for fish of various sizes. Both the abundance and diversity of fish species
occurring in the fishladder increased over the three-year period (Fig. 1). Various
hypotheses for the observed increase in abundance and species diversity have been
proposed including seasonal effect and time of sampling.
