Abstract:The transformation of grassland by bush encroachment causes socioeconomic problems in arid and semi-arid regions. At the moment, de-bushing is the only way to control bush encroachment. In this context, we conducted two independent projects within SASSCAL. First, in a greenhouse experiment, we investigated the morphological plant response to damage of four diff erent bush encroacher species in order to understand if intervention in the plants' early life stage may reasonably fi ght bush encroachment and if treated plants are used diff erently by livestock (e.g., sheep and goats). In a second project, we investigated the infl uence of bush clearing on the habitat utilisation of diff erent large herbivores (e.g., greater kudu, warthog, and gemsbok). Specifi cally, we wanted to know if typical grazers (e.g., warthog and gemsbok) are found at open cleared sites and typical browsers (greater kudu) in encroached regions and if vegetation parameters (e.g., grass cover) drive this distribution. For our greenhouse experiment, we found that all seedlings reacted morphologically to the damage of top-shoots, but to diff erent extents. Damaged plants show species-specifi c responses, like diff erences in branching and thorn sizes and survival rates. In contrast to sheep, goats were not absolutely deterred by mechanical defences of the off ered plant species. Therefore, we assume that under controlled grazing regimes, goat feeding could be a useful tool to interfere with the establishment of large numbers of seedlings. In our second project, the animal distribution did not consistently match our expectations. While warthog and cattle shared open bush-cleared sites, we found gemsbok utilising non-cleared sites with high thornbush cover of medium height, which was similar to patterns shown by greater kudu. The results are discussed in light of competition, risk avoidance, and habitat heterogeneity.Resumo: A transformação dos prados pela densifi cação de plantas lenhosas causa problemas s ocioeconómicos em regiões áridas e semi-áridas. De momento, a remoção de plantas lenhosas é a única maneira de controlar a sua densifi cação. Assim, conduzimos dois projectos independentes no contexto do SASSCAL. Numa experiência numa estufa, investigámos a resposta morfológica a danos de quatro espécies invasoras diferentes, de modo a compreender se a intervenção no estádio inicial de vida é razoável para combater a invasão das lenhosas, bem como se estas plantas tratadas são usadas de forma diferente pelo gado (ovelhas e cabras). Num segundo projecto, investigámos a infl uência do desmatamento na utilização do habitat por diferentes grandes herbívoros (cudo, javali-africano e órix). Especifi camente, queriamos saber se típicos herbívoros de pasto (e.x.: javali-africano e órix) eram encontrados em locais abertos, e típicos browsers (cudo) em regiões invadidas, e se os parâmetros da vegetação (e.x.: cobertura de gramíneas) conduzem esta distribuição. Na nossa experiência na estufa, descobrimos que todas as plântulas reagiram morfologic...
Bush encroachment is reported from savannah regions worldwide. Different management strategies are used to rehabilitate these areas. In this context, the mutual interaction between vegetation and large herbivore's distribution is evident. We studied effects of land management on vegetation structure in regard to encroaching species and the subsequent habitat use of two grazing (oryx, Oryx gazella L.; common warthog, Phacochoerus africanus GMELIN) and one browsing (greater kudu, Tragelaphus strepsiceros PALLAS) herbivore species. We assumed that (i) cleared areas will be favoured by grazers and (ii) noncleared areas will be favoured by browsers.Specifically, we asked: Which factors determine the habitat use of these different feeding guilds? Consistently with our expectations, we found that warthog favoured sites with high grass cover. For oryx, surprisingly shrubs with a height of 80-150 cm influenced their distribution positively, whereas for kudu, only the interactivement leur distribution, alors que pour les koudous, seule l'interaction du site
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