Browsing by Author "Kimaro, Houssein Samwel"

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Encroachment dynamics of Acacia drepanolobium in Maswa game reserve
(NM-AIST, 2019-04) Kimaro, Houssein Samwel
Habitat degradation, caused in particular by woody plant encroachment, has been a common phenomenon in savanna ecosystems. With increasing woody plant cover in open savanna grassland, structural changes and their associated impact need to be assessed and quantified. We analyzed the extent of woody plant encroachment via remote sensing and assessed encroached sites and open grassland of Maswa Game Reserve on the ground to identify and examine encroaching woody plant species and their associated impacts on herbaceous plant and herbivore species. We found that woody plant cover increased by 0.5% to 2.6% per annum. Acacia drepanolobium dominated the woody encroaching species, and the number of stems in heavily encroached sites was seven times and three times higher than in open grassland and at medium encroached sites, respectively. Our results show that woody plant encroachment reduces grazers and mixed feeder species occurrence. Furthermore, the number of herbaceous species slightly increased with increase of woody plant encroachment, while herbaceous cover was negatively correlated with increase of woody plant cover. Fire significantly reduced germination success of A. drepanolobium. Intermediate simulated rainfall was more beneficial to seedling emergence success than infrequent simulated rainfall, while seedling shoots growth was significantly higher in frequent and intermediate simulated rainfall treatments than under infrequent simulated rainfall. Hence, our study suggests that the recent bush encroachment phenomena might have been stipulated by suppression of bush fires and frequent low rainfall. This understanding will contribute in management of vegetation specifically woody plants in savanna ecosystems that are important wildlife habitats.
Rainfall, fire and large-mammal-induced drivers of Vachellia drepanolobium establishment: Implications for woody plant encroachment in Maswa, Tanzania
(John Wiley & Sons, Inc., 2021-05-13) Kimaro, Houssein Samwel; Treydte, Anna C.
Worldwide, open grass areas of savannah ecosystems are being transformed into shrubland. This woody plant encroachment is likely a result of factors such as rainfall, fire and secondary dispersal by ungulate herbivory. However, few experiments have been conducted to disentangle and quantify the role of these factors for seed germination in savannahs. We assessed in situ germination success of Vachellia drepanolobium seeds under simulated rainfall variability patterns, fire treatments and dung experiments in Maswa Game Reserve, Tanzania. Fire reduced seed germination by more than 13%, whereas germination in buffalo and elephant dung increased by 1% and 3% respectively. Additionally, intermediate simulated rainfall was more beneficial for seedling emergence success than large, infrequent simulated rainfall amounts, while shoot growth was twice as high under frequent and intermediate simulated rainfall treatments than under large infrequent simulated rainfall. Our results provide insights that bush fires, drought stress, and large rainfall events can suppress V. drepanolobium seedling emergence and growth. Hence, bush encroachment may be linked to management practices such as fire regimes and climatic conditions, i.e., frequent low rainfall conditions. Our results can help predict future patterns of encroachment under varying rainfall and fire events.