Forest and woodland regeneration dynamics and persistence in the human- modified landscape of Greater Gombe Ecosystem, Tanzania

Abstract

AbstractThe clearing of tropical forests and woodlands for human use puts many species at risk of extinction. Vast areas of forests and woodlands have been converted to fragmented patches located within mosaics of different land uses (e.g., agricultural lands and human settlements). Some conservationists have argued that community-managed forests can be an effective strategy for promoting forest regeneration, persistence of mature forest patches, and conservation in human-modified landscapes. However, few studies have systematically evaluated its effectiveness. In particular, limited empirical evidence exists on the influence of these reserves on promoting the persistence and recovery of forest structure, carbon stock, and feeding habitat quality for vulnerable species, such as chimpanzees. To properly assess the influence of this management strategy, we need to take into account other factors likely to affect forest attributes, including, topographic factors (e.g., slope), anthropogenic factors (e.g., wildfire), and plant functional traits (e.g., dispersal mode) on the variation of forest structure in these reserves. To provide insights on these issues, I used various data sources to assess forest cover changes, factors affecting those changes, and patterns of forest structure, composition, carbon stock, and feeding habitat quality for primates in 16 Village Land Forest Reserves (VLFRs) in the Greater Gombe Ecosystem (GGE), in western Tanzania. The data sources include, remote sensing confirmed with ground-truthing, forest inventory plots, spatially explicit forest monitoring data, and previously collected information on primate food tree preference. These VLFRs were established through a community-based planning process, facilitated by the Jane Goodall Institute and the Tanzanian government. In this dissertation, I used three chapters to assess the effectiveness of community forest management at this site. In Chapter 1, I used multi-temporal satellite images from 2006, 2013, 2016, and 2021 to assess possible pathways of forest and woodland cover change in these reserves compared to unprotected village land. In Chapter 2, I quantify the relative influence of topographic and anthropogenic factors on the variation of forest cover change in these reserves. In Chapter 3, I determined how VLFRs promoted permanence and recovery of forest structure, carbon stock, and feeding habitat quality for primates and compared them with a nationally protected area, the Gombe National Park representing the reference scenario. Also in Chapter 3, I assess the relative influence of anthropogenic and topographic factors, as well as plant functional traits on the variation of forest structure in VLFRs. My results show that (1) between 2006 and 2021, forest cover increased by 66% in the area designated as VLFRs but declined by 22% in unprotected village land; (2) accounting for factors such as forest age, and iv topography, the factors that most impacted forest cover included a negative impact of fire frequency and a positive impact of village-led patrol effort; and (3) in comparison to the mature woodlands in the VLFRs, the second-growth woodlands in the VLFRs that have regenerated over the 15-years period since the intervention started exhibited basal area, carbon stock, and abundance of chimpanzee food plants at around 75%, 50%, and 77% respectively of the corresponding values observed in the mature woodlands within VLFRs. Furthermore, these forest attributes in the mature woodlands in the VLFRs exceeded 60% of the values found in Gombe mature woodlands. When accounting for factors such as forest age, dispersal mode, and topography, a factor that most impacted above-ground biomass and stem density included the positive influence of village-led patrols. The insights gained from this dissertation can provide valuable lessons for enhancing community forest management practices in similar tropical contexts, critical for increasing habitat quality for wildlife, improving landscape-scale connectivity, and contributing to climate change mitigation.