Drivers of tropical deforestation and forest regeneration in Tanzania

Forest cover change affects ecosystem services including climate and biodiversity. Global efforts to reduce deforestation, and restore forest cover, depend on understanding the rates and drivers of forest cover change. Knowledge gaps are greatest around rates and drivers of forest regeneration, and drivers of deforestation in Africa. Determinants of the rate of biomass and species accumulation in regenerating forests, are also poorly understood. Although deforestation rates have been well-studied, published rates still vary significantly, particularly in African woodlands. This thesis investigates rates and drivers of deforestation and natural forest regeneration, with a focus on Tanzania, a country with the fifth highest net deforestation, globally. Using innovative, inter-disciplinary methods, the study presents new empirical evidence on rates and drivers of forest cover change. Linking this to policy, the thesis provides new insights on the challenges of using an energy-transition policy, to reduce deforestation. New datasets show that deforestation exceeds regeneration by >0.5 Mha y-1. Tanzania’s national gross mean annual deforestation rate is calculated at 1.42% or 0.562 Mha y-1 (0.46 – 0.66 Mha y-1) (2010 – 2017). For village land, a land class that excludes protected areas, the gross mean annual deforestation rate is higher, at 1.9% or 0.608 Mha y-1 (0.46 – 0.78 Mha y-1) for the more recent period of 2011 – 2021. The gross mean annual regeneration rate on village land is far lower at 0.0132 Mha y-1 (0.004 – 0.03 Mha y-1) (1987 – 2021). New evidence is presented that agriculture causes most deforestation (81% of deforestation events), compared with only 12% attributable to charcoal. In regenerating woodlands, agricultural fallows were the most frequent regeneration driver, while biomass and species accumulation were most affected by regeneration time and precipitation. While forest and energy policies have sought to curb deforestation through an energy transition away from woodfuel, the policies have been ineffective for two reasons. Firstly, they do not address the main deforestation driver, agriculture. Secondly, they have had limited impact on charcoal consumption, with 88% of Dar es Salaam households still using charcoal in 2018. Reducing deforestation and amplifying natural regeneration both require closer inter-sectoral coordination. With most deforestation occurring on village-owned land in Tanzania, there is an urgent need for more effective strategies to enable communities to retain forest products and services critical to livelihoods

The Nguru mountains of Tanzania, an outstanding hotspot of herpetofaunal diversity

Despite the vicinity of a major road, the rainforests of the South Nguru Mountains in eastern Tanzania were virtually unexplored until 2004, particularly from a herpetological point of view. Several surveys were conducted between 2004 and 2006 with the aim of providing a comprehensive list of the amphibian and reptile species of this overlooked hotspot of biological diversity. The surveys resulted in this assessment of the herpetofaunal diversity, with 92 species recorded, of which 15 represent new records for this area, and the discovery of 16 species new to science, all of which are likely to be strictly endemic to the Nguru Mountains. Pressure on the forests, particularly the lowland forests, remains high. A conservation planning process is now underway that is attempting to address the loss of these critically important forests. These results, documenting the high species richness and the outstanding number of putative endemics of the forests, strongly highlight the biological importance of the South Nguru Mountains and place them among the most important sites for the conservation of herpetofauna in Africa

Phylogenetic relationships of African microhylid frogs inferred from DNA sequences of mitochondrial 12S and 16S rRNA genes

The phylogenetic relationships of microhylid frogs are poorly understood. The first molecular phylogeny for continental African microhylids is presented, including representatives of all subfamilies, six of the eight genera, and the enigmatic hemisotid Hemisus. Mitochondrial 12S and 16S rRNA sequence data were analysed using parsimony, likelihood and Bayesian methods. Analyses of the data are consistent with the monophyly of all sampled subfamilies and genera. Hemisus does not nest within either brevicipitines or non-brevicipitines. It is possibly the sister group to brevicipitines, in which case brevicipitines might not be microhylids. Phrynomantis and Hoplophryne potentially group with non-African, non-brevicipitine microhylids, in agreement with recent morphological and molecular data. Within brevicipitines, Breviceps is recovered as the sister group to a clade of Callulina+Spelaeophryne+Probreviceps. The relationships among the genera within this latter clade are unclear, being sensitive to the method of analysis. Optimal trees suggest the Probreviceps macrodactylus subspecies complex might be paraphyletic with respect to P. uluguruensis, corroborating preliminary morphological studies indicating that P. m. rungwensis may be a distinct species. P. m. loveridgei may be paraphyletic with respect to P. m. macrodactylus, though this is not strongly supported. Some biogeographic hypotheses are examined in light of these findings

Land cover change and carbon emissions over 100 years in an African biodiversity hotspot

Agricultural expansion has resulted in both land use and land cover change (LULCC) across the tropics. However, the spatial and temporal patterns of such change and their resulting impacts are poorly understood, particularly for the pre-satellite era. Here we quantify the LULCC history across the 33.9 million ha watershed of Tanzania's Eastern Arc Mountains, using geo-referenced and digitised historical land cover maps (dated 1908, 1923, 1949 and 2000). Our time series from this biodiversity hotspot shows that forest and savanna area both declined, by 74% (2.8 million ha) and 10% (2.9 million ha), respectively, between 1908 and 2000. This vegetation was replaced by a five-fold increase in cropland, from 1.2 million ha to 6.7 million ha. This LULCC implies a committed release of 0.9 Pg C (95% CI: 0.4-1.5) across the watershed for the same period, equivalent to 0.3 Mg C ha(-1) yr(-1) . This is at least three-fold higher than previous estimates from global models for the same study area. We then used the LULCC data from before and after protected area creation, as well as from areas where no protection was established, to analyse the effectiveness of legal protection on land cover change despite the underlying spatial variation in protected areas. We found that, between 1949 and 2000, forest expanded within legally protected areas, resulting in carbon uptake of 4.8 (3.8-5.7) Mg C ha(-1) , compared to a committed loss of 11.9 (7.2-16.6) Mg C ha(-1) within areas lacking such protection. Furthermore, for nine protected areas where LULCC data is available prior to and following establishment, we show that protection reduces deforestation rates by 150% relative to unprotected portions of the watershed. Our results highlight that considerable LULCC occurred prior to the satellite era, thus other data sources are required to better understand long-term land cover trends in the tropics. This article is protected by copyright. All rights reserved

Correction to: Quantifying and understanding carbon storage and sequestration within the Eastern Arc Mountains of Tanzania, a tropical biodiversity hotspot

Abstract Upon publication of the original article [1], the authors noticed that the figure labelling for Fig. 4 in the online version was processed wrong. The top left panel should be panel a, with the panels to its right being b and c. d and e should be the panels on the lower row, and f is correct. The graphs themselves are all correct. It is simply the letter labels that are wrong

Detecting and predicting forest degradation: A comparison of ground surveys and remote sensing in Tanzanian forests

Funder: Critical Ecosystem Partnership Fund; Id: http://dx.doi.org/10.13039/100013724Funder: Global Environment Facility; Id: http://dx.doi.org/10.13039/100011150Funder: Danish International Development Agency; Id: http://dx.doi.org/10.13039/501100011054Funder: Scottish Government’s Rural and Environment Science and Analytical Services DivisionFunder: Finnish International Development AgencyFunder: Leverhulme Trust; Id: http://dx.doi.org/10.13039/501100000275Societal Impact Statement: Large areas of tropical forest are degraded. While global tree cover is being mapped with increasing accuracy from space, much less is known about the quality of that tree cover. Here we present a field protocol for rapid assessments of forest condition. Using extensive field data from Tanzania, we show that a focus on remotely‐sensed deforestation would not detect significant reductions in forest quality. Radar‐based remote sensing of degradation had good agreement with the ground data, but the ground surveys provided more insights into the nature and drivers of degradation. We recommend the combined use of rapid field assessments and remote sensing to provide an early warning, and to allow timely and appropriately targeted conservation and policy responses. Summary: Tropical forest degradation is widely recognised as a driver of biodiversity loss and a major source of carbon emissions. However, in contrast to deforestation, more gradual changes from degradation are challenging to detect, quantify and monitor. Here, we present a field protocol for rapid, area‐standardised quantifications of forest condition, which can also be implemented by non‐specialists. Using the example of threatened high‐biodiversity forests in Tanzania, we analyse and predict degradation based on this method. We also compare the field data to optical and radar remote‐sensing datasets, thereby conducting a large‐scale, independent test of the ability of these products to map degradation in East Africa from space. Our field data consist of 551 ‘degradation’ transects collected between 1996 and 2010, covering >600 ha across 86 forests in the Eastern Arc Mountains and coastal forests. Degradation was widespread, with over one‐third of the study forests—mostly protected areas—having more than 10% of their trees cut. Commonly used optical remote‐sensing maps of complete tree cover loss only detected severe impacts (≥25% of trees cut), that is, a focus on remotely‐sensed deforestation would have significantly underestimated carbon emissions and declines in forest quality. Radar‐based maps detected even low impacts (<5% of trees cut) in ~90% of cases. The field data additionally differentiated types and drivers of harvesting, with spatial patterns suggesting that logging and charcoal production were mainly driven by demand from major cities. Rapid degradation surveys and radar remote sensing can provide an early warning and guide appropriate conservation and policy responses. This is particularly important in areas where forest degradation is more widespread than deforestation, such as in eastern and southern Africa

The Marginalization of Sustainable Charcoal Production in the Policies of a Modernizing African Nation

Charcoal is the main cooking fuel for urban populations in many African countries. Urbanization and population growth are driving an increase in demand for charcoal, whilst deforestation reduces biomass stocks. Given increasing demand for charcoal, and decreasing availability of biomass, policies are urgently needed that ensure secure energy supplies for urban households and reduce deforestation. There is potential for charcoal to be produced sustainably in natural woodlands, but this requires supportive policies. Previous research has identified policy issues that have contributed to the charcoal sector remaining informal and environmentally destructive. In this paper, we describe how national policies in Tanzania on energy, forests, agriculture, land, and water, consider charcoal, and the degree to which they do, and do not, support sustainable charcoal production. The paper identifies policy gaps and a cross-sector tendency to marginalize natural forest management. By adopting a nexus approach, the paper highlights the inter-connections between sustainable charcoal production, ecosystem services, and trade-offs in the allocation of land, labor, and net primary production. In conclusion, sustainable charcoal production has been marginalized in multiple national policies. As a result, potential benefits of sustainable charcoal production are lost to multiple sectors