Monitoring and assessment of environmental resources in the changing landscape of Ethiopia: a focus on forests and water.

Monitoring and Assessment (M&A) of environmental resources aims to support the formulation of policies and follow up on outcomes of their implementation. In this study, the state of M&A is explored for Ethiopia with a focus on forests and water resources. The study is intended to serve as recommendations for future M&A applications in Ethiopia, as well as fulfillment of SDGs and other national and international commitments. Expert meetings, key informant interviews, and selected document analysis served as sources of information. The findings were summarized using qualitative grading and institutional mapping. Basic results of the study are that monitoring data on climate and streamflow are standardized in forms that can be communicated to policymakers. Scantier and less standardized are environmental data on soils, sediment transport, forests, biodiversity, and air quality. Water quality, soil moisture, groundwater level, forest biomass, and soil carbon are rarely monitored and can only be found in reports or studies for the fulfillment of academic degree requirements. Resources like nutrient fluxes have rarely been documented, not at all in some cases. There is considerable scope for tapping both technological advances and experiences of citizen science and local participation in environmental governance to rapidly expand and improve monitoring from local to regional and national scales. The study showed that there is a need for establishing a coordinated national system for monitoring and assessing the status of the environment, including the use of natural resources. Communicating such data to the scientific and wider public will support evidence-based planning and policy-making towards national development.

Grazing exclosures increase soil organic carbon stock at a rate greater than "4 per 1000" per year across agricultural landscapes in Northern Ethiopia.

The establishment of grazing exclosures is widely practiced to restore degraded agricultural lands and forests. Here, we evaluated the potential of grazing exclosures to contribute to the "4 per 1000" initiative by analyzing the changes in soil organic carbon (SOC) stocks and sequestration (SCS) rates after their establishment on degraded communal grazing lands in Tigray region of Ethiopia. We selected grazing areas that were excluded from grazing for 5 to 24 years across the three agroecological zones of the region and used adjacent open grazing lands (OGLs) as control. Soil samples were collected from two depths (0-15 cm and 15-30 cm) and SOC and aboveground C stocks were quantified in both exclosures and OGLs. The mean SOC stock and SCS rate in exclosures (0-30 cm) were 31 Mg C ha-1 and 3 Mg C ha-1 year-1, which were respectively 166% and 12% higher than that in the OGLs, indicating a positive restoration effect of exclosures on SOC storage. With increasing exclosure age, SOC stock and SCS rate increased in the exclosures but decreased in the OGLs. Higher SOC stock and SCS rate were recorded in 0-15 cm than in 15-30 cm. The relative (i.e., to the SOC stock in OGLs) rates of increase in SOC stocks (70-189‰ year-1) were higher than the 4‰ year-1 and were initially high due to low initial SOC stock but declined over time after a maximum value of SOC stock is reached. Factors such as aboveground biomass, altitude, clay content and precipitation promoted SOC storage in exclosures. Our study highlights the high potential of exclosures for restoring SOC in the 0-30 cm soil depth at a rate greater than the 4‰ value. We argue that practices such as grazing exclosure can be promoted to achieve the climate change mitigation target of the "4‰" initiative.

Structural diversity consistently mediates species richness effects on aboveground carbon along altitudinal gradients in northern Ethiopian grazing exclosures.

Grazing exclosures have been promoted as an effective and low-cost land management strategy to recover vegetation and associated functions in degraded landscapes in the tropics. While grazing exclosures can be important reservoirs of biodiversity and carbon, their potential in playing a dual role of conservation of biodiversity and mitigation of climate change effects is not yet established. To address this gap, we assessed the effect of diversity on aboveground carbon (AGC) and the relative importance of the driving biotic (functional diversity, functional composition and structural diversity) and abiotic (climate, topography and soil) mechanisms. We used a dataset from 133 inventory plots across three altitudinal zones, i.e., highland, midland and lowland, in northern Ethiopia, which allowed local- (within altitudinal zone) and broad- (across altitudinal zones) environmental scale analysis of diversity-AGC relationships. We found that species richness-AGC relationship shifted from neutral in highlands to positive in mid- and lowlands as well as across the altitudinal zones. Structural diversity was consistently the strongest mediator of the positive effects of species richness on AGC within and across altitudinal zones, whereas functional composition linked species richness to AGC at the broad environmental scale only. Abiotic factors had direct and indirect effects via biotic factors on AGC, but their relative importance varied with altitudinal zones. Our results indicate that the effect of species diversity on AGC was altitude-dependent and operated more strongly through structural diversity (representing niche complementarity effect) than functional composition (representing selection effect). Our study suggests that maintaining high structural diversity and managing functionally important species while promoting favourable climatic and soil conditions can enhance carbon storage in grazing exclosures.

Frankincense tapping reduces the carbohydrate storage of Boswellia trees.

Carbohydrates fixed by photosynthesis are stored in plant organs in the form of starch or sugars. Starch and sugars sum to the total non-structural carbohydrate pool (TNC) and may serve as intermediate pools between assimilation and utilization. We examined the impact of tapping on TNC concentrations in stem-wood, bark and root tissues of the frankincense tree (Boswellia papyrifera (Del.) Hochst) in two natural woodlands of Ethiopia. Two tapping treatments, one without tapping (control) and the other with tapping at 12 incisions, are applied on experimental trees. Trees are tapped in the leafless dry period, diminishing their carbon storage pools. If storage pools are not refilled by assimilation during the wet season, when crowns are in full leaf, tapping may deplete the carbon pool and weaken Boswellia trees. The highest soluble sugar concentrations were in the bark and the highest starch concentrations in the stem-wood. The stem-wood contains 12 times higher starch than soluble sugar concentrations. Hence, the highest TNC concentrations occurred in the stem-wood. Moreover, wood volume was larger than root or bark volumes and, as a result, more TNC was stored in the stem-wood. As predicted, tapping reduced the TNC concentrations and pool sizes in frankincense trees during the dry season. During the wet season, these carbon pools were gradually filled in tapped trees, but never to the size of non-tapped trees. We conclude that TNC is dynamic on a seasonal time scale and offers resilience against stress, highlighting its importance for tree carbon balance. But current resin tapping practices are intensive and may weaken Boswellia populations, jeopardizing future frankincense production.

Leaf gas exchange in the frankincense tree (Boswellia papyrifera) of African dry woodlands.

A conceptual model was tested for explaining environmental and physiological effects on leaf gas exchange in the deciduous dry tropical woodland tree Boswellia papyrifera (Del.) Hochst. For this species we aimed at (i) understanding diurnal patterns in leaf gas exchange, (ii) exploring cause-effect relationships among external environment, internal physiology and leaf gas exchange, and (iii) exploring site differences in leaf gas exchange in response to environmental variables. Diurnal courses in gas exchange, underlying physiological traits and environmental variables were measured for 90 trees on consecutive days at two contrasting areas, one at high and the other at low altitude. Assimilation was highest in the morning and slightly decreased during the day. In contrast, transpiration increased from early morning to midday, mainly in response to an increasing vapor pressure deficit (VPD) and gradual stomatal closure. The leaf water potential varied relatively little and did not influence gas exchange during the measurement period. Our results suggest that the same cause-effect relationships function at contrasting areas. However, leaves at the higher altitude had higher photosynthetic capacity, reflecting acclimation to higher light levels. Trees at both areas nevertheless achieved similar leaf assimilation rates since assimilation was down-regulated by stomatal closure due to the higher VPD at the higher altitude, while it became more light limited at the lower altitude. Gas exchange was thus limited by a high VPD or low light levels during the wet season, despite the ability of the species to acclimate to different conditions.