Trees in agricultural landscapes enhance provision of ecosystem services in Sub-Saharan Africa

Mapping the Abundance of Multipurpose Agroforestry Faidherbia albida Trees in Senegal

Multi-purpose Faidherbia albida trees represent a vital component of agroforestry parklands in West Africa as they provide resources (fodder for livestock, fruits and firewood) and support water lifting and nutrient recycling for cropping. Faidherbia albida trees are characterized by their inverse phenology, growing leaf flowers and pods during the dry season, thereby providing fodder and shedding leaves during the wet season, which minimizes competition with pastures and crops for resources. Multi-spectral and multi-temporal satellite systems and novel computational methods open new doors for classifying single trees and identifying species. This study used a Multi-Layer Perception feedforward artificial neural network to classify pixels covered by Faidherbia albida canopies from Sentinel-2 time series in Senegal, West Africa. To better discriminate the Faidherbia albida signal from the background, monthly images from vegetation indices were used to form relevant variables for the model. We found that NDI54/NDVI from the period covering onset of leaf senescence (February) until end of senescence (leaf-off in June) to be the most important, resulting in a high precision and recall rate of 0.91 and 0.85. We compared our result with a potential Faidherbia albida occurrence map derived by empirical modelling of the species ecology, which deviates notably from the actual species occurrence mapped by this study. We have shown that even small differences in dry season leaf phenology can be used to distinguish tree species. The Faidherbia albida distribution maps, as provided here, will be key in managing farmlands in drylands, helping to optimize economic and ecological services from both tree and crop products.

Tree diversity and carbon stocks in agroforestry systems in northern Ethiopia

BACKGROUND

Agroforestry (AF) is an ancient tradition in Ethiopian dryland farming system. Several studies have examined system design, soil fertility management and system interactions, but the biodiversity and mitigation aspects of climate change have received less focus. We assessed the diversity of woody species, biomass carbon (C), and soil organic carbon (SOC) stock associated with indigenous dryland AF practices. A total of 197 smallholder farmers representing four AF practices (home garden, parkland, boundary plantation, and woodlot) from lowland, midland, and highland areas were systematically selected. The inventory of woody species was carried out on each farm's randomly formed plot.

RESULTS

We identified a total of 59 woody species representing 48 genera and 32 families. Shannon diversity index (H') was highest in home garden and parkland AF, while woodlots had the highest mean total stock of biomass C (31 Mg C ha^-1). C stocks for smallholding systems (total biomass C and SOC 0-60 cm) ranged from 77-135 Mg ha^-1. Total biomass C stocks were significantly correlated with abundance (Spearman r = 0.333; p = 0.002) but biomass components were not significantly correlated with H'. SOC soil depth stock (0-60 cm) was positively and significantly associated with H' (Spearman r = 0.291 & 0.351; p < 0.01).

CONCLUSIONS

We report greater species richness in home garden and parkland AF systems than in woodlots. While parkland AF produce lower biomass and SOC stock relative to other AF systems. The strategic use of home gardens and boundary planting can improve tree diversity and carbon storage in Ethiopian dryland ecosystems.

Assessing Context-Specific Factors to Increase Tree Survival for Scaling Ecosystem Restoration Efforts in East Africa

Increasing tree cover in agricultural lands can contribute to achieving global and national restoration goals, more so in the drylands where trees play a key role in enhancing both ecosystem and livelihood resilience of the communities that depend on them. Despite this, drylands are characterized by low tree survival especially for tree species preferred by local communities. We conducted a study in arid and semi-arid areas of Kenya and Ethiopia with 1773 households to assess how different tree planting and management practices influence seedling survival. Using on-farm planned comparisons, farmers experimented and compared tree survival under different planting and management practices as well as under varying socioeconomic and biophysical contexts in the two countries. Seedling survival was monitored at least six months after planting. Results show that watering, manure application, seedling protection by fencing and planting in a small hole (30 cm diameter and 45 cm depth) had a significant effect on tree seedling survival in Kenya, while in Ethiopia, mulching, watering and planting niche were significant to tree survival. Household socioeconomics and farms’ biophysical characteristics such as farm size, education level of the household head, land tenure, age of the household head had significant effects on seedling survival in both Ethiopia and Kenya while presence of soil erosion on the farm had a significant effect in Kenya. Soil quality ranking was positively correlated with tree survival in Ethiopia, regardless of species assessed. Current findings have confirmed effects of context specific variables some involving intrahousehold socioeconomic status such education level of the household head, and farm size that influence survival.

Water, Forests, People: The Swedish Experience in Building Resilient Landscapes

A growing world population and rapid expansion of cities increase the pressure on basic resources such as water, food and energy. To safeguard the provision of these resources, restoration and sustainable management of landscapes is pivotal, including sustainable forest and water management. Sustainable forest management includes forest conservation, restoration, forestry and agroforestry practices. Interlinkages between forests and water are fundamental to moderate water budgets, stabilize runoff, reduce erosion and improve biodiversity and water quality. Sweden has gained substantial experience in sustainable forest management in the past century. Through significant restoration efforts, a largely depleted Swedish forest has transformed into a well-managed production forest within a century, leading to sustainable economic growth through the provision of forest products. More recently, ecosystem services are also included in management decisions. Such a transformation depends on broad stakeholder dialog, combined with an enabling institutional and policy environment. Based on seminars and workshops with a wide range of key stakeholders managing Sweden's forests and waters, this article draws lessons from the history of forest management in Sweden. These lessons are particularly relevant for countries in the Global South that currently experience similar challenges in forest and landscape management. The authors argue that an integrated landscape approach involving a broad array of sectors and stakeholders is needed to achieve sustainable forest and water management. Sustainable landscape management-integrating water, agriculture and forests-is imperative to achieving resilient socio-economic systems and landscapes.