Estimating Evapotranspiration of Mediterranean Oak Savanna at Multiple Temporal and Spatial Resolutions. Implications for Water Resources Management

Mediterranean oak savanna is composed of a mixture of scattered oak trees, crops, pasture, and shrubs. It is the most widespread agroforestry landscape in Europe, and its conservation faces multiple threats including water scarcity, which has been exacerbated by global warming and greater climate variability. Evapotranspiration (ET) can be used as a proxy of the vegetation water status and response to water shortage conditions, providing relevant information about the ecosystem stability and its hydrological dynamics. This study evaluates a framework to estimate ET at multiple spatial and temporal scales and applies it to the monitoring of the oak savanna vegetation water consumption for the years 2013–2015. We used a remote sensing-based energy balance model (ALEXI/DisALEXI approach), and the STARFM data fusion technique to provide daily ET estimates at 30 m resolution. The results showed that modeled energy balance components compared well to ground measurements collected by an eddy covariance system, with root mean square error (RMSE) values ranging between 0.60 and 2.18 MJ m−2 d−1, depending on the sensor dataset (MODIS or Landsat) and the flux. The daily 30 m ET series generated by STARFM presented an RMSE value of 0.67 mm d−1, which yielded a slight improvement compared to using MODIS resolution or more simple interpolation approaches with Landsat. However, the major advantage of the high spatio-temporal resolution was found in the analysis of ET dynamics over different vegetation patches that shape the landscape structure and create different microclimates. Fine-scale ET maps (30 m, daily) provide key information difficult to detect at a coarser spatial resolution over heterogeneous landscapes and may assist management decisions at the field and farm scale.

The impact of wood cutting and of bush fires on the dynamics of the herbal strata of Sudano-Guinean Savanna

Few studies were carried out on the impact of wood cutting and bush fires on the dynamics of the herbal strata in savannahs of Adamawa, Cameroon. This study has as objectives to evaluate: 1. the recovery of the vegetation of shrub and grass savanna, 2. the evolution of the number of herbs with regards to time, 3. the floristic and specific contribution of the herbal specie. The inventories of herbaceous plants were carried out through quadra method in 9 sub-plots of 10 m × 10 m for each vegetal formation. The experimental design was split-plot with two (02) factors (savanna trees and shrubs), three (3) treatments (felling without fire, with fire and witness) and three (3) rehearsals/repetitions (portions). The analysis of variance (ANOVA) was used to compare means between treatments by using STATGRAPHIC XVII, and XLSAT to obtain result shown that 103 herbaceous plants divided in 73 genres and 23 families. The rate of recovery of savanna vegetation the herbs are more numerous 60% in the CSF, 50% in the CAF and 45% in witness site (wood savanna), Adversely, 30% in a witness site, 40% in the CSF and 50% in the CAF (shrub savanna). The number the species have grown from 3 to 45 in the tree’s savanna and 2 to 34 for the shrub savanna. The specific contribution of herbaceous varies according to the sites and the species.

Soil Aggregates Stability of Forest Islands and Adjacent Ecosystems in West Africa

In the more mesic savanna areas of West Africa, many areas of relatively tall and dense vegetation with a species composition more characteristic of forest than savanna are often found around villages areas. These ‘forest islands’ may be the direct action of human activity. To better understand these patches with relatively luxuriant vegetation, our study focused on how they influence soil aggregation in comparison with nearby areas and natural savanna vegetation across a precipitation transect in West Africa for which mean annual precipitation at the study sites ranges from 0.80 to 1.27 m a-1. Soil samples were taken from 0 to 5 cm and 5 to 10 cm depths and aggregate groups with diameters: > 500 μm, 500-250 μm and 250-53 μm (viz. “macroaggregates”, “mesoaggregates” and “microaggregates”) determined using the wet sieving method. The results showed significantly higher proportion of stable meso and macroaggregates in forest islands and natural savanna compared to agricultural soils (p <0.05). On the other hand, although there was no effect of land-use type on microaggregates stability, there was a strong tendency for the microaggregate fraction across all land use types to increase with increasing precipitation. Soil organic carbon and iron oxides contents are the most important factors influencing aggregate stability in West African ecosystems. By increasing soil structural stability, forest islands contribute to soil erosion reduction and the control of land degradation.

DIVERSITY AND DISTRIBUTION OF NIGERIAN LEGUMES (FABACEAE)

This study provides the first comprehensive checklist and analysis of the species of Fabaceae from Nigeria, based on over 5000 herbarium collections and the completed "Flora of West Tropical Africa (FWTA)". We report 552 taxa, belonging to 540 species in 155 genera from six subfamilies, with an outstanding number of taxa (36) representing new records for the country. We mapped the distribution of the species using their occurrence records obtained from GBIF and our own field and herbarium collections. The majority of taxa (43%) was distributed in the savanna vegetation of northern Nigeria, followed by the adjacent tropical forest formations of southern Nigeria (34%), and they were found in highest percentages in Papilionoideae (67%) and Caesalpinioideae (19%), followed by Deterioideae (11%), Cercidoideae and Dialioideae (6% each) and Duparquetioideae (<1%) subfamilies. Endemic and native taxa were 5 and 73% respectively. The most prevalent subfamilies in terms of endemicity were Papilionoideae (14 species), and Deterioideae (11 species), while the most prevalent genera were Indigofera (three species), Dalbergia (three species), Brachystegia (two species) and Cryptosepalum (two species). We found that the majority (37%) of the species were phanerophytes and the fewest were cryptophytes (0.7%). These results suggest that Nigeria has a considerable diversity of legumes, with a predominant distribution in the savanna, probably due to the demanding environmental conditions limiting the dispersion of generalists or invasive species. The diversity of growth forms and distribution patterns of Nigerian legumes could be useful in screening these plants for other potential uses, such as conservation planning or specific agricultural purposes. We recommend a similar study on other families as this will help locals, natural scientists, governments and conservation bodies to recognise and appreciate the flora of the country.

The Natural Forages of Northern Nigeria I. Nitrogen and Mineral composition of Grasses and Browse from the Northern Guinea Savanna and Standing Hays from the different Savanna Zones

THE mineral status of nine native grass species and ten browse species from the Northern Guinea Savanna Vegetation was investigated together with the mineral Composition of standing hays from Daura and Kano areas of the Sudan Savanna, Bauchi ranch of the sub-Sudan, Samaru (Shika Kadama) of the Northern Guinea Savanna and Jos area of the Plateau vegetation, in Northern Nigeria. All forage types (grasses, browse and standing hays) which were sampled in April of 1975 were analysed for nitrogen (N), Phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), zinc (Zn) and copper (Cu). The grass species included: Andropogon gayanus, A. ascinodis, Brachiaria jubata, Cynodon dactylon, Hyparthelia dissoluta, Pancium phragmitoides, Setaria anceps, Sporobolus pyramidalis and Urelytram muricatum, while the browse consisted of Adenodolichos panicu latus, Annogeissus leocarpus, Briddelia ferruginea, Crossopteryx febrifug, Dichrostachys cenerea (glometata), Khaya senegalensis, Mimosa pigra, Parinari curatellifolis, Psorospermum guineense, and Pterocarpus erinaceus. Both grass and browse species were leafy materials from among those Species considered to be highly consumed by cattle. in general, the average values for Na, P, and Zn in the grasses, browse and standing hays were inadequate for the nutritional needs of cattle one standing hays from all locations contained suboptimum amounts of N, Ca, P, K, Mg, Na and The Cu content of all three forage types was adequate for cattle nutrition. The grass and browse species contained adequate amounts of N, K, Mg and Cu. The trace elements and Ca and Mg tended to be more concentrated in the browse species than in the grass species. The opposite was true of K. Grasses, browse and standing hays contained equal amounts of Na. Similarly, the grass and browse species contained identical amounts of P. Supplementation of mineral concentrates to include Na, P, K, Ca and Zn was suggested.

Leveraging TLS as a Calibration and Validation Tool for MLS and ULS Mapping of Savanna Structure and Biomass at Landscape-Scales

Savanna ecosystems are challenging to map and monitor as their vegetation is highly dynamic in space and time. Understanding the structural diversity and biomass distribution of savanna vegetation requires high-resolution measurements over large areas and at regular time intervals. These requirements cannot currently be met through field-based inventories nor spaceborne satellite remote sensing alone. UAV-based remote sensing offers potential as an intermediate scaling tool, providing acquisition flexibility and cost-effectiveness. Yet despite the increased availability of lightweight LiDAR payloads, the suitability of UAV-based LiDAR for mapping and monitoring savanna 3D vegetation structure is not well established. We mapped a 1 ha savanna plot with terrestrial-, mobile- and UAV-based laser scanning (TLS, MLS, and ULS), in conjunction with a traditional field-based inventory (n = 572 stems > 0.03 m). We treated the TLS dataset as the gold standard against which we evaluated the degree of complementarity and divergence of structural metrics from MLS and ULS. Sensitivity analysis showed that MLS and ULS canopy height models (CHMs) did not differ significantly from TLS-derived models at spatial resolutions greater than 2 m and 4 m respectively. Statistical comparison of the resulting point clouds showed minor over- and under-estimation of woody canopy cover by MLS and ULS, respectively. Individual stem locations and DBH measurements from the field inventory were well replicated by the TLS survey (R2 = 0.89, RMSE = 0.024 m), which estimated above-ground woody biomass to be 7% greater than field-inventory estimates (44.21 Mg ha−1 vs 41.08 Mg ha−1). Stem DBH could not be reliably estimated directly from the MLS or ULS, nor indirectly through allometric scaling with crown attributes (R2 = 0.36, RMSE = 0.075 m). MLS and ULS show strong potential for providing rapid and larger area capture of savanna vegetation structure at resolutions suitable for many ecological investigations; however, our results underscore the necessity of nesting TLS sampling within these surveys to quantify uncertainty. Complementing large area MLS and ULS surveys with TLS sampling will expand our options for the calibration and validation of multiple spaceborne LiDAR, SAR, and optical missions.

Sustainable use of Savanna Vegetation in West Africa in the Context of Climate and Land use Change

West African savannas undergo severe changes due to climate change and land use pressure, resulting in degradation and biodiversity loss. These changes directly impact local rural livelihoods, as many cash poor rural communities depend on the provisioning ecosystem services of their environments. In a case study of the interdisciplinary research project UNDESERT, the increasingly challenging sustainable use of wild plant species in West African savannas was investigated. In this study, we present the results and give examples of how scientific results can serve for practical actions to foster sustainable use of important plant resources.