Acacia Woodland Research Articles

Assessment on Acacia Woodland Degradation in Dire-Dawa Administration, Eastern Ethiopia

Dry woodlands are vegetation formations which comprise of scrubs, bush lands, thickets, wooded grasslands and dense woodlands. The largest share of Ethiopia’s landmass is categorized as dryland, experiencing moisture stress during most days of the year. Hence, lowland woodlands are the largest remaining forests in Ethiopia, covering an estimated 55 million ha (48-6 per cent) of land. Beyond the socio-economic and ecological importance of forests Ethiopia experienced rapid loss of woodland vegetation annually. At country level the loss is attributed to low level of standard of living of farming community and their close dependency on forest and woodlands. Jeldessa, Gerba-Anano and Chiri-miti kebelles of Dire-Dawa administration which is located in the eastern part of the Ethiopia has a dense acacia woodland species occupying a total area of at 12250 hectare mainly found in Hurso, Jeldessa, Gerba-Anano and Chiri-miti kebelles. The dry forest which was home and source of forage to wildlife and local pastoral communities is dwindling from time to time. As there has been no study on site specific, this study was conducted to assess the recent degradation of dry land forest in Jeldessa, Gerba-Anano and Chiri-miti kebelles of Dire-Dawa administration. The study has employed questionnaire, interview, group discussions and field observation. The findings of the study shows acacia woodland vegetation of the kebelles have been subjected to degradation due to the ease accessibility of the kebelles connected by all-weather roads has triggered fetching of charcoal. Besides, easy money making from charcoal and its rising price has anticipated poor peoples to practice it as a means of livelihood. On the other hand, concentration of livestock, recurrent drought and prosopis juliflora invasion has perceived as major factors degradation. Therefore, the cumulative negative effect of the above factors has contributed to the fast deterioration of acacia woodland coverage. To this end, all concerned body’s particularly local customary institutions, agricultural and police departments have to work in harmony on providing alternative off farm activities. Furthermore, the government induced sedentary agriculture was widely practiced along the river sides of all kebelles therefore, further study on sustainable usage of grazing and woodland forest is very mandatory.

<b>The ecology of Harwood’s Francolin <I>Pternistis harwoodi</I> (Aves: Galliformes: Phasianidae) at Merhabete District, central highlands of Ethiopia: implications for conservation</b>

This paper investigates the abundance, density and habitat preference of Harwood’s Francolin, and considers threats posed to this species at Merhabete District, Ethiopia. A total of 20 line transects ranging from 0.5–1.2 km, each 150–400 m apart, were placed in four study blocks. Habitat preferences were evaluated by digital elevation model (DEM) analysis and slope. Human pressures were also quantified based on circular plot placements along each line transect. Hence, distance sampling survey was used to count population data. The estimated population size and density were 184±26.46 birds and 43.48±6.25 birds/km2, respectively, with an overall encounter rate of 8.52 birds/km in Jema and Jara valleys. This species mainly preferred dry evergreen scrublands mixed with grassy, rock areas and dispersed acacia woodlands. However, based on stepwise regression model, the main threats to this species were burning, cutting, firewood collection and grazing. Generally, only cutting and firewood collection were the most important predictors that affected the focal species. This finding could be used to plan conservation of the species with the joint contribution of scientists, government and local communities.

GPS tracking cattle as a monitoring tool for conservation and management

The emergence of GPS technology has resulted in significant advances in the ease and flexibility of studying animal movement patterns, yet barriers remain to the widespread use of GPS units for animal tracking. Here, we developed a low-cost, logistically simple approach, deploying small and inexpensive GPS units to monitor cattle movements and habitat use and to assess the impact of cattle grazing on vegetation. Cattle were collared with i-gotU loggers to track fine-scale and broad-scale movements within an integrated ecosystem (cattle and wildlife) in Laikipia, central Kenya. At the fine scale, cattle exerted a significant impact on vegetation quantity and quality; increasing grazing intensity showed a negative relationship to grass height, but a positive correlation to green-up after rain. At the broad scale, cattle movement density varied notably by herd type and habitat availability, with acacia woodland and savanna grassland habitats used most predominantly. Overall, these small GPS loggers provided a flexible and relatively cheap method of tracking cattle movements, and demonstrated potential for collaring of cattle as a tool for monitoring ecosystem health and assisting management decisions.

Quantitative Analysis of Ngoma Forest in Kafue National Park, Zambia

Ngoma Forest is one of the eleven major vegetation types in Kafue National Park. Between 1997 and 2002, a study was undertaken to quantify the vegetation and landscape of Ngoma Forest. The key vegetation measurement variables taken from fourteen 20m X 20m sampling plots were: height, diameter at breast height (DBH) and crown size. In addition to vegetation measurements, data on terrain, soil, water and fire occurrence were recorded from each sampling plot. Observations regarding the presence of faunal species were done based on actual sightings and signs such as droppings, nests, foot prints, debarking of trees, feathers, hairs and sounds. Results of the study indicates that Ngoma Forest terrain is almost flat to very flat with generally straight slope of 0 to 3% and altitude ranging from 1,050m to 1,120m above sea level. The Forest occurs on strong acidic and well-drained sandy-clay and sandy-loam with pH range of 4.4 to 5.3. Baphia massaiensis, Friesodielsia obovata, Baikiaea plurijuga, Pterocarpus lucens, Combretum celastroides C. mossambicense , and C. elaeagnoides contribute more than 80% to the physical structure. The tree layer consists of tall trees in the height range of 18 to 22m and is dominated by Baikiaea plurijuga and Pterocarpus lucens with isolated stands of Entandrophragma caudatum, Ficus sur, Burkea africana and Erythrophleum africanum . The second layer consists of trees above 6m but less than 18m and is characterized by Philenoptera violacea, Pterocarpus rotundifolius, Xeroderis stuhlmannii, Dalbergiella nyasae, Strychnos potatorum and S. pungens . The third layer consist of small trees and shrubs rarely reaching the height of 6m and is characterized by Croton megalobotrys, Friesodielsia obovata, Combretum elaeagnoides, C. mossambicense, C. celastroides, Duranta erecta, Citropsis daweana, Grewia flavescens, Dalbergia martinii, Pteleopsis anisoptera and P. myrtifolia . The species diversity of Ngoma Forest is relatively low but comparatively higher than Mopane, Combretacea and Acacia woodlands. The tree / shrub density calculations indicated 1,475 stems per hectare while the mean biomass calculations were 122.6 tons per hectare and 1.5 tons per hectare for trees and shrubs respectively. The extent of Ngoma Forest in 1985 was 34km 2 but the Forest had shrunk to about 18km 2 by 2002. The Forest is likely to shrink further while the scrubland around the Forest is going to expand. This habitat shift is bound to adversely affect the habitat range of a number of ungulates, carnivores, primates, rodents and birds. Some management interventions have been suggested in order to protect this unique habitat.

Edaphic constraints on seed germination and emergence of three Acacia species for dryland restoration in Saudi Arabia

In situ edaphic factors affecting seed germination and seedling emergence of three framework species of Acacia were investigated with the intent of developing fundamental and scalable restoration capacity for Arabian dryland restoration. Direct seeding represents the most efficient means to restore vegetation at the landscape scale and this study provides insight into edaphic and ecological limitations, as well as effective protocols governing the use of native seeds for restoration in hyper-arid environments. The study was conducted in extant Acacia woodland habitat on conserved land (Thumamah Nature Park) in close proximity to Riyadh, Saudi Arabia. Broad-scale direct seeding using un- and pretreated Acacia gerrardii, A. tortilis, and A. ehrenbergiana seed, and two seed burial depths were implemented across three sites with distinct soil surface characteristics. Eight weeks post-sowing, random samples for each species × seed treatment × burial depth combination were excavated, sieved, and categorized as follows: failed to germinate, germinated but died prior to emerging, or successfully emerged. We show that germination and emergence of Acacia gerrardii, A. tortilis, and A. ehrenbergiana were driven by a three-way interaction among species, site, and seed burial depth. Treating seed with the signaling compound Moddus did not have a definitive effect, positive or negative, on any of the species investigated. Acacia gerrardii was the only species that exhibited widespread emergence, though emergence was not consistent across sites or burial depths. Germination was highest in disturbed soil (up to 69% for A. gerrardii), but very few (<2%) successfully emerged; a greater proportion of germinants in sandy soil emerged (up to 44% for A. gerrardii) even though the overall germination was less. Though species-dependent, a 2-cm sowing depth was most effective in sand; while in disturbed soil, sowing depths of 1 and 2 cm were comparable; and no germination was observed in gravelly clay soil. Sandy soil exhibited rapid water infiltration (107.6 mm min−1), and post-sowing surface crusting was a non-factor (0.44 kg cm−2). Disturbed soil exhibited moderate water infiltration (1.46 mm min−1) and post-sowing surface crusting was double that of sand (0.88 kg cm−2) and restrictive on seedling emergence. Gravelly clay exhibited extremely poor water infiltration (0.12 mm min−1), and surface crusting was severe (4.49 kg cm−2) and an order of magnitude greater than sand. The medium-coarse sand fraction, a key driver of the observed soil surface processes, was greatest in sand (55%) and significantly less and uniform in the disturbed (22%) and gravelly clay (22%) soils. Our findings demonstrate that soil surface characteristics and associated processes can dictate ecological processes at depths as shallow as 1–2 cm, and that soil crusts that slow water infiltration and impede seedling emergence rapidly reconstitute after disturbance; both are important considerations for restoring dryland vegetation.

Unleached Prosopis litter inhibits germination but leached stimulates seedling growth of dry woodland species

Prosopis chilensis-Prosopis juliflora hybrid (hereinafter referred to as Prosopis species) invade riverine Acacia woodlands and replace indigenous Acacia tortilis through mechanism that are not yet well understood. Therefore, we tested the hypothesis that dense shade and allelopathic effects of Prosopis species may reduce the germination and growth of A. tortilis more strongly than that of Prosopis species through greenhouse studies. We first evaluated the germination of A.tortilis and Prosopis species seeds with increasing concentration of unleached and leached Acacia or Prosopis litter in soil. Subsequently, we evaluated the growth of A. tortilis and Prosopis species seedling in response to concentration of Acacia or Prosopis litter at different light intensity regimes. Unleached Prosopis litter inhibited germination of A. tortilis and Prosopis species seeds with increase in litter concentration in the soil. Leached Acacia or Prosopis litter had no effect on seed germination but enhanced growth and shoot nutrient concentrations of A. tortilis and Prosopis species seedlings. Growth response to light intensity treatments was similar in both A. tortilis and Prosopis species seedling. The findings suggest that the lack of A. tortilis seedlings under Prosopis canopies in nature may be partially explained by Prosopis litter allelopathy on A. tortilis seed germination.

Bat species diversity and distribution in a disturbed regime at the Lake Bogoria National Reserve, Kenya

AbstractHuman population growth drives intrusion and progressive conversion of natural habitats for agriculture. We evaluated human impacts on bat species diversity and distribution among four vegetation types in and around Lake Bogoria National Reserve between November 2012 and July 2013. Plants were surveyed using the Braun–Blanquet cover/abundance method, whereas bats were sampled using standard mist nets erected on poles at ground level. Floristic similarity analysis revealed three broad vegetation assemblages, namely riverine vegetation, farmland and Acacia woodland/Acacia–Commiphora woodland. Two hundred and 33 bats representing eleven species in eleven genera and seven families were recorded. These were Epomophorus minimus, Rhinolophus landeri, Hipposideros caffer, Cardioderma cor, Lavia frons, Nycteris hispida, Chaerephon pumilus, Mops condylurus, Neoromicia capensis, Scotoecus hirundo and Scotophilus dinganii. Species richness estimators indicated that sampling for bats at ground level was exhaustive. Bat species richness and diversity were highest in the more structurally complex Acacia woodland compared to more homogenous farmlands where we recorded only common and generalist species that often occur in open habitats. The higher bat species richness and diversity in the Acacia woodland as compared to farmland underscore the importance of remnant natural savannah woodlands in the conservation of bats and other elements of biodiversity.

MODIS vegetation products as proxies of photosynthetic potential along a gradient of meteorologically and biologically driven ecosystem productivity

Abstract. A direct relationship between gross ecosystem productivity (GEP) estimated by the eddy covariance (EC) method and Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation indices (VIs) has been observed in many temperate and tropical ecosystems. However, in Australian evergreen forests, and particularly sclerophyll and temperate woodlands, MODIS VIs do not capture seasonality of GEP. In this study, we re-evaluate the connection between satellite and flux tower data at four contrasting Australian ecosystems, through comparisons of GEP and four measures of photosynthetic potential, derived via parameterization of the light response curve: ecosystem light use efficiency (LUE), photosynthetic capacity (Pc), GEP at saturation (GEPsat), and quantum yield (α), with MODIS vegetation satellite products, including VIs, gross primary productivity (GPPMOD), leaf area index (LAIMOD), and fraction of photosynthetic active radiation (fPARMOD). We found that satellite-derived biophysical products constitute a measurement of ecosystem structure (e.g. leaf area index – quantity of leaves) and function (e.g. leaf level photosynthetic assimilation capacity – quality of leaves), rather than GEP. Our results show that in primarily meteorological-driven (e.g. photosynthetic active radiation, air temperature, and/or precipitation) and relatively aseasonal ecosystems (e.g. evergreen wet sclerophyll forests), there were no statistically significant relationships between GEP and satellite-derived measures of greenness. In contrast, for phenology-driven ecosystems (e.g. tropical savannas), changes in the vegetation status drove GEP, and tower-based measurements of photosynthetic activity were best represented by VIs. We observed the highest correlations between MODIS products and GEP in locations where key meteorological variables and vegetation phenology were synchronous (e.g. semi-arid Acacia woodlands) and low correlation at locations where they were asynchronous (e.g. Mediterranean ecosystems). However, we found a statistical significant relationship between the seasonal measures of photosynthetic potential (Pc and LUE) and VIs, where each ecosystem aligns along a continuum; we emphasize here that knowledge of the conditions in which flux tower measurements and VIs or other remote sensing products converge greatly advances our understanding of the mechanisms driving the carbon cycle (phenology and climate drivers) and provides an ecological basis for interpretation of satellite-derived measures of greenness.

Soil moisture controls on phenology and productivity in a semi-arid critical zone

The Earth's Critical Zone, where physical, chemical and biological systems interact, extends from the top of the canopy to the underlying bedrock. In this study, we investigated soil moisture controls on phenology and productivity of an Acacia woodland in semi-arid central Australia. Situated on an extensive sand plain with negligible runoff and drainage, the carry-over of soil moisture content (θ) in the rhizosphere enabled the delay of phenology and productivity across seasons, until conditions were favourable for transpiration of that water to prevent overheating in the canopy. Storage of soil moisture near the surface (in the top few metres) was promoted by a siliceous hardpan. Pulsed recharge of θ above the hardpan was rapid and depended upon precipitation amount: 150mm storm−1 resulted in saturation of θ above the hardpan (i.e., formation of a temporary, discontinuous perched aquifer above the hardpan in unconsolidated soil) and immediate carbon uptake by the vegetation. During dry and inter-storm periods, we inferred the presence of hydraulic lift from soil storage above the hardpan to the surface due to (i) regular daily drawdown of θ in the reservoir that accumulates above the hardpan in the absence of drainage and evapotranspiration; (ii) the dimorphic root distribution wherein most roots were found in dry soil near the surface, but with significant root just above the hardpan; and (iii) synchronisation of phenology amongst trees and grasses in the dry season. We propose that hydraulic redistribution provides a small amount of moisture that maintains functioning of the shallow roots during long periods when the surface soil layer was dry, thereby enabling Mulga to maintain physiological activity without diminishing phenological and physiological responses to precipitation when conditions were favourable to promote canopy cooling.

Dynamics of soil carbon stock, total nitrogen, and associated soil properties since the conversion of Acacia woodland to managed pastureland, parkland agroforestry, and treeless cropland in the Jido Komolcha District, southern Ethiopia

ABSTRACTIn the arid, low biomass producing areas of Ethiopia, Acacia woodlands suffered a severe degradation due to exploitation for various uses, and conversion to grazing and cultivated lands. However, little is known on the impact of agricultural land uses on soil organic carbon (SOC), total nitrogen (TN) stocks, and other soil quality indicators. This study was planned to evaluate SOC and TN stock changes under parkland agroforestry (PAF), managed pastureland (MPL), and treeless cropland (TLCL) regimes by considering the remnant protected woodland (PWL) as a reference. We found that SOC and TN stocks were significantly higher in PWL and MPL areas. Conversion of Acacia woodlands to MPL, PAF, and TLCL resulted in the loss of SOC stock by 23, 50, and 56%, respectively. Higher SOC and TN stocks were found under PWL (144.3 Mg ha−1) and MPL (108.2 Mg ha−1). Significant changes in available phosphorous (P), exchangeable cations, and cation exchangeable capacity were observed following the woodland conversion to different land use types. Available P was the highest in MPL compared with the other land use regimes. Within the study area, the MPL land use type was the best land management option for protecting SOC and TN soil stocks.

Productivity and evapotranspiration of two contrasting semiarid ecosystems following the 2011 global carbon land sink anomaly

Global carbon balances are increasingly affected by large fluctuations in productivity occurring throughout semiarid regions. Recent analyses found a large C uptake anomaly in 2011 in arid and semiarid regions of the southern hemisphere. Consequently, we compared C and water fluxes of two distinct woody ecosystems (a Mulga (Acacia) woodland and a Corymbia savanna) between August 2012 and August 2014 in semiarid central Australia, demonstrating that the 2011 anomaly was short-lived in both ecosystems. The Mulga woodland was approximately C neutral but with periods of significant uptake within both years. The extreme drought tolerance of Acacia is presumed to have contributed to this. By contrast, the Corymbia savanna was a very large net C source (130 and 200gCm−2yr−1 in average and below average rainfall years, respectively), which is likely to have been a consequence of the degradation of standing, senescent biomass that was a legacy of high productivity during the 2011 anomaly. The magnitude and temporal patterns in ecosystem water-use efficiencies (WUE), derived from eddy covariance data, differed across the two sites, which may reflect differences in the relative contributions of respiration to net C fluxes across the two ecosystems. In contrast, differences in leaf-scale measures of WUE, derived from 13C stable isotope analyses, were apparent at small spatial scales and may reflect the different rooting strategies of Corymbia and Acacia trees within the Corymbia savanna. Restrictions on root growth and infiltration by a siliceous hardpan located below Acacia, whether in the Mulga woodland or in small Mulga patches of the Corymbia savanna, impedes drainage of water to depth, thereby producing a reservoir for soil moisture storage under Acacia while acting as a barrier to access of groundwater by Corymbia trees in Mulga patches, but not in the open Corymbia savanna.

Susceptibility of soil to wind erosion in arid area of the Central Rift Valley of Ethiopia

In Central Rift Valley (CRV) of Ethiopia, renewable land resources are under pressure. Acacia woodland clearance, frequent cultivation, crop residue removal and mono-cropping are among the major land mis-management practices in the area. This has largely been affecting the soil quality. The current study is aimed at assessing the impact of Acacia woodland conversion, and the subsequent mis-managements on selected soil physical properties, and their relation to the prevailing wind erosion in the area. For this study, four land use/land cover types, namely protected woodland (PWL), managed pastureland (MPL), parkland agroforestry (PAF) and treeless cropland (TLCL) were considered. Higher (P 0.25 mm) fraction of soil was found under PWL and MPL while higher fraction of micro-aggregates (0.053–0.25 mm) of soil was found under PAF and TLCL. Soil under PAF and TLCL had higher (P < 0.001) proportion of aggregates of < 1 mm, implying potential susceptibility of the soil to wind erosion. Higher soil bulk density (BD) was found in the most top layer (0–15 cm) of TLCL and PAF, and this could be attributed to the trampling effect by animals freely released to these land use types. In the study area, conversion of native woodland to PAF and TLCL and the subsequent mismanagements negatively affected some soil physical properties, thereby enhancing severity of soil erosion by wind. In contrast, although not commonly practiced by smallholder farmers, soil under MPL is more stable and less susceptible to wind erosion.

English

The objective of this research paper was to assess the spatial and temporal Land Use/Land Cover Changes (LU/LCC) in Arsi Negele District. Rapid population growth, agricultural expansion, environmental fluctuations, degradation of natural resource and loss of biodiversity are the most visible socio-economic and environmental problem in the study area. Satellite imagery, ground control point data and household level socioeconomic survey were used to produce land cover maps and explaining the historical trends of the study area. ERDAS Imagine and ArcGIS software was used to accomplish the analysis. The analysis result showed that in 1973 most of the study area had been covered by dense acacia woodland and shrub land. Between 1973 to 1986, cultivated grass and bare land increased by 8.98, 33.9, and 36.5 ha respectively. While, shrub and acacia woodland decreased by 6.17 and 73.21 ha, respectively. Between 1986 and 2010, cultivated acacia woodland and land increased by 15.38, 4.63, and 38.52 ha. However, bare and grass land decreased by 19.23 and 39.3 ha, respectively. Furthermore, the trend and magnitude of LU/LCC between 1973 to 2010 acacia woodland and land decreased by 22.72 and 13.58 ha, but shrub land and cultivated land increased by 22.82 and 13.14 ha. Socio-economic survey result revealed that acacia woodland and shrub land decreased, but cultivated land land and grass land increased in the derg regime. However, currently, natural resource conservation activity has got a great emphasis, thus spatial coverage of acacia woodland has increased. Expansion of agricultural land, population growth and the associated demand for land were the major driving forces for the observed LU/LCC changes in the study area. Therefore, loss of biodiversity, soil degradation, and environmental deterioration are largely the results of LU/LCC. Hence, land resources management practices, utilization of alternative energy sources and family planning education are some of the appropriate interventions to reduce this dramatic change. Key words: Remote sensing, GIS, land use/land cover changes (LU/LCC), accuracy, landsat, imagery.

Lessons learned from developing offsets in the Brigalow Belt of Queensland

Origin Energy—on behalf of the Australia Pacific LNG Project, the upstream tenures for which occupy some 570,000 ha—has established an offsets project in the Brigalow Belt of Queensland. This belt of Acacia woodland runs between the tropical rainforest of the coast and the semi-arid interior of Queensland, and is one of 15 bio-regions in Queensland. Its reduction to less than 8% of its distribution makes it a significant part of Australia's natural environment. The offsets project has the aim of re-establishing areas of Brigalow and associated vegetation communities and fauna habitats for impacts on matters of federal or state significance. This should result in a long-term reduction in environmental impacts. Given the long-term decline in Queensland's biodiversity, such work is vital and its associated challenges—such as gaining long-term access to and protection of appropriate land, comparatively new and evolving regulatory requirements and, at times, working on the edge of scientific knowledge—requires persistence and innovation. This extended abstract presents valuable lessons learned to help inform future offsetting projects.

Amphibian and reptile communities and functional groups over a land‐use gradient in a coastal tropical forest landscape of high richness and endemicity

AbstractInformation on the response of herpetofauna to different land uses is limited although important for land‐use planning to support conservation in human‐modified landscapes. Although transformation is dogmatically associated with extinction, species respond idiosyncratically to land‐use change, and persistence of species in habitat fragments may depend on careful management of the human‐modified matrix. We sampled herpetofauna over a vegetation‐type gradient representative of regional land uses [old‐growth forest, degraded forest, acacia woodland (i.e. new‐growth forest), eucalyptus plantation and sugar cane cultivation] in the forest belt skirting the southeastern coast of Africa, part of a biodiversity hotspot hosting many endemic herpetofaunal species in a highly transformed landscape. We categorized species into trait‐derived functional groups, and assessed abundance and richness of groups and compared community metrics along the gradient. We further assessed the capacity of environmental variables to predict richness and abundance. Overall, old‐growth forest harbored the highest richness and abundance, and amphibians and reptiles responded similarly to the gradient. Richness was low in cultivation, and surprisingly, in degraded forest, but substantial in acacia woodland and plantation. Composition differed between natural vegetation types (forest, degraded forest) and anthropogenic types (plantation, cultivation), while acacia woodland grouped with the latter for amphibians and the former for reptiles. Functional group richness eroded along the gradient, a pattern driven by the sensitivity of fossorial/ground‐dependent amphibians (A2) and reptiles (R2) and vegetation‐dwelling amphibians (A4) to habitat change. Variables describing temperature, cover and soil were good predictors of amphibian abundance, particularly of functional groups, but not for reptiles. Conserving forest and preventing degradation is important for forest herpetofaunal conservation, restoration and plantations have intermediate value, and cultivation is least beneficial. Our study demonstrates the utility of function‐related assessments, beyond traditional metrics alone, for understanding community responses to transformation. Particularly, fossorial/ground‐dependent amphibians and reptiles, and vegetation‐dwelling amphibians should be closely monitored.

Effect of elephant browsing on selected species of &lt;i&gt;Acacia&lt;/i&gt; along the great Ruaha River in Ruaha National Park, Tanzania

Elephant damage was assessed in 1,007 Acacia trees and responses between Acacia tortilis and A. kirkii in Ruaha National park were compared in 30 transects randomly placed in 38.8 km2 on the northern bank of Great Ruaha River (GRR) basing on six browsing categories and four debarking classes. There was no significant difference in browsing (F1, 10 = 0.6, p&gt;0.05) and debarking (F1, 6 = 0.16, p &gt; 0.05) between A. kirkii and A. tortilis. Trees were classified into three height and twelve diameter classes. About 3613 trees &lt;1 m in height represented response in addition to coppices. The difference between the two species was observed only in regeneration potential (F1,58 = 41.4, p &lt; 0.05). In addition, low regeneration potential, severely browsed trees and restricted distribution made A. kirkii more vulnerable to elephant feeding compared to A. tortilis. The high A. tortilis regeneration potential suggests that the study area could become an Acacia bushland or woodland if fire is controlled. Further studies need to investigate, the suppressed regeneration of Acacia trees at Msembe, variations in vegetation utilization along the GRR and effects of fire and small browsers on Acacia species including monitoring of vegetation and animal trends.Key words: Elephants, Acacia, Tree damage, Regeneration, Ruaha River

Ecological correlates of small mammal assemblage structure at different spatial scales in the savannah biome of South Africa

We sampled the seasonal diversity of rodents and shrews in two neighboring game reserves in the savannah biome and assessed the influence of competition and abiotic processes on species composition patterns at habitat and reserve scales. We used null models and multivariate analyses to test whether the observed patterns differed significantly from those expected by chance. Species richness estimators indicated that rodent and shrew inventories were relatively complete. Rarefaction curves showed that small mammal species richness was higher at the Mkhuze Game Reserve than the Kube Yini Game Reserve, though it was highest in the Acacia woodlands. Rodent diversity was highest during winter. Rodent and shrew species composition was significantly correlated with grass height, tree density, and ground cover. Furthermore, rodent and shrew assemblages were nested at the reserve scale. Only nestedness at the broadest scale (both reserves, both seasons combined) was significantly correlated with landscape and microhabitat variables. Conversely, there was little evidence that competition influenced rodent and shrew species composition. Results showed that species composition patterns of small mammals in the savannah biome are related to abiotic processes operating at local and regional scales, suggesting that microhabitat characteristics and regional processes like immigration and extinction drive assemblage structure.

The sociality of nesting in Rüppell's Weaver Ploceus galbula and the Lesser Masked Weaver Ploceus intermedius in an Ethiopian acacia woodland

Rüppell's Weaver Ploceus galbula and the Lesser Masked Weaver Ploceus intermedius nest prominently in the Awash National Park, Ethiopia. In both species the sociality or degree of aggregation of their nesting is varied. Rüppell's Weaver can nest singly or in small clusters, or in association with the Lesser Masked Weaver, which itself can nest in loose aggregations or bustling colonies. This variation suggests a continuum of nesting sociality in weavers, from solitary nesting through associative and gregarious nesting to full coloniality.

Spatial patterns and temporal dynamics in savanna vegetation phenology across the North Australian Tropical Transect

The phenology of a landscape is a key parameter in climate and biogeochemical cycle models and its correct representation is central to the accurate simulation of carbon, water and energy exchange between the land surface and the atmosphere. Whereas biogeographic phenological patterns and shifts have received much attention in temperate ecosystems, much less is known about the phenology of savannas, despite their sensitivity to climate change and their coverage of approximately one eighth of the global land surface. Savannas are complex assemblages of multiple tree, shrub, and grass vegetation strata, each with variable phenological responses to seasonal climate and environmental variables. The objectives of this study were to investigate biogeographical and inter-annual patterns in savanna phenology along a 1100km ecological rainfall gradient, known as North Australian Tropical Transect (NATT), encompassing humid coastal Eucalyptus forests and woodlands to xeric inland Acacia woodlands and shrublands. Key phenology transition dates (start, peak, end, and length of seasonal greening periods) were extracted from 13years (2000–2012) of Moderate Resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index (EVI) data using Singular Spectrum Analysis (SSA).Two distinct biogeographical patterns in phenology were observed, controlled by different climate systems. The northern (mesic) portion of the transect, from 12°S, to around 17.7°S, was influenced by the Inter-Tropical Convergence Zone (ITCZ) seasonal monsoon climate system, resulting in strong latitudinal shifts in phenology patterns, primarily associated with the functional response of the C4 grass layer. Both the start and end of the greening (enhanced vegetation activity) season occurred earlier in the northern tropical savannas and were progressively delayed towards the southern limit of the Eucalyptus-dominated savannas resulting in relatively stable length of greening periods. In contrast, the southern xeric portion of the study area was largely decoupled from monsoonal influences and exhibited highly variable phenology that was largely rainfall pulse driven. The seasonal greening periods were generally shorter but fluctuated widely from no detectable greening during extended drought periods to length of greening seasons that exceeded those in the more mesic northern savannas in some wet years. This was in part due to more extreme rainfall variability, as well as a C3/C4 grass-forb understory that provided the potential for extended greening periods. Phenology of Acacia dominated savannas displayed a much greater overall responsiveness to hydroclimatic variability. The variance in annual precipitation alone could explain 80% of the variances in the length of greening season across the major vegetation groups. We also found that increased variation in the timing of phenology was coupled with a decreasing tree-grass ratio. We further compared the satellite-based phenology results with tower-derived measures of Gross Ecosystem Production (GEP) fluxes at three sites over two contrasting savanna classes. We found good convergence between MODIS EVI and tower GEP, thereby confirming the potential to link these two independent data sources to better understand savanna ecosystem functioning.

Model highlights likely long‐term influences of mesobrowsers versus those of elephants on woodland dynamics

AbstractThe potential long‐term influences of mesobrowsers versus those of savannah elephants on woodland dynamics have not been explored. This may be a critical omission especially in southern African savannahs, where efforts to preserve existing woodlands are typically directed at elephant management. We describe a simple browse–browser model, parameterized from an extensive review of the literature and our own data, including quantitative assessment of impala impact, from the study site, iMfolozi Park, South Africa. As there is a paucity of species‐specific demographic data on savannah woody species, we modelled, in a novel approach, functional groups of plant species typical of Acacia woodlands. Outputs suggest that over the long term (100 years), low‐to‐moderate densities of impala will have a similar impact on woodland structure, in terms of density of adult trees, as low‐to‐moderate densities of elephant. Further, the outputs highlight the apparently strong synergistic effect impala and elephant impacts combined have on woodland dynamics, suggesting that reduction or removal of either impala or elephant will radically reduce long‐term destruction of savannah woodlands. Recorded changes in adult tree numbers in iMfolozi broadly supported the model's outputs.