Acacia Etbaica Research Articles

<i>Acacia etbaica</i> as a Potential Low-Cost Adsorbent for Removal of Organochlorine Pesticides from Water

The presence of pesticides in the environment is of great concern due to their persistent nature and chronic adverse effect on human health and the environment. Water bodies are subject to pollution by organochlorine pesticides, especially in developing countries, where water pollution is a key sustainability challenge. Hence, activated carbon is considered a universal adsorbent for the removal of organochlorine pollutants from water. Activated carbon from Acatia etbaica was prepared using traditional kilns with low investment costs. Pesticides such as aldrin, dieldrin and DDT were selected for adsorption because of their common usage in agricultural and malaria control activities and may occur in high concentrations in surface waters that are used as drinking water sources. The effect of the adsorbent dose and initial concentration were investigated. To describe the equilibrium isotherms the experimental data were analyzed by the Langmuir and Freundlich isotherm models. The Freundlich model gave the best correlation with the experimental data. Activated carbon prepared from Acacia etbaica was found to be an effective and low-cost alternative for the removal of organochlorine pesticides from aqueous solutions. The preparation method allows the use of this material by local communities for effective remediation of pollution by pesticides.

Arbuscular mycorrhizal impacts on competitive interactions between Acacia etbaica and Boswellia papyrifera seedlings under drought stress

Aims Arbuscular mycorrhizal fungi can have a substantial effect on the water and nutrient uptake by plants and the competition between plants in harsh environments where resource availability comes in pulses. In this study we focus on interspecific competition between Acaia etbaica and Boswellia papyrifera that have distinctive resource acquisition strategies. We compared the extent of interspecific competition with that of intraspecific competition. Methods In a greenhouse study we examined the influence of Arbuscular Mycorrhiza (AM) and pulsed water availability on competitive interactions between seedlings of the rapidly growing species A. etbaica and the slowly growing species B. papyrifera. A factorial experimental design was used. The factors were AM, two water levels and five species combinations Important Findings Seedlings of both species benefitted from AM when grown alone, and the positive growth response to pulsed water availability in B. papyrifera seedlings was in contrast with the negative growth response for A. etbaica seedlings. AM also affected the competitive performance of both species. B. papyrifera was not affected by intraspecific competition, whereas A. etbaica was negatively affected compared to the seedlings grown alone. This effect was stronger in the presence of AM. In interspecific competition, A. etbaica outcompeted B. papyrifera. Mycorrhiza and pulsed water availability did not affect the outcome of interspecific competition, and the aggressivity index of A. etbaica remained unchanged. The extent to which AM influences plant competition in a drought-stressed environment may depend on belowground functional traits of the species. AM and pulsed water availability could modify the balance between intraspecific and interspecific competition. By affecting the balance between intraspecific and interspecific competition, both factors could impact the establishment and survival of seedlings.

Medicinal plants and their uses by the people in the Region of Randa, Djibouti

Ethnopharmacological relevanceThe article presents the local knowledge on medicinal plants and their relevance in managing health problems. Important ethnobotanical leads are given with priority species and disease categories, casting insight on future phytochemical and pharmacological studies. Aim of the studyThe use of traditional medicinal plants has been an integral part of the traditional healthcare systems in Djibouti. However, scientific studies on the traditional herbal healing systems of the various cultural groups have never been undertaken. This study has, therefore, aimed at assessing plant-related ethnomedicinal knowledge of the people in Randa Region; prioritising the plants with respect to common disease categories and inferring about prospects of new pharmacological products. Materials and methodsInterview-based ethnobotanical field study was carried out to document the plant-based ethnomedicinal knowledge handed down to the present by the oral tradition of people living in 24 villages in Tadjourah District of Randa Region (north Djibouti). Informant Consensus Factors (ICF) and Fidelity Level (FL) values of the medicinal plants were calculated to check the level of informant agreement and the healing potentials of the species. ResultsA total of 91 plant species that belong to 72 genera and 40 families were documented. Most of these species (92%) were collected from non-cultivated areas. Their local names and traditional uses in medicine were also studied. The plant family Fabaceae was represented by the highest number of taxa (17 species). Strong informant agreements hinted at good healing potentials of some species as shown by high values of consensus factors for eye diseases (0.98), mouth diseases (0.93), kidney problems (0.89) and microbial infections (0.84). Dodonea angustifolia, Solanum cordatum, Grewia erythraea, Acalypha indica, Acacia etbaica, Fagonia schweinfurthii, Solanum coagulans, Senna alexandrina and Grewia tembensis scored high FL values emerging as promising priority species for future pharmacological screening against microbial infections. ConclusionThe results of this study may inspire further ethnobotanical and ethnopharmacological research and investigations toward drug discovery in Djibouti and beyond.

Population structure of woody plants in the arid cloud forests of Dhofar, southern Oman

Abstract This study evaluates the size frequency distribution of 11 trees and shrubs in the cloud forest in Wadi Garziz, southern Oman, in order to assess their current situation, which is affected by cutting, overgrazing and other constraints. A size class distribution and a vegetation structure analysis were applied in order to analyze the dynamics of this forest using census data from 51 plots selected across 5 transects covering the hill-slope andwadi-bed habitats. Some of the trees inhabiting the hill-slopes (e.g. Acacia senegal and Commiphora spp.) were found to exhibit an inverse J-shaped distribution with constant regeneration, whilst in the wadi bed these same trees exhibited a J-shaped distribution (i.e. of declining populations). On the other hand, Acacia etbaica inhabiting the hill-slopes exhibited a tendency towards a J-shaped distribution and an inverse J-shaped distribution in the wadi-bed. All the populations (i.e. inhabiting the hill-slopes and the beds) of Anogeissus dhofarica had a J-shaped distribution whereas all the populations of Blepharispermum hirtum had a more or less inverse J-shaped distribution. The Ziziphus spina- -christi and Acacia tortilis populations, meanwhile, exhibited the bi-modal shape of size distribution. The shrubs inhabiting the hill-slopes (e.g. Coroton confertus and Ormocarpum dhofarense) exhibited a tendency towards a J-shaped distribution; such distribution characterizes a declining population with a limited regenerational capacity. Overall, most of the examined populations, except those of Acacia etbaica in wadi-bed and Blepharispermum hirtum, seemed to be under stress from both environmental and human factors, particularly in the wadi bed. This type of study can provide a basis for the development of a management plan to support the conservation and sustainable use of forest vegetation in an arid region.

Altitudinal variation and conservation priorities of vegetation along the Great Rift Valley escarpment, northern Ethiopia

Understanding plant species distribution patterns along environmental gradients is fundamental to managing ecosystems, particularly when habitats are fragmented due to intensive human land-use pressure. To assist management of the remaining vegetation of the Eastern Afromontane Biodiversity Hotspot, plant species richness and diversity patterns were analyzed along the main elevation gradient (1,000–2,760 m) of the Great Rift Valley escarpment in northern Ethiopia, using 29 plots established at 100-m elevation intervals. A total of 129 vascular plant species belonging to 59 families was recorded. Species richness and diversity showed a hump-shaped relationship with elevation, peaking at mid-elevation (1,900–2,200 m). Beta diversity values indicated medium species turnover along the elevation gradient and were lowest at mid-elevation. Elevation strongly partitioned the plant communities (r = 0.98; P < 0.001). Four plant communities were identified along the elevation gradient: Juniperus procera–Clutia lanceolata community (2,400–2,760 m), Abutilon longicuspe–Calpurnia aurea community (1,900–2,300 m), Dracaena ombet–Acacia etbaica community (1,400–1,800 m), and Acacia mellifera–Dobera glabra community (1,000–1,300 m). To optimize conservation of species and plant communities, it is recommended that a conservation corridor be established along the elevation gradient that includes all four plant communities. This strategy—in contrast to creating single isolated reserves in zones with high species richness—is necessary for the habitat protection of species with narrow elevational ranges, in particular the globally endangered Nubian dragon tree (Dracaena ombet).

Coupling vegetation organization patterns to soil resource heterogeneity in a central Kenyan dryland using geophysical imagery

In dryland ecosystems, understanding the effects of heterogeneity in soil moisture and geophysical properties on vegetation structure and dynamics poses a suite of challenging research questions. Heterogeneity in soil depth can affect resource availability and the subsequent organization of woody vegetation, while spatiotemporal variation in soil moisture can reveal important ecohydrological feedbacks that govern the outcome of anthropogenic activities on the organization of dryland vegetation. In this research we investigate two cases of soil resource heterogeneity that affect the organization of dryland vegetation patterns by expanding previous electromagnetic induction (EMI) imaging techniques. In the first case we examine the influence of soil depth as a control on soil resource availability on hillslopes in tree‐grass systems in central Kenya. Our results indicate that woody vegetation clumping occurs where soil depth changes, and the deeper rooted Acacia tortilis occurs on deep soils while the drought tolerant Acacia etbaica occurs on shallow soils. In the second case we examine daily patch–interpatch scale moisture dynamics following two different‐sized rain events in a degraded landscape. With the aid of a numerical subsurface flow model, EMI, and soil moisture data, we have identified a possible positive feedback mechanism (“soil moisture halo effect”) that we believe may have contributed to the proliferation and two‐phase pattern formation of a native succulent Sansevieria volkensii in degraded ecosystems of Kenya. By determining how different plants respond to, and modify, the soil environment, we can better understand resource capture and dynamics, which in the longterm will help to develop management strategies.

Vegetation Composition in Hugumbirda-Gratkhassu National Forest Priority Area, South Tigray

The floristic composition and structure of the vegetation of Hugumbirda-Grat-Khassu forest, South Tigray, Northern Ethiopia is described and related to environmental factors. To analyze the vegetation and environmental data seventy-four relevè ( 20m x 20m) were used. For each species the cover/abundance value was estimated. Height and diameter at breast height (DBH) of all woody individuals taller than 2 m and thicker than 2 cm were measured. Importance Value Index was calculated for 24 tree/shrub species and the result helped to identify the five dominant tree/shrub species and to show the overall forest situation. The species and relevès were classified with the two-way indicator species analysis program TWINSPAN. We recorded 102 species belonging to 83 genera and 50 families. Five community types are described: Allophylus macrobotrys-Ficus sur, Nuxia congesta-Podocarpus falcatus, Acacia abyssinica-Olea europaea, Myrica salicifolia-Erica arborea-Maesa lanceolata and Acacia etbaica- Dichrostachys cinerea-Acacia tortilis type. Of these, community type 2 has high species richness while community type 3 is poor in species richness. The general arrangement of all species was found to show high density at lower height and DBH classes. Based on the cumulative results of Importance Value Index, Juniperus procera, Olea europaea subsp. cuspidata, Nuxia congesta, Cassipourea mallosana and Olinia rochetiana were identified to be the most dominant tree species of the forest and they contributed 71.43% of the basal area. Analysis of community-environment relationships didn’t show significant differences except for altitude and slope. Key words: Community, DBH, Floristic composition, Forest structure, Releve, Vegetation classification.

Establishment and management of woody seedlings in gullies in a semi-arid environment (Tigray, Ethiopia)

In the north Ethiopian highlands, gully erosion is a significant land degradation process. Although the protective role of vegetation has been demonstrated in many studies, efforts previously made in using woody species for erosion control in the research area are limited, and when applied, survival of the planted seedlings was very low. Lack of experience and fundamental knowledge on species autecology and traits are two important bottlenecks. This study therefore aims at better understanding seedling establishment and growth in a context of tree plantings, with the view to further control gully erosion in a semi-arid environment. To this end survival, growth and development of seedlings of Acacia etbaica Schweinf., Sesbania sesban (L.) Merr. and Dodonaea angustifolia L.f. were monitored during 26 months in a field trial under different site conditions and treatments. The experiment was established at two sites characterized by topographic and edaphic conditions (Vertisol and sandy colluvium) representative for the study area. At each site, seedlings were subjected to different treatments of watering, sheltering and planting position (gully floor, sidewall and shoulder), and a large set of plant growth variables was regularly monitored. Height and biomass growth was fastest for Sesbania, even if affected by different pests. Regardless of the species, plants growing in the (nutrient-rich) Vertisol site had a higher survival rate and an overall better development. Shelter protection significantly increased survival and resulted in taller seedlings. Notwithstanding these general trends, treatment effects were often varying over time and strongly influenced by specific edaphic conditions. Generally, Acacia performed best on gully shoulder and wall, Sesbania on the gully floor and Dodonaea on shoulder positions. Recommendations for planting practice and follow-up research are discussed.

Feeding Acacia etbaica and Dichrostachys cinerea fruits to smallholder goats in northern Ethiopia improves their performance during the dry season

Acacia etbaica Schweinf. and Dichrostachys cinerea (L.) Wight et Arn. are among the common woody browse plants that naturally grow in many arid and semi-arid rangelands in sub Saharan Africa. An experiment was conducted to compare the voluntary dry matter intake, body weight gain, nitrogen balance, carcass composition and sensory attributes of goats supplemented with different levels of A. etbaica and D. cinerea fruits. Average initial body weight of the goats was 20.4 kg (± 0.8SE) and received one of the following fruit supplementation regimes for 120 days (on body weight basis, n = 4 goats per group): (1) Control, no supplement; (2) 0.5% of A. etbaica; (3) 0.5% of D. cinerea; (4) 1.0% of A. etbaica; (5) 1.0% of D. cinerea; (6) 1.5% of A. etbaica; (7) 1.5% of D. cinerea. All groups were allowed to graze/browse during the day. Compared to A. etbaica, D. cinerea fruits contained higher amounts of crude protein (182 vs 135 g/kg DM), metabolizable energy (11 vs 8.4 MJ/kg DM), and in vitro dry matter digestibility coefficient (0.7 vs 0.6). The concentrations of acid detergent fiber (ADF), sulphuric acid solubulized lignin, and tannin (soluble and condensed) were lower ( P < 0.05) in D. cinerea than in A. etbaica fruits. A. etbaica fruits, however, contained higher amounts of Na, K, Fe, and Zn concentrations than D. cinerea fruits. Dry matter intake was markedly higher in supplemented groups than in the control group without supplement. Similarly, body weight gain in the control group was negative and lower ( P < 0.05) than any of the supplemented groups. During the course of the experimental period (120 days) the group placed in the 1.5% D. cinerea fruit diet gained 2.6 kg whereas the control group lost 2.0 kg. Thus, the difference between these two groups was 4.6 kg, which suggests about 22.5% increment of the goats' initial body weight. N retention was negative for the control group and varied little among the remaining treatment groups. Dressing percent increased with increased level of either type of fruit supplement, the highest (51.8%) being achieved at the 1.5% D. cinerea level. There was no difference in bone tissue across treatment groups. D. cinerea fruit intake also resulted in juicy/watery flavor and tender carcass. D. cinerea fruits appeared to have no adverse effects when included at the highest level (1.5%) and could be collected and stored as dry season supplement to smallholder goats. This study shows that poor farmers can increase goat performance substantially through supplement feeding with wild fruits. Areas in Ethiopia originally set aside for provision of ecological services and biodiversity protection can also be used for wild fruit production and feeding of small stock. The effect of increasing D. cinerea fruits above the 1.5% body weight level should be a focus of future investigation. Further work on deactivation mechanism of tannins is required for A. etbaica fruits included at levels higher than 1.0%.

Restoration of Dry Afromontane Forest Using Pioneer Shrubs as Nurse‐Plants for Olea europaea ssp. cuspidata

Abstract Shrubs are often considered competitive barriers for seedlings planted in reforestation programs, although they can facilitate tree recruitment, especially in ecosystems under high abiotic stress. An alternative reforestation technique using pioneer shrubs as nurse‐plants for Olea europaea ssp. cuspidata was tested in exclosures in northern Ethiopia. Seedlings were planted in three different microhabitats, and their survival was monitored. The microhabitats were bare soil patches between shrubs, patches under the dominant shrub Acacia etbaica, and patches under Euclea racemosa, an evergreen shrub, which supports the majority of naturally established Olea recruits. The ability of shrubs to offer protection against browsing goats was tested experimentally. Controlled shading was used to determine whether solar irradiation causes seedling mortality in environments without water stress. Data were analyzed using Kaplan–Meier survival analysis, Kruskal–Wallis analysis of variance (ANOVA), and one‐way ANOVA. Olea survival was significantly higher and shoot damage by goats was lower when planted under shrub cover compared to bare soil patches, particularly under Euclea canopies, although high shade levels reduced seedling performance. Reduction of solar radiation by shrub canopies and thus control of soil–water evaporation and seedling transpiration most likely controlled the observed facilitation. Planting under shrubs may increase seedling survival and assist regeneration of dry Afromontane vegetation. Preserving pioneers also reduces soil erosion and conserves biodiversity. Excluding livestock is essential for Olea woodland restoration and allows persistent but morphologically modified Olea shrubs to develop vigorous regrowth. Facilitative processes are guiding principles for assisted forest restoration, but above‐average rains may be critical to restore higher biomass levels in semiarid areas.

Restoring dry Afromontane forest using bird and nurse plant effects: Direct sowing of Olea europaea ssp. cuspidata seeds

To identify the perspectives of seed sowing for reforestation of degraded dry Afromontane savanna in exclosures in northern Ethiopia, seeds of a fleshy-fruited, secondary climax tree, Olea europaea ssp. cuspidata, were placed under two pioneer shrub species ( Euclea racemosa and Acacia etbaica) and in open microhabitats. Seed removal and germination rates were examined. The effects of bird ingestion, manual pulp removal and mechanical endocarp treatments on germination rates were also studied. Pulp removal promoted seed germination, in particular in seeds without endocarp manipulation. Seed removal, presumably by rodents, was concentrated in narrow strips along linear soil conservation structures, and not different between shrubs and open microhabitats. In the absence of water stress, humus types did not have a significant effect on germination rates. Under field conditions however, germination was higher under Euclea canopies. The observed facilitative effect of Euclea shrubs on germination may be attributed to moisture retention effects, related to the deep humus layer and canopy architecture, preventing desiccation and promoting imbibition of seeds. When readily available Olea seeds are not used for seedling production, direct sowing of seeds in the humus under dense Euclea shrubs could offer a cheap complement to planting of nursery-raised seedlings for forest restoration projects in recovering Afromontane savanna.

Effects of pioneer shrubs on the recruitment of the fleshy‐fruited tree Olea europaea ssp. cuspidata in Afromontane savanna

AbstractQuestion: Is seedling recruitment of a fleshy‐fruited tree in degraded Afromontane savanna dependent on shelter from pioneer shrubs, and is shelter availability related to shrub traits?Location: Degraded montane savanna in northern Ethiopia (13°36′N, 39°21′E).Method: Nurse plants of Olea europaea ssp. cuspidata seedlings were recorded using T‐square plotless sampling and clustered according to shrub traits, using Ward's method after Principal Components Analysis. Facilitation was further examined through experimental planting and Kaplan‐Meier survival analysis.Results: Both in grazed and protected areas, Olea recruits were found exclusively under shrubs, primarily under Euclea racemosa although Acacia etbaica was more abundant. Olea recruitment is distributed randomly at landscape scale, but depends on shelter at patch scale. Shelter ability is related to shrub shape and species identity. Dense multi‐stemmed shrubs with a wide base and crown on a mulch‐rich mound are key recruitment foci. Euclea shrubs have these favoured traits and probably act as preferential perching sites for avian seed dispersers. Soil and organic matter accumulation under Euclea shrubs may also create favourable conditions for Olea germination and survival. Experimentally planted seedlings had a better chance for survival under Euclea.Conclusions: Olea regeneration is probably subject to both passive (disperser‐mediated) and active facilitation. Small changes of shrub traits can alter the suitability of a patch for Olea recruitment. Protection of shrubs can increase facilitation for seedlings, while pruning may reduce competition for saplings and thus enhance forest succession. Planting of raised Olea seedlings under Euclea shrubs in years with a good rainy season may further assist forest restoration.

Effects of pioneer shrubs on the recruitment of the fleshy-fruited tree Olea europaea ssp. cuspidata in Afromontane savanna

Abstract Question: Is seedling recruitment of a fleshy-fruited tree in degraded Afromontane savanna dependent on shelter from pioneer shrubs, and is shelter availability related to shrub traits? Location: Degraded montane savanna in northern Ethiopia (13°36′ N, 39°21′ E). Method: Nurse plants of Olea europaea ssp. cuspidata seedlings were recorded using T-square plotless sampling and clustered according to shrub traits, using Ward's method after Principal Components Analysis. Facilitation was further examined through experimental planting and Kaplan-Meier survival analysis. Results: Both in grazed and protected areas, Olea recruits were found exclusively under shrubs, primarily under Euclea racemosa although Acacia etbaica was more abundant. Olea recruitment is distributed randomly at landscape scale, but depends on shelter at patch scale. Shelter ability is related to shrub shape and species identity. Dense multi-stemmed shrubs with a wide base and crown on a mulch-rich mound are key recruitment foci. Eu...

Surface runoff and seed trapping efficiency of shrubs in a regenerating semiarid woodland in northern Ethiopia

In forest restoration areas in northern Ethiopia, natural regeneration of Olea europaea ssp. cuspidata only occurs under pioneer shrubs. To assess the impact of erosion on the spatial distribution of Olea recruits, secondary dispersal of olive seeds by surface runoff was determined in and near the micro-environment of two important pioneers ( Acacia etbaica and Euclea racemosa). We hypothesized that (1) Olea seeds deposited under the protective crowns of shrubs are less likely to be lost by surface wash than seeds in the bare inter-plant areas and (2) that seeds in the latter are more prone to be translocated by runoff to microsites under shrubs than to open areas. Runoff experiments were conducted in August–September 2003 in ten 3 × 3 m 2 plots laid out around isolated shrubs in two sites. Twenty-eight marked tracer seeds were dropped at the upper end of each plot at 0.10 m intervals. Ten seeds marked in another way were deposited under the crown in each plot simulating seed dispersal by birds. The seeds were collected after the rainy season and their positions recorded. In a third experiment, mulch under shrubs was removed and ten marked seeds were deposited under each crown. Rainfall simulation experiments were conducted with a maximum intensity of 120 mm h − 1 for a 10 min duration. For all experiments, seed movement was analyzed in relation to slope and shrub variables. Seed movement was limited in one site, where only 21% of the seeds were translocated. Movement was significantly higher in the other site (61%) although it had a lower slope gradient. The number of seeds moved by surface runoff was not significantly related to shrub species, slope gradient or slope roughness. There was a strong linear relationship between the distance parallel to the contour from the shrub center to the seed and the extent of the downhill translocation. No seeds moved to a position under a shrub crown and no shrub lost a seed deposited under its crown. Simulated rainfall after mulch removal resulted in a seed loss of nearly 33%. Micro-topographic structures under shrubs, especially under E. racemosa, cause some soil and sediment retention, but more importantly divert runoff water and concentrate flows to rills alongside shrubs. From an eco-geomorphological point of view, shrubs show poor seed trapping efficiency contradictory to expectation. Seeds in sediment flows are deposited in the bare inter-plant areas. However, seeds under shrubs are not likely to be lost by surface wash. Surface runoff has little effect on the general pattern of the primary seed rain. Since Olea recruits were exclusively found under shrubs and not in the spaces between shrubs in the studied field sites, it appears plausible that seeds deposited in the open field are almost without doubt lost to post-dispersal seed predation, unsuccessful germination or seedling predation and mortality. Recovery of O. europaea in degraded shrubland communities therefore depends upon directed dispersal of seeds under shrubs by frugivorous birds.

The use of plant water relations to characterize tree species and sites in the drylands of northern Ethiopia

Water relations of four tree species were studied in four sites in the drylands of northern Ethiopia. Predawn water potentials were significantly higher at all sites as compared to midday measurements for Acacia etbaica and Boswellia papyrifera. In contrast, Lannea fruticosa revealed this significant difference only once, while Terminalia brownii at only two of the four sites. An analysis of variance showed that A. etbaica has a wider tolerance range as compared to the other species. There was no significant difference among the four sites in terms of predawn, midday and diurnal ranges of water potential. The study revealed that A. etbaica and B. papyrifera are performing better as compared to T. brownii and L. fruticosa under the current climatic conditions. Understanding the physiological basis of survival, productivity, ability to cope with low moisture availability, and growth potential of indigenous species in the drylands is essential for the utilization and promotion of these and other species.

The role of enclosures in the recovery of woody vegetation in degraded dryland hillsides of central and northern Ethiopia

The role of enclosures in the recovery of woody vegetation was investigated by studying species composition, density, diversity and regeneration status of woody species and soil seed banks in enclosures and adjacent open areas at two widely separated sites known as Biyo–Kelala and Tiya in central and northern Ethiopia, respectively. Fifty-eight woody species, representing 30 plant families, were recorded at Biyo–Kelala, of which only 25 were recorded both in the enclosure and open area while two were recorded outside of the sample plots. At Tiya, 31 woody species, representing 19 families, were recorded in the enclosure but only 15 of these species were encountered in the open area. Woody plant densities were 1746 and 2215 individuals/ha in the enclosure and open area at Biyo–Kelala, respectively, and 3705 and 3048 individuals/ha in the enclosure and open area at Tiya, respectively. Dodonaea angustifolia and Acacia etbaica were the most dominant species at Biyo–Kelala and Tiya, respectively. The enclosure at Biyo–Kelala had about twice the diversity value of the open area, while the corresponding values were 2.5 and 2 for the enclosure and open area at Tiya, respectively. The total numbers of species recovered from the soil samples collected in Biyo–Kelala site were 48 for the enclosure and 30 for the open area with mean seed densities of 2765 (±124) and 1663 (±117) seedsm2, respectively. At Tiya, 30 and 16 species were recovered in the enclosure and open area, respectively, with mean seed densities of 2811 (±276) and 996 (±243) seedsm2, respectively. The diversity of all plant species in the soil seed bank was greater in the enclosure than the open area at both sites. Herbs and grasses dominated the soil seed banks at both sites while several of the woody species recorded in the above-ground vegetation were not represented at all. Overall results from this study indicate strongly that establishment of enclosures is very advantageous over other methods since it is a fast, cheap and lenient method for the rehabilitation of degraded lands.

Physicochemical characteristics and pollen spectrum of some Saudi honeys

Ten unifloral Saudi honeys were studied and botainically typified: Sidir Aseer ( Ziziphus Spina-christi (L)), Sidir Albaha ( Ziziphus Spina-christi L), Talh Tehamh ( Acacia spp.), Samra Taif ( Acacia Etbaica), Magra Aseer ( Hypericum perforatum), Doarm Taif ( Levandula Dentata), Shorm Taif ( Ocimum repandra), Talh Medina ( Acacia spp.), Farm Riyadh ( Heliantemum chamaecistus), and Farm Qaseem ( Cheno Podium spp.). Honeys were considered to be unifloral when the dominant pollen was over 40% of total pollen. All samples were examined for moisture, refractive index, specific gravity, viscosity, total solids, water-insoluble solids, ash content, pH, total acidity, hydroxy methyl furfural, diastase, invertase activity, optical rotation, minerals and sugars. These samples were found to meet all major national and international honey specifications.

Functions for multi-phase assessment of biomass in acacia woodlands of the Rift Valley of Ethiopia

In this article, single-tree biomass functions for acacia woodland tree species are presented. The main aim of developing the functions was for utilizing them in a multi-phase sampling design in estimating the woody biomass in acacia woodlands of the Rift Valley of Ethiopia. Eighty-five trees (5–35 cm diameter) were selected randomly from the five dominant tree species: Acacia tortilis (Forsk.) Hayne, Acacia senegal (L) Willd., Acacia seyal Del., Acacia etbaica Schweif. and Balanites aegyptiaca (L) Del. Four categories of functions were developed. These were (i) functions with crown area as independent variable, to be applied using high resolution satellite images or aerial photos; (ii) functions with crown area and tree height as independent variables, to be applied using data from aerial photos; (iii) functions for quick estimation in ground surveys, based on the diameter at 0.8 m; and (iv) functions for thorough estimation in ground surveys, in which the diameter at 0.8 m, the diameter at stump height, and the crown area were included. Also, two sets of functions were developed, one with and one without species indicator variables. In gathering data for developing biomass functions, the selection of sample discs from trees for determining the ratio between dry weight and fresh weight is important. In addition to the functions, a robust method for the disc sampling is proposed.