Dichrostachys Cinerea Research Articles

Influences of fallow age and season on the foraging behavior and diet selection pattern of goats (Capra hircus L.)

A study was undertaken to determine the foraging behavior and diet selection pattern of goats maintained on communal exclosures in relation to the influence of fallow age (years since effective protection initiated; <8 years vs. >12 years) and season (long rainy, dry, and short rainy seasons). The frequency of browsing was higher ( P < 0.05) in the exclosures fallowed for >12 years compared to those fallowed for <8 years and this frequency was also highest during the short rainy season. More ( P < 0.05) herbaceous bites were recorded in the <8 years fallow exclosures, compared to the >12 years fallow exclosures. Herbaceous species bites were maximized during the long rainy season whereas woody species bites were maximized during the dry season. The goats foraged upon 48 plant species of which 69% were woody species, 19% grasses, and the rest comprised of various forb species. The top species that significantly ( P < 0.05) contributed to the diet of goats were Acacia etbaica , Balanites aegyptica , Cadaba farinosa , Capparis tomentosa , Dichrostachys cinerea , and Ocimum forskolei . The goats targeted taller woody species than the average of the exclosures. Maurea angolensis , Jasminium abyssinicum , C. farinosa , and Ormocarpum pubescence were among the preferred species that appeared to be on the verge of disappearance in most of the exclosures investigated in this study and require immediate attention. Using goats to reduce the threat of potential bush infestation appears to be a viable option for managing and sustaining production from exclosures since the goats showed preference for D. cinerea , the species considered a prolific invader plant. There is, however, a need to conduct further research on the impacts of direct browsing by the goats and this should also entail the determination of optimum number of goats/unit area.

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%.

Chemical composition and in vitro ruminal fermentation of common tree forages in the semi-arid rangelands of Swaziland

Browse plants play an important role in providing feed for livestock in semi-arid rangelands of Africa. Chemical composition and in vitro ruminal fermentation of leaves collected from Acacia burkei, Acacia tortilis, Acacia nilotica, Dichrostachys cinerea and Ehretia obtusifolia in communal grazing lands in the lowveld of Swaziland is presented. Leaves were collected from trees located on two soil types ( i.e., lithosol and vertisol) in the communal land but it had no effect on the chemical composition of tree leaves. The NDFom and ADFom content were highest in D. cinerea and A. burkei and lowest in E. obtusifolia and A. nilotica. Crude protein (CP) contents ranged between 108 g/kg and 122 g/kg DM. D. cinerea had the highest Ca and Mg content, while A. tortilis had the lowest. There were marked variations in K level amongst browse species, with A. tortilis (9.1 g/kg DM) having the highest value. The P, Zn and Fe did not differ between browse species. Soil type and tree species interaction impacted in vitro fermentation parameters. Extent of fermentation, as measured by 48 h cumulative gas production, and organic matter degradability was highest in E. obtusifolia leaves and lowest in D. cinerea leaves within soil type. Fermentation efficiency, as measured by partitioning factors, was highest in A. nilotica leaves. Leaves of E. obtusifolia could be a valuable supplementary feedstuff for ruminant livestock due to its in vitro fermentation characteristics as well as low fibre and moderate CP levels.

English

Compounds of pharmacological interest (tannins) were isolated from Dichrostachys cinerea and assayed against Staphylococcus aureus, Shigella boydii, Shigella flexneri, Escherichia coli and Pseudomonas aeruginosa using the agar diffusion method. Tannins exhibited antibacterial activities against all the test microorganisms. Sh. flexneri was the most resistant to tannins isolated from the plant material followed by Sh. boydii, E. coli, Staph. aureus and P. aeruginosa respectively. Minimum inhibitory concentration of the tannins ranged between 4.0 and 5.5 mg/ml while the minimum bactericidal concentration ranged between 4.5 and 6.0 mg/ml.

Disturbance and the frequency of root suckering in an invasive savanna shrub, Dichrostachys cinerea

The ecology of clonal species has rarely been studied in savannas. Dichrostachys cinerea, a common invasive shrub in southern African savannas, forms root suckers. This paper examines the effect of disturbance type and frequency on this form of clonal spread. Small plants were excavated (n = 370) at 11 sites exposed to different fire frequencies and grazing intensities and classified were as either seedlings or root suckers. Most of the plants (55%) were found to be root suckers. There was no significant effect of disturbance type and frequency on 'seedling' establishment from seeds versus root suckers. Even when burnt annually, D. cinerea continued to form root suckers. The combination of establishment from seeds and spread by root suckers makes this species a formidable native invasive woody shrub.

Chemical composition and in vitro fermentation of tannin-rich tree fruits

Dry and mature tree fruits are a potential source of protein for goats in the semi-arid areas of southern Africa, but their chemical composition and feeding value is largely unknown. This study presents the chemical composition and in vitro fermentation of indehiscent whole fruits and separated seed and hull fractions from Acacia nilotica, Acacia erubescens, Acacia sieberiana, Acacia erioloba, Piliostigma thonningii and Dichrostachys cinerea trees. Results indicate that the N contents of whole fruits ranged between 13.5 g/kg DM ( A. nilotica) and 27.1 g/kg DM ( A. erubescens). Seeds had a higher N content than hulls for all tree species. A. nilotica, D. cinerea and P. thonningii fruits had high levels of extractable phenolics (758, 458 and 299 g/kg DM, respectively). Soluble phenolics (SPh) and ytterbium precipitable phenolics (YbPh) levels were negatively correlated to in vitro gas production but positively correlated to in vitro organic matter degradability (iOMD). Partition factors for whole fruits at 48 h ranged between 3.6 mg/ml for A. erioloba and 7.8 mg/ml for A. nilotica. Seeds of A. erioloba, A. erubescens and P. thonningii were consistently fermented more efficiently throughout the incubation period compared to their whole fruits or hulls. Estimating in vitro degradability of phenolic-rich substrates through filtration procedures can give erroneous results due to the loss of soluble phenolics, which are not necessarily degradable. The feeding value of fruits from D. cinerea and A. nilotica tree species may be reduced due to the presence of high levels of phenolics.

The relative importance of different regeneration mechanisms in a selectively cut savanna-woodland in Burkina Faso, West Africa

Savanna plant species are capable of regenerating both sexually and asexually. The importance of each regeneration mechanism depends on the species, the type and the intensity of disturbance. This paper describes the relative importance of sexual and asexual regeneration for the restoration of a selectively cut savanna woodland in Burkina Faso. Plantlets regenerated sexually or asexually were determined by excavating the below ground system and assessing basal and aerial sprouts within 144 quadrats along transects in 2, 5, 10 year-cut and control plots. The result shows that seedling sprouts were predominant (83%) compared to root sucker (4%), coppice (5%), water sprout (2%) and layering (less than 1%). True seedlings constituted a minor component (5%) of the plantlet population. A total of 54 woody species was found in the plantlet population with 52 presenting seedling sprouts. Twelve species were found regenerating from both seeds and root buds; of which Dichrostachys cinerea, Pteleopsis suberosa and Detarium microcarpum had the highest number of plantlets. Feretia apodanthera was the only layering species encountered in the sampled area. Coppices, root suckers and water sprouts showed higher height and bigger collar diameter compared to seedling sprouts and true seedlings. It can be concluded that sexual reproduction is the dominant mechanism of seedling recruitment in this disturbed savanna-woodland, and that its success relies on the ability of plantlets of seed origin to resprout abundantly.

Disturbance and the frequency of root suckering in an invasive savanna shrub, Dichrostachys cinerea

The ecology of clonal species has rarely been studied in savannas. Dichrostachys cinerea, a common invasive shrub in southern African savannas, forms root suckers. This paper examines the effect of disturbance type and frequency on this form of clonal spread. Small plants were excavated (n = 370) at 11 sites exposed to different fire frequencies and grazing intensities and classified were as either seedlings or root suckers. Most of the plants (55%) were found to be root suckers. There was no significant effect of disturbance type and frequency on ‘seedling' establishment from seeds versus root suckers. Even when burnt annually, D. cinerea continued to form root suckers. The combination of establishment from seeds and spread by root suckers makes this species a formidable native invasive woody shrub.Keywords: bush encroachment, clonal, fire, savannaAfrican Journal of Range & Forage Science 2007, 24(2): 73–76

The effectiveness of adapted rumen fluid versus PEG to ferment tannin-containing substrates in vitro

This study investigated the potential of the goat's ruminal adaptation to reduce the negative effect of tannins on in vitro fermentation. Rumen fluid was obtained from goats fed a mixture of tannin-containing tree fruits (adapted rumen fluid) or tannin-free commercial protein supplements (unadapted rumen fluid) for 85 days. Dry, mature fruits of Acacia nilotica, Acacia erubescens, Acacia erioloba, Dichrostachys cinerea and Piliostigma thonningii were used as substrates for the in vitro fermentation. The effectiveness of adapted rumen fluid to ferment tannin-containing substrates was compared to the extent of fermentation when tannins were inactivated with polyethylene glycol (PEG), a known tannin-binding agent. Adapted rumen fluid (P<0.05) increased gas production from all five substrates between 15.8% and 73.7%. In A. nilotica, D. cinerea and P. thonningii, this increase was less than that obtained through PEG treatment. When PEG was added to adapted rumen fluid a further improvement in extent of fermentation was observed in four out of the five fruit samples. The largest PEG effect when incubated with adapted rumen fluid was observed in A. nilotica (43.1%) and D. cinerea (42.9%) fruits. It is concluded that some tannin-rich feedstuffs may still benefit from treatment even when these are offered to adapted animals.

Comparative resprouting response of Savanna woody plant species following harvesting: the value of persistence

Understanding the relative ability of favoured fuelwood species to resprout following harvesting is integral to designing strategies for sustainable woodland resource utilisation. Harvester preference for particular woody plant species and plant size was examined in a formerly protected area, severely harvested over a short period of time. The resprouting response of harvested plants was measured five months after harvesting, towards the end of the wet season. Although a large proportion of stems of the dominant species ( Terminalia sericea and Dichrostachys cinerea) had been harvested, certain less common species were particularly targeted (e.g., Pterocarpus rotundifolius and Peltophorum africanum). Harvested plants were mostly larger than 4 cm in stem diameter. Almost all harvested plants of all species resprouted. Species differed in whether resprout growth was channelled into many small resprout shoots or fewer large shoots. The species most highly favoured by harvesters produced relatively large resprout shoots. Plant stem diameter was the most important determinant of resprout output, with both shoot number and their composite diameter increasing with increasing plant size. Cut height, although having no significant effect on resprout output, influenced the location of resprouting, with taller stumps having a higher proportion of resprout shoots originating from the stem than from the root crown. For all species, approximately a third of the resprout shoots of harvested plants died during the five months following harvesting. Shoots originating from the stem had a higher dieback than those growing from the root crown. Resprout biomass production over the five month period was considerable, amounting to 989 kg ha −1 (wet mass). An abundance of seedlings of the most common species may be a consequence of woodland thinning through harvesting.

Adaptation of five co-occurring tree and shrub species to water stress and its implication in restoration of degraded lands

The open savanna woodlands in Ethiopia, distributed over very large areas of the Rift valley in southern and eastern parts of the country, have suffered from deforestation due to excessive tree cutting and overgrazing. Previous reforestation programs attempting to counteract the effects of deforestation have failed mainly due to lack of knowledge on site–species matching. This research was set out to asses the effect of disturbance on water status of both plants and their respective sites, explain differences among species in survival and distribution and determine their relative suitability for restoration of degraded lands. Plant water potentials of five common co-occurring species were measured in the field at midday and predawn in the dry season. The water potential values of the species at different sites of biophysical settings and diurnal differences revealed significant difference among the species. The differences in degradation status in terms of tree density, ground cover and overgrazing did not show a clear pattern in water potential changes among the species and sites. Acacia tortilis, Balanites aegyptiaca and Dichrostachys cinerea, which exhibited low midday (−3.05 to −4.85 MPa), predawn (−1.98 to −3 MPa) and wide diurnal (1.16–2.25 MPa) plant water potential ranges had wider capacities to withstand water changes and, hence, can be considered as suitable candidates for reforestation in drought prone areas. Though Acacia senegal and Acacia seyal with highest midday (−1.55 to −2.68 MPa), predawn (−0.83 to −2.09 MPa) and narrow diurnal (0.32–1.1 MPa) plant water potential ranges could be categorized as drought avoider (sensitive) species, they have a combination of mechanisms to avoid drought and grow in dry areas. Particularly, their better growth performances during moist years could make them suitable candidates in areas of non-limiting water conditions. Both exotic and indigenous species, with similar water potentials to those found in the respective sites, may have a better chance of survival in those sites and in areas that have similar ecological and climatological conditions to the ones the current research covered.

Vegetation and habitat types of the Umkhanyakude Node

The aim of the study was to identify and classify the woodlands, bushland and grasslands of the Umkhanyakude Integrated Sustainable Rural Development Node (also known as Maputaland) into homogenous management units to assist with the natural resource audit and monitoring program initiated by the Department of Agriculture. The Node is situated in KwaZulu-Natal Province at the extreme northern border between South Africa and Mozambique. Two hundred and twenty-five surveys were conducted during March–July 2002 within 400 random plots created within ARCVIEW 3.2. Ecological data were analysed using multivariate ordination and classification techniques. Four broad plant communities within two geographically separated vegetation types were described. The Coastal Sandveld occurs on the coastal plain on recent arenaceous sediments. The Clay Thornveld occurs in the interior and is associated with a variety of terrain types and geological formations but predominantly rhyolite, basalt, shale and mudstones. Communities within the major vegetation types were differentiated based on climate (temperature and precipitation differences associated with differences in elevation and topography) and anthropogenic disturbances such as old fields, settlements and deforested plantations. The two major plant communities were subdivided into two sub-communities that can be used as management units since they have approximately the same physiognomy, grass composition and habitat characteristics. The four broad management units are the Acacia nilotica – Acacia karroo – Dichrostachys cinerea Community (Clay Thornveld); the Cissus rotundifolia – Enteropogon monostachyos ( Valley Bushveld) Community; the Panicum maximum – Brachylaena discolor Community (Coastal Bushveld) and the Themeda triandra – Urelytrum agropyroides Community (Grass – Palmveld).

Dichrostachys cinerea and Acacia nilotica fruits as dry season feed supplements for goats in a semi-arid environment: Summary of a DFID funded project in Zimbabwe

Indehiscent fruits of six tree species, common in Matabeleland were examined in in vitro and in vivo trials. The results for two of them, Acacia nilotica and Dichrostachys cinerea are presented here. Acacia nilotica contained more total phenolics than D. cinerea, but less nitrogen (N) and fibre (ADF and NDF). After 48 h incubation, in vitro OMD of both species was increased by PEG and NaOH or wood ash treatment, except when NaOH or wood ash were used in combination with PEG with D. cinerea fruits. DM intake, DMD were lowest and N-retention negative in goats fed A. nilotica as supplement. However when fed a supplement of D. cinerea, untreated or treated with PEG or NaOH, digestibility and N-retention were highest, and similar to a commercial goat meal, with the untreated fruit. In a trial in which milking does were supplemented with D. cinerea fruits, for 65 before and 65 days after kidding, kid birthweight and weaning weight were increased by supplementation. Deaths of twin-born kids were lowest in the supplemented but unmilked group. Supplementation with D. cinerea fruit resulted in improved goat performance. The only treatment applied of practical significance, wood ash, is currently being tested in an in vivo study. More research is required on detoxification of tannins, especially with A. nilotica.

The effect of catena position and stump characteristics on the coppice response of three savannah fuelwood species

Fuelwood is still the primary energy source for rural households across the savannah biome of Africa. Coppice growth is an important species-specific trait that strongly influences fuelwood production and regeneration, and yet coppice growth patterns are poorly understood in African savannahs. It is therefore vital that factors affecting coppice growth of species, such as environment conditions and harvesting technique, be better understood in order to develop models for sustainable fuelwood use. This study investigated coppice growth and resource allocation strategies in relation to (1) position along the landscape catena and (2) harvesting technique, for three savannah fuelwood tree species: Dichrostachys cinerea, Albizia harveyi and Combretum collinum. The study was conducted in a dystrophic semi-arid savannah in the far north-east of South Africa. A total of 1146 harvested stumps were sampled in topland and bottomland sites in three locations around a rural village. Stump characteristics (diameter and height) and coppice shoot variables (number of shoots, length and diameter of each shoot, length of longest shoot, and diameter of fattest shoot) were measured for each stump. Three soil samples were taken in each site for physical and chemical analysis. No statistically significant differences were found in soil variables between topland and bottomland sites, probably due to low sample size. Coppice resource allocation strategies varied between species. D. cinerea exhibited a ‘quantity-driven’ strategy, with the production of large numbers of relatively small coppice shoots with high length:diameter ratio (shoot taper function). C. collinum exhibited a ‘quality-driven’ strategy, characterized by the production of a relatively low number of larger coppice shoots. Coppice growth variables for A. harveyi were intermediate between those of the other two species, suggesting a strategy where allocation of resources to the number and growth of shoots is more balanced. However, allocation of resources relative to the size of the cut stem, indexed by total shoot basal area:stump basal area ratio, did not differ significantly between species. Coppice growth was strongly favoured in bottomland sites for D. cinerea, and to a lesser degree, C. collinum. Catenal position had a negligible influence on coppice growth of A. harveyi. Number of shoots produced increased with cutting height for all three species. For all three species the number of shoots increased with stump diameter, and mean shoot size also increased with stump size for D. cinerea. There was a significant negative relationship between stump diameter and total shoot basal area:stump basal area ratio for A. harveyi and C. collinum. A framework for optimizing different coppice growth variables according to species, catenal position and harvesting technique is given.

Heavy Metal Content of Some Savanna Plant Species in Relation to Air Pollution

The Sb, Cr, Ni, As, Pb and Cu contents in leaves of Dichrostachys cinerea, Ficus platyphylla, Isoberlinia doka and Securiniga virosa growing around the Kaduna Refinery and Petrochemical Complex (KRPC) were compared with heavy metal contents of the same species growing in a relatively “clean” environment, during the rainy and dry seasons of 2001.

&lt;b&gt;Chemical constituents of the ethyl acetate extracts of the stem bark and fruits of &lt;i&gt;Dichrostachys cinerea&lt;/i&gt; and the roots of &lt;i&gt;Parkia bicolor&lt;/i&gt;&lt;/b&gt;

The antibacterial activities of ethyl acetate, methanol and aqueous extracts of the stem bark of Dichrostachys cinerea and the roots of Parkia bicolor have been evaluated. Ethyl acetate extracts have been investigated, studies that led to a series of known compounds, amongst which many are reported here for the very first time from both the species. KEY WORDS: Dichrostachys cinerea, Parkia bicolor, Chemical constituents, Antibacterial activity Bull. Chem. Soc. Ethiop. 2004 , 18(1), 111-115.

Tanniniferous Dichrostachys cinerea fruits do not require detoxification for goat nutrition: in sacco and in vivo evaluations

This study investigated the potential of Dichrostachys cinerea fruits as a protein supplement in semi-arid areas of Zimbabwe. The tanniniferous fruits were treated with aqueous solutions of polyethylene glycol (PEG) or sodium hydroxide (NaOH). Both treatments increased the soluble fraction, rate of degradation and effective degradability (ED) of nitrogen (N) in sacco. The PEG effects were higher than the NaOH effects (e.g. a 25% vs. 6% increase in effective N degradabilities, respectively). Five treatments were evaluated in a N-balance trial using Matebele goats: ground, PEG- or NaOH-treated D. cinerea fruits, a commercial protein supplement (CPS) and no supplement. Animals offered ground fruits or CPS retained most N (3.7 or 4.1 g N/day, respectively), while those offered NaOH- or PEG-treated fruits retained significantly less N (2.7 or 1.0 g/day, respectively). Unsupplemented animals were in negative N balance (−2.4 g/day). PEG treatment deactivated the tannins more than the NaOH treatment. PEG treatment resulted in excessive protein degradation in the rumen leading to high urine N loss. It is concluded that the D. cinerea fruits were beneficial for goat N-nutrition and that the tannins did not require inactivation. D. cinerea fruits can, therefore, replace the expensive commercial protein supplement. It is also suggested that the collection and grinding of fruits could be used as a management tool to control bush encroachment.

Termitaria as browsing hotspots for African megaherbivores in miombo woodland

Thirteen termite mounds and 13 similar-sized control plots were surveyed in central Zimbabwe in order to study large mammalian browsing and vegetation characteristics. The mounds supported almost twice as many tree species as the control plots and the woody vegetation was denser on mounds compared with the woodland plots. Species of woody plants were recorded along with the percentage of branches browsed (cumulative browsing score) by black rhino, Diceros bicornis, elephant, Loxodonta africana and other browsers combined. In addition we measured how the cumulative browsing score on three woody plant species, Acacia nilotica, Colophospermum mopane and Dichrostachys cinerea, which were common both on and off mounds, was related to the distance from mound centre. Both black rhino and elephant cumulative browsing scores were significantly higher on the mound plants compared with the woodland plots. Cumulative browsing score was negatively related to distance from the mound centre for Dichrostachys cinerea, Colophospermum mopane and Acacia nilotica. We propose that termite mound construction in miombo woodland contributes to sustaining populations of megaherbivores and perhaps some woody species in these areas.

Post-fallow decomposition of woody roots in the West African savanna

Fallowing is a common practice for the management of soil fertility in low-input cropping systems of the West-African savanna, but has been threatened by the growing need for land in the sub-region for the past few decades. Proposals for alternatives to traditional fallowing must rely on a proper understanding of the soil biochemical dynamics occurring after fallow conversion to cropping. Two mesh-bag experiments were thus conducted in two sites (dry and sub-humid tropical climates) in Senegal to assess the role of site-related factors (climate, macrofaunal activity) and root-related factors (tree species, root diameter) on the decomposition of tree roots after clearing of fallow vegetation as measured from mass loss. Root decomposition was fastest – and even faster than predicted from a global model – in the wettest site (first order disappearance rate: 1.00 y−1 and 1.46–1.49 y−1 under dry and sub-humid conditions, respectively). Macrofauna accounted for half of root mass loss in the sub-humid site, with biomass removal occurring even during the dry season. Fastest disappearance for roots with ∅<5 mm occurred for Dichrostachys cinerea, and Combretum glutinosum. The influence of root chemical composition on decomposition patterns among tree species and root diameter classes was not clear, with effects of cell wall composition and nutrient content changing throughout the incubation period. Fast disappearance of dead roots suggests that cropping practices that allow conservation of live stumps, such as no-tillage and direct sowing, be promoted wherever possible to ensure soil conservation. It also suggests the possible management of tree species composition and, to a much lesser extent, of macrofauna during the fallow period to control root decomposition patterns and related nutrient transfers to crop biomass after fallow conversion.

Effects of fire and fire intensity on the germination and establishment of Acacia karroo, Acacia nilotica, Acacia luederitzii and Dichrostachys cinerea in the field

BackgroundWhile fire has been used in some instances to control the increase of woody plants, it has also been reported that fire may cause an increase in certain fire-tolerant Acacia tree species. This study investigated germination of Acacia karroo, A. luederitzii and Dichrostachys cinerea, thought to be increasing in density, as well as the historically successful encroaching woody species, A. nilotica, in savanna grassland, Hluhluwe-iMfolozi Park, South Africa. A. karroo is thought to be replacing A. nilotica as the dominant microphyllous species in the park. We tested the hypothesis that observed increases in certain woody plants in a savanna were related to seed germination and seedling establishment. Germination is compared among species for burnt and unburnt seeds on burnt and unburnt plots at three different locations for both hot and cool fires.ResultsAcacia karroo showed higher germination (A. karroo 5.1%, A. nilotica 1.5% and A. luederitzii 5.0%) levels and better establishment (A. karroo 4.9%, A. nilotica 0.4% and A. luederitzii 0.4%). Seeds of the shrub Dichrostachys cinerea did not germinate in the field after fire and it is thought that some other germination cue is needed. On average, burning of A. karroo, A. nilotica and A. luederitzii seeds did not affect germination. There was a significant difference in the germination of burnt seeds on burnt sites (4.5%) and burnt seeds on unburnt plots (2.5%). Similarly, unburnt seeds on unburnt sites germinated better (4.9%) than unburnt seeds on burnt sites (2.8%).ConclusionWe conclude that a combination of factors may be responsible for the success of A. karroo and that fires may not be hot enough or may occur at the wrong time of year to control A. karroo establishment in HiP. Although germination and establishment of A. karroo was higher than for A. nilotica a competitive advantage after fire could not be shown.