Diet of the brown hare (Lepus europaeus) and food availability in northern Patagonia (Mendoza, Argentina)

The brown hare, a Leporid widespread in the world, is now dispersed across Argentina after its introduction at the end of the 19th century. Studies on hare feeding ecology are important to evaluate a potential competition with domestic and native wild herbivores. This study analyses the brown hare diet in relation to food availability, and dietary overlaps with several herbivores in northern Patagonia. Food availability was estimated by point-quadrat transects, and hare diet by microhistological analysis of faeces, carried out in five habitats in five seasonal samplings. Significant differences were detected by Kruskall–Wallis ANOVA with multiple comparisons by Tukey test. Feeding selection was detected by χ² test, and dietary preferences by the confidence interval of Bailey. Grasses and chamaephytes were the most available plant categories, with Stipa, Panicum and Acantholippia as main species. Grasses and phanerophytes were the main dietary categories, including Poa, Panicum, Bromus, Adesmia and Prosopidastrum. The phanerophytes Prosopidastrum and Ephedra were more eaten in winter, when the main food item (Poa) presented lower availability. A higher dietary proportion of the chamaephyte Acantholippia occurred in rocky habitats, where the coarse dominant grasses were always avoided. Hares shared most food items with several wild and domestic herbivores in northern Patagonia. The lack of preference for forbs differentiates brown hares from other herbivores. However, hares exhibited important dietary similarities with plain and mountain vizcachas, goats and horses, and an interspecific competition for food is highly probable.     

Trophic interactions between two medium-sized mammals: the case of the native Dolichotis patagonum and the exotic Lepus europaeus in a hyper-arid ecosystem

As medium-sized herbivores, the exotic Lepus europaeus (European hare) and the native Dolichotis patagonum (mara) have been considered ecological equivalents. These species coexist in Ischigualasto Provincial Park, a hyper-arid ecosystem with scarce food resources. Our objective was to evaluate diet composition, relationship between diets and food availability, and trophic relationships between both herbivores. Collection of feces and vegetation sampling were made in the Mesquite woodland community. Diet composition was analyzed by microhistological analysis of feces. In both seasons, shrub species represented the most abundant cover type in the area, and annual forbs and grasses appeared in the wet season. Herbivores showed similar dietary ecology: shrubs were the main food items along the year, showing a higher plasticity compared to their diets in other ecosystems, where they selected mostly grasses. The mara selected shrubs such as Atriplex sp. and Prosopis torquata, whereas the European hare selected Cyclolepis genistoides, Atriplex sp., and Bulnesia retama. During the wet season, both herbivores supplemented their diets with grasses and annual forbs. In the dry season, there was increased consumption of cacti, such as Tephrocactus sp. The mara and the European hare are likely close ecological equivalents, in terms of dietary similarity, and they showed strong dietary overlap across the dry season (over 60 %). Thus, we can assume the existence of a potential trophic competition between mara and European hare, especially during the season when food resources are scarce. These results can be important for the management of drylands in South America, where populations of threatened herbivorous species, such as the mara, coexist with exotic animals, sharing spatial and trophic resources even in protected areas.     

Diet selection by European hares (Lepus europaeus) in the alpine zone of the Snowy Mountains, Australia

European hares (Lepus europaeus) are grazers and open grassland specialists that are replaced in mountain areas of their natural range in the northern hemisphere by browsing/intermediate feeding mountain hares (Lepus timidus), but in their introduced range in the southern hemisphere, occupy the alpine zone. We used micro-histological identification of plant fragments and germination of seeds in faecal pellets of L. europaeus from the Snowy Mountains, Australia, to determine diet. We asked whether diet shifted and/or diet breadth expanded in response to seasonally reduced food availability, particularly during winter. If so, did the constraints of food availability in the alpine zone lead to the diet mirroring that of L. timidus in its native alpine habitat. The diet of L. europaeus was dominated by grasses, herbs and shrubs. The main diet items in summer were grasses (70 %) and herbs (28 %). Grasses declined in the diet between summer and autumn when herbs increased to co-dominance, with a further change after establishment of the winter snowpack to a greater preponderance of shrubs (43 % compared with a maximum of 3 % in snow-free months). L. europaeus selected a wider range of plants in winter (59 species compared with 39 in summer) and diet was significantly more variable in winter than in autumn or summer (and in autumn than summer). We concluded that the persistence of L. europaeus in alpine areas of the southern hemisphere is testament to their ability to expand their dietary breadth to occupy mountain climatic zones normally occupied by L. timidus.     

Food selection by the guanaco (Lama guanicoe) along an altitudinal gradient in the Southern Andean Precordillera (Argentina)

Wild ungulates like the guanaco are exposed to important changes in climate and plant diversity along altitudinal gradients in the Andes Mountains, such as in the Southern Andean Precordillera where three phytogeographic provinces are present in altitudinal belts. The guanaco’s diet and food availability were seasonally analyzed using microhistological analysis and point-quadrat transects at six sampling sites, representative of the phytogeographic belts along the altitudinal gradient. Plant cover and diversity decreased with growing altitude. Richness of plant species was poorer at the summit than in the lower altitudes, whereas the proportion of species eaten by guanacos increased with altitude. The diet included 77 species. Grasses were preferred and shrubs were avoided all year round. The grass Poa spp. occupied more than 50 % of the diet at all altitudes. Grasses were the main dietary item even at low altitudes, where shrubs constituted the main food available. Decreasing generalism with descending phytogeographic belts agrees with the prediction for altitudinal gradients. The increase of diversity in the diet during the winter decline of plant cover at high and middle altitudes follows that expected from the optimal foraging theory. The winter decline of vegetation and the dietary shift from grazing to browsing proved to be stronger as altitude increases and the climate become more rigorous. Plant species richness, food scarcity, and climate severity are relevant variables to explain altitudinal and seasonal changes in the diet of adaptive ungulates in mountain environments, such as the guanaco in the Southern Andean Precordillera.     

Grassland composition,structure, and diversity patterns along major environmental gradients in the Central Tien Shan

What species and traits signal vegetation types along prominent environmental gradients in the Central Tien Shan and what are the corresponding diversity patterns? Vegetation was sampled at 41 sites throughout the Kyrgyz Republic using quadrats stratified throughout a 1,000-m² sample area. Relationships among major environmental gradients, vegetation structure, and species composition were explored with nonmetric multidimensional scaling. Species distributions were examined to characterize phytogeographic patterns. Seven vegetation types ranging from desert grassland to meadow steppe were identified with cluster analysis, ordered primarily along elevation/mean annual temperature gradients. Four arid grassland types were distinguished, ranging mainly from 900 to 1,700 m elevation, and characterized by co-dominance of grasses and forbs with secondary dominance by shrubs. Annual and biennial forbs equaled perennial forbs in total importance. Grasses include C3 and C4 species. Three montane grassland types were recognized and characterized by co-dominance of perennial C3 grasses and forbs. Transition to montane steppe occurred from 1,500 to 1,900 m and is correlated with absence of C4 grasses and dominance of Festuca valesiaca. Highest diversity was found at intermediate elevations, from 1,800 to 2,600 m, in meadow steppe habitats. Forty-six percent of 580 identified species are Middle Asian endemics and remaining species primarily have distributions including Eastern Europe, the Caucasus, and western Siberia. Although grassland degradation from overgrazing has been chronic throughout the region, grasslands are widespread throughout the Kyrgyz Republic and many, particularly mid-elevation meadow steppes, retain high levels of native species diversity.     

Effects of experimental rainfall manipulations on Chihuahuan Desert grassland and shrubland plant communities

Aridland ecosystems are predicted to be responsive to both increases and decreases in precipitation. In addition, chronic droughts may contribute to encroachment of native C₃ shrubs into C₄-dominated grasslands. We conducted a long-term rainfall manipulation experiment in native grassland, shrubland and the grass–shrub ecotone in the northern Chihuahuan Desert, USA. We evaluated the effects of 5 years of experimental drought and 4 years of water addition on plant community structure and dynamics. We assessed the effects of altered rainfall regimes on the abundance of dominant species as well as on species richness and subdominant grasses, forbs and shrubs. Nonmetric multidimensional scaling and MANOVA were used to quantify changes in species composition in response to chronic addition or reduction of rainfall. We found that drought consistently and strongly decreased cover of Bouteloua eriopoda, the dominant C₄ grass in this system, whereas water addition slightly increased cover, with little variation between years. In contrast, neither chronic drought nor increased rainfall had consistent effects on the cover of Larrea tridentata, the dominant C₃ shrub. Species richness declined in shrub-dominated vegetation in response to drought whereas richness increased or was unaffected by water addition or drought in mixed- and grass-dominated vegetation. Cover of subdominant shrubs, grasses and forbs changed significantly over time, primarily in response to interannual rainfall variability more so than to our experimental rainfall treatments. Nevertheless, drought and water addition shifted the species composition of plant communities in all three vegetation types. Overall, we found that B. eriopoda responded strongly to drought and less so to irrigation, whereas L. tridentata showed limited response to either treatment. The strong decline in grass cover and the resistance of shrub cover to rainfall reduction suggest that chronic drought may be a key factor promoting shrub dominance during encroachment into desert grassland.     

The dietary overlap between red kangaroos (Macropus rufus) and sheep (Ovis aries) in the arid rangelands of Australia

Abstract The interaction between red kangaroos and sheep in the more arid areas of Australia was examined by means of a large-scale manipulative experiment. The diets of red kangaroos and sheep grazing together and separately in large paddocks were studied to assess whether competition for food might influence diet selection in these species. Diets and the amount of intra- and interspecific dietary overlap varied in accordance with pasture conditions. At pasture biomasses ranging from 50 to 200 g m^?2 (dry weight [wt]), the diets of red kangaroos and sheep overlapped by 58–73%, with forbs and grasses being the major items in the diets of both species. The diets of both sheep and red kangaroos under different experimental regimes were similar. In dry times (pasture biomass 40–50 g m^?2 (dry wt) more shrubs were eaten by both species and the amount of dietary overlap tended to be lower (52–66%). The diets of kangaroos were similar between paddocks. However, in paddocks containing both species sheep consumed proportionately more chenopodaceous shrubs and fewer grasses than those in ‘kangaroo-free’ paddocks.     

沿干旱梯度小叶锦鸡儿灌丛化对草本植物叶片矿质元素浓度及地上生物量累积的影响

草原灌丛化通过改变物种之间的相互作用深刻影响着群落的结构和功能。然而,当前有关灌木如何影响不同功能群草本植物对矿质元素吸收和累积的研究仍明显不足。在内蒙古草原沿干旱梯度选取了4个研究地点,对比分析了小叶锦鸡儿(Caragana microphylla)灌丛斑块内和斑块外群落中禾草和非禾草功能群植物叶中矿质元素浓度以及地上生物量生产的差异,旨在阐明干旱和灌木对群落草本植物叶元素累积的影响,揭示灌草间相互作用的元素利用特征及其随干旱梯度的变化。结果显示：1)随干旱加剧,灌丛斑块内的非禾草功能群植物地上生物量保持恒定,但叶中的K、Ca、Mg、Fe、Mn和Cu元素浓度显著增加(P<0.05)。该结果表明群落中的非禾草功能群植物通过提高叶中的矿质元素水平来抵御和适应干旱胁迫。2)随干旱加剧,灌丛对非禾草功能群植物地上生物量,叶中Ca、Fe、Cu和Zn,禾草功能群植物叶中的P的累积影响从负(RII<0)或中性(RII=0)转变为正效应(RII>0)。该结果与胁迫梯度假说相符,表明灌木对草本植物的促进效应随干旱胁迫加剧而增加。3)灌丛的“沃岛”效应是驱动灌木对草本植物元素累积正效应...     

Ecological attributes of a native and exotic emergent subtropical marsh community in lake okeechobee, Florida (USA)

Ecological attributes of native Eleocharis cellulosa and exotic-invasive Panicum repens communities were compared in the western littoral marsh of Lake Okeechobee, USA. Water quality, periphyton and macroinvertebrates were monitored for 2 years. Fish and zooplankton were monitored during the second year. Mean dissolved oxygen, pH and Secchi transparency were significantly higher in Eleocharis while total phosphorus was marginally higher in Panicum. Periphyton biomass was higher in Panicum but biovolumes were higher in Eleocharis. There were clear differences in the within-habitat periphyton assemblages, less difference in the among-habitat assemblages and moderate to clear differences in periphyton over time in both habitats. Both habitats were dominated by small omnivorous fish. Habitat and date were the most influential factors in differences among both macroinvertebrates and zooplankton, although these differences were marginal to moderate in both cases. Macroinvertebrate densities were higher in Eleocharis while zooplankton densities were higher in Panicum. These data suggest that contrary to the paradigm that Panicum is undesirable as habitat, sparse (<1,000 stems m^?2) Panicum in close proximity to Eleocharis may exhibit a similar suite of ecological attributes. Both habitats also appear to contain similar food webs to nearby Everglades marsh communities.     

Tree-shrub interactions in a subtropical savanna parkland: competition or facilitation?

Abstract. Prosopis glandulosa var. glandulosa has played a central role in the encroachment of woody plants in southern Texas, grasslands and savannas by acting as a nurse plant for various shrubs that establish in its understory. To test for continued facilitation of established understory shrubs by Prosopis and to determine if established shrubs compete with the Prosopis nucleus, selective removal experiments were conducted and monitored over a 2–5 yr period. Short-term (1–3 days) and long-term (2 yr) growth and physiological activities (midday net photosynthesis and leaf/shoot water potential) of two common understory shrubs, Zanthoxylum fagara and Berberis trifoliolata, growing with Prosopis, were generally comparable to those of individuals occurring in clusters where Prosopis was removed. Shrubs growing with an intact Prosopis occasionally showed significantly higher leaf-[N] and pre-dawn water potentials than those in clusters lacking a live Prosopis, especially under drought conditions; however, these differences did not translate into greater midday leaf gas exchange or shoot growth. By comparison, removal of understory shrubs elicited large increases in Prosopis net photosynthesis, annual trunk growth in each of the 5 yr monitored, and seed pod production in three of the four years monitored. Seven of 26 Prosopis plants in experimental clusters with an intact understory died over a 5-yr period, compared to only two of the 26 plants in clusters with the cleared understory. Results indicate that (1) the founding overstory Prosopis plant may continue to facilitate understory shrubs following their establishment, but these beneficial effects appear to be small and transitory, and (2) the understory shrubs have a pronounced negative effect on Prosopis, such that competition between overstory and understory woody plants is strongly asymmetrical. These findings suggest that understory shrubs will likely persist despite changes in microclimate and soils (potentially) that occur after the Prosopis plant, which facilitated their ingress or establishment, has died. Soil resource depletion by shallow-rooted understory shrubs appears to be a primary factor contributing to the demise of the deeply rooted, overstory Prosopis plants, especially on upland sites with duplex soils where below-ground competition is accentuated.     

The impact of herbivore exclusion on forb diversity: Comparing species and functional responses during a drought

Rainfall and herbivory shape savannah herbaceous communities, but these disturbances are being altered globally. To assess potential consequences of such alterations, we evaluated herbivore effects on species and functional diversity during an episodic drought in a sodic savannah using data collected from long-term herbivore exclosures in the Kruger National Park, South Africa. Herbaceous life forms are rarely acknowledged as distinct functional entities. Moreover, the functional ecology of forbs remains elusive. Here, we present disturbances–responses by forbs separately from grasses. We hypothesised that combinations of intense utilisation and drought would be associated with low diversity and high dominance at species and functional levels for both life forms. Contrary to our hypothesis, low forb and grass diversity was associated with long-term herbivore exclusion, which exceeded expected undesirable effects of intense utilisation and drought. Grasses responded less sensitively, suggesting that forbs respond dynamically to changes in herbivore assemblage when these alterations are combined with drought. Consistent with patterns in savannah systems, forbs contributed significantly to species and functional trait diversity. High forb diversity is suggested to enhance resilience of this nutrient-rich ecosystem against declines in its functioning when subjected to drought and alterations in herbivory.     

“Seeds” of wild grasses: A major food of Southwestern Indians

A search of the ethnobotanical literature revealed wild grasses to be a major food of Southwestern Indians. Oryzopsis, Sporobolusand Panicumwere shown to be especially important throughout the Southwest, though a large number of other genera were of local importance. Reasons for the preference of some species over others are discussed. The proportion of annual and perennial species used as food is equivalent to the proportions of annuals and perennials in the grass flora of the region.     

Diet overlap between small ruminants and the European hare in a Mediterranean shrubland

Seasonal diets of goats, sheep and European hares (Lepus europaeus) were examined using microhistological analysis of feces collected when these herbivores grazed together in a typical Mediterranean shrubland. Approximately half of the total diet content of goats was shrubs (mainly kermes oak, Quercus coccifera), while that of hares was grasses (mostly brush grass, Chrysopogon gryllus). Sheep had a more balanced diet consisting mainly of grasses, forbs, and shrubs. Dietary overlap between goats and sheep was high throughout the year. In contrast, there was very low dietary overlap between small ruminants and hares. Dietary diversity was high in spring and low in winter across all species, with sheep in general displaying higher dietary diversity across all seasons than goats and hares. Goats had intermediate and hares had low dietary diversity across all seasons. Communal grazing by small ruminants and hares ensures that there is a more uniform use of the available forage resources than if a single herbivore is left to graze an area.     

黑麂食物组成及其季节变化

2002年12月至2003年11月在浙江省九龙山和古田山自然保护区,分季节采集黑麂 (Muntiacus crinifrons)粪便,采用粪便显微组织学分析方法为主,辅以野外观察,对其食性进行研究。结果表明 :黑麂食物包括29科43种(属)植物。食物中的植物类型包括乔木、灌木、藤本、非禾草类草本和禾草类草本五种类型;灌木是黑麂全年的主要食物,它在食物组成所占的比例为55.4%;三尖杉 (Cephalotaxus fortunei)、光叶菝葜(Smilax glabra)、矩圆叶鼠刺(Itea chinensis var. oblonga)、南五味子(Kadsura longipedunculata)和络石(Trachelospermum jasminoides)为黑麂四季都取食且在食物组成中所占比例较高的植物,分别为 17%、16.5%、9%、8.7%和 4.3%,是黑麂取食的主要食物。方差分析表明 :黑麂的主要食物及其主要种类都存在季节变化。夏秋季节,乔木植物在黑麂食物组成的比例低于冬春季节 ,而藤本植物和草本植物则相反,灌木植物变化较小;黑麂取食的五种主要食物中,其中三尖杉和光叶菝葜季节变化极显著,在冬季,三尖杉和光叶菝葜在食物组成比例中最高,达到 21.7%和 24 .3%;在夏季,它们在食物组成比例中下降到最低点,分别是 11.3%和 11.6%,但相对密度(RD)值仍保持最高序位 ;矩圆叶鼠刺和南五味子变化较平缓 ,基本变化趋势相同:冬春季节比例较高,夏秋季节比例有所下降;络石季节变化不明显;由于黑麂的食物组成中禾草类占的比例很小,说明黑麂更接近嫩食者     

Spatial organization and monogamy in the mara Dolichotis patagonum

Maras, Dolichotis patagonum , were observed and radio-tracked in Argentina. They travelled as monogamous pairs that bred either alone at solitary burrows or communally at settlements where up to 29 pairs shared warrens.
Members of a mara settlement grazed within 2.5 km of the communal warrens, using intensively about 1 ha per day, within drifting daily ranges of 11 ha, seasonal ranges of 98 ha and annual ranges of 193 ha.
Their home ranges drifted continuously. Consequently, the long-term movements of neighbouring pairs overlapped substantially, but at any given moment they were territorially spaced.
Monogamous, drifting territoriality is explained by the patchy dispersion of food, the need to minimize interference competition, and a cycle of grazing and fallowing in the use of food plants.
Two hypotheses explaining the adaptive significance of settlements are evaluated: one relates to resource availability (through the indirect effect of ground water and sheep dung on vegetation); and the other relates to predation (through the protective influence of human dwellings). The size of sheep flocks grazing at outstations during January provide a measure of the resource richness of patches where maras graze, and the richness of these patches in the dry season appear to limit the number of maras breeding at each settlement during the following wet season.
Maras face extremes of resource dispersion between the wet and dry seasons: in the former, sparsely dispersed grazing and interference competition favour spacing out and territoriality; in the latter, clumping of resources facilitates pairs congregating in herds around outstations and dry lagoons. Superimposed upon the ecological factors favouring spacing out during the wet season are the sociological factors that cause the maras to den communally. The resulting compromise is a social system unique among mammals.     

Context-dependent outcomes of subarctic grass-endophyte symbiosis

Symbiotic interactions are often context-dependent. We explored how different habitats have modified the symbiosis between the grass Festuca rubra and the endophyte Epichloë festucae. We grew endophytic and endophyte-free grasses originating from subarctic meadows and open river banks in a growth chamber with a hemiparasitic plant (Rhinanthus minor) and a competitor (Achillea millefolium), representing typical plant-plant interactions in meadows. Grasses from meadows were more adapted to plant species interactions than river bank grasses, and the presence of the endophyte strengthened this difference further. Endophyte-infected meadow grasses did not suffer from the hemiparasite, but the endophyte decreased the tolerance of the river bank grasses to the hemiparasite. Endophytic river bank grasses invested more than meadow grasses in vegetative spread. These results suggest differentiation of grass-endophyte symbiota between the habitats, and underline the context dependency of species interactions as well as the role of symbionts in the habitat adaptation of plants.     

氮磷添加对内蒙古温带草原植物功能群氮含量的影响

植物功能群氮含量既是理解氮沉降对生物多样性影响的关键指标,也是生产力过程模型模拟的重要参数,极易受氮素可利用性的影响和磷元素的限制。基于内蒙古温带草原4年氮磷添加试验(N10、N40、P5、P10及其交互,数字代表添加剂量,单位为g m^-2 a^-1),分析氮磷添加对植物群落及三种植物功能群(禾本科、灌木和杂类草)氮含量的影响。结果表明:(1)氮添加显著增加了群落及各功能群的氮含量,同一处理水平下禾本科(N10)和灌木(N10和N40)的氮含量显著高于杂类草,同一功能群不同氮添加剂量间无显著差异;(2)磷添加对群落和三种功能群的氮含量无显著影响;(3)与单独氮添加相比,氮磷同时添加显著增加了群落、禾本科和杂类草氮含量,且高剂量氮磷添加的促进作用更大;(4)与单独氮添加相比,氮磷同时添加显著增加群落和三种功能群磷含量而降低氮磷比,相同处理水平下禾本科和杂类草磷含量增加幅度最大。本研究将为草原生态系统管理和应对全球变化提供科学依据。     

The roles of exotic grasses and forbs when restoring native species to highly invaded southern California annual grassland

Many semi-arid shrublands in the western US have experienced invasion by a suite of exotic grasses and forbs that have altered community structure and function. The effect of the exotic grasses in this area has been studied, but little is known about how exotic forbs influence the plant community. A 3-year experiment in southern California coastal sage scrub (CSS) now dominated by exotic grasses was done to investigate the influence of both exotic grasses (mainly Bromus spp.) and exotic forbs (mainly Erodium spp.) on a restoration seeding (9 species, including grasses, forbs, and shrubs). Experimental plots were weeded to remove one, both, or neither group of exotic species and seeded at a high rate with a mix of native species. Abundance of all species varied with precipitation levels, but seeded species established best when both groups of exotic species were removed. The removal of exotic grasses resulted in an increase in exotic and native forb cover, while removal of exotic forbs led to an increase in exotic grass cover and, at least in one year, a decrease in native forb cover. In former CSS now converted to exotic annual grassland, a competitive hierarchy between exotic grasses and forbs may prevent native forbs from more fully occupying the habitat when either group of exotics is removed. This apparent competitive hierarchy may interact with yearly variation in precipitation levels to limit restoration seedings of CSS/exotic grassland communities. Therefore, management of CSS and exotic grassland in southern California and similar areas must consider control of both exotic grasses and forbs when restoration is attempted.     

Influence of an overstorey tree (Prosopis glandulosa) on associated shrubs in a savanna parkland: implications for patch dynamics

The arborescent legume, honey mesquite (Prosopis glandulosa), appears to play a central role in patch dynamics of southern Texas savannas by modifying soils and microclimate and by facilitating the ingress, establishment and/or growth of shrubs in its understorey. As an indirect test for the occurrence and persistence of facilitation in mature shrub clusters (patches), we examined the gas exchange, water relations and production of associated shrubs growing in patches where a Prosopis overstorey was present and in patches where Prosopis had succumbed to natural mortality. Surface (0–10 cm) soils associated with shrub patches were enriched in total [N] and [C] compared to soils of neighboring herbaceous zones. However, there were no detectable differences in soil [N] or [C] in patches with and without Prosopis. Foliar [N] and biomass of various shrub species were also statistically comparable for patches with and without Prosopis. These results are in accordance with other studies that indicate the nutrient legacy associated with Prosopis occupation of a patch may persist for decades after its demise. In comparison to plants growing in the absence of Prosopis, leaf water potentials (predawn and midday), and net photosynthesis and water vapor conductance (morning and midday) of outer-canopy sunlit leaves over an annual growth cycle were comparable for two common evergreen shrubs, Zanthoxylum fagara and Berberis trifoliolata, growing in patches with a live Prosopis. These findings indicate that the presence of Prosopis was not enhancing the growth or activity of mature understorey shrubs; facilitation may, therefore, be important only during early stages of cluster development. In addition, we found no indication that the loss of Prosopis has initiated a downward phase in a cyclic succession of patch initiation, growth and death. Rather, the understorey shrubs appear to be able to maintain growth and productivity in the absence of a Prosopis overstorey, and may, therefore, represent persistent components of woody patches on these savanna landscapes.     

Secondary dune succession on Inhaca Island,Mozambique

Old field succession was studied on coastal dunes supporting tropical evergreen forest on Inhaca Island, Mozambique. Plots of 10×10 m were sited in three early successional stages and in relatively undisturbed forest. Woody species increased in number during succession; leptophylls were most frequent in younger vegetation, whereas microphylls and mesophylls were most frequent in forest. Grasses, shrubs and forbs dominated initially following abandonment, and shrubs persisted as dominants in the three early successional stages. The initial floristic composition model was generally supported by the pattern of species sequences, with many forest species entering early in the succession. Of the few species conforming to the relay floristic model, many were grasses and forbs of the forest understorey. Similarity between plots of equivalent vegetation age indicated that, at least in early succession, there was linearity in the successional pathway; there was no evidence for divergence or multiple pathways. In early succession, no accumulation was detected in either soil organic matter or extractable nutrients, thus providing little support for the facilitation model of succession. It is stressed that the findings are probably scale-dependent.