Aeolian process effects on vegetation communities in an arid grassland ecosystem

Many arid grassland communities are changing from grass dominance to shrub dominance, but the mechanisms involved in this conversion process are not completely understood. Aeolian processes likely contribute to this conversion from grassland to shrubland. The purpose of this research is to provide information regarding how vegetation changes occur in an arid grassland as a result of aeolian sediment transport. The experimental design included three treatment blocks, each with a 25 × 50 m area where all grasses, semi-shrubs, and perennial forbs were hand removed, a 25 × 50 m control area with no manipulation of vegetation cover, and two 10 × 25 m plots immediately downwind of the grass-removal and control areas in the prevailing wind direction, 19° north of east, for measuring vegetation cover. Aeolian sediment flux, soil nutrients, and soil seed bank were monitored on each treatment area and downwind plot. Grass and shrub cover were measured on each grass-removal, control, and downwind plot along continuous line transects as well as on 5 × 10 m subplots within each downwind area over four years following grass removal. On grass-removal areas, sediment flux increased significantly, soil nutrients and seed bank were depleted, and Prosopis glandulosa shrub cover increased compared to controls. Additionally, differential changes for grass and shrub cover were observed for plots downwind of vegetation-removal and control areas. Grass cover on plots downwind of vegetation-removal areas decreased over time (2004-2007) despite above average rainfall throughout the period of observation, while grass cover increased downwind of control areas; P. glandulosa cover increased on plots downwind of vegetation-removal areas, while decreasing on plots downwind of control areas. The relationships between vegetation changes and aeolian sediment flux were significant and were best described by a logarithmic function, with decreases in grass cover and increases in shrub cover occurring with small increases in aeolian sediment flux.     

Large herbivores maintain a two‐phase herbaceous vegetation mosaic in a semi‐arid savanna

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Effect of grazing on plant patterns in arid ecosystems of Patagonian Monte

Our objective was to assess the relationship between the spatial patterning of perennial grasses (total, grazed, and non‐grazed) and shrub patches in rangelands under different grazing pressures of the Patagonian Monte. We selected three grazed paddocks with the usual stocking rate for the area, where previous studies showed that a piosphere formation is common. At each paddock, we analysed the grain of heterogeneity at sites located at two distances from the single watering point (near, far), using high‐resolution aerial photographs. At these sites, we also assessed in the field the density, size, cover, and spatial patterning of grazed and non‐grazed perennial grasses and shrub patches. The grain of heterogeneity of shrub patches was coarser in sites near the watering point than in those distant from it, as a consequence of the increase in size of both, bare soil and shrub patches. Field sampling showed that a coarse grain of heterogeneity relative to fine‐grained sites resulted from changes in species composition, increased bare soil areas and reduced perennial grass cover. In coarse‐grained sites, lower perennial grass cover resulted from lower density and/or smaller size of grass bunches than in fine‐grained sites. We did not find significant differences among sites in the proportion of perennial grazed grasses. Since the density and cover of perennial grasses was higher in fine‐ than in coarse‐grained sites, we suggested that fine‐grained sites are more important as feeding stations than coarse‐grained sites. The consequences of this differential use could lead to degradation of fine‐grained sites and to higher homogeneity in spatial plant structure and floristic composition within paddocks with respect to the condition observed at present, increasing the size of the highly degraded zone within the piosphere. At the patch level, we found that at about one third of the sampled transects, both total and non‐grazed perennial grasses were spatially aggregated with shrub patches. However, in most transects grazed perennial grasses were indifferently distributed in relation with shrub patches, showing that grazers display high selectivity of foraging sites at macro level (i.e. high and low grazing pressure sites at the paddock level), but random occupancy of vegetation units (randomness in the distribution of grazed perennial grasses at the patch level). The intensity of the positive association between non‐grazed grasses and shrub patches was higher in fine‐grained than in coarse‐grained sites and may be attributed to higher protection against herbivores associated to denser shrub patches in fine‐ relative to coarse‐grained sites. We concluded that a feedback exists between the spatial distribution of species preferred by grazers and the spatial patterning of use of these species.     

Grazing and productivity alter individual grass size dynamics in semi-arid woodlands

The spatial arrangement of perennial vegetation is critical for ecosystem function in drylands. While much is known about how vegetation patches respond to grazing and abiotic conditions, the size dynamics of individual plants is mostly limited to theoretical studies. We measured the size distribution (mean, variance, skewness) and density of individual grasses, and grass species composition at 451 sites spanning a range of grazing intensities across three broad vegetation communities in semi-arid eastern Australia. We assessed the relative role of grazing by livestock (cattle and sheep), native (kangaroos) and introduced (rabbits) free ranging herbivores, and several environmental measures (productivity, diversity, composition and groundstorey plant cover) on the size distribution and density of individual grasses. We found mean grass size and density were more sensitive to shifts in grazing intensity and environmental conditions than size variance or the frequency of the smallest individuals (skewness), and shifts were mostly driven by site productivity and cattle and kangaroo grazing. Sheep grazing only reduced mean grass size, and rabbit grazing had no consistent effects. Importantly, we found that site productivity and species composition altered the impacts of grazing on grass density and size distribution. For example, increasing cattle grazing led to larger grasses in low productivity sites. It also led to larger, denser, more variable-sized grasses among grass species from sites with finer soil texture. Increasing kangaroo grazing led to smaller, denser individuals among grass species from sites with coarse soil texture. At high diversity sites kangaroo grazing led to denser, more homogenised grass sizes with a lower frequency of small individuals. Understanding the in situ response of individual plant sizes gives us insights into the processes driving shifts in perennial vegetation patchiness, improving our ability to predict how the spatial arrangement of ecosystems might change under global change scenarios.     

Grassland structure in native pastures: links to soil surface condition

Summary When grassland is grazed by livestock, the structure of the sward changes in a patchy manner. With continuous selective grazing there is a mosaic of short and tall patches but as grazing intensifies the area of short‐grazed patch increases until the paddock has a lawn‐like appearance. This mosaic of patch structures can be stable, as short patches tend to attract repeated grazing and tall patches tend to be avoided. Because heavy grazing can detrimentally affect soil and water functions in grassland (ultimately resulting in erosion), we aimed to assess how well the physical structure of the sward reflects soil surface condition. We described four grassland patch structures that were assumed to reflect different levels of present grazing, and to some extent, past grazing pressure. We assessed patch structure and two other grass‐related variables (basal area of a ‘large tussock’ functional group and basal area of all perennial grass) as possible indicators of soil surface condition. Three indices of condition were measured in the field. The infiltration and nutrient cycling index declined progressively across patch structures, consistent with increasing grazing pressure. The stability index was found to be reduced only for the most heavily grazed grass structure (short patches). We found the ‘large tussock’ grass functional group to be a more sensitive indicator of soil surface condition than the group consisting of all perennial grasses. We found no evidence of sudden soil surface condition decline beyond a certain level of grass basal area, that is, there was no evidence of thresholds, rather, incremental loss of condition accompanied grass decline. We are thus not able to further refine an earlier proposed management recommendation ‘Graze conservatively to maintain dominance of large and medium tussock grasses over 60–70% of the native pastures’, except to suggest the use of short patches as a more practical indicator, rephrasing the recommendation as ‘Graze conservatively to allow a maximum of 30% short‐grazed patches in native pastures’.     

Population and clonal level responses of a perennial grass following fire in the northern Chihuahuan Desert

Relationships involving fire and perennial grasses are controversial in Chihuahuan Desert grasslands of southern New Mexico, USA. Research suggests that fire delays the resprouting of perennial grasses well after two growing seasons. However, such results are confounded by livestock grazing, soil erosion, and drought. Additionally, post-fire grass responses may depend on initial clone size. We evaluated the effects of fire, grazing, and clone size on Bouteloua eriopoda (black grama) in southern New Mexico grasslands. Four 2-ha plots were established in each of four sites. Fire and grazing were applied or not applied in 1999 such that four treatment combinations were assigned randomly to plots within each site. Within each plot, small (0–10 cm² basal area), medium (10–30 cm²), and large ( > 30 cm²) clones were initially mapped in five 0.91-m² quadrats where grass attributes and litter cover were evaluated before and at the end of two growing seasons following fire. Maximum fire temperature was also measured. At a population level, canopy and litter cover were each approximately 50% less in burned than unburned areas. However, compared to initial levels, canopy height had increased by 10% at the end of the study, regardless of fire. At a clonal level, basal cover reductions were attributed mostly to large clones that survived fire. Smaller clone densities had decreased by as much as 19% in burned compared to unburned areas, and fire reduced the basal cover of medium clones. Basal and canopy cover, recruitment, and clone basal area decreased with increased fire temperatures. Almost all responses were independent of grazing, and interactive effects of grazing and fire were not detected. Fire did not kill all perennial grass clones, regardless of size. However, rapid responses were likely influenced by above-average precipitation after fire. Future studies in desert grasslands should examine how perennial grass dynamics are affected by fire, precipitation patterns, and interactions with grazing.     

Effects of grazing on patch structure in a semi‐arid two‐phase vegetation mosaic

Abstract. Question: What are the grazing effects in the spatial organization and the internal structure of high and low cover patches from a two‐phase vegetation mosaic? Location: Patagonian steppe, Argentina. Methods: We mapped vegetation under three different grazing conditions: ungrazed, lightly grazed and heavily grazed. We analysed the spatial patterns of the dominant life forms. Also, in each patch type, we determined density, species composition, richness, diversity, size structure and dead biomass of grasses under different grazing conditions. Results: The vegetation was spatially organized in a two‐phase mosaic. High cover patches resulted from the association of grasses and shrubs and low cover patches were represented by scattered tussock grasses on bare ground. This spatial organization was not affected by grazing, but heavy grazing changed the grass species involved in high cover patches and reduced the density and cover of grasses in both patch types. Species richness and diversity in high cover patches decreased under grazing conditions, whereas in low cover patches it remained unchanged. Also, the decrease of palatable grasses was steeper in high cover patches than in low cover patches under grazing conditions. Conclusions: We suggest that although grazing promotes or inhibits particular species, it does not modify the mosaic structure of Patagonian steppe. The fact that the mosaic remained unchanged after 100 years of grazing suggests that grazing does not compromize population processes involved in maintaining patch structure, including seed dispersal, establishment or biotic interactions among life forms.     

Slow recovery in desert perennial vegetation following prolonged human disturbance

Questions: How long may it take for desert perennial vegetation to recover from prolonged human disturbance and how do different plant community variables (i.e. diversity, density and cover) change during the recovery process? Location: Sonoran Desert, Arizona, USA. Methods: Since protection from grazing from 1907 onwards, plant diversity, density and cover of perennial species were monitored intermittently on ten 10 m × 10 m permanent plots on Tumamoc Hill, Tucson, Arizona, USA. Results: The study shows an exceptionally slow recovery of perennial vegetation from prolonged heavy grazing and other human impacts. Since protection, overall species richness and habitat heterogeneity at the study site continued to increase until the 1960s when diversity, density and cover had been stabilized. During the same period, overall plant density and cover also increased. Species turnover increased gradually with time but no significant relation between any of the three community variables and precipitation or Palmer Drought Severity Index (PDSI) was detected. Conclusions: It took more than 50 yr for the perennial vegetation to recover from prolonged human disturbance. The increases in plant species richness, density, and cover of the perennial vegetation were mostly due to the increase of herbaceous species, especially palatable species. The lack of a clear relationship between environment (e.g. precipitation) and community variables suggests that site history and plant life history must be taken into account in examining the nature of vegetation recovery processes after disturbance.     

Pastoralist's livestock and settlements influence game bird diversity and abundance in a savanna ecosystem of southern Kenya

We investigated the vegetation structure and density of game birds along a successional gradient created by varying intensity of human settlement in a pastoral community in Shompole group ranch in southern Kenya. We examined four habitat types including heavily-grazed grass in currently occupied settlements, short grass in seasonal settlements, patches of bushed woodland in settlement sites that had been abandoned up to 30 years ago, and tall grass in a wildlife sanctuary. Vegetation biomass was the highest in the sanctuary where livestock are excluded and the lowest in the vicinity of currently occupied settlements. Abundance of doves ( Oena spp . and Streptopelia spp. ) was best associated with moderate grazing and per cent green grass, which provide good foraging opportunities. Francolin and spurfowl ( Francolinus spp .) were positively associated with vegetation biomass. Quail ( Coturnix spp .) were positively associated with tree cover. These data reflect the importance of maintaining a balance of wildlife and livestock grazing with patches of ungrazed grasslands and bushed woodlands in providing a mosaic of habitats that support a diverse population of game birds. The results have wide application for an integrated management approach to livestock, wildlife and game bird management in the savannas.     

Regional productivity mediates the effects of grazing disturbance on plant cover and patch‐size distribution in arid and semi‐arid communities

Patch‐size distribution and plant cover are strongly associated to arid ecosystem functioning and may be a warning signal for the onset of desertification under changes in disturbance regimes. However, the interaction between regional productivity level and human‐induced disturbance regime as drivers for vegetation structure and dynamics remain poorly studied. We studied grazing disturbance effects on plant cover and patchiness in three plant communities located along a regional productivity gradient in Patagonia (Argentina): a semi‐desert (low‐productivity community), a shrub‐grass steppe (intermediate‐productivity community) and a grass steppe (high‐productivity community). We sampled paddocks with different sheep grazing pressure (continuous disturbance gradients) in all three communities. In each paddock, the presence or absence of perennial vegetation was recorded every 10 cm along a 50 m transect. Grazing effects on vegetation structure depended on the community and its association to the regional productivity. Grazing decreased total plant cover while increasing both the frequency of small patches and the inter‐patch distance in all communities. However, the size of these effects was the greatest in the high‐productivity community. Dominant species responses to grazing explained vegetation patch‐ and inter‐patch‐size distribution patterns. As productivity decreases, dominant species showed a higher degree of grazing resistance, probably because traits of species adapted to high aridity allow them to resist herbivore disturbance. In conclusion, our findings suggest that regional productivity mediates grazing disturbance impacts on vegetation mosaic. The changes within the same range of grazing pressure have higher effects on communities found in environments with higher productivity, markedly promoting their desertification. Understanding the complex interactions between environmental aridity and human‐induced disturbances is a key aspect for maintaining patchiness structure and dynamics, which has important implications for drylands management.     

Hippopotamus and livestock grazing: influences on riparian vegetation and facilitation of other herbivores in the Mara Region of Kenya

Riparian savanna habitats grazed by hippopotamus or livestock experience seasonal ecological stresses through the depletion of herbaceous vegetation, and are often points of contacts and conflicts between herbivores, humans and their livestock. We investigated how hippopotamus and livestock grazing influence vegetation structure and cover and facilitate other wild herbivores in the Mara region of Kenya. We used 5 km-long transects, each with 13 plots measuring 10 × 10 m², and which radiate from rivers in the Masai Mara National Reserve and adjoining community pastoral ranches. For each plot, we measured the height and visually estimated the percent cover of grasses, forbs, shrubs and bare ground, herbivore abundance and species richness. Our results showed that grass height was shortest closest to rivers in both landscapes, increased with increasing distance from rivers in the reserve, but was uniformly short in the pastoral ranches. Shifting mosaics of short grass lawns interspersed with patches of medium to tall grasses occurred within 2.5 km of the rivers in the reserve in areas grazed habitually by hippos. Hence, hippo grazing enhanced the structural heterogeneity of vegetation but livestock grazing had a homogenizing effect in the pastoral ranches. The distribution of biomass and the species richness of other ungulates with distance from rivers followed a quadratic pattern in the reserve, suggesting that hippopotamus grazing attracted more herbivores to the vegetation patches at intermediate distances from rivers in the reserve. However, the distribution of biomass and the species richness of other ungulates followed a linear pattern in the pastoral ranches, implying that herbivores avoided areas grazed heavily by livestock in the pastoral ranches, especially near rivers.     

Effect of artificial shade and grazing removal on degraded grasslands: Implications of woody restoration for herbaceous vegetation

Extensive degraded short tussock grasslands of New Zealand's eastern South Island were dominated by woody vegetation prior to burning and livestock grazing associated with human settlement starting 800 years ago. There is increasing interest in restoring some of these grasslands back to a woody state. However, because of the long time frames involved in establishing a woody cover, it is difficult to predict the impacts that woody restoration will have on the extant herbaceous flora. Using a factorial trial with artificial shade and grazing exclusion, we assessed the potential impact of woody restoration on the structure and composition of the herbaceous flora over a six‐year period. The imposition of artificial shade resulted in significant increases in total species richness and the total cover of herbaceous vegetation, increases in cover of several individual forb and grass species and decreases in the cover of bare ground, moss and lichen in shade treatments. There were also changes in the overall community composition of shaded treatments reflecting these changes in vegetation cover and species richness. We found no statistically significant effects of grazing exclusion. We suggest that increased soil moisture resulting from shade addition plays an important role in increasing the herbaceous component of the flora. While woody restoration will have a range of effects on the herbaceous understorey, for example through competition and changes in soil conditions, our findings are important for planning future woody restoration in these degraded tussock grasslands. In particular, our results suggest that the best approach to ensure the persistence of herbaceous vegetation in woody restorations might be to ensure that restoration plantings result in a spatially heterogeneous vegetation arrangement.     

Nest‐site selection and productivity of Vesper Sparrows breeding in grazed habitats

ABSTRACT Livestock grazing in the shortgrass steppe of the Intermountain region of British Columbia may have a negative impact on ground‐nesting birds, but evidence of such an impact is lacking. We examined nest‐site selection and productivity of ground‐nesting Vesper Sparrows (Pooecetes gramineus) across sites with different grazing histories. From 2006 to 2008, we monitored Vesper Sparrow nests and measured vegetation characteristics known to be affected by grazing within nest patches. We used an information‐theoretic approach to test the relative importance of grazing‐affected vegetation variables as predictors of nest‐site selection, nest survival, and nestling condition. Vesper Sparrows selected nest sites with greater cover of late‐seral grass species that decrease in occurrence in response to grazing (i.e., “decreasers”) than was available in random patches in the same territories. Daily nest survival was also lower for nests surrounded by shorter vegetation (odds ratio = 1.12). However, “decreaser” cover was not associated with either of the two indices of productivity measured (daily nest survival probability and nestling condition). In addition, vegetation height, although an important driver of success, was not linked with nest‐site selection, and no vegetation‐cover variable was positively associated with productivity, despite nest concealment being central to our predictions. This suggests that predation risk for nests in areas with shorter vegetation was being elevated through some factor unrelated to concealment. Our results show that grazing reduced both the availability of suitable habitat for and nesting success of Vesper Sparrows, indicating that grazing could pose a threat to population persistence at a broader scale and could potentially contribute to observed declines. Additional research is needed to determine if grazing guidelines in the Intermountain region of British Columbia should be amended, better enforced, or both to prevent regional declines in populations of ground‐nesting grassland birds.     

Potential metapopulation structure and the effects of habitat quality on population size of the endangered False Ringlet butterfly

The False Ringlet (Coenonympha oedippus) is a European butterfly species, endangered due to the severe loss and fragmentation of its habitat. In Hungary, two remaining populations of the butterfly occur in lowland Purple Moorgrass meadows. We studied a metapopulation occupying twelve habitat patches in Central Hungary. Our aim was to reveal what measures of habitat quality affect population size and density of this metapopulation, estimate dispersal parameters and describe phenology of subpopulations. Local population sizes and dispersal parameters were estimated from an extensive mark–release–recapture dataset, while habitat quality was characterized by groundwater level, cover of grass tussocks, bush cover, height of vegetation and grass litter at each habitat patch. The estimated size of the metapopulation was more than 3,000 individuals. We estimated a low dispersal capacity, especially for females, indicating a very low probability of (re)colonization. Butterfly abundance and density in local populations increased with higher grass litter, lower groundwater level and larger area covered by tussocks. We suppose that these environmental factors affect butterfly abundance by determining the microclimatic conditions for both larvae and adult butterflies. Our results suggest that the long-term preservation of the studied metapopulation needs the maintenance of high quality habitat patches by appropriate mowing regime and water regulation. Management also should facilitate dispersal to strengthen metapopulation structure with creating stepping-stones or gradually increase habitat quality in present matrix.     

A hierarchical model for analysing the stability of vegetation patterns created by grazing in temperate pastures

Questions: Does vegetation structure display any stability over the grazing season and in two successive years, and is there any correlation between the stability of these spatial patterns and local sward composition? Location: An upland grassland in the French Massif Central. Method: The mosaic of short and tall vegetation stands considered as grazed and ungrazed patches respectively is modeled as the realization of a Boolean process. This method does not require any arbitrarily set sward‐height thresholds to discriminate between grazed and ungrazed areas, or the use of additional variables such as defoliation indexes. The model was validated by comparing empirical and simulated sward‐height distributions and semi‐variograms. Results: The model discriminated between grazed and ungrazed patches at both a fine (1 m²) and a larger (500 m²) scale. Selective grazing on legumes and forbs and avoidance of reproductive grass could partly explain the stability of fine‐scale grazing patterns in lightly grazed plots. In these plots, the model revealed an inter‐annual stability of large‐scale grazing patterns at the time peak biomass occurred. At the end of the grazing season, lightly grazed plots showed fluctuating patch boundaries while heavily grazed plots showed a certain degree of patch stability. Conclusion: The model presented here reveals that selective grazing at the bite scale could lead to the creation of relatively stable patches within the pasture. Locally maintaining short cover heights would result in divergent within‐plot vegetation dynamics, and thus favor the functional diversity of vegetation.     

Postwildfire seeding to restore native vegetation and limit exotic annuals: an evaluation in juniper‐dominated sagebrush steppe

Reestablishment of perennial vegetation is often needed after wildfires to limit exotic species and restore ecosystem services. However, there is a growing body of evidence that questions if seeding after wildfires increases perennial vegetation and reduces exotic plants. The concern that seeding may not meet restoration goals is even more prevalent when native perennial vegetation is seeded after fire. We evaluated vegetation cover and density responses to broadcast seeding native perennial grasses and mountain big sagebrush (Artemisia tridentata Nutt. spp. vaseyana [Rydb.] Beetle) after wildfires in the western United States in six juniper (Juniperus occidentalis ssp. occidentalis Hook)‐dominated mountain big sagebrush communities for 3 years postfire. Seeding native perennial species compared to not seeding increased perennial grass and sagebrush cover and density. Perennial grass cover was 4.3 times greater in seeded compared to nonseeded areas. Sagebrush cover averaged 24 and less than 0.1% in seeded and nonseeded areas at the conclusion of the study, respectively. Seeding perennial species reduced exotic annual grass and annual forb cover and density. Exotic annual grass cover was 8.6 times greater in nonseeded compared to seeded areas 3 years postfire. Exotic annual grass cover increased over time in nonseeded areas but decreased in seeded areas by the third‐year postfire. Seeded areas were perennial‐dominated and nonseeded areas were annual‐dominated at the end of the study. Establishing perennial vegetation may be critical after wildfires in juniper‐dominated sagebrush steppe to prevent the development of annual‐dominated communities. Postwildfire seeding increased perennial vegetation and reduced exotic plants and justifies its use.     

Influence of Grazing on Soil Seed Banks Determines the Restoration Potential of Aboveground Vegetation in a Semi‐arid Savanna of Ethiopia

Species composition, number of emerging seedlings, species diversity and functional group of the soil seed banks, and the influence of grazing on the similarity between the soil seed banks and aboveground vegetation, were studied in 2008 and 2009 in a semi‐arid savanna of Ethiopia. We tested whether the availability of persistent seeds in the soil could drive the transition from a degraded system under heavy grazing to healthy vegetation with ample perennial grasses. A total of 77 species emerged from the soil seed bank samples: 21 annual grasses, 12 perennial grasses, 4 herbaceous legumes, 39 forbs, and 1 woody species. Perennial grass species dominated the lightly grazed sites, whereas the heavily grazed sites were dominated by annual forbs. Heavy grazing reduced the number of seeds that can germinate in the seed bank. Species richness in the seed bank was, however, not affected by grazing. With increasing soil depth, the seed density and its species richness declined. There was a higher similarity in species composition between the soil seed bank and aboveground vegetation at the lightly grazed sites compared with the heavily grazed sites. The mean similarity between the seed banks and aboveground vegetation was relatively low, indicating the effect of heavy grazing. Moreover, seeds of perennial grasses were less abundant in the soil seed banks under heavy grazing. We concluded that restoration of grass and woody species from the soil seed banks in the heavily grazed areas could not be successful in semi‐arid savannas of Ethiopia.     

Relationships Between Plant Spatial Patterns, Water Infiltration Capacity, and Plant Community Composition in Semi-arid Mediterranean Ecosystems Along Stress Gradients

Water redistribution from bare soil to vegetation patches is a key feature of semi-arid ecosystems, and is responsible for their patchy vegetation patterns. The magnitude of water redistribution depends on the properties of the bare soil (which determine the amount of water run-off) and the capacity of vegetation patches to trap water run-on. We examined the relationships between plant spatial patterns, water infiltration into bare soil, and plant community composition in semi-arid sites with different hydro-physical properties (silty and gypseous soils) in NE Spain. We also studied the effect of two stressors, aridity and grazing, on water infiltration and plant spatial patterns. Our results indicate a negative correlation of bare soil sorptivity (the capacity to absorb water by capillarity) and vegetation aggregation. There was a strong positive correlation between perennial grass cover and the spatial aggregation of vegetation, but aggregation was not associated with positive associations of different plant types. The aggregation of vegetation was positively correlated with species richness and the overall extent of vegetation cover. Grazing reduced water infiltration into silty soils, which are prone to compaction. In contrast, soil crust affected the hydrology of gypseous soils, especially in the most arid sites, where grazing increased infiltration, reducing surface sealing due to breaking of the soil crust. Together, our results suggest that biotic and abiotic factors affect the hydro-physical properties of soils in the semi-arid ecosystems of NE Spain, which is linked to the plant communities through the spatial distribution of plants.     

Low‐cost grass restoration using erosion barriers in a degraded African rangeland

Rangeland degradation, typified by extensive bare ground and soil erosion, is a serious problem around the world. In sub‐Saharan Africa, rangeland degradation threatens the food security of millions of people who depend on livestock and the region's large mammalian wildlife diversity. We tested the ability of five simple, low‐cost erosion barriers to promote grass and forb establishment in a bare ground‐dominated rangeland in Kenya. These treatments were: (1) trenches with small berms; (2) bundles of branches; and bundles of branches with (3) elephant dung balls, (4) burlap sacking, or (5) nylon mesh sacking inside them. We also tested whether barrier performance depended on (1) supplemental seeding with the grass Cenchrus ciliaris and (2) whether a barrier was located next to existing vegetation patches versus in the open. Within months, the trench and nylon mesh barriers had accumulated 20–50% more sediment than other treatments and had greater grass and forb seedling establishment. Seeding with Cenchrus resulted in higher herbaceous cover but was not necessary for other grasses to establish. After 3 years, the trench and nylon mesh barriers had created patches of new vegetation averaging 18–63% larger than patches created by the other treatments. Barriers that were initially adjacent to existing vegetation had created new vegetation patches averaging 65% larger than those created by solitary barriers. Results suggest that all barrier types increase grass cover but that trenches—especially if placed next to existing vegetation patches—are a particularly cost‐effective way to reduce bare ground and erosion in degraded rangelands.