Grass Species Composition Research Articles

Effect of Balanites glabra canopy cover on grass production, organic matter and soil moisture in a southern Kenyan rangeland

A study was undertaken in Kenya's southern savanna rangelands to determine the seasonal effect of Balanites glabra canopy cover on aboveground grass biomass, grass species composition, soil organic matter and soil moisture content. The study was conducted during the period June to December 1999 in order to capture both the dry and wet season effects. The grass biomass in the sub-canopy zone (2-4m from tree trunk) was found to be significantly higher than in the mid-canopy (0-2m from tree trunk) and open grassland zones (4-6m from tree trunk) during the dry season. However, the difference between the sub-canopy and the open grassland was not significant during the wet season, implying that the role of a tree canopy in enhancing grass biomass is greater during the dry than the wet season. Variations in percent grass species composition from the mid-canopy to the adjacent open grassland were observed, indicating that while B. glabra canopy cover favours certain grass species, other species find the micro-climatic conditions under the canopy unfavourable. Soil organic matter in the mid-canopy zone was significantly higher than in the sub-canopy and adjacent open zones during both dry and wet season. Although the sub-canopy zone exhibited significantly higher soil moisture content than the mid-canopy and open grassland zones during the dry season, the difference between the sub-canopy and the adjacent open grassland during the wet season was not significant, suggesting that the tree canopy influence on soil moisture is more pronounced in the dry than the wet season.

Patterns of sedimentation in a salt marsh-dominated estuary.

in significantly higher growth rates for this organism. Furthermore, the observed seaward encroachment of P. australis is slowly pushing out D. spicata, the species that we found to have the highest nutritional quality (2). Given a continued shoreward migration of S. alterniflora due to sea-level rise and the seaward spread of P. australis, the overall food quality of marsh detritus for this invertebrate could decline. This suggests that changes in marsh grass species composition could affect higher trophic levels in this salt-marsh ecosystem. This research was supported by an NSF-REU fellowship through the Plum Island Ecosystem LTER to AMA.

Influence of an exotic species, Acroptilon repens (L.) DC. on seedling emergence and growth of native grasses

Our objective was to evaluate the effects of an invasive perennial forb, Acroptilon repens (Russian knapweed), on seed emergence and seedling survival of four native grass species that are important in semiarid grasslands of North America. Greenhouse experiments and field studies conducted at three sites in Colorado, USA were used to examine the response by four perennial grasses: Bouteloua gracilis, Koelaria cristata, Sporobolus cryptandrus, and Agropyon smithii to A. repens. In the greenhouse, seeds of each species were sown in pots that contained either live A. repens roots, A. repens litter on the soil surface, or both roots and litter. Field transects were placed inside stands of A. repens with adjacent control transects in the surrounding grass-dominated community. Emergence and initial survival were decreased by the presence of A. repens roots for K. cristata (35%), B. gracilis (31%), and S. cryptandrus (44%) in the greenhouse, and 57, 32, and 36%, respectively, in the field. Root weight was decreased by the presence of A. repens roots for both B. gracilis and K. cristata by more than 55% in the greenhouse. A. smithii survival and growth were unaffected by A. repens in either the greenhouse or the field. These species-specific responses to the presence of A. repens may explain, at least in part, differences in susceptibility and recovery of sites with different native grass species composition.

Challenges faced in the conservation of rare antelope: a case study on the northern basalt plains of the Kruger National Park

The conservation of rare antelope has long been one of the goals of the Kruger National Park. The roan antelope Hippotragus equinus, and to a lesser extent the tsessebe Damaliscus lunatus, represent low-density species or rare antelope in the park. Specific management approaches representing the older equilibrium approach, have been employed to conserve these antelope. Of these, the supply of artificial water over many decades was the most resource intensive. The sudden, severe drop in the roan antelope population towards the end of the 1980s was unexpected and, retrospectively, attributed to the development of a high density of perennial waterpoints. The postulated mechanism was that the perennial presence of water allowed Burchell’s zebra Equus burchelli to stay permanently in an area that was previously only seasonally accessible. The combined effect of a long, dry climatic cycle, high numbers of zebra and their associated predators was proposed to be the cause of this decline. As part of the new nature evolving or ecosystem resilience approach, twelve artificial waterpoints were closed in the prime roan antelope habitat in 1994 in an attempt to move the zebra out of this area. The zebra numbers declined as the rainfall increased. Closure of waterholes clearly led to redistribution of zebra numbers on the northern plains, zebra tending to avoid areas within several kilometres of closed waterpoints. However, at a larger scale, regional densities appeared similar in areas with and without closed waterpoints. There was an initial drop in the lion numbers in 1995, after which they stabilised. In spite of an improvement in the grass species composition and an increase in biomass the roan antelope population did not increase. The complexity of maintaining a population at the edge of their distribution and the problems associated with the conservation of such populations are discussed in terms of management options and monitoring approaches that may be employed in this process.

Vegetation gradients around artificial water points in the Central Kalahari Game Reserve of Botswana

AbstractVegetation was assessed in plots sited at varying distances along two line transects radiating from each of nine artificial water points. Environmental variables such as distance from water point, soil type and ground cover were related to grass species composition. Grass species composition in calcrete soils differed significantly from that found in sandy soils. On calcrete soils, distance from water point did not have a significant effect on species composition. On sandy soils, distance from water point had a significant effect on species composition at two of the nine water points sampled. At these two water points, grass species that are usually associated with disturbed areas dominated close to the water points while those that dominated far from the water points were those that are usually associated with undisturbed sites. The results therefore indicate that there was no severe degradation of habitat around water points.

Quantified range condition assessment of open Camelthorn savanna along a degradation gradient

Measurements were taken at 20 different sites in a relatively homogenous area of open Camelthorn savanna in eastern Namibia. Ordination of grass species composition did not provide a good degradation gradient, due to domination by different species of annual grasses at many of the sites. However a centred PCA ordination of perennial grass species indicated a degradation gradient. This gradient was used to allocate a range condition score to each site, which was then correlated with other measurements. The range condition score did not correlate well with mulch cover, basal cover, proportion of bare soil, above-ground grass biomass, proportion of moribund grass, proportion of seedlings amongst the perennial grasses, density of woody plants lower than O.5m and canopy cover of browsable woody plants over 0.5m tall. A weak correlation (r2 = 0.68, p<0.0001, n = 20) was obtained through a power trend line with woody canopy cover of only the bush thickening species. A better correlation (r2 = 0.90, p<0.0001, n = 20) was obtained with mean distance from sampling point to the nearest perennial grass. This may therefore be an appropriate indicator to include in range condition score for such types of savanna.

Effect of Season on Grazing Native-Grass Pastures11Kansas Agric. Exp. Stn. Contribution No. 00-60-E.

Abstract A total of 2,269 mixed-breed steers (256 kg) grazed burned (April), native-grass pastures for nine grazing seasons from 1990 to 1998. Steers were allotted randomly to graze for either 1/2 season (short season [SS]) from late April to July 15 (an average of 81 d, at one steer per 0.81 ha), or for 3/4 season [intermediate season (IMS)] from late April to August 15 (an average of 112 d, at one steer per 1.21 ha). The grass species composition was measured in yr 1, 4, and 8 of the study. The economics of steers grazing the two systems were determined by stocker and feeder cattle prices at Dodge City, adjusted to southeast Kansas. The steers grazing SS gained more per day (1.26 vs 1.13 kg, P 0.10) between systems for big bluestem, little bluestem, switch-grass, Indiangrass, and total perennial grass. However, percentage basal cover of perennial grass increased more for SS (P

Effect of Season and Fertilizer on Species Composition and Nutritive Value of Native Grasses

Effect of Season and Fertilizer on Species Composition and Nutritive Value of Native Grasses

The effect of long-term mowing and ungulate exclusion on grass species composition and soil nutrient status on the Athi-Kapiti plains, central Kenya

The long-term (>30 years) impacts of mowing (for hay-making) and ungulate exclusion, on natural, unfertilised rangelands were investigated. Changes in grass species composition and soil nutrient status were measured The study site, situated on the Athi-Kapiti plains of central Kenya, comprised of an ungulate exclusion camp, subjected to an annual mow, and an adjacent control plot, exposed to herbivory from cattle and game. Significant changes were noted in four of the seventeen grass species. Relative percentages of Pennisetum mezianum and P. stramineum increased significantly within the mowed/exclusion plot, while those of Microchloa kunthii and Sporobolus iocladus showed a significant drop. No significant differences were noted in relative frequency of grass species designated as 'decreasers', or in basal cover index. Analysis of soils inside the mowed/exclusion plot showed significantly higher soil pH, and soil Ca levels, but significantly lower plant available soil P and inorganic N, when compared to the control plot. The long-term treatment of mowing/herbivore exclusion, has resulted in severe depletion of plant available soil P and inorganic soil N. Results suggest that differences in species composition can be primarily attributed to the lower defoliation levels, and shading effects inside the exclusion plot, while differences in soil nutrient status can be attributed primarily to the export of nutrients with bailed hay, and to the absence of the stimulating effect that large herbivores have on nutrient recycling. Results are consistent with the hypothesis that herbivory plays an important role in maintaining P recycling in plant available forms, particularly for soils where P may be limiting.

Resilience of South African communal grazing lands after the removal of high grazing pressure

A paired site study was conducted of communally grazed eutrophic and dystrophic grasslands and adjacent ungrazed areas of varying periods of exclusion from communal grazing. This allowed determination of the rate and extent of change of a number of vegetation and soil variables following the removal of high and continuous grazing pressure characteristic of communal lands. Similarity indices for grass species composition between the grazed and adjacent ungrazed areas showed a significant exponential decrease with increasing time since protection from continuous grazing. Most change in grass species composition occurred within four to nine years of protection from communal grazing in eutrophic grasslands, and in six to nine years in dystrophic grasslands. In both grassland types palatability increased with time since protection. In eutrophic sites the abundance of perennials showed a significant increase with time since protection, while the abundance of annuals showed a concomitant decrease. This relationship was not evident in dystrophic grasslands. Grass species diversity, basal cover and density showed no relationship with time since protection in the eutrophic sites, but a general increase with time since protection was found in dystrophic sites. Soil bulk density, field capacity, pH and soil nutrients showed no evidence of a relationship with time since protection for either grassland type, while soil porosity increased significantly with time since protection at eutrophic sites, but not dystrophic sites. These relatively rapid changes following the removal of the high grazing pressure indicate that these systems are characterized by relatively high resilience. Copyright © 1999 John Wiley & Sons, Ltd.

Resilience of South African communal grazing lands after the removal of high grazing pressure

A paired site study was conducted of communally grazed eutrophic and dystrophic grasslands and adjacent ungrazed areas of varying periods of exclusion from communal grazing. This allowed determination of the rate and extent of change of a number of vegetation and soil variables following the removal of high and continuous grazing pressure characteristic of communal lands. Similarity indices for grass species composition between the grazed and adjacent ungrazed areas showed a significant exponential decrease with increasing time since protection from continuous grazing. Most change in grass species composition occurred within four to nine years of protection from communal grazing in eutrophic grasslands, and in six to nine years in dystrophic grasslands. In both grassland types palatability increased with time since protection. In eutrophic sites the abundance of perennials showed a significant increase with time since protection, while the abundance of annuals showed a concomitant decrease. This relationship was not evident in dystrophic grasslands. Grass species diversity, basal cover and density showed no relationship with time since protection in the eutrophic sites, but a general increase with time since protection was found in dystrophic sites. Soil bulk density, field capacity, pH and soil nutrients showed no evidence of a relationship with time since protection for either grassland type, while soil porosity increased significantly with time since protection at eutrophic sites, but not dystrophic sites. These relatively rapid changes following the removal of the high grazing pressure indicate that these systems are characterized by relatively high resilience. Copyright © 1999 John Wiley & Sons, Ltd.

The influence of tree thinning on the establishment of herbaceous plants in a semi-arid savanna of southern Africa

The investigation was conducted on an area covered by a dense stand of Colophospermum mopane. Seven plots (65 m × 180 m) were subjected to different intensities of tree thinning, ranging from a totaly cleared plot (0%) to plots thinned to the equivalent of 10%, 20%, 35%, 50% and 75% of the leaf biomass of a control plot (100%) with a tree density of 2 711 plants ha−1. Thinning was completed during 1989 and a study on the establishment of herbaceous plants in response to reduced competition from the woody plants was conducted during the 1989/1990, 1990/1991 and 1991/1992 seasons. A poor ground cover, mainly characterized by bare ground and the dwarf grass Oropetium capensis, existed in the 50%, 75% and 100% plots. This state proved to be relatively independent of rainfall, typical of an induced or pseudo-drought condition. It can be concluded that the tree density of the 50% plot (mean: 3 620 ETTE ha−1, where 1 ETTE = mean leaf volume of a 1.5 m single-stemmed tree = 500 cm3 leaf volume) had already exceeded the critical point of detrimental grass-tree competition. Colonization of bare ground by herbaceous plants increased from increased levels of tree thinning. Annual grasses were the main colonizers of bare ground, while perennial grasses on(v constituted a small proportion of the grass species composition. The successional order of establishing grasses following thinning was Tragus berteronianus, Brachiaria deflexa and Aristida species, terminating in a state where Enneapogon cenchroides predominated. Perennial grasses showed a general lack of successional trends.

Spatial Distribution of Ataenius spretulus, Aphodius granarius (Coleoptera: Scarabaeidae), and Predaceous Insects Across Golf Course Fairways and Roughs

In Michigan, scattered damage to fairway turf from Ataenius spretulus (Haldeman) or Aphodius granarius (L.) is reported by golf course superintendents every year. Yet, little is known about the distribution of these insects on golf courses or why outbreaks occur. In 1992 and 1993, A. spretulus and A. granarius larvae were 10-fold more abundant on fairways compared with adjacent roughs of 3 Michigan golf courses. In 1994, glass vials were used as pitfall traps to sample adult A. spretulus and A. granarius and surface-dwelling insects at 2 golf courses. A. spretulus adults were 4-fold more abundant in the fairway, whereas staphylinids and formicids were 5- to 10-fold more abundant in the rough. At 1 location in 1995, and at a different location in 1996, pitfall traps were placed along replicated transects running into the fairway and rough. In total, 112 pitfall traps were changed weekly from early May to early July. In 1995, 341 A. granarius , 1,131 A. spretulus , 4,703 Formicidae, 2,693 Carabidae, 2,304 Staphylinidae, and 579 Histeridae were captured in pitfall traps. Approximately ⅓ as many insects were trapped in 1996. A. spretulus adults were again more abundant in the fair-way, whereas the numbers of A. granarius adults captured in the fairway and rough were similar. The numbers of predatory insects captured in pitfall traps declined sharply when crossing from the rough into the fairway. We found a strong inverse relationship ( r = −0.62) between the distribution of A. spretulus adults and predators caught in pitfall traps, and a weaker inverse relationship between larvae and predators. At all 5 golf course sites, plots in the fairway and rough received a similar level of irrigation, fairways were mowed at an average height of 13 mm and roughs at 51 mm, more fertilizer was applied to fairways (1.25 kg N/yr) than roughs (0.75 kg N) and no insecticides were applied. In 1996, grass species composition was the same in the fairway and rough. Potential causes of a high density of A. spretulus and a low density of surface predators in golf course fairways are discussed.

Grass species composition, yield and quality under and outside tree crowns in a semi‐arid rangeland in south‐western Zimbabwe

A two‐year study was conducted in lightly grazed areas of Matopos Research Station, Zimbabwe, to evaluate the impact of widely spaced trees on understorey grass composition, yield and quality. The study trees were Terminalia sericea and Acacia karroo. Ordination techniques using grass density and biomass as indices separated quadrats according to soil type but not grass species according to understorey or open areas or according to tree species. Grass yield under tree crowns was similar to open areas, in contrast with most reports where understorey areas had higher yields. The high understorey grass quality that has been reported from savanna areas exhibiting grass composition differences was not expressed. Selective grazing of palatable perennial grasses growing in association with tree crowns and their eventual replacement by low‐yielding and less‐palatable grasses that normally grow in open areas is proposed as an explanation of the unique tree‐grass interaction scenario of this study. In areas where this replacement has occurred, recovery may require management interventions.

Vegetation, Soil, and Animal Indicators of Rangeland Health

We studied indicators of rangeland health on benchmark sites with long, well documented records of protection from stress by domestic livestock or histories of environmental stress and vegetation change. We measured ecosystem properties (metrics) that were clearly linked to ecosystem processes. We focused on conservation of soil and water as key processes in healthy ecosystems, and on maintenance of biodiversity and productivity as important functions of healthy ecosystems. Measurements from which indicators of rangeland health were derived included: sizes of unvegetated patches, cover and species composition of perennial grasses, cover and species composition of shrubs and herbaceous perennials, soil slaking, and abundance and species composition of the bird fauna. Indicators that provided an interpretable range of values over the gradient from irreversibly degraded sites to healthy sites included: bare patch index, cover of long-lived grasses, palatability index, and weighted soil surface stability index. Indicators for which values above a threshold may serve as an indicator of rangeland health include: cover of plant species toxic to livestock, cover of exotic species, and cover of increaser species. Several other indicator metrics were judged not sensitive nor interpretable. Examples of application of rangeland health indicators to evaluate the success of various restoration efforts supported the contention that a suite of indicators are required to assess rangeland health. Bird species diversity and ant species diversity were not related to the status of the sample site and were judged inadequate as indicators of maintenance of biodiversity.

衛星データによる草地の経年化に伴う分光反射特性変化の把握

Satellite remote sensing provides wide-ranging and temporal information on grasslands, which are indispensable for proper grassland management. In this study the satellite monitoring of annual changes of grasslands is discussed. By applying a new method which utilizes a Grassage Standard Map to a study area in Konsen Plain, Hokkaido, Japan, increases in reflectance according to the aging of grasslands were identified from the data observed in May. The increases were considered to be a result of dead leaf accumulation on the ground surface of grasslands. In the June data, sudden decreases of reflectance in the near infrared and middle-infrared bands were identified within the 4 years period after the grass-renovation. The decreases may be a result of changes in grass biomass and grass species composition. The results demonstrate the significance of the new method for grassland monitoring.

Native prairie grasses and microbial community responses to reclamation of taconite iron ore tailing

The effect of reclamation treatments on seeded native grass cover and species composition, soil microbial biomass carbon, and populations of actinomycetes, fungi, free-living N2-fixing bacteria, and aerobic heterotrophic bacteria was compared in field plots in coarse taconite tailing. Reclamation treatments consisted of all possible combinations of three rates of composed yard waste, three rates of fertilizer, and inoculation with arbuscular mycorrhizal fungi. Composted yard waste increased plant cover, soil microbial biomass, and populations of all groups of microorganisms compared with unamended, non-inoculated control plots. Microbial populations and biomass in tailing plots were low compared with natural soils and were correlated with plant cover and available P. Mycorrhizal inoculation resulted in a 6% increase in plant cover, although this was not significant, and significantly enhanced N2-fixer populations in June but did not affect other groups of microorganisms. There were no differences between moderate and high rates of composted yard waste. We conclude that incorporation of a moderate rate of organic matter can ameliorate the stressful conditions of coarse taconite tailing and can enhance the initiation of a functional soil ecosystem able to support the establishment of seeded native prairie grasses and may provide a long-term solution to reclamation of taconite tailing. Key words: arbuscular mycorrhizal fungi, mine reclamation, soil microorganisms, composted yard waste.

Shortgrass Range Vegetation and Steer Growth Response to Intensive-Early Stocking

A 9-year grazing trial was conducted to compare shortgrass vegetation and steer responses under intensive-early stocking (IES) at 2 stocking rates to season-long stocking (SLS). The stocking rates were (1) equal to SLS, with twice as many steers used for the first half of the SLS grazing season (2X-IES), and (2) greater than SLS. with 3 times as many steers used for the same period (3X-IES). The hypothesis tested was that SLS and 2X-IES would be similar and sustainable in terms of productivity and vegetation composition, whereas 3X-IES would be different and not sustainable. The 3 treatments were assigned to 6 pastures in a randomized-complete block. Grazing was initiated on or near 1 May each year and continued until about 15 July for IES and about 1 October for SLS. Steers were weighted at initiation of grazing and in mid-July, and SLS steers were weighed in October. Vegetation data were collected in July and October in each pasture from 10 randomly located plots. Species composition of grasses was estimated, and grasses and forbs were clipped separately to determine biomass availability. Steer total gain and average daily gain (ADG) under SLS and 2X-IES were equal (P>0.10) during the early season, but 3X-IES gain and ADG were less (P 0.10). Grass and total biomass availability were reduced (P<0.10) over time by 3X-IES. The hypothesis was supported: SLS and 2X-IES were equal in terms of both livestock performance and vegetation responses, but livestock performance and biomass availability were reduced and vegetation composition changed under 3X-IES. Thus, 3X-IES was not sustainable. While SLS and 2X-IES appear biologically equal, using them simultaneously on separate land areas may reduce market variability risk by marketing twice per year.

Grasses of the Precambrian Shield region in eastern lowland Bolivia. I. Habitat preferences

ABSTRACTThe habitat distribution and relative abundance of 113 species of Gramineae were documented by releves in 82 stands near Conception, Santa Cruz, Bolivia. A factor analysis was used to compare the floristic similarity of stands situated in semideciduous forest, cerradao, cerrado, campo rupestre, valley-side campo, pantanal complex or on granite outcrops. Individual grass species usually had a preferred habitat and occurred with decreasing abundance in stands judged to be transitional by physiognomic, edaphic, and floristic criteria. Stands situated in cerrado vegetation were most similar to one another in grass species composition. Cerradao was transitional to semideciduous forest and cerrado but certain grasses were characteristic of this vegetation type. The floristic composition of the single campo rupestre locality was somewhat similar to cerrado; however, several of the more abundant grass species of this vegetation type did not occur in any nearby cerrado stand. Granite outcrops had a distinct grass flora and showed little similarity to other vegetation types. In savanna wetland communities, grass species distribution was influenced by water regime. Differences between stands on valley-side campo corresponded to topographic position on a gradient of increasing water surplus. Seasonally humid/dry stands on valley-side campo and pantanal complexes had a high degree of similarity. Stands lower on the catenary sequence of pantanal complexes and valley-side campos were increasingly dissimilar, a result of the different edaphic conditions of the seasonally flooded soils of pantanal complexes when compared with the permanently saturated (but never flooded) soils of valley-side campos. Pantanal complexes had the richest grass flora of all vegetation types because their microtopographic variability creates numerous micro-habitats with distinct water regimes, each supporting different grass species.

Selectivity in large generalist herbivores: feeding patterns of African ungulates in a semi‐arid habitat

SummaryFeeding habits of free‐ranging wildebeest and zebra were monitored in a semi‐arid nature reserve, bordering the southwestern part of Kruger National Park, South Africa. The purpose of study was to distinguish and define the feeding niches of two roughage grazers that occur in similar habitat types. The monthly compositions of diets were evaluated by direct observations of feeding bouts over a period of two years when rainfall patterns were average and animal populations were stable. Other analyses evaluated the standing biomass of grass species in the reserve during the wet summer and dry winter seasons.A considerable overlap of grass species composition was found in the diets of wildebeest and zebra. Ordination of bi‐monthly records of the diet composition showed greater variations in scores of grasses in zebra diet in comparison to wildebeest. Seasonal patterns were more apparent in the wildebeest diet. Preference ranking of grass species indicated that zebra diet remained constant in winter and summer. Wildebeest diet however, alternated with seasons, showing high preferences during the winter months for grass species which were rejected during summer.The combined assessment of results from three separate statistical methods analysing temporal patterns and preferences in diet composition revealed contradictory trends. The solution, however, relied on the initial assumptions posed. Hence, wildebeest and zebra are essentially generalist feeders which show a limited amount of preference in their choice of diet.