Tussock Grass Research Articles

Studying the post-fire performance of tussock grasses in Patagonia: Survival, biomass production and early competition

Patagonia grasslands are subjected to two main disturbances, fire and grazing, but little information is available about its effects on vegetation. We studied post-fire survival and resprouting ability of two dominant grass species, Stipa speciosa and Festuca pallescens, for four years; evaluated the effect of early post-fire defoliation on both species; and tested whether competition is important in post-fire recovery in San Ramón Ranch, NW Patagonia (Argentina). To simulate grazing, a clipping treatment was applied at the beginning and end of growing seasons. Survival rates were high (>60%) and, after three years, biomass of both species in the burned area was similar to the unburned area. Competition seems to play an important role in the early post-fire recovery of both species, particularly in the case of F. pallescens that increased 87% the biomass production without competition. Fire may improve forage quality by eliminating the standing dead material, but early post-fire grazing might endanger the persistence of F. pallescens. We suggest requiring a resting period before livestock introduction and controlling grazing intensity.

Comparing biodiversity between protected savanna and adjacent non-protected farmland in the southern Kalahari

In this study we investigated the effect of different land use options (wildlife versus livestock) on species richness of plants and reptiles in the protected Kgalagadi Transfrontier Park (KTP) versus adjacent non-protected farmland within the same savanna habitat type (Aoub dune veld) in the southern Kalahari, South Africa. Our results show that both plant and reptile species richness as well as plant cover and reptile abundance was significantly higher in the protected KTP than in the non-protected farmland. The higher proportion of shrub but lower proportions of perennial grass cover, herb cover, and herb species richness in the farmland can be explained by higher stocking rates and the differences in feeding behaviour between native wild ungulates (e.g. Antidorcas marsupialis, Oryx gazella) and livestock (mainly sheep). The reptile’s prey availability and microhabitats (perennial grass tussocks and rodent burrows) for thermoregulation and protection against predators were significantly lower in the farmland. To conclude, our results clearly show that long term effects of different land use options (wildlife in protected KTP versus extensive livestock production in the non-protected farmland) even within the same habitat type have led to significant changes in vegetation composition, availability of microhabitat structures and in the reptile community.

Effects of simulated storm sizes and nitrogen on three Chihuahuan Desert perennial herbs and a grass

Establishment and growth of three perennial herbs and a small tussock grass were studied in an experiment that provided simulated rainfall of 6 mm week −1 or 25 mm once per month and nitrogen fertilization in combination with the different simulated rainfall regimes. Wild onion , Allium macropetalum, failed to establish in plots receiving 25 mm month −1 simulated rainfall. The perennial composite, Bahia absinthifolia, occurred at higher densities in plots that were not irrigated but there were no differences in biomass in any of the irrigation or fertilization treatments. Desert holly, Perezia nana, failed to establish in nitrogen fertilized plots and developed higher abundance and biomass in plots receiving 25 mm month −1. Nitrogen fertilization had either no effect or an adverse effect on the perennial herbs. The tussock grass, Dasychloa pulchella exhibited highest abundance and biomass with 6 mm week −1 added water plus nitrogen. Since global climate change will affect both rain storm frequency and size and atmospheric nitrogen deposition, the results of this study are applicable to understanding vegetation responses climate change.

Fire and grazing differentially affect aerial biomass and species composition in Andean grasslands

Grazing and fire have been the most common disturbances in many grasslands ecosystems for many centuries. However, some mountain regions are currently experiencing a decrease in land use, and therefore in frequency or intensity of these disturbances. In this study, we evaluated how fire and grazing affect vegetation structure in mountain grasslands of NW Argentina. We hypothesized that they would have differential effects on plant species richness, vegetation composition and aerial biomass dynamics, predicting that fire would have a stronger effect on these variables than grazing. We tested this hypothesis by performing a controlled field experiment in which we manipulated fire and compared grazed plots with ungrazed exclosures, simulating current (high frequent fires and low livestock load) and future (fire suppression and grazing exclosure) scenarios. We recorded total of 90 species with 40 shared among all treatments. Tussock grasses ( Elionurus muticus), followed by three shrubs represented the main contribution to live biomass in all treatments. Species richness, equitativity and diversity were higher in burned plots. Multivariate ordination indicated that burning is more important than grazing in determining plot to plot similarity in species composition. Burning reduced total aerial biomass, standing dead biomass and litter, as well as live biomass, that was also reduced by grazing. Burning also reduced standing dead biomass and litter proportions, but increased live biomass contribution, showing a more evident effect within the grazed plots. Burning, seasonality and growing season had significant effects on the relative contribution of all biomass categories. Biomass consumption showed a strong seasonality, being significantly higher in January of both growing seasons, and it was not affected by burning. We conclude that under the current fire and grazing scenario, fire plays a more important role than grazing in shaping these grasslands dynamics.

Mortality of Australian alpine grasses (Poa spp.) after drought: species differences and ecological patterns

Aims Australian alpine ecosystems currently experience high precipitation in the snow-free season, but they are predicted to experience drier conditions under climate change. We observed high mortality of the dominant alpine grasses following drought in 2007. Our aims were as follows: to test the involvement of plant-available water (PAW) and other environmental variables in grass mortality in the field; to detect possible species differences in drought response and to link soil moisture to precipitation using soil properties and climate data. Methods The dominant tussock grasses of the Australian alpine zone, Poa hothamensis var. hothamensis N.G. Walsh, Poa hiemata Vickery and Poa phillipsiana Vickery (Poaceae), all exhibited mortality following drought in the Bogong High Plains, Victoria, Australia in 2007. PAW was calculated using soil water potential measurements, and past drought occurrence was modelled using climate data. We then tested the effects of PAW and soil depth on grass survival both at a large spatial scale spanning the elevational range of the alpine zone and at a smaller scale. Poa hothamensis and P. phillipsiana were compared in a common-garden experiment to test drought tolerance. Important Findings Poa hothamensis survival was predicted by dry-season PAW at the small spatial scale; at the large scale, soil depth and elevation were more important predictors of P. hothamensis survival, but dry-season PAW predicted P. hiemata survival. Common-garden experiments supported field observations that P. hothamensis is more droughtsensitive than is P. phillipsiana. We also present a simple polynomial relationship between rainfall and field soil moisture, which predicts that the alpine soils dry below wilting point several times a year. We suggest the timing of long rain-free periods may be more important than their duration.

Belowground zone of influence in a tussock grass species

Belowground plant competition is strong and mediated by resource depletion as well as by high variety of exudates. Both factors contribute to active root segregation, affecting neighbours’ growth. In field and greenhouse experiments we investigated the belowground zone of influence of Stipa tenacissima, a tussock-forming grass which is the dominant species in many semiarid communities of the western Mediterranean Basin. Sometimes tussocks show a fringe nearly devoid of annual plants, most likely caused by competition or interference. Fringe size was a function of water availability, so that the more water available the smaller the fringe and vice-versa. Aboveground mass of annual plants was higher in gaps than in the fringe, but root mass was higher in the fringe. More species emerged in soils from gaps than in soils from the fringe, and productivity was ten times higher in soils from gaps than in soils from the fringe. Growth of barley plants was inhibited in the vicinity of S. tenacissima tussocks. S. tenacissima produced a belowground zone of influence around the tussock through resource depletion, particularly water, but also likely through root exudates. Both mechanisms might inhibit the establishment of other annual and grass species within the fringe. Fringe area has important effects for plant establishment, influencing population and community dynamics in these semiarid environments.

Assessing the relationship between fire and grazing on soil characteristics and mite communities in a semi-arid savanna of northern Australia

Northern Australian tropical savannas are subjected to pressures from both grazing and planned and unplanned burning. We know little about the effects of these processes on the below-ground environment. The aim of this study was to investigate the effects of fire, grazing and season on environmental and biological properties of the soil at the base of grass tussocks in a semi-arid savanna rangeland of north Australia. A long-term fire and grazing exclusion experiment was used to test the effects of season, fire and grazing on soil physicochemical factors (soil organic carbon, total nitrogen, ammonium, nitrate levels and bulk density) and soil mite abundance and diversity. Grazed plots were associated with small but significant reductions in total soil nitrogen and organic carbon when compared to 30 year old plots where grazing and fire had been excluded. This suggests slow, long-term losses of nitrogen and soil carbon from an ecosystem with limited available nutrients. Fire had a limited impact on soil properties, but this may reflect the modest experimental fire intensity resulting from fuel reduction due to grazing. Treatment effects on soil bulk density were also negligible. Season had a significant impact on total soil mite abundance and diversity, whereas burning and grazing treatments had no impact on soil mites. Only two morpho-species, one each from the families Cunaxidae and Stigmaeidae, decreased in abundance as a result of grazing. Increased moisture levels in the wet season were associated with increased total nitrogen and the highly mobile nitrate. Changes in mite abundance and diversity reflected these changes in levels of nitrogen and it is possible that increasing total nitrogen availability and soil moisture, is a determinant of mite abundance.

Fire tolerance of perennial grass tussocks in a savanna woodland

AbstractGrass populations in tropical savannas are highly resilient in relation to different fire regimes, but the mechanisms conferring such resilience have been poorly studied. Here we examine one such mechanism, high adult survival during fire, for three perennial grass species in an Australian savanna: Eriachne triseta Nees ex Steud, Eriachne avenacea R.Br and Chrysopogon latifolius S.T.Blake. The study examined survivorship after 3 years, at plots subject to experimental fire regimes (experiencing 0, 1, 2 or 3 fires over the study period) at the Territory Wildlife Park near Darwin in the Northern Territory, Australia. Mean survivorship was 79.9%, 64.3% and 62.0% for E. avenacea, E. triseta and C. latifolius respectively. For the two species of Eriachne, mean survivorship was highest (E. avenacea, 94.6%; E. triseta, 77.1%) in unburnt plots, whereas survivorship of C. latifolius was highest (71.7%) under highest fire frequency. However, variation in survivorship among fire regime treatments was not statistically significant for any of the study species. This negligible difference in survivorship among regimes points to fire tolerance (sprouting ability) as an important mechanism contributing to the resilience and persistence of perennial grasses in these savannas.

Effects of arbuscular mycorrhizal colonisation on shoot and root decomposition of different plant species and species mixtures

We studied the decomposition of shoot and root tissues of four plant species from central Argentina belonging to contrasting functional types: a deciduous shrub ( Acacia caven ), a perennial forb ( Hyptis mutabilis ), an annual forb ( Bidens pilosa ) and a tussock grass ( Jarava pseudoichu ). They were grown from seed in a greenhouse in isolation or in 2- or 4-species mixtures, with and without arbuscular mycorrhizal fungi (AMF), and then placed to decompose under natural conditions in the field. AMF significantly enhanced decomposition of shoots, but not that of roots, independently of species identity and species-mixture composition. Our results suggest that AMF may be significantly affecting ecosystem functioning through the observed plant-mediated effects on decomposition. ► AMF significantly enhanced decomposition of shoots, but no that of roots. ► AMF improved decomposition independently of species identity and species mixture. ► Our results extend the evidence on the positive effects of AMF on decomposition. ► AMF may be playing a main role at ecosystem level via the decomposition pathway.

Effects of predation risk on the nocturnal activity budgets of thin-billed prions Pachyptila belcheri on New Island, Falkland Islands

Predation is a major ecological and evolutionary driver of natural populations, greatly influencing fitness and behaviour of prey species. Small, long-lived petrels are vulnerable to predation at the breeding colonies and are expected to evolve behavioural strategies to minimize predation risks. Using an automatic nest monitoring system and nightly aerial counts, we examined the effect of vegetation cover and moonlight on colony attendance patterns and levels of burrow activity of breeding thin-billed prions, Pachyptila belcheri, on New Island, Falkland Islands. We further investigated how these parameters were related to predation by Falkland skuas. We monitored up to 32 nests in two habitats, one with Tussock grass and one with low vegetation cover. Individuals in both areas were more active at the nest before hatching, and those breeding in the low cover habitat were more active and arrived at the colony earlier, which might reflect an effect of reaction time over predation risk. Nocturnal activity peaks shifted in time as the season progressed, indicating behavioural adjustments to sunrise hours. Moon phase did not affect attendance and activity levels of breeders in either habitat or overall aerial activity, but influenced arrival time at the colony during chick-rearing, individuals arriving later in periods of full moon. Skua capture rates were positively correlated with aerial and nest activity but not with overall breeder attendance and were unaffected by moon phase. Thin-billed prions activity budgets are influenced by environmental parameters that affect their likelihood of being predated.

Abscission of leaf laminas – An unnoticed factor in tussock grass formation

Drop of leaves at structurally defined abscission zones is a typical feature of dicotyledonous angiosperms. It is rare in monocots including the grass family (Poaceae). Some grass species have an odd, yet poorly studied pattern of leaves disarticulating regularly between the leaf sheath and the leaf lamina. Using species of three distantly related genera, such disarticulation zones were anatomically studied for the first time to clarify the structural background of shedding. The abscission zones of the three species turned out strongly different from each other in position, spatial arrangement and cellular architecture of different tissues, which is described and illustrated in detail. Breakpoints of the lamina were consistently defined by a sharp delineation of parenchymatous against sclerenchymatous tissue, irrespective of how these tissue types were arranged, e.g., sclerenchyma on the top of the sheath ( Danthoniastrum), at the base of the lamina ( Macrochloa), or alternating longitudinally with parenchyma ( Aristida). The tussock grasses Danthoniastrum and Macrochloa had the most complicated and elaborately structured abscission zones. The results suggest that precise and efficient shedding of leaf laminas is an important factor enabling grasses to form tussocks as implicitly addressed already in 1890 by the agrostologist E. Hackel. Tussocks are a habitually conspicuous and ecologically important growth form of grasses in arid and/or alpine vegetation zones across the world. Judging from our exemplary results it must be expected that even further structural and mechanic patterns of precise leaf blade abscission will be found in tussock grasses of other grass subfamilies, such as the panicoids, chloridoids or arundinoids.

Impact of habitat type and landscape structure on biomass, species richness and functional diversity of ground beetles

This study investigated how local habitat type and landscape structure affects the biomass, species richness and functional diversity of ground beetles sampled from a 1000 ha UK arable farm. At a local scale habitat type was either crop (winter wheat and oilseed rape) or one of five field margin habitats. Surrounding each of these sampling areas, landscape structure was defined using remote sensed data from Specim AISA Eagle (400–970 nm) and Hawk (970–2450 nm) hyperspectral sensors. Ground beetles were divided into predatory and phytophagous trophic levels. Local habitat type only affected phytophagous ground beetle biomass, which was lowest within crops. Total biomass of predatory beetles was negatively correlated, and species richness positively correlated, with landscape habitat diversity. Only the functional diversity of predatory ground beetles responded to landscape structure, showing positive correlations with the proportion of Tussock Grass field margins. Predatory ground beetles show a greater dependence on landscape structure than phytophagous species, a response that is attributed to their high mobility needed for movement between dynamically variable food resources.

Glyphosate effects on floristic composition and species diversity in the Flooding Pampa grassland (Argentina)

Temperate grasslands of Argentina are extensively grazed by domestic livestock. Primary production follows a seasonal pattern, with maximum vegetation growth in late spring and minimum in winter. During the last decade, winter forage productivity has been encouraged by promoting the growth of cool-season annual grasses through late summer applications of glyphosate. The aim of this study was to describe structural changes in grassland vegetation associated with glyphosate treatments, as applied in a commercial livestock farm in the Flooding Pampa. Vegetation composition was assessed from spring 2006 to late summer 2008, in three paddocks that had never been exposed to any kind of herbicide, and three other paddocks treated with glyphosate in late summer in the previous 5 years. In the paddocks treated with glyphosate, basal cover of cool-season annual grasses and forage value in spring were greater but basal cover of cool-season perennial grasses, warm-season tussock grasses, warm-season legumes, total basal vegetation cover and forage value in summer were much lower respect to untreated paddocks. The shift in floristic composition resulted in less rich and even assemblages, dominated by an annual species and impoverished in native and perennial species. These structural changes may alter ecosystem processes through the increase of soil salinization and water losses in summer, may affect the seasonal pattern of productivity and may threaten biodiversity conservation and sustainability of wild life.

Comparison between grassland communities with and without disturbances

Grassland management with fire and grazing is considered one of the main factors determining plant physiognomy and composition in grassland ecosystem. In that sense, it is thought that intermediate disturbances, neither high frequent and/or intense, nor absent, could enhance grasslands diversity by diminishing the competitive exclusion. Therefore, the present study evaluated the effect of disturbance exclusion over grassland plant communities in Plateau region of Southern Brazil. Two grasslands were sampled: one excluded of disturbances over the past 16 years, and other with fire and grazing disturbances. Six plots (1m2) were sorted inside each area. Inside each plot, plant species composition was described, while plant richness and evenness were assessed based on cover proportion of each species. The data analysis showed that the grassland without disturbances presented higher richness and evenness. Furthermore, there were differences in the species composition between the grasslands, with less tussock dominance in the disturbed grassland. In addition, plots’ compositions were more homogeneous in areas submitted to disturbances, despite of the high richness. It is concluded that dominant tussock grasses in the grassland without disturbances suppressed many forbs, leading to reducing the species richness and evenness. On the other hand, the presence of disturbances limits the tussocks growth allowing the development of other forbs species. Key words: grassland management, fire, cattle grazing, intermediate disturbance.

Comparison between grassland communities with and without disturbances

Grassland management with fire and grazing is considered one of the main factors determining plant physiognomy and composition in grassland ecosystem. In that sense, it is thought that intermediate disturbances, neither high frequent and/or intense, nor absent, could enhance grasslands diversity by diminishing the competitive exclusion. Therefore, the present study evaluated the effect of disturbance exclusion over grassland plant communities in Plateau region of Southern Brazil. Two grasslands were sampled: one excluded of disturbances over the past 16 years, and other with fire and grazing disturbances. Six plots (1m2) were sorted inside each area. Inside each plot, plant species composition was described, while plant richness and evenness were assessed based on cover proportion of each species. The data analysis showed that the grassland without disturbances presented higher richness and evenness. Furthermore, there were differences in the species composition between the grasslands, with less tussock dominance in the disturbed grassland. In addition, plots’ compositions were more homogeneous in areas submitted to disturbances, despite of the high richness. It is concluded that dominant tussock grasses in the grassland without disturbances suppressed many forbs, leading to reducing the species richness and evenness. On the other hand, the presence of disturbances limits the tussocks growth allowing the development of other forbs species. Key words: grassland management, fire, cattle grazing, intermediate disturbance.

Using native riparian barriers to reduce Giardia in agricultural runoff to freshwater ecosystems

Waterway degradation in agricultural settings is caused by direct and diffuse sources of pollution. Waterway fencing focuses on reducing direct faecal contamination, but the extent to which it reduces overland surface runoff of pathogens is unknown. This study evaluated the potential of four riparian treatments to reduce Giardia in saturation excess surface runoff entering the waterway. Treatment 1 comprised exotic pasture grass and weeds that regenerated from bare soil between the fence and the waterway in the absence of cattle grazing and was compared with three others comprising monocultural plantings of New Zealand native grassland plants. Runoff experiments involving Giardia were performed after planting, both prior to and following the summer growing season. Giardia was not detected from any plot prior to cyst addition. In spring the native 'C. secta', 'A. lessoniana' and 'C. richardii' treatments showed significantly greater reductions in Giardia in runoff than the 'exotic grasses' treatment, while in autumn the 'C. richardii' treatment reduced Giardia more than the 'exotic grasses/weeds'. A reduction in public health risk should follow from riparian vegetation, whether exotic or native, but with an added benefit in the case of the native tussock grass C. richardii, due to the associated lower runoff rate.

Biological soil crusts modulate nitrogen availability in semi-arid ecosystems: insights from a Mediterranean grassland

Biological soil crusts (BSCs) greatly influence the N cycle of semi-arid ecosystems, as some organisms forming them are able to fix atmospheric N. However, BSCs are not always taken into account when studying biotic controls on N cycling and transformations. Our main objective was to understand how BSCs modulate the availability of N in a semi-arid Mediterranean ecosystem dominated by the tussock grass Stipa tenacissima. We selected the six most frequent soil cover types in the study area: S. tenacissima tussocks (ST), Retama sphaerocarpa shrubs (RS), and open areas with very low (BS), low (LC) medium (MC) and high (HC) cover of well developed and lichen-dominated BSCs. The temporal dynamics of available N dynamics followed changes in soil moisture. Available NH 4 + -N did not differ between microsites, while available NO 3 - -N was substantially higher in the RS than in any other microsite. No significant differences in the amount of available NO 3 - -N were found between ST and BS microsites, but these microsites had more NO 3 - -N than those dominated by BSCs (LC, MC and HC). Our results suggest that BSCs may be inhibiting nitrification, and highlight the importance of this biotic community as a modulator of the availability of N in semi-arid ecosystems.

Alpine Peatlands of the Andes, Cajamarca, Peru

An ecological analysis of wetlands in the high mountain jalca above 3700 m elevation in the Andes near Cajamarca, Peru, indicated that most wetlands are groundwater-supported peat-accumulating fens. The floristic composition of fen communities was controlled largely by groundwater chemistry, which was highly variable and influenced by watershed bedrock composition. Watersheds with highly mineralized rock discharged water as acidic as pH 3.7, which was high in CaSO4, while watersheds with limestone, marble, and skarn produced groundwater as basic as pH 8.2 and high in CaHCO3. Of the 125 plots sampled in 36 wetland complexes, >50% of plots had at least 3 m of peat, and 21 plots had peat thicker than 7 m. Most soil horizons analyzed had 18 to 35% organic carbon, indicating high C storage. A total of 102 vascular plants, 69 bryophytes, and 10 lichens were identified. Study plots were classified using TWINSPAN into 20 plant communities, which were grouped into four broad categories by dominant life form: (1) cushion plant communities, (2) sedge- and rush-dominated communities, (3) bryophyte and lichen communities, and (4) tussock grass communities. Direct gradient analysis using canonical correspondence analysis indicated that Axis 1 was largely a water chemistry gradient, while Axis 2 was a complex hydrology and peat thickness gradient. Bryophytes and lichens were more strongly separated in the ordination space than vascular plants and were better indicators of specific environmental characteristics.

Antagonistic effects of large- and small-scale disturbances on exotic tree invasion in a native tussock grassland relict

It is generally accepted that disturbances increase community invasibility. Yet the role of disturbance in plant invasions may be less predictable than often assumed, due to the influence of environmental stochasticity and interactions between disturbance regimes. We evaluated the single and interactive effects of prescribed burning (large-scale, infrequent event) and animal diggings (small-scale, frequent events) on the invasion success of Gleditsia triacanthos L. in a tussock grassland relict of the Inland Pampa, Argentina. Tree seedling emergence and survival were monitored over 4 years, after adjusting for propagule pressure through copious seed addition to all disturbance treatments. Burning altered community structure by suppressing tussock grasses and promoting exotic forbs, whereas simulated, armadillo-like diggings had little impact on herbaceous composition. Overall, seedling emergence rather than survival represented the main demographic bottleneck for tree invasion. Tree establishment success varied among seedling cohorts emerged in different climatic years. In a dry year, emergence was only slightly affected by disturbances. In contrast, for two consecutive wet years, initial burning and armadillo-like diggings exerted strong, antagonistic effects on tree recruitment. Whereas fire alone increased recruitment, the simulated burrowing regime prevented seedling emergence in both burned and unburned plots. The latter effect might be explained by reduced soil moisture, and increased seed burial and predation in excavated patches. Thus, the impact of a single, large-scale perturbation promoting woody plant invasion was overridden by a regime of small-scale, frequent disturbances. Our results show that grassland invasibility was contingent on inter-annual climatic variation as well as unexpected interactions between natural and anthropogenic disturbance agents.

Organic and inorganic fertilizer effects on a degraded Patagonian rangeland

The forest-steppe ecotone in NW Patagonia is a semiarid ecosystem affected by natural and anthropogenic fires, and overgrazing by sheep. Following a wild fire in the driest portion of this ecotone, a 3-year study was conducted to assess the impacts of a single application of inorganic and organic fertilizers on soil and vegetation recovery. Organic fertilizers were composts derived from biosolids and municipal solid wastes. Six treatments were evaluated: screened and unscreened biosolids compost and municipal solid wastes compost (40 Mg ha−1), inorganic fertilizer (100 kg N and 35 kg P ha−1), and no application. Soils were chemically characterized, and soil microbial activity was assessed as potential respiration and N-mineralization. Vegetation responses included plant cover, composition, phytomass, and N resorption prior to abscission, and leaf litter quality of the dominant species. Organic fertilizers increased soil organic matter, nutrients and microbial activity. Plant cover and aboveground phytomass, dominated by the native perennial tussock grass Poa ligularis, showed a higher increase with inorganic than with organic fertilization. While vegetation responded more to inorganic fertilizer, due to its higher initial pulse of available N, organic fertilizers had a positive impact on soil chemical and biological properties.