Tussock Cover Research Articles

Moderate grazing intensities modulate canopy structure that influences short‐term intake rate of heifers grazing a natural grassland

AbstractGrazing management frequently relies on forage availability as an indicator of performance. However, canopy structure and composition can play an important role in foraging behavior and intake in native grasslands. Here, we aim to (1) assess the effect of grazing management on herbage biomass, tussock cover, average canopy and inter‐tussock canopy height, and to (2) study the effect of these canopy structure components on short‐term intake rate (STIR) and patch selectivity of beef cattle, in a native grassland in the Campos region in southern Brazil. Ten 1000 m2 experimental units were built in five paddocks (two per paddock) managed with different herbage allowance (HA) treatments: four fixed year‐round HA (1 to 4 kg dry matter [DM]/kg live weight [LW]) and one variable HA (2 and 3 kg DM/kg LW during spring and the rest of the year, respectively). The experimental units were grazed individually with four heifers during 45 min, in two grazing cycles. Before each grazing session, we assessed the total herbage mass, average and inter‐tussock canopy height, and tussock cover. During the 45‐min grazing sessions, we evaluated the STIR (g DM/kg LW0.75/min) and grazing time in tussock and inter‐tussock strata. Increasing the HA increased the total herbage mass, canopy height and tussock cover. The STIR was maximized with herbage mass of 2200 kg DM/ha and a tussock cover of ~7%, canopy structures related with moderate grazing intensities (i.e., 2 and 3 kg DM/kg LW), which increased the selection opportunity by herbivores. Canopy structures associated with heavy (1 kg DM/kg LW) and lenient grazing intensity (4 kg DM/kg LW) determined linear decreases of 50% in STIR.

Holistic versus continuous grazing in Patagonia: A station-scale case study of plant and animal production

We compared animal and vegetation responses of a 13 600-ha area under holistic grazing management (HGM) with a similar area under continuous grazing (CGM) in a Patagonian station. Limitations were a dry 2012−2016 experimental period, poorer soils, and grazing of native guanacos (Lama guanicoe) in the HGM area. Forage standing crop in this area before the experience was lower and remained so during the study: (194 ± 31 HGM vs. 244±33 kg dry matter.ha−1 CGM). Six monitoring sites showed similar and remarkable (though mostly nonsignificant) vegetation improvements in total cover (10.6% HGM vs. 10.9% CGM) and cover of short palatable grasses (21.4% vs. 23.9%, respectively). Species richness showed small changes (−1 vs. −6%), bare soil interpatches decreased (−11.9 vs. −5.4%), and land function indicators of Stability (5.4% vs. 9.9%), Infiltration (12.4% vs. 12.0%), and Nutrient recycling (4.2% vs. 20.6%) increased. Tussock cover changed significantly with grazing management, as it decreased −6% (ns) in HGM and grew 42% (P = 0.03) under CGM, probably due to coarse tussock forage consumption in HGM. Sheep under HGM were 15% lighter (43.9 ± 0.5 HGM vs. 51.7 ± 0.5 kg.ewe−1 CGM P < 0.001), ewes scored 28% lower body condition (1.60 vs. 2.25, P < 0.001), and lambing rates were 36% lower (48.3 ± 2.1% vs. 74.2 ± 1.9%). Rotation ended in 2015 as a consequence of low lambing rates, and sheep body condition and reproductive rates recovered to similar values in both areas. Positive vegetation changes in both areas may be driven by residual effects of destocking 3 decades ago and show that improvement is possible using moderate stocking rates. Although it could be argued that rest periods of HGM may be positive in the long term, its negative effects on animal production should be addressed, and fast regeneration using intense management in these severely restricted habitats should not be expected. Slow, persistent progress under careful management seems achievable under both grazing systems.

Predicted effects of climate change on a Mediterranean keystone plant species

Keystone plant species are known to provide various essential ecosystem services. The Mediterranean keystone species Stipa tenacissima improves soil functioning and facilitates the establishment of different plant species, so it is used in restoration programmes. In this paper, we aimed to predict the impacts of climate (aridity) and soil texture (sand content) on the establishment and development of S. tenacissima (number, cover and width of tussocks) and on soil properties underneath S. tenacissima tussocks. This research demonstrated a significant positive effect of S. tenacissima on LFA (landscape function analysis) indices, revealing the importance of this key species in the soil stabilization, water infiltration and nutrient cycling. Similarly, soil nutrient contents (organic carbon and total nitrogen) and enzyme activities (s-glucosidase and phosphatase) were highly improved underneath S. tenacissima compared to bare ground areas. However, increases of aridity and sand content showed strong negative effects on soil organic carbon, total nitrogen and activities of the hydrolytic enzymes both on bare ground areas and underneath S. tenacissima tussocks. Furthermore, we found that the climate is the main controller of the number of S. tenacissima tussocks, cover and width. Soil sand content influences the colonization of S. tenacissima, as it affects soil water potentials. In general, this study demonstrates the non-sustainability of S. tenacissima under a warmer and drier climate, which will negatively affect its ability to create islands of fertility in South Mediterranean grasslands.

Physiognomic responses of páramo tussock grass to time since fire in northern Ecuador

Ecologically-sound management plans for high-altitude grasslands of the Andes depend on an understanding the responses of plants to fire, especially the dominant tussock grasses. This study considers physiognomic responses of tussock grass in 13 sites in northern Ecuador with a known fire history, with time since fire 0.5–10 y, and a control site which had not been burned for at least 40 y. At each site, we assessed vegetation height, basal cover of the tussocks, and the ratio of dead:live leaves in tussocks. We also measured light at ground level. As recovery time increased, tussock cover and number decreased, while tussock height increased. Light levels fell sharply below the tussock canopies as recovery took place, and dead leaves accumulated quickly, reaching 60 – 70% by just two years after fire. The modification of physical tussock structure is likely to influence a much wider ecosystem response to fire, and determines directly the fuel load for future fires. Despite these clear changes in tussock characteristics, they were too variable to be used as a reliable bioindicator of time since fire. However, a better understanding of the responses of tussock grasses to fire and particularly its impact on other species should become the focus of further attention in future.

Vegetation composition and structure are important predictors of oviposition site selection in an alpine butterfly, the Mountain Ringlet Erebia epiphron

Knowledge of species’ ecological requirements is key for designing effective conservation management. In butterflies, the needs of larval stages are often the most specialised part of the life-cycle, but for many species information on this is lacking. The Mountain Ringlet Erebia epiphron is a cold-adapted butterfly found in alpine grasslands in mountainous regions of Europe. Efforts to devise conservation strategies for this climate change-threatened species are hampered due to its basic ecology being poorly understood. Here, we describe a study on the autecology of Mountain Ringlets at sites across its British distribution, focusing on the habitat preferences of egg-laying females as a proxy for larval preferences. Female Mountain Ringlets placed their eggs predominantly on Nardus stricta and Festuca ovina, but also on several other host plant species, suggesting larvae may be more broadly polyphagous than previously realised. Sites chosen for eggs had higher abundance of larval host plants, intermediate leaf litter cover, and lower cover of grass tussocks than random locations, as well as a shorter and sparser grass sward. Although the main host plant is ubiquitous in upland areas of Britain, our findings suggest that this butterfly’s egg and larval stages have specialised ecological requirements, requiring specific microhabitat features characterised by a narrow range of vegetation composition and structural characteristics. Many habitat associations are liable to be explicable as adaptations to ensure placement of eggs and larvae in sites within optimal (warm or buffered) microclimates. We tentatively suggest that the distribution of Mountain Ringlets in the landscape is thermally-constrained.

Context-dependent variation of SLA and plant height of a dominant, invasive tall grass (Brachypodium genuense) in sub-Mediterranean grasslands

The cessation of semi-extensive farming and the abandonment of settlements are threatening European pastoral landscapes and their biodiversity, affecting species assemblage and ecosystem functioning. This process typically involves invasion by coarse tall grasses, mostly with competitive stress-tolerant strategies, and rapid development of mono-dominance stands. A key species in this respect is Brachypodium genuense (DC.) Roem. et Schult., an endemic, rhizomatous, tall-grass that grows in the semi-natural grasslands of the Italian peninsula over 1200–1400m a.s.l.We hypothesized that B. genuense was able to spread and dominate the grassland communities subjected to a wide range of environmental conditions through its broad spectrum of performances. In fact, it has considerable morphological variability, mirrored by high variations of traits, namely Specific Leaf Area (SLA), individual height, and tussock cover values. The study area encompassed the Monti Sibillini National Park (central Italy). We found that in more productive conditions (deeper soil, medium/high pH values, north-facing slopes, and “conservative” landforms) populations of B. genuense had higher SLA, plant height and cover values than in low productive conditions (south-facing slopes, shallow soils, lower pH values). This indicates a fast-growing strategy based on a high rate of resource acquisition and use, as well as high competitive ability for aboveground resources such as light under productive conditions. Under unproductive and/or dry conditions decreased SLA, plant height and cover value indicate a slow-growing strategy with high conservation and low rate of resource acquisition. In addition, we found that a very high amount of nitrogen in the soil might have a detrimental effect on B. genuense individuals, decreasing the SLA values, thus requiring the plant to change its growth strategy. Finally, we inferred that the observed variability in SLA might have a paramount role in the invasive/dominant behavior of Brachypodium genuense.

Effects of sheep grazing exclusion on alpine tall tussock grasslands

Substantial areas of alpine tall tussock grasslands are being retired from grazing as part of Crown pastoral lease tenure review because of the perceived negative impact of grazing livestock. However, relatively little is known about the effect of sheep exclusion on these grasslands. We analysed data from five grazing exclosure plots over a 6-year period to examine the effect merino sheep have relative to hares and rabbits in alpine tall tussock grasslands used for summer grazing. Unfortunately, because of snow damage to fences, we were unable to detect any significant hare and rabbit effects. Over the time of this study, there was no evidence for significant vegetation recovery after exclusion of sheep grazing. This may be because of other grazing animals in the system, or the low stocking rates and non-random grazing behaviour of merino ewes. There was, however, a significant increase in the cover of exotic herbs Pilosella officinarum and P. praealta and a significant decrease in the cover of native tussocks Festuca novae-zelandiae and Poa colensoi regardless of grazing exclusion. While this pattern has been previously documented in studies at lower elevations and usually with a history of burning, our results demonstrate that alpine grasslands with no burning history can also be invaded by Pilosella spp. over relatively short time frames. Replicated grazing exclosure trials such as the one described in this paper are important for providing objective information on both long-term trends in vegetation composition and the impacts of grazing animals in alpine grasslands as a basis for making informed decisions on their future management.

A conceptual model for changes in floristic diversity under grazing in semi-arid Patagonia using the State and Transition framework

Effect of grazing on plant diversity was studied based in 92 sites of the semiarid Magellan Steppe, South Patagonia, Argentina. 85 species were registered, 96% of them perennials and mostly native and endemic, with only 7.6% exotics. Cover of tussock grass Festuca gracillima was used as a Proxy variable for grazing intensity. Maximum likelihood analysis of diversity vs. tussock cover selected a quadratic function with a maximum at intermediate grazing intensities, closer to predictions of equilibrium models (MSL) for sub humid environments with a long history of grazing than those for semi arid-short evolutionary grazing history. State and Transition (ST) models indicate that the most diverse areas have probably lost tussock cover by intense use in their grazing history but are at present under lower grazing pressure, as this induces gain of diversity of short grasses without reestablishing tussock cover. A new model is proposed combining previous MSL and ST models. It shows a smaller increase in diversity with intermediate/high grazing, loops in the trajectory and multiple alternate states under low grazing depending on the management history. It may be an example of non-linear models that are supposed to be common in semiarid areas but have few published examples.

Can animal performance be predicted from short-term grazing processes?

Despite all the biotic and abiotic factors affecting foraging by ruminants, there is a common and fundamental process, which is bite gathering. We hypothesised that because the mechanics of bite formation dominate the foraging process, changes in short-term bite mass are reflected in longer-term animal performance across a wide range of sward conditions. We focus at the meal level of foraging, using experiments in which the effect of abiotic factors and digestive constrains are minimised, making intake rate the main currency. We estimated bite mass across a wide range of structural challenges to large-herbivore foraging in a long-term experiment with heterogeneous native grasslands. A conceptual model was developed for average daily gain, where energy gain and energy costs were proximate causal variables. Energy gain was a function of diet quality and components of daily intake rate, where bite mass was the main component estimated. In turn, components of intake rate were determined by sward structure and bodyweight. Energy costs were a function of bodyweight and abiotic conditions. Finally, sward structure, bodyweight and abiotic conditions were determined by experimental treatments, seasons and years. Then, the conceptual model was translated into statistical models that included variables measured or estimated, and coefficients representing all links in the conceptual model. Weight gain was a function of bite mass, forage characteristics, and animal and abiotic conditions. Models were set up to test whether forage and stocking conditions affected monthly gain beyond the effects through bite mass, after correcting for abiotic factors. Forage mass, height and disappearance did help predict monthly gain after bite mass was included in the model, which supported our hypothesis. However, stocking treatments and season had significant effects not incorporated in bite mass. Although the model explained 77.9% of liveweight gain variation, only 35.2% was due to fixed effects, with 10.8% accounted by bite mass and its interactions. Concomitant experiments showed that sward structure (first with sward height and the second with tussock cover) does determine bite mass and short-term intake rate in the complex native grasslands we studied. Yet, other temporal varying components of monthly gain not correlated with bite mass, temperature or wind, added most of the observed variation in monthly animal performance. Part of the model failure to account for variation in performance may be related to a significant and temporally variable grazing of tussocks. We used a bite mass model that assumed no tussock grazing. In light of these results and a parallel experiment, we conclude that tussock grazing must be incorporated in future versions of the model.

Videographic Analysis of Eriophorum Vaginatum Spatial Coverage in an Ombotrophic Bog

The use of Remotely Piloted Aircraft Systems (RPAS) as well as newer automated unmanned aerial vehicles is becoming a standard method in remote sensing studies requiring high spatial resolution (&lt;1 m) and very precise temporal data to capture phenological events. In this study we use a low cost rotorcraft to map Eriophorum vaginatum at Mer Bleue, an ombrotrophic bog located east of Ottawa, ON, Canada. We focus on E. vaginatum because this sedge plays an important role in methane (CH4) gas exchange in peatlands. Using the remote controlled rotorcraft we were able to record, process, and mosaic 11.1 hectares of 4.5 cm spatial resolution imagery extracted from individual frames of video recordings (post georegistration RMSE 4.90 ± 4.95 cm). Our results, based on a supervised classification (96% accuracy) of the red, green, blue image planes, indicate a total tussock cover of 2,417 m2. Because the basal area of the plant is more relevant for calculating its contribution to the CH4 flux, the tussock area was related to the basal area from field data (R2 = 0.88, p &lt; 0.0001). Our final results indicate a total basal area of 1,786 ± 62.8 m2. Based on temporal measurements of CH4 flux from the peatland as a whole that vary over the growing season, we estimate the E. vaginatum contribution to range from 3.0% to 17.3% of that total. Overall, our low cost approach was an effective non-destructive way to derive E. vaginatum coverage and estimate CH4 exchange over the growing season.

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.

Foraging behaviour of beef heifers and ewes in natural grasslands with distinct proportions of tussocks

In natural grasslands, plant species preferred by grazing animals are intermixed with less preferred species. We hypothesise that increasing proportion of Eragrostis plana Nees tussocks, a non-preferred diet item in natural grassland, will constrain the accessibility of the preferred diet item for grazing animals, and sheep would be less restricted than cattle. The experimental paddocks contained approximately 0, 25, 50 and 75% E. plana, in vegetative stage. Inter-tussock areas were proportionally maintained at a non-limiting forage allowance. Records were made every 1-min of the stratum (tussock, inter-tussock or intra-tussock) grazed by each of four beef heifers or four ewes. Short-term intake rate was calculated for each 45-min grazing session by weighing the animals before and after grazing, and correcting for insensible weight losses (evaporative and gaseous losses). Beef heifers reduced grazing time on the inter-tussock areas by 0.60% per each 1% increment in tussock cover, whilst ewes exhibited a smaller reduction of 0.36% (P<0.05). Virtually all of beef heifers’ reduction in inter-tussock grazing time was replaced by tussock grazing. However, the ewes were more selective and attempted to find preferred food in the intra-tussock stratum. Ewes adjusted their foraging strategies and maintained a constant short-term intake rate regardless of percentage of tussock cover. Beef heifers exhibited the highest short-term intake rate with 34% tussock cover. Beef heifers bite mass decreased when tussock cover increased over 44%, whereas no trend was detected for ewes. Tussocks may act as a vertical and/or horizontal barrier interfering with the process of bite formation and affecting bite mass of beef heifers. Conversely, ewes were able to adapt their grazing behaviour with increasing tussock cover, so that no effects on the measures taken in this study were observed. This response is consistent with the finer resolution of grazing selectivity by ewes and with the allometry of short-term intake rate.

The role of habitat complexity on spider communities in native alpine grasslands of New Zealand

Abstract. 1. Physical structure and species composition of vegetation determine spider diversity through habitat availability. Here, we assess, for the first time, the role of plant structure on spider communities in New Zealand native alpine tussock grasslands. We investigate the specific associations between spider assemblages and plant communities and test the hypothesis that spider diversity increases with plant diversity and tussock cover.2. Spiders were sampled using density‐ and abundance‐activity‐dependent methods. Data on physical characteristics and species composition of plants revealed gradients in vegetation, driven by distinct intra‐ecosystem plant communities. Effects of vegetation on spider diversity and composition were assessed through linear mixed‐effects models. Redundancy analysis was used to determine and visualise the spider species–level response to gradients in plant compositions.3. There was a positive relationship between plant diversity and spider diversity, while the effects of tussock cover varied with spider taxa. Overall, physical structure and species composition of vegetation had effects on the abundance of a similar number of spider species and families.4. Gradients in vegetation were matched to gradients in spider communities, whose diversity and composition varied according to their habitat preference. The family Orsolobidae was associated with wetland vegetation, and Linyphiidae with shrubs. The abundance of certain spider families and species, such as Lycosidae and Anoteropsis hilaris, was consistently affected by vegetation.5. Environmental factors, such as soil moisture, may affect plant species composition and physical structure in tussock grasslands, which in turn determine spider assemblages. Lycosidae were identified as potential indicators of structural changes in tussock grassland plants and could be valuable for ecological monitoring in conservation management.

Linking Land-use, Water Body Type and Water Quality in Southern New Zealand

Land-use and vegetation cover have been linked to the nutrient levels (nitrogen, phosphorus) of surface waters in several countries. However, the links generally relate to streams and rivers, or to specific types of standing water, for example shallow lakes in a geologically defined region. We measured physical variables and nutrient chemistry of 45 water bodies representative of the wide range of lentic wetland environments (swamps, riverine wetlands, estuaries, reservoirs, shallow lakes, deep lakes) in Otago, New Zealand, and related these to catchment variables and land-use in order to assess the potential influence of catchment modification on water quality of these diverse wetlands. Catchment boundaries and land cover were derived from maps using ArcView GIS software. Our predictions that concentrations of nutrients and other components of water quality would correlate positively with the nature and intensity of catchment modification were confirmed in multivariate analyses. Physical and chemical measures were positively related to the extent of modification in the catchment (percentage of the catchment in pasture, planted forest, scrub and urban areas), and negatively related to lack of catchment modification (more of the catchment in bare ground, tussock grassland and indigenous forest). The strong negative correlations between nutrient concentrations, suspended sediment, water colour and the percentage of tussock cover in the catchment imply that increased conversion of the␣native tussock grassland to pastoral farming in␣Otago will increase nutrient concentrations and␣reduce water quality of the diverse lentic ecosystems.

Vegetation Structure and Soil Properties in Ecuadorian Páramo Grasslands with Different Histories of Burning and Grazing

High-altitude grasslands in the north Andes (páramos) are subject to frequent fires that are usually set by farmers to support traditional cattle-raising systems. Apparently, this practice has caused dramatic changes in the structure and composition of native vegetation, but the mechanisms, magnitude, and direction of these changes still need to be documented for a broader range of conditions. This paper describes the differences in selected soil properties, ground cover, grass tussock structure, and populations of giant Andean rosettes (Espeletia pycnophylla) in four páramo sites in northwestern Ecuador, characterized by contrasting patterns of burning and grazing. The only differences between the soil properties of the sites were the higher pH in the least disturbed site, and the high concentration of P in the more recently burned site. Along the sequence of least impacted to most impacted sites, we observed a decrease in grass tussock cover, and an increase in the amount of bare ground and number of fragments per tussock. In the most undisturbed site tussock coverage was extremely low due to the dominance of shrubs. The density of giant Andean rosettes was higher in the sites with intermediate disturbance regimes, while the mortality of adult stem rosettes was significantly higher at the more recently burned site. The significance of these differences is discussed in the context of the regeneration of páramo vegetation after burning and grazing disturbance.

Status of white-chinned petrels Procellaria aequinoctialis Linnaeus 1758, at Bird Island, South Georgia

The white-chinned petrel (Procellaria aequinoctialis) is an abundant, widespread petrel breeding in tussock grassland at sub-Antarctic islands. Over the last decade it has been killed in large numbers in temperate and sub-tropical longline fisheries. However no data are available on the global population status. We assessed the status of white-chinned petrels at Bird Island, South Georgia by comparing the distribution and density of occupied burrows in 1981 and 1998. In both surveys white-chinned petrel burrows occurred in one-quarter of the 460–477 36-m2 quadrats surveyed. The total number of burrows in each quadrat was consistent between each survey but we estimate an overall decrease of 28% in those occupied (with considerable variation between sites). Concurrent data on breeding frequency and success showed that white-chinned petrels are essentially annual breeders at Bird Island; breeding success was consistent at around 44%. Significant factors determining densities of occupied burrows were crown height and percent tussock cover (accounting for 77% of variance). The former has decreased significantly, the latter increased significantly between 1981 and 1998 but there was no relationship between white-chinned petrel occupancy rate and habitat modification due to the presence of fur seals (Arctocephalus gazella). This suggests that any population decline is due to factors operating away from the breeding colony, such as those attributed to fishing.

Impact of rewetting on the vegetation of a cut‐away peatland

Abstract. We tested whether rewetting improved environmental conditions during peatland restoration and promoted colonization and development of mire vegetation. Vegetation change was monitored in a cut‐away peatland one year before, and four years after, rewetting. Colonizers before rewetting were perennials, mostly typical of hummocks or bare peat surfaces. The main variation in vegetation was related to variation in the amounts of major nutrients and water table level. The wettest site with the highest nutrient level had the highest total vegetation cover and diversity, as well as some species typical of wet minerotrophic mires. Raising the water table level above, or close to, the soil surface promoted development of wet minerotrophic vegetation. Diversity initially decreased because of the disappearance of hummock vegetation but started to recover in the third year. Eriophorum vaginatum and Carex rostrata were both favoured, and bryophytes typical of wet habitats colonized the site. Moderate rewetting promoted the development of Eriophorum vaginatum seedlings and an increase in the cover of tussocks. Bryophytes typical of disturbed peat surfaces spread. In the control site development continued slowly towards closed hummock vegetation. The study showed that raising the water level to, or above, soil surface promotes conditions wet enough for a rapid succession towards closed mire vegetation.

Spatial variability of organic carbon in a tussock grassland, Manorburn, Central Otago, New Zealand

The variability of topsoil organic carbon (OC) to a depth of 7.5 cm was measured in two adjacent tussock grassland plots to determine the effect of the proximity to tussock plants on OC levels and the effect of tussock abundance on OC variance and spatial variation. The plots were on Tawhiti soils near the Upper Manorburn Reservoir in Central Otago. A substantial cover of red tussock (Chionochloa rubra) was present on one plot but absent from the other. In both plots OC showed weak spatial dependency with nugget more than 50% of the sill. The range of spatial dependency of about 2 m was consistent with the natural spacing of tussock plants which was less than 1.5 m, with a mode of 0.5 m. However, no direct relationship was observed between OC levels of individual samples and tussock proximity. Weak spatial anisotropy in the variability was indicated with higher variance in the across‐slope direction than the down‐slope direction. Mean values of OC were significantly lower in the plot with low tussock cover than the plot with substantial cover of red tussock, but variance and spatial variability of carbon were not significantly influenced by the type of vegetative cover. Sampling strategies on similar soils should not have to take into account either species abundance or the proximity of samples to tussock plants. Sampling must be randomised to avoid a natural periodicity of about 2 m wavelength. At least 26 samples are required for an estimate of a mean with a 95% confidence interval of about ±0.25% OC concentration. OC values showed periodicity with wavelengths of about 2, 4, and 8 m when plotted along the sampled transects. This was confirmed by semivariograms. The maxima and minima were approximately circular in shape. The periodicity may be related to the clustering of tussock plants but there is no positive correlation between cluster density and OC.

Vegetative structure, microclimate, and leaf growth of a páramo tussock grass species, in undisturbed, burned and grazed conditions

In neotropical alpine grasslands (paramo), the natural tussock grass vegetation is extensively grazed and occasionally burned. The low productivity of the tussock grass seems to be the reason for the disappearance of this growth form in the most frequently intervened areas. The structure, microclimate and leaf elongation rates of new emerging leaves were studied for the dominant tussock grass species Calamagrostis effusa, at an undisturbed, a moderately grazed (7 year after fire) and a heavily grazed (3.5 years after fire) site. In absence of grazing and burning, the tussocks had a high standing crop (1.07±0.09 kg DW · m-2) and leaf area per projected tussock cover (LAI: 9.6±1.4). Two thirds of the total mass was dead and more than half of the leaves were in horizontal position. The tussock growth form protects the meristems from severe climatic conditions. At midday, the temperature was higher at meristem level than in the rest of the tussock. At this level, photosynthetic irradiance (PI) was almost extinct at 2.9±0.74% of PI above the vegetation. The red/far red ratio (R/FR) was strongly decreased. Initial leaf elongation of new born leaves was 2.3 mm · day-1, and constant during the year; estimated net annual production was 198±73.8 g m-2. At the moderately grazed and the heavily grazed study sites, the tussocks were smaller, greener and more erect than those at the undisturbed site. More PI reached the meristems and R/FR was higher at the base of grazed tussocks. Leaf elongation rates were lower. Most of the litter disappeared during the fires. The lower elongation rate of leaves in the grazed areas might be a response to defoliation, resulting in increased tillering and a lack growth associated with poor temperature insulation and more UV-B damage.

Monitoring the effects of pastoral use on upland and high country soils in South Island, New Zealand

This paper reports on chemical changes that have occurred since 1978 in topsoils (O-7.5 cm depth) of upland and high country farms at 3 sites: Longslip and Glencaim Stations near Omarama, north Otago, and the east Otago uplands between Middlemarch and Alexandra. Between 1978 and 1992 on Longslip, on fertilised and oversown hilly and steep slopes, mean soil organic C increased by 67%, total N value changed little, and pH declined by 0.41 units. Associated with the soil changes were declines in the amount of bare ground and snow tussock cover, and increases in legume and hieracium cover. The organic C change was equivalent to an increase of about 11 t C/ha between 1978 and 1992. Over the same time period no topsoil changes on lower landscape positions were apparent. On Glencairn, under grazing but no topdressing, mean organic C declined by lo%, total N declined by 25% and pH declined by 0.43 units between 1978 and 1993). The organic C and N changes were equivalent to a decline of about 1.7 t C/ha and 0.4 t N/ha between 1978 and 1993. In contrast, within unfertilised and fertilised plots of exclosures that had not been mown or grazed for 9 years, organic C rose by 40-55%, total N rose by 21-36%, and there was no significant change of pH. Vegetation changes outside the exclosures included an increase of hieracium and briar cover. On the east Otago uplands under light grazing and little or no fertiliser application no significant changes of pH, organic C or total N were~recorded between 1978 and 1994. The results show that soil monitoring can give useful information about the changes associated with pastoral use and the options available to maintain or enhance soil organic matter and pH levels. Keywords: high country, monitoring, organic C, pH, sustainability, total N