Do mussel patches provide a refuge for algae from grazing gastropods?

On rocky shores, cover of macroalgae is often greater growing epibiotically on mussels compared to algae growing directly attached to rock. A survey of two shores on the east coast of Ireland confirmed that mussel beds contained greater percentage algal cover and more diverse algal assemblages compared to those on rock. The reasons for this difference are not clear. It has been suggested that mussel beds provide a refuge for algae from grazing gastropods. Surprisingly, we found no evidence to support this. Using wax discs, gastropod grazing patterns were found to be similar within the mussel beds as on rock. The mussel beds do not appear to provide a refuge for algae from grazing activity at this scale and we suggest other possible mechanisms for the prevalence of epibiotic algal cover on mussels. Intertidal grazers may in fact affect the epibiotic algae on mussels and thereby affect indirectly the persistence of mussel beds.

The impact of grazing by eastern grey kangaroos (macropus giganteus) on vegetation recovery after fire at Reef Hills regional park, Victoria

In southeastern Australia ecological burning is frequently used to maintain a number of plant and animal populations. However, many of these prescribed fires are small, and may focus intense grazing activity on new regrowth. At Reef Hills Regional Park, Victoria shrub species have senesced, presumably due to the absence of fire. Ecological burning may be necessary to promote regeneration, however, the population density of the Eastern Grey Kangaroo (Macropus giganteus) is high (approx 38 per km2), and grazing pressure presents a significant risk to postfire vegetation recovery. An assessment of grazing patterns and their effects on postfire recovery was carried out at Reef Hills Regional Park through grazing exclusion plots. Preferential grazing by Eastern Grey Kangaroos occurred on small burnt plots compared to adjacent unburnt areas as determined by faecal pellet counts. On burnt areas, there was a significant reduction in shrub diversity on grazed plots compared to ungrazed plots. Most observations of kangaroos were of animals grazing on farmland surrounding the Park, and it is likely that any burning might shift grazing from farmland to burnt areas when new growth occurs. This needs to be considered before any ecological burn plan is applied to manage vegetation communities, particularly if the plan requires small areas to be burnt. We recommended that a large area up to 200 ha area be burnt and monitored to determine whether burning larger areas disperses grazing pressure from macropods to a level where impacts on vegetation are reduced and localized plant extinctions do not occur.

放牧对内蒙古冷蒿小禾草草原植物群落特征的影响

了解天然草原放牧生态系统中，不同管理措施对草－畜系统的影响及系统中草－畜互作方式，是实现草原生态系统持续管理的基础。在内蒙古典型草原区，我们建立了24hm2围栏放牧实验样地。本文通过对试验样地5个放牧率（1.33，2.67，4.00，5.33和6.67羊／hm2）和两种放牧方式下（连续放牧与轮牧）一年排除放牧后植被变化的研究，试图揭示8年的放牧对草地群落的作用结果，探寻放牧率与植物群落生产力、种类组成和演替方向的关系，以求为建立合理的放牧制度提供佐证。 研究发现：①不同的放牧率下8年的放牧使地上生物量出现显著差异，中度放牧（SR3）下的草原群落达到了最大地上生物量，在较轻的放牧率（SR1，SR2）下有超补偿生长出现，地下生物量随着放牧率的升高而下降。②放牧使群落植物组成发生重大变化，随着放牧率的升高，表现出明显的向星毛委陵菜退化草原演替的趋势，无牧的群落表现出恢复演替的趋势。③在轻牧（SR1）处理下植物群落达到了最高的多样性，在多样性与生物量之间，不能发现较具规律性的关系。④轮牧群落的生产力潜力显著高于连续放牧，连续放牧方式造成植物斑块状分布，降低了草场的利用效率。⑤放牧造成了草原植物生态位分化。

川西北高寒草甸土壤呼吸研究：季节动态和放牧效应

除植被冠层的光合作用之外，土壤的呼吸作用是陆地生态系统碳收支中最大的通量。土壤呼吸即使发生较小的变化也能显著地减缓或加剧大气中CO2浓度的增加，从而明显影响到全球气候变化。土壤呼吸速率变化与否以及变化的方向可以反映生态系统对环境变化的敏感程度和响应模式。尽管如此，土壤呼吸仍是一个为人们了解不多的生态系统过程。 草地生态系统是陆地生态系统的一个重要组成部分。针对草地土壤呼吸进行野外实验研究和相应方法论的探讨将对区域乃至全球碳源汇性质的准确估算具有重要的科学意义。然而，近几年来关于草地土壤呼吸的主要研究工作都集中在温带草原和部分热带草原，而针对高寒草甸生态系统土壤呼吸的研究报道还很少。 2008年4月至2009年4月期间，我分别在2008年6、8、10、12月和2009年2月和4月分6次对川西北的典型高寒草甸群落的土壤呼吸进行观测，分析了不同类型高寒草甸群落土壤呼吸的季节变化特征以及环境因子和放牧模式对其影响。主要研究结果如下： 1）该地区高寒草甸生态系统在生长季（6月～8月）土壤呼吸速率较大（6.07～9.30μmolCO2¡m-2¡s-1 ） ， 在非生长季（ 12 月～ 2 月） 较小（ 0.16 ～0.49μmolCO2¡m-2¡s-1 ） 。土壤CO2 年累积最大释放量为3963 ～ 5730gCO2¡m-2¡yr-1，其中，生长季土壤CO2的释放量占年总释放量的85%～90%。非生长季占10%～15%。非生长季所占比例略小于冬季积雪覆盖地区的冬季土壤呼吸占年土壤呼吸量的比例（14%～30%）。温度，尤其地温，是影响该地区高寒草甸生态系统土壤呼吸速率的最主要环境因子。土壤呼吸速率与地上生物量和土壤水分之间没有显著相关性，但是土壤含水量过大会导致土壤呼吸速率下降。 2）在观测期内，草丘区的土壤呼吸显著高于对照区的土壤呼吸，其最大土壤呼吸速率为16.77μmolCO2¡m-2¡s-1，土壤CO2 年累积最大释放量为8145gCO2¡m-2¡yr-1，是对照区的近2 倍。由于草丘在高寒草甸中占有较大的面积比例（近30%），因此，它将对高寒草甸生态系统的碳循环起着重要的作用。 3）放牧模式不仅可以影响高寒草甸群落的土壤CO2 排放，而且还可以改变土壤呼吸的温度敏感性（Q10）。本研究表明，在生长季有长期放牧活动干扰时将会增加土壤向大气中释放二氧化碳的速度，促使土壤碳库中碳的流失。禁牧样地的土壤呼吸速率在刚禁牧时先迅速增大，随着禁牧时间的延长土壤呼吸速率将会下降。此外，与其它放牧模式相比，冬季放牧将高寒草甸群落土壤呼吸速率在生长季达到最大值的时间明显向后推迟。不同放牧模式下高寒草甸群落土壤呼吸的Q10 值大小顺序为：禁牧一年群落>冬季放牧群落>禁牧三年群落>夏季放牧群落>自由放牧群落。 4）基于呼吸室技术的观测方法中，测量前的剪草处理可以明显改变该地区高寒草甸群落的土壤温度和土壤呼吸速率。在生长季，剪草处理将使土壤呼吸速率的瞬时响应增加90%左右。由于剪草处理明显增加了剪草样方白天的土壤温度，而土壤温度与土壤呼吸之间存在着极显著的指数相关关系，因而剪草处理导致土壤呼吸速率迅速增加。因此，在高寒地区基于呼吸室技术观测的土壤呼吸应当进行校正。 综上所述，川西北高寒草甸生态系统土壤呼吸速率在生长季较高，而在非生长季较低。土壤温度是影响该地区土壤呼吸的最主要环境因子。在实验观测期，草丘区土壤呼吸速率显著高于对照区的，是对照区土壤呼吸速率的近2倍。由于测量前的剪草处理可以明显改变待测点的土壤呼吸速率，因此，应对在高寒地区基于呼吸室技术观测的土壤呼吸进行校正。 Soil respiration is the second largest component (less than plant phtotosynthesis) of carbon dioxide flux between terrestrial ecosystems and the atmosphere. A minor change in soil respiration rate can significantly slow down or accelerate the increase of atmospheric CO2 concentration that is closely related to global climatic change. In turn, the change in the flux direction and rate of soil respiration may indicate the elasticity and stability of ecosystems to global changes and human disturbance. However, soil respiration is still an ecosystem process that has been poorly understood. Grassland ecosystem is an important component of the terrestrial ecosystem. Accurately estimating the CO2 flux from soil to atmosphere in situ is the key to evaluating the carbon resource and sink regionally or globally. Despite of extensive studies on the temperate and tropic grasslands, the soil respiration of alpine meadows has not substantially been measured. In the current study, soil respiration was measured for an annual cycle from April, 2008 to April, 2009 for the alpine meadow in northwestern Sichuan Province of China to determine the seasonal variation of soil respiration for the typical plant communities. The results are shown as follows: 1) Large seasonal variation of soil respiration was observed in the alpine meadow. The rate of soil respiration was the greatest (6.07～9.30μmolCO2¡m-2¡s-1) in June and the smallest (0.16 ～ 0.49μmolCO2¡m-2¡s-1) occurred from December to February in the non-growing season. The total emission of soil CO2 was estimated as 3963～5730 gCO2¡m-2¡yr-1, 85%~90% of which was released during the growing season, and 10%~15% during the non-growing season which was slightly less than the ratio of winter and annual CO2 flux from soil. Temperature, particularly the soil temperature, was the major environmental factor regulating the soil respiration. Significant and positive relationships were not found between soil respiration and soil moisture and between soil respiration and plant above-ground biomass, but excessive soil water content would decrease in the rate of soil respiration. 2) The rate of soil respiration in grass hummock communities was up to 16.77μmolCO2¡m-2¡s-1, which was about twice as great as in the controls (communities located in low and even sites). Considering the large proportion (about 30% on average) of hummock area in the meadow, it can be concluded that the hummocks played an important role in the carbon cycling of the study ecosystem. 3) Grazing patterns affected the flux of CO2 emission and the temperature sensitivity of soil respiration (Q10) in the alpine meadow. Grazing during growing season increased the rate of soil respiration. The rate of soil respiration increased significantly immediately after the alpine meadow being fenced, but thereafter decreased. In addition, grazing in winter delayed the peak respiration rate relative to the non-grazing mode. The Q10 value was the largest in the non-grazed area for one year, and next came the area with grazing in winter, followed by the non-grazed area for three years, the area with grazing in summer, and the non-limited grazed area. 4) In the chamber-based techniques, clipping manipulation before each measurement increased the transient rate of soil respiration by about 90% in the summer of the alpine meadow. As increase in soil temperature at daytime in the clipped plots by clipping and the exponential relationship between soil respiration and temperature, clipping manipulation led to increase in the rate of soil respiration. This suggested that a correction should be done for the techniques if employed in alpine and cold regions. In summary, the rate of soil respiration in the alpine meadow was the greatest in June and the smallest occurred from ecember to February in the non-growing season. Soil temperature was the major environmental factor regulating the soil respiration. The rate of soil respiration in grass hummock communities was up to 16.77μmolCO2¡m-2¡s-1, which was about twice as great as in the controls. A correction should be done for the techniques if employed in alpine and cold regions, because of the effect of clipping manipulation on soil temperature and respiration.

(Table 1) Bioclimatic subzones and soil characteristics along the Yamal Arctic Transect, northwestern Siberia

Sustainability of tundra vegetation under changing climate on the Yamal Peninsula, northwestern Siberia, home to the world's largest area of reindeer husbandry, is of crucial importance to the local native community. An integrated investigation is needed for better understanding of the effects of soils, climate change and grazing on tundra vegetation in the Yamal region. In this study we applied a nutrient-based plant community model - ArcVeg - to evaluate how two factors (soil organic nitrogen (SON) levels and grazing) interact to affect tundra responses to climate warming across a latitudinal climatic gradient on the Yamal Peninsula. Model simulations were driven by field-collected soil data and expected grazing patterns along the Yamal Arctic Transect (YAT), within bioclimate subzones C (high arctic), D (northern low arctic) and E (southern low arctic). Plant biomass and NPP (net primary productivity) were significantly increased with warmer bioclimate subzones, greater soil nutrient levels and temporal climate warming, while they declined with higher grazing frequency. Temporal climate warming of 2 °C caused an increase of 665 g/m**2 in total biomass at the high SON site in subzone E, but only 298 g/m**2 at the low SON site. When grazing frequency was also increased, total biomass increased by only 369 g/m**2 at the high SON site in contrast to 184 g/m**2 at the low SON site in subzone E. Our results suggest that high SON can support greater plant biomass and plant responses to climate warming, while low SON and grazing may limit plant response to climate change. In addition to the first order factors (SON, bioclimate subzones, grazing and temporal climate warming), interactions among these significantly affect plant biomass and productivity in the arctic tundra and should not be ignored in regional scale studies.

Patterns of distribution in intertidal rocky shores: the role of grazing and competition in structuring communities

Tese de doutoramento, Ciências do Mar, Faculdade de Ciências do Mar e do Ambiente, Universidade do Algarve, 2000

Grazing response patterns indicate isolation of semi-natural European grasslands

Identifying drivers of species diversity is a major challenge in understanding and predicting the dynamics of species-rich semi-natural grasslands. In particular in temperate grasslands changes in land use and its consequences, i.e. increasing fragmentation, the on-going loss of habitat and the declining importance of regional processes such as seed dispersal by livestock, are considered key drivers of the diversity loss witnessed within the last decades. It is a largely unresolved question to what degree current temperate grassland communities already reflect a decline of regional processes such as longer distance seed dispersal. Answering this question is challenging since it requires both a mechanistic approach to community dynamics and a sufficient data basis that allows identifying general patterns. Here, we present results of a local individual- and trait-based community model that was initialized with plant functional types (PFTs) derived from an extensive empirical data set of species-rich grasslands within the `Biodiversity Exploratories' in Germany. Driving model processes included above- and belowground competition, dynamic resource allocation to shoots and roots, clonal growth, grazing, and local seed dispersal. To test for the impact of regional processes we also simulated seed input from a regional species pool. Model output, with and without regional seed input, was compared with empirical community response patterns along a grazing gradient. Simulated response patterns of changes in PFT richness, Shannon diversity, and biomass production matched observed grazing response patterns surprisingly well if only local processes were considered. Already low levels of additional regional seed input led to stronger deviations from empirical community pattern. While these findings cannot rule out that regional processes other than those considered in the modeling study potentially play a role in shaping the local grassland communities, our comparison indicates that European grasslands are largely isolated, i.e. local mechanisms explain observed community patterns to a large extent.

Simulating pasture growth rates in Australian and New Zealand grazing systems

DairyMod, EcoMod, and the SGS Pasture Model are mechanistic biophysical models developed to explore scenarios in grazing systems. The aim of this manuscript was to test the ability of the models to simulate net herbage accumulation rates of ryegrass-based pastures across a range of environments and pasture management systems in Australia and New Zealand. Measured monthly net herbage accumulation rate and accumulated yield data were collated from ten grazing system experiments at eight sites ranging from cool temperate to subtropical environments. The local climate, soil, pasture species, and management (N fertiliser, irrigation, and grazing or cutting pattern) were described in the model for each site, and net herbage accumulation rates modelled. The model adequately simulated the monthly net herbage accumulation rates across the range of environments, based on the summary statistics and observed patterns of seasonal growth, particularly when the variability in measured herbage accumulation rates was taken into account. Agreement between modelled and observed growth rates was more accurate and precise in temperate than in subtropical environments, and in winter and summer than in autumn and spring. Similarly, agreement between predicted and observed accumulated yields was more accurate than monthly net herbage accumulation. Different temperature parameters were used to describe the growth of perennial ryegrass cultivars and annual ryegrass; these differences were in line with observed growth patterns and breeding objectives. Results are discussed in the context of the difficulties in measuring pasture growth rates and model limitations.

Spatial and temporal effects of grazing management and rainfall on the vertebrate fauna of a tropical savanna

Grazing by domestic livestock is one of the most widespread uses of the rangelands of Australia. There is limited information on the effects of grazing by domestic livestock on the vertebrate fauna of Australia and the establishment of a long-term grazing experiment in north-eastern Queensland at Wambiana provided an opportunity to attempt an examination of the changes in vertebrate fauna as a consequence of the manipulation of stocking rates. The aim was to identify what the relative effects of vegetation type, stocking rate and other landscape-scale environmental factors were on the patterns recorded. Sixteen 1-ha sites were established within three replicated treatments (moderate, heavy and variable stocking rates). The sites were sampled in the wet and dry seasons in 1999-2000 (T-0) and again in 2003-04 (T-1). All paddocks of the treatments were burnt in 1999. Average annual rainfall declined markedly between the two sampling periods, which made interpretation of the data difficult. A total of 127 species of vertebrate fauna comprising five amphibian, 83 bird, 27 reptile and 12 mammal species were recorded. There was strong separation in faunal composition from T-0 to T-1 although changes in mean compositional dissimilarity between the grazing stocking rate treatments were less well defined. There was a relative change in abundance of 24 bird, four mammal and five reptile species from T-0 to T-1. The generalised linear modelling identified that, in the T-1 data, there was significant variation in the abundance of 16 species explained by the grazing and vegetation factors. This study demonstrated that vertebrate fauna assemblage did change and that these changes were attributable to the interplay between the stocking rates, the vegetation types on the sites surveyed, the burning of the experimental paddocks and the decrease in rainfall over the course of the two surveys. It is recommended that the experiment is sampled again but that the focus should be on a rapid survey of abundant taxa (i.e. birds and reptiles) to allow an increase in the frequency of sampling and replication of the data. This would help to articulate more clearly the trajectory of vertebrate change due to the relative effects of stocking rates compared with wider landscape environmental changes. Given the increasing focus on pastoral development in northern Australia, any opportunity to incorporate the collection of data on biodiversity into grazing manipulation experiments should be taken for the assessment of the effects of land management on faunal species.

Patterns of distribution of macrolichens in western parts of Nanda Devi Biosphere Reserve

A total of 76 species of macrolichens were recorded from 16 transects of 50 m x 10 m between altitudes of 2100 m and 4500 m in western parts of Nanda Devi Biosphere Reserve of Garhwal Himalayas. Forty-one of these are lignicolous species occurring on woody, 14 are terricolous growing on soil and 10 are saxicolous inhabiting rocks only, The other 11 species occur on more than one major types of substrate, Lichen species diversity is at its highest in middle altitudes between 2700 m and 3700 m where all three major substrates are simultaneously available, Lichen species diversity of Nanda Devi Biosphere Reserve appears to be under threat from deforestation and fires, as well as from loss of soil microhabitats due to overgrowth of weeds seemingly caused by cessation of summer grazing in alpine pastures.

Response of Polygonum viviparum species and community level to long-term livestock grazing in alpine shrub meadow in Qinghai-Tibet Plateau

Grazing by domestic herbivores is generally recognized as a major ecological factor and an important evolutionary force in grasslands. Grazing has both extensive and profound effects on individual plants and communities. We investigated the response patterns of Polygonum viviparum species and the species diversity of an alpine shrub meadow in response to long-term livestock grazing by a field manipulative experiment controlling livestock numbers on the Qinghai-Tibet Plateau in China. Here, we hypothesize that within a range of grazing pressure, grazing can alter relative allocation to different plant parts without changing total biomass for some plant species if there is life history trade-offs between plant traits. The same type of communities exposed to different grazing pressures may only alter relative species' abundances or species composition and not vary species diversity because plant species differ in resistant capability to herbivory. The results show that plant height and biomass of different organs differed among grazing treatments but total biomass remained constant. Biomass allocation and absolute investments to both reproduction and growth decreased and to belowground storage increased with increased grazing pressure, indicating the increasing in storage function was attained at a cost of reducing reproduction of bulbils and represented an optimal allocation and an adaptive response of the species to long-term aboveground damage. Moreover, our results showed multiform response types for either species groups or single species along the gradient of grazing intensity. Heavy grazing caused a 13.2% increase in species richness. There was difference in species composition of about 18%-20% among grazing treatment. Shannon-Wiener (H') diversity index and species evenness (E) index did not differ among grazing treatments. These results support our hypothesis.

Dynamic and complex microclimate responses to warming and grazing manipulations

Synthesis efforts that identify patterns of ecosystem response to a suite of warming manipulations can make important contributions to climate change science. However, cross-study comparisons are impeded by the paucity of detailed analyses of how passive warming and other manipulations affect microclimate. Here we document the independent and combined effects of a common passive warming manipulation, open-top chambers (OTCs), and a simulated widespread land use, clipping, on microclimate on the Tibetan Plateau. OTCs consistently elevated growing season averaged mean daily air temperature by 1.0-2.0 degrees C, maximum daily air temperature by 2.1-7.3 degrees C and the diurnal air temperature range by 1.9-6.5 degrees C, with mixed effects on minimum daily air temperature, and mean daily soil temperature and moisture. These OTC effects on microclimate differ from reported effects of a common active warming method, infrared heating, which has more consistent effects on soil than on air temperature. There were significant interannual and intragrowing season differences in OTC effects on microclimate. For example, while OTCs had mixed effects on growing season averaged soil temperatures, OTCs consistently elevated soil temperature by approximately 1.0 degrees C early in the growing season. Nonadditive interactions between OTCs and clipping were also present: OTCs in clipped plots generally elevated air and soil temperatures more than OTCs in nonclipped plots. Moreover, site factors dynamically interacted with microclimate and with the efficacy of the OTC manipulations.These findings highlight the need to understand differential microclimate effects between warming methods, within warming method across ecosystem sites, within warming method crossed with other treatments, and within sites over various timescales. Methods, sites and scales are potential explanatory variables and covariables in climate warming experiments. Consideration of this variability among and between experimental warming studies will lead to greater understanding and better prediction of ecosystem response to anthropogenic climate warming.

Grazing intensity alters soil respiration in an alpine meadow on the Tibetan plateau

Grazing intensity may alter the soil respiration rate in grassland ecosystems. The objectives of our study were to (1) determine the influence of grazing intensity on temporal variations in soil respiration of an alpine meadow on the northeastern Tibetan Plateau; and (2) characterise, the temperature response of soil respiration under different grazing intensities. Diurnal and seasonal soil respiration rates were measured for two alpine meadow sites with different grazing intensities. The light grazing (LG) meadow site had a grazing intensity of 2.55 sheep ha(-1), while the grazing intensity of the heavy grazing (HG) meadow site, 5.35 sheep ha(-1), was approximately twice that of the LG site. Soil respiration measurements - showed that CO2 efflux was almost twice as great at the LG site as at the HG site during the growing season, but the diurnal and seasonal patterns of soil respiration rate were similar for the two sites. Both exhibited the highest annual soil respiration rate in mid-August and the lowest in January. Soil respiration rate was highly dependent on soil temperature. The Q(10) value for annual soil respiration was lower for the HG site (2.75) than for the LG site (3.22). Estimates of net ecosystem CO2 exchange from monthly measurements of biomass and soil respiration revealed that during the period from May 1998 to April 1999, the LG site released 2040 g CO2 m(-2) y(-1) to the atmosphere, which was about one third more than the 1530g CO2 m(-2) y(-1) released at the HG site. The results suggest that (1) grazing intensity alters not only soil respiration rate, but also the temperature dependence of soil CO2 efflux; and (2) soil temperature is the major environmental factor controlling the temporal variation of soil respiration rate in the alpine meadow ecosystem. (C) 2003 Elsevier Ltd. All fights reserved.