Age- and stage-based bud demography of Salix arctica under contrasting muskox grazing pressure in the High Arctic

Adaptability of the structure and biomass of Arundinaria spanostachya clonal populations grazing by wild giant pandas

To understand the defense mechanism of Arundinaria spanostachya clonal populations in response to grazing by giant pandas, dynamic variations in A. spanostachya clonal population structure and biomass allocation in a wild giant panda habitat at the Liziping Nature Reserve were evaluated, as well as whether the clonal populations would be continuously used by the wild giant pandas. The population density of each age-class in the grazed and control plots after grazing (2014a and 2015a) was similar to that before grazing (2013a). The effects of grazing on the size-class and height-class structures were relatively lower. Before and after grazing, the perennial individuals showed the highest total biomass, followed by the biennial and annual individuals, and the maximum dry matter content in each module was found in the culm, followed by the branch and leaf. The dry matter content of A. spanostachya individuals increased as the age class increased, whereas the total water content decreased. The maximum water content allocation in the modules was observed in the culm, and no significant differences were found between the shoot and leaf. Thus, foraging by the wild giant pandas had no impact on the size-class and height-class structures and biomass allocation of A. spanostachya clonal populations, and the clonal populations have established an adaptive mechanism against grazing by giant pandas. After grazing, the A. spanostachya clonal populations showed greater self-adjustment ability to restore the status to that before grazing and, thus, continuously supply food for the giant pandas. Further management intervention of A. spanostachya clonal populations after the foraging of wild giant pandas is not needed, which has implications for understanding the impact of co-evolutionary mechanisms between giant panda and its staple bamboo species.

Grazing exclusion promotes grasses functional group dominance via increasing of bud banks in steppe community

To understand the bud banks response to grazing exclusion, we conducted a demographic experiment in long-term grazing exclusion (20 year and 30 year) typical steppe. Results showed that grass functional group constituted the vast majority of the aboveground vegetation and belowground bud bank in all treatments. Long-term grazing exclusion significantly increased total aboveground biomass (2.5 and 2.6 times in 20y and 30y grazing exclusion grasslands, respectively), and decreased total stem density (31% and 37% in 20y and 30y grazing exclusion grasslands, respectively). Grazing exclusion for 20 and 30 years increased grass aboveground biomass respectively by 6.0 and 8.0 times, and decreased grass stem density by 38% and 33%. Grazing exclusion had different effects on belowground bud density of grass and forb functional group. Long-term grazing exclusion significantly increased plant buds and bud bank size (25% and 37% in 20y and 30y grazing exclusion grasslands, respectively), especially for grass functional group (49% and 95% in 20y and 30y grazing exclusion grasslands, respectively), but had no significant effects on forb bud density. Changes of aboveground community were significantly related to changes of belowground bud bank under both grazing and grazing exclusion grasslands. The bud bank density of grass functional group was significantly positive with total (R² = 0.33, P < 0.05) and grass aboveground biomass (R² = 0.36, P < 0.01), while negative related with total (R² = -0.27, P < 0.05) and grass stem density (R² = -0.22, P < 0.05). Grazed grasslands, 20y and 30y grazing exclusion grasslands all were not meristem limited and had large reserve bud banks, which would completely replace the aboveground stem population during the growing season. These findings indicate that grazing exclusion could not only improve a large bud bank for grassland restoration but also improve the dominance of grass functional group by increasing grass belowground bud banks in typical steppe community. We propose that the belowground bud bank might be a good approach to indicating potential succession direction of aboveground community.

Grazing buffers the effect of climate change on the species diversity of seedlings in an alpine meadow on the Tibetan Plateau

Climate change predominated by warming over the past decades has affected plant biodiversity, distribution, and ecosystem functioning in alpine grasslands. Yet, little is known about the interactive effect of climate change and grazing on biodiversity and ecosystem functioning. Here, we conducted a vegetation translocation experiment (ten soil-vegetation blocks were translocated from high-altitudinal site 3,245 m to low-altitudinal site 3,045 m) combined with grazing treatment in an alpine meadow on the Tibetan Plateau. The results showed that (a) translocation induced effect of climate change from harsh, high-altitudinal site to benign, low-altitudinal site significantly promoted species richness, and density of asexual and sexual seedling, with an increase in the proportion of asexual recruitment to sexual recruitment; (b) grazing decreased the proportion of asexual seedling to sexual recruitment within community, led to a shift in the dominant plant functional groups from graminoids and legumes to forbs; and (c) grazing partly offset the increased species richness of seedling, but not seedling density, induced by climate change. These findings suggest that moderate grazing may buffer the effect of climate change on the plant community composition, and thus, functional role in alpine meadows. Further understanding the influence of climate change on grassland ecosystems needs to consider the non-additive effect of grazing and climate change to sustainability of grassland services.

Interaction webs in arctic ecosystems: Determinants of arctic change?

How species interact modulate their dynamics, their response to environmental change, and ultimately the functioning and stability of entire communities. Work conducted at Zackenberg, Northeast Greenland, has changed our view on how networks of arctic biotic interactions are structured, how they vary in time, and how they are changing with current environmental change: firstly, the high arctic interaction webs are much more complex than previously envisaged, and with a structure mainly dictated by its arthropod component. Secondly, the dynamics of species within these webs reflect changes in environmental conditions. Thirdly, biotic interactions within a trophic level may affect other trophic levels, in some cases ultimately affecting land-atmosphere feedbacks. Finally, differential responses to environmental change may decouple interacting species. These insights form Zackenberg emphasize that the combination of long-term, ecosystem-based monitoring, and targeted research projects offers the most fruitful basis for understanding and predicting the future of arctic ecosystems.

Effects of grazing regimes on plant traits and soil nutrients in an alpine steppe, Northern Tibetan Plateau

Understanding the impact of grazing intensity on grassland production and soil fertility is of fundamental importance for grassland conservation and management. We thus compared three types of alpine steppe management by studying vegetation traits and soil properties in response to three levels of grazing pressure: permanent grazing (M1), seasonal grazing (M2), and grazing exclusion (M3) in the alpine steppe in Xainza County, Tibetan Plateau. The results showed that community biomass allocation did not support the isometric hypothesis under different grassland management types. Plants in M1 had less aboveground biomass but more belowground biomass in the top soil layer than those in M2 and M3, which was largely due to that root/shoot ratios of dominant plants in M1 were far greater than those in M2 and M3. The interramet distance and the tiller size of the dominant clonal plants were greater in M3 than in M1 and M2, while the resprouting from rhizome buds did not differ significantly among the three greezing regimes. Both soil bulk density and soil available nitrogen in M3 were greater than in M1 at the 15-30 cm soil depth (P = 0.05). Soil organic carbon and soil total nitrogen were greater in M3 than in M1 and M2 (P = 0.05). We conclude that the isometric hypothesis is not supported in this study and fencing is a helpful grassland management in terms of plant growth and soil nutrient retention in alpine steppe. The extreme cold, scarce precipitation and short growing period may be the causation of the unique plant and soil responses to different management regimes.

Divergence in Defence against Herbivores between Males and Females of Dioecious Plant Species

Defensive traits may evolve differently between sexes in dioecious plant species. Our current understanding of this process hinges on a partial view of the evolution of resistance traits that may result in male-biased herbivory in dioecious populations. Here, we present a critical summary of the current state of the knowledge of herbivory in dioecious species and propose alternative evolutionary scenarios that have been neglected. These scenarios consider the potential evolutionary and functional determinants of sexual dimorphism in patterns of resource allocation to reproduction, growth, and defence. We review the evidence upon which two previous reviews of sex-biased herbivory have concluded that male-biased herbivory is a rule for dioecious species, and we caution readers about a series of shortcomings of many of these studies. Lastly, we propose a minimal standard protocol that should be followed in any studies that intend to elucidate the (co)evolution of interactions between dioecious plants and their herbivores.

Effects of herbivory and its timing across populations of Trillium grandiflorum (Liliaceae)

The goal of this study was to identify the degree to which the frequency and timing of herbivory by white-tailed deer (Odocoileus virginianus) and subsequent plant response varied across 12 populations of the perennial herb Trillium grandiflorum. Effects of natural and experimental herbivory on the stage and size of reproductive plants were measured. Both the frequency and timing of herbivory varied across T. grandiflorum populations. Reproductive plants were more likely to regress to nonreproductive stages in the next growing season when (1) reproductive plants were consumed by deer (vs. intact reproductive plants); (2) reproductive plants were consumed early in the growing season (vs. reproductive plants consumed late in the growing season); (3) reproductive plants were smaller in size. Clipped plants that remained reproductive were smaller in the following season than unclipped controls. Plant size was positively correlated with the number of ovules, suggesting that reductions in the growth rate of reproductive plants diminish their future reproductive success. Populations with high levels of natural herbivory had a greater proportion of reproductive plants that regressed to nonreproductive stages, probably because reproductive plants in these populations were smaller in size. However, the plant response to herbivory was similar across populations.