57 research outputs found
Community assembly and functional leaf traits mediate precipitation use efficiency of alpine grasslands along environmental gradients on the Tibetan Plateau
The alpine grasslands on the Tibetan Plateau are sensitive and vulnerable to
climate change. However, it is still unknown how precipitation use efficiency
(PUE), the ratio of aboveground net primary productivity (ANPP) to
precipitation, is related to community assembly of plant species, functional
groups or traits for the Tibetan alpine grasslands along actual environmental
gradients. We conducted a multi-site field survey at grazing-excluded pastures
across meadow, steppe and desert-steppe to measure aboveground biomass (AGB)
in August, 2010. We used species richness (SR), the Shannon diversity index,
and cover-weighted functional group composition (FGC) of 1-xerophytes,
2-mesophytes, and 3-hygrophytes to describe community assembly at the species
level; and chose community-level leaf area index (LAIc), specific leaf area
(SLAc), and species-mixed foliar δ13C to quantify community assembly at the
functional trait level. Our results showed that PUE decreased with increasing
accumulated active temperatures (AccT) when daily temperature average is
higher than 5 °C, but increased with increasing climatic moisture index (CMI),
which was demined as the ratio of growing season precipitation (GSP) to AccT.
We also found that PUE increased with increasing SR, the Shannon diversity
index, FGC and LAIc, decreased with increasing foliar δ13C, and had no
relation with SLAc at the regional scale. Neither soil total nitrogen (STN)
nor organic carbon has no influence on PUE at the regional scale. The
community assembly of the Shannon index, LAIc and SLAc together accounted for
46.3% of variance in PUE, whilst CMI accounted for 47.9% of variance in PUE at
the regional scale. This implies that community structural properties and
plant functional traits can mediate the sensitivity of alpine grassland
productivity in response to climate change. Thus, a long-term observation on
community structural and functional changes is recommended for better
understanding the response of alpine ecosystems to regional climate change on
the Tibetan Plateau
Estimating soil degradation in montane grasslands of North-eastern Italian Alps (Italy)
Grasslands cover a large portion of the terrestrial ecosystems, and are vital for biodiversity conservation, environmental protection and livestock husbandry. However, grasslands are degraded due to unreasonable management worldwide, i.e., soil erosion indirectly due to the damage of overgrazing on vegetation coverage and soil texture. An in-depth investigation is necessary to quantify soil erosion in alpine pastures, in order to manage grasslands more sustainably. In this work, we collected freely available satellite images and carried out intensive field surveys for the whole Autonomous Province of Trento (Northeastern Italian Alps) in 2016. The area (and volume) of soil erosions were then estimated and shown in maps. The average of the depths of soil erosion measured in field was used as a reference for estimating soil erosion of the entire study area. High-resolution DEMs difference in soil surface conditions was also computed in two representative areas between pre- and post-degradation to estimate the volume and the average depth of eroded soils. The degradation of soil in the study areas has been estimated in 144063 m2 and an estimated volume of 33610 ± 1800 m3. Results indicate that our procedure can serve as a low-cost approach for a rapid estimation of soil erosion in mountain areas. Mapping soil erosion can improve the sustainability of grazing management system and reduce the risk of pastureland degradation at large spatial scales
Plant functional trait diversity regulates the nonlinear response of productivity to regional climate change in Tibetan alpine grasslands
The biodiversity-productivity relationship is still under debate for alpine
grasslands on the Tibetan Plateau. We know little about direct and indirect
effects of biotic and abiotic drivers on this relationship, especially in
regard to plant functional trait diversity. Here, we examine how aboveground
net primary productivity (ANPP) and precipitation use efficiency (PUE) respond
to climate, soil and community structure across alpine grasslands on the
Northern Tibetan Plateau. We found that both ANPP and PUE showed nonlinear
patterns along water availability and site altitude variation, which together
accounted for 80.3% and 68.8% of variation in ANPP and PUE, respectively, by
optimal generalized additive models. Functional trait divergence (FTD) and
community weighted mean (CWM) of plant functional traits were as important as
plant species diversity (PSD) for explaining the nonlinear productivity-
climate relationship. These findings were confirmed by results from principal
component analyses and structural equation models. We also found that FTD was
negatively correlated with PSD across different alpine grasslands. Our results
implicate: first, the combinatorial influences of temperature and
precipitation gradients are important for predicting alpine grassland
dynamics; second, the convergence and divergence of plant functional traits
may have the potential to elucidate the effect of plant diversity on ecosystem
functionality
Changes in plant species richness distribution in Tibetan alpine grasslands under different precipitation scenarios
Species richness is the core of biodiversity-ecosystem functioning (BEF) research. Nevertheless, it is difficult to accurately predict changes in plant species richness under different climate scenarios, especially in alpine biomes. In this study, we surveyed plant species richness from 2009 to 2017 in 75 alpine meadows (AM), 199 alpine steppes (AS), and 71 desert steppes (DS) in the Tibetan Autonomous Region, China. Along with 20 environmental factors relevant to species settlement, development, and survival, we first simulated the spatial pattern of plant species richness under current climate conditions using random forest modelling. Our results showed that simulated species richness matched well with observed values in the field, showing an evident decrease from meadows to steppes and then to deserts. Summer precipitation, which ranked first among the 20 environmental factors, was further confirmed to be the most critical driver of species richness distribution. Next, we simulated and compared species richness patterns under four different precipitation scenarios, increasing and decreasing summer precipitation by 20% and 10%, relative to the current species richness pattern. Our findings showed that species richness in response to altered precipitation was grassland-type specific, with meadows being sensitive to decreasing precipitation, steppes being sensitive to increasing precipitation, and deserts remaining resistant. In addition, species richness at low elevations was more sensitive to decreasing precipitation than to increasing precipitation, implying that droughts might have stronger influences than wetting on species composition. In contrast, species richness at high elevations (also in deserts) changed slightly under different precipitation scenarios, likely due to harsh physical conditions and small species pools for plant recruitment and survival. Finally, we suggest that policymakers and herdsmen pay more attention to alpine grasslands in central Tibet and at low elevations where species richness is sensitive to precipitation changes
Identifying the Relative Contributions of Climate and Grazing to Both Direction and Magnitude of Alpine Grassland Productivity Dynamics from 1993 to 2011 on the Northern Tibetan Plateau
Alpine grasslands on the Tibetan Plateau are claimed to be sensitive and
vulnerable to climate change and human disturbance. The mechanism, direction
and magnitude of climatic and anthropogenic influences on net primary
productivity (NPP) of various alpine pastures remain under debate. Here, we
simulated the potential productivity (with only climate variables being
considered as drivers; NPPP) and actual productivity (based on remote sensing
dataset including both climate and anthropogenic drivers; NPPA) from 1993 to
2011. We denoted the difference between NPPP and NPPA as NPPpc to quantify how
much forage can be potentially consumed by livestock. The actually consumed
productivity (NPPac) by livestock were estimated based on meat production and
daily forage consumption per standardized sheep unit. We hypothesized that the
gap between NPPpc and NPPac (NPPgap) indicates the direction of vegetation
dynamics, restoration or degradation. Our results show that growing season
precipitation rather than temperature significantly relates with NPPgap,
although warming was significant for the entire study region while
precipitation only significantly increased in the northeastern places. On the
Northern Tibetan Plateau, 69.05% of available alpine pastures showed a
restoration trend with positive NPPgap, and for 58.74% of alpine pastures,
stocking rate is suggested to increase in the future because of the positive
mean NPPgap and its increasing trend. This study provides a potential
framework for regionally regulating grazing management with aims to restore
the degraded pastures and sustainable management of the healthy pastures on
the Tibetan Plateau. View Full-Tex
Climate Variability Rather Than Livestock Grazing Dominates Changes in Alpine Grassland Productivity Across Tibet
Alpine grasslands on the Tibetan Plateau, being vulnerable to environmental and anthropogenic changes, have experienced dramatic climate change and intensive livestock grazing during the last half-century. Climate change, coupled with grazing activities, has profoundly altered alpine grassland function and structure and resulted in vast grassland degradation. To restore degraded grasslands, the Central Government of China has implemented the Ecological Security Barrier Protection and Construction Project since 2008 across the Tibetan Autonomous Region. However, the relative effect of climate change and grazing activities on the variation in alpine grassland productivity is still under debate. In this study, we quantified how aboveground net primary production (ANPP) varied before (2000-2008) and after (2009-2017) starting the project across different alpine grasslands and how much variance in ANPP could be attributed to climate change and grazing disturbance, in terms of temperature, precipitation, solar radiation, and grazing intensity. Our results revealed that Tibet's climate got warmer and wetter, and grazing intensity decreased after starting the project. Mean ANPP increased at approximately 81% of the sites, on average from 27.0 g C m(-2) during 2000-2008 to 28.4 g C m(-2) during 2009-2017. The ANPP positively correlated with annual temperature and precipitation, but negatively with grazing intensity for both periods. Random forest modeling indicated that grazing intensity (14.5%) had a much lower influence in controlling the dynamics of grassland ANPP than precipitation (29.0%), suggesting that precipitation variability was the key factor for alpine grassland ANPP increase across Tibet
Grazing Exclusion to Recover Degraded Alpine Pastures Needs Scientific Assessments across the Northern Tibetan Plateau
The northern Tibetan Plateau is the most traditional and important semi-
nomadic region in Tibet. The alpine vegetation is sensitive and vulnerable to
climate change and human activities, and is also important as an ecological
security in protecting the headwaters of major rivers in Asia. Therefore, the
Tibetan alpine grasslands have fundamental significance to both Mainland China
and South Asia. The pasture degradation, however, likely threatens the
livelihood of residents and the habitats of wildlife on this plateau. Since
2004, the government has launched a series of ecological restoration projects
and economic compensatory payment polices. Many fences were additionally built
on degraded pastures to prevent new degradation, to promote functionality
recovery, and to balance the stocking rate with forage productivity. The
grazed vs. fenced paired pastures across different zonal grassland communities
along evident environmental gradients provide us with a natural comparative
experiment platform to test the relative contributions of natural and
anthropogenic factors. This study critically reviews the background,
significance of and debates on short-term grazing exclusion with fences in
this region. We also aim to figure out scientific and standardized workflows
for assessing the effectiveness of grazing exclusion and compensatory payments
in the future. View Full-Tex
Climate Sensitivity of the Arid Scrublands on the Tibetan Plateau Mediated by Plant Nutrient Traits and Soil Nutrient Availability
Climate models predict the further intensification of global warming in the future. Drylands, as one of the most fragile ecosystems, are vulnerable to changes in temperature, precipitation, and drought extremes. However, it is still unclear how plant traits interact with soil properties to regulate drylands’ responses to seasonal and interannual climate change. The vegetation sensitivity index (VSI) of desert scrubs in the Qaidam Basin (NE Tibetan Plateau) was assessed by summarizing the relative contributions of temperature (SGST), precipitation (SGSP), and drought (temperature vegetation dryness index, STVDI) to the dynamics of the normalized difference vegetation index (NDVI) during plant growing months yearly from 2000 to 2015. Nutrient contents, including carbon, nitrogen, phosphorus, and potassium in topsoils and leaves of plants, were measured for seven types of desert scrub communities at 22 sites in the summer of 2016. Multiple linear and structural equation models were used to reveal how leaf and soil nutrient regimes affect desert scrubs’ sensitivity to climate variability. The results showed that total soil nitrogen (STN) and leaf carbon content (LC), respectively, explained 25.9% and 17.0% of the VSI variance across different scrub communities. Structural equation modeling (SEM) revealed that STN and total soil potassium (STK) mediated desert scrub’s VSI indirectly via SGST (with standardized path strength of −0.35 and +0.32, respectively) while LC indirectly via SGST and SGSP (with standardized path strength of −0.31 and −0.19, respectively). Neither soil nor leave nutrient contents alone could explain the VSI variance across different sites, except for the indirect influences of STN and STK via STVDI (−0.18 and 0.16, respectively). Overall, this study disentangled the relative importance of plant nutrient traits and soil nutrient availability in mediating the climatic sensitivity of desert scrubs in the Tibetan Plateau. Integrating soil nutrient availability with plant functional traits together is recommended to better understand the mechanisms behind dryland dynamics under global climate change
Soil Moisture and Soluble Salt Content Dominate Changes in Foliar δ13C and δ15N of Desert Communities in the Qaidam Basin, Qinghai-Tibetan Plateau
Changing precipitation and temperature are principal drivers for nutrient cycling dynamics in drylands. Foliar isotopic carbon (C) and nitrogen (N) composition (δ13C and δ15N) are often used to describe the plant’s water use efficiency and nitrogen use strategy in plant ecology research. However, the drivers and mechanisms under differential foliar δ13C and δ15N among plant species and communities are largely unknown for arid high-elevation regions. This study collected 462 leaf samples of ten top-dominant plant species (two or three replicates per species) across 16 sites in 2005 and 2010 to measure the community-weighted means (CWMs) of foliar δ13C and δ15N, northeastern Qaidam Basin, Qinghai-Tibetan Plateau. Our results showed that the CWM of foliar δ15N was higher in 2005 than in 2010 and was lower in the warm-dry season (July and August) than the cool-wet one (June and September) in 2010. Similarly, the CWM of foliar δ13C was higher in 2005 than in 2010, but no difference between warm-dry and cool-wet seasons in 2010. C4 plants have higher δ13C and generally grow faster than C3 species under warm-wet weathers. This might be why the CWM of foliar δ13C was high, while the CWM of foliar δ15N was low in the wet sampling year (2010). The general linear mixed models revealed that soil moisture was the most critical driver for the CWM of foliar δ15N, which explained 42.1% of the variance alone. However, the total soluble salt content was the crucial factor for the CWM of foliar δ13C, being responsible for 29.7% of the variance. Growing season temperature (GST) was the second most vital factor and explained 28.0% and 21.9% of the variance in the CWMs of foliar δ15N and δ13C. Meanwhile, remarkable differences in the CWMs of foliar δ15N and δ13C were also found at the species level. Specifically, Kalidium gracile and Salsola abrotanoides have higher foliar δ15N, while Ephedra sinica and Tamarix chinensis have lower foliar δ15N than other species. The foliar δ13C of Calligonum Kozlov and H. ammodendron was the highest among the ten species. Except for the foliar δ13C of E. sinica was higher than Ceratoide latens between the two sampling years or between the cool-wet and warm-dry seasons, no significant difference in foliar δ13C was found for other species. Overall, the CWMs of foliar δ15N and δ13C dynamics were affected by soil properties, wet-dry climate change, and species identity in high-elevation deserts on the Qinghai Tibetan Plateau
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