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Experimental warming, not grazing, decreases rangeland quality on the Tibetan Plateau
Ecological Applications
Abstract
We investigated experimental warming and simulated grazing (clipping) effects on rangeland quality, as indicated by vegetation production and nutritive quality, in winter-grazed meadows and summer-grazed shrublands on the Tibetan Plateau, a rangeland system experiencing climatic and pastoral land use changes. Warming decreased total aboveground net primary productivity (ANPP) by 40 g x m(-2) x yr(-1) at the meadow habitats and decreased palatable ANPP (total ANPP minus non-palatable forb ANPP) by 10 g x m(-2) x yr(-1) at both habitats. The decreased production of the medicinal forb Gentiana straminea and the increased production of the non-palatable forb Stellera chamaejasme with warming also reduced rangeland quality. At the shrubland habitats, warming resulted in less digestible shrubs, whose foliage contains 25% digestible dry matter (DDM), replacing more digestible graminoids, whose foliage contains 60% DDM. This shift from graminoids to shrubs not only results in lower-quality forage, but could also have important consequences for future domestic herd composition. Although warming extended the growing season in non-clipped plots, the reduced rangeland quality due to decreased vegetative production and nutritive quality will likely overwhelm the improved rangeland quality associated with an extended growing season. Grazing maintained or improved rangeland quality by increasing total ANPP by 20-40 g x m(-2) x yr(-1) with no effect on palatable ANPP. Grazing effects on forage nutritive quality, as measured by foliar nitrogen and carbon content and by shifts in plant group ANPP, resulted in improved forage quality. Grazing extended the growing season at both habitats, and it advanced the growing season at the meadows. Synergistic interactions between warming and grazing were present, such that grazing mediated the warming-induced declines in vegetation production and nutritive quality. Moreover, combined treatment effects were nonadditive, suggesting that we cannot predict the combined effect of global changes and human activities from single-factor studies. Our findings suggest that the rangelands on the Tibetan Plateau, and the pastoralists who depend on them, may be vulnerable to future climate changes. Grazing can mitigate the negative warming effects on rangeland quality. For example, grazing management may be an important tool to keep warming-induced shrub expansion in check. Moreover, flexible and opportunistic grazing management will be required in a warmer future.
... However, some studies have shown that the nutrition quality of graminoids is lower than that of forbs [1]. Previous studies have found that the impact of climate warming on the yield of graminoids and forbs is controversial [18,19]. Therefore, it is necessary to further strengthen the research on the response of forage nutrition quality and storage to climate warming in the natural grasslands of the Qinghai-Xizang Plateau. ...
... Trade-offs between forage nutrition quality and forage production were not observed in this study, which is in contrast with some previous studies [7,22] but in line with other previous studies [1,18]. These inconsistent findings are likely to be attributed to one or more reasons. ...
... The nutrition quality of forbs was greater than that of gramineous, especially in a warming climate, and responses of forage nutrition quality to warming varied with plant functional groups. These findings were in line with some previous studies [1,18,24] and may be linked to one or more reasons. Firstly, nitrogen use efficiency and nitrogen resorption efficiency among different functional groups of plants and their sensitivities to warming are different [24,29]. ...
Effects of climate warming on nutrition quality and storage of alpine grasslands are still controversial, which is not conducive to the management and utilization of alpine grasslands. A long-term warming experiment (with open-top chambers used to elevate temperature) was conducted at three elevations (relatively low, mid-, and high elevations with 4313, 4513, and 4693 m) of Northern Tibet in 2010 to compare the differences in forage nutritional quality and storage response to warming among three elevations and to explore the relationships between forage nutritional quality and production. In 2019, community surveys, observations of forage biomass and nutrition quality, and soil physicochemical properties were carried out. Forage nutrition quality included crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), ether extract (EE), crude ash (Ash), and water-soluble carbohydrate (WSC) content. Warming did not affect community aboveground biomass (AGB) at the three elevations. Warming improved community nutrition quality by increasing community CP content by 25.80% and decreasing community NDF content by 15.51% at the low elevation. In contrast, warming reduced community nutrition quality by increasing community CP, ADF, and NDF contents by 13.45%, 23.68%, and 17.43%, respectively, and decreasing Ash content by 39.50% at the high elevation. Warming did not affect community CP, ADF, NDF, EE, Ash, or WSC contents at the mid-elevation. Warming increased community nutrition storage by increasing community CP, ADF, and NDF storges by 74.69%, 88.18%, and 79.71%, respectively, at the high elevation. Warming did not affect community nutrition storages at the low or mid-elevations. Overall, forbs had higher CP, EE, Ash, and WSC contents and lower ADF and NDF contents compared with graminoids. Community EE content increased with community AGB, but community CP, ADF, NDF, EE, Ash, and WSC contents were not related to community AGB. Therefore, from the low to high elevation, the effects of warming on forage nutrition quality gradually changed from improving to inhibiting. Warming altered rangeland quality by affecting forage nutrition quality rather than forage production. There were no trade-offs between forage nutrition quality and forage production.
... Understanding how biological communities will respond to global change is a major challenge in ecology (Sala et al. 2000;Suding et al. 2008). A growing number of studies has demonstrated that community responses are difficult to predict without considering explicitly the complex and interactive effects of climate and land use drivers (Grime et al. 2000;Christensen et al. 2004;Klein et al. 2004Klein et al. , 2007Pyke and Marty 2005;Diaz et al. 2007). In drylands, continued aridification and changes in grazing regime are expected to produce significant consequences for ecosystem functions (Maestre et al. 2016;Vandandorj et al. 2017;Gaitán et al. 2018;Nandintsetseg et al. 2021;Maestre et al. 2022), by altering species occurrence and abundance, ultimately changing the functional structure of plant communities, i.e., the distribution of plant trait values (Suding et al. 2008;Valencia et al. 2015;Funk et al. 2017;Gross et al. 2017;. ...
... Providing forage for vertebrate grazers is a primary land use in grassland ecosystems, but grazing regimes are changing with human cultural practices (Kahmen and Poschlod 2008). Grazing can greatly influence standing biomass, litter accumulation, community composition, and carbon and nutrient cycles (Facelli and Pickett 1991;Peco et al. 2012;Spence et al. 2014;Kohli et al. 2021) and be of key importance in plant-community responses to climate change (Pyke and Marty 2005;Klein et al. 2007;Post and Pedersen 2008;Maestre et al. 2022). Some evidence suggests that aridity and grazing can select for similar traits and that aridity can promote resistance to grazing (Milchunas et al. 1988;Adler et al. 2004;Quiroga et al. 2010;Koerner and Collins 2014). ...
... There was considerable interaction between grazing and warming as trait responses mainly occurred in the absence of grazing, illustrating the importance of considering climate change in the context of land use (Pyke and Marty 2005;Klein et al 2007;Post and Pedersen 2008;Maestre et al. 2022). Local cessation of grazing is increasingly likely to occur based on contemporary changes in Mongolian lifestyles (Morris and Bruun 2005). ...
Changes in climate and grazing intensity influence plant-community compositions and their functional structure. Yet, little is known about their possible interactive effects when climate change mainly has consequences during the growing season and grazing occurs off growing season (dormant season grazing). We examined the contribution of trait plasticity to the immediate responses in the functional structure of plant community due to the interplay between these two temporally disjunct drivers. We conducted a field experiment in the northern Mongolian steppe, where climate was manipulated by open-top chambers (OTCs) for two growing seasons, increasing temperature and decreasing soil moisture (i.e., increased aridity), and grazing was excluded for one dormant season between these two growing seasons. We calculated the community-weighted mean (CWM) and the functional diversity (FD) of six leaf traits. Based on a variance partitioning approach, we evaluated how much of the responses in CWM and FD to OTCs and dormant season grazing occur through plasticity. The interactive effect of OTCs and the dormant season grazing were detected only after considering the role of trait plasticity. Overall, OTCs influenced the responses in CWM more than in FD, but the effects of OTCs were much less pronounced where dormant season grazing occurred. Thus, warming (together with decreased soil moisture) and the elimination of dormant season grazing could interact to impact the functional trait structure of plant communities through trait plasticity. Climate change effects should be considered in the context of altered land use, even if temporally disjunct.
... The ideal temperature ranges for winter crops and summer crops are from 25-31 °C and 31-37 °C respectively (Al-Rajab, 2021) [2] . Higher air temperatures have a negative impact on plant growth, pollination, and the reproductive process after a certain point (Klein et al. 2007) [17] . One of the primary factors impacting the growth and development of cucumbers is temperature (Farazmand, 2020) [6] . ...
... The ideal temperature ranges for winter crops and summer crops are from 25-31 °C and 31-37 °C respectively (Al-Rajab, 2021) [2] . Higher air temperatures have a negative impact on plant growth, pollination, and the reproductive process after a certain point (Klein et al. 2007) [17] . One of the primary factors impacting the growth and development of cucumbers is temperature (Farazmand, 2020) [6] . ...
... Degraded grasslands currently account for about 30-40 % of 1.5 million km 2 of natural alpine grasslands (Akiyama and Kawamura, 2007;Gao et al., 2010;Zhou et al., 2023), and severely degraded grassland accounts for approximately 16 % of an alpine grassland on the Tibetan Plateau (Wang et al., 2006). Many studies have reported that climatic warming resulted in lower plant height, coverage, and plant diversity (Klein et al., 2004(Klein et al., , 2007Wang et al., 2012;Harrison et al., 2015;Duchicela et al., 2021), because warming induced water limitation will change the availability of water, thus the positive effects will be offset . In addition, some studies have found that water restrictions will delay the green up days of plants, and shortens the growing season, which to some extent is not conducive to the improvement of productivity (Yu et al., 2010;Xu et al., 2021). ...
... Many researchers have reported that warming promotes the growth of tundra and plateau plants (Aerts et al., 2006;Walker et al., 2006;Wu et al., 2011). Klein et al. (2007Klein et al. ( , 2008 stated that warming reduced ANPP and especially reduced the proportion of graminoid plants and enhanced the proportion of forbs. Some other studies have suggested that warming would enhance plant productivity only when N availability and soil water are not limiting factors (Wu et al., 2011;Natali et al., 2012). ...
It is still debated whether warming induces degradation of alpine grasslands and whether warming accelerates the restoration of degraded alpine grasslands. Here we conducted a warming experiment using open top chambers to explore warming effects on plant composition and diversity, aboveground net primary productivity (ANPP) and net ecosystem carbon exchange (NEE) in alpine grassland at three degradation levels (i.e., no-degradation, moderate degradation and desertification) on the Tibetan Plateau from 2014 to 2016. There were no interactive effects between warming and degradation level on the variables measured in our study, except for plant diversity. Warming enhanced plant species diversity at no-degradation sites but had no significant influence on species diversity at sites of moderate degradation and desertification. Generally, warming alone had no significant effects on ANPP or seasonal average NEE during the experimental period, but its effect on them varied with year. In addition, compared with non-degraded sites, heavy degradation decreased ANPP by 35.8%, 44.2% and 63.8%, and reduced NEE by 71.8%, 63.4% and 70.3% in 2014, 2015 and 2016, respectively. The effects of moderate degradation on ANPP and NEE varied with year, enhancing ANPP by 37.3% and 37.7% in 2015 and 2016, but moderate degradation had no remarkable influence on seasonal average NEE compared with non-degraded sites. These results suggest that warming neither accelerates degradation of alpine grasslands nor promotes restoration of degraded alpine grasslands on the Tibetan Plateau.
... Pollinator-mediated reproductive interactions may affect the resilience of plant communities subject to environmental change. The Qinghai-Tibetan plateau is characterized by a harsh environment, and its ecosystem is vulnerable to climate change and human activities (Klein et al. 2007;Harris 2010;Chen et al. 2013). To restore and conserve alpine meadows under the influence of climate change, the local government has recently formulated a grazing regime involving exclusion of grazers during the plant growing season from April to September in areas with serious land degradation. ...
... All stigmas of each flower were collected with clean forceps and stored in a clean centrifuge tube containing 70% ethanol (Harder and Aizen 2004). We placed the stigmas on glass slides, stained it with a drop of alkaline magenta solution (Kearns and Inouye 1993), and covered it with a cover glass for observations and photography under a 400× microscope. Because the stigmas were stored in ethanol, some of the pollen deposited on the stigma fell off into the eluent. ...
1. Co-flowering plant species often interact through shared pollinators, with effects ranging from positive (facilitation) to negative (competition). It remains unclear how this variation relates to variation in floral density, floral trait distinctiveness, and local environmental conditions. We studied the effect of grazer exclusion, a proposed local management strategy, on pollinator-mediated plant-plant interactions in heavily degraded alpine meadows of the Qinghai-Tibet Plateau.
2. We studied the effect of experimental grazer exclusion on plant reproduction and pollinator-mediated reproductive interactions quantified through pollen transfer networks. We also explored potential mechanisms of pollinator-mediated interspecific pollen transfer and its effect on plant reproductive fitness, including local floral abundance and floral trait distinctiveness among co-flowering species.
3. Grazer exclusion led to greater pollen deposition onto stigmas. The overall quantitative effects of pollinator-mediated interspecific interactions on the receptor species were mainly positive (facilitative) or neutral (with no detectable effect). The frequency of positive relative to negative quantitative effects for pairwise donor-receptor pairs tended to increase after grazer exclusion. Plants with floral traits similar to those of local ‘hub species’ appeared to benefit from pollinator-mediated interactions.
4. Our results suggest an overall positive effect of excluding grazers during the plant growing season on plant reproduction. Facilitative species interactions predominate in harsh environments such as the alpine, and the benefits of pollinator-mediated interactions among plants seemed to exceed the cost of conspecific pollen loss associated with pollinator sharing. This suggest that species invasions into alpine plant communities, an expected consequence of climate change, may not necessarily have negative effects on the reproduction of resident plant species.
... Our findings would offer empirical field evidence to project the radiation balance of high mountains in a changing climate (Körner, 2003;Marty et al., 2002). Meanwhile, the comparisons in radiation partitioning between the meadow and shrub would present another underlying mechanism for explaining the occurring shrub encroachment (Li et al., 2023;Reinhardt et al., 2022), which has resulted in lower grass production quality (Klein et al., 2007) but higher water-holding capacity (Dai et al., 2021; in alpine grasslands. ...
... The shrub had the lowest R u and thus the highest net shortwave radiation (Figure 4), suggesting that the shrub received more radiation energy than the meadow and forb Zhang et al., 2018), which could produce larger non-radiative components (latent and sensible heat fluxes) and subsequently creating a warmer and wetter microclimate for the underlying vegetation. Such energy translation manner in the shrub would probably improve plant physiological performance under harsh alpine climates (Eugster et al., 2002;Li et al., 2023) and facilitate shrubs outcompete and expand into neighboring meadows (Klein et al., 2007;. ...
Quantifying the elevation dependency of radiation partitioning in high‐altitude mountains is crucial for projecting regional energy balance while remains highly uncertain. We compared the surface radiation partitioning parameters across a meadow (3,200 m), shrub (3,400 m), and forb (3,600 m) along a southern slope of the Qilian Mountains. At a daily scale, the downward shortwave radiation (Rs) fluctuated minimally among the grassland types probably induced by similar site orientations. The greatest downward and upward longwave radiation (Ld and Lu) happened at the lowest meadow while the largest net shortwave (Sn) and longwave (Ln) radiation occurred at the deciduous shrub. The net all‐wave radiation (Rn) of the meadow and shrub was similar and exceeded that of the forb by ∼20%. The differences in Rn between the sites were jointly explained by those of upward shortwave radiation (Ru) and Lu, more than by Rs and Ld, suggesting the importance of surface attributes. The monthly normalized effective terrestrial radiation (λ, the ratio of Ln to Rs) varied insignificantly among the sites and averaged 0.25 ± 0.05, which was comparable to the global mean value (0.26). The smallest surface albedo (α, the ratio of Ru to Rs) and largest radiation efficiency (η, the ratio of Rn to Rs) were 0.13 ± 0.02 and 0.64 ± 0.09, respectively, both at the shrub. Grassland type dominated the spatial variations of monthly α and η. These findings highlighted the importance of grassland types to explain the spatiotemporal variations of radiation partitioning parameters in high‐altitude alpine grasslands.
... Global changes (Butchart et al., 2010;Griggs et al., 2013;Maes et al., 2016) and human activities have resulted in a decline in biodiversity (Dirzo et al., 2014;Vogel, 2017;Leather, 2018), which in turn affects ecosystem functioning and services (Loreau and Hector, 2001;Cardinale et al., 2012;Isbell et al., 2017). For instance, experimental warming and livestock grazing have been shown to significantly alter plant species composition and net primary production in alpine grasslands on the Tibetan Plateau, particularly the relative abundance of grasses, sedges, and herbs (Klein et al., 2007;Wang et al., 2012;Liu et al., 2018). However, the impact of plant species loss on other trophic levels, such as consumer diversity and multitrophic structure, has rarely been investigated in natural grasslands (Hooper et al., 2005;Duffy et al., 2007;Haddad et al., 2009;Scherber et al., 2010). ...
... The experiment focuses on the impacts of plant diversity loss on arthropod diversity and their functional groups. This approach reflects realistic scenarios observed in ecosystems affected by overgrazing (Mu et al., 2016;Wang and Wesche, 2016;Niu et al., 2016a;Abdalla et al., 2018), human activities (such as grazing exclusion and fertilizer addition), and climate change (such as experimental warming) (Klein et al., 2007;Chen et al., 2013;Niu et al., 2014;Zhang et al., 2015), which can lead to changes in plant species abundance and composition. ...
Plant species loss, driven by global changes and human activities, can have cascading effects on other trophic levels, such as arthropods, and alter the multitrophic structure of ecosystems. While the relationship between plant diversity and arthropod communities has been well-documented, few studies have explored the effects of species composition variation or plant functional groups. In this study, we conducted a long-term plant removal experiment to investigate the impact of plant functional group loss (specifically targeting tall grasses and sedges, as well as tall or short forbs) on arthropod diversity and their functional groups. Our findings revealed that the removal of plant functional groups resulted in increased arthropod richness, abundance and the exponential of Shannon entropy, contrary to the commonly observed positive correlation between plant diversity and consumer diversity. Furthermore, the removal of different plant groups had varying impacts on arthropod trophic levels. The removal of forbs had a more pronounced impact on herbivores compared to graminoids, but this impact did not consistently cascade to higher-trophic arthropods. Notably, the removal of short forbs had a more significant impact on predators, as evidenced by the increased richness, abundance, the exponential of Shannon entropy, inverse Simpson index and inverse Berger-Parker index of carnivores and abundance of omnivores, likely attributable to distinct underlying mechanisms. Our results highlight the importance of plant species identity in shaping arthropod communities in alpine grasslands. This study emphasizes the crucial role of high plant species diversity in controlling arthropods in natural grasslands, particularly in the context of plant diversity loss caused by global changes and human activities.
... Potentilla parvifolia is mainly distributed in the midhigh altitudes of the QLMs (Yanyan et al., 2022). Warming experiments have shown that the growth and abundance of P. parvifolia in alpine meadows has increased under climate change in cold regions (Elmendorf et al., 2012;Klein et al., 2007) and that they tend to migrate to higher latitudes. ...
... As the dominant shrub in the QLMs, P. parvifolia has important effects on soil properties and microenvironment (Drewnik et al., 2016;Tai et al., 2013). In general, larger shrub types have strong nutrient accumulation capacities (Klein et al., 2007; Science -Soil Science and Hydrology, 2019), which may contribute to the growth and enrichment of root zone-dominant microbial community Ye et al., 2014). In addition, P. parvifolia increased the soil C/N ratio, ...
The Qilian Mountains (QLMs) form an important ecological security barrier in western China and a priority area for biodiversity conservation. Potentilla parvifolia is a widespread species in the mid‐high altitudes of the QLMs and has continuously migrated to higher altitudes in recent years. Understanding the effects of P. parvifolia on microbial community characteristics is important for exploring future changes in soil biogeochemical processes in the QLMs. This study found that P. parvifolia has profound effects on the community structure and ecological functions of soil microorganisms. The stability and complexity of the root zone microbial co‐occurrence network were significantly higher than those of bare soils. There was a distinct altitudinal gradient in the effect of P. parvifolia on soil microbial community characteristics. At an elevation of 3204 m, P. parvifolia promoted the accumulation of carbon, nitrogen, and phosphorus and increased sucrase activity and soil C/N while significantly improving the community richness index of fungi ( p < .05) compared with that of bacteria and the relative abundance of Ascomycota . The alpha diversity of fungi in the root zone soil of P. parvifolia was also significantly increased at 3550 m altitude. Furthermore, the community similarity distance matrix of fungi showed an evident separation at 3204 m. However, at an altitude of 3750 m, P. parvifolia mainly affected the bacterial community. Potentilla parvifolia increased the bacterial community richness. This is in agreement with the findings based on the functional prediction that P. parvifolia favors the growth and enrichment of denitrifying communities at 3550 and 3750 m. The results provide a scientific basis for predicting the evolutionary trends of the effects of P. parvifolia on soil microbial communities and functions and have important implications for ecological governance in the QLMs.
... Each temperature elevations method presents different advantages and disadvantages. For example, although infrared emitters are cost-effective, they display low heating efficiency [18], while using cables during heating may present a fire hazard [18], and open-top chambers display lower heating efficacy during cooler months [19]. Therefore, suitable temperature elevation equipment should be selected according to the climatic conditions in the experimental area. ...
Soil organic carbon (SOC) represents the most dynamic component of the soil carbon pool and is pivotal in the global carbon cycle. Global temperature rise and increasing drought severity are now indisputable realities, making soil organic carbon cycling under climate warming a critical research priority. This review elucidates the mechanism of the SOC response to temperature increase in terms of both extrinsic and intrinsic factors. The extrinsic factors are temperature elevation methods, rainfall, and land use. Different methods of temperature increase have their own unique advantages and disadvantages. Indoor warming methods exclude other factors, making temperature the only variable, but tend to ignore carbon inputs. In situ field warming and soil displacement methods help researchers explore the response of the complete ecosystem carbon cycle to temperature increase but cannot exclude the interference of factors such as rainfall. Elevated rainfall mitigates the adverse effects of elevated temperatures on organic carbon sequestration. In addition, the response of SOC to temperature elevations vary among different land use types. The temperature sensitivity of SOC is higher in peatland (high organic matter) alpine meadows (colder regions). The intrinsic factors that affect the response of SOC to elevated temperatures are SOC components, microorganisms, SOC temperature sensitivity, and SOC stability. The SOC decomposition rate is influenced by variations in the ratios of decomposable (easily oxidizable organic carbon (EOC), dissolved organic carbon (DOC), and microbial biomass carbon (MBC)) and stabilizing (inert organic carbon (IOC), alkyl carbon, and aromatic carbon) SOC to total organic carbon (TOC). Furthermore, temperature elevations also affect the soil microenvironment, resulting in microbial community reorganization such as changes in bacterial and fungal ratios and abundance. At the same time, soil aggregates, clay minerals, and iron and aluminum oxides protect the SOC, making it difficult to be utilized by microbial decomposition. The systematic clarification of the mechanism behind the SOC response to higher temperatures is crucial for accurately predicting and modeling global carbon cycles and effectively responding to the loss of SOC pools due to global temperature elevations.
... The Tibetan Plateau, as one of the most sensitive and vulnerable terrestrial ecosystems (Klein et al. 2007;Sun et al. 2020), is being affected by factors such as climate change and human activities. Alpine grasslands, the largest vegetation type, covering more than 50% of the plateau , are experiencing varying degrees of degradation, which has triggered a series of ecological consequences (Mao et al. 2013;Zhou et al. 2005b). ...
Background and aims
The degradation of the alpine grasslands on the Qinghai-Tibet Plateau has been mitigated in some regions, while it persists to varying degrees in others. Soil seed banks (SSBs), reflecting the past, present, and future potential of plant communities, are critical for restoration. This study assessed fencing, a nature-based solution, addressing regional biases and limited cross-regional synthesis in prior research.
Methods
Paired plots of free grazing and fenced grazing were established through field sampling. Community and SSB characteristics were compared between fenced and grazed areas using vegetation and seed bank surveys, seed germination experiments, and statistical analyses. Structural equation modeling (SEM) was employed to identify regulatory pathways influencing seed density under both management regimes.
Results
Fencing increased seed density (346–20,961 seeds/m²) compared to grazed areas (346–14,378 seeds/m², p < 0.05). The Sørensen similarity index indicated altered community structure and retrogressive succession (fenced: 0.803; grazed: 0.766). Fencing raised the importance value (IV) of Poaceae by 8.70% but reduced non-grass species richness and IV by 8.13%. SEM explained 95.04% (fenced) and 97.30% (grazed) of seed density variation, with fencing weakening seed density response to precipitation.
Conclusions
Fencing significantly affects SSBs by altering seed density, community structure, composition, and diversity. These changes reduce the sensitivity of SSBs to precipitation and may contribute to retrogressive succession in alpine grasslands. This study provides theoretical support for utilizing SSBs as a target for nature based solution to restore degraded alpine grasslands on the Qinghai-Tibet Plateau.
... The Qinghai-Tibet Plateau is one of the most sensitive and fragile terrestrial ecosystems in the world [1,2]. Alpine grasslands, which cover more than 50% of the plateau, represent the largest vegetation type in this region [3]. ...
Alpine grasslands are a critical component of the Qinghai–Tibet Plateau ecosystem, but their soil seed bank (SSB) patterns and driving mechanisms remain unclear under the influence of climate change and human activities. This study analyzed grazing exclusion (via fencing) and grazing effects using 12 sites in the alpine steppe (AS) and alpine desert steppe (AD) in northern Tibet to analyze the effects of fencing and grazing management, as well as hydrothermal and soil factors, on the SSB density and diversity. Linear regression models were applied to explore the relationships between the SSB density and environmental factors, while comparisons of the management modes revealed the potential impacts of fencing. The results show that fencing significantly increased the SSB density and diversity, especially in the AS, while grazing negatively impacted the SSB density and the Pielou evenness index. Hydrothermal factors strongly influenced the SSB in the AS, with the density positively correlated with precipitation and negatively with temperature, while responses in the AD were weak. Soil factors, such as the available phosphorus (SAP) and available potassium (SAK), were key to SSB formation in the AD, whereas ammonium nitrogen (NH4_N) and the pH were critical in the AS. Fencing optimized the hydrothermal conditions and nutrient availability, promoting SSB recovery, though its effects varied between the grassland types. This study provides scientific insights for alpine grassland restoration and sustainable management.
... Further plant community analyses revealed a total of 11 distinct plant species assemblages on the Tibetan Plateau's grassland, many of which align on a moisture gradient or are distinct by the cover fraction of K. pygmaea (Miehe et al. 2011a, Miehe et al. 2011b). Finally, Klein et al. (2007) also linked warming-induced changes in plant community composition to a decline in fodder quality. ...
The ongoing vegetational change on the Tibetan Plateau, where pastoralism has been the predominant way of life, is of regional and global importance. Although recent influential research suggests that the vegetation on the Tibetan Plateau has been greening, or improving, local yak herders in Nagchu (Tibetan Autonomous Region, China) report that their grassland has deteriorated. To understand this discrepancy, we critically analysed and contrasted remote sensing observations and ethnographic accounts within the framework of valuation studies. We argue that these seemingly contradictory observations are not mutually exclusive because the remote sensing data mainly focuses on the spatial vegetation coverage, whereas herders care about vegetation height and its nutritional quality as yak fodder. Taking into account that these two sets of data evade a direct comparison, valuation studies help to understand in what respect the underlying perspectives and observations—i.e. remote sensing and local experiences—can be understood as social activities in which assessments are made based on different criteria. Our study argues that a pluralistic way of understanding the grassland dynamics helps to understand the complexity of the changing environment.
... Alpine grassland play a vital role in enhancing biodiversity, sequestering carbon, maintaining productivity, and supporting the livelihoods of pastoral communities on the Qinghai-Tibetan Plateau (QTP) [5]. However, under climate warming and overgrazing, grassland are experiencing significant degradation [6]. Specifically, approximately 40% of the world's grassland exhibit varying levels of degradation [7]; this diminishes their ability to sustain biodiversity, provide essential ecosystem services, and support the well-being of local populations [8]. ...
Alpine grassland degradation in permafrost regions seriously affects the provision of ecosystem services, posing a threat to ecological security. Revegetation is a key strategy for the restoration of alpine grassland ecosystems on the Qinghai–Tibetan Plateau (QTP). However, there is a lack of comprehensive research evaluating ecosystem services after revegetation, especially in permafrost regions. In this study, we assessed the changes in ecosystem services following revegetation in the alpine permafrost regions of the QTP through on-site monitoring and sampling, using extremely degraded alpine grassland as a control. In addition, we analyzed trade-offs among ecosystem services and identified key drivers. Our results indicate that (1) revegetation significantly increased forage supply, carbon storage, and soil retention values (p < 0.05), while water retention and permafrost stability showed no significant changes (p > 0.05); (2) vegetation restoration effectively reduced the trade-offs among ecosystem services; and (3) the main drivers were vegetation coverage, precipitation, belowground biomass, and restoration duration. Overall, this study demonstrates that revegetation improves ecosystem services. The enhancement in these services provides valuable data for future research on ecosystem services in alpine grassland.
... The Qinghai-Tibet Plateau is characterized by a harsh environment, and its ecosystem is vulnerable to climate change and human activities (Chen et al., 2013;Gao et al., 2021;Harris, 2010;Klein et al., 2007). Some studies have found that pollinators are relatively rare and taxonomically less diverse in high-altitude habitats so that the plants occurring in these communities seem susceptible to pollen limitation of reproduction (Gao et al., 2021;Tur et al., 2016). ...
Pollinator‐mediated reproductive interactions among co‐flowering plant species provide a canonical example of how biotic factors may contribute to species coexistence, yet we lack understanding of the exact mechanisms. Flowering‐dominant and unusually attractive “magnet species” with disproportionate contributions to pollination may play key roles in such reproductive interactions, but their relative roles within the same community have rarely been assessed. We experimentally removed either a flowering‐dominant or a highly attractive magnet species and compared effects on visitation frequency, pollinator richness, and seed set of co‐flowering plants. Removal of either the flowering‐dominant species or the magnet species reduced community‐level pollinator visitation. Removal of the magnet species had the most consistent effect, including reduced pollinator visitation and richness, and reduced seed set of most co‐flowering plants. These results suggest that the magnet species, which interacts with a wider range of pollinator species than does the dominant species, promotes the visitation and reproductive fitness of most other species. Removal of the flowering‐dominant species affected only certain species, perhaps because these plants had floral traits similar to the dominant species. Our results highlight the role of attractive magnet species within a community in structuring reproductive interactions and identify potential mechanisms involved in coexistence facilitated by reproductive interactions.
... Albeit the high-altitude northwestern Tibetan Plateau is rarely inhabited by humans, the fragile ecosystem over this region is greatly threatened by nocturnal heat. The warming may influence the plant species richness, rangeland quality and ecological stability, reducing their ability to provide reliable ecosystem services for humanity [34][35][36] . Moreover, the extreme warming may accelerate the glacier retreat and permafrost thawing, causing hydrological Fig. 2c, d, but for the detrended compound events between the flood over (a1-b1) northeastern India in South Asia (purple contour in a1 additionally shows the significant 500-hPa specific humidity anomaly aloft the terrain; units: g kg -1 ; intervals: 0.2 g kg -1 ; the Tibetan Plateau is outlined at 500 hPa and shaded with black at 850 hPa), (a2-c2) the Great Plains in the US, (a3-c3) the Central American isthmus, (a4-c4) the North African monsoon region and the adjacent nocturnal heat. ...
... According to the International Panel on Climate Change (IPCC), global temperatures are expected to increase by 1.0-3.7 °C by 2100 [11]. The combined effects of climate change and overgrazing on plant productivity, phenology, and ecosystem characteristics are also known from the literature [12,13]. Several studies of geothermally heated areas in Iceland show that soil warming affects plant phenology, with plant phenology accelerating with increasing temperature [14]. ...
The study investigates the impact of varying grazing intensities on the biochemical composition of Artemisia diffusa, a key species in rangeland ecosystems. Grazing, an essential ecological process, can significantly influence plant biochemistry, affecting both nutritional value and ecological interactions. This research was conducted in a semi-arid Karnabchul desert rangelands, where A. diffusa samples were collected from plots subjected to different grazing intensities: (low grazing and heavy grazing). Biochemical analyses focused on key constituents such as crude protein, fiber, carbohydrates including. The results indicated significant variations in the biochemical composition of A. diffusa across different grazing intensities. Light grazing led to a moderate increase in protein and carbohydrate contents, enhancing the plant's nutritional value. In contrast, heavy grazing caused a reduction in these protein and carbohydrate but significantly not change the concentrations of fiber, likely as a defensive response to grazing pressure.
... * Richa Hu huricha159349@gmail.com; d20a3001k@edu.tottori-u.ac.jp 1 production (Lin et al. 2010;Wang et al. 2012aWang et al. , 2019, there are reports of cases with no effect (Saleska et al. 2002) or with decreasing plant biomass in response to warming (Klein et al. 2007;Liu et al. 2021). Few studies, however, have focused on the effects of warming on plant regrowth after grazing, and the results of those limited studies were sometimes inconsistent. ...
Global warming may pose a threat to the productivity of grazed grasslands. In this study, we investigated changes in the warming response of aboveground regrowth with the repetition of simulated grazing in two Mongolian pasture species, Agropyron cristatum and Stipa krylovii. Plants were grown under warming or non-warming conditions and subjected to repeated clipping of aboveground parts three times at 4-week intervals. Aboveground parts collected at each clipping and whole plants harvested at the end of the experiment were dried and weighed. Specific leaf area (SLA) and the content of nitrogen (N) and crude fiber (CF) in leaves were measured to evaluate leaf morphology and pasture nutritional value. In both species, warming had little effect on regrowth when clipping was repeated one or two times. In A. cristatum, however, warming significantly diminished regrowth when clipping was repeated three times. Belowground biomass decreased with clipping–regrowth cycles only in A. cristatum, and the decline was enhanced by warming, implying that the depletion of belowground reserves contributed to the reduction of regrowth in this species. SLA and the N and CF contents were similar in the warming and non-warming treatments, indicating that warming had little effect on leaf morphology and pasture nutritive value in these Mongolian pasture species. Our results suggest that warming would likely have little effect on regrowth performance of grassland plants under lightly grazed conditions, but warming can decrease regrowth when grazing frequency is high, with the degree of decrease being species dependent.
... Shrub encroachment is an important ecological problem for global grassland ecosystems under the effect of climate change and overgrazing (Elmendorf et al. 2012;Klein et al. 2007). Shrub encroachment destroys the original ecosystem of grassland vegetation, reduces the species diversity and primary productivity of grassland (; Lyon 2011). ...
The dioecious plant, Hippophae rhamnoides, is a pioneer species in community succession on the Qinghai-Tibet Plateau (QTP), plays great roles in various ecosystem services. However, the males and females of the species differ both in their morphology and physiology, resulting in a change in the ratio of male to female plants depending on the environment. To further explore the functional traits critical to this sex-based distinctive response in the alpine grassland, we have surveyed the sex ratios, measured their photosynthetic parameters, height, leaf area and biomass allocation. The results showed that (i) The males had higher Pn, light saturation point, apparent quantum efficiency, Amax and lower water-use efficiency (WUE), which exhibited higher utilization efficiency or tolerance to strong light, while the females indicated higher utilization efficiency for low light and water. And it showed sex-specific biomass allocation patterns. (ii) H. rhamnoides populations across the successional stages all showed a male-biased sexual allocation, which was closely related to sex-specific WUE, Pn, root biomass/total biomass and root–crown ratio. (iii) The leaf traits of H. rhamnoides changed from higher Narea, Parea and leaf mass per area in the early and late to lower in the middle, which meant they moved their growth strategy from resource rapid acquisition to conservation as the succession progressed. (iv) The increasing soil total phosphorus mostly contributed to regulating the sex bias of populations and variations of traits during the succession. The results are vital for the management of grassland degradation and restoration due to shrub encroachment on the QTP.
... According to the International Panel on Climate Change (IPCC), global temperatures are expected to increase by 1.0-3.7 °C by 2100 [11]. The combined effects of climate change and overgrazing on plant productivity, phenology, and ecosystem characteristics are also known from the literature [12,13]. Several studies of geothermally heated areas in Iceland show that soil warming affects plant phenology, with plant phenology accelerating with increasing temperature [14]. ...
The study investigates the impact of varying grazing
intensities on the biochemical composition of Artemisia
diffusa, a key species in rangeland ecosystems. Grazing, an
essential ecological process, can significantly influence
plant biochemistry, affecting both nutritional value and
ecological interactions. This research was conducted in a
semi-arid Karnabchul desert rangelands, where A. diffusa
samples were collected from plots subjected to different
grazing intensities: (low grazing and heavy grazing).
Biochemical analyses focused on key constituents such as
crude protein, fiber, carbohydrates including. The results
indicated significant variations in the biochemical
composition of A. diffusa across different grazing
intensities. Light grazing led to a moderate increase in
protein and carbohydrate contents, enhancing the plant's
nutritional value. In contrast, heavy grazing caused a
reduction in these protein and carbohydrate but significantly
not change the concentrations of fiber, likely as a defensive
response to grazing pressure.
... The potential impact of climate-related migration on a global scale is a concern, with predictions suggesting that a billion people could be permanently displaced by climate-related phenomena such as droughts, floods, and storms (Klein et al., 2007). The concept of "climate refugees" has been debated, with some arguing that environmental factors are a significant driver of migration, while others question the concept. ...
This chapter examines the causes of climate-induced displacement, commonly referred to as “climate refugees,” and the significant challenges to livelihoods in the Bundelkhand region. In today’s global discourse, climate change has become a pressing issue at national and international levels, profoundly impacting governance worldwide and exacerbating unsustainable livelihood practices. The geophysical and hydrological conditions in Bundelkhand play a crucial role in climate change, necessitating urgent interdisciplinary attention to find sustainable solutions. The region is burdened with labels such as “water poverty region,” “backward region,” “livelihood crisis region,” “farmer’s suicide region,” and “ecologically fragile region” due to the adverse effects of climate change, resulting in a triad of challenges: drought, deprivation, and depopulation.
To gain empirical insights into the region’s livelihoods, primary surveys were conducted, informing the content of this paper. Various factors have been identified as the root causes of livelihood challenges, prompting individuals to become climate refugees and seek refuge in urban metropolitan cities. This study presents innovative strategies that prioritize human well-being and address livelihood challenges by emphasising the roles of government, non-governmental organisations (NGOs), and self-help groups (SHGs). These strategies aim to ensure equitable access to affordable, accessible, and high-quality food grains, education, healthcare, employment opportunities, constitutional rights, crop diversification, and the utilisation of traditional knowledge systems (TKS) in agroforestry business and water resource management.
Furthermore, this study explores the potential of cutting-edge technologies such as artificial intelligence, cloud computing, data banking, the fourth industrial revolution, and 5G technology in mitigating unsustainable livelihood challenges. These advancements offer promising avenues for sustainable development, fostering resilience in the face of climate change impacts. By addressing the complex web of challenges faced by the Bundelkhand region, this research endeavours to provide a comprehensive understanding of climate change-induced livelihood crises and offers practical solutions to promote sustainable development. The proposed strategies underscore the importance of collaborative efforts between stakeholders and the integration of innovative technologies to achieve a resilient and prosperous future for the region.
... Climate change might have a more complicated influence on tree lines (Harsch et al., 2009;Gottfried et al., 2012) and rangelands, since it can modify plant competition and growth patterns, productivity, and plant-animal interactions, as well as reduce rangeland quality (IPCC, 2014). Warming trends affect the timing of snowmelts, grass production, and plant phenology (Klein et al., 2007). As a result, it is vital to research climate change because agriculture is less favored for livelihood than livestock farming owing to challenging topography and harsh conditions (Liverman, 2008;Fereja, 2017). ...
The livelihood of the Himalayan Mountain inhabitants is inextricably linked to the region’s climate. Therefore, every change in climatic conditions has a considerable impact on mountain livelihoods. The Himalayan region has been witnessing the climate change repercussions. This research analyses the People’s perspectives towards climatic changes as well as the accompanying dynamics. The calculation of land surface temperature (LST) shows that there has been a significant increase in temperatures at high altitudes. The majority of the people feel the weather has become warmer in general, as well as an abrupt changes in the rainfall has been witnessed. The intensity, duration, and type of precipitation have all been observed to have varied significantly. Also, water scarcity has increased and the agricultural field has also shown reduced productivity. There have been several alterations in the livelihood pattern of the people due to the changing environmental scenario. As a result, the diversification of livelihood has gained importance. Therefore, there is an urgent need to characterize, analyze, and comprehend the vulnerability of dependent communities in mountain regions. The findings of this study reveal that local people seem cognizant of climate variability and its effects and they have shifted towards diverse livelihood sources. Thus, climate change and its driving variables must be clearly understood in order to accomplish successful management of natural resources as well as the well-being of the local community.
... Alpine grassland ecosystems constitute the primary vegetation cover on the Qinghai-Xizang Plateau and serve as representative examples of global alpine ecosystems [14][15][16]. Numerous studies have been conducted on the relationships between soil NH 4 + -N, NO 3 − -N and/or AP and environmental factors in alpine grassland regions of the Qinghai-Xizang Plateau [17,18]. These studies offer crucial scientific and technological insight into the mechanisms underlying changes in available nitrogen and phosphorus nutrition in alpine grasslands of global transformations, as well as their impacts on the structure and function of alpine grassland ecosystems. ...
There is still a lack of high-precision and large-scale soil ammonium nitrogen (NH4⁺-N), nitrate nitrogen (NO3⁻-N) and available phosphorus (AP) in alpine grasslands at least on the Qinghai–Xizang Plateau, which may limit our understanding of the sustainability of alpine grassland ecosystems (e.g., changes in soil NH4⁺-N, NO3⁻-N and AP can affect the sustainability of grassland productivity, which in turn may alter the sustainability of livestock development), given that nitrogen and phosphorus are important limiting factors in alpine regions. The construction of big data mining models is the key to solving the problem mentioned above. Therefore, observed soil NH4⁺-N, NO3⁻-N and AP at 0–10 cm and 10–20 cm, climate data (air temperature, precipitation and radiation) and/or normalized vegetation index (NDVI) data were used to model NH4⁺-N, NO3⁻-N and AP in alpine grasslands of Xizang under fencing and grazing conditions. Nine algorithms, including random forest algorithm (RFA), generalized boosted regression algorithm (GBRA), multiple linear regression algorithm (MLRA), support vector machine algorithm (SVMA), recursive regression tree algorithm (RRTA), artificial neural network algorithm (ANNA), generalized linear regression algorithm (GLMA), conditional inference tree algorithm (CITA), and eXtreme gradient boosting algorithm (eXGBA), were used. The RFA had the best performance among the nine algorithms. Climate data based on the RFA can explain 78–92% variation of NH4⁺-N, NO3⁻-N and AP under fencing conditions. Climate data and NDVI together can explain 83–93% variation of NH4⁺-N, NO3⁻-N and AP under grazing conditions based on the RFA. The absolute values of relative bias, linear slopes, R² and RMSE values between simulated soil NH4⁺-N, NO3⁻-N and AP based on RFA were ≤8.65%, ≥0.90, ≥0.91 and ≤3.37 mg kg⁻¹, respectively. Therefore, random forest algorithm can be used to model soil available nitrogen and phosphorus based on observed climate data and/or normalized difference vegetation index in Xizang’s grasslands. The random forest models constructed in this study can be used to obtain a long-term (e.g., 2000–2020) raster dataset of soil available nitrogen and phosphorus in alpine grasslands on the whole Qinghai–Tibet Plateau. The raster dataset can explain changes in grassland productivity from the perspective of nitrogen and phosphorus constraints across the Tibetan grasslands, which can provide an important basis for the sustainable development of grassland ecosystem itself and animal husbandry on the Tibetan Plateau.
... Plant communities are especially sensitive to: fluctuation in their supported stocking rates [7,8] and to climate warming (the increase in average temperatures and changes in annual rainfall [9][10][11]). The effects of climate warming on vegetation have also been verified in other mountains of the world (Asia and Europe) [12][13][14][15]. ...
The certainty of global warming is leading to the programming of activities and management practices for a future in which conditions will be very different from today. In the case of subalpine mountain pastures (or upland summer grasslands), it is necessary to know the changes that have taken place in the three most important variables: biomass production, forage quality and diversity. This work was carried out in the high-mountain pastures of the Aigüestortes National Park (located above 2000 m a.s.l.) in the Spanish Pyrenees during a period of twenty years, with sampling every five years. The three most abundant types of pasture of the National park, which occupy 60% of its area (Festuca eskia, Nardus and Nardus+Festuca nigrescens) were taken and used to measure aboveground biomass production by means of cuts, forage quality through bromatological analyses of biomass and Pastoral value, and the diversity through transects. Simultaneously, climatic data from three nearby official climatic stations were collected to relate rainfall and temperature variations to vegetation data. The results show that changes in total production are more linked to annual climatology (more temperature in the growth period, less production), whereas general climate warming leads to a decrease in forage quality (more temperature and more rain in the growth period, higher fiber content) and an increase in specific richness (more temperature more diversity). In the future in order to maintain these highly diverse pastures for optimal feeding of the livestock, a downward adjustment of stocking rates will have to be programmed, in accordance with production and quality trends: the pastures will feed fewer animals.
... Livestock grazing is one of the most common utilization pattern of land in natural grasslands that influences plant community structure (Klein et al., 2007;Álvarez-Martínez et al., 2016;Su et al., 2017;Tarhouniet al., 2017) and soil physicochemical properties Xie et al., 2014;Li et al., 2016). Meanwhile, livestock grazing was considered as one of the key disturbance factors in grassland degradation (Oesterheld and Sala, 1990). ...
Grazing is a main land use of natural grasslands in the world, which has both positive and negative impact on plant community structure and ecosystem functioning. However, the effects of long-term grazing management on the plant–soil system, in particular above- and belowground community characteristics, are still not well understood in alpine meadow community. In this study, we investigated the vegetation, roots, and soil properties under three management types (16 years of fencing since 2004-2020, moderate grazing and heavy grazing managements) in an alpine meadow on the Tibetan Plateau. The results showed that, compared with moderate grazing meadows, long-term fencing increased plant community cover, above- and belowground biomass, proportion of grass and litter but reduced forbs and soil bulk density, which caused the increases in soil organic carbon, total nitrogen and water content and the decreases in soil pH. However, heavy grazing led to opposite changes in proportion of grass, community biomass and soil physicochemical properties. The maximum of species richness and plant density appeared in moderate grazing meadows, supporting the intermediate disturbance hypothesis, and it can maintain above- and belowground biomass and soil physicochemical properties at medium level. Grazing increased the root: shoot ratio and caused root system shallow, which is consistent with the optimal partitioning hypothesis. Overall, our study suggested that moderate grazing is a more reasonable grazing management for sustainable development in alpine meadows of Tibetan Plateau, fencing could be an effective management strategy for vegetation restoration as well as for nutrient sequestration in degraded grasslands, but long-term fencing dose not benefit for biodiversity maintenance.
... Therefore, studying the effects of plant diversity on grassland productivity and its stability at the spatial scale in alpine regions are of great significance for understanding the effect of plant diversity on grassland ecosystem functioning under the background of climate change. Previous studies focused on the effects of precipitation and temperature changes on various variables in alpine grassland ecosystems, such as productivity, grassland quality, litter, etc. (Klein et al. 2007;Haynes et al. 2014). Nevertheless, few researches have focused on the effects of plant diversity on grassland productivity stability at the spatial scales and along climate gradients. ...
Plant diversity can significantly affect the grassland productivity and its stability. However, it remains unclear how plant diversity affects the spatial stability of natural grassland productivity, especially in alpine regions that are sensitive to climate change. We analyzed the interaction between plant (species richness and productivity, etc.) and climatic factors (precipitation, temperature, and moisture index, etc.) of alpine natural grassland on the Qinghai-Tibetan Plateau. In addition, we tested the relationship between plant diversity and spatial stability of grassland productivity. Results showed that an increase in plant diversity significantly enhanced community productivity and its standard deviation, while reducing the coefficient of variation in productivity. The influence of plant diversity on productivity and the reciprocal of productivity variability coefficient was not affected by vegetation types. The absolute values of the regression slopes between climate factors and productivity in alpine meadow communities with higher plant diversity were smaller than those in alpine meadow communities with lower plant diversity. In other words, alpine meadow communities with higher plant diversity exhibited a weaker response to climatic factors in terms of productivity, whereas those with lower plant diversity showed a stronger response. Our results indicate that high plant diversity buffers the impact of ambient pressure (e.g., precipitation, temperature) on alpine meadow productivity, and significantly enhanced the spatial stability of grassland productivity. This finding provides a theoretical basis for maintaining the stability of grassland ecosystems and scientifically managing alpine grasslands under the continuous climate change.
... Our conclusion that litter accumulation in long-term exclosure suppresses grass production but favors shrub expansion by promoting its growth and recruitment echoes a similar effect of herbivore loss on vegetation communities and suggests that disturbance is a premise for maintaining grassy biomes in semiarid grasslands. Although mowing is widely used to mimic grazing (Jung et al., 2022;Klein et al., 2007), the distinct feature of foraging behavior between them is worth nothing. Mowing is just done on the average plant community height, but grazing by livestock has differential preferences between plants with different traits (Wang et al., 2012). ...
Shrub expansion is increasing in grasslands worldwide and has profound effects on biodiversity and ecosystem functions. Shrub expansion has primarily been explained by extrinsic factors such as climate change and human activities, yet the roles of intrinsic shrub demographic population dynamic and shrub–grass interaction remain poorly understood. With a paired mown and exclosure comparison experiment and baseline levels of shrub abundance in a semiarid grassland, we confirmed that long‐term livestock exclusion promotes expansion of two native shrubs, Artemisia sacrorum and Caragana brachypoda . Shrub abundance increased during the livestock exclusion period. Shrub biomass in fenced plots was about 5‐ to 10‐fold greater than in mown plots. Both increase in population density and individual size (especially height) contributed to shrub increase. The mechanism behind this was the divergent effects of litter accumulation on shrubs and grasses. Litter accumulation suppressed grass production, while facilitating shrub recruitment and growth. Our findings highlight the potential role of litter accumulation‐mediated shifts in shrub–grass interactions, which should be incorporated into grazing top‐down control to better predict the restoration outcomes of grassland management changes. The identified internal biotic mechanism raises the possibility that removal of accumulated litter by grazing or mowing may be an alternative way to maintain or restore a grass‐dominated state in shrub expansion areas.
... Light intensity and temperature increased during late sowing time, according to environmental data. Beyond a certain limit, higher air temperatures have a deleterious impact on plant growth, pollination, and reproductive stages of a plant(Klein et al., 2007). High temperatures throughout the productive period affect fertilization, and grain development, all of which have an impact on the crop's yield (Hat eld and Prueger, 2015). ...
A study on the “effect of sowing dates on lettuce yield, grown in the Open field and partial shade” was conducted at the Ornamental Nursery, Department of Horticulture, The University of Agriculture Peshawar, during 2020–2021. The randomized complete block design (RCBD) with a split-plot arrangement having two factors, replicated three times was used in the experiment. The lettuce ( Lactuca sativa L.), variety ‘Large Speed’ was grown in two growing conditions (open field and partial shade) at different sowing and transplanting dates, and their effect was studied. The seeds of lettuce were sown on six different dates i.e., 24th December 2020, 8th January, 23rd January, 7th February, 22nd February, and 9th March 2021. The results showed that the growing conditions and sowing dates significantly affected the growth and yield of the lettuce crop. Regarding the growing conditions, the plants grown in the open field produced maximum chlorophyll content, number of leaves plant − 1 , head diameter, head fresh weight, head dry weight, leaf Area, number of seeds plant − 1 , seed yield, and root length plant − 1 . On the other hand, maximum head height plant − 1 , days to flowering, days to seed production, plant height, and better taste were recorded in partial shade. In terms of sowing dates, maximum chlorophyll content, number of leaves plant − 1 , head height, head diameter, head fresh weight, head dry weight, leaf area, number of seeds plant ¹ , seed yield, root length, taste, days to flowering, days to seed production and plant height were recorded for the plants of first sowing and transplanting date (24th Dec). These parameters decreased with delayed sowing and transplanting.
... The P. fruticosa meadow represents the second most abundant species vegetation type after Kobresia humilis meadow on the Tibetan Plateau (Zhou and Wu, 2001). Warming experiments have shown that growth and abundance of P. fruticosa is increasing with temperature particularly in cold regions (Klein et al., 2007;Elmendorf et al., 2012). We hypothesized that shrubby P. fruticosa has a greater capacity to allocate photosynthate C belowground due to larger root biomass of P. fruticosa, compared with herbs. ...
Distribution of shrubs expanding in grasslands-shrubification-is ongoing worldwide in grasslands and is common on the Qinghai-Tibetan Plateau (QTP). But the consequences of shrubification for plant carbon (C) input and fate in soil are unclear. We used 13 C pulse labelling in a meadow on the QTP to compare photosynthetic capacity and photosynthate distribution in shoots, roots, soil and microbial functional groups between herba-ceous plants (herbs) and shrubby Potentilla fruticosa. During 3 h of labeling in 13 CO 2 atmosphere, the 13 C amount assimilated by shrubs (0.81 g C/m − 2) was only 38 % of that by herbs. Over 8 days after labeling, 13 C amount respired jointly by roots and soil microorganisms under shrubs (0.049 g m − 2) was less than half of that under herbs. The mean residence time of 13 C for respiration jointly by roots and rhizosphere microorganisms was longer under shrubs (0.61 day) than under herbs (0.44 day). Within 22 days after labelling, 13 C amounts in roots, soil, and microorganisms were consistently smaller under shrubs than those under herbs. Consequently, shrub P. fruticosa had not only smaller photosynthetic potential, but also allocated less photosynthate belowground and slowed down C cycling in soil compared with herbs. The distribution of total 13 C in microbial functional groups indicated by PLFA analysis was similar between herbs and shrubs. Averaged over vegetation patch types, gram negative bacteria and AMF accounted for 22 % and 4 % of the total microbial PLFAs in the 0-20 cm, respectively, but these two functional groups took up 51 % and 23 % of the total 13 C absorbed by microorganisms, respectively. This indicates that gram negative bacteria and AMF are major consumers of rhizodeposits. Concluding, shrubification leads to smaller C allocation belowground and slows down C cycling in the soil.
... Global warming can affect the regrowth performance of grassland species because plant physiological processes-including photosynthesis and respiration-are strongly temperature dependent (Luo 2007;Tjoelker and Zhou 2007). Although warming generally increases plant biomass production (Lin et al. 2010; S.P. Wang et al. 2012; Wang et al. 2019), there are reports of cases with no effect (Saleska et al. 2002) or with decreasing plant biomass in response to warming (Klein et al. 2007; Liu et al. 2021). Few studies, however, have focused on the effects of warming on plant regrowth after grazing, and the results of those limited studies were sometimes inconsistent. ...
Global warming may pose a threat to the productivity of grazed grasslands. In this study, we investigated changes in the warming response of aboveground regrowth with the repetition of simulated grazing in two Mongolian pasture species, Agropyron cristatum and Stipa krylovii. Plants were grown under warming or non-warming conditions and subjected to repeated clipping of aboveground parts three times at 4-week intervals. Aboveground parts collected at each clipping and whole plants harvested at the end of the experiment were dried and weighed. In both species, warming had little effect on regrowth when clipping was repeated one or two times. In A. cristatum, however, warming significantly diminished regrowth when clipping was repeated three times. Belowground biomass decreased with clipping–regrowth cycles only in A. cristatum, and the decline was enhanced by warming, implying that the depletion of belowground reserves contributed to the reduction of regrowth in this species. Our results suggest that warming would likely have little effect on regrowth performance of grassland plants under lightly grazed conditions, but warming can decrease regrowth when grazing frequency is high, with the degree of decrease being species dependent.
... A large body of studies has explored how community composition and productivity in healthy vegetation respond to climate change (Schuur et al. 2007;Sistla et al. 2013;Crowther et al. 2016;Hopping et al. 2018;Liu et al. 2018). Most manipulative warming experiments on the QTP have reported a decrease or increase in productivity (Klein et al. 2007;Wang et al. 2012), as well as a dramatic decline in plant species diversity over short time frames (Klein et al. 2004). Liu et al. (2018) reported that productivity of alpine meadow presented resistant to climate warming and did not change with warming over decades. ...
On-going climate warming is threatening the ecological function of grassland ecosystems. However, whether warming has positive effects on community microhabitats and appearance, especially in degraded grasslands, remains elusive. To address this issue, we conducted a 2-year field experiment on the severely degraded alpine meadow and undegraded alpine meadow with no warming and warming treatments. Community coverage and height in degraded meadow significantly increased under warming, while these changes were not significant in undegraded meadow. Two-year warming increased the community height of degraded meadow and undegraded meadow by 56.55% and 10.99%, respectively. Warming also increased community coverage by 41.88% in degraded meadow and decreased community coverage by 3.01% in undegraded meadow. Moreover, the response of topsoil temperature to warming was stronger in degraded meadow (6.89%) than in undegraded meadow (− 0.26%), while the negative response of topsoil moisture to warming was weaker in degraded meadow (− 13.95%) than in undegraded meadow (− 20.00%). The SEMs further demonstrated that warming had positive effects on topsoil temperature and community height, while had negative effects on topsoil moisture both in degraded and undegraded meadows. Our results confirm that warming-induced soil drying is an important pathway affecting the community appearance in alpine meadows. These findings highlight that warming has positive effects on community height and coverage and is particularly effective in improving community coverage appearance in severely degraded alpine meadow with topsoil drying.
... Relatedly, we hypothesized adult survival of mountain goats would respond indirectly to annual variation in the prevailing moisture regime (i.e., year-long drought), acting through the quantity and quality of available forage, and thence through the nutritive reserves individual animals are able to accumulate prior to winter (Parker et al. 2009). In the absence of data on protein or energetic content of likely forage species, we reasoned that nutritive quality would generally be higher in years of greater precipitation, and conversely, lower in years characterized by drought (Lenart et al. 2002, Klein et al. 2007). ...
Elucidating patterns of adult survival rates is key to understanding population dynamics of large mammals. We used data from 7 separate studies of mountain goats (Oreamnos amer-icanus) conducted from 2002 through 2022 in western Washington, USA, to quantify survival rates in relation to key biotic and abiotic factors using known fate models implemented in program MARK. We monitored 324 (206 females, 118 males) radio-marked mountain goats for 178,339 days. A substantial number of mountain goats in our sample (n = 217) had been translocated from the Olympic Peninsula to the Cascade Mountains on Washington's mainland, providing an added opportunity to examine translocation effects. We adopted a sequential modeling approach, first building a set of models to examine fundamental survival patterns by age, sex, season, study area, and translocated status. We used variables retained from the top model in a second set to investigate relationships between annual survival and local weather covariates hypothesized by previous studies to influence mountain goat behavior, habitat selection, and vital rates. Survival among adult females in spring was slightly lower than other sex and age categories, but seasonal patterns were otherwise not evident. There were significant negative relationships between survival and winter snow depth, an index of the previous year's drought, and mean daily temperature during the previous May, and a positive relationship with Journal of Wildlife Management 2024;88:e22495. wileyonlinelibrary.com/journal/jwmg
... However, many alpine regions have experienced significant shifts in plant composition, biodiversity and biomass in response to climate change and human activities in the past few decades, (Elmendorf et al., 2012;Hopping et al., 2018;Klein et al., 2005). On the Qinghai-Tibetan Plateau, such shifts in plant composition have been widely documented (Klein et al., 2007;Liu, Fang, Huang, et al., 2023;Shen et al., 2022). Mattic epipedon fragmentation and disappearance of normal alpine meadow, accompanied by encroachment of noxious weed species to form degraded meadow communities is one possible pathway that alpine meadows may take in response to these changes in climate and grazing (Nyima, 2018;Zeng et al., 2013). ...
Global climate change and overgrazing are driving shifts in the plant composition of grassland communities, which may profoundly affect the function of grassland ecosystems in regulating runoff and soil erosion. Here, we examined the shift effects of normal hillslope alpine meadow to shrub and severely degraded meadow states on runoff and sediment generation under natural rainfall conditions, and determined the contributions of plant and soil properties changes to soil erodibility, runoff and sediment generation by in situ rainfall experiment and monitoring on the hillslope of Qinghai-Tibetan Plateau. The results showed that normal meadow shift into severely degraded meadow state, mean weight diameter, soil saturated hydraulic conductivity, soil cohesion and soil erodibility K-factor at the topsoil decreased by 70.3%, 73.1%, 80.3% and −13.1%, respectively, and when normal meadows shift into shrub meadow state, they reduced by 49.1%, −1.3%, 49.4%, and −8.3%, respectively. Runoff and soil loss significantly changed by - 40.0% and 177.8% when normal meadow shifted into a severely degraded meadow state, while runoff and soil loss significantly changed by + 65.0% and +77.8% when normal meadow shifted into a shrub meadow state. Our findings highlight that the two divergent shifts both increased soil loss compared to the normal hillslope alpine meadows. Overall, our results indicate that the divergent shifts of normal alpine meadows exacerbated soil erodibility and soil loss of hillslope alpine meadows. These results obtained here offer a novel perspective on the regulation of runoff and soil erosion in the alpine meadow ecosystem.
The allocation of net primary productivity (NPP) between aboveground and belowground components (ANPP and BNPP) is essential for comprehending the dynamics of ecosystems processes and functions. In the alpine grasslands on the Qinghai-Tibet Plateau (QTP), the optimal proportion of BNPP (fBNPP) in NPP holds critical importance for productivity dynamics and the rational management of grass resources due to high sensitivity to climate and human-induced changes. However, direct evidence from field research regarding NPP components and fBNPP remains relatively scarce and fragmented. Here, we compiled 704 field observations from the existing studies and published alpine grasslands NPP data to investigate the distribution patterns of NPP allocation and explore the effects of climate and human activities on NPP allocation in the alpine grasslands. Results showed that the alpine grasslands of the QTP had an average fBNPP value of 0.65, with a wide variation ranging from 0.15 to 0.99. Warming and grazing significantly altered the trends of productivity components in response to changes in temperature and precipitation. Our results showed that both warming and grazing increase fBNPP—by 18.01 % under warming and 3.74 % under grazing—through different mechanisms: warming enhanced both ANPP and BNPP, but BNPP showed a greater degree of change. However, grazing reduced both ANPP and BNPP and had a stronger suppressive effect on ANPP. Generally, the spatial fBNPP of alpine grasslands on the QTP exhibited a trend of increasing initially and then decreasing with rising temperatures, differing from the linearly-decreasing pattern on a global scale. Our results emphasized the unique complexity of alpine grasslands NPP allocation on the QTP in response to environmental changes. This study provided significant evidence and theoretical support for the accurate assessment of productivity dynamics and the rational utilization of resources of alpine grasslands.
Carbon (C), nitrogen (N), and phosphorus (P) act as pivotal regulators of biogeochemical cycles, steering organic matter decomposition and carbon sequestration in terrestrial ecosystems through the stoichiometric properties of photosynthetic organs. Deciphering their multi-scale spatiotemporal dynamics is central to unraveling plant nutrient strategies and their coupling mechanisms with global element cycling. In the current study, we modeled biogeochemical parameters (C/N/P contents, stoichiometry, and pools) in plant aboveground parts by using the growing mean temperature, total precipitation, total radiation, and maximum normalized difference vegetation index (NDVImax) across nine models (i.e., random forest model, generalized boosting regression model, multiple linear regression model, artificial neural network model, generalized linear regression model, conditional inference tree model, extreme gradient boosting model, support vector machine model, and recursive regression tree) in Xizang grasslands. The results showed that the random forest model had the highest predictive accuracy for nitrogen content, C:P, and N:P ratios under both grazing and fencing conditions (training R² ≥ 0.61, validation R² ≥ 0.95). Additionally, the random forest model had the highest predictive accuracy for C:N ratios under fencing conditions (training R² = 0.84, validation R² = 1.00), as well as for C pool and P content and pool under grazing conditions (training R² ≥ 0.62, validation R² ≥ 0.90). Therefore, the random forest algorithm based on climate data and/or the NDVImax demonstrated superior predictive performance in modeling these biogeochemical parameters.
This study examines the future of pastoral livelihoods in rural Yarkhun Valley, Pakistan, in the context of the broader literature on changing pastoralism and the challenges faced by pastoralist communities. The study is based on three months of ethnographic fieldwork in Yarkhun Valley. Using discourse analysis and the lens of rural political ecology, it analyses changes in land use, climate projects, formal education, and urban migration, to elucidate the shift from the pastoral way of life towards a neoliberal lifestyle. The study explores the biases held by educated elites, non-governmental organisations and government institutions against local pastoralists – in particular the way they have stigmatised the practice of goat husbandry by associating it with flooding. Additionally, the paper looks at the impact of conservation and privatisation of the commons on pastoral livelihoods. It shows how pastoralist elders have held on to their traditional way of life despite pressure from the forces of modernisation and globalisation, and concludes that the future of pastoralism is precarious and uncertain.
This article was published open access under a CC BY-NC 4.0 licence: https://creativecommons.org/licenses/by-nc/4.0/ .
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The drylands on the Qinghai–Xizang Plateau are extremely sensitive to climate change and grazing activities. However, there is a lack of quantitative study of the combined effects of aridity and grazing pressure, which are vital in determining the sustainable grazing areas. In this study, a 2-dimensional threshold model was employed to assess the maximum allowable grazing pressure and determine the sustainable grazing areas under both historical conditions and projected climate change scenarios up to 2100. Results showed that 62.2% of the drylands under historical condition were unsuitable for grazing and 6.7% exceeded the ecological threshold, while 31.1% fell within the areas with sustainable grazing. Model projections indicate a trend toward humidification across the drylands under the climate change scenarios of RCP 4.5 and RCP 8.5. This process is expected to partially alleviate the negative impact of grazing, leading to an expansion of sustainable grazing areas to approximately 41.0% by 2100. These findings provide valuable insights for optimizing grazing strategies in the drylands of the Qinghai–Xizang Plateau in the future.
The drylands on the Qinghai–Xizang Plateau are extremely sensitive to climate change and grazing activities. However, there is a lack of quantitative study of the combined effects of aridity and grazing pressure, which are vital in determining the sustainable grazing areas. In this study, a 2-dimensional threshold model was employed to assess the maximum allowable grazing pressure and determine the sustainable grazing areas under both historical conditions and projected climate change scenarios up to 2100. Results showed that 62.2% of the drylands under historical condition were unsuitable for grazing and 6.7% exceeded the ecological threshold, while 31.1% fell within the areas with sustainable grazing. Model projections indicate a trend toward humidification across the drylands under the climate change scenarios of RCP 4.5 and RCP 8.5. This process is expected to partially alleviate the negative impact of grazing, leading to an expansion of sustainable grazing areas to approximately 41.0% by 2100. These findings provide valuable insights for optimizing grazing strategies in the drylands of the Qinghai–Xizang Plateau in the future.
Cet article évalue l'impact des changements climatiques sur les rendements des principales cultures céréalières au Sénégal. Notre démarche empirique consiste à combiner une analyse des coefficients de corrélation linéaire à celle de régression multivariée du lien rendement céréalier-changement climatique. Nos résultats montrent que les niveaux de température et de précipitation influencent positivement les rendements céréaliers au Sénégal. Toutefois, l'effet économique de la variation des températures est plus important que celui de la variation des précipitations sur le rendement des produits céréalier. Donc, au Sénégal, le faible niveau des températures expliquerait une bonne part des faibles rendements dans la filière céréalière. Les températures moyennes sont encore en-deçà des 290C qui ne permettent pas de doper la productivité dans la filière céréalière. Ces résultats impliquent d'importantes mesures de politiques économiques dans la filière.
Aims to deal with some topics on the environmental geography of Sudan that could work on acknowledging them as serious problems and challenges to the future of the country unless being resolved by appreciate development planning.
Soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP) and their ratios are important parts of global carbon, nitrogen and phosphorus cycle, but their responses to climate change and human activities remain controversial in alpine grasslands of the Tibetan Plateau. In this study, we quantified the influences of climate change and human activities on SOC, TN, TP and their ratios at three depths (0–10, 10–20 and 20–30 cm) during 2000–2020 across the Tibetan alpine grasslands. Under the combined influences of climate change and human activities, spatially average SOC, TN, TP, C:N, C:P and N:P at 0–10 cm, and C:N and C:P at 10–20 cm decreased by 3.42%, 1.35%, 0.99%, 0.39%, 1.75%, 0.51%, 0.03% and 0.88%, respectively, but the others increased by 0.01–3.26%. Under the single influence of climate change, spatially TP at 0–10 and 20–30 cm decreased by 0.30% and 1.05%, respectively, but the others increased by 0.14–4.35%. Under the single influence of human activities, spatially TN at 0–10 and 10–20 cm, C:P at 0–10 cm and N:P at 10–20 cm decreased by 15%, 1%, 7% and 4%, respectively, but the others increased by 1–157%. No matter under the double pressure of climate change and human activities or their individual pressure, the changes of SOC, TN, TP, C:N, C:P and N:P not always increased or decreased, but vary with longitude, latitude and elevation. The changes of SOC, TN, TP, C:N, C:P and N:P did not necessarily and linearly increase or decrease with their background values. Compared to precipitation change and warming, radiation change had a stronger influence on the change of SOC at 10–20 cm and TP at 20–30 cm under the double pressure of climate change and human activities, and the single pressure of human activities, respectively. Radiation change also had stronger influences on the change of SOC at 10–20 cm, TN at 0–10 cm, C:N at 20–30 cm, C:P at 0–10 and 10–20 cm, N:P at 0–10 and 10–20 cm under the single pressure of climate change. Therefore, in the past 20 years, the single effect of climate change or human activities on soil organic carbon, total nitrogen, total phosphorus and their ratios underestimated or overestimated their interactive effects in the Tibetan grasslands. Climate change and human activities reconstructed the spatial distribution patterns of soil organic carbon, total nitrogen, total phosphorus and their ratios. Radiation change should be given the same importance as warming and precipitation change, at least for the change of soil organic carbon, total nitrogen and total phosphorus of the Tibetan alpine grasslands.
The alpine meadow of the Qinghai–Tibetan Plateau is an essential terrestrial ecosystem that provides a livelihood for approximately 9.8 million local inhabitants and serves as a habitat for millions of livestock. Changing facets of the global environment, such as increased nitrogen deposition, have not only affected the abundance and quality of forgeable plants but have also increased the prevalence and severity of plant diseases caused by pathogens. However, whether or not and to what extent these pathogens affect the rangeland quality of the alpine meadow remains unclear. We conducted a factorial experiment with the exclusion of fungal and oomycete pathogens to investigate the impact of various pathogens on rangeland quality in an alpine meadow in the Qinghai–Tibetan Plateau. We measured forage production for each plant species, forage quality (including measurements of organic matter, crude protein, phosphorus, total phenolics, neutral detergent fiber (NDF), metabolizable energy, and digestibility) for 11 abundant species, and community composition. We found that fungal pathogen exclusion and the combination of fungal and oomycete pathogen exclusion primarily affected nutrient production by altering forage production rather than changing community composition or forage quality. Exclusion of both fungal and oomycete pathogens led to a significant increase in community forage production, although no significant effect was observed for individual exclusion of fungal or oomycete pathogens. Excluding either fungal pathogens alone or simultaneous exclusion of both fungal and oomycete pathogens significantly increased the metabolizable energy content of the community. In contrast, oomycete pathogen exclusion significantly decreased the forage metabolizable energy content of the community. The exclusion of both fungal and oomycete pathogens also considerably increased the yield of organic matter, total phenolics, NDF, digestible dry matter, and metabolizable energy. However, the direction and magnitude of the effect of fungal and oomycete pathogen exclusion varied widely across the different species studied. These results suggest that the interaction of fungal and oomycete pathogens constitutes an essential limiting factor in rangeland quality that has not been previously recognized. Greater attention should be placed on overall forage production rather than forage quality in the context of grassland pathogen control strategies. Furthermore, metabolizable energy content may serve as an effective indicator for predicting the impact of pathogenic activity on forage quality.
Climate change is threatening ecosystem functioning and sustainability worldwide. In silvopastoral systems, ongoing warmer and drier conditions could impact productivity and quality of pastures (in terms of protein content and digestibility), with important economic consequences. However, the extent to which climate change could alter other nutritional traits with a potential role in livestock nutrition and production, such as essential fatty acids and amino acids, is a question that remains poorly known. We designed a field manipulative experiment of increased temperature (+2–3 °C) and rainfall exclusion (−30%) aimed to evaluate the influence of forecasted climate variations on the yield and nutritional composition of pastures (i.e. proteins, lipids, fibers, amino acids, fatty acids and digestibility) in a Mediterranean silvopastoral system. To test whether scattered trees typical of these ecosystems could buffer the effects of higher aridity, experimental plots were installed under trees and in open grasslands. First, we found that plant communities under tree canopies were less productive but exhibited higher quality than those located in open grasslands, likely due to the shade and higher soil fertility provided by trees. Both climatic stressors had a significant influence on pasture productivity and nutritional composition. Thus, pastures subjected to rainfall reduction produced less biomass with higher content in nitrogen, proteins, essential amino acids and lipids, likely as a mechanism of plant tolerance to water stress. In contrast, warming increased plant productivity and enhanced the proportion of unsaturated fatty acids, likely mediated by alterations in plant community composition. Finally, our results suggest that trees might slow the impact of climate change on productivity and specific amino acids in pasture. These results could be also applied for the design of management strategies to ensure the ecologic and economic value of silvopastoral ecosystems under future climate scenarios.
This article reports the results of a 2-yr study in the Menyuan pastoral system, a mesic alpine ecosystem in northeastern Qinghai Province, China. Research was conducted among households of transhumant pastoralists who herd sheep and yak along the slopes and ajacent valleys of the Qilian Mountains. An analysis of data from household interviews indicated that harvest has been the most important influence on livestock population dynamics since decollectivization of the herd in 1984. Where winter mortality and low survival rate of lambs born in the early spring have been problems, such sources of density-independent mortality have not been large enough to influence the trend of population growth. In fact, mortality from these sources has decreased since 1984. According to pastoralists, vegetative cover on fenced winter pastures has improved, but increases in summer herd sizes since decollectivization (sheep: 3.9%/yr; yak: 2.4%/yr) continue to negatively affect rangeland soil and vegetation quality on common summer grazing land. -from Authors
Climate-induced environmental changes are likely to have pronounced impacts on CO2 flux patterns in arctic ecosystems. We initiated a long-term experiment in 1994 in moist tussock and dry heath tundra in arctic Alaska in which we increased summer air temperature (ca. 2°C) and increased winter snow accumulation (shortening the growing season approximately 4 wk). During the 1996 snow-free season, we measured ecosystem CO2 flux weekly in order to quantify net carbon gain or loss from these systems. Over the duration of the snow-free season, both dry heath and moist tussock tundra exhibited a net loss of carbon to the atmosphere, ranging from 12 to 81 g C m-2 depending upon experimental treatment. Elevated summer temperatures accelerated net CO2 loss rates over ambient temperatures in both deep and ambient snow treatments, and increased the total amount of carbon emitted during the snow-free season by 26 to 38% in ambient snow plots and by 112 to 326% in deep snow plots. Increased snow accumulation had less impact on CO2 flux than did warming, and snow effects on total carbon loss were not consistent between the two temperature regimes. Ecosystem respiration exceeded assimilation on most sampling dates throughout the season. These data, coupled with winter carbon losses recently demonstrated in the same ecosystems, indicate that the moist and dry arctic ecosystems we examined are currently net sources of atmospheric carbon on an annual basis, and that anticipated global warming may increase carbon losses from these systems.
In a high-altitude (above 4860 m), semiarid grazing ecosystem in western Tibet, only 28% of summer grazing areas supported aboveground net primary productivity greater than 10 g m-2. The frequencies of vegetation types selected for grazing were unique for each herd type (yak, small ruminant) in each area. Herd type and grazing area were both significant factors in daily horizontal and vertical displacement of herds from encampments. Yak were versatile foragers, consuming coarse forages when encountered, but adept at grazing small (<3 cm high) sedges. Whereas browse was a minor component of yak diets (4.1%), it was heavily selected by goats (31.2%) and sheep (17.9%). All ruminant livestock readily consumed spinulose forbs when encountered. Statistical differences in dietary quality were attributed to grazing area effects. The overriding determinant of grazing behavior appeared to be the vegetational characteristics of the area within which livestock producers held grazing rights. Differentiating factors in these areas were (1) the availability of "low risk" vegetation (forage demonstrating predictable emergence and growth) in riparian areas watered by glacier-fed springs, versus more unpredictable nonriparian forage sources fed by monsoonal rainfall; and (2) the topographic situation of forage-yielding vegetation types.
2 Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado 80309 USA Abstract. Topography controls snowpack accumulation and hence growing-season length, soil water availability, and the distribution of plant communities in the Colorado Front Range alpine. Nutrient cycles in such an environment are likely to be regulated by interactions between topographically determined climate and plant species composition. We investigated variation in plant and soil components of internal N cycling across to- pographic gradients of dry, moist, and wet alpine tundra meadows at Niwot Ridge, Colorado. We expected that plant production and N cycling would increase from dry to wet alpine tundra meadows, but we hypothesized that variation in N turnover would span a propor- tionately greater range than productivity, because of feedbacks between plants and soil microbial processes that determine N availability. Plant production of foliage and roots increased over topographic sequences from 280 g·m 22 ·yr 21 in dry meadows to 600 g·m 22 ·yr 21 21 in wet meadows. In all communities, the belowground component accounted for the majority of biomass, production, and N use for production. Allocation belowground also differed among communities, accounting for 70% of total production and 80% of N use for production in dry meadows compared to 55% of production and 65% of N use for production in moist meadows. Variation in microbial processes was highly related to soil moisture, and we found very consistent relationships among microbial respiration, gross N mineralization, and N immobilization among communities. These re- sults indicate that the topographic soil moisture gradient is in fundamental control of the patterns of N turnover among communities and that differences in plant species do not appear to be as important.
We studied the effects of a seven-year warming experiment on 11 forb species in the Rocky Mountains of Colorado in 1996 and 1997. Previous work on this experiment focused on ecosystem and community responses to warming. Our purpose here is to report on species responses. We found significant positive responses to warming for two species and negative responses for four species in terms of abundance, size, flowering, or frost damage. Because previous results from the warming experiment showed that artificial warm- ing decreases soil moisture and increases nitrogen mineralization, we used nitrogen and water addition experiments on the two dominant forbs to determine whether species re- sponses in the warming experiment could be due to shifts in resource availability. We found that Erigeron speciosuswas limited more clearly by water than by nitrogen and Helianthella quinquenervis was limited by both nitrogen and water. These responses are consistent with the hypothesis that a primary effect of warming on plants occurs via changes in soil resource availability, but more complicated factors including competition are likely to be important to warming effects as well. Because previous work on this experiment indicated that annual forb detrital production is a key component of the carbon cycle of this system, we also asked which species responded to warming with changes in aboveground biomass. Over 1996 and 1997, four of nine perennial species had significantly lower biomass in the warmed plots, and in 1997 one species had significantly higher biomass. The biomass differences of Erigeron and Helianthella were almost equal and opposite, but while the decline in Erigeron was statistically significant the increase in Helianthella was smaller and not significant. In one year, a major effect of warming was to protect Helianthella from frost damage, which illustrates the importance of extreme weather events. Our study points to the potential importance of understanding ecosystem responses to climate change in terms of species responses.
Three 60 m long, 2·8 m high snowfences have been erected to study long-term effects of changing winter snow conditions on arctic and alpine tundra. This paper describes the experimental design and short-term effects. Open-top fiberglass warming chambers are placed along the experimental snow gradients and in controls areas outside the fences; each warming plot is paired with an unwarmed plot. The purpose of the experiment is to examine short- and long-term changes to the integrated physical-biological systems under simultaneous changes of winter snow regime and summer temperature, as part of the Long-Term Ecological Research network and the International Tundra Experiment. The sites were at Niwot Ridge, Colorado, a temperate high altitude site in the Colorado Rockies, and Toolik Lake, Alaska, a high-latitude site. Initial results indicate that although experimental designs are essentially identical at the arctic and alpine sites, experimental effects are different. The drift at Niwot Ridge lasts much longer than do the Toolik Lake drifts, so that the Niwot Ridge fence affects both summer and winter conditions, whereas the Toolik Lake fence affects primarily winter conditions. The temperature experiment also differs in effect between the sites. Although the average temperature increase at the two sites is similar (daily increase 1·5 °C at Toolik and 1·9 °C at Niwot Ridge), at Toolik Lake there is only minor diurnal variation, whereas at Niwot Ridge the daytime increases are extreme on sunny days (as much as 7-10 °C), and minimum nighttime temperatures in the chambers are often slightly cooler than ambient (by about 1 °C). The experimental drifts resulted in wintertime increases in temperature and CO2 flux. Temperatures under the deep drifts were much more consistent and warmer than in control areas, and at Niwot Ridge remained very close to 0 °C all winter. These increased temperatures were likely responsible for observed increases in system carbon loss. Initial changes to the aboveground biotic system included an increase in growth in response to both snow and warming, despite a reduced growing season. This is expected to be a transient response that will eventually be replaced by reduced growth. At least one species, Kobresia myosuroides, had almost completely died at Niwot Ridge three years after fence construction, whereas other species were increasing. We expect in both the short- and long-term to see the strongest effects of snow at the Niwot Ridge site, and stronger effects of temperature at Toolik Lake.
To understand global change, natural scientists must consider the social context influencing human impact on the environment. This overview paper discusses three questions central to the issue: How are land-use changes contributing to global environmental changes (land-management practices, growing human populations, regional differences in technology and wealth). What social-economic factors determine land use, and how will they change (understanding human response to past change, productivity of agroecosystems, social and political systems, production systems, economics of the third world). How does land use modify processes that influence global change (changes in natural imputs of energy, water and nutrients, plant community changes, community development, landscape characteristics). Finally the research interface between social and ecological sciences is examined. 39 refs., 1 fig.
Global models project impending climate changes that could significantly alter plant species composition in ecosystems. Climate manipulation experiments provide an opportunity to investigate such effects. Here we describe and apply a method for extracting the age-detrended growth rate of sagebrush (Artemisia tridentata Nutt.) and show that experimental ecosystem warming enhances the growth rate of this shrub. Snowmelt date, not soil temperature or moisture, is demonstrated to be the dominant climate variable controlling the observed effect. Our findings suggest that global climate change will result in increased growth and range expansion of sagebrush near northern or high-elevation range boundaries in the Western United States.
One of China's newest large-scale 'ecological construction' projects, 'converting pastures to grasslands' (tuimu huancao), calls for the creation of three new types of zones on existing pastures: zones in which grazing is to be permanently banned, zones in which grazing is to cease for a period of several years, and zones in which pasture is to be seasonally closed. This project is likely to significantly alter the livelihoods of tens of thousands of pastoralists living in Western China. The paper discusses the policy context in which tuimu huancao emerged, analyzing both continuities with and disjunctures from previous ecological restoration and rangeland management policies, including 'Open up the West,' the Sloping Land Conversion Project, and the 'four that form a complete set' (si peitao). Differences suggest that tuimu huancao constitutes a deepening of state control over territory, and can be understood as an emergent form of green governmentality in China. The paper then discusses tuimu huancao implementation on the Tibetan plateau, specifically in Qinghai and Sichuan provinces. Finally, directions for future research are outlined.
1] We integrated two methods, experimental heating and observations across natural climate gradients, to elucidate both short-and long-term climatic controls on ecosystem carbon storage and to investigate carbon-cycle feedbacks to climate in montane meadows. A 10-year heating experiment warmed and dried heated plot soils and substantially decreased (by $200 ± 150 g C m À2) the amount of carbon stored in soil organic matter, a positive feedback to warming. In situ CO 2 flux measurements, laboratory soil incubations, and a heating-induced shift in vegetation community composition from high-to low-productivity species indicate that a decline in community productivity and resultant decrease in soil inputs from plant litter caused most of the soil carbon decrease. An alternative widely hypothesized mechanism for soil carbon decrease under warming is stimulation of soil respiration, but we observed no increase in seasonally integrated soil respiration in our experiment (soil drying inhibited microbial decomposition even as soil warming stimulated it). To extend our analysis from the short-term transient response represented by the heating experiment to the presumed long-term approximate steady state represented by natural climate gradients, we tested a hypothesized relation between vegetation community composition (which controls both litter input rate and average litter quality) and soil carbon along the climate gradient. The gradient analysis implies that the experimentally induced decline in soil carbon is transient and will eventually reverse as lower quality litter inputs from the increasingly dominant low-productivity species reduce soil respiration losses. This work shows that ecological processes can control both short-and long-term responses to climate change, confirming some model-based predictions about the importance of vegetation shifts, but challenging the widely held hypothesis that the effect of temperature change on respiration will dominate soil carbon changes., Plant community composition mediates both large transient decline and predicted long-term recovery of soil carbon under climate warming, Global Biogeochem. Cycles, 16(4), 1055, doi:10.1029/2001GB001573, 2002.
The capacity of cetyl trimethylammonium bromide to dissolve proteins in acid solution has been utilized in development of a method, called acid-detergent fiber method (ADF), which is not only a fiber determination in itself but also the major preparatory step in the determination of lignin. The entire procedure for determining fiber and lignin is considerably more rapid than presently published methods. Compositional studies show ADF to consist chiefly of lignin and polysaccharides. Correlations with the new fiber method and digestibility of 18 forages (r = —0.79) showed it to be somewhat superior to crude fiber (r = —0.73) in estimating nutritive value. The correlation of the new lignin method and digestibility was -0.90 when grass and legume species were separated.
Tibetan nomadic societies have developed sophisticated ways of managing range resources which outsiders often do not understand or fail to acknowledge. Nomadic existence on the Tibetan Plateau-undoubtedly the world's harshest pastoral area-yet today is proof of the rationality for and efficacy of many aspects of traditional Tibetan nomadic pastoral production practices. Over centuries, Tibetan nomads acquired complex knowledge and understanding of the environment in which they lived and upon which their lives depended. The fact that numerous, prosperous pastoral groups remain to this day bears witness to the extraordinary knowledge and animal husbandry skills of the nomads. Animal husbandry will continue to be the main land use in the high plateau environment of the Tibetan Plateau. Livestock will be the primary source of livelihood for people residing in these rangelands for many years to come. As such much greater effort needs to be directed towards rangeland research and pastoral development. There are no simple solutions to addressing pastoral development in the harsh environment of the Tibetan Plateau and due to the multifaceted dimensions of the problems, actions will need to be taken on several levels: at the central policy level; at the university and research center level; at the level of range and livestock extension services, and at the nomad level.
The capacity of cetyl trimethylammonium bromide to dissolve proteins in acid solution has been utilized in development of a method, called acid-detergent fiber method (ADF), which is not only a fiber determination in itself but also the major preparatory step in the determination of lignin. The entire procedure for determining fiber and lignin is considerably more rapid than presently published methods. Compositional studies show ADF to consist chiefly of lignin and polysaccharides. Correlations with the new fiber method and digestibility of 18 forages (r = —0.79) showed it to be somewhat superior to crude fiber (r = —0.73) in estimating nutritive value. The correlation of the new lignin method and digestibility was —0.90 when grass and legume species were separated.
Alpine meadow and shrub are the main pasture types on the Tibetan Plateau, and they cover about 35% of the total land area. In order to understand the structural and functional aspects of the alpine ecosystem and to promote a sustainable animal production system, the Haibei Alpine Meadow Research Station was established in 1976. A series of intensive studies on ecosystem structure and function, including the energy flow and nutrient cycling of the ecosystem, were the main tasks during the first 10 years. Meanwhile, studies with 5 different grazing intensities on both summer and winter pasture have been conducted. In the early years of the 1990s, the research station started to focus its research work on global warming, biodiversity and sustainable animal production systems in pastoral areas. Various methods for improving degraded pasturelands have been developed in the region.
This article (the first in a three part series) provides information and insight about Tibetan nomads and their nomadic pastoral practices in one of the least-known rangeland areas of the world. Based on understanding gained from seventeen different trips to Tibetan nomadic pastoral areas over the last ten years by the author, the article outlines the geography and climate of the Tibetan Plateau and traces the history of nomadic pastoralism there. Parts Two and Three, which will appear in later issues of Rangelands, describe the present nomadic pastoral production systems and discuss the challenges Tibetan nomads are facing today as they try to maintain their unique way of life. It is also hoped that these articles will excite more American range ecologists, livestock production and pastoral development specialists, ranchers, cowboys, and cowgirls to want to visit Tibetan rangelands in western China.
Since decollectivization, Chinese government policies have promoted household enclosures as the best solution to maximize pastoral productivity and control desert expansion in grassland areas. Recent fieldwork from Inner Mongolia contradicts this optimism. Data and participant-observation reveal that enclosures, as implemented through village level social context, actually compound grazing problems for most residents and the wider ecosystem. Expanding household enclosures function to intensify hyper-critical stocking ratios on highly vulnerable rangeland, exacerbating wind and soil erosion processes across vast territories only to protect small isolated fields dedicated to poorly financed fodder cultivation. This case study indicates that privatization of land in modernizing pastoral societies can be less meaningful for good resource management than other factors, such as secure tenure, equitable access to community resources, and meaningful institutional supports in the form of credit, production services, and legal protection.
On tallgrass prairie vegetation, in the Konza Prairie Research Natural Area, defoliation history largely controlled whether or not defoliated plants overcompensated (exhibited enhanced production compared to undefoliated controls) for tissue removal. Plants on chronically grazed sites only compensated for foliage removed by grazers. Production on plots mowed prior to the year of measurement was similar to that on chronically grazed sites, while previously unmowed plots exhibited substantial aboveground overcompensation. Aboveground production was maximized by the most frequent mowing treatment and by intermediate mowing heights. Nitrogen and P concentrations and amounts in aboveground tissues were increased by mowing and grazing. Current mowing regime was more important than mowing history in determining N concentrations except very early in the growing season. Frequent mowing appeared to limit accumulation of belowground N reserves and biomass. In North American grasslands, overcompensation is a nonequilibrium plant response to grazing. Photosynthate that would be stored as reserves and used for root growth and flower and seed production instead is used to replace lost leaf area, resulting in higher foliage productivity. However, under chronic grazing or mowing, vegetation is prevented from maintaining high nutrient and water uptake capacity (large root biomass) and accumulating reserves that allow overcompensation responses. -Authors
Ecological research can be misinterpreted by the popular press and misapplied in land management. One example of this concerns the controversial concepts of overcompensation by grazed plants and herbivore optimization of plant productivity (or, as popularly phrased, the idea that plants benefit from being grazed). Although available evidence indicates that whole-plant overcompensation and optimization of productivity rarely occur and may have little or no evolutionary or applied significance, these concepts have been accepted by some popular writers and land managers, and are being used to justify heavy livestock grazing on western North American rangelands. There may be many reasons for this acceptance of unsubstantiated hypotheses, including uncritical reading and overly broad extrapolations by writers and managers, as well as failure by scientists to clearly and accurately communicate results and conclusions.
We have implemented a long-term snow-fence experiment at the Niwot Ridge Long-Term Ecological Research (NWT) site in the Colorado Front Range of the Rocky Mountains, U.S.A., to assess the effects of climate change on alpine ecology and biogeochemical cycles. The responses of carbon (C) and nitrogen (N) dynamics in high-elevation mountains to changes in climate are investigated by manipulating the length and duration of snow cover with the 2.6 × 60 m snow fence, providing a proxy for climate change. Results from the first year of operation in 1994 showed that the period of continuous snow cover was increased by 90 d. The deeper and earlier snowpack behind the fence insulated soils from winter air temperatures, resulting in a 9°C increase in annual minimum temperature at the soil surface. The extended period of snow cover resulted in subnivial microbial activity playing a major role in annual C and N cycling. The amount of C mineralized under the snow as measured by CO2 production was 22 g m-2 in 1993 and 35 g m-2 in 1994, accounting for 20% of annual net primary above-ground production before construction of the snow fence in 1993 and 31% after to snow fence was constructed in 1994. In a similar fashion, maximum subnivial N2O flux increased 3-fold behind the snow fence, from 75 μg N m-2 d-1 in 1993 to 250 μg N m-2 d-1 in 1994. The amount of N lost from denitrification was greater than the annual atmospheric input of N in snowfall. Surface litter decomposition studies show that there was a significant increase in the litter mass loss under deep and early snow, with no significant change under medium and little snow conditions. Changes in climate that result in differences in snow duration, depth, and extent may therefore produce large changes in the C and N soil dynamics of alpine ecosystems.
Carefully-managed livestock grazing has been offered as a tool to improve the forage quality of graminoids on big game winter range. Formal testing of this theory has thus far been done using hand clippers rather than livestock grazing. We report winter standing reproductive culm, crude protein, in vitro dry matter digestibility, and standing crop responses of bluebunch wheatgrass (Agropyron spicatum [Pursh] Scribn. & Smith), Idaho fescue (Festuca idahoensis Elmer), and elk sedge (Carex geyeri Boott) to late-spring domestic sheep grazing. The study was conducted in 1993 and 1994 on a big game winter range in the Blue Mountains of northeastern Oregon. Sheep grazing and exclusion treatments were applied to 20-ha plots at 3 sites on the study area. Targeted utilization for grazed plots was 50% graminoid standing crop removal during the boot stage of bluebunch wheatgrass. Grazing did not influence the number of standing reproductive culms per plant in bluebunch wheatgrass. Crude protein and in vitro dry matter digestibility of bluebunch wheatgrass in grazed plots increased by 1.0 and 4.3 percentage points, respectively, over ungrazed plots. Grazing reduced the standing crop of bluebunch wheatgrass by 116.9 kg ha-1 DM. Standing Idaho fescue reproductive culms decreased by 0.7 culms under grazing. Crude protein of Idaho fescue in grazed plots was 1.3 percentage points greater than in ungrazed plots. Crude protein and in vitro dry matter digestibility responses of elk sedge were inconsistent between years and may be related to utilization or growth differences between years. The levels of forage quality improvement in bluebunch wheatgrass and Idaho fescue obtained in this study could benefit the nutritional status of wintering Rocky Mountain elk (Cervus elaphus nelsoni Bailey). More research is needed regarding the effects of grazing on the winter forage quality of elk sedge.
Within large grassland ecosystems, climatic and topographic gradients are considered the primary controls of soil processes. Ungulates also can influence soil dynamics; however the relative contribution of large herbivores to controlling grassland soil processes remains largely unknown. In this study, we compared the effects of native migratory ungulates and variable site ('landscape') conditions, caused by combined climatic and topographic variability, on grassland of the northern winter range of Yellowstone National Park by determining soil C and N dynamics inside and outside 33-37 yr exclosures at seven diverse sites. Sites included hilltop, slope, and slope bottom positions across a climatic gradient and represented among the driest and wettest grasslands on the northern winter range. We performed two experiments: (1) a 12-mo in situ net N mineralization study and (2) a long-term (62-wk) laboratory incubation to measure potential N mineralization and microbial respiration. Results from the in situ experiment indicated that average net N mineralization among grazed plots (3.8 g N · m-2 · yr-1) was double that of fenced, ungrazed plots (1.9 g N · m-2 · yr-1). Mean grazer enhancement of net N mineralization across sites (1.9 g N · m-2 · yr-1) approached the maximum difference in net N mineralization among fenced plots (2.2 g N · m-2 · yr-1), i.e., the greatest landscape effect observed. Furthermore, ungulates substantially increased between-site variation in mineralization; grazed grassland, 1 SD = 2.2 g N · m-2 · yr-1, fenced grassland, 1 SD = 0.85 g N · m-2 · yr-1. In the long-term incubation, potential microbial respiration and net N mineralization were positively related to total soil C and N content, respectively. There was greater variation in potential respiration and net N mineralization early in the incubation, when labile material was processed, compared to late in the incubation, when more recalcitrant substrate was processed, suggesting that between-site variation in labile organic matter was greater than that of recalcitrant material. Herbivores improved the organic matter quality of soil, increasing the labile fractions and reducing the recalcitrant fractions. Grazers reduced C respired/N mineralized ratios, an index of microbial N immobilization, by an average of 21%. However, the largest landscape influence on the immobilization index was 13-fold greater than the grazer effect. Given that the greatest landscape influence on in situ net mineralization (2.2 g N · m-2 · yr-1) was similar to the average grazer impact on that rate (1.9 g N · m-2 · yr-1), we hypothesize that the landscape effect on field N availability was primarily caused by variation in microbial immobilization, while the grazing effect was primarily due to stimulation of gross mineralization. These results indicate that the relative importance of ungulates in controlling soil N cycling may be more important than previously suspected for grasslands supporting large herds of migratory ungulates, and that the dominant mechanisms underlying the landscape and ungulate influences on soil mineral fluxes may differ.
The Qinghai-Tibet plateau, which has been called the roof of the world and the third pole, is a vast territory which includes a large area of grassland. It is one of the four main areas of animal husbandry in China. This paper, discusses the causes and development of grassland degradation in the region, and the countermeasures which have been proposed for protecting the grassland resource and preventing grassland degradation. Grassland degradation is an important component of eco-environme ntal degradation in the world today, and grassland protection represents an important aspect of eco-environment protection. The Qinghai-Tibet plateau, which has been called the roof of the world and the third pole covers a vast territory and includes a large area of grassland. It is one of the four main areas of animal husbandry in China. Study of the degradation and protection of grassland in the region is important for the protection of the eco-environment of the Qinghai-Tibet plateau and for the assessment of global environmental change. There is evidence that the degradation of the grassland has become increasingly serious with the developing animal husbandry during recent years, but further investigations are required. This paper analyses the causes and trends of grassland degradation, and reviews the measures that have been proposed for protecting the grassland resource and preventing grassland degradation in the Qinghai-Tibet plateau. A BACKGROUND TO GRASSLAND DEGRADATION IN THE QINGHAI-TIBET PLATEAU The Qinghai-Tibet plateau is located in the southwest of China, and includes the whole of the Tibet Autonomous Region, and most of Qinghai Province, west Sichuan Province and northwest Yunnan Province. The total area of land is approximately 2.269 x 10 6 km2, which represents 23% of China. The area of grassland is approximately 1.33 x 10 8 ha, accounting for 58.8% of the Qinghai-Tibet plateau and 30% of the grassland in China respectively. Grassland degradation has become an important, widespread and growing
The response of plants to temperature has gained renewed interest as researchers speculate on the biotic response to climate change. It is of particular interest in the Arctic, due to recent warming trends and anticipated continued warming for the region. This long-term, multispecies study confirms that changes in temperature affect the functioning of plants in their natural environment. It also demonstrates that the influence of temperature should be considered in the context of natural variability within a given location. The study examined natural temperature gradients, interannual climate variation, and experimental warming at sites near Barrow (71®18' N, 156°40' W) and Atqasuk (70°29' N, 157°25' W) in northern Alaska, USA. At each of the four sites, 24 plots were experimentally warmed for 5-7 years with small, open-top chambers, and plant growth and phenology were monitored; an equal number of unmanipulated control plots were monitored. The response of seven traits from 32 plant species occurring in at least one site is reported when there were at least three years of recordings. Plants responded to temperature in 49% of the measured traits of a species in a site. The most common response to warming was earlier phenological development and increased growth and reproductive effort. However, the total response of a species, for all traits examined, was individualistic and varied among sites. In 14% of the documented responses, the plant trait was correlated with thawing degree-day totals from snowmelt (TDD sm), and temperature was considered the dominant factor. In 35% of the documented responses, the plant trait responded to warming, but the interannual variation in the trait was not correlated with TDD sm and temperature was considered subordinate to other factors. The abundance of temperature responses that were considered subordinate to other factors suggests that prediction of plant response to temperature that does not account for natural variability may overestimate the importance of temperature and lead to unrealistic projections of the rate of vegetation change due to climate warming.
Large-scale changes in climate may have unexpected effects on ecosystems, given the importance of climate as a control over almost all ecosystem attributes and internal feedbacks. Changes in plant community productivity or composition, for example, may alter ecosystem resource dynamics, trophic structures, or disturbance regimes, with subsequent positive or negative feedbacks on the plant community. At northern latitudes, where increases in temperature are expected to be greatest but where plant species diversity is relatively low, climatically mediated changes in species composition or abundance will likely have large ecosystem effects. In this study, we investigated effects of infrared loading and manipulations of water-table elevation on net primary productivity of plant species in bog and fen wetland mesocosms between 1994 and 1997. We removed 27 intact soil monoliths (2.1 m2 surface area, 0.5-0.7 m depth) each from a bog and a fen in northern Minnesota to construct a large mesocosm facility that allows for direct manipulation of climatic variables in a replicated experimental design. The treatment design was a fully crossed factorial with three infrared-loading treatments, three water-table treatments, and two ecosystem types (bogs and fens), with three replicates of all treatment combinations. Overhead infrared lamps caused mean monthly soil temperatures to increase by 1.6-4.1°C at 15-cm depth during the growing season (May-October). In 1996, depths to water table averaged -11, -19, and -26 cm in the bog plots, and 0, -10, and -19 cm in the fen plots. Annual aboveground net primary production (ANPP) of bryophyte, forb, graminoid, and shrub life-forms was determined for the dominant species in the mesocosm plots based on species-specific canopy/biomass relationships. Belowground net primary production (BNPP) was estimated using root in-growth cores. Bog and fen communities differed in their response to infrared loading and water-table treatments because of the differential response of life-forms and species characteristic of each community. Along a gradient of increasing water-table elevation, production of bryophytes increased, and production of shrubs decreased in the bog community. Along a similar gradient in the fen community, production of graminoids and forbs increased. Along a gradient of increasing infrared loading in the bog, shrub production increased whereas graminoid production decreased. In the fen, graminoids were most productive at high infrared loading, and forbs were most productive at medium infrared loading. In the bog and fen, BNPP:ANPP ratios increased with warming and drying, indicating shifts in carbon allocation in response to climate change. Further, opposing responses of species and life-forms tended to cancel out the response of production at higher levels of organization, especially in the bog. For example, total net primary productivity in the bog did not differ between water-table treatments because BNPP was greatest in the dry treatment whereas ANPP was greatest in the wet treatment. The differential responses of species, life-forms, and above- and belowground biomass production to the treatments suggest that bog and fen plant communities will change, in different directions and magnitudes, in response to warming and changes in water-table elevation. Further, results of this and complementary research indicate that these peatlands may mediate their energy, carbon, and nutrient budgets through differential responses of the plant communities. Thus, predictions of the response of peatlands to changes in climate should consider differences in plant community structure, as well as biogeochemistry and hydrology, that characterize and differentiate these two ecosystems.
Lengthening of the growing season at high latitudes, observed by satellites with the Normalized Difference Vegetation Index (NDVI), has been ascribed to climate warming. To test this assumption, and to verify whether changes in vegetation greenness are quantitative or qualitative, we experimentally warmed patches of High Arctic tundra with infrared heating in Northeast Greenland. By analyzing digital images of the vegetation, changes in cover were distinguished from changes in senescence. During the season, experimental warming significantly increased green cover, for example, at the time of peak cover, the total green cover was enhanced from 59.1 to 67.3%. The dominant wavelength (hue) reflected by our tundra plots shifted from yellow-green to yellow. Experimental warming with 2.5 degrees C delayed this hue-shift by 15 d. The results demonstrate that higher summer temperatures do not only promote plant growth at these latitudes but also retard and/or postpone the senescence process, contrary to indications from previous research that late-season phenology in the High Arctic is governed by photoperiod.
The authors manipulated air temperature in tussock tundra near Toolik Lake, Alaska, and determined the consequences for total plant biomass, aboveground net primary production (ANPP), ecosystem nitrogen (N) pools and N uptake, and ecosystem COâ flux. After 3.5 growing seasons, in situ plastic greenhouses that raised air temperature during the growing season had little effect on total biomass, N content, or growing-season N uptake of the major plant and soil pools. Similarly, vascular ANPP and net ecosystem COâ exchange did not change with warming, although net primary production of mosses decreased with warming. Such general lack of response supports the hypothesis that productivity in tundra is constrained by the indirect effects of cold temperatures rather than by cold growing-season temperatures per se. Despite no effect on net ecosystem COâ flux, air warming stimulated early-season gross photosynthesis (GP) and ecosystem respiration (ER) throughout the growing season. This increased carbon turnover was probably associated with species-level responses to increased air temperature. Warming increased the aboveground biomass of the overstory shrub, dwarf birch (Betula nana), and caused a significant net redistribution of N from the understory evergreen shrub, Vaccinium vitis-idaea, to B. nana, despite no effects on soil temperature, total plant N, or N availability.
In the present study, we used the eddy covariance method to measure CO2 exchange between the atmosphere and an alpine shrubland meadow ecosystem (37°36’N, 101°18’E; 3 250 m a.s.l.) on the Qinghai-Tibetan Plateau, China, during the growing season in 2003, from 20 April to 30 September. This meadow is dominated by formations of Potentilla fruticosa L. The soil is Mol-Cryic Cambisols. During the study period, the meadow was not grazed. The maximum rates of CO2 uptake and release derived from the diurnal course of CO2 flux were -9.38 and 5.02 μmol·m-2·s-1, respectively. The largest daily CO2 uptake was 1.7 g C·m-2·d-1 on 14 July, which is less than half that of an alpine Kobresia meadow ecosystem at similar latitudes. Daily CO2 uptake during the measurement period indicated that the alpine shrubland meadow ecosystem may behave as a sink of atmospheric CO2 during the growing season. The daytime CO2 uptake was correlated exponentially or linearly with the daily photo synthetic photon flux density each month. The daytime average water use efficiency of the ecosystem was 6.47 mg CO2/g H2O. The efficiency of the ecosystem increased with a decrease in vapor pressure deficit.
(Managing editor: Ya-Qin HAN)
We investigated the potential effects of global climate change on arctic tundra vegetation used as caribou forage. A total of 96 experimental plots was established at six sites on the coastal plain of the Arctic National Wildlife Refuge, Alaska, in 1993 and 1994. We erected snow-fences to increase the amount of snow deposition, and therefore delay the date of the snowmelt on 48 plots (referred to as increased snow/late melting plots). We used black mesh netting on the surface of the snow to increase the rate of melting on 24 plots; the remaining 24 plots served as controls. In July 1994, we collected green leaves from Eriophorum vaginatum, Salix planifolia, and Betula nana and analysed these samples for total carbon and total nitrogen content. Ratios of carbon to nitrogen differed among treatments for all three species. Generally, C:N ratios for B. nana and E. vaginatum on increased snow/late melting plots were lower than on control plots. C:N ratios for S. planifolia on increased snow/late melting plots did not differ from controls, but were lower than on plots which started to melt early. These results may be due to the timing of nitrogen translocation from leaf and stem tissue into storage organs, or due to an increase in available nitrogen input to the system. Further sampling is needed to adequately determine the mechanism responsible for increased nitrogen content of caribou forage in areas with increased amount of snow and delayed snowmelt.
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°C, maximum daily air temperature by 2.1–7.3°C and the diurnal air temperature range by 1.9–6.5°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°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.
The high altitude-induced permafrost of the Tibet Plateau reflects a geothermal regime characterized by a strong diurnal pattern, high solar radiation inputs at the surface, and a high geothermal gradient. As a result, the permafrost is relatively "warm' and sensitive to thermal disturbance. Typical permafrost-related processes, such as ice segregation and thermal contraction cracking, are not widespread, and patterned ground phenomena (circles and nets) are restricted to sites of locally high moisture and variable grain size. Ice-rich sediments on north-facing slopes occur mainly as silty colluviums derived from local argillaceous bedrock. Mean annual ground temperatures are usually warmer than -3.5°C. Temperatures at 20 m depth have increased by an average of 0.2 to 0.3°C during the past 15 years. If one assumes continued warming, permafrost is likely to become relict within the next 200 years, and an increase in degradation (i.e. thermokarst processes) is to be expected. -Authors
1. Responses to a spring warming treatment were measured on five common herbaceous species grown in outdoor microcosms in Northern England. Although elevated temperature had a beneficial effect on canopy height and plant cover in monospecific cultures of all species, strongly divergent responses to warming occurred in mixtures.
2. We show that the effect of interspecific competition was to modify and amplify the vegetation response to the warming treatment through effects on phenology and morphological development.
3. The observed responses between the species to warming are consistent with predicted differential responses linked to genome size.
4. We conclude that the mechanism of competitive interaction proposed by Boysen-Jensen (1929) coupled with the insights related to genome size provide a basis for explaining and predicting the role of interannual variation in temperature in determining year to year fluctuations in the relative abundance of species in productive perennial herbaceous vegetation.
In many of the world's drylands, human-induced alteration of grazing and fire regimes over the past century has promoted the replacement of grasses by woody vegetation. Here, we evaluate the magnitude of changes in plant and soil carbon and nitrogen pools in a subtropical landscape undergoing succession from grassland to thorn woodland in southern Texas. Our approach involved linking a process-based ecosystem model to a transition matrix model. Grass and forest production submodels of CENTURY were pa-rameterized with field data collected from herbaceous and wooded landscape elements broadly representative of habitats in global savanna systems. The Markov (transition matrix) model simulated the displacement of grassland communities under land use practices typical of many modern grasslands and savannas (heavy livestock grazing; no fire) and climate events. The modeled landscape was initialized for pre-Anglo-European settlement grassland conditions and then subjected to heavy, continuous livestock grazing and elimination of fire beginning in the mid-1800s. Rates of woody plant encroachment were directed by the Markov model, and the consequences for net primary production and plant and soil C and N pools were tracked by CENTURY. Modeled output of plant and soil organic C were in good agreement with those quantified for present-day patch types, suggesting our reconstructions were reasonable. Results in-dicated that, in the absence of woody plant encroachment, heavy grazing and fire suppression would have reduced soil organic carbon mass in southern Texas grasslands 17% (clay loam lowlands) to 18% (sandy loam uplands) by the 1990s. Soil and plant carbon stocks in current (mid-1900s) Prosopis woodlands are estimated to exceed those of the pristine grasslands they have replaced by 1.3 and 10, respectively. Our reconstructions thus suggest that an initial degradation phase induced by heavy livestock grazing was followed by a woody-plant-induced aggradation phase that is still in progress. Under climatic/at-mospheric conditions of the past 100 years, future landscapes would equilibrate at soil and plant C densities that would be 3 and 15–24 that of the pristine, presettlement grasslands they have replaced. Replacement of grasslands and savannas by woodlands in this biocli-matic region has thus resulted in significant and ongoing increases in landscape-scale ecosystem carbon stocks in a relatively short (100 years) period of time.
Passive open-top devices have been proposed as a method to experimentally increase temperature in high-latitude ecosystems. There is, however, little documentation on the efficacy of these devices. This paper examines the performance of four open-top chambers for altering temperature at six sites in the Arctic and Antarctica. Most of the heating effect was due to daytime warming above ambient; occasional night-time cooling below ambient, especially of air temperatures, depressed mean daily temperature. The mean daily temperatures at four arctic sites were generally increased by 1.2–1.8 °C; but occasionally, temperature depressions also occurred. Under optimal conditions at the antarctic site (dry soils, no vegetation, high radiation) mean daily soil temperatures were increased by +2.2 °C (–10 cm) to +5.2 °C (0 cm). Protection from wind may play a more important role than temperature per se in providing a favourable environment for plant growth within open-top devices. Wind speed had a generally negative impact on mean daily temperature. Daily global radiation was both positively and negatively related to chamber temperature response. The effect of chambers on snow accumulation was variable with the Alexandra Fjord site showing an increased accumulation in chambers but no difference in the date of snowmelt, while at Latnjajaure in a deep snowfall site, snowmelt occurred 1–2 weeks earlier in chambers, potentially increasing the growing season. Selection of a passive temperature-enhancing system requires balancing the temperature enhancement desired against potential unwanted ecological effects such as chamber overheating and altered light, moisture, and wind. In general, the more closed the temperature-enhancing system, the higher is the temperature enhancement, but the larger are the unwanted ecological effects. Open-top chambers alter temperature significantly and minimize most unwanted ecological effects; as a consequence, these chambers are a useful tool for studying the response of high-latitude ecosystems to warming.
Recent warming of Northern Hemisphere (NH) land is well documented and typically greater in winter/spring than other seasons. Physical environment responses to warming have been reported, but not details of large-area temperate growing season impacts, or consequences for ecosystems and agriculture. To date, hemispheric-scale measurements of biospheric changes have been confined to remote sensing. However, these studies did not provide detailed data needed for many investigations. Here, we show that a suite of modeled and derived measures (produced from daily maximum–minimum temperatures) linking plant development (phenology) with its basic climatic drivers provide a reliable and spatially extensive method for monitoring general impacts of global warming on the start of the growing season. Results are consistent with prior smaller area studies, confirming a nearly universal quicker onset of early spring warmth (spring indices (SI) first leaf date, −1.2 days decade−1), late spring warmth (SI first bloom date, −1.0 days decade−1; last spring day below 5°C, −1.4 days decade−1), and last spring freeze date (−1.5 days decade−1) across most temperate NH land regions over the 1955–2002 period.
However, dynamics differ among major continental areas with North American first leaf and last freeze date changes displaying a complex spatial relationship. Europe presents a spatial pattern of change, with western continental areas showing last freeze dates getting earlier faster, some central areas having last freeze and first leaf dates progressing at about the same pace, while in portions of Northern and Eastern Europe first leaf dates are getting earlier faster than last freeze dates. Across East Asia last freeze dates are getting earlier faster than first leaf dates.
We investigated the independent and combined effects of experimental warming and grazing on plant species diversity on the north-eastern Tibetan Plateau, a region highly vulnerable to ongoing climate and land use changes. Experimental warming caused a 26–36% decrease in species richness, a response that was generally dampened by experimental grazing. Higher species losses occurred at the drier sites where N was less available. Moreover, we observed an indirect effect of climate change on species richness as mediated by plant–plant interactions. Heat stress and warming-induced litter accumulation are potential explanations for the species’ responses to experimental warming. This is the first reported experimental evidence that climate warming could cause dramatic declines in plant species diversity in high elevation ecosystems over short time frames and supports model predictions of species losses with anthropogenic climate change.