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Mountain grasslands provide valuable ecosystem services for sustainable development and human wellbeing
. These habitats have suffered important changes related with their physiognomic (biomass) and physiologic (greenness) properties. Some of these changes received significant attention i.e. woody encroachment, while others, like the changes in biomass and greenness of those grasslands that have not experienced woody encroachment are almost unknown. We calculated physiognomic and physiologic properties for dense grasslands not affected by woody encroachment through the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Infrared Index (NDII) from Landsat-5 Thematic Mapper. Imagery taken in the late-1980s and late-2000s in the Spanish Pyrenees were analyzed with multi-temporal vectors to detect increases or decreases of biomass and greenness. To understand the source of these changes, we modeled them with anthropogenic (land use, i.e. grazing, ski resorts, and related infrastructures) and environmental factors (topographic, lithologic and climatic). Anthropogenic factors were most strongly correlated with decrease in the biomass and greenness, showing degradation patterns of the grasslands at localized patches. Nonetheless, environmental factors were most strongly correlated with positive changes in both indices, detecting a continuous pattern in the increase in biomass and greenness. In areas that had high livestock stocking rates, grasslands biomass and greenness decrease, while in areas that had low stocking rates, biomass and greenness increases. Grasslands at low elevation showing decrease in biomass and greenness were either on gentle slopes and largely affected by human activities, or on steep slopes locally affected by ski resorts. In areas that have been disturbed by anthropogenic factors, the increase of rain in early summer trigger erosion processes, enhancing the negative effect of anthropic pressure on grassland greenness and biomass. In contrast, grasslands at high elevations, on steep slopes, and those that had north or west aspects and that had an acidic lithology, with less continentality, and that received more rain, had the most increase in biomass and greenness. Those results suggest that changes in mountain grasslands, apart from woody encroachment, are deeply altering their physiology and physiognomy, pointing out direct relationships with current management practices and climate trends
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Wang, M.; Yang, G.; Gao, Y.; Chen, H.; Wu, N.; Peng, C.; Zhu, Q.; Zhu, D.; Wu, J.; He, Y.; Tian, J.; Zhao, X.; Zhang, Y.
In order to understand the carbon fate of alpine peatlands under climate change, this study aimed to measure carbon accumulation in recent decades and that during the Holocene at seven representative peat sites on the Zoige Plateau using empirical peat core data (14C and 137CS) and modeling approaches
. The observed apparent carbon accumulation rate over the past 50 years was 75 (35–123) g C m−2 yr−1, nearly four times that of 19 (7–30) g C m−2 yr−1over the whole Holocene. With decomposition history included in consideration by using modeling approaches, the average expected peat carbon accumulation rate was still nearly 1.6 times that of the modeled net carbon uptake rate of peats accumulated over the whole Holocene, though exceptions were found for Denahequ and Hongyuan peat cores with extremely low water table levels. The newly accumulated peat carbon of the Zoige Plateau amounted to 0.4 Tg C yr−1 (1 Tg = 1012 g) during recent decades. Overall, the effect of climate warming on recent C accumulation of peatlands on the Zoige Plateau is dependent on their water conditions. The peat C storage on the alpine Plateau is threatened by human activities (drainage) and continuous climate change with increasing temperature and decreasing precipitation which cause dryness of peatlands
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Although photoperiod is known to be the main factor driving plant senescence in perennial plants, temperature has also been shown to modulate this process, which suggests that climate warming will significantly impact the length of plant growing season and affect terrestrial productivity
. To test this assumption, we measured the effects of simulated autumn warming on four perennial herbaceous species, i.e. Elymus nutans, Koeleria macrantha, Vicia unijuga and Allium atrosanguineum, representing two major plant functional groups (grasses and forbs), in a typical alpine meadow of the Tibetan Plateau. Warming was simulated using open-top chambers, and its effects on degradation of chlorophyll and nitrogen (N) concentration in leaves and stems were determined during the senescence processes in autumn. The potential effects of autumn warming on total non-structural carbohydrate (TNC) in roots, growth and flowering phenology were further investigated in the following year. We found that warming delayed chlorophyll degradation of perennial herbs in early phase but accelerated it in later phase, regardless of functional groups, which led to higher N concentrations in leaves and stems during the whole senescence period. Autumn warming also significantly increased TNC in roots as a result of the delayed process of chlorophyll degradation, although the magnitudes were dependent on functional groups, which may be explained by inherent differences in growth patterns and phenology between grasses and forbs. We demonstrate that warming can increase carbohydrate accumulation not only by enhancing activities of photosynthetic enzymes proved by many previous studies but by altering chlorophyll degradation and preferential allocation of resources to different compartments. Furthermore, these results suggest that the net effect of climate warming on terrestrial ecosystems will be determined by floristic composition, as contrasting immediate and lasting (one year) changes in nutrient use and carbon allocation in response to warming were observed among species
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