Relationships between aboveground biomass and plant cover at two spatial scales and their determinants in northern Tibetan grasslands

Jiang, Yanbin; Zhang, Yangjian; Wu, Yupeng; Hu, Ronggui; Zhu, Juntao; Tao, Jian; Zhang, Tao

doi:10.1002/ece3.3308

Cited by 22 publications

(14 citation statements)

References 49 publications

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“…First, our finding of AGB peak increasing with precipitation ( Figure 4a) was in good agreement with previous studies on the Tibetan Plateau [65][66][67][68] and Eurasian temperate grasslands [15,25]. A critical step we went further in this study was that we examined relationship of AGB peak with the temporal variability of precipitation.…”

Section: Discussionsupporting

confidence: 90%

Temporal Variability of Precipitation and Biomass of Alpine Grasslands on the Northern Tibetan Plateau

Song

et al. 2019

Remote Sensing

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The timing regimes of precipitation can exert profound impacts on grassland ecosystems. However, it is still unclear how the peak aboveground biomass (AGBpeak) of alpine grasslands responds to the temporal variability of growing season precipitation (GSP) on the northern Tibetan Plateau. Here, the temporal variability of precipitation was defined as the number and intensity of precipitation events as well as the time interval between consecutive precipitation events. We conducted annual field measurements of AGBpeak between 2009 and 2016 at four sites that were representative of alpine meadow, meadow-steppe, alpine steppe, and desert-steppe. Thus, an empirical model was established with the time series of the field-measured AGBpeak and the corresponding enhanced vegetation index (EVI) (R2 = 0.78), which was used to estimate grassland AGBpeak at the regional scale. The relative importance of the three indices of the temporal variability of precipitation, events, intensity, and time interval on grassland AGBpeak was quantified by principal component regression and shown in a red–green–blue (RGB) composition map. The standardized importance values were used to calculate the vegetation sensitivity index to the temporal variability of precipitation (VSIP). Our results showed that the standardized VSIP was larger than 60 for only 15% of alpine grassland pixels and that AGBpeak did not change significantly for more than 60% of alpine grassland pixels over the past decades, which was likely due to the nonsignificant changes in the temporal variability of precipitation in most pixels. However, a U-shaped relationship was found between VSIP and GSP across the four representative grassland types, indicating that the sensitivity of grassland AGBpeak to precipitation was dependent on the types of grassland communities. Moreover, we found that the temporal variability of precipitation explained more of the field-measured AGBpeak variance than did the total amount of precipitation alone at the site scale, which implies that the mechanisms underlying how the temporal variability of precipitation controls the AGBpeak of alpine grasslands should be better understood at the local scale. We hypothesize that alpine grassland plants promptly respond to the temporal variability of precipitation to keep community biomass production more stable over time, but this conclusion should be further tested. Finally, we call for a long-term experimental study that includes multiple natural and anthropogenic factors together, such as warming, nitrogen deposition, and grazing and fencing, to better understand the mechanisms of alpine grassland stability on the Tibetan Plateau.

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Section: Discussionsupporting

confidence: 90%

Temporal Variability of Precipitation and Biomass of Alpine Grasslands on the Northern Tibetan Plateau

Song

et al. 2019

Remote Sensing

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“…In spite of slow restoration of green cover after extremes, the productivity of the alpine grassland in our study did bounce back faster. Cover and biomass are not necessarily correlated, as the latter also depends on plant height, canopy structure and community composition (Axmanová et al, 2012 ; Jiang et al, 2017 ). In our case, the graminoid fraction in the vegetation, with its more erect growth form, likely compensated for the reduced share of forbs compared to communities not exposed to drought, which led to restored community productivity in spite of lower green cover.…”

Section: Discussionmentioning

confidence: 99%

Legacy Effects of Climate Extremes in Alpine Grassland

et al. 2018

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Climate change is particularly apparent in many mountainous regions, with warming rates of more than twice the global average being reported for the European Alps. As a result, the probability of climate extremes has increased and is expected to rise further. In an earlier study, we looked into immediate impacts of experimentally imposed heat waves in alpine grassland, and found that these systems were able to cope with heat as long as enough water was available. However, concomitant drought led to increased stress, and reduced aboveground biomass production and green plant cover. Here, we studied the legacy effects (lag-effects) of the imposed climate extreme to see whether delayed responses occurred and how fast the alpine grassland could rebound from the initial changes. Green cover continued to be suppressed the two following years in communities that had been exposed to the most intense hot drought, while aboveground biomass production had returned to control levels by year 2. The initial lower resistance of the forb fraction in the communities was not compensated by faster recovery later on. This resulted in alpine communities that became (and remained) relatively enriched with graminoids, which resisted the original extreme better. The responses of alpine grassland to heat extremes with or without drought observed in this study resemble those typically found in lowland grassland in the short term. However, alpine grassland exhibited longer legacy effects from an annual perspective, with delayed recovery of aboveground production and persistent changes in community composition. This suggests that once initial resistance thresholds are exceeded, impacts may be longer-lasting in alpine grassland, where recovery is constrained by both the short growing season and difficult seedling establishment.

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“…Another mechanism for lower species richness on the southern slope could be different patterns of rainfall and soil moisture gradients. However on the northern slope, the mean annual precipitation ranges from 50 to 800 mm (Jiang et al 2017). The southern slope of our study site is located in a rain shadow area of the Trans-Himalayan region, with a mean annual precipitation of 344 mm (Kharal et al 2017).…”

Section: Comparison Of Aboveground Biomass and Species Richness On Nomentioning

confidence: 99%

“…But at our study site, permanent snow cover is absent on mountain tops and soil moisture recharge from snow melt water during growing season is low. However on the northern slope, the mean annual precipitation ranges from 50 to 800 mm (Jiang et al 2017). Due to higher precipitation on the northern slope, the soil moisture gradient may be higher, as soil moisture positively correlates with precipitation (Laporte et al 2002) and favors higher species richness in this region.…”

Section: Comparison Of Aboveground Biomass and Species Richness On Nomentioning

confidence: 99%

Effect of altitude and soil properties on biomass and plant richness in the grasslands of Tibet, China, and Manang District, Nepal

Bhandari

Zhang

2019

Ecosphere

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Citation: Bhandari, J., and Y. Zhang. 2019. Effect of altitude and soil properties on biomass and plant richness in the grasslands of Tibet, China, and Manang District, Nepal.Abstract. A positive relationship between plant species richness and biomass has often documented in temperate grassland systems but is still largely lacking in the Himalayan region. Considering altitude and soil properties as major factors influencing species richness and biomass in the Himalayan grasslands, we tested the hypothesis that peak aboveground biomass and species richness increase with higher levels of soil nutrients and decrease with altitude. Our study was conducted in the grasslands of Tibet, China, and Manang District, Nepal, which represent, respectively, the northern and southern slopes of the central Himalayan grasslands. During the growing seasons, we measured vegetation aboveground biomass and soil properties along an altitudinal gradient on the northern slope in 2011 and 2012, and on the grasslands of the southern slope in 2017. Data were analyzed with a Spearman correlation analysis, classification and regression tree model, and the structural equation modeling (SEM) to identify the key factors determining aboveground biomass and species richness. The results demonstrated that aboveground biomass and species richness on the southern slope were significantly greater at the lowest altitude zone compared to middle and higher zones, whereas on the northern slope, aboveground biomass and species richness were not significantly different at three altitudinal zones. There was a significant positive correlation between aboveground biomass and species richness on both northern and southern slopes. However, the slope was found higher in grasslands of southern slope compared to the grasslands of northern slope. Classification and regression tree analysis and SEM indicated that altitude is most closely associated with large-scale variations in aboveground biomass and species richness. The Spearman correlation analysis revealed that altitude and soil pH were negatively related to aboveground biomass in these grasslands. This study demonstrates that on northern and southern slopes of the Himalayan Range, a positive relation between plant species richness and biomass is determined more by altitude than soil nutrients.

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Relationships between aboveground biomass and plant cover at two spatial scales and their determinants in northern Tibetan grasslands

Cited by 22 publications

References 49 publications

Temporal Variability of Precipitation and Biomass of Alpine Grasslands on the Northern Tibetan Plateau

Temporal Variability of Precipitation and Biomass of Alpine Grasslands on the Northern Tibetan Plateau

Legacy Effects of Climate Extremes in Alpine Grassland

Effect of altitude and soil properties on biomass and plant richness in the grasslands of Tibet, China, and Manang District, Nepal

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