Vegetation response to extreme climate events on the Mongolian Plateau from 2000 to 2010

Climate change has led to more frequent extreme winters (aka, dzud) and summer droughts on the Mongolian Plateau during the last decade. Among these events, the 2000–2002 combined summer drought–dzud and 2010 dzud were the most severe on vegetation. We examined the vegetation response to these extremes through the past decade across the Mongolian Plateau as compared to decadal means. We first assessed the severity and extent of drought using the Tropical Rainfall Measuring Mission (TRMM) precipitation data and the Palmer drought severity index (PDSI). We then examined the effects of drought by mapping anomalies in vegetation indices (EVI, EVI2) and land surface temperature derived from MODIS and AVHRR for the period of 2000–2010. We found that the standardized anomalies of vegetation indices exhibited positively skewed frequency distributions in dry years, which were more common for the desert biome than for grasslands. For the desert biome, the dry years (2000–2001, 2005 and 2009) were characterized by negative anomalies with peak values between �1.5 and �0.5 and were statistically different (P \u3c 0:001) from relatively wet years (2003, 2004 and 2007). Conversely, the frequency distributions of the dry years were not statistically different (p \u3c 0:001) from those of the relatively wet years for the grassland biome, showing that they were less responsive to drought and more resilient than the desert biome. We found that the desert biome is more vulnerable to drought than the grassland biome. Spatially averaged EVI was strongly correlated with the proportion of land area affected by drought (PDSI \u3c �1) in Inner Mongolia (IM) and Outer Mongolia (OM), showing that droughts substantially reduced vegetation activity. The correlation was stronger for the desert biome (R2 D 65 and 60, p \u3c 0:05) than for the IM grassland biome (R2 D 53, p \u3c 0:05). Our results showed significant differences in the responses to extreme climatic events (summer drought and dzud) between the desert and grassland biomes on the Plateau

Common Features in Electronic Structure of the Fe-Based Layered Superconductors from Photoemission Spectroscopy

High resolution photoemission measurements have been carried out on non-superconducting LaOFeAs parent compound and various superconducting R(O1-xFx)FeAs (R=La, Ce and Pr) compounds. We found that the parent LaOFeAs compound shows a metallic character. Through extensive measurements, we have identified several common features in the electronic structure of these Fe-based compounds: (1). 0.2 eV feature in the valence band; (2). A universal 13~16 meV feature; (3). A clear Fermi cutoff showing zero leading-edge shift in the superconducting state;(4). Lack of superconducting coherence peak(s); (5). Near EF spectral weight suppression with decreasing temperature. These universal features can provide important information about band structure, superconducting gap and pseudogap in these Fe-based materials.Comment: 5 pages,4 figure

Notch signaling in T helper cell subsets: Instructor or unbiased amplifier?

For protection against pathogens, it is essential that naïve CD4+ T cells differentiate into specific effector T helper (Th) cell subsets following activation by antigen presented by dendritic cells (DCs). Next to T cell receptor and cytokine signals, membrane-bound Notch ligands have an important role in orchestrating Th cell differentiation. Several studies provided evidence that DC activation is accompanied by surface expression of Notch ligands. Intriguingly, DCs that express the delta-like or Jagged Notch ligands gain the capacity to instruct Th1 or Th2 cell polarization, respectively. However, in contrast to this model it has also been hypothesized that Notch signaling acts as a general amplifier of Th cell responses rather than an instructive director of specific T cell fates. In this alternative model, Notch enhances proliferation, cytokine production, and anti-apoptotic signals or promotes co-stimulatory signals in T cells. An instructive role for Notch ligand expressing DCs in the induction of Th cell differentiation is further challenged by evidence for the involvement of Notch signaling in differentiation of Th9, Th17, regulatory T cells, and follicular Th cells. In this review, we will discuss the two opposing models, referred to as the "instructive" and the "unbiased amplifier" model. We highlight both the function of different Notch receptors on CD4+ T cells and the impact of Notch ligands on antigen-presenting cells

Differentiating anthropogenic modification and precipitation-driven change on vegetation productivity on the Mongolian Plateau

Context: The Mongolian Plateau, comprising Inner Mongolia, China (IM) and Mongolia (MG) is undergoing consistent warming and accelerated land cover/land use change. Extensive modifications of water-limited regions can alter ecosystem function and processes; hence, it is important to differentiate the impacts of human activities and precipitation dynamics on vegetation productivity. Objectives: This study distinguished between human-induced and precipitation-driven changes in vegetation cover on the plateau across biome, vegetation type and administrative divisions. Methods: Non-parametric trend tests were applied to the time series of vegetation indices (VI) derived from MODIS and AVHRR and precipitation from TRMM and MERRA reanalysis data. VI residuals adjusted for rainfall were obtained from the regression between growing season maximum VI and monthly accumulated rainfall (June–August) and were used to detect human-induced trends in vegetation productivity during 1981–2010. The total livestock and population density trends were identified and then used to explain the VI residual trends. Results The slope of precipitation-adjusted EVI and EVI2 residuals were negatively correlated to total livestock density (R2 = 0.59 and 0.16, p \u3c 0.05) in MG and positively correlated with total population density (R2 = 0.31, p \u3c 0.05) in IM. The slope of precipitation-adjusted EVI and EVI2 residuals were also negatively correlated with goat density (R2 = 0.59 and 0.19, p \u3c 0.05) and sheep density in MG (R2 = 0.59 and 0.13, p \u3c 0.05) but not in IM. Conclusions Some administrative subdivisions in IM and MG showed decreasing trends in VI residuals. These trends could be attributed to increasing livestock or population density and changes in livestock herd composition. Other subdivisions showed increasing trends residuals, suggesting that the vegetation cover increase could be attributed to conservation efforts

Proportion of vegetated area in the Mongolian Plateau covered by < − 1 standardized anomalies of EVI and EVI2 during June–July–August (JJA) in summer and January–February (JF) land surface temperature anomalies in winter

<p><b>Table 1.</b>  Proportion of vegetated area in the Mongolian Plateau covered by < − 1 standardized anomalies of EVI and EVI2 during June–July–August (JJA) in summer and January–February (JF) land surface temperature anomalies in winter. Summer droughts of 2001 and 2009 and <em>dzud</em> of 2010 are highlighted in bold. </p> <p><strong>Abstract</strong></p> <p>Climate change has led to more frequent extreme winters (aka, <em>dzud)</em> and summer droughts on the Mongolian Plateau during the last decade. Among these events, the 2000–2002 combined summer drought–<em>dzud</em> and 2010 <em>dzud</em> were the most severe on vegetation. We examined the vegetation response to these extremes through the past decade across the Mongolian Plateau as compared to decadal means. We first assessed the severity and extent of drought using the Tropical Rainfall Measuring Mission (TRMM) precipitation data and the Palmer drought severity index (PDSI). We then examined the effects of drought by mapping anomalies in vegetation indices (EVI, EVI2) and land surface temperature derived from MODIS and AVHRR for the period of 2000–2010. We found that the standardized anomalies of vegetation indices exhibited positively skewed frequency distributions in dry years, which were more common for the desert biome than for grasslands. For the desert biome, the dry years (2000–2001, 2005 and 2009) were characterized by negative anomalies with peak values between −1.5 and −0.5 and were statistically different (<em>P</em> < 0.001) from relatively wet years (2003, 2004 and 2007). Conversely, the frequency distributions of the dry years were not statistically different (<em>p</em> < 0.001) from those of the relatively wet years for the grassland biome, showing that they were less responsive to drought and more resilient than the desert biome. We found that the desert biome is more vulnerable to drought than the grassland biome. Spatially averaged EVI was strongly correlated with the proportion of land area affected by drought (PDSI <− 1) in Inner Mongolia (IM) and Outer Mongolia (OM), showing that droughts substantially reduced vegetation activity. The correlation was stronger for the desert biome (<em>R</em>² = 65 and 60, <em>p</em> < 0.05) than for the IM grassland biome (<em>R</em>² = 53, <em>p</em> < 0.05). Our results showed significant differences in the responses to extreme climatic events (summer drought and <em>dzud</em>) between the desert and grassland biomes on the Plateau.</p

Area averaged means of June–July–August EVI plotted with the proportion of area covered by < − 1 PDSI in desert ((a), (b)) and grassland ((c), (d)) biomes for Inner Mongolia (IM) and Outer Mongolia (OM)

<p><strong>Figure 6.</strong> Area averaged means of June–July–August EVI plotted with the proportion of area covered by < − 1 PDSI in desert ((a), (b)) and grassland ((c), (d)) biomes for Inner Mongolia (IM) and Outer Mongolia (OM). Linear regression of July–August EVI with the proportion of area covered by < − 1 PDSI in desert (e) and grassland (f) biomes for Inner Mongolia (IM) and Outer Mongolia (OM).</p> <p><strong>Abstract</strong></p> <p>Climate change has led to more frequent extreme winters (aka, <em>dzud)</em> and summer droughts on the Mongolian Plateau during the last decade. Among these events, the 2000–2002 combined summer drought–<em>dzud</em> and 2010 <em>dzud</em> were the most severe on vegetation. We examined the vegetation response to these extremes through the past decade across the Mongolian Plateau as compared to decadal means. We first assessed the severity and extent of drought using the Tropical Rainfall Measuring Mission (TRMM) precipitation data and the Palmer drought severity index (PDSI). We then examined the effects of drought by mapping anomalies in vegetation indices (EVI, EVI2) and land surface temperature derived from MODIS and AVHRR for the period of 2000–2010. We found that the standardized anomalies of vegetation indices exhibited positively skewed frequency distributions in dry years, which were more common for the desert biome than for grasslands. For the desert biome, the dry years (2000–2001, 2005 and 2009) were characterized by negative anomalies with peak values between −1.5 and −0.5 and were statistically different (<em>P</em> < 0.001) from relatively wet years (2003, 2004 and 2007). Conversely, the frequency distributions of the dry years were not statistically different (<em>p</em> < 0.001) from those of the relatively wet years for the grassland biome, showing that they were less responsive to drought and more resilient than the desert biome. We found that the desert biome is more vulnerable to drought than the grassland biome. Spatially averaged EVI was strongly correlated with the proportion of land area affected by drought (PDSI <− 1) in Inner Mongolia (IM) and Outer Mongolia (OM), showing that droughts substantially reduced vegetation activity. The correlation was stronger for the desert biome (<em>R</em>² = 65 and 60, <em>p</em> < 0.05) than for the IM grassland biome (<em>R</em>² = 53, <em>p</em> < 0.05). Our results showed significant differences in the responses to extreme climatic events (summer drought and <em>dzud</em>) between the desert and grassland biomes on the Plateau.</p

Standardized anomalies of EVI2, white sky albedo and EVI in 2001 ((a), (c), (e)) and 2009 ((b), (d), (f)) summer droughts (June–July–August)

<p><strong>Figure 2.</strong> Standardized anomalies of EVI2, white sky albedo and EVI in 2001 ((a), (c), (e)) and 2009 ((b), (d), (f)) summer droughts (June–July–August). Negative VI anomalies ((a), (e) and (b), (f)), correlate with positive albedo anomalies ((c) and (d)) respectively.</p> <p><strong>Abstract</strong></p> <p>Climate change has led to more frequent extreme winters (aka, <em>dzud)</em> and summer droughts on the Mongolian Plateau during the last decade. Among these events, the 2000–2002 combined summer drought–<em>dzud</em> and 2010 <em>dzud</em> were the most severe on vegetation. We examined the vegetation response to these extremes through the past decade across the Mongolian Plateau as compared to decadal means. We first assessed the severity and extent of drought using the Tropical Rainfall Measuring Mission (TRMM) precipitation data and the Palmer drought severity index (PDSI). We then examined the effects of drought by mapping anomalies in vegetation indices (EVI, EVI2) and land surface temperature derived from MODIS and AVHRR for the period of 2000–2010. We found that the standardized anomalies of vegetation indices exhibited positively skewed frequency distributions in dry years, which were more common for the desert biome than for grasslands. For the desert biome, the dry years (2000–2001, 2005 and 2009) were characterized by negative anomalies with peak values between −1.5 and −0.5 and were statistically different (<em>P</em> < 0.001) from relatively wet years (2003, 2004 and 2007). Conversely, the frequency distributions of the dry years were not statistically different (<em>p</em> < 0.001) from those of the relatively wet years for the grassland biome, showing that they were less responsive to drought and more resilient than the desert biome. We found that the desert biome is more vulnerable to drought than the grassland biome. Spatially averaged EVI was strongly correlated with the proportion of land area affected by drought (PDSI <− 1) in Inner Mongolia (IM) and Outer Mongolia (OM), showing that droughts substantially reduced vegetation activity. The correlation was stronger for the desert biome (<em>R</em>² = 65 and 60, <em>p</em> < 0.05) than for the IM grassland biome (<em>R</em>² = 53, <em>p</em> < 0.05). Our results showed significant differences in the responses to extreme climatic events (summer drought and <em>dzud</em>) between the desert and grassland biomes on the Plateau.</p

Standardized anomalies (summer June–July–August 2010) of MODIS-derived EVI, (MOD13A3) on the Mongolian Plateau, as compared to the decadal mean overlaid with terrestrial ecoregion (WWF) biome boundaries: desert (I), grassland (II) and forest (III)

<p><strong>Figure 1.</strong> Standardized anomalies (summer June–July–August 2010) of MODIS-derived EVI, (MOD13A3) on the Mongolian Plateau, as compared to the decadal mean overlaid with terrestrial ecoregion (WWF) biome boundaries: desert (I), grassland (II) and forest (III).</p> <p><strong>Abstract</strong></p> <p>Climate change has led to more frequent extreme winters (aka, <em>dzud)</em> and summer droughts on the Mongolian Plateau during the last decade. Among these events, the 2000–2002 combined summer drought–<em>dzud</em> and 2010 <em>dzud</em> were the most severe on vegetation. We examined the vegetation response to these extremes through the past decade across the Mongolian Plateau as compared to decadal means. We first assessed the severity and extent of drought using the Tropical Rainfall Measuring Mission (TRMM) precipitation data and the Palmer drought severity index (PDSI). We then examined the effects of drought by mapping anomalies in vegetation indices (EVI, EVI2) and land surface temperature derived from MODIS and AVHRR for the period of 2000–2010. We found that the standardized anomalies of vegetation indices exhibited positively skewed frequency distributions in dry years, which were more common for the desert biome than for grasslands. For the desert biome, the dry years (2000–2001, 2005 and 2009) were characterized by negative anomalies with peak values between −1.5 and −0.5 and were statistically different (<em>P</em> < 0.001) from relatively wet years (2003, 2004 and 2007). Conversely, the frequency distributions of the dry years were not statistically different (<em>p</em> < 0.001) from those of the relatively wet years for the grassland biome, showing that they were less responsive to drought and more resilient than the desert biome. We found that the desert biome is more vulnerable to drought than the grassland biome. Spatially averaged EVI was strongly correlated with the proportion of land area affected by drought (PDSI <− 1) in Inner Mongolia (IM) and Outer Mongolia (OM), showing that droughts substantially reduced vegetation activity. The correlation was stronger for the desert biome (<em>R</em>² = 65 and 60, <em>p</em> < 0.05) than for the IM grassland biome (<em>R</em>² = 53, <em>p</em> < 0.05). Our results showed significant differences in the responses to extreme climatic events (summer drought and <em>dzud</em>) between the desert and grassland biomes on the Plateau.</p

Frequency distributions of standardized MODIS EVI and VIP EVI2 June–July–August ((a)–(d)) anomalies in the grassland biome (2000–2010) for Inner Mongolia (IM) and Outer Mongolia (OM)

<p><strong>Figure 5.</strong> Frequency distributions of standardized MODIS EVI and VIP EVI2 June–July–August ((a)–(d)) anomalies in the grassland biome (2000–2010) for Inner Mongolia (IM) and Outer Mongolia (OM). The distributions of dry years are not statistically different (<em>p</em> < 0.001) from relatively wet years in the grassland biome as compared to the desert biome (note: this may suggest that the grassland ecosystems are more stable than deserts).</p> <p><strong>Abstract</strong></p> <p>Climate change has led to more frequent extreme winters (aka, <em>dzud)</em> and summer droughts on the Mongolian Plateau during the last decade. Among these events, the 2000–2002 combined summer drought–<em>dzud</em> and 2010 <em>dzud</em> were the most severe on vegetation. We examined the vegetation response to these extremes through the past decade across the Mongolian Plateau as compared to decadal means. We first assessed the severity and extent of drought using the Tropical Rainfall Measuring Mission (TRMM) precipitation data and the Palmer drought severity index (PDSI). We then examined the effects of drought by mapping anomalies in vegetation indices (EVI, EVI2) and land surface temperature derived from MODIS and AVHRR for the period of 2000–2010. We found that the standardized anomalies of vegetation indices exhibited positively skewed frequency distributions in dry years, which were more common for the desert biome than for grasslands. For the desert biome, the dry years (2000–2001, 2005 and 2009) were characterized by negative anomalies with peak values between −1.5 and −0.5 and were statistically different (<em>P</em> < 0.001) from relatively wet years (2003, 2004 and 2007). Conversely, the frequency distributions of the dry years were not statistically different (<em>p</em> < 0.001) from those of the relatively wet years for the grassland biome, showing that they were less responsive to drought and more resilient than the desert biome. We found that the desert biome is more vulnerable to drought than the grassland biome. Spatially averaged EVI was strongly correlated with the proportion of land area affected by drought (PDSI <− 1) in Inner Mongolia (IM) and Outer Mongolia (OM), showing that droughts substantially reduced vegetation activity. The correlation was stronger for the desert biome (<em>R</em>² = 65 and 60, <em>p</em> < 0.05) than for the IM grassland biome (<em>R</em>² = 53, <em>p</em> < 0.05). Our results showed significant differences in the responses to extreme climatic events (summer drought and <em>dzud</em>) between the desert and grassland biomes on the Plateau.</p