No abstract

: Landscape evolution of a bedrock peneplain on the southern Tibetan Plateau revealed by in situ-produced cosmogenic 10Be and 21Ne.-Geomorphology, [153][154][192][193][194][195][196][197][198][199][200][201][202][203][204] AbstractLow-relief bedrock surfaces that occur at high altitude are a common feature of Cenozoic mountain belts and have often been used to infer a significant amount of rock uplift after their generation at low elevation. The timescale over which such surfaces can be preserved at high elevation and the rate at which they are modified by weathering and erosion are poorly known. Here we use cosmogenic 10 Be and 21 Ne to quantify the landscape evolution of a bedrock peneplain in southern Tibet that occurs at an altitude of ~5300 m. The peneplain is developed in Cretaceous granitoids and Jurassic metasediments of the northern Lhasa block (90°E, 31°N) and originally had a minimum extent of ~150 km east-west and ~75 km northsouth. It has been dissected by small rivers that generated a few hundred meters of relief and formed additional bedrock surfaces of limited extent at lower elevation. Local denudation rates for the peneplain and the lower bedrock surfaces -based on 10 Be concentrations in grus samples and amalgamated quartz clasts -cluster between 5 and 11 m Ma -1 (mean = 8.1 m Ma -1 ) and are thought to be representative for the long-term rate of downwearing of these surfaces. Samples from bedrock outcrops and bedrock blocks yield more variable rates (3-20 m Ma -1 ), which partly overestimate the long-term lowering rate, presumably due to block tilting and bedrock inhomogeneity. Spatially averaged 10 Be denudation rates for small river catchments range from 9 to 16 m Ma -1 (mean = 11.8 m Ma -1 ) and are only slightly higher than the local denudation rates. Hence, the incision and widening of valleys proceeds at low rates, which demonstrates that the landscape of the peneplain region is remarkably stable. The combined 21 Ne and 10 Be data in a subset of the samples suggest that the bedrock surfaces have experienced a simple exposure history without periods of burial. Thus, our data do not provide any evidence for extended periods of shielding by ice during past glaciations, which is consistent with the absence of erratic boulders and moraines in the peneplain region.

An effective assessment of future climate change, especially future precipitation forecasting, is an important basis for the rational development of adaptive strategies for Northwest China, where the ecological environment is fragile and encompasses arid and semiarid regions. In this work, the performance of a regional climate model is assessed; then, climate changes in the near future (2018–2037), middle future (2050–2069), and distant future (2080–2099) are analyzed under representative concentration pathways (RCPs) RCP2.6, RCP4.5, and RCP8.5. The following conclusions are drawn: (1) Compared to the Met Office Hadley Centre Earth System (HadGEM2‐ES) global climate model, the latest regional climate model, RegCM4.6, with a community land model land surface process scheme and Tiedtke cumulus convective parameterization, can create a good simulation of the present‐day mean climatology over Northwest China, including temperature, precipitation, and climate extremes, and can also provide finer‐scale climate information in complex terrain and better correct the cold bias than HadGEM2‐ES. At the same time, RegCM4 inherited the bias from HadGEM2‐ES, for example, both the RegCM4 and the HadGEM2‐ES overestimated precipitation in DJF in the southeast of the study area. (2) The future near surface air temperature will experience continuous warming over Northwest China under the RCP8.5 scenario, and the warming will become more significant and exceed 6 °C by the end of the 21st century. In RegCM4, future precipitation will continue to increase and will increase by 50 mm by the end of the 21st century relative to historical data. The extreme climate index summer days will continue to increase, indicating that high temperatures will be more frequent in Northwest China. In contrast, the consecutive dry days will decrease, likely because of the increase in precipitation.

The accurate and nondestructive determination of individual leaf area (LA) of plants, by using leaf length (L) and width (W) measurement or combinations of them, is important for many experimental comparisons. Here, we propose reliable and simple regressions for estimating LA across different leaf-age groups of eight common evergreen broadleaved trees in a subtropical forest in Gutianshan Natural Reserve, eastern China. During July 2007, the L, W, and LA of 2,923 leaves (202 to 476 leaves for each species) were measured for model construction and the respective measurements on 1,299 leaves were used for model validation. Mean L, W, LA and leaf shape (L:W ratio) differed significantly between current and older leaves in four out of the eight species. The coefficients of one-dimension LA models were affected by leaf age for most species while those incorporating both leaf dimensions (L and W) were independent of leaf age for all the species. Therefore, the regressions encompassing both L and W (LA = a L W + b), which were independent of leaf age and also allowed reliable LA estimations, were developed. Comparison between observed and predicted LA using these equations in another dataset, conducted for model validation, exhibited a high degree of correlation (R 2 = 0.96-0.99). Accordingly, these models can accurately estimate the LA of different age groups for the eight evergreen tree species without using instruments.Additional key words: evergreen broadleaved trees; leaf age; leaf area; leaf length and width; subtropical forest.