[Responses of transpiration to variation in evaporative demands and soil water in a larch plantation at the south side of Liupan Mountains, China]. / å ­ç›˜å±±å—ä¾§åŽåŒ—è½å¶æ¾äººå·¥æž—è’¸è ¾å¯¹åœŸå£¤æ°´åˆ†å’Œæ½œåœ¨è’¸æ•£çš„å“åº”.

Quantifying the response of tree transpiration (T) to the variation of soil water supply capability and atmospheric evaporative demand is beneficial for a better prediction of water use and hydrological cycles in forests and deepen the understanding of the relationship between forest and water. Larix principis-rupprechtii in the Xiangshuihe watershed at the south side of Liupan Mountains was used as the research object. We simultaneously monitored sap flow density by thermal diffusion probe and the environmental factors. The response of the T to the soil volumetric water content (VWC) and potential evapotranspiration (PET) was analyzed. The results showed the response curve of T to VWC was quite similar under any different PET levels. With increasing VWC, T increased rapidly and then slowly, and began to be stable when VWC reached a threshold. This process could be well fitted by the saturated exponential function. However, the VWC threshold was different, and its value increased with rising PET. The relationship of daily T to PET was a quadra-tic equation, and PET also had a threshold effect. A stand transpiration model considering the effect of soil water supply capacity and atmospheric evaporative potential was founded which coupled the response relationship of T to PET and VWC in the rapid growth season. This model could well estimate the diurnal variation of transpiration, and provide guidance for the management of plantation water control.

[Canopy transpiration of Larix principis-rupprechtii plantation and its impact factors in diffe-rent slope locations at the south side of Liupan Mountains, China.] / å ­ç›˜å±±å—ä¾§åŽåŒ—è½å¶æ¾äººå·¥æž—å† å±‚è’¸è ¾åŠå ¶å½±å“å› å­çš„å¡ä½å·®å¼‚.

Based on a continuous field observation in the Larix principis-rupprechtii plantation plots, located at the upper (P1), middle-upper (P2), middle (P3), middle-lower (P4), and lower (P5) positions, in a southeast-facing slope of the Xiangshuihe watershed of Liupan Mountains, China, the stem sap flow was observed with the thermal diffusivity probe method. The soil water potential and meteorological factors were monitored from May to October, 2014. We found significant differences among slope positions in the daily forest transpiration (Tr, mm·d-1), with an order of P2 (0.975)＞P4 (0.876)＞P3 (0.726)＞P1 (0.653)＞P5 (0.628). Tr was significantly positively correlated with the daily maximum temperature (Tmax), daily mean solar radiation (SR), daily mean saturated vapor pressure deficit (VPD), potential evapotranspiration (PET), and daily mean soil water potential (Ψ), but negatively correlated with the daily mean air relative humidity (RH), daily precipitation (P), and daily minimum temperature (Tmin). According to the upper boundary line ana-lysis, significant differences were found in the degree of Tr responding to each single environmental factor among slope positions. The degree of its responses gradually decreased for average daily air temperature (T), RH, VPD, PET and Ψ, whereas increased for the SR and daily average volumetric soil water content (VSM) from the upper position to the lower. Results from regression and partial correlation analysis showed that variation of Tr was mainly controlled by VPD, PET and RH in different slope positions. Tr was also strongly affected by Ψ and T in the upper-slope positions and by SR, Tmin and VSM at the lower-slope positions. Generally, the Tr difference among slope positions was a consequence of joint contributions of soil water and meteorological factors. It is necessary to consider the changes of soil water and meteorological factors in different positions along the slope when examining slope-scale or watershed-scale forest transpiration with sap flow estimated from xylem sap flux density measurements of a particular plot.

[Evapotranspiration characteristics of artificial and natural forests in Liupan Mountains of Ningxia, China during growth season].

In order to understand the effects of the structure of forest ecosystem on the hydrological processes, a comparative study by using thermal dissipation technique and hydrological methodology was made on the evapotranspiration (ET) and its components of Larix principis-rupprechtii plantation and Pinus armandi natural forest in two adjacent stands in a small catchment Xiangshuihe of Liupan Mountains during the growth season (May-October) in 2009. Throughout the growth season, the total ET from the plantation was 518.2 mm, which accounted for 104.6% of the precipitation and was much higher than that (420.5 mm) of the natural forest. The allocation of ET in the vertical layers performed similarly between the two stands, with the order of canopy layer > herb and soil layer > shrub layer, but the ratio of each component to total ET differed significantly. The plantation consumed 0.2 and 0.9 times more water for canopy interception (19.6 mm per month) and tree transpiration (25.2 mm per month) than the natural forest, respectively. However, the transpiration from the plantation was 4.4 mm per month, and took up 23.4% of the natural forest. In contrast, the sum of soil evaporation and herbage evapotranspiration consumed 37.1 mm water per month in the plantation, which was 0.8 times higher than that in the natural forest. The ET was calculated by Penman-Monteith equation to compare the results estimated by sap flow measurements, and the values estimated by the two methods were similar.

[Growth process of Larix principis-rupprechtii stands with different density on south slope of Liupan Mountains].

By the method of sample trees stem analysis, this paper studied the growth process and diameter structure of 21-year-old Larix principis-rupprechtii plantations with the densities of 1200, 1500, and 2000 stems x hm(-2) in the head-water area on the southern slope of Liupan Mountain in Ningxia Hui Autonomous Region. The results showed that there were no significant differences in the growth status of L. principis-rupprechtii stands among the three densities when the stand age was less than 10 years. However, obvious differences were observed in the diameter and timber volume of individual trees and in the stand volume when the stand age was more than 10 years. The tree growth status in low-density stand was apparently better than that in medium- and high-density stands, but the height growth had no significant difference among the three densities. There was a significant difference in the skewness coefficient (Sk) of diameter distribution among the stands with different density, being higher (Sk = 0.338) in high-density stand than in medium-density stand (Sk = 0.072) and low-density stand (Sk = 0.015). The diameter distribution in high-density stand deviated from normal distribution, with a zenith tending to left, while that in medium- and low-density stands approached a normal distribution, with a more reasonable density structure. The kurtosis coefficient (K = 1.691) of medium-density stand was higher than that of high-density stand (K = 1.532) and low-density stand (K = 0.665), indicating a lower degree of polarization of tree growth in medium-density stand than in other two stands. The reasonable remaining density of 21-year-old L. principis-rupprechtii plantations was suggested to be 1200 stems x hm(-2).