Interannual Variation of Transpiration and Its Modeling of a Larch Plantation in Semiarid Northwest China

Abstract

Quantifying the variation of forest transpiration (T) is important not only for understanding the water and energy budget of forest ecosystems but also for the prediction, evaluation, and management of hydrological effects as well as many other ecosystem services of forests under the changes of climate, vegetation, and anthropological impacts. The accurate prediction of T, a key component of water used by forests, requires mechanism-based models describing the T response to environmental and canopy conditions. The daily T of a larch (Larix principis-rupprechtti) plantation was measured through monitoring the sap flow in the growing season (from May to September) of a dry year (2010), a normal year (2012), and a wet year (2014) at a shady slope in the semi-arid area of Liupan Mountains in northwest China. Meanwhile, the meteorological conditions, soil moisture, and forest canopy leaf area index (LAI) were monitored. To get a simple and easily applicable T model, the numerous influencing parameters were grouped into three factors: the atmospheric evapotranspiration demand indicated by the potential evapotranspiration (PET), the soil water supply ability indicated by the relative extractable soil water content (REW), and the vegetation transpiration capacity indicated by the forest canopy LAI. The T model was established as a continuous multiplication of the T response equations to individual factors, which were determined using the upper boundary lines of measured data. The effect of each factor on the T in a dry year (2010) or normal year (2012) was assessed by comparing the measured T in the baseline of the wet year (2014) and the model predicted T, which was calculated through inputting the actual data of the factor (i.e., PET) to be assessed in the dry or normal year and the measured data of other two factors (i.e., REW, LAI) in the baseline of the wet year. The results showed that the mean daily T was 0.92, 1.05, and 1.02 mm; and the maximum daily T was 1.78, 1.92, and 1.89 mm in 2010, 2012, and 2014, respectively. The T response follows a parabolic equation to PET, but a saturated exponential equation to REW and LAI. The T model parameters were calibrated using measured data in 2010 and 2012 (R2 = 0.89, Nash coefficient = 0.88) and validated using measured data in 2014 satisfactorily (R2 = 0.89, Nash coefficient = 0.79). It showed a T limitation in the dry year 2010 for all factors (18.5 mm by PET, 11.5 mm by REW, and 17.8 mm by LAI); while a promotion for PET (1.4 mm) and a limitation for REW (4.2 mm) and LAI (14.3 mm) in the normal year 2012. The daily T model established in this study can be helpful to assess the individual factor impact on T and improve the daily T prediction under changing environmental and canopy conditions.

Canopy Transpiration and Stomatal Conductance Dynamics of Ulmus pumila L. and Caragana korshinskii Kom. Plantations on the Bashang Plateau, China

“…E c responded to REW as a saturated exponential function for C. korshinskii in this study (Figure 5c,d), which was in agreement with results reported for broadleaved and coniferous trees under different climates [41], a larch plantation in the semiarid Northwest China [42], a black locust plantation [43], and C. korshinskii [44] on the Loess Plateau. However, the REW threshold in this study is similar to or relatively higher than those in the studies reported above.…”

How does spatial heterogeneity affect inter‐ and intraspecific growth patterns in tundra shrubs?

“…During the mounting process of the dendrometers, we removed the dead outer bark to place the sensor as close to the living tissue as possible, following a common practice for dendrometer measurements of trees (e.g. Grams et al., 2021; Oberhuber et al., 2020; Wang et al., 2020). This ensures that hygroscopic shrinkage and swelling of dead tissues from the outer bark does not influence the diameter measurements.…”

: On growth patterns and mechanisms in arctic-alpine shrubs

“…Here, comparative studies revealed a complex interplay of xylem as well as phloem growth and pressure-induced size changes, which simultaneously affect radial stem change and are thus captured by the dendrometers (TURCOTTE et al, 2011;KNÜSEL et al, 2021). Following a common practice for dendrometer measurements of trees (e.g., WANG et al, 2020), the dead outer bark was therefore removed to place the sensor as close to the living tissue as possible and to eliminate the effects of such processes.…”

“…We mounted our dendrometers on one major aboveground stem of a randomly chosen specimen per site, horizontally to the ground surface and as close to the assumed root collar as possible. During this process, we removed the dead outer bark (periderm) to place the sensor as close to the living tissue as possible, following a common practice for dendrometer measurements of trees Wang et al, 2020;. This ensures that hygroscopic shrinkage and swelling of dead tissues from the outer bark do not influence the diameter measurements.…”

“…During the mounting process of the dendrometers, we removed the dead outer bark to place the sensor as close to the living tissue as possible, following a common practice for dendrometer measurements of trees (e.g. Wang et al, 2020). This ensures that hygroscopic shrinkage and swelling of dead tissues from the outer bark does not influence the diameter measurements.…”