Abstract
Fine-resolution studies on the stem radius variation at short timescale can provide useful information about the tree growth process and the major environmental variables that trigger and drive stem radius variation. This study investigated the stem radius variation of Larix principis-rupprechtii Mayr growing in the semi-humid Liupan Mountains of Northwest China at daily and seasonal scales using high-resolution automatic band dendrometers from May to October in 2015. The results showed that the stem radius variation of Larix principis-rupprechtii has a clear diurnal pattern which can be divided into contraction, recovery, and increment phases; and also a seasonal pattern which can be divided into three stages: (1) the rapid growth stage in spring (stage 1) with the radius increment of 94.0% of the total in the entire growing period; (2) the persistent shrinkage stage in the dry summer (stage 2) with a negative diurnal radius increment for most days, and a significantly larger amplitude of stem contraction and recovery than other stages; (3) the minimal growth stage in autumn (stage 3), mainly caused by the lowering temperature and leaf area. The amplitude of stem contraction was significantly correlated with air temperature (both the mean and highest value) in all three stages: vapor pressure deficit (VPD) in stage 1; relative humidity (RH), VPD and soil moisture (Ms) in stage 2; and soil temperature (Ts) in stage 3. This indicates that the stem radius contraction was mainly controlled by the factors influencing tree transpiration rate in spring and autumn stages, but jointly controlled by the factors influencing both the tree transpiration rate and the soil moisture availability in the dry summer stage. The factors controlling the stem radius recovery was similar to the stem contraction. The amplitude of stem increment was significantly correlated with the rainfall amount and air temperature (both the mean and highest value) in stage 1 and 3, Ms in stage 2, and the lowest air temperature and Ts in stage 3. This indicates that temperature and precipitation were the key factors controlling the stem radius increment in the spring and autumn stages, and soil moisture was the main factor limiting the stem radius increment in the dry summer stage at the study site with semi-humid climate in Northwest China.
Highlights
Under the increasing influence of global climate change, the growth of trees has been affected by the change of annual values of meteorological parameters, and by the variation of Forests 2017, 8, 382; doi:10.3390/f8100382 www.mdpi.com/journal/forestsForests 2017, 8, 382 environmental factors in short timescale, such as the hourly or daily values of soil moisture and weather parameters, and especially the extreme weather events [1,2,3,4,5,6]
Our results showed that the radius growth during early growing season was related to air temperature
The variation of stem radius of Larix principis-rupprechtii has a clear diurnal pattern, which is generally composed of three phases, namely, daytime contraction, nighttime recovery and increment; and a clear growing seasonal pattern which can be divided into three stages: a spring stage with the most rapid growth; a summer drought stage with the persistent shrinkage; and an autumn stage with the minimal growth
Summary
Under the increasing influence of global climate change, the growth of trees has been affected by the change of annual values of meteorological parameters, and by the variation of Forests 2017, 8, 382; doi:10.3390/f8100382 www.mdpi.com/journal/forestsForests 2017, 8, 382 environmental factors in short timescale, such as the hourly or daily values of soil moisture and weather parameters, and especially the extreme weather events (i.e., high temperature, drought, freeze injury) [1,2,3,4,5,6]. Studies at short-term timescale (i.e., diurnal and seasonal) are required for a more precise assessment, interpretation, and prediction of tree growth response to environmental stresses at larger timescales [10]. The dendrometer can automatically and continually record intra-annual stem radius variation with high temporal resolution [11], providing a possibility to study the diurnal and seasonal dynamics of stem radius and their response to environmental factors at shorter timescales. Based on such dendrometer data, several studies were reported in recent years [12,13,14]. Vieira et al [15] reported that the continuous positive stem radius increment of Pinus pinaster Ait
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