Intra-annual stem diameter growth of Tamarix ramosissima and association with hydroclimatic factors in the lower reaches of China’s Heihe River

Abstract

High-resolution observations of cambial phenology and intra-annual growth dynamics are useful approaches for understanding the response of tree growth to climate and environmental change. During the past two decades, rapid socioeconomic development has increased the demand for water resources in the oases of the middle reaches of the Heihe River in northwestern China, and the lower reaches of the Heihe River have changed from a perennial river to an ephemeral stream with a decreased and degraded riparian zone. Tamarisk (Tamarix ramosissima) is the dominant shrub species of the desert riparian forest. In this study, the daily and seasonal patterns of tamarisk stem diameter growth, including the main period of tree ring formation, were examined. Observations concerning the driving forces of growth changes, along with implications for the ecology of the dendrohydrological area and management of desert riparian forests in similar arid regions, are also presented. The diurnal-seasonal activity of stem diameter and the dynamics of growth ring formation were studied using a point dendrometer and micro-coring methods during the 2012 growing season in shrub tamarisk in a desert riparian forest stand in the lower reaches of the Heihe River in Ejin Banner, Inner Mongolia of northwestern China. Generally, the variation in diurnal diameter of tamarisk was characterized by an unstable multi-peak pattern, with the cumulative stem diameter growth over the growing season following an S-shaped curve. The period from late May to early August was the main period of stem diameter growth and growth-ring formation. Among all of the hydroclimatic factors considered in this study, only groundwater depth was significantly correlated with stem diameter increment during this period. Therefore, for the dendrochronological study, the annual rings of the tamarisk can be used to reconstruct processes that determine the regional water regime, such as river runoff and fluctuations in groundwater depth. For the management of desert riparian forests, suitable groundwater depths must be maintained in the spring and summer to sustain tree health and a suitable stand structure.

Groundwater-dependent ecosystems: recent insights from satellite and field-based studies

“…Tree rings represent the history of past growth events, which are often but not always annual (Prior et al, 2012). Quantification of growth rates from tree rings can be used to reconstruct fluctuations in the supply water from precip-4242 D. Eamus et al: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies itation and groundwater (Oberhuber et al, 1998;Bogino and Jobbagy, 2011;Perez-Valdivia and Sauchyn, 2011;Xiao et al, 2014). In mountainous regions where the regional water supply is derived from snowmelt, tree growth and groundwater depth are correlated with precipitation during the year prior to growth because much of the snow received in the winter melts in the year after it fell (Oberhuber et al, 1998;Perez-Valdivia and Sauchyn, 2011).…”

Hydroclimate Correlations Between the Alxa Desert and Adjacent Mountains in Northwestern China: Evidence From Meteorological and Tree‐Ring Data

“…Seasons were defined as spring (March to May), summer (June to August), autumn (September to November), and winter (December to February). Inter-annual stem-growth studies indicate that the stem-growth growing season (for our study area) extends from April to August (Peng et al, 2017;Ren et al, 2015;Xiao et al, 2014aXiao et al, , 2014bZeng et al, 2017). Because the precipitation data showed a nonnormal distribution, we used a nonparametric Mann-Kendall trend test to evaluate the statistical significance of the trends.…”

Groundwater-dependent ecosystems: recent insights, new techniques and an ecosystem-scale threshold response

“…Soil texture is used to estimate soil moisture characteristics in each layer of the model, and groundwater uptake by vegetation is assumed to occur when ET exceeds rainfall, when also accounting for soil water storage for each month. ET is estimated from total evaporation using the Budyko framework (Budyko, 1974;Donohue et al, 2007;Yang et al, 2008;Roderick and Farquhar, 2009). The risk model in Leaney et al (2011) uses the Choudhury-Yang formulation of the Budyko equation:…”

“…Tree rings represent the history of past growth events, which are often but not always annual (Prior et al, 2012). Quantification of growth rates from tree rings can be used to reconstruct fluctuations in the supply water from precip-4242 D. Eamus et al: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies itation and groundwater (Oberhuber et al, 1998;Bogino and Jobbagy, 2011;Perez-Valdivia and Sauchyn, 2011;Xiao et al, 2014). In mountainous regions where the regional water supply is derived from snowmelt, tree growth and groundwater depth are correlated with precipitation during the year prior to growth because much of the snow received in the winter melts in the year after it fell (Oberhuber et al, 1998;Perez-Valdivia and Sauchyn, 2011).…”