Mingchang Wang

Response of daily stem radial growth of Platycladus orientalis to environmental factors in a semi-arid area of North China

AbstractKey messageThe daily stem radial growth ofP. orientalisduring the main growing period in semi-arid areas of North China is mainly limited by moisture availability.Abstract Finer resolution studies of tree stem radial growth on short temporal scales can be useful for exploring the main environmental variables that trigger radial growth. The objective of this study was to determine the most important environmental factors that impact the intra-annual radial growth of Platycladus orientalis (Linn.) Franco in a semi-arid area of North China. The stem radial growth of P. orientalis was studied daily during the growing season (May to October 2013) using high-resolution automatic point dendrometers. Our results showed that the daily stem radial increment (SRI) of P. orientalis during the main growing period was primarily impacted by relative air humidity, precipitation, vapor pressure deficit and daily maximum air temperature. Those environmental factors mainly influenced the moisture availability to the trees, thereby affecting their daily stem radial growth. The rapid release of stem radial growth was observed when heavy precipitation events occurred after a drought period. The maximum stem growth rate of P. orientalis was observed in early August and was regulated by soil water content in the summer; this was regarded as an adaptation to the local climate conditions. Our results have further implications for sensitivity analyses of tree growth to climate changes in semi-arid areas.

Divergent responses to climate factors in the radial growth of Larix sibirica in the eastern Tianshan Mountains, northwest China

Key messageThe radial growth ofLarix sibiricahas exhibited divergent responses to temperatures in the growing season due to the temperature-driven drought stress in the eastern Tianshan Mountains of Northwest China.AbstractThe warming of the continental interior of the Northern Hemisphere in the latter half of the twentieth century has led to divergent responses between trees growth and climate factors at high latitudes. This study explored the variability in the responses of radial growth to climate factors and the temporal stability of growth–climate relationships under climate change for Siberia larch (Larix sibirica Ledeb.) in the mid-latitude area of the eastern Tianshan Mountains. The results indicated as follows: (1) Analysis of the relationships between tree-ring width chronology and climate factors before and after the abrupt increases in temperature demonstrated that divergent responses of radial growth occurred in the eastern Tianshan Mountains, suggesting that correlation coefficients with temperature varied significantly in the growing season. (2) Examination of variations in the climate factors limiting radial growth in the two time periods demonstrated that the minimum temperature played a key role from 1989 to 2012. (3) Assessment of the temporal stability of growth–climate relationships by a moving correlation function demonstrated that the positive sensitivity of Siberia larch to temperature during the growing season decreased. The reasons for this ‘divergence problem’ were the increased drought stress and changes in the physiological responses of trees. (4) Simulation of the trend of basal area increment by linear regression showed that the growth rate of Siberia larch first increased and then decreased. The future effects of increasing temperature may cause significant alterations in forest ecosystems, with greater effects on forests in arid and semi-arid areas.

Radial Growth of Two Dominant Montane Conifer Tree Species in Response to Climate Change in North-Central China

North-Central China is a region in which the air temperature has clearly increased for several decades. Picea meyeri and Larix principis-rupprechtii are the most dominant co-occurring tree species within the cold coniferous forest belt ranging vertically from 1800 m to 2800 m a.s.l. in this region. Based on a tree-ring analysis of 292 increment cores sampled from 146 trees at different elevations, this study aimed to examine if the radial growth of the two species in response to climate is similar, whether the responses are consistent along altitudinal gradients and which species might be favored in the future driven by the changing climate. The results indicated the following: (1) The two species grew in different rhythms at low and high elevation respectively; (2) Both species displayed inconsistent relationships between radial growth and climate data along altitudinal gradients. The correlation between radial growth and the monthly mean temperature in the spring or summer changed from negative at low elevation into positive at high elevation, whereas those between the radial growth and the total monthly precipitation displayed a change from positive into negative along the elevation gradient. These indicate the different influences of the horizontal climate and vertical mountainous climate on the radial growth of the two species; (3) The species-dependent different response to climate in radial growth appeared mainly in autumn of the previous year. The radial growth of L. principis-rupprechtii displayed negative responses both to temperature and to precipitation in the previous September, October or November, which was not observed in the radial growth of P. meyeri. (4) The radial growth of both species will tend to be increased at high elevation and limited at low elevation, and L. principis-rupprechtii might be more favored in the future, if the temperature keeps rising.