Manyu Dong

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.

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.

Early monsoon failure and mid-summer dryness induces growth cessation of lower range margin Picea crassifolia

Key messageThe frequency of stem-growth cessation in Picea crassifolia has increased significantly as the frequency of extreme climate events has increased.AbstractExtreme climatic events are increasingly recognized as important drivers of tree growth, forest dynamics, and range contractions. Understanding tree growth responses to extreme events is important for forest conservation and management, especially under climate change. Here, we studied the patterns of growth cessation of Picea crassifolia Kom., an endemic species to Central Asia, across its distributional range in the Helan Mountains of Northwestern China, to test the hypotheses that (1) tree growth and growth cessations are limited by moisture availability, and (2) that this relationship is constant over the diverse set of conditions covered in our elevational gradient. While tree growth across our gradient was significantly limited by low precipitation in June, we found growth cessation events at the lower distributional margin to increase in severity and frequency in recent decades. We found that the combination of low precipitation early in the monsoon season (June) and high mid-summer (July) vapor pressure deficit likely caused the increased frequency of growth cessation events. Because these populations are already experiencing a high frequency of growth cessation events, the mortality rate of the lower distributional margin trees could further increase if the current trends of decreasing moisture and increasing heat stress continue into the future. Our results strongly suggest that growth cessation events are more than the dendrochronological curiosity they are usually considered to be, and can be important indicators of increased tree growth stress and be potentially useful in identifying tipping points prior to forest change.

Stem Radial Growth Features of Picea meyeri Responding to Environmental Factors at the Treeline of Luya Mountain

The Stem Radial Growth (SRG) was measured by dendrometer from 6 sample trees of Picea meyeri at the tree-line of Luya Mountain, North China, combined with synchronized instrumental observation and measurement of habitat temperature, moisture, etc., from July the 15 th to August the 7 th (summer phase) and from September the 5 th to October the 9 th (autumn phase) in 2007. The preliminary analytic results were as follows: 1) the diameter of stems varied on sunny days with a daily fluctuation but steadily widened, while on rainy days it continuously increased during the rain but shrank rapidly after the rain. 2) The SRG pattern in both phases was fitted with a quadratic curve, showing a positive value in summer phase; whereas declining to a negative figure in the first stage of autumn phase --early September, and then kept as a constant zero from middle September on. 3) The distance analysis showed a relative warmer and moister environment was suitable for the growth of Picea meyeri in autumn phase, whereas an environment with a high relative humidity (RH) in the air and moisture in the soil was suitable in summer phase. Thus the water regime was the controlling factor for Picea meyeri growth on treeline of Luya Mountain.