Xiaochun Wang

Temperature signals in tree-ring width and divergent growth of Korean pine response to recent climate warming in northeast Asia

Key messageTemperature is a major limiting factor of Pinus koraiensis radial growth, while which exhibited various growth responses at different sites of its distribution area to recent climate warming.AbstractSix Korean pine (Pinus koraiensis) tree-ring chronologies were developed in northeast Asia. Growth trends in recent decades were compared and main factors limiting growth were identified within each site. The spatio-temporal stability of climate–growth relationships were also tested for important climate variables. Results showed that temperature played a key role in controlling Korean pine growth, while recent growth showed strong geographic patterns. Tree growth in recent decades at two south and high altitude sites increased with temperature, remained constant for two low-altitude sites at its central distribution, and decreased for two moderately altitude sites at its distribution north margin. Tree-ring principle of the ecological amplitude was proved again, i.e., trees growing near the margin of its natural range has higher climate sensitivity. Drought stress due to temperature increases appeared to be a primary reason for Korean pine growth decline, whereas varying degrees of drought stress were distinctly dependent on site conditions. Variation of climate-growth relationships over time for different sites was consistent with their recent growth. Two average chronologies for six sites revealed a decreased (Heihe, Mudanjiang, and Liangshui) or inverse (Dunhua, WPS, and Wuying) growth response to rapid warming since 1980, which was possibly related to unique site conditions and various large-scale climate impacts. In addition, our results indicated that modeling possible reactions of forest to global warming or reconstructing past climate need to consider diverse spatio-temporal variations of climate-growth relationships of Korean pine in northeast Asia.

Roots of forbs sense climate fluctuations in the semi-arid Loess Plateau: Herb-chronology based analysis

Growth of herbaceous plants responds sensitively and rapidly to climate variability. Yet, little is known regarding how climate warming influences the growth of herbaceous plants, particularly in semi-arid sites. This contrasts with widely reported tree growth decline and even mortality in response to severe water deficits due to climate warming around the world. Here, we use the relatively novel approach of herb-chronology to analyze the correlation between climatic factors and annual ring width in the root xylem of two perennial forb species (Medicago sativa, Potentilla chinensis) in the Loess Plateau of China. We show that warming-induced water deficit has a significant negative effect on the growth of herbaceous plants in the Loess Plateau. Our results indicate that the growth of forbs responds rapidly and sensitively to drought variability, implying that water availability plays a dominant role in regulating the growth of herbaceous plants in semi-arid areas. If warming and drying in the Loess Plateau continue in the future, further affects the growth of herbaceous plants, potentially driving regional changes in the relationship between herbaceous vegetation and climate.

Recent rising temperatures drive younger and southern Korean pine growth decline

The Earth has experienced an unequivocal warming, with the warmest period of the past 150 years occurring in the last three decades. Korean pine (Pinus koraiensis), a key tree species in northeast Asia, is predicted to be particularly vulnerable to climate change. Here, we use dendrochronological methods to test whether the observed growth decline of Korean pine in northeast China is related to climate warming and whether climate-growth responses varied with age. A total of 628 cores from 401 trees across 16 sites were sampled over the entire distribution area of Korean pine in China. Samples were divided into three age classes: younger (50-130 years), middle (131-210 years), and older trees (>210 years), and measured by the ring-width index and basal area increment (BAI). Results showed a significant decline in BAI in most sites coinciding with an increase of temperature in the growing season and a decrease in precipitation since the 1980s. Meanwhile, we found that temperature-induced growth decline was significantly related to tree age. The BAI of younger trees decreased significantly and sharply (0.44 cm2 year-1, P < 0.0001), while old trees either decreased slightly or stabilized (0.04 cm2 year-1, P = 0.33). Tree growth in the southernmost locations was more likely to decline, what was most likely a result of forest-stand age. The age-related growth decline induced by climate warming might be explained by tree species traits, differences in growth rates between age classes and their relation to stress, changes in root system, competition/stand structure or physiological mechanisms. Our results might also predict that early stand process-thinning is exacerbated by warming and drying. This research informs that the age effect of growth response to rising temperature should be considered in forest management under climate change, and particularly models of future carbon cycle patterns and forest dynamics.

Spatial Variability in Growth‐Climate Relationships of Amur Cork Tree (Phellodendron amurense) and Their Connections With PDO in Northeast China

We used a dendrochronological approach to identify the spatial variability in growth-climate relationships of Amur cork tree (Phellodendron amurense), using a network of 12 sites across its natural range in Northeast China. Results showed that the signal-noise ratio, expressed population signal, and mean interseries correlations of the site chronologies decreased significantly with decreasing latitude. Correlation matrix, cluster, and rotated empirical orthogonal function (EOF) analysis all indicated that the 12 chronologies can be classified into two groups, the southern and northern chronologies. Minimum temperature (Tmin) was a major factor limiting Amur cork tree growth at regional scales. Almost all sites had positive correlations with monthly temperature, while correlation coefficients with precipitation were much lower than minimum temperature correlations, and only a few months (January, April, and July) were significant (p < 0.05). The positive effects of summer Tmin on tree growth were significantly decreased with increasing latitude (except BSL site), while positive effects of summer precipitation increased significantly with latitude and longitude and decreased significantly with altitude. The southern nine site chronologies (EOF-1) were significantly positively correlated with the seasonal or annual Pacific Decadal Oscillation (PDO) index of the previous year and the current spring, while the northern three chronologies (EOF-2) showed different relationships, which is consistent with the spatial relationship between PDO and local temperature. The spatial variability in growth-climate relationships of Amur cork tree can be affected by PDO, which can modulate the spatiotemporal variation of spring onset, autumn termination, and the effective accumulated temperature by affecting local temperature.

Evaluation of Tree Growth Relevant Atmospheric Circulation Patterns for Geopotential Height Field Reconstructions for Asia

AbstractAtmospheric circulations influence local and regional weather conditions and, thus, tree growth. To identify summer weather types relevant for tree growth, and their associated synoptic-sca...