Assessing the stability of radial growth responses to climate change by two dominant conifer trees species in the Tianshan Mountains, northwest China
Introduction
Global climate change is one of the serious challenges facing mankind today, and it is associated with marked spatiotemporal variations in temperature and precipitation (Hoerling et al., 2012). On a temporal scale, the average surface temperature over the last 30 years has been higher than at any time since 1850 and likely in the past 1400 years; on a spatial scale, global warming patterns are not uniform in different regions, and the highest temperature increases are in the middle-high latitudes of the northern hemisphere (IPCC, 2013). The characteristics of climate change also significantly differ; for example, there has been strong climatic change from warm-dry to warm-wet in northwest China in the hinterland of the Eurasian continent. In addition, there has been an increase in temperature and precipitation over the past 50 years, most notably in areas of Xinjiang (Shi et al., 2007). Global climate warming has had profound effects on forest ecological systems, including causing changes in the composition and function of forests, affecting the growth and development of trees, and reducing carbon assimilation over wide regions (Engelbrecht, 2012). Moreover, all types of forests have shown differential ecological responsiveness to climate change (Sánchez-Salguero et al., 2017).
Tree-ring formation as a reliable indicator of climate effect have been used a technique to explore the forest ecosystem capacity to adapt to climate change (Boden et al., 2014). However, the latest researches provided valuable insights in trees complex respond processes to climate and challenged the ‘the uniformity principle’ of traditional dendroclimatology emphasized the linear stable growth-climate relationship (D'Arrigo et al., 2008, Fritts, 1976). Meanwhile, the results on the instabilities of radial growth responses to climate change were much more complex. The unstable responses have been mainly observed in the high latitudes or high elevations of the northern hemisphere, while these have also been found in the middle-low latitudes and elevations in fewer studies (Briffa et al., 2004, White et al., 2014). For different tree species, the observations were inconsistent. Picea engelmannii and Abies lasiocarpa in Jasper National Park of Canada; Pinus nigra, Pinus sylvestris and Abies alba in the mountainous regions of the Mediterranean; Pinus sibirica, P. sylvestris and Larix sibirica in north-central Mongolia; and Pinus tabulaeformis and Sabina przewalskii in northwest China have been verified as having divergent responses (Zhang et al., 2009, De Grandpre et al., 2011, Lebourgeois et al., 2012, Hart and Laroque, 2013, Zhuang et al., 2017). However, Larix decidua in the European Alps; P. nigra, P. sylvestris and A. alba in the mountainous regions of the Mediterranean; and Picea crassifolia sites in the mid-latitudes of northwest China exhibited relatively stable responses to the limiting climate factors (Büntgen et al., 2008, Zhang et al., 2009, Lebourgeois et al., 2012, Hou et al., 2016).
It is very important to accurately predict the changes in forest ecological systems, but the effects of global climate warming on growth patterns and productivity might differ between forest types and tree species (Camarero et al., 2015). Despite an increase in temperature over the last decades, the increased growth of A. alba and the strong decline in growth of Picea abies and Fagus sylvatica were evident in European forests with the three co-occurring species (Castagneri et al., 2014, Bosela et al., 2017); based on the VS-Lite model, growth reductions and an increase in the vulnerability of Abies durangensis and Picea chihuahuana were predicted after the 2050s, whereas Cupressus lusitanica growth showed very low sensitivity to future warmer and drier climatic conditions in northern Mexico (Pompa-García et al., 2017).
Forest ecosystems in arid and semiarid regions have been affected more seriously by climate change because the trees close to their drought limit would be particularly sensitive and vulnerable (Jiao et al., 2017). The Tianshan Mountains are the largest mountain range in central Asia and the source of water resources for arid inland rivers, functioning as the main support of arid oases and social development (Chen and Yuan, 2016). Despite the fact that a large number of tree-ring studies have been carried out in the Tianshan Mountains since the 1960s, they mainly focused on historical climate reconstruction and the linear growth-climate relationship (Zhang et al., 2016). There is a lack of research on the response of ecological mechanisms and their stability to climate change. In particular, the mixed larch-spruce forests represent an important forest ecosystem that forms an essential part of the eastern Tianshan Mountains, but studies comparing the growth-climate relationship stabilities between the two co-occurring species have not been conducted to date. Meanwhile, the climate shift from warm-dry to warm-wet has provided a good opportunity to further investigate the effects of the climate on forest ecosystems in Xinjiang of northwest China. However, the vegetation coverage in northern Xinjiang has increased since the 1980s based on remote sensing data, but the trend in tree growth of the Asian inland arid areas, such as the Tianshan Mountains, decreased significantly after the 1990s according to tree-ring data (Piao et al., 2005, Liu et al., 2013). As a result, there is still a high degree of uncertainty about the spatiotemporal dynamic patterns between different coniferous tree species linked to regional climate transformation in the Tianshan Mountains.
The strategies and adjustments of forest management should depend on detailed information on the responses of different tree species to climate change. Therefore, we choose an area with greater drought in the eastern Tianshan Mountains as the study area and compared differences in responses and growth dynamics of two co-occurring species, Siberian larch (L. sibirica) and Schrenk spruce (Picea schrenkiana), to climate change. The objectives of this study were (1) to identify the dominant climate factors restricting the radial growth of Siberian larch and Schrenk spruce; (2) to assess the responses and temporal stability of radial growth for the two tree species to climate change; and (3) to compare differences in the radial growth trends of the two species under the climate transition.
Section snippets
Study area and climate
The study area is located on the northern slopes of the eastern Tianshan Mountains in northwest China (Fig. 1). The regional climate is strongly shaped by drought from the central Asian westerly circulation (Xu et al., 2014). Mean monthly temperatures (1960–2012) from meteorological records of the Barkol station (43°36′ N, 93°03′ E, 1677 m a.s.l.) ranged from −17.6 °C in January to 18.1 °C in July, and precipitation peaked in the spring and summer, accounting for 70% of annual rainfall (Fig. 2
Tree-ring chronology characteristics
Tree-ring chronology characteristics of Siberian larch and Schrenk spruce are shown in Table 2. The higher value of SNRs and values of EPSs of more than 0.85 indicated the higher quality and greater climate information of the two development tree-ring chronologies. The values of MS, SD and PC1 of blk(P) (MS: 0.318, SD: 0.312, PC1: 0.587) were higher than for blk(L) (MS: 0.223, SD: 0.190, PC1: 0.453), suggesting that Schrenk spruce was more sensitive than Siberian larch to climate. Comparing the
The effect of climate change on the response stability of different trees
Tree rings are the most valuable and the most widely used material to substitute for data of climate measurements at the millennium-scale, but the unstable response of radial growth to climate is also a challenge to the application of traditional dendrochronology theory (D'Arrigo et al., 2008). Therefore, it is also necessary to conduct verification studies over larger areas and with more tree species.
There were significant differences in the response stability of Siberian larch and Schrenk
Conclusion
The two dominant conifers trees species, Siberian larch and Schrenk spruce, have exhibited different responses of temporal stability and radial growth patterns since the 1960s under the same climate change conditions. Results suggest the responses stability assessment of radial growth to climate change should be considered when reconstruction history climate and simulation forest development trend. The radial growth of Siberian larch was found to have an unstable response to the main limiting
Acknowledgements
This research was supported by the National Natural Science Foundation of China (Projects No. 41630750, 41771051 and 41861006) and the Scientific Research Program of Higher Education Institutions of Gansu Province (2018C-02). We especially thank Xiaolong Shang for sampling work in the field. We are grateful to Yiping Zhang and Yan Wen for their assistance in data analysis and laboratory work. We also thank the anonymous referees for helpful comments on the manuscript.
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