A ring-width series was used as a proxy to reconstruct
the past 414-year record of April–July minimum temperature at Laobai
Mountain, northeast China. The chronology was built using standard tree-ring
procedures for providing comparable information in this area while
preserving low-frequency signals. By analyzing the relationship between the
tree-ring chronology of Korean pine (
Global climate change presents major challenges for humans and the natural systems that provide ecosystem services. Consequently, it is urgent to better understand climate change and its forcing mechanisms. Instrumental records are typically less than 100 years and often less than 50 years in most areas of the world. It is necessary to put the present climate regime in the context of long-term perspectives, which forces a reliance on natural proxy records to reconstruct the past climate. Tree rings have been widely applied in global climate change studies and paleoclimate reconstructions on both regional and global scales because they offer accurate and continuous temporal record as well as being are widespread and easily replicated (Corona et al., 2010; Popa and Bouriaud, 2014; Kress et al., 2014).
Northeast China, an area sensitive to global climate change, is located in the ecotone from a temperate to cold temperate zone, belonging to a monsoon fringe area. Due to the interannual instability of monsoon, frequent climate extremes (especially cold damage or frost disaster) seriously affect agriculture and forest ecosystems. In addition, previous studies suggest that climate change in northeast China was also linked to the solar activities and global land–sea atmospheric circulation during certain pre-instrumental periods (Chen et al., 2006; Wang et al., 2011; Liu et al., 2013). It is generally accepted that the climate warms during periods of strong solar activity (e.g., the Medieval Warm Period) and cools during periods of low solar activity (e.g., the Little Ice Age; Lean and Rind, 1999; Bond et al., 2001). Recently, the warming in northeast China has been significantly affected by the global warming since the 20th century (Ding and Dai, 1994; Wang et al., 2004; Zhao et al., 2009), which is often caused by a faster rise in night or minimum temperature (Karl et al., 1993; Ren and Zhai, 1998; Tang et al., 2005). To explore whether climate warming is abnormal and predict the future trend of temperature change in this area, we must fully understand the history of climate changes over a long period. However, tree-ring series were rarely used to reconstruct past climate (especially temperature) in this area because of the exceptional hydrothermal conditions. Several temperature-sensitive tree-ring chronologies were developed on Changbai Mountain (e.g., Shao and Wu, 1997; Zhu et al., 2009; Wang et al., 2012; Li and Wang, 2013) and Xiaoxing'an Mountain (Yin et al., 2009; Zhu et al., 2015), but almost no records were obtained for a period of over 250 years, which can reflect the low-frequency climate variations. This limits our understanding of a longer timescale of climate regime in northeast China. Temperature reconstructions are also far from adequate and do not satisfy the demands of scientific research. Therefore, there is a requirement for higher-quality climate reconstructions in a greater number of areas over longer periods and a larger group of climatic indicators for verification in this region. For this reason, more information on regional past climate variations registered in a long-term tree-ring series is needed, and it is important to understand the impacts of climate change on forest ecosystems and the ecosystem services provided to humans in northeast China.
Map of the sampling site, the compared temperature series, nearby temperature series, and the meteorological station in northeast China. The photo shows the sampled site on Laobai Mountain and the remarkable vertical vegetation distribution along altitude changes.
Currently, a significant climate warming (especially the minimum temperature increase) is occurring in northeast China since the 1980s. However, there still remains a lack of long-term climatic records (at least more than 250 years) in this area to explore what is the temperature regime in the past one thousand or half a thousand years and whether the current warming is unprecedented. Therefore, the main objectives of this study are (1) to develop for the first time a more than 400-year ring-width chronology in northeast China; (2) to analyze the regime of temperature variation during the past 4 centuries in northeast China; (3) to identify the recent warming amplitude in a long-term context; and (4) to analyze the extreme low-temperature events. Our new minimum temperature record supplements existing data in northeast China and provides new evidence of past climate variability. There is the potential to better understand future climatic trajectories from these data in northeast China.
The study area is located at Laobai Mountain (128
This region belongs to a temperate continental monsoon climate. Climate data
are collected from the nearest meteorological station in Dunhua. The mean
annual temperature from 1956 to 2013 is 3.3
Major statistical characteristics for the chronology of
Mean monthly temperature (
Korean pine tree-ring samples were obtained from the south slope of Laobai Mountain along an elevational gradient from 950 to 1050 m from an almost pristine area containing well-preserved old forests largely uninfluenced by human activity. One or two cores per undamaged tree (71 cores from 41 trees) were extracted from cross-slope sides of the trunks at breast height using an increment borer. Cores were air dried, glued firmly to grooved wooden mounts and sanded with progressively finer grade abrasive paper up to 800 grit. Then the samples were cross-dated using a skeleton plot method (Stokes and Smiley, 1968); each tree-ring width was measured with a precision of 0.001 mm using the Velmex tree-ring width measurement system (Velmex, Inc., Bloomfield, NY, USA). Data were checked for missing or false rings and dating errors using the quality control program COFECHA (Holmes, 1983).
The ARSTAN program was used to detrend and standardize cross-dated tree-ring width series into a tree-ring chronology (Cook, 1985). During this detrending process, to remove biological factors (such as age-related trends) and non-climatic variations and preserve as much low-frequency signal as possible, each ring-width series was fitted with a straight line or negative exponential function. A 67 % cubic smoothing spline with a 50 % cutoff frequency was further used in a few cases when anomalous growth trends occurred. The detrended data from individual tree cores were then averaged using a bi-weight robust mean to develop the standard (std) and residual (RES) chronologies (Cook and Kairiukstis, 1990).
Variations of the std
Statistical characteristics for the std and RES chronologies of
Meteorological data were obtained from the National Meteorological
Information Center (
To identify climate–growth relationships of Korean pine on Laobai Mountain,
a Pearson's correlation was performed between climate variables and tree
growth. The stability and reliability of the reconstruction equation was
assessed by the split-period calibration and verification analyses (Fritts,
1976; Cook and Kairiukstis, 1990) for the two periods 1956–1984 and
1985–2013. The Pearson's correlation coefficient (
Correlation coefficients between the std chronology and the climate data of different month combinations during the common period of 1956–2013. Months are given as follows: c4–c7 – current April to July; c4–c8 – current April to August; c4–c9 – current April to September; c5–c7 – current May to July; c5–c8 – current May to August; c5–c9 – current May to September; c6–c8 – current June to August; c6–c9 – current June to September; p7–c8 – previous July to current August.
Correlations between the monthly mean meteorological data
(including mean temperature, mean maximum temperature, mean minimum
temperature, and total precipitation) from Dunhua meteorological station
(1956–2013) and
Relationships between the std and RES chronologies and monthly climate data
in Dunhua were shown in Fig. 4. Temperatures were more crucial to Korean
pine growth compared with precipitation. In contrast, the correlation
coefficients between Korean pine chronologies and mean minimum temperature
were positive and higher than those for maximum and mean temperature. The significant correlation months between std chronology
(Fig. 4a) and mean minimum temperature were not found in the RES chronology
(Fig. 4b). This indicated that the std chronology recorded the minimum
temperature signals in low frequency but not at high frequencies. Different
combinations of months were also considered (Table 2). The best-correlated
3-month season, April–July (
It was generally accepted that extreme temperatures limited tree growth at
the tree line or at high-latitude forests, especially spring or early summer
minimum temperature (Wilson and Luckman, 2002; Körner and Paulsen, 2004;
Porter et al., 2013; Yin et at., 2015). Moreover,
Interannual variation of the mean maximum
This may have two reasons. One, the sampling site was located at high elevations close to the upper limit of the Korean pine distribution, which may cause tree growth to be more sensitive to minimum temperature (Szeicz and MacDonald, 1995; D'Arrigo et al., 2009; Li et al., 2011; Yu et al., 2011; Flower and Smith, 2012). High minimum temperatures in the early growing season can inhibit frost damage and thus allow the formation of a wider ring (Wu, 1990; Akkemik, 2000; Mäkinen et al., 2003). High nighttime temperatures can also promote tree respiration and enhance physiological activities, thereby producing more auxin, promoting cell enlargement and forming a wider ring in growing season (Fritts et al., 1976). Increasing temperature may allow trees to conduct photosynthesis at the early stage of the growing season, which might produce more auxin. A crucial growth period of Korean pine in every year was from April to July. During this period, temperature could have direct effects on the photosynthesis rate, cambium activity, and respiration efficiency, etc., which affect the formation of ring width (Li et al., 2000; Yu et al., 2011). Therefore, Korean pine radial growth was positively correlated with the average minimum temperature from April to July.
Calibration and verification statistics of the reconstruction equation for the common period of 1956–2013.
Based on the above analysis, a linear regression equation was established to
reconstruct the April–July MMT. The transfer function was as follows:
The reconstructed average April–July MMT variations since AD 1600 and its
11-year moving average were shown in Fig. 6b. The 11-year moving average of
the reconstructed series was used to obtain low-frequency information and
analyze temperature variability in this region. The mean value of the 414-year
reconstructed temperature was 7.66
Cold and warm periods based on the 11-year moving average April–July mean minimum temperature on Laobai Mountain during AD 1600–2013.
To further evaluate the reliability of this reconstruction, we compared our
reconstruction series with two nearby tree-ring-based reconstruction
temperature series from Dunhua (Li and Wang, 2013; Fig. 7a) and Changbai
Mountain (Zhu et al., 2009; Fig. 7b) and the Northern Hemisphere temperature
reconstruction (D'Arrigo et al., 2006; Fig. 7d). Interestingly, a
significant negative correlation (
It was widely believed that the LIA in China exhibited three cold periods in the 15th, 17th, and 19th centuries (Wang et al., 2003), and this was confirmed by our reconstruction series (Fig. 7c and Table 4). The first cold period in our series was less obvious, while the second one was the most obvious of all. A different beginning and ending year of the second cold period in our reconstruction was found (Fig. 7c and Table 4). In addition, there existed a regional difference for the third cold period, that is, it was obvious in south China, while had the opposite phase in northeast China (Wang et al., 1998; Wang et al., 2003). The third cold period in 19th century was not obvious in our reconstruction, which was consistent with Wu (2013) and Wang et al. (1998). This also led to a bad match with the Northern Hemisphere temperature (D'Arrigo et al., 2006). Another notable feature in Fig. 7 was a sharp temperature increase since the 1980s, and temperature rose to a peak in the early 2000s. The temperature increase in this area was consistent with the report from the Intergovernmental Panel on Climate Change (IPCC, 2007). This series displayed similar patterns of low-frequency variations suggesting that the reconstructed temperature in northeast China was significantly correlated with large-scale variations (Fig. 7).
Cold damage or frost disaster events recorded in historical archives in Heilongjiang Province since 1675 (Sun et al., 2007).
Unfortunately, three compared temperature series also showed dissimilar variations in some cold and warm years (Fig. 7). This might be due to differences in reconstructed temperature months, parameters (such as mean, minimum, and maximum temperature), and habitat conditions in different sampling areas. Recent studies suggested that the mean, minimum, and maximum temperature variations were often asymmetric (Karl et al., 1993; Xie and Cao, 1996; Wilson and Luckman, 2002, 2003; Gou et al., 2008). Global warming over the past decades was mostly owing to the faster rise of night or minimum temperatures but not maximum temperature. The unsynchronized variability among mean, minimum, and maximum temperatures was found at Dunhua meteorological station (Fig. 5). The sampled site was located at a border zone between Jilin and Heilongjiang provinces, further north than Changbai Mountain. Meanwhile, some differences in the reconstructed temperature series were explained reasonably well from the comparison with analogous regions. Consequently, these findings could reveal more characteristics of regional climate variations and provide reliable data for larger-scale climate reconstructions in northeast China.
As the minimum temperature approached or fell below the freezing point, it may have limited biological activity and growth. Therefore, years with low temperatures were often accompanied by cold damage or severe frost events. The evidence from historical documents (Sun et al., 2007) showed that cold damage or frost disaster events have occurred in Heilongjiang Province since 1675 (Table 5). Extremely cold damage or frost disaster events were in good agreement with eight low-temperature years (1675, 1682, 1689, 1699, 1730, 1748, 1812, and 1885 in Fig. 6b and Table 4) in reconstructed April–July MMT series during the 1600s–1800s. At the beginning of 20th century, three severe frost periods occurred in the periods 1909–1918, 1934–1945, and 1956–1972 in Heilongjiang Province (Sun et al., 2007) and were represented in our reconstruction (Fig. 6b and Table 4). In addition, other low-temperature years in our reconstruction corresponded to extreme frost disaster events occurred in the periods 1902–1903, 1912–1914, 1920, 1932, 1934–1936, 1940, 1947, 1956–1961, 1964–1965, 1967, and 1969 (Fig. 6b and Table 4). The results revealed that 27 of the 30 cold damage or frost disaster events corresponded to the April–July MMT lower than the 27-year moving average, while the remaining three events corresponded to higher than April–July MMT values. In contrast, we found a decreasing trend in the annual extreme low-temperature frequency and cold damage or severe frost events with the warming since the 1980s. In summary, the reconstructed April–July MMT on Laobai Mountain strongly revealed the cold damage or frost disaster events in the past 414 years.
A significant positive correlation between the tree-ring width of Korean pine and the April–July MMT was found on Laobai Mountain, northeast China, and the April–July MMT was reconstructed for the past 414 years (1600–2013). The reconstructed and instrumental temperature series exhibited coherence over the common periods. The reconstructed series showed interannual to multidecadal temperature variations over the past 414 years. The cold and warm periods of the reconstructed minimum temperature record were also observed in historical documents and several proxy temperature records in northeast China. The most notable feature of the reconstructed series was obviously a rapid warming trend since the 1980s, which was also confirmed by other reconstructed temperature series. Additionally, the correspondence between the low-temperature years and the historical cold damage or severe frost events demonstrated the potential relationship between April and July MMT and extreme cold events. This temperature record may provide new and valuable information for the longest temperature variation period in northeast China.
The April–July minimum reconstruction on Laobai Mountain will be available
in the Supplement of the original publication
(
This research was supported by the National Natural Science Foundation of China (nos. 41471168 and 31370463), the Key Project of the Special Focus on “Global Change and Mitigation” of the China National Key Research and Development Plan (2016YFA0600800), the Program for Changjiang Scholars and Innovative Research Team in University (IRT-15R09), and the Program for New Century Excellent Talents in University (NCET-12-0810). We greatly appreciate the three anonymous referees for their constructive and helpful comments in revising and improving our manuscript a lot. We thank the staff of Laobai Mountain Forestry Bureaus for their assistance in the field. Meanwhile, we greatly appreciate Neil Pederson at Harvard Forest, Harvard University, for his assistance in English-language editing of parts of the paper. Edited by: J. Guiot Reviewed by: three anonymous referees