A July–August Mean-Temperature Dataset Reconstructed based on the Maximum Latewood Density of Hailar Pine in the North Greater Khingan Mountains (1781–2013)

Li, M. Q.^1*  Lan, Y.²

1. Key Laboratory of Land Pattern and Simulation, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China;

2. Guangdong Meteorological Observatory, Guangdong, Guangzhou 510640, China

Abstract: Tree-ring cores (10 mm) of Hailar pine (Pinus sylvestris var. mongolica) were collected at the upper tree lines (51.79??N, 123.08??E, 950 m a.s.l.) from the Huzhong National Nature Reserve in the north Greater Khingan Mountains in September 2013. The maximum latewood density (MXD) was obtained using a DENDRO 2003 densimeter and an MXD chronology was developed. A correlation analysis was carried out between the MXD chronology and climate variables from the Mohe meteorological station, and the strongest correlation was found with the July–August mean temperature. Therefore, the July–August mean temperature was reconstructed back to 1781 A.D. for the north Greater Khingan Mountains. The reconstruction explained 31.1% of the variance in the instrumental period (1959–2013 A.D.). The dataset includes: (1) the geolocation of the sampling site; (2) tree-ring MXD standard chronology; (3) reconstructed July–August temperature series from 1781 to 2013 in the north Greater Khingan Mountains and 11-year smoothing-average data; (4) statistics of 39 raw tree-ring MXD measurements. The dataset is archived in .shp and .xlsx data formats, and it consists of nine data files with a total size of 27.2 KB (this is compressed to one single file with a size of 24 KB).

Keywords: tree rings; maximum latewood density; North Greater Khingan Mountains; temperature reconstruction

DOI: https://doi.org/10.3974/geodp.2022.03.09

CSTR: https://cstr.escience.org.cn/CSTR:20146.14.2022.03.09

Dataset Availability Statement:

The dataset supporting this paper was published and is accessible through the Digital Journal of Global Change Data Repository at: https://doi.org/10.3974/geodb.2022.04.02.V1 or https://cstr.escience.org.cn/CSTR:20146.11.2022.04.02.V1.

1 Introduction

Tree-ring is an important proxy for studying paleoclimate due to its accurate dating, high resolution, wide distribution, and good replication^[1]. It is playing an important role in reconstructing temperature^[2], precipitation, and dry/wet variations^[3–5] on centennial to millennial timescales. Among the tree-ring data used for climate reconstruction, the maximum latewood density (MXD) is a well-known proxy for summer or early-fall temperatures^[6–9]. Northeast China is one of the three major forest areas in China, and it has an area of more than 30 million hectares^[10]. In addition, it is a major agricultural region, and its production of grain was 20.26% of the national total in 2018^[11]. Temperature is an important factor affecting agriculture and forest production. Therefore, studying historical temperature variations and exploring the regular pattern of climate change in Northeast China is of great significance for guiding agricultural and forestry production.

MXD data have been used for studying temperature variations in the Greater Khingan Mountains^[12]. However, there have been few MXD-based reconstructions, and the reconstruction span in our study area is currently less than 200 years. The purpose of this study was thus to reconstruct a 233-year temperature record based on MXD standard chronology from Pinus sylvestris var. mongolica in the north Greater Khingan Mountains, Northeast China (Figure 1 and Table 1). This will provide basic data for predicting future climate-change scenarios and for guiding agriculture and forest production.

Table 1  Location of sampling site

Figure 1  Map showing the locations of the sampling site and the meteorological station

2 Metadata of the Dataset

The metadata of the Reconstruction dataset of yearly July-August mean temperature from tree-ring maximum latewood density of Pinus sylvestris var. mongolica at North Greater Khingan Mountains (1781-2013) is summarized in Table 2^[13]. It includes the dataset full name, short name, authors, year of the dataset, temporal resolution, data format, data size, data files, data publisher, and data sharing policy, etc.

3 Methods

3.1 The MXD Chronology Development and Temperature Reconstruction

The MXD standard chronology was developed using the ARSTAN software package. Each MXD series of tree-ring measurements was fitted with an 80 cubic smoothing spline to remove the non-climatic trends^[15]. Each detrended index series was calculated as the ratio of the tree-ring value to the corresponding spline curve value of a given year, by which the densitometry series were transformed to dimensionless time series. All index series of tree-ring data from the site were then averaged to form a mean MXD chronology using a bi-weight robust mean value function^[16].

To investigate the tree-growth–climate relationship, we calculated Pearson??s correlation coefficients between the MXD standard chronology (x) and climatic variables (y) (monthly mean temperature and monthly precipitation) from the Mohe meteorological station during the instrumental period of 1959–2013. The results indicated that the July–August mean temperature is the major factor limiting tree growth. The correlation coefficients (r) were calculated using the equation:

                                                                                                     (1)

where ?? is the standard error.

Based on the tree-growth–climate relationship, a linear regression produced a transfer function between the MXD standard chronology (MXD) and the July–August mean temperature (T_mean7–8). We then reconstructed the regional temperature series. The following equation was used for this calculation:

         T_mean7−8 = aMXD + b                            (2)

where a and b are constants.

3.2 Data Collection and Processing

We collected 61 tree-ring cores from 28 Pinus sylvestris var. mongolica trees at the study site (51.79??N, 123.08??E, 950 m a.s.l.) in Huzhong National Nature Reserve from the north Greater Khingan Mountains in September 2013. In the tree-ring laboratory of the Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, all cores were carefully cross-dated after air drying and sanding; we selected 39 tree-ring cores from 22 trees for temperature reconstruction. The tree-ring widths were measured using LinTab, and the tree-ring density data were measured using a DENDRO 2003 densimeter. We then developed the MXD chronology based on this tree-ring density data. In addition, we also collected the instrumental data from the Mohe meteorological station[1] and analyzed the correlations between these data and the MXD chronology to find the major limiting factor for MXD in Pinus sylvestris var. mongolica. Based on the tree-growth–climate relationship, we reconstructed the past temperature series in our study area. A flowchart for this process is shown in Figure 2.

4 Data Results and Validation

4.1 Data Composition

The dataset comprises the following parts: (1) the geolocation of the sampling site; (2) statistics

Table 2  Metadata summary of the Reconstruction dataset of yearly July-August mean temperature from tree-ring maximum latewood density of Pinus sylvestris var. mongolica at North Greater Khingan Mountains (1781-2013)

of 39 raw tree-ring MXD measurements (Table 3); (3) tree-ring MXD st­a­n­dard chronology (Figure 3); (4) rec­o_­nstructed July–August temperature from 1781 to 2013 in North Greater Kh­ingan Mountains and 11-year smo­othing-average data (Figure 4).

4.2 Data Products and Validation

The MXD standard chronology covers the period 1722–2013 A.D. (Figure 3). The period 1901–2000 A.D., as common period, was analyzed when we developed the MXD standard chronology. The mean inter-series correlation coefficient is 0.408, the mean correlation coefficients within trees and between trees are 0.560 and 0.406, respectively. The signal-to-noise ratio is 22.09. In addition, the expressed population signal is 0.957. These statistics are similar to those of other tree-ring chronologies in our study area^[12], and the results indicate that the chronology can be used for

Table 3  Statistics of 39 raw tree-ring MXD measurements

paleoclimate analysis. The subsample signal strength exceeded 0.85 in 1781 with seven cores. Therefore, we considered 1781 as the beginning year for reconstruction.

Based on the relationships between the MXD chronology and climate variables, we reconstructed the July–August mean temperature during the period 1781–2013 A.D. in the north Greater Khingan mountains (Figure 4). The transfer function is T_mean7–8 = 3.46MXD + 13.5, and the model explained 31.1% of the variance in July–August mean temperature with good ??leave-one-out?? cross-validation results during the instrumental period 1959–2013. The sign test result was statistically significant at the 0.01 level for the original data. The value of the reduction of error (RE) and product mean t-test results were found to be high, suggesting good estimation ability, with the correlation as 0.52 (n = 55, p < 0.01). Split-period validations were also conducted. The calibration periods were set to be 1959–1988 and 1984–2013, and the validation periods were 1989–2013 and 1959–1983, respectively. The results showed that RE (0.279 and 0.319) and the coefficient of error (0.278 and 0.315) were above zero, although the sign-test result was just statistically significant at the 0.01 level for the original data for the calibration period 1959–1988. Furthermore, the correlation coefficients between the reconstructed series and the instrumental data were 0.59 and 0.58 for the validation periods 1989–2013 and 1959–1983. The validation results suggest that the model is relatively robust with sufficient skills of estimation, and the MXD standard chronology can thus be used for regional climate reconstruction.

5 Discussion and Conclusion

In this study, we obtained tree-ring density data and developed an MXD chronology based on incremental cores collected from Pinus sylvestris var. mongolica on the Huzhong National Nature Reserve in the north Greater Khingan Mountains, Northeast China. Based on the relationship between the MXD chronology and climate variables, we reconstructed the July–August mean temperature for a period of 233 years in our study area, covering 1781–2013 A.D. with a temporal resolution of one year. This study increases the number and spatial distribution of climate-reconstruction sites. It also provides base data for understanding past climate change, exploring the regular pattern of climate change, and predicting future climate-change scenarios.

Author Contributions

Li, M. Q. designed the algorithms for the dataset. Li, M. Q. and Lan, Y. contributed to the data processing and analysis. Li, M. Q. wrote the manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

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