Xianliang Zhang

The effect of anthropogenic activities on the reduction of urban tree sensitivity to climatic change: dendrochronological evidence from Chinese pine in Shenyang city

To understand how urban tree growth has responded to the accelerating expansion in population and urbanization, an understanding of the tree-climate–urban ecosystem relationship is necessary. To this end, a metropolitan, suburban, and rural forest stand in and near Shenyang; and a rural forest stand in Weichang, were sampled in southern Northeast China. Radial growth variability of 109 Chinese pines (Pinus tabulaeformis Carr.), established before 1900 within and around the city, was measured. The contents of trace elements in tree rings were also examined to detect the possible relationship to urban environmental contamination. All sampled trees crossdated well, indicating a homogeneous common influence of regional climate. For the common period of 1901–2000, the radial growth of all trees was significantly affected by local and regional climate, especially temperature and precipitation in winter and spring, respectively. From the rural to the metropolitan areas, a significant decreasing relationship in the response of trees to climatic factors was detected. These decreases occurred over time and in tree stands within the same location or between different sites, and also corresponded with the increasing influence of local urbanization and industrialization on the urban environment during the last century. Particularly strong influences are the increase of population, urban built-up area, and urban agricultural and industrial activities. Decreases in mean sensitivity of Chinese pines were also found and are most likely related to the intensification of anthropogenic activities and environmental change. Based on tree-ring width growth in rural areas, a growth pattern of urban trees without anthropogenic disturbances was established. After removing the climate-related signals from actual urban tree growth, the impact of anthropogenic disturbances was chronologically developed. The results indicate that the periods of heaviest disturbances occurred from 1914 to 1922, 1932 to 1935, 1943 to 1946, 1955 to 1969, and 1973 to 2000.

Reconstruction of the regional summer ground surface temperature in the permafrost region of Northeast China from 1587 to 2008

To extend the historical temperature record in the permafrost region of Northeast China, we reconstruct the regional ground surface temperature (GST) for the past four centuries based on a network of Dahurian larch (Larix gmelinii Rupr.) tree-ring width chronologies. Seven standard tree-ring chronologies, which correlate well with each other, are averaged to create a regional mean chronology. GST is the major limiting factor for tree growth in this region. The optimum range of GSTs is from 30 May to 26 August (summer GST), identified by combining the days on which tree growth was strongly influenced by the daily GST data. The summer GST was significantly correlated with the regional mean chronology (r = 0.704, p < 0.001) over the common period 1971–2008 and was reconstructed for the period 1587–2008. The reconstructed GST accounts for 49.4% of the actual variance in the GST over the period 1971–2008 and captures four warm periods (1597–1603, 1716–1723, 1781–1788, and 1925–1929) and three cold periods (1639–1647, 1686–1711, and 1799–1805). The reconstructed GST is consistent with the northern hemisphere temperature in the Little Ice Age, and the warming rate from 1857 to 2008 is similar to a previously reported temperature reconstruction in the Xiao Xing’an Mountains. The low frequency of the reconstructed GST is well matched with that of the permafrost thawing depth. The reconstructed GST represents the longest temperature record in this study region and may be used as a reference for the permafrost thawing depth.