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Questions: Sand storms from east Inner Mongolia are a major threat to the ecological safety of North China and actions are desirable to control further desertification. Small patches of relict Pinus tabulaeformis could play a major role in this. The climate signal recorded in the tree-ring widths and the dates of past regeneration episodes of these trees growing at the northern border of their natural distribution are considered here.

Location: Ortindag Sand Land in North China.

Methods: We collected increment cores from relict P. tabulaeformis trees at five sites, built a standard tree-ring chronology for each site and a regional tree- ring chronology from the three longest site chronologies, analysed the tree growth/climate relationships and determined the germination years of the trees to recognize past regeneration dynamics.

Results: Monthly precipitation and relative air humidity in the previous and current growing seasons are the major limiting factors for the radial growth of P. tabulaeformis. Years with a high frequency of absent tree rings are characterized by particularly extreme dry conditions. These results are supported by negative correlations between radial growth and monthly maximum temperature and evaporation during the growing season. In a 163-year time series of precipitation from previous July to current June reconstructed from the tree rings, cycles with wave lengths of 2-3, 17.4 and 20.5 years are significant.

Conclusion: P. tabulaeformis trees are reliable recorders of high and low frequency variations of dry/wet environmental conditions in the Ortindag Sand Land. Their age structures within the forest patches prove that they regenerate preferen-they regenerate preferen-preferentially in less dry periods.