Divergence in responses of juniper tree rings to climate conditions along a high-mountain transect in the semi-arid Fann Mountains, Pamir-Alay, western Tajikistan

Abstract

This paper reports on a detailed dendrochronological and dendroclimatological study of juniper trees (Juniperus seravschanica Kom. and J. semiglobosa Regel), sampled at seven sites having different elevations (2200 – 3100 m) and exposures (south-north) in the Pamir-Alay mountains, north-western Tajikistan. We developed seven new, well-replicated ring-width chronologies extending back over the last 219–1320 years. Our results confirm that the main climate factor influencing radial growth in this semi-arid region is variability in precipitation. However, they also indicate that there is a divergence in dendroclimatic responses between low- and high-elevation sites, where different limiting factors play a dominant role. The radial growth of J. semiglobosa at the uppermost treeline locations is the most sensitive to winter precipitation. Tree-ring formation in J. seravschanica at low-elevation sites is strongly limited by spring-summer drought conditions and by winter temperatures. The results of PCA analysis indicate that the relationships between growth and climate are linked more to elevation than to exposure. It was also found that negative growth extremes at low elevation sites may be triggered by strong dust storm events. Our findings clearly show that precisely planned selections of topographically differentiated sites, including elevation and exposure, are crucial for the possible reconstruction of different climatic elements in the high mountains of Central Asia for the last hundreds to thousands of years.