Relationships between tree increment, climate and above-ground biomass of grass: a case study in the typical steppe, north China

Meyer spruce (Picea meyeri Rehd. et Wils.) is a relict conifer, and Chinese leymus (Leymus chinensis [Trin.] Tzvel.) is a dominant grass in typical steppe of the Xilin River Basin, northern China. Herein, we evaluated the relationships between tree-ring width index of Meyer spruce, climate and above-ground biomass of Chinese leymus, and reconstructed above-ground biomass of Chinese leymus from 1955 to 1994 using tree rings. Both Meyer spruce and Chinese leymus exhibited significant positive (P < 0.05) growth response to May precipitation during the current growing season. In addition, the growth of Chinese leymus was significantly correlated (P < 0.05) with the sum of current July and August precipitation. Two predominant linear relationships between ring width and annual grass production were found, and each corresponding to different precipitation patterns in this region. With reference to seasonal precipitation patterns, the above-ground biomass of Chinese leymus from 1955 to 1994 was reconstructed using two models derived from tree-grass growth relationships. The comparison of climate-growth relationships between relict Meyer spruce and dominant Chinese leymus pointed to the different adaptation strategies of two ecosystem elements to the semi-arid steppe climates. The reconstruction of grass production could reduce the gap in our knowledge of the past dynamics of typical steppe, allowing verification of model estimates of natural climate fluctuations. This may be also an important step towards understanding the response of different ecosystem components to future climate change in the typical steppe, and delivering the baseline reference for a sound steppe management plan. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved