Stem Radial Growth Features of Picea meyeri Responding to Environmental Factors at the Treeline of Luya Mountain

The Stem Radial Growth (SRG) was measured by dendrometer from 6 sample trees of Picea meyeri at the tree-line of Luya Mountain, North China, combined with synchronized instrumental observation and measurement of habitat temperature, moisture, etc., from July the 15^th to August the 7^th (summer phase) and from September the 5^th to October the 9^th (autumn phase) in 2007. The preliminary analytic results were as follows: 1) the diameter of stems varied on sunny days with a daily fluctuation but steadily widened, while on rainy days it continuously increased during the rain but shrank rapidly after the rain. 2) The SRG pattern in both phases was fitted with a quadratic curve, showing a positive value in summer phase; whereas declining to a negative figure in the first stage of autumn phase -early September, and then kept as a constant zero from middle September on. 3) The distance analysis showed a relative warmer and moister environment was suitable for the growth of Picea meyeri in autumn phase, whereas an environment with a high relative humidity (RH) in the air and moisture in the soil was suitable in summer phase. Thus the water regime was the controlling factor for Picea meyeri growth on treeline of Luya Mountain.