© 2003 Heron Publishing—Victoria, Canada
Variation in needle longevity of Pinus tabulaeformis forests at different geographic scales
Y. Xiao
Department of Forest Resources, University of Idaho, Moscow, ID 83844, USA (yxiao@uidaho.edu) / Received April 24, 2002; accepted October 26, 2002; published online April 1, 2003
Summary
Needle longevity of conifer species is known to increase with latitude, but little is known about intraspecific variation
and associated factors within a location. Chinese pine (Pinus tabulaeformis Carr.) forests were investigated to identify patterns of needle longevity at seven sites with distinctive climatic conditions
along a latitudinal gradient (33–38° N) in Shaanxi province, northwest China. A demographic approach was used to quantify
needle longevity as an index of entire foliage population adjusted to needle-age-specific mortality rates. There were significant
differences in needle longevity of Chinese pine stands across sites and across sample plots within a site. Individual tree
needle longevity ranged from 0.62 to 3.75 years for 276 samples across sites. Needle longevity increased with latitude (R2 = 0.40, P < 0.0001), but decreased with mean January temperature (R2 = 0.63, P < 0.0001). Foliage retention of Chinese pine stands at the regional level was generally associated with climatic variability,
indicating that variation in needle longevity was primarily an environmental acclimation to low temperature in winter. Stand
characteristics were closely associated with needle longevity at three sites located within the same climatic zone. Needle
longevity was positively correlated with tree age (R2 = 0.48, P < 0.0001) and stand density (R2 = 0.26, P = 0.0015) at Huanglong and Huangling, respectively, whereas it was negatively associated with total tree height at Zhidan
(R2 = 0.50, P < 0.0001). It is concluded that, at the stand and individual tree level, intraspecific variation in needle longevity is
most likely a result of adaptation to patchy microsite environments.
Keywords:
climatic variability, intraspecific variation, latitude, life expectancy, life table, stand characteristics, temperature.
