Analyses of growth rings of Pinus merkusii from Lao P.D.R.

We present the first tree-ring chronologies of total ring width (RW), earlywood width (EWW) and latewood width (LWW) from Lao P.D.R., from 52 core samples from 26 mature pines (Pinus merkusii Junghuhn & De Vriese), from Phu Khao Khouay National Biodiversity Conservation Area northeast of Vientiane. The chronologies span the 262-year period from 1743 to 2005 a.d., and at least for RW and LWW exhibit strong signal strength back to the late 1700s. Correlation analyses with climate data from a composite of 13 nearby stations in Thailand indicate statistically significant (p ≤ 0.05) negative correlation with prior year June rainfall, and positive correlation with August–September maximum temperature. Annual radial increment is also significantly negatively correlated with percent cloud fraction, leading us to believe that growth may be adversely affected by light availability (i.e., reduced growth during periods of low light) and not positively affected by high temperature per se. Spatial correlation with sea surface temperature fields highlights the influence of the central and eastern tropical Pacific Ocean, particularly for EWW. Wavelet analysis reveals multi-decadal scale variability between 30 and 60 years for all three indices, and higher frequency power for RW and LWW between 2 and 7 years, the typical range of ENSO. While RW, EWW and LWW all appear to respond to monsoon climate, we highlight the need for far more detailed ecophysiological response studies for this species, particularly with regard to the role of light availability and temperature during the peak monsoon.