Environmental Controls on Tree-Ring Growth in an Age-Sequence of Planted Pine Forests

English Abstract:

The objective of this study was to assess the effect of regional climate patterns and forest management on growth rates of an age-sequence of three white pine (Pinus strobus L.) plantation forests established in 1939 (TP39), 1974 (TP74) and in 1989 (TP89) in southern Ontario, Canada. These sites are a part of the Turkey Point Flux Station and global Fluxnet. To evaluate the effects of climate and land management on annual biomass accumulation, surface area of growth rings was measured on 15 white pine discus (tree slices at DBH) cut in 2004 and compared to historical climate records from 1939 to 2004 (temperature and precipitation) for each of the three sites. The combination of annual climate variability and decadal scale climate oscillations such as the Arctic Oscillation and El Niño Southern Oscillation show relatively strong correlation in growth. Forest response to annual temperature changes show strongest correlation (r² = 0.37) with a 2-year lag in growth, as compared to growth year (r² = 0.29) and 1-year lag (r² = 0.33). Decreased growth was observed across the chronosequence in 1975, 1989 and 1999, corresponding to decrease annual temperatures and shortened growing seasons accompanying strong La Niña years. Precipitation does not show a strong correlation with growth except during extreme drought years. As expected, plantations on former agricultural land (TP89) approach maximum growth rate much faster (at 11 yrs of age) due to nutrient residue, as compared to stands planted on former oak savannah (TP39 and 74) (at 13 yrs of age). Impacts of canopy closure begin 25 years after afforestation as shown by decreased growth rates. Thinning at the oldest site (TP39) in 1983 enhanced annual biomass accumulation for 20 years following the treatment.