Vegetation control effects on untreated wood, crude cellulose and holocellulose δ¹³C of early and latewood in 3- to 5-year-old rings of Douglas-fir

Abstract

The stable carbon (C) composition of tree rings expressed as δ¹³C, is a measure of intrinsic water-use efficiency and can indicate the occurrence of past water shortages for tree growth. We examined δ¹³C in 3- to 5-year-old rings of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees to elucidate if decreased water supply or uptake was a critical factor in the observed growth reduction of trees competing with understory herb and shrub vegetation compared to those growing without competition. We hypothesized that there would be no differences in δ¹³C of earlywood in trees growing in plots with competing vegetation and those in plots receiving complete vegetation control during 5 years because earlywood formed early in the growing season when soil water was ample. We also hypothesized that δ¹³C in latewood, which was formed during the latter half of the growing season when precipitation was low, would be greater (less negative) in trees in plots without vegetation control. We then separated early and latewood from rings for three consecutive years and analyzed their δ¹³C composition. No significant differences in earlywood δ¹³C in years 3-5 were observed for trees in the two vegetation control treatments. δ¹³C of untreated latewood separated from wood cores was greater in 4- and 5-year-old rings of trees growing with competing vegetation compared to trees growing without vegetation competition (i.e., -25.5 vs. -26.3 percent for year 4, and -26.1 vs. -26.8 percent for year 5). Results suggest that water shortages occurred in Douglas-fir trees on this coastal Washington site in the latewood-forming portion of the growing season of years 4 and 5 in the no-vegetation-control treatment. We also compared δ¹³C from untreated wood, crude cellulose extracted with the Diglyme-HCl method, and holocellulose extracted with toluene-ethanol to see if the extraction method would increase the sensitivity of the analysis. δ¹³C values from the two extraction methods were highly correlated with those from untreated samples (r² = 0.97, 0.98, respectively). Therefore, using untreated wood would be as effective as using crude cellulose or holocellulose to investigate δ¹³C patterns in young Douglas-fir.

Citation

Ares, Adrian; Harrington, Constance A.; Terry, Thomas A.; Kraft, Joseph M. 2009. Vegetation control effects on untreated wood, crude cellulose and holocellulose δ¹³C of early and latewood in 3- to 5-year-old rings of Douglas-fir. Trees. 22(5): 603-609