Vegetation control effects on untreated wood, crude cellulose and holocellulose ~13C 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 (513C, is a measure of intrinsic water-use efficiency and can indicate the occurrence of past water shortages for tree growth. We examined (513C 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 dif-ferences in (5 l3C of early wood in trees growing in plots with competing vegetation and those in plots receiving complete vegetation control during 5 years because early-wood formed early in the growing season when soil water was ample. We also hypothesized that (513C in latewood which was formed during the later 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 (513C composition. No significant differences in earlywood (513C in years 3-5 were observed for trees in the two vegetation control treatments