Evaluation of physiological responses of balsam fir and red spruce trees growing in two pre-commercial thinned (PCT) and four never-pre-commercial thinned (N-PCT) sites in Maine, USA

These data contain biochemical parameters that were measured in foliage and sapwood of red spruce (Picea rubens) and balsam fir (Abies balsamea) trees growing at six sites in northern Maine that are part of Maine's Commercial Thinning Research Network (CTRN). Two different types of experiments were conducted by CTRN using a total of 12 sites. In one experiment, two removal intensities (33% and 50%) were applied to six sites at three different timings of entry for thinning (thin immediately, delay thinning by 5 year, or 10 years) that had been previously commercially thinned (PCT). In the second experiment various commercial thinning (CT) methods (low, crown, dominant) were applied at two removal intensities (33% and 50%) to six sites that had not been pre-commercially thinned (N-PCT). Pre-commercial thinning took place in 1983-1985. Commercial thinning treatments began in 2000. We collected samples from the two pre-commercial thinned (PCT) and four N-PCT CTRN sites. Depending upon the site, annual collections of foliage and sapwood were made 1 to 7 years after applying CT treatment. Fifteen randomly chosen red spruce and balsam fir trees were sampled from designated plots (61 meters x 61 meters). Foliar and sapwood data include free polyamines, free amino acids, and soluble ions analyzed by HPLC and ICP-OES. Chlorophyll and soluble protein data analyzed by UV/VIS spectrophotometry are also included for foliar samples. In total, there are 1500 foliar and 573 sapwood samples included in this dataset.
The objectives of the two studies were to: (1) quantify effects of CT timing of entry and thinning intensity in previously PCT stands on stand structure, residual stand growth, merchantable products (sawlog and pulpwood), and financial value and (2) quantify the effects of CT method (low, crown, and dominant) and intensity in older spruce-fir stands that had never received PCT on stand structure, residual stand growth, merchantable products (sawlog and pulpwood), and financial value. The overall goal was to use select metabolites as markers of tree health and productivity as influenced by timing of the first commercial thinning entry and the residual density on subsequent stand response.
These sites are part of those included in Maine's Commercial Thinning Research Network and are part of a collaborative project with the Cooperative Forestry Research Unit, University of Maine, Orono. More site & study information can be found at: https://umaine.edu/cfru/wp-content/uploads/sites/224/2015/05/Prospectus-2006-2010.pdf and in the following publications: Ward et al. (2004), Hiesl et al. (2017), and Olson et al. (2014).