Abstract
BackgroundStem radial growth in forests is not uniform. Rather, it is characterized by periods of relatively fast or slow growth, or sometimes no growth at all. These fluctuations are generally a function of varying environmental conditions (e.g. water availability) and, importantly, will also be associated with adjustments in properties in the wood formed. Stand level conditions and forest management, particularly thinning and stand density will, however, also have a major influence on patterns of growth variation. We explore how different thinning histories and/or stand densities influence these dynamics of tree growth in the important commercial plantation species Pinus radiata D. Don.MethodsDaily stem size change was measured using electronic point dendrometers over two growing seasons on P. radiata trees at two sites, subjected to different thinning regimes. Timing, rates and periodicity of annual growth were calculated from these data.ResultsGreater overall cross-sectional growth in thinned plots was driven mainly by two dynamics. First, the cessation of seasonal growth occurred at least 3 weeks later in the stands in which thinning had taken place. There was no difference between thinned/unthinned stands, however, in the timing of growth onset. Second, within the longer season, trees in thinned plots had more growth days (as much as 20% more) than unthinned plots. The rates of growth on days when growth occurred were not different, however. In this context, it is notable that in trees in the unthinned plots experiencing the most severe competition there were strong “pulses” of growth following drought-breaking rainfall events. Unthinned plots at high stand densities also maintained a smaller (but consistent) zone of dividing cells throughout the season than thinned plots.ConclusionsIn Pinus radiata growing under conditions as in our study, conditions late in summer, particularly drought, have an important effect on the timing of cessation of growth. Early season temperature appears to have no effect in determining timing of annual growth. Limiting conditions during the season reduce growing duration, and thus total growth, more in unthinned stands than thinned stands. These findings are valuable in developing new generations of fine-scale growth and wood property models.
Highlights
Stem radial growth in forests is not uniform
While some work has been done in this area on fast growing plantations of other species in countries like Australia and South Africa (Downes et al 1999; Drew et al 2008; Zweifel et al 2014) and a relatively large literature exists for northern hemisphere forests (e.g. Deslauriers et al 2007; Steppe et al 2015) only a small amount of older work (e.g. Worrall 1966; Skene 1969) has been published for P. radiata to our knowledge
We have reported here on intra-annual growth patterns in Pinus radiata, a plantation species of important in several countries (Lavery and Mead 1998; Ivković et al 2016)
Summary
Stem radial growth in forests is not uniform Rather, it is characterized by periods of relatively fast or slow growth, or sometimes no growth at all. In order to develop a finer and more precise understanding of growth at this level, it is of great value to understand better the periodicity and temporal variability of growth in forest trees (Rossi and Deslauriers 2007; Drew and Downes 2015; Bosio et al 2016; Brinkmann et al 2016). While some work has been done in this area on fast growing plantations of other species in countries like Australia and South Africa (Downes et al 1999; Drew et al 2008; Zweifel et al 2014) and a relatively large literature exists for northern hemisphere forests (e.g. Deslauriers et al 2007; Steppe et al 2015) only a small amount of older work (e.g. Worrall 1966; Skene 1969) has been published for P. radiata to our knowledge
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