Growth at the microscale: long term thinning effects on patterns and timing of intra-annual stem increment in radiata pine

Abstract

Background: 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. 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. Methods: Daily 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. Results: Greater 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. Conclusions: In 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.

Number of growth days and not length of the growth period determines radial stem growth of temperate trees

“…Days with growth were also not homogenously distributed, but occurred mainly during the first part of the growth period (April/May–June), explaining the stronger impact of spring compared to summer droughts on tree growth (Bose et al, 2021 ; Martin‐Benito et al, 2018 ). Although, discontinuity and irregularity of stem growth processes have been discussed since long (Kozlowski & Pallardy, 1996 ), general assumptions in annual tree growth models (Fatichi et al, 2019 ; Peltier & Ogle, 2020 ) or yield studies (Drew & Downes, 2018 ) often imply linear growth responses to environmental conditions. However, days with growth appeared quite irregularly and could on average only be predicted by environmental conditions in 45% of cases (27% to 68%, Table S4 ), confirming the non‐linearity of growth processes not only on an annual scale (Wilmking et al, 2020 ), but also on shorter time‐scales (Peltier & Ogle, 2020 ).…”

“…On shorter time scales, however, cambial activity is non‐linear (Peltier & Ogle, 2020 ; Zweifel et al, 2021b ) and highly discontinuous. This intermittent growth can result from unfavourable environmental conditions including droughts and tree water deficits (Cabon et al, 2020b ; Peters et al, 2020 ; Zweifel et al, 2016 ), internal tree processes related to phenology or resource allocation (Devine & Harrington, 2009 ), or involve responses to competition (Drew & Downes, 2018 ) or pathogens (Schuldt et al, 2017 ). However, such intra‐annual variations are not well understood, because analyses of fine‐resolution intra‐annual stem growth dynamics across species, sites and years are scarce (Forrest & Miller‐Rushing, 2010 ).…”

Trees Talk Tremor—Wood Anatomy and Content Reveal Contrasting Tree‐Growth Responses to Earthquakes

“…We assumed a uniform uncertainty of ±10 days for the day of tracheid formation and a uniform DBH measurement accuracy of ±1%. We estimated a date for each tracheid cell and ‐increment using the Gompertz growth model (Rossi et al., 2003), which is widely used for dating xylem growth in conifers, including Pinus radiata (Drew & Downes, 2018) which we solved for the time of cell formation ( t ) where y is the cumulative number of cells, A is the asymptotic maximum number of cells, β is a location parameter, k is a rate change parameter (1/ t ), and t is time in days starting on June 1 ( t = t 1 ). To avoid infinite values, we fixed the upper asymptote at A + 1 (Rossi et al., 2003).…”

Radial growth anisotropy and temporality in fast-growing temperate conifers

“…Those secondary oscillations are typically episodes of reduced or interrupted radial growth. They may be observed during unfavourable environmental conditions such as drought-rain alternance (Larson 2012) or deficit in tree water storage (Zweifel et al 2016), in relation to competition status (Drew and Downes 2018), phenology (Morel et al 2015), or an internal redirection of resources during secondary flushes (Devine and Harrington 2009) or towards reproductive growth. Those sub-seasonal oscillations have been the subject of very few studies, but they indicate that cambial activity may be semi-discrete in time.…”