Interpreting tree responses to thinning and fertilization using tree‐ring stable isotopes

Abstract

Summary• Carbon sequestration has focused renewed interest in understanding how forest management affects forest carbon gain over timescales of decades, and yet details of the physiological mechanisms over decades are often lacking for understanding long-term growth responses to management.• Here, we examined tree-ring growth patterns and stable isotopes of cellulose (d 13 C cell and d 18 O cell ) in a thinning and fertilization controlled experiment where growth increased substantially in response to treatments to elucidate physiological data and to test the dual isotope approach for uses in other locations.• • Tree-ring isotopic records, particularly d 13 C cell , remain a viable way to reconstruct long-term physiological mechanisms affecting tree carbon gain in response to management and climate fluctuations.

Improvement of water and light availability after thinning at a xeric site: which matters more? A dual isotope approach

“…In our case, higher g s values related to higher water availability caused a depletion of D 18 O leaf-water that affected our d 18 O tree-ring values but to a lesser extent than the enrichment in source water (Fig. 5) (Brooks & Mitchell, 2011 18 O tree-ring records. The fact that the general isotope patterns after thinning could also be explained when varied initial parameters were applied demonstrates the general robustness of our model assumptions and the correctness of the mechanisms we derived from the model output.…”

“…The d 13 C in tree-ring cellulose (d 13 C tree-ring ) can be used to document changes in the intrinsic water use efficiency, defined as the ratio of leaf CO 2 assimilation (A) to stomatal conductance (g s ) (L evesque et al, 2014;Saurer et al, 2014;Frank et al, 2015). Some studies found that d 13 C tree-ring was unaffected by thinning, implying either that g s and A did not change or that they changed with the same magnitude, that is, the ratio A/g s remained constant (Martin-Benito et al, 2010;Powers et al, 2010;Brooks & Mitchell, 2011;Moreno-Gutierrez et al, 2011). In this case, it can be useful to include d 18 O data, as they are strongly constrained by the isotopic ratio of the source (xylem) water (Roden et al, 2000), and they also integrate the stomatal response to vapour pressure deficit (VPD) via leaf water isotopic enrichment (Yakir & DeNiro, 1990;Barbour et al, 2004;Treydte et al, 2014).…”

Forest Restoration Using Variable Density Thinning: Lessons from Douglas-Fir Stands in Western Oregon

“…Restoration treatments that reduce tree densities increase available resources for residual trees [27,28]. As expected, the lower post-treatment densities resulted in increased average tree diameter growth [15,29].…”

The effects of thinning intensity and tree size on the growth response to annual climate in Cedrus atlantica: a linear mixed modeling approach

“…Unbiased fixed-effect predictions were required to isolate the climate-driven component of the growth time series from the effects of tree age and thinning. Without additional ecophysiological measurements, the interpretation of the retained fixed effects is not straightforward because the dendrometric variables used in the LMM are proxies accounting for complex functional responses (Brooks and Mitchell 2011;Sohn et al 2013). In particular, the predicted transient growth increase induced by thinning likely accounts for an improvement of the resource availability (Nambiar and Sands 1993;Bréda et al 1995), for the enhancement of the remaining tree crown areas (Pretzsch 2014) and/or for the possible mobilization of stored non-structural carbohydrates in support of growth.…”