The effect of competition on responses to drought and interannual climate variability of a dominant conifer tree of western North America

Abstract

1.To accurately predict how ecosystems will respond to climate changeand how management actions can influence such responsesscientists and managers need a better understanding of how and when biotic interactions modify climate-growth relationships. However, current research has largely ignored the role of competition in modulating climate-growth relationships of mature trees. In this study, we assessed the effect of competition on tree responses to drought and interannual climate variability as well as linkages between climate sensitivity and morphological characteristics of the stem wood. 2. We sampled 10 sites in north-eastern Washington, USA, and used dendroecology to quantify responses of Douglas-fir (Pseudotsuga menziesii) to drought and climate variability. Tree-ring series were converted to basal area increment series, and the effects of competition on climate-growth relationships were assessed at the tree and site levels using a combination of correlation analyses and linear mixed-effects models. 3. Competition did not affect tree responses to extreme drought. When soil moisture was below average, tree growth was tightly coupled to climate variability for all trees, regardless of their competitive status. However, in wet years, competition had a pronounced, positive effect on climate sensitivity of growth. 4. Trees with more competition from neighbours exhibited a significantly higher proportion of sapwood area in latewood (a morphological trait associated with greater drought resistance). 5. Synthesis. Our results suggest that a tree's ability to cope with environmental variability is driven not just by the proximate effects of neighbours on resource availability, but also by phenotypic plasticity and long-term adaptations to competitive stress (such as changes in carbon allocation). Findings have important implications for individual-tree and stand-level growth models and may help managers better understand how their activities will modify tree responses to climate change.

Local range boundaries vs. large‐scale trade‐offs: climatic and competitive constraints on tree growth

“…A number of tree ring studies have quantified both climatic and competitive constraints, but typically are not designed to detect range constraints (e.g. Martin-Benito et al 2011;Carnwath & Nelson 2016, but see Buechling et al 2017). A few studies do show increasing competitive constraints at low elevation or wet range boundaries (Callaway 1998;Coomes & Allen 2007;Copenhaver-Parry & Cannon 2016;Louthan et al 2018but see Barton 1993Sanchez-Salguero et al 2015).…”

Impacts of growing‐season climate on tree growth and post‐fire regeneration in ponderosa pine and Douglas‐fir forests

“…). Local conditions, such as competition or changes in microclimate, can also alter growth responses to climate over time (Ettinger and HilleRisLambers , Carnwath and Nelson ). The possibility of changing growth–climate relationships further complicates our understanding of how future climate may impact tree regeneration, growth, and ultimately survival.…”

“…For example, increasing precipitation variability, along with underlying directional trends in temperature, may alter growth sensitivity due to underlying physiological thresholds being crossed and/or an increased frequency of extreme climate conditions (Carrer andUrbinati 2006, Hayles et al 2007). Local conditions, such as competition or changes in microclimate, can also alter growth responses to climate over time (Ettinger andHilleRisLambers 2013, Carnwath andNelson 2016). The possibility of changing growth-climate relationships further complicates our understanding of how future climate may impact tree regeneration, growth, and ultimately survival.…”

Forest management in the Sierra Nevada provides limited carbon storage potential: an expert elicitation

“…, Anderegg et al. , Carnwath and Nelson , Clark et al. ) as well as the potential for multidecadal changes in vegetation type, species composition, and stand density (Collins and Roller , Earles et al.…”

“…Recent studies highlight the significant role of humans in wildfire ignition likelihood and in altering fire regimes through pathways such as fire suppression, land-cover change, and hydrological engineering (Mann et al 2016, Balch et al 2017. Projections of future fuel levels are complicated not only by fire regime but also by uncertain impacts of climate change and drought , Anderegg et al 2015, Carnwath and Nelson 2016, Clark et al 2016 as well as the potential for multidecadal changes in vegetation type, species composition, and stand density (Collins and Roller 2013, Earles et al 2014, Coppoletta et al 2016, Van Gunst et al 2016.…”