DOI: 10.5061/dryad.127fg
title: Data from: The effect of competition on responses to drought and interannual climate variability of a dominant conifer tree of western North America

description: To accurately predict how ecosystems will respond to climate change – and
 how management actions can influence such responses – scientists 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. 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. 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. Trees with more competition from neighbours
 exhibited a significantly higher proportion of sapwood area in latewood (a
 morphological trait associated with greater drought resistance).
 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.
description: Tree ring and competiton
 data from northeast Washington, USAData collection methods
 are described in Methods. Tree-level completion data was collected in the
 field and tree ring data was measured in laboratory using standard
 techniques. Year = Calendar year of tree ring; ST_ID = Unique ID for each
 subject tree; Canopy_Class = Canopy position of subject tree, either
 dominant (DO) or intermediate (IN); ST_DBH = diameter at breast height of
 subject tree; HCI = Hegyi's Competition Index; DIB = Diameter inside
 bark; Comp_Class = Categorical grouping based on HCI; SW = avg. distance
 (cm) of sapwood on increment cores; Age = age at breast height when tre
 was sampled; Stand_ID = Unique ID for each stand; PLW_Class = Categorical
 grouping based on PLW; BAI = Basal area increment; BAI.rwi = Index based
 on BAI; EWA = Earlywood area increment; EWA.rwi = Index based on EWA; LWA
 = Latewood area increment; LWA.rwi = index based on LWA; PDSI = Palmer
 Drought Severity Index for NCDC WA Div 9; PLW = Proportion of
 latewoodCarnwath_Nelson_Data.csv