Data from: Quantifying neighbour effects on tree growth: are common “competition” indices biased?

We used tree growth data from the Australian Forest Evenness Experiment (AFEX; Gerwin et al., 2020) to demonstrate how neighbour indices can be correctly incorporated into a regression analysis of tree growth. The AFEX is a cool temperate experimental forest established in April 2013 with seeds of four locally-dominant native tree species: Eucalyptus delegatensis, E. regnans, Pomaderris apetala and Acacia dealbata. Permission to establish the experiment and to access the site for measurements was provided by Sustainable Timbers Tasmania who manages the site on behalf of the State Government of Tasmania, Australia. In winter 2018, 114 permanent mapped neighbourhood plots were established around 56 E. delegatensis and 58 E. regnans focal trees in the centre of an approximately 2 m radius neighbourhood (12.6 m2 total area). We refer to the focal trees in these neighbourhoods as ‘non-isolated’. The 2 m radius was substantially larger than a previous recommendation of 40 times the mean focal tree diameter (0.95 cm) (Sutherland et al., 1991) and was selected as the largest neighbourhood within which we could feasibly sample all neighbouring plants. For every tree in the neighbourhood sampling area (focal and neighbours) we recorded the height (m), diameter at breast height (DBH; cm) and GPS location (accuracy of < 10 cm). In total, 114 non-isolated focal trees and 7854 neighbours were mapped and measured, capturing a range of community compositions ranging in density from 0.8–13.5 plants m-2 (Supporting Information Fig S1). In addition, in winter 2018, we measured the height and DBH of 34 focal trees that had no neighbours within 2 m, which we refer to as ‘isolated’ focal trees. All focal trees (non-isolated and isolated) were remeasured in winter 2019, 2020 and 2021 to determine three years of annual incremental growth.