Scars from human-tree interactions: pollarding, pathogens, body reserves, and long-term response by Salix fragilis L. (Salicaceae) in Scodovacca, Italy

Arboriculture provides opportunities for assessing long-term tree-environment interactions. We assessed the surrounding context, scars, re-sprouts, and absolute width-growth of twenty-four Salix fragilis trees pollarded by the grandfather, father, and son of one family covering 120 years, quantifying the effects of cut, microorganism-infection, and body-accumulated photosynthate on the pollards' resprout-and-growth. We determined pollard diameter, age, scars-number (C) and basal area (CAB), median times pruned (Cmn), putrid holes number (H), cumulative length (HL), and length-average (HAV), and two indicators of remaining photosynthate (Q, and QAV). Response variables were number of re-sprouts (RN), re-sprout-basal area (RAB), and trunk's Absolute Growth (AG; Classic (MLR), and Bayesian Multiple Linear Regressions (BMLR)). The pollards experienced similar incoming light, water, CO2, nutrients, and temperatures. Higher C-values for 40-year-old pollards produced higher H-values (Linear Regression, R2 = 0.54, p = 0.02; Bayesian Linear Regression: BF10 = 3.79, n = 8) suggesting more infection when cutting. RN slightly changed in response to life-long accumulated CAB, Cmn, H, and HAV (BMLR, BF10 from 1.10 to 2.82, n = 24). RAB slightly changed responding to C, H, HAV, Q, and QAV (BMLR, BF10 = 1.11; MLR: p < 0.05, n = 24). AG declined in response to Cmn (MLR, R2 = 0.38, p < 0.001, n = 24). Thus, under favourable conditions severely wounded-and-infected trees keep re-sprouting and growing, even if growth is reduced.