Simulated beetle defoliation on willow genotypes in mixture and monotype plantations

Abstract

The effect of simulated beetle damage (0%, 25%, 50% and 75% mechanical defoliation) on 12 willow genotypes, grown in short-rotation coppice, was studied in a modified criss-cross experimental design. The design enabled the aboveground effects of monoculture and mixed planting to be assessed. Repeated measurements were modelled to produce derived variables in terms of time or, more appropriately, in terms of accumulated day length (i.e. 'developmental time') units. These derived variables were then analysed using the REsidual Maximum Likelihood (REML) method implemented in GenStat TM (2001). No significant competition effect between the genotypes due to planting regime was detected. Genotypes Salix viminalis  Salix schwerinii 'Beagle' and S. viminalis  S. schwerinii 'Torhild' were found to have the greatest rate of increase in leaves regardless of defoliation and also the greatest height prior to defoliation. Genotype Salix dasyclados 'Loden' showed the highest rate of growth under the stress of defoliation. When assessing height at the end of the growing season, S. viminalis  S. schwerinii 'Olof' was the highest genotype for 25% and 75% levels of defoliation, but genotypes Salix aurita  Salix cinerea 'Delamere', Loden and S. viminalis  Salix burjatica 'Ashton Parfitt' appeared to be most tolerant by having consecutively lower base day lengths (i.e. increasing the accumulation of developmental units and the length of the growing season) for increasing defoliation. Shorter genotypes tended to be more tolerant, but of the higher genotypes reaching a control height of greater than 3 m by the end of the growing season, S. viminalis  S. schwerinii 'Tora' and Beagle performed best to 50% defoliation.

Effects of Leaf Loss by Artificial Defoliation on the Growth of Different Poplar and Willow Varieties

“…A common procedure to study the effects of leaf area loss on the growth and yield of plants is the simulation of leaf feeding of phyllophagous pest insects by artificial defoliation [24,[29][30][31][32]. The main advantage of this procedure is the ability to precisely control and modify the extent, number, and timing of defoliation, whereas the difference in the duration between natural and artificial defoliation as well as the potential lack of herbivore-induced plant volatiles due to a merely mechanical damage are disadvantageous [30,33,34].…”

Effect of defoliation intensity and timing on the growth of Populus alba and Salix babylonica x Salix alba

“…and Populus spp. have genetic and morphological distinctness (Karrenberg et al 2002, Zalesny et al 2005; also ecological differences emerge in studies comparing genus, species or hybrids in traits as tolerance to damage (Nordman et al 2005, Powers et al 2006, growth strategies adopted throughout the season (Tharakan et al 2005), root development (McIvor et al 2013), suitability for phytoremediation purposes (Dos Santos et al 2007, Borghi et al 2008 or suitability for short rotation coppice (Laureysens et al 2005, Tharakan et al 2005. Thus, this versatility in plant characteristics of poplars and willows would explain the differences in responses to defoliation observed in our study.…”

“…In poplars, Bassman et al (1982) observed reductions in height and diameter growth of about 20 % and Reichenbacker et al (1996) recorded reductions in height and diameter growth of 12 % and 9 %, respectively. In willows, Powers et al (2006) reported a reduction in height growth between 5 and 20 %; whereas Peacock et al (2002) observed a significant increase in height in only one of the eleven tested hybrids of Salix viminalis L. Differences in tree growth among studies may be caused by multiple factors including genetic variation among clones or environmental conditions.…”

“…Usually, light defoliations have either a negligible negative effect on tree health or an increase in the photosynthetic capacity (Trumble et al 1993). In contrast, severe defoliations often cause growth reduction (Bassman et al 1982, Reichenbacker et al 1996, Powers et al 2006, induce physiological changes affecting the susceptibility of trees to subsequent defoliations (Karban and Baldwin 1997) and increase mortality of trees subjected to repeated defoliations (Kulman 1971). Severe defoliations result in economic loss to commercial forestry plantations because it may lead to tree mortality and longer rotation periods (Cedervind 2003).…”

Development of a sink–source interaction model for the growth of short-rotation coppice willow andin silicoexploration of genotype×environment effects

“…Potential stem elongation is modelled using a linear function of day length multiplied by a Heaviside function for the effect of daily average air temperature ( Powers et al , 2006 ) (Eq. S5 at JXB online).…”