Wind-induced leaning (toppling) in young Pinus radiata plantations in Chile

Abstract

The toppling of young trees considerablyreduces the value of the first log in Pinus radiata plantations.Although wind is the main cause of toppling, the quality and type of plants,planting techniques, soil fertility and soil preparation may play an importantrole in the susceptibility of the species to toppling. This article analyzesthe influence of ripping and soil type on the probability of P. radiatatoppling after severe windstorms in central south Chile. To this aim, pairs ofsimilar trees with and without toppling were selected in 2001 in six soil typeswith and without soil ripping. Root system differences in toppled versusstraight trees were compared to gain better insight into the causes of thephenomenon. Among all root measurements, the quality of thetap root measured through the Menzies scale was significantly correlated with the probability oftoppling. Trees with a strong, dominant and well-developed tap root (Menziesvalue equal to zero) showed a toppling probability of 0.34 (1 of each 3 treesbeing damaged). At the other extreme, trees with a horizontal tap root or withno tap root (Menzies value equal to 10) showed a toppling probability of 0.72 (i.e.,three of each four trees were damaged). A toppling probability of 0.50 (ordamage observed in one of each two trees) was found for trees with a tap rootdistinctly hooked but functional (Menzies value equal to 4). Ripping reducedthe toppling probability from 0.56 to 0.44 by improving the quality of the taproot consistently across all soil types from Menzies 5.7 to Menzies 2.5. Theworst tap root qualities were found for sandy soils (Menzies equal to 7.0,toppling probability of 0.62), followed by metamorphic soils (Menzies equal to4.5, toppling probability of 0.52). Alluvial, granitic, red clay and volcanicash soils did not differ in tap root quality (Menzies equal to 3.3, topplingprobability of 0.47). In conclusion, the study suggests that all measures favoring a strong, dominant andwell-developed tap root, in the nursery and in the field, are likely to considerablyreduce toppling damage in young P. radiata plantations in Chile