Modeling the effect of crown shedding and streamlining on the survival of loblolly pine exposed to acute wind

Abstract

A simulation model using empirical data was developed to determine the effect of crown shedding and streamlining from stem and branch bending on the survival of mature loblolly pine (Pinustaeda L.) trees exposed to acute wind. Data collected from tree winching experiments were used to derive the forces necessary to cause stem failure. These data, combined with data on the vertical distribution of biomass and frontal surface area of sampled trees and hypothetical within-stand wind profiles, were used to calibrate models of static wind effect. Data collected on crown biomass, stem deflection, and branch bending were employed in the model to conduct a sensitivity analysis of the relative contribution of various crown adjustment mechanisms in preventing stem breakage or windthrow. Compared with the base-line model, which included no crown adjustment mechanisms, crown loss of 25% or greater provided the greatest protection against stem breakage or windthrow from forces generated by a hurricane winds of average strength (165 km/h), followed (in order of greatest to least protection) by stem bending, branch streamlining, and crown loss of 10%. However, at the highest wind velocities modeled (249 km/h), stem bending afforded greater protection against wind-generated mortality than 25% crown loss or branch streamlining, but not more than 50% crown loss. Generally, study trees most susceptible to windthrow were tall with a high center of gravity, large crown weight, and small stem taper.