Predicting the severity of <i>Cyclaneusma minus</i> on <i>Pinus radiata</i> under current climate in New Zealand

Abstract

Despite being a damaging foliar disease of Pinus species, little research has characterized spatial variation in disease severity of Cyclaneusma needle cast at a macroscale. Using an extensive data set describing Cyclaneusma needle cast (S sev ) on plantation-grown Pinus radiata D. Don stands distributed widely across New Zealand, the objectives of this research were to (i) develop a regression model describing S sev , (ii) use this model to identify key drivers of S sev and their functional form and relative importance, and (iii) develop spatial predictions of S sev for New Zealand P. radiata under current climate. Using an independent validation data set, the final model accounted for 73% of the variance in S sev using four significant (P &lt; 0.001) explanatory variables and an isotrophic exponential model to account for the spatial covariance in the data. S sev was most sensitive to elevation followed by mean winter air temperature, mean relative humidity during July, and then stand age. S sev increased to a maximum at mean winter air temperatures of between 7 and 9 °C before declining. Relationships between S sev and all other variables were linear and positive. Spatial predictions of S sev varied widely throughout New Zealand. Values of S sev were highest in moderately warm, wet, and humid high-elevation environments located in the central North Island. In contrast, relatively low values of S sev were predicted in drier eastern and southern regions of New Zealand.