Temporal Trends in Fusiform Rust Infections and Their Relationships with Stand Structure in Pine Plantations in East Texas

摘要

Fusiform rust is the most important disease affecting plantations of loblolly (Pinus taeda L.) and slash pine (Pinus elliottii Engelm.) in east Texas. Losses to fusiform rust on loblolly pine and slash pine in the South amount to 35 million dollars a year from the death of infected trees and from its degrading effect on products cut from the tree. This study, based on long-term measurements on permanent plots established on pine plantations across east Texas, assessed rust infection trends from 1984 to 2014 and the relationships between rust infections and common tree and stand variables for pine plantations in east Texas. Results showed that ratios of trees with rust-infected branches declined quickly from 1984 to early 1990s and thereafter leveled off. Ratios of stem-infection peaked in the period 1987-99 and then decreased over time. For both ratios, slash pine had higher values than loblolly pine at any given year. Multilevel logit models were developed to assess effects of tree variables (e.g., DBH, tree height, height to live crown, and crown class) and stand variables (e.g., age, site index, quadratic mean diameter, trees per acre, and basal area per acre) on the probabilities of fusiform rust infection levels (branch-and stem-infection). Results showed that height to live crown and site index were the most important variables; the branchand stem-infection probabilities increased with increasing height to live crown and decreasing site index for both pines, although the changes were larger for slash pine than for loblolly pine. In addition, the larger DBH trees had a higher probability of branch-and stem-infection for loblolly pine. Older trees or trees growing in plantations of greater density (more trees per acre) had a higher probability of stem-infection for slash pine. Results should be incorporated into the regional pine plantation management planning to reduce loss due to fusiform rust infection.