资源环境科技发展态势分析平台

Forest pathogens are one of the key drivers of the dynamics and diversity of forested landscapes, contributing to structural and compositional complexity at multiple scales in space and time. Growth and yield models help guide forest management decisions but the roles of abiotic and biotic disturbance agents including pathogens are often overlooked. In our study of mid-rotation spruce plantations in northwest British Columbia (BC), Canada, we examine the influence of tomentosus root disease on the oldest managed stands in a previously unmanaged landscape allowing us to witness pathogen expression in a first rotation setting over the longest duration available. Our 10 one-hectare stem-mapped plots capture the spatial variability of root disease expression and their large size, coupled with their random selection without any prior knowledge of the pathogen, make our study unique. We found tomentosus root disease accounted for nearly 90% of both the number and the volume of spruce trees that died and that the incidence of the disease more than doubled over a 16-year period from stand age similar to 30-46. The volume growth of trees that were initially healthy but became infected was 17% less than that of the trees that remained healthy, while the volume growth of trees that were infected since plot establishment was 28% less than that of trees that remained healthy. We found a weak relationship between infected stumps from the previous stand and the condition of trees surrounding those stumps at age 30, but more critically we found a similarly weak relationship between infected trees at age 30 and the condition of the neighbouring trees 16 years later. Using the growth and yield model TASS II v2.7.75, we found model projections of spruce volume exceeded measured plot volume by an average of 30.5%. TASS is based on the same foundational tenets that are the dominant paradigm in forestry where the prediction of forest growth is based on the assessment of site index (dominant stand height and age), Eichhorn's rule (which implies that when the dominant tree height is known, stand yield can be easily estimated now and then projected into the future), and the thinning response hypothesis. Our results reflect the influential role of a forest pathogen that is operating on a different scale and following a different set of rules. This, in combination with the unexpected behaviour of the forest pathogen itself, represents a multifaceted challenge in forecasting forest growth.