Pathology > Forest Pathology > Introduction

Introduction

Plant pathology is the study and control of diseases affecting plants. Forest pathology is the subset of plant diseases affecting both coniferous and deciduous forest trees. Organisms causing disease in trees, usually fungi, bacteria, mistletoes or viruses, are commonly called pathogens and can spread from tree to tree. Also included under pathology are non-infectious diseases and damages caused by abiotic agents such as weather and air or soil contaminants. Disease or damage occurs when a biotic or abiotic agent alters a plant such that it grows differently than it would in the absence of the agent. Disease symptoms range from gradual decline of plant growth to defects in affected plant parts to outright mortality.

Frost damage on western hemlock. Abiotic disease agents such as frost are included under forest pathology.

There are four broad classes of disease affecting trees: 1) foliage and branch diseases, 2) stem diseases, 3) cone and seed diseases, and 4) root diseases. Nationally, diseases claim approximately one-third of Canada's annual forest productivity losses. Stem decays, followed by root disease, cause the most significant pathogen-related productivity losses in Canada's forests.

Hemlock dwarf mistletoe (Arceuthobium tsugense) is a parasitic plant that only survives by obtaining nutrients from host trees.

Forest diseases together with fire and insects are the principal agents driving forest succession. All of these agents have effects on the terrestrial carbon cycle and subsequently on climate. Forest pathologists play a critical role in conducting research to understand the balance between pathogens and forest trees such that disease does not affect sustainable forest practice. Sustainability is a balance between social, environmental, and economic concerns in the forest. Forest diseases can affect all three of these and therefore play a major role in sustainability.

Research Staff