Introduction

Abstract

Forest systems have enormous variability. Forests may differ in soil type, climate, aspect, elevation, species composition, age, and health. Forests may be uneven aged, even aged, all aged or overmature. Forests may be reproduced by seed, by coppice, or by planting. Some forests have their structure completely shaped by natural forces, some may be influenced by human forces as well as natural forces, while other forests may be completely artificial in design and establishment. Forest trees may be arrayed along a continuum of human management efforts ranging from no management to intensive management (Table 1-1). All of this variability makes generalizations about forest tree systems and their stresses very difficult to formulate, but it also makes them essential to attempt.