Studying Widespread Tree Mortality Rates in Western North America

Dr Lori Daniels contributed to an international study showing widespread increase in tree mortality rates in old forests in the western North America using forest plots established in 1992 in the Capilano and Seymour River watersheds.

Tree death rates have more than doubled over the last few decades in old-growth forests of the western United States and southwestern British Columbia, and the most probable cause of the worrisome trend is regional warming.

This study compares population changes in forests in southern British Columbia, Washington, Oregon, California, Idaho, Colorado and Arizona, monitoring 76 permanent plots that include 58,736 trees. During that time 11,095 trees died and tree mortality rates have more than doubled in recent decades.

Although tree death is a natural part of old-growth forest dynamics, this long-term monitoring of many types of old forests shows that tree mortality has been increasing, but the establishment and growth of replacement trees has not. As a result, the forests are losing trees faster than they are gaining them. Ultimately increased mortality rates could lead to substantial changes in western forests. As trees die, they change the composition and structure of the forest, which can have cascading effects, such as altering habitat for wildlife species.

Lori Daniels

Lori Daniels
Department of Forest and Conservation Sciences
#3030 – 2424 Main Mall
Vancouver, BC V6T 1Z4
Phone: 604–822–3442