Importance of Previsual Detection

Minimizing the elapsed time between when a tree becomes infested with an insect and when that infestation is detected can increase the treatment options available to forest managers. Detection of an infestation prior to when the foliage begins to visibly fade should give managers more time to respond. Active resistance mechanisms by a host tree to insect attack can be energy intensive to maintain and utilize. The decline that occurs within a host following infestation by adelgids may be categorized into various levels as characterized for hemlock infested with hemlock woolly adelgid (Pontius and others 2005) or balsam fir infested with balsam woolly adelgid (Luther and Carroll 1999). Changes in foliar chemistry that are related to tree stress can be manifested in measurable spectral changes within the foliage. Much of the literature with regard to another tree-killing insect, mountain pine beetle (Dendroctonus ponderosae), is reviewed by Wulder and others (2006). The review suggests that remotely sensed data is useful for detecting infestations of mountain pine beetle damage and that future experimental work be conducted at several spatial scales.