Tracking the Health of Trees Over Time on Forest Health Monitoring Plots

-The Forest Health Monitoring (FHM) Program was initiated in 1990 as a cooperative effort between the USDA Forest Service and the National Association of State Foresters. Program efforts include detecting changes in tree health from a national grid of one-sixth acre permanent sample plots. Tree data have been collected in various states since 1991, and include species, diameter at breast height (dbh), status (l ive, dead, or cut), and various ratings of crown condition and damage. In this study, remeasured tree data were used to track changes in health over a 4-year period, by using status (l ive, dead, or cut), crown dieback, transparency, and density, and damage measurements of type, severity, and location. Initial analyses identified categories of individual crown and damage measurements associated with trees that eventually died. These thresholds were then integrated into categorical models to estimate the probability of mortality for trees with different combinations of crown and damage conditions. Separate models were constructed for different groups of tree species, with the premise that each group has a unique set of tolerable amounts of damage and foliage loss. Analyses also included stat ist ical tests to verify differences among models . Results wil l be incorporated into a f ield guide for use by land managers to help assess tree health, predict the l ikelihood of mortali ty, and rate the health of forest stands. Use of this tool will also help foresters make silvicultural decisions to select trees to be cut when regeneration, thinning, pre-salvage, or salvage operations are considered. The Forest Health Monitoring (FHM) Program was initiated in 1990 as a cooperative effort between the USDA Forest Service and National Associat ion of State Foresters. A main objective of the program is to detect spatial and temporal changes in tree health from a national grid of permanent sample plots. The health of individual t rees is assessed by col lect ing quanti ta t ive measurements of different crown condit ions and types of stem and root damage. Several years of data have now been collected from 18 states and summarized (Stolte 1997). To date, the FHM program has focused on reporting descriptive stat ist ics of measured values of tree health. However, interpretations of differences among tree species, locations, and measurement years are l imited without a corresponding knowledge of what values represent healthy and unhealthy trees. Conversely, evaluations of tree health could be improved if models depicting overall condit ions of trees were based on an integrated set of health indicators (Gillespie 1995). Research Scientist , USDA Forest Service, Northeastern Research Station, Radnor, PA, USA. 334 The primary purpose of this paper is to provide addit ional meaning to values of tree health indicators by relat ing them to tree longevity. Analytical methods were used to first identify the best integrated set of indicators of imminent tree mortality. These indicators were then used to quantify cri t ical condit ions that precede tree death. Addit ional analyses determined how far in advance dying trees can be dist inguished from ones that survive. Associated procedures were used to evaluate the conditions of trees that are cut for comparison with conditions of trees that die or stay al ive.