United States 

 Department of 

 Agriculture 



Forest Service 



Northeastern Forest 

 Experiment Station 



Research Note NE-340 



Site Productivity and Tree 

 Mortality on New Frontiers 

 of Gypsy Moth Infestation 



David A. Gansner 



--- 



Abstract 



Recent analysis of forest stand losses to gypsy moth has 

 provided basic information for analyzing the relationship 

 between forest site productivity and tree mortality on new 

 frontiers of infestation. Poor timber-growing sites had the 

 lowest rates of mortality. Oak mortality (number of trees) 

 amounted to 18 percent on poor sites compared with 26 

 percent on medium and 28 percent on good sites. 



A number of studies have explored the relationship between 

 forest site productivity and tree mortality in forest stands 

 infested with gypsy moth. Results have been mixed. For 

 example, Kegg (1973) and Herrick (1982) found higher mor- 

 tality rates associated with poorer timber-growing sites. But 

 Hicks and Fosbroke (1987) and Statler and Serrao (1983) 

 discovered greater mortality on better sites. To add to the 

 body of research on this subject, we analyzed the relation- 

 ship between mortality rates and forest site productivity on 

 new frontiers of infestation in central Pennsylvania. 



DAVID A. GANSNER is a research forester, Northeastern 

 Forest Experiment Station, Broomall, Pennsylvania. 



Measurements have been taken each year since 1978 to 

 monitor and evaluate impacts of the gypsy moth on forest 

 trees in central Pennsylvania. The project, a cooperative 

 venture of the Pennsylvania Bureau of Forestry and the 

 USDA Forest Service, uses a network of some six hundred 

 1/10-acre plots located between Carlisle and State College, 

 Pennsylvania. This was the leading edge of gypsy moth 

 infestation in 1978 when the plots were established, before 

 the stands were infested. Herrick and Gansner (in press) 

 contains a complete description of the plot network. 



Of particular interest in this paper are estimates of site pro- 

 ductivity, tree mortality, and timber-value loss. Cumulative 

 mortality rates were recorded on 574 central Pennsylvania 

 plots from 1979 through 1985 for nearly 15,000 trees 3.0 

 inches d.b.h. and larger. Site indexes were estimated for 

 each plot from age and height data for dominant northern 

 red oaks (Quercus rubra) within or in the immediate vicinity 

 of the plots. Trees that had been suppressed in the past 

 were avoided. Site-index estimates were determined from 

 Schnur's (1937) chart for upland oaks. Plots and their 

 respective sample trees were sorted into three site index 

 (SI) classes— poor (SI < 55), medium (SI 55 to 74), and 

 good (SI 75 +). 



