Tree-value conversion standards (Mendel et al. 1976; 

 DeBald and Mendel 1976) were used to estimate timber- 

 value losses. These standards represent consistent regional 

 measures of a standing tree's net value (marginal value 

 product or shadow price) in the production of 4/4-inch 

 lumber and/or pulpwood, allowing for the cost of conver- 

 sion. They account for a tree's species, diameter, merchant- 

 able height, and tree grade (based on butt-log grade 

 measures). For example, a 16-inch-diameter red oak with a 

 grade 2 butt log and merchantable height of two logs, con- 

 taining 180 board feet (International 1/4-inch rule), was 

 valued at $7.08 on the stump. 



Results 



Table 1 summarizes observed rates of tree mortality and 

 losses in basal area and timber value for the central Penn- 

 sylvania plots by species group and site productivity class. 

 As expected, the oaks bore the brunt of gypsy moth attacks 

 and suffered much higher mortality rates than other less 



vulnerable species. By 1985, the cumulative mortality rate 

 for oak trees was 23 percent. The rate of timber-value loss 

 for oaks was 4 times that for all other species combined. 



Generally, poor 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. Rates of loss in oak basal area and timber 

 value also were significantly lower on poor sites. 



Why mortality rates for oak were lower on poorer timber- 

 growing sites remains a mystery. One hypothesis is that 

 trees on poor sites develop root systems and crown struc- 

 tures that make them more adaptable to stresses brought 

 on by things like gypsy moth defoliation and short-term 

 drought. Another related theory is that shoestring root rot 

 and the two-lined chestnut borer (both major mortality 

 agents) are less active on poorer sites. These are matters for 

 future study. 



Table 1.— Mortality associated with gypsy moth in central Pennsylvania (1978-85), by 

 site productivity class and species group 



No f Mortality rate for: 



Site No. of Species sample Basal Timber 

 class plots group trees Trees area value 



Percent 



Poor 



189 



Oaks 



2,985 



18 



13 



12 







Other 



2,343 



10 



9 



8 







All 



5,328 



14 



12 



11 



Medium 



269 



Oaks 



3,320 



26 



23 



23 







Other 



3,335 



15 



11 



7 







All 



6,655 



21 



20 



20 



Good 



116 



Oaks 



1,056 



28 



24 



18 







Other 



1,649 



17 



12 



4 







All 



2,705 



21 



19 



13 



All 



574 



Oaks 



7,361 



23 



20 



20 







Other 



7,327 



14 



11 



5 







All 



14,688 



19 



17 



16 



