. An analysis of Pennsylvania's forest resources. Forests and forestry Pennsylvania; Forest management Pennsylvania. Pennsylvania forests also ex- perienced a sizeable increase in saw- timber volume, from to bil- lion board feet —a 48-percent in- crease. The magnitude of the saw- timber volume increase is larger than those observed in the neighboring states, in part because Pennsylvania was logged over before those states. There are a number of factors that help explain the sizeable grow- ing-stock and proportionately larger sawtimber increase, the most impor- tant of which is that P
. An analysis of Pennsylvania's forest resources. Forests and forestry Pennsylvania; Forest management Pennsylvania. Pennsylvania forests also ex- perienced a sizeable increase in saw- timber volume, from to bil- lion board feet —a 48-percent in- crease. The magnitude of the saw- timber volume increase is larger than those observed in the neighboring states, in part because Pennsylvania was logged over before those states. There are a number of factors that help explain the sizeable grow- ing-stock and proportionately larger sawtimber increase, the most impor- tant of which is that Penn's Woods are maturing. A significant portion of the trees have reached large pole- timber or small sawtimber size—a time in the life of trees when annual growth rates are high. While the amount of timber volume grown in a given year is influenced by a host of favorable and unfavorable factors, the annual trend since the last survey has been for successively larger amounts of volume to be added to the growing-stock inventory (see Growth and Removals). The maturation of the forests may be easily seen in Figures 15 and 16. In Figure 15, the distribution of numbers of growing-stock trees by diameter class, shows proportionate- ly more trees in the 10-inch class and above and proportionately fewer trees in the 6- and 8-inch classes in 1978 than in 1965. Figure 16 shows the growing-stock volumes by diame- ter class for the two surveys. In es- sence, a bulge of timber volume which entered the growing stock in- ventory probably around the time of the first survey in the early 1950's is passing through the diameter classes. This bulge originated in the early decades of this century when most of Pennsylvania's forest lands were logged, often repeatedly. About the same time, large acreages of farmland, mostly of marginal produc- tivity, were abandoned. People were leaving the farms for jobs in the state's rapidly expanding industrial cities. As a result, large blocks of land revert
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