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Browse of forest understory vegetation by deer and other large ungulates alters ecosystem processes, making it difficult to regenerate forest land in herbivory-stressed areas. Seventy years ago, Aldo Leopold identified problem areas in the United States where overpopulation of whitetailed deer (Odocoileus virginianus) was likely to lead to overbrowsing of nutritive plants. Species of plants with little or no nutritive value would thereby gain a competitive advantage. Recent measurements of browse impacts on regionwide forest inventory plots in the midwestern and northeastern United States provide the opportunity to review the work of Leopold and others. A visualization of the probability of browse impact levels that warrant consideration during regeneration planning is presented for comparison to historical maps.Currently, 59 percent of the 182.4 million acres of forest land inventoried in the Midwest and Northeast was estimated to have moderate or high browse impacts. The Mid-Atlantic region had the highest proportion of forest land with moderate or high browse impacts (79 percent). The oak/hickory (Quercus/Carya) and maple/beech/birch (Acer/Fagus/Betula) forest-type groups each had percentages of forest land with moderate or high impacts above the regional average, 69 percent and 65 percent, respectively. The problem areas described by Leopold and others persist

Stem dissection and dendroecological methods were used to examine the effects of thinning and defoliation by gypsy moth (Lymantria dispar L.) on wood volume increment in oaks (Quercus rubra L., Q. alba L., Q. prinus L.). A model was developed to evaluate radial volume increment growth at three time periods: before defoliation, during defoliation and after defoliation, as a function of species, defoliation intensity and crown position. Volume increment during these same time periods was also compared at different stem locations. Trees were defoliated for two consecutive years and results indicated that volume loss was greater during the second year of defoliation with complete recovery taking 2-3 years after defoliation. Oaks in thinned stands had similar reductions in annual volume increment during defoliation as those in the unthinned stand. Annual volume increment demonstrated a decreasing trend from stump to base of the live crown and volume increment of the lowest log (from stump height to 1.37 m), was always higher than upper log sections, even during defoliation. Both earlywood and latewood increments were reduced during defoliation; however, latewood reductions were distributed along entire stems while earlywood reductions were greater on upper stem sections within the crown.

The causes of canopy stratification were investigated in five mixed stands of red spruce (Picearubens Sarg.), hemlock (Tsugacanadensis (L.) Carr.), and white pine (Pinusstrobus L.) in eastern Maine. All species were present in all crown classes; however, there was a clear pattern of pine dominance and eventual emergence. Red spruce was prevalent in the middle stratum, and hemlock most common in the lower strata. Canopy stratification was caused by interspecific differences in shade tolerance and height growth, and by multicohort structures. The multicohort structures developed as a result of episodic partial disturbances such as spruce budworm (Choristoneurafumiferana Clemens) outbreaks and partial harvesting that both initiated regeneration and released previously suppressed trees of older, surviving cohorts. Spatial and temporal variability in disturbances created extremely variable patterns of competition among cohorts, resulting in a more complex developmental pattern than would be found in a single-cohort model involving stand-replacing disturbances.