it. These holes become avenues for disease and insects and occasionally a 

 tree is completely girdled. Birds also can affect tree reproduction, by 

 consuming seeds and nipping the buds from young trees. The mobility of birds 

 makes them important in seed dispersal and as vectors of various diseases 

 (Shugart et al. 1975; and Warner 1976). Woodpeckers were considered a major 

 factor in the spread of the chestnut blight and birds have been implicated as 

 important long-distance vectors of the parasite Arceuthobium vaginitum (dwarf 

 mistletoe) in Colorado (Hudler 1976). [A morphologically similar congener (A. 

 pusillujn ) occurs in the characterization area.] 



Cedar waxwings (often called cherry birds) and other fruit-loving species 

 disperse seeds of pin cherries ( Prunus pennsylvanica ) and raspberries ( Rubus 

 spp.). Both are important pioneering species in secondary plant succession 

 (Marks 1974). Insectivorous birds (e.g., warblers, vireos, and thrushes) can 

 be effective in preventing or delaying the outbreak of spruce budworm 

 populations, by consuming sufficient numbers of insects while populations are 

 low. Once the budworm population has erupted, however, birds are capable of 

 consuming only a small fraction of the budworm population (George and Mitchell 

 1948). 



Mammals found in Maine's forests are either primary or secondary consumers or 



both. Major herbivores are deer, moose, hares, mice, chipmunks, and 



squirrels. Secondary consumers are foxes, weasels, fishers, coyotes, minks, 

 bobcats, shrews, and bats. 



The influence of herbivorous mammals on forest vegetation is, for the most 

 part, insignificant. Only 2.5% of total net production in a pine-oak forest 

 on Long Island was consumed by herbivores, only a small portion of which was 

 due to mammals (Woodwell and Whittaker 1968). However, browsing by deer and 

 hares sometimes removes significant portions of the vegetation (see 

 "Terrestrial Mammals," chapter 17). Deer and hares can inhibit regeneration 

 by consuming seedlings and growing tips of saplings. Squirrels and mice can 

 destroy up to 90% of a forest's seed crop (Baker 1950); the extent to which 

 this is a problem in Maine is not known. On some large coastal islands where 

 hunting is restricted (Mt. Desert Island and Isle au Haut) deer populations 

 sometimes severely inhibit forest regeneration (Baird 1966). Concentrations 

 of deer in winter yarding areas can lead to overbrowsing of the vegetation in 

 the wintering area. White cedar, a preferred winter food, is particularly 

 vulnerable . 



ABIOTA 



Forest vegetation influences its environment by affecting the penetration of 

 solar radiation, the interception of precipitation, and wind and temperature 

 profiles. The degree of its influence depends on the density of the forest 

 canopy. As a rule, tolerant trees (i.e., sugar maple, beech, hemlock, and red 

 spruce) form dense crowns and intolerant trees (such as aspen, paper birch, 

 and pines) have more open canopies; consequently trees exert an increasing 

 influence over the forest environment as succession progresses. 



Solar Radiation 



The amount of light penetrating a forest canopy is a major factor affecting 

 plants in the understory and on the ground. Under dense canopies as little 



9-24 



