prepared the way for the later entrance of fungi, 

 iimjji-eating species, and j^redaceoiis forms. 



In tlie decay of logs of such nothern trees as pine, 

 >pruce, and fir, the character of the food available is 

 important to the succession that occurs (Graham 

 l"i5. Ingles 1931). Bark beetles require fresh green 

 tissues of the inner bark and cambium, and hence 

 occupy the tree only for the few weeks that these 

 tissues remain. The long-horned beetles and wood 

 liorers retjuire green tissue for their younger stages. 

 As they mature, they are able to digest the solid 

 wood. Tlie horntail larva can digest solid wood as 

 soon as it hatches. The outer bark is most difficult 

 to digest but it does furnish food for some species of 

 Lepidoptera and Diptera. 



In addition to invertebrates, there are several 

 vertebrates, particularly mice, shrews, moles, am- 

 pliibians, and reptiles, that may be mentioned as part 

 of the soil and ground fauna. These animals often 

 have extensive underground runways and feed on the 

 invertebrates in the soil, as well as on each other. 



Foliage arthropods 



Foliage insects and spiders are represented by 

 large numbers both of species and individuals (Gra- 

 ham 1952). Spiders, ants, flies, beetles, leafhoppers, 

 bugs, and larvae ordinarily predominate (Table 9-7 ) ; 

 population depends directly on the amount of green 

 foliage present. The species present depend on the 

 type of vegetation, stratum, season, time of day, lo- 

 cality, and climate. Outbreaks of particular species 

 may occur irregularly or periodically and several 

 hundreds or even thousands of individuals may occur 

 in each tree. Spruce budworms and walkingsticks 

 are sometimes so abundant that their excrement or 

 eggs dropping to the ground sounds like the patter 

 of raindrops. 



Birds 



Breeding-bird populations in forest communi- 

 ties vary with the fertility of the forest, but are com- 

 monly between 100 and 400 pairs per -K) hectares ( 100 

 acres), which would be equivalent to 5 to 20 indi- 

 vidual birds per hectare (2 to 4/acre) (Table 9-11). 

 In addition, there is often a large non-breeding popu- 

 lation present. On a 16 hectare (40 acre) spruce-fir 

 forest in Maine there were 154 territorial males 

 present prior to June 13. Between June 21 and July 

 5 a determined effort w^as made to reduce the popula- 

 tion of songbirds, and a total of 352 males was taken 

 from the area, more than w-ere actually nesting at the 

 start of the operations. Yet on July 11 there were 

 still 40 males present and proclaiming territories. 



FIG. 9-11 Adult red-shafted flicker and young at nest in an 

 aspen forest, Oregon (courtesy U.S. Forest Service). 



One hundred twenty-six females and 49 individuals 

 of undetermined sex were also removed (Hensley 

 and Cope 1951). This floating population is more 

 numerous than the number of nest sites available in 

 the community, but it functions as a pool from which 

 individuals may replace any nesting birds that die, 

 or take over any suitable niche that becomes avail- 

 able for one or another reason. This population pres- 

 sure doubtless keeps the community saturated with 

 breeding birds, tends to maintain the nesting popula- 

 tion at a high peak of efficiency, and is a challenge to 

 individuals to exploit new adaptations and to occupy 

 new niches. It is therefore a potent factor in evolu- 

 tion. 



In a mixed deciduous-coniferous forest in Europe, 

 a bird population of 662 individuals per 40 hectares 

 (100 acres) was estimated to have a biomass of 47 

 kg (103 lb). In the same area, there were 528 in- 

 dividual mammals of biomass 264 kg (580 lb) (Tur- 

 cek 1952). The number and biomass of birds is gen- 

 erally less than that of mammals (Hamilton and Cook 

 1940). 



Mammals 



Rodents (mice, chipmunks, squirrels) and in- 

 sectivores (shrews, moles) are the most abundant 

 small mammals of forest communities. Resident sum- 



Grassland, forests, and forest-edges 135 



