Primary Producers 



Trees that make up the canopy of a forest are the dominant producers, 

 sometimes accounting for 98% or more of the above-ground biomass and net 

 productivity (Ovington 1965). The relative abundance of the important 

 softwood and hardwood tree species (>6 inches; 15 cm dbh) for each of the 

 three forest units along coastal Maine is listed in table 9-5. In the Capitol 

 unit (which represents regions 2, 3, and 4) softwoods slightly outnumber 

 hardwoods (56% and 44% respectively); balsam fir is the most abundant species 

 (18%), followed by the soft maples (red and silver, combined 16%), and white 

 pine (11%). The abundance of pine in this region reflects the importance of 

 the pine-hardwood-hemlock forest type along the southwest coast of Maine. The 

 species composition of forests in the Washington and Hancock units 

 (representative of regions 5 and 6) is similar, where about 75% of the 

 commercial trees are softwoods. The most abundant species are red spruce 

 (27%), balsam fir (20% to 23%), and soft maples (10% to 12%). 



Forest vegetation beneath the canopy consists of immature or overtopped trees 

 (understory) , shrubs, nonwoody vascular plants, ferns, mosses, grasses, and 

 lichens. The extent to which these plants are present depends on the density 

 of the canopy, which controls the amount of light reaching the understory. 

 For example, the open canopy characteristic of aspen and birch stands allows 

 for the growth of a well-developed understory that usually is comprised of 

 young spruce and fir (that may eventually become dominant), shrubs, grasses, 

 ferns, and other herbaceous plants. Pine stands also have open canopies with 

 understories of hardwoods (often oak). Stands dominated by beech-birch-maple 

 are usually too dense for development of good herbaceous layers but seedlings 

 and saplings of overstory trees sometimes survive. In dense spruce-fir stands 

 the only vegetation beneath the canopy, if any, is a sparse growth of mosses 

 and lichens on the forest floor (Davis 1966). 



Forest biomass . Forest biomass, as the term is used here, refers to the 

 weight of the living vegetation on an area. This includes both above-ground 

 portions (stems, trunks, and leaves) and below-ground portions (roots) of all 

 plants. Biomass is usually represented on a dry-weight basis, which is 

 roughly equivalent to 50% of fresh weight. 



Fully stocked, mature, second growth forests in Maine support between 56 to 85 

 tons/acre (125 to 190 t/ha) of dry weight biomass (above and below ground; 

 Young et al. 1976). A survey of over 64,220 acres (26,000 ha) of forest land 

 in northern Maine indicates that second growth and mature softwood stands have 

 the greatest biomass, 78 to 84 tons/acre (175 and 188 t/ha), respectively, 

 followed by mixed stands, 63 and 78 tons/acre (141 and 175 t/ha) for second 

 growth and mature respectively and hardwoods, 56 and 70 tons/acre (125 and 157 

 t/ha; table 9-6; Young et al. 1976). Young stands support about one-third of 

 the biomass of older stands, and young hardwood biomass (26 tons/acre; 58 

 t/ha) is greater than for either softwoods (24 tons/acre;54 t/ha) or for mixed 

 species (13 tons/acre;29 t/ha). In a typical Maine forest nearly all (98%+) 

 of the living plant biomass is in the trees; the remainder is in shrubs and 

 herbs (table 9-7; Young et al. 1976). 



9-13 



10-80 



