t/ha; Bureau of Census 1977). This is far lower than the 67 to 85 tons/acre 

 (150 to 190 t/ha) of biomass in Maine's forests. 



In spite of their low plant biomass, agricultural lands produce as much plant 

 material (weight/unit area) each year as forest land (Lieth 1963). On a 

 world-wide basis mechanized agriculture is 1.5 times more productive than 

 moist temperate forests and 4 times more productive than boreal coniferous 

 forests. The energy and nutrient subsidies provided in the form of machinery, 

 fertilizers, pesticides, herbicides, and irrigation make the high productivity 

 of farms possible. Without mechanization farmland is only about equally 

 productive as boreal forests and less than half as productive as moist 

 temperate forests. No data are available on the productivity of Maine's 

 agricultural land. Farm productivity is measured in bushels or pounds of 

 usable product and does not include roots and unmerchantable stems or leaves. 



The plant material produced on agricultural land is utilized primarily by 

 people or domestic livestock. A hypothetical energy budget constructed for a 

 field of soy beans indicated that 43% of the net primary production was used 

 by people (Odum 1971). Decomposition accounted for 44% (compared to nearly 

 99% in forest systems), insect and invertebrate pests consumed nearly 7%, and 

 beneficial symbiotic organisms utilized the remaining 7%. 



To maximize the plant material harvested from farmland, the primary consumers 

 that feed on crops are controlled. The most important consumers are 

 invertebrate and insect pests which are controlled with chemical pesticides. 

 As a rule, vertebrate consumers cause only local problems in Maine. Some 

 vertebrates that can be pests on agricultural lands are red-winged blackbirds, 

 grackles, robins, sparrows, starlings, mice, woodchucks, hares, deer, bears, 

 and raccoons. 



Higher level consumers found on farmland are those that feed primarily on 

 invertebrates and small vertebrates. These include songbirds, raptors (hawks 

 and owls), shrews, weasels, foxes, and coyotes. For the most part these 

 species utilize the edges of farmland, where it intersperses with forests, 

 wetlands, and oldfields, because agricultural land lacks consistent food and 

 cover throughout the year. 



Abiotic Factors 



The vegetation on farmland is generally sparse and may be absent for much of 

 the year; consequently, it exerts very little influence over microclimatic 

 features, such as rainfall, temperature, wind, and solar radiation. These 

 variables fluctuate more widely on agricultural land than in forests. 



Growing seasons along the Maine coast range between 130 and 160 days in length 

 (table 10-4) . They are influenced by the marine climate throughout the 

 characterization area and differences in growing season are due to local 

 topography. Mean frost data for several locations along the coast also are 

 shown in table 10-4. Because agricultural lands lack the protective 

 vegetation of forest lands, spring frosts may occur up to 14 days later and 

 fall frosts 15 to 40 days earlier on agricultural lands than in forests (Sartz 

 1957). 



10-5 



10-80 



