02-10-1997 Council Packet - Laserfiche WebLink

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MAPLE-BASSWOOD FORESTS OF HENNEPIN COUNTY: A THREATENED HABITAT June 1995 j p ne-hundred fifty years ago, Big Woods forest V-r covered close to one-half of Hennepin County. Today the forest persists only in isolated patches. Unless actively protected, these small remnants are likely to be destroyed within the next few years by suburban development. In 1856, when John Brunius and E. N. Darling of the United States General Land Office Survey divided Hennepin County into sections to sell to farmers, railroad companies, and speculators, they recorded that 154,000 acres of land in the county were covered by Big Woods (see map). The Big Woods were moist, shady forests of t^l, straight elm, sugar maple, basswood, and red oak trees. In the cool shade beneath the trees grew such distinctive herbs as ginseng, trout lilies, and spring beauties. In 1995, just 140 years after Brunius and Darling surveyed these primeval forests, the Big Woods have all but disappeared from Hennepin"County. About 1,100 acres, or less than 1% of the 1850 acreage of Big Woods, remain.The original extent of Big Woods in Hennepin County (shaded), as interpreted by Frances J. Marschner using Public Land Survey records from 1853-55. The Minnesota County Biological Survey has found that less than 1% of the Big Woods remains in 1995. Much of the Big Woods, or maple-basswood forest as it is now often called, was cleared for farmland in the early decades of Euro-American settlement. It is hard to give precise figures for how rapidly this clearing took place, although aerial photographs indicate that by the late 1930s the Big Woods had been reduced to a patchwork of mostly 40- to 80-acre parcels. What is very clear, however, is that in the decades following World War II the remainder of the county ’s maple-basswooa forest has been steadily eroded by spreading suburban development In fact more than 10% of the maple-basswood forest remaining in the county is slated for development within the next few months. While much of rural Hennepin County is experiencing high development pressure, forested sites appear to be especially targeted because they make shady, secluded and scenic lots for new homes. The ecological distinctiveness of a maple-basswood forest is dependent on its dense, nearly continuous tree canopy. V^en the tree canopy is fragmented by driveways, houses, and trails, the cool and moist conditions characteristic of the shady interior of the forest are altered. More sunlight reaches the forest floor and the shade-tolerant species typical of the forest are replaced by species more tv ’pical of open habitats and forest edges. Tnis forest fragmentation also promotes displacement of native forest shrubs and herbs by aggressive exotic species such as the ornamental shrubs common buckthorn and Tatarian honeysuckle. In addition, fragmentation leads to a decline in the diversity of native forest shrubs and herbs because the smaller populations that remain are more likely to be destroyed by pollution and physical damage. These include herbicide- and fertilizer-laden runoff from lawns and erosion or compaction of soils during construction. The end result of development, even where patches of trees are spared, is conversion of the maple-basswood forest into a degraded woodlot with houses in it.