Urban Forests and Arboriculture

Mapping Soil Drainage for Better Care of the Landscape and Collections

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Since 1922, the Arboretum’s globally important collections of trees and plants have been planted on what was once farmland, much of it in a floodplain. Farmers in the 19th and early 20th centuries drained a large proportion of this land by burying networks of clay pipes, called drain tiles, to carry water away. Some of these drain tiles already have been located and removed to restore the natural water flow, which has allowed for restoration of substantial areas of native plant communities. But many of the underground pipes remain.

The current survey aims to locate all these old drain tiles and assess their condition. The data will be combined with early surveys of drain tiles in natural areas, historical data, and GIS maps to create a full map of the altered hydrology, or water flow, of the Arboretum’s 1,700 acres. In some areas, the survey will require digging trenches to locate the old clay pipes. Guided by this comprehensive data, the Arboretum’s staff will be able to decide, based on the needs of plants in different areas of the collections and natural areas, whether to keep, repair, or remove the drain tiles in each location.

The Arboretum’s trees and plants include endangered species from around the world with substantial taxonomic and conservation value, as well as collections of oaks, elms, maples, magnolias, and crabapples that are recognized as significant by the North American Plant Collections Consortium. Although they all are adapted to the Arboretum’s temperate climate, they come from a wide variety of habitats, with varying needs for soil and water conditions.

Some of these species evolved along rivers and wetlands, where soils are often wet. Others evolved high on slopes and mountainsides, where water drains away much more completely. Keeping or removing drain tiles can make it possible to control soil drainage to suit different species. The knowledge provided by this comprehensive hydrologic mapping project will enable the Arboretum to make informed decisions about how to maximize soil conditions to help these important trees and plants live long, healthy lives.


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