Aspen Bibliography


Temperature of upland and peatland soils in a north central Minnesota forest


D.S. Nichols

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Canadian Journal of Soil Science





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Soil temperature strongly influences physical, chemical, and biological activities in soil. However, soil temperature data for forest landscapes are scarce. For 6 yr, weekly soil temperatures were measured at two upland and four peatland sites in north central Minnesota. One upland site supported mature aspen forest, the other supported short grass. One peatland site was forested with black spruce, one supported tall willow and alder brush, and two had open vegetation — sedges and low shrubs. Mean annu- al air temperature averaged 3.6°C. Mean annual soil temperatures at 10- to 200-cm depths ranged from 5.5 to 7.6°C among the six sites. Soils with open vegetation, whether mineral or peat, averaged about 1°C warmer annually and from 2 to 3°C warmer dur- ing summer than the forested soils. The tall brush peatland was cooler than all other sites due to strong groundwater inputs. The mineral soils warmed more quickly in the spring, achieved higher temperatures in the summer, and cooled more quickly in the fall than the peat soils; however, the greatest temperature differences between mineral and peat soils occurred at or below 50 cm. In the upper 20 cm, vegetation and groundwater had greater effects on temperature than did soil type (mineral or peat). Summer soil temperatures were higher, relative to air temperature, during periods of greater precipitation. This effect was minimal at upland sites but substantial in the peatlands. In spite of the persistent sub-freezing air temperatures typical of Minnesota winters, signifi- cant frost developed in the soils only in those years when severe cold weather arrived before an insulating cover of snow had accu- mulated.