Assessing the Rate, Mechanisms, and Consequences of the Conversion of Tallgrass Prairie to Juniperus virginiana Forest |
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Authors: | John M Briggs Greg A Hoch Loretta C Johnson |
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Institution: | (1) Division of Biology, Kansas State University, Manhattan, Kansas 66502, USA, US;(2) Department of Plant Biology,, Arizona State University, Tempe, Arizona, USA, US |
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Abstract: | We assessed the determinants and consequences of the expansion of Juniperus virginiana L. (red cedar) populations into central US grasslands using historical aerial photos and field measurements of forest extent,
tree growth, fire-induced mortality, and responses in herbaceous species diversity and productivity. Photos from northeast
Kansas dating back to 1956 indicate that native tallgrass prairie can be converted to closed-canopy red cedar forest in as
little as 40 years (a 2.3% increase in forest cover per year). Mean tree density in 21 forested sites ranged from 130 to 3500
trees/ha, with most sites at more than 800 trees/ha. In younger stands, maximum growth rates of individual red cedar trees
exceeded 20 cm/y in height. Land management practices were critical to the establishment and growth of red cedar forest. Grazing
reduced the fuel loads by more than 30% in tallgrass prairie. Based on measurements of mortality for more than 1800 red cedar
trees, fire-induced mortality in grazed areas averaged 31.6% versus more than 90% at ungrazed sites. When tallgrass prairie
was converted to red cedar forest, herbaceous species diversity and productivity were drastically reduced, and most grassland
species were virtually eliminated. Consequently, community structure shifted from dominance by herbaceous C4 species to evergreen woody C3 species; this shift is likely to be accompanied by alterations in carbon storage and other ecosystem processes in a relatively
short time period. Here we present a conceptual model that integrates the ecological and socioeconomic factors that underlie
the conversion of grassland to red cedar forest.
Received 29 August 2001; accepted 5 February 2002. |
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Keywords: | : forest expansion Juniperus virginiana tallgrass prairie land-cover change land-use change fire grazing red cedar |
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