@article {KNZ001095,
	title = {Altered ecosystem nitrogen dynamics as a consequence of land cover change in tallgrass prairie},
	journal = {American Midland Naturalist},
	volume = {158},
	year = {2007},
	pages = {432 -445},
	abstract = {In recent decades, substantial areas of North American tallgrass prairie have been lost to the establishment and expansion of woodlands and forests, including those dominated by eastern redcedar (Juniperus virginiana). This shift in dominant plant life form, from C4 grasses to coniferous trees, may be accompanied by changes in productivity, standing stocks of biomass and nutrients and biogeochemical cycles. The goal of this study was to quantify and compare major pools and fluxes of nitrogen in recently established (<= 80 y) redcedar forests and adjacent native grasslands. Three former grassland sites in the Flint Hills region of Kansas that developed closed-canopy redcedar forests in the recent past were paired with adjacent grassland sites on similar soil type and topographic position (n  =  3 sites/land cover type), and selected soil and plant nitrogen pools and fluxes were measured in replicate plots (n  =  6/site) along transects in each forest or grassland site over a 20-mo period. We found few significant differences in median soil inorganic N pools or net N mineralization rates between the forest and grassland sites, though there was a trend for greater concentrations of inorganic N in grassland sites on most sample dates, and cumulative growing season net N mineralization averaged 15\% less in forest sites (14.3 kg N{\textperiodcentered}ha-1{\textperiodcentered}yr-1) than in grassland sites (16.9 kg N{\textperiodcentered}ha-1{\textperiodcentered}yr-1). Mean aboveground plant productivity of forest sites (9162 kg ha-1 yr-1) was about 2.5{\texttimes} greater than that of comparable grasslands (similar soils and topographic position), in spite of similar levels of soil N availability. This resulted in an ecosystem-level nitrogen use efficiency (ANPP:litterfall N) in forests that was more than double that of the grasslands they replaced. Additional changes in N cycling associated with redcedar forest development included large accumulations of N in aboveground biomass and transfer to the forest floor via litterfall; redcedar aboveground biomass contained 617 kg N/ha, forest floor litter N was 253 kg N/ha, and litterfall N flux was 41 kg ha-1{\textperiodcentered}yr-1. These are substantial increases in aboveground biomass N accumulation, surface litter N inputs, and surface litter N accumulation compared to the native grasslands characteristic of this region. These fundamental shifts in ecosystem patterns and processes have the potential to alter regional biogeochemistry and both nitrogen and carbon storage throughout areas of the eastern Central Plains where coverage of redcedars is increasing.},
	keywords = {LTER-KNZ},
	doi = {10.1674/0003-0031(2007)158[432:AENDAA]2.0.CO;2},
	author = {Norris, M.D. and John M. Blair and Johnson, L.C.}
}
@article {KNZ0011,
	title = {Assessing the rate, mechanism and consequences of conversion of tallgrass prairie to Juniperus virginiana forest},
	journal = {Ecosystems},
	volume = {5},
	year = {2002},
	pages = {578 -586},
	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.},
	keywords = {LTER-KNZ, fire, forest expansion, Grazing, Juniperus virginiana, land-cover change, land-use change, red cedar, tallgrass prairie},
	doi = {10.1007/s10021-002-0187-4},
	author = {Hoch, G.A. and J. M. Briggs and Johnson, L.C.}
}
@article {KNZ00781,
	title = {Assessing changes in biomass, productivity, and C and N stores following Juniperus virginiana  forest expansion into tallgrass prairie},
	journal = {Canadian Journal of Forest Research},
	volume = {31},
	year = {2001},
	pages = {1940 -1946},
	abstract = {An increase in woody plant abundance in regions historically dominated by grasses is a recent land cover change in grasslands worldwide. In tallgrass prairies of North America, this increase in woody plant cover includes the development of dense stands of eastern redcedar (Juniperus virginiana L.). To evaluate the consequences of this ongoing land cover change for ecosystem functioning, we developed allometric equations, using data from Kansas and Oklahoma, to estimate aboveground biomass and productivity in closed-canopy redcedar stands. We then applied these equations to three closed-canopy redcedar stands, 3580 years old, which developed on sites formerly dominated by tallgrass prairie in eastern Kansas. Aboveground plant biomass for these redcedar-dominated sites ranged from 114 100 kg/ha for the youngest stand to 210 700 kg/ha for the oldest. Annual aboveground net primary productivity (ANPP) ranged from 7250 to 10 440 kg{\textperiodcentered}ha1{\textperiodcentered}year1 for the oldest and younger redcedar stands, respectively. Estimates of ANPP in comparable tallgrass prairie sites in this region average 3690 kg{\textperiodcentered}ha1{\textperiodcentered}year1 indicating a large increase in C uptake and aboveground storage as a result of the change from prairie to redcedar forests. Therefore, the widespread occurrence of redcedars across the woodlandprairie ecotone suggests that this land-cover change may have important consequences for regional net C storage.},
	keywords = {LTER-KNZ, tallgrass prairie},
	doi = {10.1139/x01-132},
	author = {Norris, M.D. and John M. Blair and Johnson, L.C. and McKane, R.B.}
}
