@inbook {KNZ001114,
	title = {Ecological consequences of the replacement of native grassland by Juniperus virginiana and other woody plants},
	booktitle = {Ecological Studies Vol. 196, Western North American Juniperus communities: A dynamic vegetation type},
	year = {2008},
	pages = {156 -169},
	publisher = {Springer-Verlag, NY},
	organization = {Springer-Verlag, NY},
	abstract = {<p>Although grasslands have been altered by humans for thousands of years (Wedel 1961; Bond et al. 2003), the loss of grassland as a result of anthropogenic activities has increased dramatically over the past 150 years. When Europeans first settled the Midwest and Great Plains, the greatest threat to native grasslands was the conversion of the most highly productive of these ecosystems to row-crop agriculture (Samson and Knopf 1994). Later, with improvements in soil moisture management and irrigation technology, even low-productivity grasslands were plowed. Today, those remnants of the most productive grasslands that escaped the plow are threatened, as are most of Earth\&rsquo;s ecosystems, by a variety of global change phenomena (Vitousek et al. 1997), with the invasion and expansion of woody species into grasslands one of the greatest of these threats. The replacement of grasslands by shrubland, woodland, and forest is a concern not only in the United States but worldwide (Archer et al. 1988; Van Auken 2000; Roques et al. 2001; Silva et al. 2001). Species of woody plants that invade grasslands may include both native plants which previously existed as more minor components of the ecosystem as well as alien species (Bragg and Hulbert 1976; Harcombe et al. 1993).</p>},
	keywords = {LTER-KNZ},
	doi = {10.1007/978-0-387-34003-6_8},
	url = {https://link.springer.com/chapter/10.1007\%2F978-0-387-34003-6_8},
	author = {Alan K. Knapp and McCarron, J.K. and Silletti, A.M. and Hoch, G.A. and Heisler, J.L. and Lett, M.S. and John M. Blair and J. M. Briggs and M.D. Smith},
	editor = {Van Auken, O.W.}
}
@article {KNZ00960,
	title = {An ecosystem in transition: causes and consequences of the conversion of mesic grassland to shrubland},
	journal = {BioScience},
	volume = {55},
	year = {2005},
	pages = {243 -254},
	abstract = {Woody plant expansion is one of the greatest contemporary threats to mesic grasslands of the central United States. In this article, we synthesize more than 20 years of research to elucidate the causes and consequences of the ongoing transition of C4-dominated grasslands to savanna-like ecosystems codominated by grasses and woody plants. This transition is contingent on fire-free intervals, which provide the opportunity for recruitment both of new individuals and of additional shrub and tree species into this grassland. Once shrubs establish, their cover increases regardless of fire frequency, and infrequent fires accelerate the spread of some shrub species. This process has resulted in a new dynamic state of shrub{\textendash}grass coexistence in the mesic grasslands of North America. Important consequences of this shift in plant life-form abundance include alterations in plant productivity, species diversity, and carbon storage. Without drastic measures such as mechanical removal of shrubs, it is unlikely that management of fire and grazing regimes alone will be sufficient to restore historic grass dominance in these ecosystems.},
	keywords = {LTER-KNZ, fire, Grasslands, Grazing, tallgrass prairie, woody vegetation},
	doi = {10.1641/0006-3568(2005)055[0243:AEITCA]2.0.CO;2},
	author = {J. M. Briggs and Alan K. Knapp and John M. Blair and Heisler, J.L. and Hoch, G.A. and Lett, M.S. and McCarron, J.K.}
}
@article {KNZ00944,
	title = {Woody plant encroachment and removal in mesic grassland: production and composition responses of herbaceous vegetation},
	journal = {American Midland Naturalist},
	volume = {153},
	year = {2005},
	pages = {217 -231},
	abstract = {The clonal shrub Cornus drummondii is rapidly displacing mesic grassland in the central U.S. due to fire suppression and changes in land use. Once established, this shrub is not readily eliminated by the return of frequent fire, leading to significant and perhaps irreversible shifts in tallgrass prairie structure and function. We assessed the impacts of C. drummondii encroachment on herbaceous aboveground net primary production (ANPP) and plant community structure in tallgrass prairie and the role this species plays in the conversion of grassland ecosystems to shrub/woodlands. We also removed established C. drummondii clones to assess the potential of the grassland ecosystem to recover after shrub dominance. Aboveground net primary production, vegetative cover and species richness and diversity (exclusive of C. drummondii) were significantly reduced beneath shrub islands relative to open grassland, with reductions in ANPP and richness of up to 94 and 45\%, respectively. Forbs were the dominant growth form in the C. drummondii understory, and 10 species primarily associated with woodland habitats occurred only within shrub islands. Upon removal of C. drummondii, ANPP, richness and diversity recovered to grassland values within 2 y; however, forbs remained the dominant growth form, comprising 73\% of total cover. These results indicate that C. drummondii exerts strong control over the structure and function of unburned mesic grassland ecosystems and that this shrub may be key in the conversion of grasslands to woodlands. Removal of C. drummondii resulted in some aspects of recovery, but the return of graminoid dominance was not attained after 2 y. This represents a legacy effect of C. drummondii of unknown duration. Prevention of woody species encroachment through frequent burning is a preferred management option for this ecosystem.},
	keywords = {LTER-KNZ},
	doi = {10.1674/0003-0031(2005)153[0217:WPEARI]2.0.CO;2},
	author = {Lett, M.S. and Alan K. Knapp}
}
@article {KNZ00892,
	title = {Influence of shrub encroachment on aboveground net primary productivity  and carbon and nitrogen pools in a mesic grassland},
	journal = {Canadian Journal of Botany},
	volume = {82},
	year = {2004},
	pages = {1363 -1370},
	abstract = {The clonal shrub Cornus drummondii C.A. Mey. is rapidly increasing in cover and displacing mesic grassland species in the central USA as a consequence of fire suppression. We assessed the impact of C. drummondii on carbon (C) and nitrogen (N) pools and C fluxes in a tallgrass prairie in eastern Kansas, USA, through a comparison of both burned and unburned C. drummondii islands with open grassland areas. Allometric equations relating C. drum mondii foliage and wood biomass to basal stem diameter were developed to estimate aboveground biomass and net primary productivity (ANPP) of C. drummondii. Within C. drummondii islands, ANPP was 496 {\textpm} 45 g C{\textperiodcentered}m2{\textperiodcentered}year1, nearly three times that within open grassland (167 {\textpm} 13 g C{\textperiodcentered}m2{\textperiodcentered}year1). As a result of greater aboveground biomass, aboveground C and N storage within shrub islands (3270 {\textpm} 466 g C{\textperiodcentered}m2, 37.9 {\textpm} 5.3 g N{\textperiodcentered}m2) was substantially greater than that within open grassland (241 {\textpm} 33 g C{\textperiodcentered}m2, 6.1 {\textpm} 0.8 g N{\textperiodcentered}m2). No change in soil organic C or total N to 10-cm depth was evident; however, soil CO2 flux was significantly reduced in C. drummondii islands relative to the open grassland. The storage of C in aboveground biomass of C. drummondii represents a significant short-term increase in C storage relative to open grassland. However, potential alterations in belowground processes must be quantified before the long-term net effect of shrub encroachment on C and N pools within this mesic grassland can be determined.Key words: aboveground biomass, Cornus drummondii, net primary productivity, shrub encroachment, tallgrass prairie.},
	keywords = {LTER-KNZ},
	doi = {10.1139/b04-088},
	author = {Lett, M.S. and Alan K. Knapp and J. M. Briggs and John M. Blair}
}
@article {KNZ00838,
	title = {Consequences of shrub expansion in mesic grassland:  resource alterations and graminoid responses},
	journal = {Journal of Vegetation Science},
	volume = {14},
	year = {2003},
	pages = {487 -496},
	abstract = {In the mesic grasslands of the central United States, the shrub Cornus drummondii has undergone widespread expansion in the absence of recurrent fire. We quantified alterations in light, water and N caused by C. drummondii expansion in tall-grass prairie and assessed the hypothesis that these alterations are consistent with models of resource enrichment by woody plants. Responses in graminoid species, particularly the dominant C4 grass Andropogon gerardii, were concurrently evaluated. We also removed established shrub islands to quantify their legacy effect on resource availability and assess the capability of this grassland to recover in sites formerly dominated by woody plants. The primary effect of shrub expansion on resource availability was an 87\% reduction in light available to the herbaceous understorey. This reduced C uptake and N use efficiency in A. gerardii and lowered graminoid cover and ANPP at the grass-shrub ecotone relative to undisturbed grassland. Shrub removal created a pulse in light and N availability, eliciting high C gain in A. gerardii in the first year after removal. By year two, light and N availability within shrub removal areas returned to levels typical of grassland, as had graminoid cover and ANPP were similar to those in open grassland. Recovery within central areas of shrub removal sites lagged behind that at the former grass-shrub ecotone. These results indicate that the apparent alternative stable state of C. drummondii dominance in tall-grass prairie is biotically maintained and driven by reductions in light, rather than resource enrichment. Within areas of shrub removal, the legacy effect of C. drummondii dominance is manifest primarily through the loss of rhizomes of the dominant grasses, rather than any long-term changes in resource availability. C. drummondii removal facilitates grassland recovery, but the effort required to initiate this transition is a significant cost of woody plant expansion in mesic grasslands. Prevention of woody plant expansion in remnant tall-grass prairies is, therefore, a preferred management option.},
	keywords = {LTER-KNZ, Cornus drummondii, Grassland recovery, land cover change, Tall-grass prairie, Woody plant expansion},
	doi = {10.1111/j.1654-1103.2003.tb02175.x},
	author = {Lett, M.S. and Alan K. Knapp}
}
@mastersthesis {KNZ00885,
	title = {Effects of shrub encroachment and removal on plant community composition and ecosystem structure and function in a mesic grassland},
	volume = {MS Thesis},
	year = {2003},
	pages = {1 -109},
	school = {Kansas State University},
	type = {M.S. Thesis},
	address = {Manhattan, KS},
	keywords = {LTER-KNZ},
	author = {Lett, M.S.}
}
@article {KNZ005,
	title = {Altered rainfall patterns, gas exchange and growth in C3 and C4 grassland species},
	journal = {International Journal of Plant Sciences},
	volume = {163},
	year = {2002},
	pages = {549 -557},
	keywords = {LTER-KNZ},
	author = {Fay, P.A. and Carlisle, J.D. and Danner, B.T. and Lett, M.S. and McCarron, J.K. and Stewart, C. and Alan K. Knapp and John M. Blair and Scott. L. Collins}
}
@article {KNZ00827,
	title = {Rainfall variability, carbon cycling and plant species diversity in a mesic grassland},
	journal = {Science},
	volume = {298},
	year = {2002},
	pages = {2202 -2205},
	abstract = {<p>Ecosystem responses to increased variability in rainfall, a prediction of general circulation models, were assessed in native grassland by reducing storm frequency and increasing rainfall quantity per storm during a 4-year experiment. More extreme rainfall patterns, without concurrent changes in total rainfall quantity, increased temporal variability in soil moisture and plant species diversity. However, carbon cycling processes such as soil CO2 flux, CO2 uptake by the dominant grasses, and aboveground net primary productivity (ANPP) were reduced, and ANPP was more responsive to soil moisture variability than to mean soil water content. Our results show that projected increases in rainfall variability can rapidly alter key carbon cycling processes and plant community composition, independent of changes in total precipitation.</p>},
	keywords = {LTER-KNZ},
	doi = {10.1126/science.1076347},
	url = {https://science.sciencemag.org/content/298/5601/2202},
	author = {Alan K. Knapp and Fay, P.A. and John M. Blair and Scott. L. Collins and M.D. Smith and Carlisle, J.D. and Harper, C.W. and Danner, B.T. and Lett, M.S. and McCarron, J.K.}
}
@article {KNZ00864,
	title = {Carbon and water relations of juvenile Quercus species in tallgrass prairie},
	journal = {Journal of Vegetation Science},
	volume = {12},
	year = {2001},
	pages = {807 -816},
	abstract = {In ecosystems where environments are extreme, such as deserts, adult plant species may facilitate the establishment and growth of seedlings and juveniles. Because high temperatures and evaporative demand characterize tall-grass prairies of the central United States (relative to forests), we predicted that the grassland-forest ecotone, by minimizing temperature extremes and moderating water stress, may function to facilitate the expansion of Quercus species into undisturbed tall-grass prairie. We assessed the carbon and water relations of juvenile Quercus macrocarpa and Q. muhlenbergii, the dominant tree species in gallery forests of northeast Kansas, in ecotone and prairie sites. To evaluate the potentially competitive effects of neighboring herbaceous biomass on these oaks, juveniles (< 0.5 m tall) of both species also were subjected to either: (1) removal of surrounding above-ground herbaceous biomass, or (2) control (prairie community intact) treatments. Herbaceous biomass removal had no significant effect on gas exchange or water relations in these oak species in either the prairie or the ecotone environment. Although the ecotone did alleviate some environmental extremes, photosynthetic rates and stomatal conductance were ca. 20 \% higher (p < 0.05) in both oaks in prairie sites vs. the ecotone. Moreover, although leaf temperatures on average were higher in oaks in the prairie, high leaf temperatures in the ecotone had a greater negative effect on photosynthesis. These data suggest that the grassland-forest ecotone did not facilitate the growth of Quercus juveniles expanding into this grassland. Moreover, the carbon and water relations of juvenile oaks in the prairie appeared to be unaffected by the presence of the dominant C4 grasses.},
	keywords = {LTER-KNZ, Ecotone, Facilitation, forest expansion, Quercus, tallgrass prairie},
	doi = {10.2307/3236868},
	author = {Fay, P.A. and Carlisle, J.D. and Danner, B.T. and Lett, M.S. and McCarron, J.K. and Stewart, C. and Alan K. Knapp and John M. Blair and Scott. L. Collins}
}
