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The keystone role of bison in North American tallgrass prairie

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... Utilizing bison, rather than livestock, also has tremendous merit as a rangeland conservation practice (Allred et al. 2011;Ratajczak et al. 2022). Bison grazing is preferable to cattle grazing because bison distribute their foraging activities over broader areas (cattle are limited by distance from water), bison are less selective, utilizing a broad array of grasses and sedges, and the combined impacts of bison grazing and other physical activities (horning, trampling, etc.) may help maintain grasslands (Coppedge and Shaw 1997;Knapp et al. 1999;Allred et al. 2011;Ranglack et al. 2023). Perhaps most importantly, bison are a native ungulate and their utilization is often consistent with goals of ecosystem maintenance and restoration (Truett et al. 2001;Allred et al. 2011;Fuhlendorf et al. 2018;Boyce et al. 2022;Ratajczak et al. 2022). ...
... Historically, bison were the dominant grazer throughout the Great Plains, affecting vegetation communities through herbivory, physical disturbance (e.g., hoofs, wallows, horning), nutrient cycling, and seed dispersal (McHugh 1958;Collins and Uno 1983;Polley and Collins 1984;Knapp et al. 1999). Bison moved both seasonally and nomadically, moving in response to seasonal changes in weather, seasonal changes in their environment, and changes in vegetation associated with fire and precipitation patterns (Samson and Knopf 1994;Plumb et al. 2009;McMillan et al. 2022). ...
... This protocol does not account for all scenarios that may arise, such as differential nutritional quality among sites with low biomass due to the development of grazing lawns. Grazing lawns are areas repeatedly clipped short by bison that have low biomass but high nutritional value (Knapp et al. 1999;Geremia et al. 2019). The number of sample plots (36) across the refuge allows site-to-site variation to be captured, and also means that the contributions of any one plot to the overall forage production estimate is somewhat small. ...
Technical Report
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The purpose of this protocol is to provide annual vegetation production information in order to help inform ruminant stocking rates. Conservation targets (desired conditions) are based on Ecological Site Descriptions (NRCS 2024b; Appendices D-N). Ecological Site Descriptions address the major plant species, plant growth habits, forage production and wildlife species, and are anchored in soil characteristics (Brown 2010; Heller et al. 2022; NRCS 2024b). Because multiple Ecological Sites occur on Rio Mora NWR grasslands, conservation targets take into account the representation (percentage) of each Ecological Site. The Ecological Site Descriptions suggest production in refuge grasslands should, depending on precipitation, range from 637 to 1,471 pounds per acre per year (lbs/ac/yr), averaging 1,074 lbs/ac/yr. The conservation target for minimum vegetation production on refuge grasslands is 637 lbs/ac/yr. The conservation target for desired forage production tis 1074 lbs/ac/yr. Estimated forage production, based on 36 random sample locations in refuge grasslands, will be used by refuge staff and partners to inform stocking decisions. Thresholds for decisions will be addressed in refuge vegetation management plans and habitat management plans.
... North American tallgrass prairie is an ecosystem defined and maintained by disturbance, primarily consisting of climatic variability, frequent fire, and the presence of large herbivores (Axelrod, 1985;Collins, 1987;Gibson & Hulbert, 1987). The latter disturbance was historically provided by large herds of American bison (Bison bison; Knapp et al., 1999), which have since been replaced by domestic cattle (Bos taurus) as the primary grazer in most of the remaining tallgrass ecosystem (Towne et al., 2005). While cattle and bison are both ruminant herbivores that fulfill similar ecological roles (Towne et al., 2005), each species possesses unique behaviors that contribute to the structure and function of the prairie ecosystem (Kohl et al., 2013). ...
... During dry periods, however, the exposed, compact surface of wallows likely experiences harsh xeric conditions. Bison wallows once played a role in maintaining the heterogeneity that defines North American tallgrass prairie (Collins & Barber, 1985;Knapp et al., 1999;McMillan et al., 2011;Miller et al., 2014;Polley & Wallace, 1986;Ratajczak et al., 2022). Wallows contribute to overall plant species diversity by providing habitat for plants dependent on disturbed patches of soil, as well as mesic or even aquatic species (Collins & Uno, 1983;Gibson, 1989;Polley & Collins, 1984;Trager et al., 2004). ...
... Collins and Uno (1983) suggested that wallows may increase local diversity by providing habitat for plants that cannot compete in the surrounding prairie. Many of the terrestrial plant species found in wallows at KPBS and other locations are annuals (Gibson, 1989;Knapp et al., 1999;Trager et al., 2004;Uno, 1989), so the composition of plant communities inside wallows can reasonably be expected to change from year to year with frequent burning (Collins & Uno, 1983). Indeed, the vegetation that is present on individual soil disturbances (i.e., wallows) has been reported to be closer in composition to the community near the disturbance than to that within other disturbances (Gibson, 1989;McMillan et al., 2011;Polley & Wallace, 1986). ...
Article
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Bison have long been considered a keystone species of North American prairies, increasing plant and animal diversity through a number of unique behaviors. One such behavior is wallowing, in which the repeated rolling of bison in the same spot leads to the formation of small, shallow, oval depressions called wallows. The objective of this study was to characterize spatial and physical attributes of bison wallows at the Konza Prairie Biological Station, a tallgrass prairie preserve in northeastern Kansas. We used aerial imagery from two different years (2011 and 2019) to assess the abundance and spatial distribution of these wallows in relation to fire frequency, elevation, and slope. We also recorded physical characteristics (2020) for a randomly selected subset of wallows and analyzed these data in relation to the same landscape features. Results from the analysis of the aerial images indicated that wallows were more abundant in areas characterized by combinations of more frequent burning, higher elevations, and little or no slope. In the 2020 physical measurements, we found that wallows were smaller in areas burned more often and shallower at higher elevations, particularly when located on grazing lawns. Terrestrial plants were found in approximately 72.1% of the wallows that were physically sampled, and their prevalence increased with increasing slope. We found some quantity of aquatic plants in approximately 7.1% of the sampled wallows. The probability of finding aquatic vegetation in wallows was higher on grazing lawns and in areas burned less frequently, particularly every 20 years. This study enhances the understanding of the distribution of wallows and their physical characteristics as a type of disturbance that could alter relationships within grassland communities.
... The American bison (Bison bison) ranged over a large portion of North America prior to the 1800s. Bison were a keystone species in the Great Plains (Knapp 1999). They wallowed on the ground, aerating the soil while also disturbing the grasses as they traveled and grazed and browsed upon prairie plants. ...
... They wallowed on the ground, aerating the soil while also disturbing the grasses as they traveled and grazed and browsed upon prairie plants. Bison browsed on primary growth of woody vegetation, assisting in maintenance of prairies that flourished post-Pleistocene (Coppock et al. 1983;Knapp et al. 1999). Grasses often outcompete forbs (which is evident in ungrazed prairies), but bison selectively graze dominant grass species and tend to avoid forbs. ...
... Grasses often outcompete forbs (which is evident in ungrazed prairies), but bison selectively graze dominant grass species and tend to avoid forbs. This results in an increase in forb presence in the prairie and subsequent increase in biodiversity of vertebrate and invertebrate species attracted to the diverse forbs (Knapp et al. 1999;Burke et al. 2020). ...
Thesis
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The effects of bison and prairie dog grazing on small mammal communities at Caprock Canyons State Park near Quitaque, Texas was examined in this investigation. This field study sought to explore the ecological interactions between bison, prairie dogs, and other small mammal species at Caprock Canyons State Park. Examining the effects of bison and prairie dog presence on small mammal communities can provide insight into the keystone role these two species play in the unique caprock ecosystem. Mark-capture release methods and quadrats were used to measure species diversity indices and vegetation cover classes, respectively, across three sites (ungrazed, bison-grazed, and prairie dog and bison-grazed). Redundancy analyses indicated that plant species richness and bare ground cover were the two main environmental variables driving the variation in the community matrix. A total of 46 individuals belonging to 11 species were captured, of which 76% were heteromyids and 36.4% were cricetids. The highest diversity indices were found in the bison-grazed area, and the lowest were in the prairie dog town site. Prairie dogs still provide habitat for many animals and can contribute to higher levels of heterogeneity and biodiversity when examined on a larger scale. In conclusion, bison grazing can promote heterogeneity across the landscape for small mammal communities, thus promoting species diversity. To further understand the active role of these two keystone species, it is recommended that this preliminary study be repeated in other Texas ecoregions where bison and prairie dogs are present.
... Grazing was a keystone process that shaped Great Plains grasslands and the evolution of their biota for thousands of years, and bison have been the primary grazer in this process. Accordingly, bison have been designated as a "keystone" or "foundation" species because of their inordinately large influence through grazing and other interactions on biodiversity of Great Plains grasslands (Milchunas et al. 1988, Knapp et al. 1999, Gross et al. 2010. Consequently, the goals and strategies for bison management must integrate the goals and strategies for conserving many other species, habitats and ecological conditions and processes, and address the socioeconomic environment in which bison conservation takes place. ...
... Observations on Konza Prairie suggest that bison alter plant community composition at the patch scale by selecting species-poor, grass-dominated sites and converting them to sites of higher diversity (Knapp et al. 1999). At the watershed and landscape scales, the longterm consequences of bison activities include a reduction in cover, dominance, and productivity of grasses; the competitive release of many subdominant species, resulting in an increase in the abundance of forbs; an overall increase in plant species richness and diversity; and increased spatial heterogeneity (Knapp et al. 1999). ...
... Observations on Konza Prairie suggest that bison alter plant community composition at the patch scale by selecting species-poor, grass-dominated sites and converting them to sites of higher diversity (Knapp et al. 1999). At the watershed and landscape scales, the longterm consequences of bison activities include a reduction in cover, dominance, and productivity of grasses; the competitive release of many subdominant species, resulting in an increase in the abundance of forbs; an overall increase in plant species richness and diversity; and increased spatial heterogeneity (Knapp et al. 1999). Bison grazing of short-and mixed-grass prairie has been shown to increase rates of nutrient cycling (Day and Detling 1990), modify plant species composition (Coppock and Detling 1986) and increase the nutritive value of grasses (Coppock et al. 1983a, 1983b, Krueger 1986). ...
Technical Report
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APR aims to achieve the following objectives for bison conservation that reinforce and build on the objectives of the original reintroduction plan and incorporate criteria of the Sanderson et al. (2008) scorecard for making an “exceptional contribution” (the highest category) to fulfilling the goals of the “Vermejo Statement” on ecological recovery of bison.
... Megaherbivores can have extensive impacts on habitat structure through grazing, browsing, and trampling (Coverdale et al. 2016), and can indirectly alter community composition and behavior of other functional groups (Pringle 2008, Shurin et al. 2020. For example, bison (Bison bison) are being reintroduced across North America to increase plant diversity and restore historical disturbance regimes (Knapp et al. 1999, Freese et al. 2007, Fuhlendorf et al. 2009). In addition to their direct effects on plant communities, bison shape the identity, diversity, and abundance of invertebrates (Nickell et al. 2018, Barber et al. 2019. ...
... We interpret these patterns as evidence of an indirect interaction between bison and small mammals. Bison grazing and wallowing reduces plant height and density (Knapp et al. 1999), causing more moonlight to reach ground level (Fig. 1C). By thinning the plant canopy, bison reduce the amount of predation refuge available to small mammals, creating a landscape of fear where cues of predation risk and refuge are heterogeneous (Gaynor et al. 2019). ...
... As a result, vegetation in burned and unburned plots intercept a similar amount of moonlight through most of the year. Whereas prescribed fire occurs at most once a year, bison repeatedly graze and wallow in the same areas, representing an ongoing press disturbance (Knapp et al. 1999). The persistent effects of bison reintroduction on vegetation therefore suggest that megaherbivores play a role in prairie ecosystems that cannot be replaced by prescribed fire alone (Fuhlendorf et al. 2009). ...
Article
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Moonlight structures activity patterns of many nocturnal species. Bright moonlight often limits the activity of nocturnal prey, but dense vegetation weakens this effect. Using 8 years of live‐trapping data, we asked whether reintroduced megaherbivores (Bison bison) indirectly altered moonlight avoidance by small mammals in tallgrass prairies. In plots with bison, plants intercepted 20% less light, allowing more moonlight to reach ground level. During nights with no moonlight, Peromyscus maniculatus activity was similar in plots with and without bison. During nights with peak moonlight, P. maniculatus activity was four times greater in plots without bison compared to plots with bison. Conversely, Microtus ochrogaster activity was twice as great during full moons compared to new moons, but only in plots with bison. We also equipped a subset of traps with temperature sensors to estimate trap‐entry time. Although M. ochrogaster was more active on bright nights, most activity occurred before moonrise or after moonset, avoiding periods of bright moonlight. We conclude that megaherbivores play an unappreciated but important indirect role in tallgrass prairies by inducing behavioral shifts in other animal species. Because overlap in activity patterns can predict the likelihood of predator–prey encounters, such activity shifts have important implications for trophic interactions throughout restored prairie food webs. Additional work to understand interspecific and intraspecific variation in response to moonlight may improve efforts to forecast changes in community assembly due to restoration and land‐use change.
... The Flint Hills ecoregion of eastern Nebraska, Kansas, and Oklahoma contains some of the largest remaining tracts of tallgrass prairie and is a stronghold for conservation of grassland birds ). Yet, much of the land is privately owned and managed with higher densities of grazing livestock and more frequent burning than was historically common (Knapp et al. 1999, Fuhlendorf et al. 2006, Mohler and Goodin 2012. These management practices often reduce spatial variation in vegetation composition and structure in prairie habitats (Knapp et al. 1999, Fuhlendorf et al. 2006) and can lower species diversity and abundance of arthropods (Joern 2005), mammals (Ricketts and Sandercock 2016), and grassland songbirds (Fuhlendorf et al. 2006, Powell 2006, Coppedge et al. 2008. ...
... Yet, much of the land is privately owned and managed with higher densities of grazing livestock and more frequent burning than was historically common (Knapp et al. 1999, Fuhlendorf et al. 2006, Mohler and Goodin 2012. These management practices often reduce spatial variation in vegetation composition and structure in prairie habitats (Knapp et al. 1999, Fuhlendorf et al. 2006) and can lower species diversity and abundance of arthropods (Joern 2005), mammals (Ricketts and Sandercock 2016), and grassland songbirds (Fuhlendorf et al. 2006, Powell 2006, Coppedge et al. 2008. Moreover, intensive grazing and frequent fires have been linked to increased rates of nest predation and brood parasitism by Brown-headed Cowbirds (Molothrus ater) of grassland songbirds (Churchwell et al. 2008, Davis et al. 2016. ...
... pyricherbivory; Engle 2001, Fuhlendorf et al. 2009). Patch-burn grazing is a rangeland management strategy that more closely resembles the effects of pyricherbivory compared to other grazing regimes currently in use (Stebbins 1981, Knapp et al. 1999, Fuhlendorf and Engle 2001. Under patch-burn grazing management, a section (or "patch") of a pasture is burned each year in a rotational scheme. ...
Article
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Intensification of livestock production has reduced heterogeneity in vegetative structure in managed grasslands, which has been linked to widespread declines in grassland songbird populations throughout North America. Patch-burn grazing management aims to restore some of that heterogeneity in vegetative structure by burning discrete pasture sections, so that cattle preferentially graze in recently burned areas. Although patch-burn grazing can increase reproductive success of grassland songbirds, we know little about possible interactions with regional variation in predator communities or brood parasite abundance, or annual variation in weather conditions. Using six years of data from two tallgrass prairie sites in eastern Kansas, USA, we tested effects of patch-burn grazing on the rates of brood parasitism, clutch size, nest survival, and fledging success of three common grassland songbirds, Dickcissels (Spiza americana), Eastern Meadowlarks (Sturnella magna), and Grasshopper Sparrows (Ammodramus savannarum), among pastures managed with patch-burn grazing versus pastures that were annually burned and either grazed or ungrazed. Dickcissel nests experienced lower parasitism (72.8 ± 4.6% SE vs. 89.1 ± 2.2%) and Eastern Meadowlarks had higher nest survival (63.2 ± 20.5% vs. 16.5 ± 3.5%) in annually burned and ungrazed pastures than pastures managed with patch-burn grazing. However, average number of host fledglings per nesting attempt did not differ among management treatments for any species. Annual variation in weather conditions had a large effect on vegetation structure, but not on reproductive success. Probability of brood parasitism was consistently high (25.5‒84.7%) and nest survival was consistently low (9.9–16.9%) for all species pooled across treatments, sites, and years, indicating that combined effects of predation, parasitism and drought can offset potential benefits of patch-burn grazing management previously found in tallgrass prairies. Although differences in reproductive success among management treatments were minimal, patch-burn grazing management could still benefit population dynamics of grassland songbirds in areas where nest predators and brood parasites are locally abundant by providing suitable nesting habitat for bird species that require greater amounts of vegetation cover and litter, generally not present in burned pastures.
... Similar behavioral patterns have been described for other grazers, including bison ( Bison bison ) in North American tallgrass prairies ( Knapp et al., 1999 ), and a range of short-grass specialists in African grasslands and savannas. This group includes warthog Phacochoerus africanus , blue wildebeest Connochaetes taurinus ( Kleynhans et al., 2011 ), white rhinoceros Ceratotherium simum and hippopotamus Hippopotamus amphibius ( Hempson et al., 2015 ). ...
... But unlike short-duration grazing management where all patches are intensely used at some point, wild ungulates consistently use preferred patches without extended rest intervals -as our results show. However, it is important to note that wild ungulates return frequently and intensely use only specific patches on limited parts of the landscape, such as grazing lawns in the case of grazers like wildebeest and bison ( McNaughton, 1983 ;Knapp et al., 1999 ;Hempson et al., 2015 ) and nutritious browsing lawns in the case of browsers ( Fornara and du Toit, 2007 ). These patterns contrast the conceptual basis of shortduration grazing, which posits that all patches are at some point used intensely ( Hoffman, 2003 ;Franke and Kotzé, 2022 ). ...
Article
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High-density short-duration grazing (SDG) is widely suggested to increase productivity. Among various SDG practices, the most widespread and popular, "holistic grazing," claims to mimic the movement patterns of wild African ungulate herds to improve rangeland health and promote biodiversity. However, this claim has rarely been empirically tested. Focusing on Karoo Escarpment Grasslands in the eastern Karoo, South Africa, we compared patch use patterns of black wildebeest (Connochaetes gnou) in a continuously grazed wildlife system with cattle paddock use on farms implementing SDG management in the same landscape. Camera trap data revealed heterogeneous wildebeest patch use over the 26-mo sampling period , with wildebeest consistently using some patches more intensely than others. Mean intensity of patch use by wildebeest varied with a factor of 10, from 0.05 LSU · ha −1 · day −1 to 0.51 LSU · ha −1 · day −1 across patches. The relative difference in mean intensity of paddock use among farms ranged across a similar magnitude from < 0.01 to 0.18 LSU · ha −1 · day −1 for least to most intensely grazed paddocks , respectively. Grazing durations in wildebeest patches ranged from 3-15 d (mean = 8 d), compared to the range of 3-60 d (mean = 18 d) for cattle. Intense grazing periods in wildebeest patches ranged from 0 to 2 d (mean = 1 d) and from 1 to 30 d (mean = 7 d) across cattle farms. The greatest difference was between rest intervals, lasting from 1 to 5 d on average across wildebeest patches, compared to 60-365 d across cattle farms. Our findings suggest that SDG systems prevalent in Karoo Escarpment Grasslands differ from the patch use patterns of black wildebeest in most aspects. These findings add to growing literature on grazing behavior of wild herbivores, and effectively contrasts these patterns with SDG cattle farming practices in the same landscape.
... In this ecosystem, frequent fire volatilizes N from plant litter, slowing the accumulation of soil organic N; therefore, fire maintains conditions in which N-limited plants and soil microbes rapidly assimilate and immobilize, and effectively retain, soil available inorganic N (Dodds et al. 1996;). In addition, tallgrass prairies were historically grazed by large mammalian herbivores, which often enhance soil N cycling rates, N heterogeneity, and soil fertility (Hobbs 1996;Frank and Evans 1997;Blair et al. 1998;Knapp et al. 1999;Bakker et al. 2003). Bison grazing can increase soil N cycling rates in areas managed with annual fire to levels equivalent to areas Abstract Nitrogen (N) is a necessary element of soil fertility and a limiting nutrient in tallgrass prairie but grazers like bison and cattle can also recycle N. Bison and cattle impact the nitrogen (N) cycle by digesting forage that is consumed, and recycled back to the soil in a more available forms stimulating soil microbial N cycling activities. ...
... Plains bison, also known as the American Buffalo (Bison bison), are keystone herbivores that once ranged across the whole North American continent (Knapp et al. 1999;Lott 2002;Anderson 2006;List et al. 2007). However, in the 1880s, extermination through settler colonization (Dunbar-Ortiz 2014) decimated bison populations which numbered in the millions to less than 1000 individuals, driving societal collapse and negative economic impacts on Native American communities that remain until this day (Hornaday, 1913;Flores 1991;Shaw 1995;Lott 2002;Feir et al. 2021). ...
Article
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Nitrogen (N) is a necessary element of soil fertility and a limiting nutrient in tallgrass prairie but grazers like bison and cattle can also recycle N. Bison and cattle impact the nitrogen (N) cycle by digesting forage that is consumed, and recycled back to the soil in a more available forms stimulating soil microbial N cycling activities. Yet we do not know how both grazers comparatively affect N cycling in tallgrass prairie. Thus, we investigated if bison and cattle had similar impacts on N cycling in annually burned tallgrass prairie relative to ungrazed conditions over a 3-year period (2020–2022) at the Konza Prairie Biological Station. We examined: soil pH, soil water content, mineralized N, nitrification potential, denitrification potential and extracellular enzyme assays. Interannual variability in precipitation controlled soil water and N cycling microbial activities but grazing effects had a stronger influence on N cycling. We found significant differences and increased soil pH, nitrification and denitrification potential and less N limitation in bison vs cattle grazed soils where bison grazed soils exhibited faster N cycling. Differences between the grazers may be attributed to the different management of bison and cattle as both can impact N cycling. Overall, these data provide some evidence that bison and cattle affect N cycling differently at this study site, and improve the ecological understanding of grazer impacts on N cycling dynamics within the tallgrass prairie ecosystem.
... A simple heuristic is that grazers often focus on grasses whereas browsers often focus on herbaceous non-grasses, hereafter forbs (Gordon and Herbert 2019). Numerous studies have shown that grazers can have large impacts on species within family Poaceae (McNaughton 1985;Augustine and McNaughton 1998;Knapp et al. 1999;Towne et al. 2005). In contrast, browsing, such as by white-tailed deer, often appears to remove forbs, which may benefit their grass competitors (Anderson et al. 2005;Wiegmann and Waller 2006;Rooney 2009). ...
... In total, our results suggest that species-specific deer florivory may be a major factor impacting competition and the relative abundances of dominant forb species (Augustine and Frelich 1998;Anderson et al. 2001Anderson et al. , 2007Geddes and Mopper 2006;Flaherty et al. 2018;Palagi and Ashley 2019). While grasslands are named for their grasses and the study of their ecology has often focused on grazing herbivores, such as Bison bison (Knapp et al. 1999;Towne et al. 2005;Ratajczak et al. 2022), our experiment suggests that selective deer florivory can also impact plant species abundances and promote plant coexistence in grasslands via plant interspecific trade-off between resistance to deer florivory and competitive abilities for limiting resources. ...
Article
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Two of the major factors that control the composition of herbaceous plant communities are competition for limiting soil resources and herbivory. We present results from a 14-year full factorial experiment in a tallgrass prairie ecosystem that crossed nitrogen (N) addition with fencing to exclude white-tailed deer, Odocoileus virginianus, from half the plots. Deer presence was associated with only modest decreases in aboveground plant biomass (14% decrease; −45 ± 19 g m⁻²) with no interaction with N addition. N addition at 5.44 and 9.52 g N m⁻² year⁻¹ led to increases in biomass. There were weak increases in species richness associated with deer presence, but only for no or low added N (1 and 2 g N m⁻² year⁻¹). However, the presence of deer greatly impacted the abundances of some of the dominant perennial forb species, but not the dominant grasses. Deer presence increased the abundance of the forb Artemisia ludoviciana by 34 ± 12 SE g m⁻² (94%) and decreased the forb Solidago rigida by 32 ± 13 SE g m⁻² (79%). We suggest that these changes may have resulted from trade-off in plant competitive ability for soil N versus resistance to deer herbivory. Field observations suggest deer acted as florivores, mainly consuming the flowers of susceptible forb species. The preferential consumption of flowers of forbs that seem to be superior N competitors appears to create an axis of interspecific niche differentiation. The overpopulation of white-tailed deer in many tallgrass reserves likely structures the abundance of forb species.
... Bison also selectively graze on grasses over forbs and woody browse, with diets that adapt to local forage availability and still reflect a broad range of food items ( Hecker et al. 2021 ). Preferential grazing by bison can lead to shifts in plant species composition and an overall increase in plant species richness and diversity ( Knapp et al. 1999 ). This increase is documented in the tallgrass prairie, where Ratajczak et al. (2022) found that reintroducing bison increased native plant species richness by 86% compared with ungrazed areas, and this richness was over twice as high as richness under cattle grazing. ...
... Research found that adding bison grazing and fire to the tallgrass prairie did not negatively impact stream water quality in terms of total suspended solids and nutrients ( Larson et al. 2013 ). Bison also preferentially graze in burned sites, likely for increased protein intake ( Raynor et al. 2016 ), which helps create a landscape of increased plant species diversity and spatial heterogeneity compared with burning alone ( Knapp et al. 1999 ). Bison interact with other wildlife, such as prairie dogs, in their grazing behavior and impacts ( Krueger 1986 ). ...
... The American bison (Bison bison), or American buffalo, has been called an ecosystem engineer and a keystone species because of the role of bison in shaping plant communities, and their interactions with other animal species (Boyce et al., 2022;Geremia et al., 2019;Gerlanc & Kaufman, 2003;Joern, 2005;Knapp et al., 1999;Krueger, 1986). ...
... For example, grazing and browsing combine with fire to stimulate productivity and increase the diversity of forbs and grasses, a dynamic observed in grassland ecosystems around the world (Knapp et al., 1999;Larson, 1940;McNaughton, 1984;Sinclair et al., 2010). ...
Article
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The American bison ( Bison bison ) is a species that strongly interacts with its environment, yet the effects of this large herbivore on quaking aspen ( Populus tremuloides ) have received little study. We documented bison breaking the stems of aspen saplings (young aspen >2 m tall and ≤5 cm in diameter at breast height) and examined the extent of this effect in northern Yellowstone National Park (YNP). Low densities of Rocky Mountain elk ( Cervus canadensis ) after about 2004 created conditions conducive for new aspen recruitment in YNP's northern ungulate winter range (northern range). We sampled aspen saplings at local and landscape scales, using random sampling plots in 87 randomly selected aspen stands. Across the YNP northern range, we found that 18% of sapling stems had been broken. The causal attribution to bison was supported by multiple lines of evidence: (1) most broken saplings were in areas of high bison and low elk density; (2) saplings were broken in summer when elk were not foraging on them; (3) we directly observed bison breaking aspen saplings; and (4) mixed‐effects modeling showed a positive association between scat density of bison and the proportion of saplings broken. In a stand heavily used by bison, most aspen saplings had been broken, and portions of the stand were cleared of saplings that were present in previous sampling in 2012. Bison numbers increased more than fourfold between 2004 and 2015, and their ecosystem effects have similarly increased, limiting and in some places reversing the nascent aspen recovery. This situation is further complicated by political constraints that prevent bison from dispersing to areas outside the park. Thus, one important conservation goal, the preservation of bison, is affecting another long‐term conservation goal, the recovery of aspen and other deciduous woody species in northern Yellowstone.
... One study suggested that cattle (Bos taurus) can disperse the fungus Ascochyta paspali in saliva containing conidia, which resulted in leaf blight disease in Paspalum dilatatum (Williams and Price 1989). Bison are known to have direct effects ( Fig. 1) on the structure of tallgrass prairie plant 60 communities (Knapp et al. 1999;Towne, Hartnett, and Cochran 2005). At Konza Prairie Biological Station (KPBS), bison selected grazing areas based on four characteristics: a high population of the dominant tallgrass prairie plant species, lower forb richness and diversity, lower plant species diversity, and higher grass to forb ratios (Vinton et al. 1993). ...
... We used a culture-based approach to isolate fungi from bison saliva to ensure that the fungi were alive. We studied fungi recovered from bison in a herd maintained at KPBS near Manhattan, Kansas, USA, that grazes native tallgrass prairie (Knapp et al. 1999). Each autumn 100 the bison are assembled for weighing, offering an opportunity to sample their saliva. ...
Article
Dispersal by grazing and browsing animals has the potential to structure plant-associated microbes in plant communities. Bison are one of the largest grazing animals in North America and charismatic symbols of the Great Plains. They have an important role in maintaining plant communities in tallgrass prairie and may have played a significant role in microbial dispersal across the Great Plains, along with other grazers and herbivores in general. To determine whether bison saliva could maintain viable fungal propagules, we sampled saliva from bison at Konza Prairie Biological Station. Fifty-nine internal transcribed spacer sequences were recovered from distinct fungal colonies on media selective for Fusarium species and Macrophomina phaseolina, representing at least 26 fungal species. Most sequences were identified as originating from potential plant pathogens, indicating that bison may play a role in spreading plant pathogens throughout the prairie. Given their historic numbers and extensive migration across North America, bison may have had a role in establishing the current structure of the prairie microbiome. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .
... Grassland restoration often requires ongoing management and the application of disturbances that mimic historical disturbance regimes to maintain structure, physiognomy, and plant diversity (Collins and Adams 1983, Knapp et al. 1999, Fuhlendorf and Engle 2004, Bond and Keeley 2005. In addition to the indirect effects of management on soil microbes via changes in plant growth and composition (Kitchen et al. 2009), management disturbances like prescribed fire, grazing, and mowing can more directly influence soil organisms through changes in the soil environment (Wagle and Gowda 2018). ...
... Further, Mantel tests comparing Bray-Curtis dissimilarity to spatial distance for spring, summer, and fall 2018 sampling all found no significant relationship (all |r| < 0.15, P > 0.7). These patterns suggest another potential explanation, that the presence of bison is driving succession along a different trajectory in these young sites, perhaps through both their direct impacts on the soil environment and indirect effects on plant communities (Knapp et al. 1999, Blackburn et al. 2020. This is important because it could mean bison reintroduction adds new heterogeneity to the environment, bolstering total biodiversity across the entire preserve, and possibly supporting variation in soil function as well. ...
Article
Knowledge of how habitat restoration shapes soil microbial communities often is limited despite their critical roles in ecosystem function. Soil community diversity and composition change after restoration, but the trajectory of these successional changes may be influenced by disturbances imposed for habitat management. We studied soil bacterial communities in a restored tallgrass prairie chronosequence over six years to document how diversity and composition changed with age, management through fire and grazing by re-introduced bison, and in comparison to pre-restoration agricultural fields and remnant prairies. Soil C:N increased with restoration age and bison, and soil pH first increased and then declined with age, although bison weakened this pattern. Bacterial richness and diversity followed a similar hump-shaped pattern as soil pH, such that the oldest restorations approached the low diversity of remnant prairies. β-diversity patterns indicated that composition in older restorations with bison resembled bison-free sites, but over time they became more distinct. In contrast, younger restorations with bison maintained unique compositions throughout the study, suggesting bison disturbances may cause a different successional trajectory. We used a novel random forest approach to identify taxa that indicate these differences, finding that they were frequently associated with bacteria that respond to grazing in other grasslands.
... Often multiple techniques are used in combination to achieve desired results. In the United States, reintroduction of Plains bison (Bison bison bison) in large, protected areas are also used as a tool in prairie restoration and management (Knapp et al. 1999;Burke et al. 2020;Bruninga-Socolar et al. 2021;Xu et al. 2021). Although bison were documented historically in Ontario it is not believed to be to the same extent as in the United States, therefore less important to the function and maintenance of the ecosystem (Martin et al. 2022). ...
... There has been a considerable amount of research on impacts of management, particularly fire on prairie plant communities (Hulbert 1986;Brudvig et al. 2007;Pavlovic et al. 2011;Larson et al. 2020) but less so on impacts to animals (Rice 1932;Knapp et al. 1999;Brawn 2006;Burke et al. 2020;Guiden et al. 2021) and fewer on bees reliant on those plant communities (Panzer 2002;Harmon-Threatt and Chin 2016;Griffin et al. 2017;Bruninga-Socolar et al. 2021). Additionally, the majority of these studies are from larger tallgrass habitat remnants in the central Midwest United States, but much less is known about the impacts of management on these habitats in smaller remnants in Ontario. ...
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Understanding how restoration and land management practices may impact the structure of native bee communities is important especially considering reported global bee declines. I assessed bee community and vegetation composition in tallgrass prairie and oak savanna, some of the most endangered and biodiverse habitats in Canada. I found distinct differences in bee abundance and diversity among land management types, with remnant sites in most cases having comparably low bee diversity. This was driven by differences in floral abundance, canopy cover, and presence of woody debris. Bee community composition was unique at each locality, and I documented several bee species for the first time in Canada. I also found more bumble bee colonies and greater floral resources at restored compared to remnant sites using non-lethal DNA sampling and microsatellite markers to estimate colony densities. Linking landscape structure with use will improve habitat management and bee conservation in this rare habitat.
... This scaledependence of remote sensing of biodiversity-meaning the degree to which our ability to remotely estimate diversity varies as a function of spatial scale (e.g., pixel size, grain size, plot size)-has been reported in previous experiments, and largely influences whether biodiversity, as traditionally defined by ecologists, can be detected with remote sensing . Second, management practices, such as prescribed fire or grazing, can promote spatial and temporal variability within and across grasslands ecosystems (Collins, 1992;Fuhlendorf et al., 2009;Knapp et al., 1999), which likely further influences biodiversity detection. Thus, we hypothesize that the impact of such management practices on grassland diversity and our ability to estimate plant diversity with remote sensing can also be highly scale-dependent, both in space and time (see Section 1.3 below and Dronova and Taddeo, 2022;Gholizadeh et al., 2020;Rossi et al., 2021a;Thornley et al., 2022). ...
... Biodiversity patterns in North America's scant remaining tallgrass prairies are driven to a large extent by management practices, particularly prescribed fire and grazing. There is strong evidence that these management practices have historically maintained grassland biodiversity, function, and structure (Collins, 1992;Collins et al., 1998;Knapp et al., 1999). Fire can suppress some invasive plants (e.g., woody plants) and therefore provide resource access to a more diverse set of persistent native species. ...
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Grassland ecosystems are under threat globally, primarily due to land-use and land-cover changes that have adversely affected their biodiversity. Given the negative ecological impacts of biodiversity loss in grasslands, there is an urgent need for developing an operational biodiversity monitoring system that functions in these ecosystems. In this paper, we assessed the capability of airborne and spaceborne imaging spectroscopy (also known as hyperspectral imaging) to capture plant α-diversity in a large naturally-assembled grassland while considering the impact of common management practices, specifically prescribed fire. We collected a robust in-situ plant diversity data set, including species composition and percent cover from 2500 sampling points with different burn ages, from recently-burned to transitional and pre-prescribed fire at the Joseph H. Williams Tallgrass Prairie Preserve in Oklahoma, USA. We expressed in-situ plant α-diversity using the first three Hill numbers, including species richness (number of observed species in a plant community), exponential Shannon entropy index (hereafter Shannon diversity; effective number of common species, where species are weighed proportional to their percent cover), and inverse Simpson concentration index (hereafter Simpson diversity; effective number of dominant species, where more weight is given to dominant species) at four different plot sizes, including 60 m × 60 m, 120 m × 120 m, 180 m × 180 m, and 240 m × 240 m. We collected full-range airborne hyperspectral data with fine spatial resolution (1 m) and visible and near-infrared spaceborne hyper-spectral data from DESIS sensor with coarse spatial resolution (30 m), and used the spectral diversity hypothesis -i.e., that the variability in spectral data is largely driven by plant diversity-to estimate α-diversity remotely. In recently-burned plots and those at the transitional stage, both airborne and spaceborne data were capable of capturing Simpson diversity-a metric that calculates the effective number of dominant species by emphasizing abundant species and discounting rare species-but not species richness or Shannon diversity. Further, neither airborne nor spaceborne hyperspectral data sets were capable of capturing plant α-diversity of 60 m × 60 m or 120 m × 120 m plots. Based on these results, three main findings emerged: (1) management practices influence grassland biodiversity patterns that can be remotely detected, (2) both fine-and coarse-resolution remotely-sensed data can detect the effective number of dominant species (e.g., Simpson diversity), and (3) attention should be given to site-specific plant diversity field data collection to appropriately interpret remote sensing results. Findings of this study indicate the feasibility of estimating Simpson diversity in naturally-assembled grasslands using forthcoming spaceborne imagers such as National Aeronautics and Space Administration's Surface Biology and Geology mission.
... Herbivory has profound effects on vegetation production and structure (Augustine & McNaughton, 1998;Hobbs, 1996;Wisdom et al., 2006), and influences both directly and indirectly ecosystem processes aboveground and belowground (Bardgett & Wardle, 2010;Frank et al., 1998Frank et al., , 2002Knapp et al., 1999;Schoenecker et al., 2004). The degree to which ungulate herbivores influence and potentially induce long-term degradation of the vegetation that supports their populations has long been of interest to ecologists, land managers, and agriculturalists. ...
... In landscapes where highly productive grassland is widespread and herbivores occur at relatively low density, many high-ANPP patches may remain ungrazed early in the growing season. These patches can develop high standing biomass and correspondingly low digestibility later in the growing season, and therefore continue to experience low grazing intensity (e.g., Knapp et al., 1999). Under these conditions, we expect an arched relationship between ANPP and ungulate consumption. ...
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Plant communities in rangeland ecosystems vary widely in the degree to which they can compensate for losses to herbivores. Ecosystem‐level factors have been proposed to affect this compensatory capacity, including timing and intensity of grazing, and availability of soil moisture and nutrients. Arid ecosystems are particularly challenging to predict because of their high degree of temporal variability in moisture inputs. We used a replicated herbivore exclusion experiment to evaluate herbaceous plant responses to grazing by large ungulates to test current theory and identify constraints on plant compensation in a dryland ecosystem. We measured nitrogen (N) yield and herbaceous production in three plant communities: meadows, willow‐associated herbaceous communities, and riparian communities. We implemented grazing exclusion treatments from 2005 to 2008 in areas with elk and bison and areas with only elk. Grazing by large ungulates increased herbaceous production and N yield in herbaceous riparian communities. In willow communities, herbaceous plants displayed equal compensation in response to grazing in total aboveground production and N yield. Our results support the idea that plant compensation in this semiarid system is contingent on soil moisture availability, wherein the most productive sites (that received substantial moisture inputs from subsurface flow) exhibited overcompensation. Although the herbaceous riparian communities we studied are isolated patches of productive grassland in an otherwise shrub‐dominated and minimally productive semiarid landscape, grazing by a combination of bison and elk removed only 44%–53% of aboveground net primary productivity (ANPP) during the growing season, and 25%–38% of production over winter. Consumption by ungulates was a positive linear function of herbaceous production, similar to reported patterns from other temperate and tropical grazing ecosystems. The slope of this relationship was affected by the analytical method used to calculate ANPP and consumption rates, but, regardless of the method, was lower or similar to reported slopes for other intensively grazed systems (Yellowstone, Serengeti, Laikipia) that have sustained high ungulate densities for decades to centuries. Given that the vegetation communities exhibited equal or overcompensation in terms of total herbaceous ANPP in both years, elk and bison population levels during our study period did not appear to occur at densities leading to degradation of herbaceous communities.
... Before European settlement and "systematic slaughter" (in the words of Hornaday, 1889) of bison across the Great Plains, reducing the population to an estimated hundreds of animals by the end of the nineteenth century, bison numbered an estimated 25-30 million, and their range spanned more than a third of the continent (Lueck, 2002). Bison are particularly integral for North American tallgrass prairies as they hold a keystone role historically and contemporarily, increasing plant diversity, soil fertility, and forage quality in their zones of influence (Knapp et al., 1999). At sites across the Great Plains, bison grazing tends to decrease the strength of the soil microbial distance-dissimilarity relationship (Allenbrand, 2020), and bison reintroduction to Tallgrass prairie can cause convergence of soil microbial communities with varied management backgrounds, with their dung implicated as an important mechanism for this homogenization (Chantos, 2017). ...
... In the context of grassland soil microbial community assembly, successful microbial passage through the ungulate digestive tract, either through dormancy or through facultatively anaerobic growth, serves as a strong filter antecedent to dispersal in dung. Before European colonization of the continent, bison migrated thousands of kilometers in mind-bogglingly high numbers across the North American Great Plains (Knapp et al., 1999). The global decline and extirpation of herbivore populations has detrimental consequences on many ecosystem attributes (Young et al., 2016). ...
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Microbial communities display biogeographical patterns that are driven by local environmental conditions and dispersal limitation, but the relative importance of underlying dispersal mechanisms and their consequences on community structure are not well described. High dispersal rates can cause soil microbial communities to become more homogenous across space and therefore it is important to identify factors that promote dispersal. This study experimentally manipulated microbial dispersal within different land management treatments at a native tallgrass prairie site, by changing the relative openness of soil to dispersal and by simulating vector dispersal via bison dung addition. We deployed experimental soil bags with mesh open or closed to dispersal, and placed bison dung over a subset of these bags, to areas with three different land managements: active bison grazing and annual fire, annual fire but no bison grazing, and no bison grazing with infrequent fire. We expected microbial dispersal to be highest in grazed and burned environments, and that the addition of dung would consistently increase overall microbial richness and lead to homogenization of communities over time. Results show that dispersal rates, as the accumulation of taxa over the course of the 3-month experiment, increase taxonomic richness similarly in all land management treatments. Additionally, bison dung seems to be serving as a dispersal and homogenization vector, based on the consistently higher taxon richness and increased community similarity across contrasting grazing and fire treatments when dung is added. This finding also points to microbial dispersal as an important function that herbivores perform in grassland ecosystems, and in turn, as a function that was lost at a continental scale following bison extermination across the Great Plains of North America in the nineteenth century. This study is the first to detect that dispersal and vector dispersal by grazing mammals promote grassland soil microbial diversity and affect microbial community composition.
... The productivity of tallgrass prairie is spatially and temporally heterogeneous (Knapp & Smith, 2001). Spatial heterogeneity in ANPP is created in part by variation in fire frequency (Blair, 1997;Knapp & Seastedt, 1986) and grazing by megaherbivores (Collins & Smith, 2006;Elson & Hartnett, 2017;Knapp et al., 1999). Long-term studies in the Flint Hills region of the North American Great Plains have shown that soil depth, which varies with topography, and nitrogen (N) availability are also deterministic drivers of ANPP in tallgrass prairie (Briggs & Knapp, 1995;Collins et al., 2018;Turner et al., 1997). ...
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Enhancing resilience in formerly degraded ecosystems is an important goal of restoration ecology. However, evidence for the recovery of resilience and its underlying mechanisms require long‐term experiments and comparison with reference ecosystems. We used data from an experimental prairie restoration that featured long‐term soil heterogeneity manipulations and data from two long‐term experiments located in a comparable remnant (reference) prairie to (1) quantify the recovery of ecosystem functioning (i.e., productivity) relative to remnant prairie, (2) compare the resilience of restored and remnant prairies to a natural drought, and (3) test whether soil heterogeneity enhances resilience of restored prairie. We compared sensitivity and legacy effects between prairie types (remnant and restored) and among four prairie sites that included two remnant prairie sites and prairie restored under homogeneous and heterogeneous soil conditions. We measured sensitivity and resilience as the proportional change in aboveground net primary productivity (ANPP) during and following drought (sensitivity and legacy effects, respectively) relative to average ANPP based on 4 pre‐drought years (2014–2017). In nondrought years, total ANPP was similar between remnant and restored prairie, but remnant prairie had higher grass productivity and lower forb productivity compared with restored prairie. These ANPP patterns generally persisted during drought. The sensitivity of total ANPP to drought was similar between restored and remnant prairie, but grasses in the restored prairie were more sensitive to drought. Post‐drought legacy effects were more positive in the restored prairie, and we attributed this to the more positive and less variable legacy response of forb ANPP in the restored prairie, especially in the heterogeneous soil treatment. Our results suggest that productivity recovers in restored prairie and exhibits similar sensitivity to drought as in remnant prairie. Furthermore, creating heterogeneity promotes forb productivity and enhances restored prairie resilience to drought.
... Interestingly, diet segregation was found in closely related American bison-faecal analysis revealed higher diet quality in American bison females, while males had greater diet breadth (Berini and Badgley 2017). However, unlike European bison, American bison inhabit more open habitats dominated by less digestible graminoid vegetation (Knapp et al. 1999;Jorns et al. 2020), which is likely to result in greater forage selectivity. ...
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The scaling relationship between digestive system and body mass shapes foraging strategies in herbivores. The Jarman-Bell principle and the forage maturation hypothesis (FMH), two of the most important predictions formulated in herbivore foraging ecology, have been used to explain this relationship.We aimed to test these predictions for the largest European herbivore-the European bison-which is highly sexually dimorphic and recognised as a refugee species in non-optimal forest habitats. We conducted our study in the Białowieża Primeval Forest, where the European bison has been recognized as a refugee species. We estimated vegetation quality and biomass along the foraging paths of male and female European bison, and the vegetation biomass at random points in different habitats and months. We found no support for the Jarmann-Bell principle at the intraspecific level in European bison, as males and females foraged on patches of similar crude protein and fibre content. However, females selected for higher biomass. The quality of vegetation on the bison foraging patches showed a significant spatio-temporal variation. It increased from May to July and then gradually decreased. It also increased with the fertility and wetness of the habitats being the highest in wet forests. Mean biomass on European bison foraging patches (131.5 g/m 2), was significantly lower than on random plots (210.5 g/m 2), which supported the FMH. Our study suggests that in rich forest habitats, the abundant food resources available in summer may not constrain the metabolic rate/gut capacity ratio of either sex, potentially leading to dietary segregation. In contrast to open habitats, where vegetation maturation is less temporally variable, European bison in rich forest habitats may optimise patch selection and energy intake by tracking a habitat-and species-specific changes in the plant phenology. Understanding the relationship between European bison forage selection and forage nutritional constraints in forest habitats may be critical for conservation programmes, as European bison are better adapted to more open habitats and are recognised as refugee species in suboptimal forest habitats.
... Movement is often accepted as linear, a hypothesis that promotes simpler measurements of displacement (e.g. flight mills) to be extrapolated as continuous movement [54,74]. Additionally, it is difficult to track organisms continuously; these methods can be limited in both study system and effectiveness. ...
Article
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Organisms that immigrate into a recipient habitat generate a movement pattern that affects local population dynamics and the environment. Spillover is the pattern of unidirectional movement from a donor habitat to a different, adjacent recipient habitat. However, ecological definitions are often generalized to include any cross-habitat movement, which limits within- and cross-discipline collaboration. To assess spillover nomenclature, we reviewed 337 studies within the agriculture, disease, fisheries and habitat fragmentation disciplines. Each study's definition of spillover and the methods used were analysed. We identified four descriptors (movement, habitat type and arrangement, and effect) used that differentiate spillover from other cross-habitat movement patterns (dispersal, foray loops and edge movement). Studies often define spillover as movement (45%) but rarely measure it as such (4%), particularly in disease and habitat fragmentation disciplines. Consequently, 98% of studies could not distinguish linear from returning movement out of a donor habitat, which can overestimate movement distance. Overall, few studies (12%) included methods that matched their own definition, revealing a distinct mismatch. Because theory shows that long-term impacts of the different movement patterns can vary, differentiating spillover from other movement patterns is necessary for effective long-term and inter-disciplinary management of organisms that use heterogeneous landscapes.
... Plains bison (Bison bison bison) is one of two recognized subspecies of American bison ( Committee on the Status of Endangered Wildlife in Canada [COSEWIC] 2013 ), the largest extant terrestrial mammal in North America. The species was originally distributed across the continent ( Campbell et al. 1994 ;Hartnett et al. 1996 ;Knapp et al. 1999 ). However, plains bison currently occupy < 1% of their historical range ( Sanderson et al. 2008 ) and as of 2008, about 20 500 bison were managed for conservation purposes across 62 herds, the majority of which had fewer than 400 animals ( Gates et al. 2010 ). ...
Article
In Canada, plains bison (Bison bison bison) was assessed by The Committee on the Status of Endangered Wildlife in Canada as threatened. While bison are no longer at risk of demographic extinction, conservation programs remain challenged by the rarity of large populations and most bison are found in small, isolated, and confined herds. In this context, proper assessment of ecological carrying capacity is critical to inform habitat management and conservation efforts for species recovery. Although estimated food-limited carrying capacity is influenced by forage availability, forage requirements, and offtake proportion, it should also consider habitat selection by animals, especially inside confined settings to help avoid overgrazing. To support bison management in Grasslands National Park Canada, we integrated remote sensing, geographic information systems, and resource selection functions (RSFs) to examine variables that were potentially associated with bison habitat selection and return a comprehensive estimate of bison carrying capacity. Relevant variables were then integrated with estimates of forage availability using remote sensing and extrapolated to the bison containment scale. Factors of relevance to the RSFs include vegetation landscape units, slope, distance to water, fence, and road. In particular, bison selected for upland and sloped grasslands, which were characterized by the highest forage availability (1 064.5 kg ha−1 and 1 238.5 kg ha−1), while avoiding water in both growing and dormant seasons. The top-performing RSFs models in growing and dormant seasons were assessed using k-fold cross validation and achieved good predictive capacity (Spearman rank correlation [rs] ≥ 0.83, P < 0.01). Application of traditional clipping biomass samples and remote sensing derived variables is helpful in estimating annual forage quantity for bison (R2 = 0.75, P < 0.05). When accounting for bison resource selection, our model resulted in a carrying capacity estimate of about 0.0424 bison ha−1 or 764−770 bison (each requiring 12.2 kg forage/d), compared with 0.0587 bison ha−1 or 1 062 animals estimated when considering only the availability of forage. Such potential to increase carrying capacity to more than 1 000 individuals stresses the importance of testing management tools to shape bison grazing and increase forage utilization across a greater proportion of the 18 000-ha containment area. By improving our understanding of the interaction of this species with the mixed-grass prairie ecosystem, the integration of RSFs with estimates of carrying capacity can help inform conservation management of bison and multispecies at-risk habitat.
... Grasses can grow rapidly and over topping neighbors in the no-grazing plots and become dominant species, which can exclude most other species (Thompson et al., 2005). Conversely, goats usually prefer taller grasses for food and reduce their competitive ability, which changes interspecific relationships and allows for more species to coexist (Knapp et al., 1999;Sternberg et al., 2015;Koerner et al., 2018;Bardgett et al., 2021). In addition, goats create bare soil patches by trampling, thereby improving habitat heterogeneity, which allows opportunistic plant species to settle down by increasing light availability (Sternberg et al., 2000;Bakker et al., 2006;Wu et al., 2009). ...
Article
The relationships between biodiversity and ecosystem functions (BEF) are crucial for ecosystem management. However, little is known about how grazing affects BEF relationships in the context of ecological succession. Here, using a 5-year experiment in a semiarid grassland of the Loess Plateau, China, we mainly focused on how grazing affected the relationships between plant species diversity and aboveground biomass (AGB) and explored the underlying mechanisms behind the relationships. In addition, we compared the plant dynamics of community composition and structure under no-grazing and grazing treatments during succession. We found that the plant species diversity-AGB relationship shifted from a negative-linear pattern in no-grazing to a humped-back model in grazing during plant community succession, suggesting that grazing could regulate dominant species and alter the availability of light resources to suppress competitive exclusion during succession. In addition, changes in annual plants over time played crucial roles in the BEF relationships. The increase in annual Salsola collina in this study, which also alters multiple mechanisms of plant interaction, had a significant effect on the negative-linear relationship both with and without grazing. On average, compared to no-grazing treatment, grazing significantly decreased the plant community density (39.53 %), cover (16.97 %), height (7.85 %), and AGB (9.35 %), but increased plant diversity, including species richness and the Shannon-Wiener index, and especially dramatically enhanced the Shannon-Wiener index (ranging from 1.55 to 2.13). These results underline the close association between grazing and the dynamics of plant communities in semiarid grasslands during succession. In particular, our findings further reveal grazing-dependent relationships between diversity and AGB, which have significant implications for the management and biodiversity conservation measures of semiarid grassland ecosystems.
... Additionally, bison and other grazers could have consumed existing grassland species or newly sprouted seeds and trampled sprouting seeds in the riparian zone, leading to poor recruitment of seedlings. We noted heavy bison use of the newly cleared riparian areas, and Knapp et al. (1998) documented that bison prefer nitrogen-rich regrowth. It is also likely that other herbivores (e.g., browsing deer, grasshoppers) prefer new growth that is most nutritious. ...
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Riparian zones and the streams they border provide vital habitat for organisms, water quality protection, and other important ecosystem services. These areas are under pressure from local (land use/land cover change) to global (climate change) processes. Woody vegetation is expanding in grassland riparian zones worldwide. Here we report on a decade‐long watershed‐scale mechanical removal of woody riparian vegetation along 4.5 km of stream channel in a before–after control impact experiment. Prior to this removal, woody plants had expanded into grassy riparian areas, associated with a decline in streamflow, loss of grassy plant species, and other ecosystem‐scale impacts. We confirmed some expected responses, including rapid increases in stream nutrients and sediments, disappearance of stream mosses, and decreased organic inputs to streams via riparian leaves. We were surprised that nutrient and sediment increases were transient for 3 years, that there was no recovery of stream discharge, and that areas with woody removal did not shift back to a grassland state, even when reseeded with grassland species. Rapid expansion of shrubs (Cornus drummondii, Prunus americana) in the areas where trees were removed allowed woody vegetation to remain dominant despite repeating the cutting every 2 years. Our results suggest woody expansion can fundamentally alter terrestrial and aquatic habitat connections in grasslands, resulting in inexorable movement toward a new ecosystem state. Human pressures, such as climate change, atmospheric CO2 increases, and elevated atmospheric nitrogen deposition, could continue to push the ecosystem along a trajectory that is difficult to change. Our results suggest that predicting relationships between riparian zones and the streams they border could be difficult in the face of global change in all biomes, even in well‐studied sites.
... The energy costs for Kootenai bison hunters are a testament to the tremendous value of bison as a keystone cultural, material, and nutritional resource even for groups peripheral to the Great Plains (Garibaldi & Turner, 2004;Knapp et al., 1999;Schuler et al., 2006). The hunters would drive bison deeper into mountain valleys away from competing tribes such as the Siksika in the east often through burning the landscape to create bison habitat . ...
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The Kootenai people of southern Canada historically traversed the Rocky Mountains, often several times annually, to hunt bison on the eastern front ranges. Some routes across this complex landscape were more energetically efficient than others so that archaeological and historical sites accumulated along least cost paths (LCP) as predicted by spatial analysis. We produced 12 least-cost path models traversing the Southern Canadian Rocky Mountains (SCRM) using varying degrees of landscape cost, ranked them for stability, and combined them into a final composite model. We expanded this composite LCP model into 3- and 5-km buffers within which we compared counts of historical and archaeological sites (total n = 5,651 points) to counts of equivalent quantities of randomly distributed points. High densities of land use indicators tend to follow paths across the SCRM predicted by the LCP model, creating persistent patterns of travel and land use. The results of this analysis indicate that human movements across the SCRM have been strongly influenced by the avoidance of high travel cost topography over multiple centuries. More broadly, our findings suggest that humans tend to optimize their patterns of spatial movement for energetic efficiency, consistent with predictions of behavioral evolution.
... In the Mediterranean ecosystems, fire is recognized as an important factor determining vegetation dynamics (Hanes, 1971 andMoreno &Oechel, 1994). Grassland ecologists have long recognized that grazing and fire are important ecological processes that contribute to the development of many grassland ecosystems (Knapp et al. 1999& Collins, 2000. The data indicated that a high significance between unburned and burned stands in the absolute density and cover. ...
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Four forage halophytes had been studied in Siwa Oasis. These species: are Alhagi graecorum(Boiss) , Imeprata cylindrica (L.), Juncus rigidus (Desf), and Phragmities australis(Cav.). The results indicated that the grazing had a negative effect on the absolute density, cover percentage and productivity of these plants. The burning of P australis causes reduction in its productivity and decreased its palatability, but improved the palatability of J. rigidus. The biomass of I. Cylindrica , J. rigidus, and P .australis were higher in the dry season than in the wet season versus in A. graecorum which was higher in the wet season than in the dry one. Most of the nutritive values were higher in the dry season than in the wet one excluding NFE. Alhagi graecorum had the higher value of TDN and DCP followed by the old sprouts of P .australis. In the dry season the carrying capacity of these halophytes was approximately twice of that in the wet season. Alhagi graecorum and the new sprouts of J. rigidus had a very high palatability.
... With the apparent improvement of forb digestibility and retention of protein, forbs may be increasingly selected when protein concentrations of grasses decline, particularly by the end of the growing season. This may change the foraging behavior of large ungulate grazers through mechanisms of increasing patch reselection (i.e., intensified grazing cycles) ( Knapp et al. 1999 ) and broadening of feeding preferences to forbs when grasses are limited or have high fiber content. Similarly, selective grazing of grasses may temporarily decrease grass biomass and increase forbs biomass in postburn areas during the growing season ( Fuhlendorf and Engle 2004 ). ...
Article
Fire and grazing are key drivers of plant community structure in the Great Plains ecoregion, with critical impacts on the quantity and quality of forage. While the impact of fire on forage quality is well understood in many ecosystems, few studies have examined this question in the northern mixed-grass prairie. We investigated the postburn nutrient content of forbs and graminoids over a 4-yr timeframe, asking 1) how forage quality changed over the 4 yr post fire and 2) whether the effect of fire on quality was impacted by the resumption of grazing. We used near-infrared spectroscopy and generalized partial least squares regression (plsRglm) methods to assess crude protein. We show that the use of generalized models provides improved estimates of percent nitrogen than the standard partial least squares approach. Both crude protein and fiber varied annually after the wildfires, with no effect of grazing on forage quality. In the first and second years, burned sites displayed higher protein than unburned locations. Fire did not affect crude protein between plant functional groups; however, forbs showed higher nutrient values than grasses throughout the 4 yr. Fire affected fiber content with grasses showing higher fiber than forbs. There was a positive relationship between neutral and acid detergent fiber and litter in burned sites. These results indicate no long-term effect of wildfire on protein content, which stabilizes in the third year post burn. The improvement of forb digestibility and retention of protein under dry conditions could modify the grazing capacity of the prairies at large scales. This may also change the foraging behavior of large ungulate grazers through mechanisms such as increasing patch reselection (i.e., intensified grazing cycles) and broadening feeding preferences to forbs when grasses are limited or have high fiber content.
... At face value it is true, we have learned over centuries that cattle, like other large herbivores, can be useful to humans in many ways, from providing food and countless byproducts, to holding spiritual significance and improving biodiversity and soil nutrient cycling on the lands they graze. [7][8][9][10][11] Geese, salmon, and bees are also useful to humans and provide essential roles in ecosystem sustainability. Do we refer to them as "tools?" ...
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On the Ground •Other worldviews offer alternative ways of thinking and being in relation to food animals. •Embracing complexities in our relationship with cattle could be a starting point for resolving common, and sometimes contentious paradoxes in our industry. •Heart-centered connections we have with food animals are somehow taboo and left out of our research, professional conversations, and communication with broader society. •Shifting our language around cattle to consider them “partners” could be transformative. •Our work may benefit from intentionality, humility, and acknowledgement of our symbiosis with cattle and the natural world.
... The ecological effects of bison helped provide vegetative conditions supporting a wide range of bird species (Askins et al., 2007). Bison grazing creates differences in vegetation structure (Tastad, 2013;Towne et al., 2005), increases heterogeneity of vegetation structure (Knapp et al., 1999), and influences the abundance of several grassland songbirds (Powell, 2006). There is substantial interest in reintroducing bison on the landscape (Fuhlendorf et al., 2018;Sanderson et al., 2008). ...
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Temperate grassland ecosystems are one of the most threatened ecosystems worldwide, and their loss endangers the grassland songbirds that rely upon them. This guild of birds has shown long‐term declines in North America. At the same time, American bison (Bison bison) are becoming more common through reintroductions, and they may make significant modifications to grassland songbird habitat. To support conservation for this guild, we sought to understand the importance of bison grazing and ecosystem productivity to the species richness, occupancy, and abundance of this avian community. We conducted dependent double‐observer bird counts, measured bison grazing intensity with patty counts, and used remote‐sensed normalized difference vegetation index (NDVI) data to measure ecosystem productivity. Our work took place in the National Bison Range near Moiese, Montana and in Yellowstone National Park in Wyoming. We found that species richness was positively correlated with patty counts and had a weak negative correlation with NDVI. Occupancy probability for six of seven grassland songbird species was positively correlated with patty counts, and for six of seven species was negatively correlated with NDVI. Abundance of vesper sparrow (Pooecetes graminueus) and western meadowlark (Sturnella neglecta) were positively correlated with patty counts, although for western meadowlark, this trend became less positive with increasing patty counts. Our work suggests that managers may want to encourage a broad range of bison grazing intensities to ensure that vegetative conditions related to bison grazing are present for all species.
... The interactive effect of periodic fire and ungulate grazing is widely recognized as a critical component of the natural disturbance regime in tallgrass prairie ecosystems (Bragg 1995;Davison and Kindscher 1999;Howe 1999;Collins 2000). These disturbances in turn interact with climatic variation to affect spatial and temporal dynamics (Collins 1987;Knapp and Seastedt 1998;Knapp et al. 1999;Collins 2000). The complex disturbance regimes of grassland systems consist of dynamic mosaics of vegetation patches scattered across the landscape, highly variable in both space and time (Collins and Glenn 1991;Collins and Glenn 1997;Collins 2000;Fuhlendorf and Engle 2001). ...
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Native and restored plant communities are part of the foundation of park ecosystems and provide a natural context to cultural and historical events in parks throughout the Heartland Inventory and Monitoring Network (HTLN). Vegetation communities across the HTLN are primarily of three types: prairie, woodland, and forest. Park resource managers need an effective plant community monitoring protocol to guide the development and adaptation of management strategies for maintaining and/or restoring composition and structure of prairies, woodland, and forest communities. Our monitoring design attempts to balance the needs of managers for current information and the need for insight into the changes occurring in vegetation communities over time. This monitoring protocol consists of a protocol narrative (this document) and 18 standard operating procedures (SOPs) for monitoring plant communities in HTLN parks. The scientific objectives of HTLN plant community monitoring are to (1) describe the species composition, structure, and diversity of prairie, woodland, and forested communities; (2) determine temporal changes in the species composition, structure and diversity of prairie, woodland, and forested communities; and (3) determine the relationship between temporal and spatial changes and environmental variables, including specific management practices where possible. This protocol narrative describes the sampling design for plant communities, including the response design (data collection methods), spatial design (distribution of sampling sites within a park), and revisit design (timing and frequency of monitoring visits). Details can be found in the SOPs, which are listed in the Revision History section and available at the Integrated Resource Management Applications (IRMA) website (irma.nps.gov). Other aspects of the protocol summarized in the narrative include procedures for data management and reporting, personnel and operating requirements, and instructions for how to revise the protocol.
... As many as sixty million bison once roamed the tallgrass prairies of the Great Plains before their near extirpation by the late 1800s. Reintroduction of bison has resulted in over 150,000 animals in the Great Plains, the restoration of large ungulate herbivory, and the realization of the keystone role bison play in altering plant species composition, changing nutrient cycling and soil resource availability, and in creating a spatial heterogeneity that is essential for the functioning of the tallgrass prairie ecosystem (Knapp et al. 1999). ...
... Reestablishing historically common disturbance regimes, such as frequent, low-intensity fire or grazing through management actions, is critical to the restoration of grassland plant diversity and function. Both fire and grazing promote diversity by removing biomass and litter; increasing plant establishment, space for plant growth, and flowering (Hulbert, 1988;Knapp et al., 1999;Old, 1969); and altering nutrient cycling (Hobbs et al., 1991;Ojima et al., 1994). Fire in tallgrass prairies in eastern and central North America is also known to promote growth of herbaceous species, increase flowering amount and synchrony (Wagenius et al., 2020), and suppress woody species. ...
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Restoring ecosystems in a changing climate requires understanding how management interventions interact with climate conditions. In tallgrass prairies, disturbance through fire, mowing, or grazing is a critical force in maintaining herbaceous plant diversity. However, unlike historical fire regimes that occurred throughout the growing season, management actions like prescribed fire and mowing are commonly limited to the spring or fall seasons. Warming winters are resulting in less snow, causing overwintering plants to experience reduced insulation from snow and these more extreme winter conditions may be exacerbated or ameliorated depending on the timing of management actions. Understanding this novel interaction between the timing of management actions and snow depth is critical for managing and restoring grassland ecosystems. Here, we applied experimental management treatments (spring and fall burn and fall mow) in combination with snow depth manipulations to test whether the type and timing of commonly implemented disturbances interact with snow depth to affect restored prairie plant diversity and composition. Overall, snow manipulations and management actions influenced soil temperature while only management actions influenced spring thaw timing. Burning in the fall, which removes litter prior to winter resulted in colder soils and earlier spring thaw timing. However, plant communities were mostly resistant to these effects. Instead, plants responded to management actions such that burning and mowing, regardless of timing, increased plant diversity and spring burning increased flowering structure cover while reducing weedy cool season grass cover. Together these results suggest that grassland plant communities are resistant to winter climate change over the short term and that burning or mowing is critical to promoting plant diversity in tallgrass prairies.
... Bison do consume some browse items (∼5%), but these species are usually <1 m in height (Plumb and Dodd 1993). Bison do not typically consume a significant amount of leaves or stems of large woody trees and shrubs like C. drummondii (Plumb and Dodd 1993, Coppedge et al. 1998, Knapp et al. 1999, Raynor et al. 2016). However, grazing by bison has indirect impacts on woody plant distributions. ...
Article
Leaf trait variation enables plants to utilize large gradients of light availability that exist across canopies of high leaf area index (LAI), allowing for greater net carbon gain while reducing light availability for understory competitors. While these canopy dynamics are well understood in forest ecosystems, studies of canopy structure of woody shrubs in grasslands are lacking. To evaluate the investment strategy used by these shrubs, we investigated the vertical distribution of leaf traits and physiology across canopies of Cornus drummondii, the predominant woody encroaching shrub in the Kansas tallgrass prairie. We also examined the impact of disturbance by browsing and grazing on these factors. Our results reveal that leaf mass per area (LMA) and leaf nitrogen per area (Na) varied ~ 3-fold across canopies of C. drummondii, resulting in major differences in the physiological functioning of leaves. High LMA leaves had high photosynthetic capacity, while low LMA leaves had a novel strategy for maintaining light compensation points (LCP) below ambient light levels. The vertical allocation of leaf traits in C. drummondii canopies were also modified in response to browsing, which increased light availability at deeper canopy depths. As a result, LMA and Na increased at lower canopy depths, leading to a greater photosynthetic capacity deeper in browsed canopies compared to control canopies. This response, along with increased light availability, facilitated greater photosynthesis and resource-use efficiency deeper in browsed canopies compared to control canopies. Our results illustrate how C. drummondii facilitates high LAI canopies and a compensatory growth response to browsing—both of which are key factors contributing to the success of C. drummondii and other species responsible for grassland woody encroachment.
... At this level, students would be able to predict and explain how changes to one or more elements of the system would impact indirect effects, and ultimately the function of the whole system (e.g., impacts of perturbations or disturbances on the system's function; 3c). They could analyze a case study (e.g., Knapp et al., 1999) to describe the direct and indirect relationships between bison and grass (3a) in order to explain why a decline in bison grazing resulted in long-term biomass increase in some grass species (3b). Students could also reason about how changes in climate (cool and wet, vs. hot and dry) could moderate bison's effect on grass biomass (3c). ...
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As biological science rapidly generates new knowledge and novel approaches to address increasingly complex and integrative questions, biology educators face the challenge of teaching the next generation of biologists and citizens the skills and knowledge to enable them to keep pace with a dynamic field. Fundamentally, biology is the science of living systems. Not surprisingly, systems is a theme that pervades national reports on biology education reform. In this essay, we present systems as a unifying paradigm that provides a conceptual framework for all of biology and a way of thinking that connects and integrates concepts with practices. To translate the systems paradigm into concrete outcomes to support instruction and assessment in the classroom, we introduce the biology systems-thinking (BST) framework, which describes four levels of systems-thinking skills: 1) describing a system's structure and organization, 2) reasoning about relationships within the system, 3) reasoning about the system as a whole, and 4) analyzing how a system interacts with other systems. We conclude with a series of questions aimed at furthering conversations among biologists, biology education researchers, and biology instructors in the hopes of building support for the systems paradigm.
... Wood bison (Bison bison athabascae) and plains bison (Bison bison bison) are classified as near threatened subspecies native to North America [1]. As a keystone species in the short-and tall-grass prairies in the south and the boreal ecosystem in the north [2,3], bison are also a cultural keystone for many Indigenous Peoples in North America [4]. Of the 500,000 bison, only 5% are maintained in wild or conservation herds and are of known origin [5,6]. ...
Article
In an effort to develop an effective, minimum-handling protocol for the conservation of wood bison, the present study was designed to determine the effects of ovarian synchronization and superstimulation on cumulus oocyte complex (COC) collection and in vitro embryo production in wood bison during the ovulatory (Exp. 1) and anovulatory seasons (Exp. 2). We tested the hypotheses that COC collection and in vitro embryo production are 1) greater after follicular wave synchronization than at random stages of the follicular wave, 2) repeatable within individuals, 3) greater after ovarian superstimulation with a single dose of eCG than without treatment, and 4) greater during the anovulatory season than the ovulatory season. In Exp. 1, ultrasound-guided COC collection was performed on Day −1 in wood bison to induce follicular wave emergence the following day (Day = 0). Immediately after the COC collection on Day −1, bison were given a single im dose of 2500 IU eCG or saline (n = 6 per group). Subsequent COC collections were on Days 4 and 9. A similar design was used in Exp. 2, with an additional treatment group given 5000 IU eCG (n = 8 per group). In Exp. 1, compared to the saline-treated group, a single dose of 2500 IU eCG resulted in a greater number of ≥8 mm follicles at the time of the Day 4 COC collection (P = 0.03), but not at the Day 9. In Exp. 2, treatment with 5000 IU eCG resulted in a greater number of ≥8 mm follicles than 2500 IU eCG or the saline treatment (37.5 ± 6.9, 17.5 ± 2.0, 16.9 ± 2.0; P = 0.01, respectively). Although the number of embryos produced/COC submitted to IVM was not different among groups (mean = 18.6%), treatment with 5000 IU eCG produced more than twice as many embryos per bison as unstimulated bison (0.8 vs 1.9). In summary, embryo production rates were higher from COC collected subsequent to follicular wave synchronization vs random stages of the wave, and ovarian superstimulation with eCG resulted in a dose-related increase in the number of ≥8 mm follicles, COC collected, and embryos produced. Repeated COC collections after successive wave synchronization resulted in similar follicular counts and embryo production rates within individuals, and the greatest number of follicles aspirated, COC collected, and embryos produced was in the anovulatory season. We conclude that the minimum-handling COC collection protocols in the present study are effective and provide realistic options for embryo production in wild bison.
... Bison are considered ecological keystone species, defined as having a disproportionately large influence on their environment relative to their abundance through their coevolution with all life forms and land use behavior (Mills and Doak, 1993). For example, bison grazing promotes plant functional-group and species richness, alters patch structure across tallgrass prairie landscapes (Knapp et al., 1999;Koerner and Collins, 2013;Eby et al., 2014), and promotes higher species richness and compositional diversity in mixed-grass prairies (McMillan et al., 2019). Bison also modify their environment by moving across the landscape and creating disturbance in the form of stomping, wallowing, seed dispersal, and grazing (Harvey and Fortin, 2013); behavior that results in increased landscape arthropod, amphibian, and plant heterogeneity (Polley and Collins, 1984;Gerlanc and Kaufman, 2003;Nickell et al., 2018). ...
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Future climate projections of warming, drying, and increased weather variability indicate that conventional agricultural and production practices within the Northern Great Plains (NGP) will become less sustainable, both ecologically and economically. As a result, the livelihoods of people that rely on these lands will be adversely impacted. This is especially true for Native American communities, who were relegated to reservations where the land is often vast but marginal and non-tribal operators have an outsized role in food production. In addition, NGP lands are expected to warm and dry disproportionately relative to the rest of the United States. It is therefore critical to identify models of sustainable land management that can improve ecological function and socio-economic outcomes for NGP communities, all while increasing resilience to a rapidly changing climate. Efforts led by Native American Nations to restore North American Plains bison (Bison bison bison) to tribal lands can bring desired socio-ecological benefits to underserved communities while improving their capacity to influence the health of their lands, their people, and their livelihoods. Ecological sustainability will depend on the restoration of bison herds and bison’s ability to serve as ecosystem engineers of North America’s Plains. The historically broad distribution of bison suggests they can adapt to a variety of conditions, making them resilient to a wide range of management systems and climates. Here we review bison’s ecological, cultural, and economic value using four case studies from tribal communities within the NGP. We discuss the potential contributions of bison to food sovereignty, sustainable economies, and conservation of a working landscape with limited protections and significant risk of conversion. The ecological role of bison within this setting has potential due to cultural acceptance and the vast availability of suitable lands; however, it is critical to address tribal needs for funding support, enhanced community capacity, and solving complex landownership for these goals to be achieved.
... Large herbivores are critically important components of terrestrial landscapes and can shape the structure and functioning of ecological systems by exerting strong top-down pressure on plants (Augustine & McNaughton, 1998;Forbes et al., 2019;Knapp et al., 1999;Milchunas et al., 1988;Wang et al., 2019). However, wild large herbivores worldwide are facing dramatic declines in diversity, distribution, and abundance due to hunting, land-use changes, and habitat fragmentation (Daskin & Pringle, 2018;Dirzo et al., 2014;Ripple et al., 2015). ...
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While large herbivores are critically important components of terrestrial ecosystems and can have pronounced top‐down effects on plants, our understanding of the underlying mechanisms driving these effects remains incomplete. Large herbivores can alter plant growth, reproduction, and abundance through direct effects (predominantly consumption) and through indirect effects via altered interactions with abiotic factors and other species. We know considerably less about these indirect effects than the direct effects. Here, we integrate medium‐ and small‐scale field experiments to investigate how a large vertebrate herbivore, cattle (Bos taurus), affects the aboveground biomass of a dominant forb species, Artemisia scoparia, via diverse direct and indirect pathways in a temperate grassland in northeast China. Although cattle consumed this forb, its biomass increased significantly in response to grazing, due to multiple indirect positive effects that outweighed the direct negative effects of consumption. Cattle preferentially consumed the competing grass Leymus chinensis, and altered Artemisia microhabitats by reducing total plant cover and litter biomass and by increasing the abundance of co‐occurring ant species (e.g., Formica spp. and Lasius spp.). This led to additional indirect positive effects on A. scoparia likely due to (1) increased light availability in understory layers and other limiting resources (e.g., soil nutrients and moisture) caused by removal of competitors and plant litter at the soil surface and (2) the changes in resource availability (e.g., soil nutrients and moisture) associated with ant colonies. Our results show that large herbivores can affect plant growth not only via direct consumption, but also via multiple indirect effects. Focusing on the causes and consequences of herbivore‐induced indirect effects will not only help us to better understand the influence of these animals in ecological systems, but will also lead to more effective land management and conservation practices in the regions they inhabit.
... A possible solution for improving vegetative diversity (i.e., species, structural) in CRP fields could be implementing grazing by domestic cattle as a mid-contract management option. Grazing by large herbivores such as bison (Bison bison) was historically an integral disturbance that maintained the structural diversity of grasslands (Knapp et al. 1999). Grazing creates spatial heterogeneity in grassland structure that can positively affect faunal diversity (Adler et al. 2001). ...
Article
The Conservation Reserve Program (CRP) is a primary tool for restoring grassland in the United States, in part as wildlife habitat, which has benefited declining grassland bird populations. Among potential mid‐contract management practices used to maintain early‐successional CRP grasslands, cattle grazing had been prohibited and is currently disincentivized during the primary nesting season for birds (much of the growing season), despite the important role that large herbivores historically played in structuring grassland ecosystems. Conservative grazing of CRP grasslands could increase spatial heterogeneity in vegetation structure and plant diversity, potentially supporting higher densities of some grassland bird species and higher bird diversity. Our objective was to determine the effect of experimental cattle grazing on species‐specific relative abundance and occupancy, species diversity, and community dissimilarity of grassland birds on CRP grasslands across the longitudinal extent of Kansas, USA (a 63.5‐cm precipitation gradient) during the 2017–2019 avian breeding seasons. Fifty‐three of 108 fields were grazed by cattle during the growing seasons of 2017 and 2018 and all fields were rested from grazing in 2019. For all analyses, we examined separate model sets for semiarid western versus more mesic eastern Kansas. Using data from line transect surveys, we modeled relative abundances of 5 songbird species: grasshopper sparrow (Ammodramus savannarum), dickcissel (Spiza americana), eastern meadowlark (Sturnella magna), western meadowlark (Sturnella neglecta), and brown‐headed cowbird (Molothrus ater). Grazing had delayed yet positive effects on abundances of grasshopper sparrow in western Kansas, and eastern meadowlark in eastern Kansas, but negative effects on dickcissel abundance in western Kansas and especially on burned fields in eastern Kansas. Somewhat counterintuitively, brown‐headed cowbirds in western Kansas were more abundant on ungrazed versus grazed fields in the years after grazing began. In addition, we modeled multi‐season occupancy of 3 gamebird species (ring‐necked pheasant [Phasianus colcicus], northern bobwhite [Colinus virginianus], mourning dove [Zenaida macroura]) and Henslow's sparrow (Centronyx henslowii); grazing did not affect occupancy of these species. In eastern Kansas, species diversity was highest in grazed, unburned fields. In western Kansas, bird communities in grazed and ungrazed fields were dissimilar, as determined from multivariate analysis. Though regionally variable, conservative stocking of cattle on CRP grasslands during the nesting season as a mid‐contract management tool might increase bird species diversity by restructuring habitat that accommodates a greater variety of species and decreasing abundances of species associated with taller, denser stands of vegetation. We found variable effects (species, annually, regionally, recently burned vs. unburned) of cattle‐grazing during the primary nesting season on abundances of grassland bird species in Conservation Reserve Program (CRP) grasslands across Kansas, USA, 2017–2019. Cattle grazing during the primary nesting season had positive effects on bird species diversity, especially in eastern Kansas CRP fields that were not burned in spring.
... The vast numbers of bison that died each year on the prairies lay where they fell, constituting a central node in the food web that was critical to these scavengers and decomposers (Dunne et al. 2002). All of the bison, scavengers, and decomposers were recycled back into the system (Knapp et al. 1999, Towne 2000, supporting a large biomass of other organisms in turn. ...
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Ranching is the dominant land use in much of the American West. Although a copious literature has examined the effects of various grazing practices on native ecosystems, we present here the idea that ranching has important impacts on the land independent of those caused by grazing itself. If biological conservation is to be successful on the western grasslands and shrublands, ranchers must be central to any plan. Focusing on the Great Plains of the United States, and on Wyoming in particular, we raise six points of concern that must be addressed before we can hope to restore or maintain native ecosystems on the range.
... Within each practice, sites were either grazed by cattle (n = 8 CP2; n = 9 CP25) or ungrazed (n = 10 CP2; n = 9 CP25). We did not perform statistical hypothesis testing (Johnson 1999) ...
Article
Bird populations in grasslands have experienced declines coinciding with loss and fragmentation of prairies. The United States Department of Agriculture (USDA)‐administered Conservation Reserve Program (CRP) is the most extensive grassland restoration program in North America and it has especially benefitted grassland birds. Grazing by domestic cattle has been restricted in CRP during avian nesting seasons despite the potential improvements in structuring habitat for a greater diversity of grassland bird species. Potential negative consequences of grazing in CRP grasslands include trampling of nests by cattle, reductions in nest concealment from predators, and attraction of brood‐parasitic brown‐headed cowbirds (Molothrus ater). We designed an experiment to test for effects of cattle grazing in CRP fields during the nesting season on nest survival and brood parasitism of 5 bird species that commonly nest in CRP grasslands: mourning dove (Zenaida macroura), grasshopper sparrow (Ammodramus savannarum), dickcissel (Spiza americana), and eastern (Sturnella magna) and western (S. neglecta) meadowlarks. Grazing was implemented during summers 2017 and 2018 on 17 of 36 fields followed by a year of rest on all fields in 2019. Of the 879 nests on grazed fields, only 4 were likely trampled by cattle (vs. 54% of all nests estimated as failing because of depredation). Experimental grazing (grazed vs. ungrazed fields) had variable effects on nest survival and cowbird parasitism among the bird species analyzed. Negative effects of grazing on daily nest survival of dickcissel and meadowlarks were apparent, at least in some years. We found no direct effects of grazing on nest survival of mourning dove or grasshopper sparrow. Probability and intensity (cowbird offspring/nest) of cowbird parasitism in dickcissel nests was higher on grazed versus ungrazed sites but only in conservation practice (CP) CP2 (vs. CP25 fields). Parasitism probability of grasshopper sparrow nests by cowbirds was higher on grazed fields in the 2 years after introduction of cattle in 2017. Greater vegetative concealment around nest sites was associated with reduced cowbird parasitism of meadowlark and grasshopper sparrow nests and higher nest survival for grasshopper sparrows. Reductions in vegetative height caused by longer‐term or high‐intensity grazing might therefore have negative consequences for some grassland birds by increasing nest site visibility and exposure to cowbird parasitism. Our results indicate that cattle grazing in CRP fields during the nesting season might have some negative effects on reproductive success of some grassland bird species, at least in the short term; however, the potential improvements of structuring habitat to accommodate more grassland bird species and increasing landowner participation in the CRP are considerable. Cattle grazing within the Conservation Reserve Program (CRP) during the primary nesting season might have some negative effects on reproductive success of some grassland bird species, though the effects of grazing were inconsistent across species, conservation practices, and years. Although there were some negative consequences, short‐term grazing in CRP grasslands might be compatible with maintaining populations of grassland birds in landscapes otherwise dominated by row‐crop agriculture.
... Tooth-wear patterns (49), isotopic analyses (64), and plant macrofossil remains retrieved from tooth pits, dung samples, and frozen mummies (8,65) all support this inferred dietary preference. In studies focused on extant grazing communities most similar to the megafauna of the steppe-tundra, large mammals have been shown to promote forb biodiversity through the selective grazing of grasses (61,66). If this relationship was replicated in the Late Pleistocene ecosystem, then large grazers may well have had a keystone role promoting herbaceous diversity within the vegetation mosaic, yet have impacted shrub vegetation to a lesser degree than their closest extant relatives. ...
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Significance Megafauna strongly influence vegetation structure, and population declines can alter ecosystem functioning. Overhunting of grazing megafauna is argued to have driven the collapse of widespread, northern steppe-tundra and its replacement by woody vegetation at the end of the ice age. However, in Alaska and Yukon, mammoth and horse became extinct around the time that steppe-tundra was replaced by shrub tundra, leaving it unclear whether this vegetation change caused, or was caused by, reduced megafauna populations. Comparison of accurately dated pollen records with a radiocarbon-dated bone chronology shows that shrubs began expanding before grazer populations declined. This indicates that climate was the primary control of steppe-tundra persistence and that climate-driven vegetation change may pose threats to faunal diversity in the future.
... (d) Average site-level areal potential denitrification rates were positively related to the site-level average mussel densities. Error bars represent ±1 SE of the mean and the regression line is the standard error around the model et al., 2017; Knapp et al., 1999;Polis et al., 2004). Molluscs are well known as structural engineers (Moore, 2006;Sansom et al., 2020), but the influence of native freshwater mussels (this study), invasive freshwater mussels (Goedkoop et al., 2011) and marine mussels (Kellogg et al., 2013) on nutrient dynamics is becoming more appreciated. ...
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Animals can have pervasive effects on ecosystems as they modify their biogeochemical and physical environments. In particular, when animals occur in high densities these effects can result in dramatic changes in the physical environment and biogeochemical hotspots or hot moments. While most research to date has focused on the direct role of animals in biogeochemical cycles, few have examined how animals indirectly influence biogeochemical cycles across scales. Freshwater mussels occur as spatially heterogeneous, dense and species‐rich aggregations in many river ecosystems world‐wide. Here we examined how mussel communities (a) directly influence the flux of particulate and dissolved nutrients and (b) indirectly effect the flux of N2 production, via denitrification, across a gradient of mussel biomass and differences in community composition at the patch‐ (0.25 m²) and stream reach‐scales (60–80 m). We combined measurements of ammonia (N) and soluble reactive phosphorous (P) excretion and C, N and P biodeposition rates for 10 species with biomass and distribution estimates for seven mixed‐species aggregations to quantify direct mussel contributions to biogeochemical cycling and the spatial heterogeneity of their impact. Additionally, we sampled sediments at a fine spatial scale to determine how mussel biomass and richness influence potential denitrification (indirect flux) rates at the patch‐ and reach‐scales. We predicted that increasing mussel biomass would lead to greater direct and indirect fluxes of nutrients, manifesting in heterogeneous nutrient redistribution within and among stream reaches. We also predicted that variation in community composition would result in differential nutrient excretion and egestion stoichiometries. Our results indicate that mussel aggregations directly influence soluble and particulate nutrient fluxes with community composition, particularly phylogenetic tribe composition, controlling the stoichiometry. Mussel aggregations also indirectly influenced nutrient fluxes as greater mussel biomass and species richness resulted in higher denitrification rates as mediated by their interactions with the sediments and enhancement of nutrient availability. Our results underscore the importance of patchy communities in acting as biogeochemical control points. A free Plain Language Summary can be found within the Supporting Information of this article.
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The manipulation of pre-colonial disturbances in U.S. forests can play a critical role in determining ecological composition, structure, and function. However, our understanding of how concurrent disturbances influence non-tree species is extremely limited in forests. To this end, we used a long-term, multi-disturbance experiment in an oak dominated forest in West Virginia, U.S.A. that factorially manipulated understory fire, deer fencing, and canopy gaps. Thirteen years after disturbance initiation, we sampled and germinated the seed bank from each disturbance treatment. We found long-term seed banks differed only in plots with understory fire, with effects contingent on canopy gaps and deer fencing. Fire combined with canopy gaps caused a 205% increase in seed abundance. Combined fire, deer fencing, and canopy gaps led to the lowest diversity of all treatments and the dominance of the shrub Rubus in the seed bank, reflecting the continued legacy of extant plants that grew immediately after disturbance. Lastly, in plots with multiple reintroduced disturbances, seed communities were distinct from extant understory species at all time points, highlighting how the seed bank is an important reservoir of biodiversity. Each reintroduced disturbance combination left a unique legacy in the seed bank that will likely influence future forest reorganization following disturbance, adding to our understanding of how disturbances influence forest succession and organization. Our study highlights the many unexpected ways that multiple disturbances can change an understudied, but influential, component of the forest for well over a decade.
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Globally, interactions between people and wildlife are increasing due to habitat loss and conversion and the movement of people and wildlife into areas in which they were not previously present. Many of these interactions involve agricultural damage, which is especially problematic for resource limited communities. One species that causes extensive agricultural damage to rural farmers are African elephants (Loxodonta africana) which forage on cultivated crops, jeopardizing food security for humans and creating conservation concerns for elephants. While the ecological drivers of this human-elephant conflict are known, there remains a gap in our knowledge about how the farmers perceive and conceptualize the conflict that is necessary for advancing conservation. Thus, the goal of this dissertation is to develop a greater understanding of the impact of human-elephant interactions on rural farmers across social, ecological, economic, and cultural dimensions to better inform policy and decision makers in wildlife agencies mitigating these interactions. To address this goal, I developed key research questions: 1) how is the use and knowledge of deterrents by farmers and their behaviors and attitudes towards elephants related to demographic variables such as age, years farming, and exposure to deterrent information? 2) what are farmer attitudes and behaviors towards environmental threats to their livelihoods, and are there sociodemographic categories that influence farmer responses to such threats? and, 3) what are farmers' mental models of elephant conflicts, including drivers of conflict that are underrepresented or unknown in the literature and potential indicators for evaluation of mitigation programs? To address these questions and the corresponding hypotheses, I conducted social surveys and participatory modeling sessions across 6 villages in the Greater Tsavo ecosystem of southeastern Kenyan. Across the villages, ~90% of respondents had never received information on mitigating crop raiding using fencing deterrents. 3 The main reason for not implementing deterrents was lack of funding. Farmers were accepting of mitigation solutions for concerns such as climate change. However, 35% had never received information on solutions such as alternative crops. Likewise, ~50% of farmers would prefer to continue farming, even if alternative ways to earn income were available. Farmers positively viewed the benefits of wildlife, suggesting local community programs may be beneficial for improving attitudes. Mental models indicated several novel drivers of conflict such as road infrastructure and soil compaction and provided additional potential sociocultural indicators for evaluating mitigation programs. The models also showed that economic and environmental interactions were central variable types conserved across all villages and impacts to income levels and feeling of security were the most important variables indicated by farmers. The findings of this research provide valuable information for wildlife managers and policy makers that value stakeholder knowledge to aid in mitigating human-elephant interactions.
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Megafauna (animals ≥45 kg) have probably shaped the Earth’s terrestrial ecosystems for millions of years with pronounced impacts on biogeochemistry, vegetation, ecological communities and evolutionary processes. However, a quantitative global synthesis on the generality of megafauna effects on ecosystems is lacking. Here we conducted a meta-analysis of 297 studies and 5,990 individual observations across six continents to determine how wild herbivorous megafauna influence ecosystem structure, ecological processes and spatial heterogeneity, and whether these impacts depend on body size and environmental factors. Despite large variability in megafauna effects, we show that megafauna significantly alter soil nutrient availability, promote open vegetation structure and reduce the abundance of smaller animals. Other responses (14 out of 26), including, for example, soil carbon, were not significantly affected. Further, megafauna significantly increase ecosystem heterogeneity by affecting spatial heterogeneity in vegetation structure and the abundance and diversity of smaller animals. Given that spatial heterogeneity is considered an important driver of biodiversity across taxonomic groups and scales, these results support the hypothesis that megafauna may promote biodiversity at large scales. Megafauna declined precipitously in diversity and abundance since the late Pleistocene, and our results indicate that their restoration would substantially influence Earth’s terrestrial ecosystems.
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The significant extinctions in Earth history have largely been unpredictable in terms of what species perish and what traits make species susceptible. The extinctions occurring during the late Pleistocene are unusual in this regard, because they were strongly size-selective and targeted exclusively large-bodied animals (i.e., megafauna, >1 ton) and disproportionately, large-bodied herbivores. Because these animals are also at particular risk today, the aftermath of the late Pleistocene extinctions can provide insights into how the loss or decline of contemporary large-bodied animals may influence ecosystems. Here, we review the ecological consequences of the late Pleistocene extinctions on major aspects of the environment, on communities and ecosystems, as well as on the diet, distribution and behavior of surviving mammals. We find the consequences of the loss of megafauna were pervasive and left legacies detectable in all parts of the Earth system. Furthermore, we find that the ecological roles that extinct and modern megafauna play in the Earth system are not replicated by smaller-bodied animals. Our review highlights the important perspectives that paleoecology can provide for modern conservation efforts.
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Fire and native large herbivore grazing were two important influences on the structure and function of North American grasslands. In 1988 and 1989 the influence of fire regime on grazing patterns of North American bison (Bison bison) was studied on the Konza Prairie in northeastern Kansas. Bison grazing was spatially and temporally nonrandom and was influenced by fire regime and local plant community composition. During the growing season, bison were observed up to 3 x more frequently than expected on watersheds burned in the spring. Summer grazing was concentrated in large watershed areas (79-119 ha) dominated by warm-season, perennial, C4 grasses. During the autumn and winter, bison grazed both burned and unburned watersheds more uniformly but grazed most intensively in areas with large stands of cool-season, C3 grasses. On a smaller spatial scale (5-10 m2), bison selected patches during the growing season with low forb cover dominated by the perennial C4 grass, Andropogon gerardii. Grazed patches were larger on frequently burned than on infrequently burned watersheds. The importance of fire history in determining patterns of bison grazing over the landscape indicates that interactions between bison grazing and fire regime may be important to the composition and spatial heterogeneity of tallgrass prairie vegetation.
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Horning and rubbing behaviors of American bison (Bison bison) and their effects on woody vegetation were investigated for 2 yr on a herd of 300+ animals reintroduced to a 1973-ha tallgrass prairie site in Oklahoma. Horning and rubbing activity was significantly higher in summer than in other seasons. Whether this increase was associated with rut, shedding of winter pelage, insect harassment, or a combination of these factors was unclear; however, these behaviors did have measurable impacts on the woody vegetation of the area. Bison injury to trees was minimal, although one willow (Salix nigra) was uprooted and killed during the study, and several other trees were seriously damaged. Bison homing had the greatest effect on saplings and shrubs, killing or severely damaging 4% of the woody plants documented within the study area and causing moderate injury to 13% and light injury to 12%. Bison showed a strong preference for small willows, killing or severely damaging 17% of the saplings and shrubs of this species during the study. Bison also used artificial, man-made objects present on the landscape such as utility poles and fenceposts. Results suggest that horning and rubbing by bison, along with fire and drought, may have influenced the historical distribution of woody vegetation in prairie environments.
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"Buffalo wallows" are depressions formed in North American grasslands by the trampling and dust-bathing of bison (Bison bison). Plant species composition and resource availability within these concave depressions differ from that of the surrounding grassland. The vegetation and soil characteristics of wallows still subject to bison activity were examined in order to possibly relate plant species heterogeneity to edaphic factors. Ordination analysis demonstrated that species cover and composition differed among wallows. Vegetational heterogeneity among wallows was related to differences in several edaphic parameters. Regression analyses indicated that differences in vegetational composition were most consistently correlated with differences in soil texture, ammonium-nitrogen and sodium. These differences, together with probabilistic events in species establishment and recurrent disturbances, produce the diverse vegetation of wallows. The heterogeneous species assemblages of wallows enhance grassland species diversity primarily because wallows increase habitat diversity.
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Discharge and N content of surface water flowing from four Karat watersheds on Konza Prairie Research Natural Area, Kansas, managed with different burn frequencies, were monitored from 1986 to 1992. The goal was to establish the influence of natural processes (climate, fire, and bison grazing) on N transport and concentration in streams. Streams were characterized by variable flow, under conditions that included an extreme flood and a drought during which all channels were dry for over a year. The estimated groundwater/stream water discharge ratio varied between 0.15 to 6.41. Annual N transport by streams, averaged across all watersheds and years, was 0.16 kg N ha-1 yr-1. Annual N transport per unit area also increased as the watershed area increased and as precipitation increased. Total annual transport of N horn the prairie via streams ranged from 0.01 to 6.0% of the N input from precipitation. Nitrate and total N concentrations in surface water decreased (P < 0.001, r values ranged from 0.140.26) as length of time since last fire increased. Increased watershed area was correlated negatively (P < 0.0001) to stream water concentrations of NO3-N and total N (r values = -0.43 and -0.20, respectively). Low N concentration is typical of these streams, with NH4/+-N concentrations below 1.0 μg L-1, NO3-N ranging from below 1.4 to 392 μg L-1, and total N from 3.0 to 714 μg L-1. These data provide an important baseline for evaluating N transport and stream water quality from unfertilized grasslands.
Chapter
This is the first volume in the Long-Term Ecological Research (LTER) Network Series. Established in 1980, the LTER program is exploring a wide variety of biomes characteristic of the United States and developing a baseline for ecosystem dynamics over long time periods and broad spatial scales. The volumes in this series will include both comprehensive reviews of research from particular sites and topical overviews which use data from many sites to examine important questions in ecology. This volume, which focuses on the Konza Prairie in northeastern Kansas, is a synthesis of over 15 years of research in pristine tallgrass prairie. It gives a comprehensive site description and summarizes the key long-term studies that form the basis for the Konza Prairie Long-Term Ecological Research Program. It then presents a synthesis of the many research areas involved and develops a foundation for future ecological studies in tallgrass prairie. With over 150 figures and tables, chapters that encompass microbial through landscape scales, and an emphasis on lessons learned from long-term studies, this volume provides a unique and comprehensive perspective on the structural and functional ecology of the grassland ecosystem that once covered most of central North America.
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We searched diaries of travels over the Southern Plains from 1806-1857 for reports ofbison, elk, and pronghorn. From these accounts we obtained indexes of abundance by dividing the number of days in which the animals were observed by the total number of days spent by the expeditions in each of the three prairie biomes. Organizedby historical period and biome type, results show that populations of these ungulates were unstable even during the first half of the nineteenth century. The most stable populations throughout the survey period were bison on mixed-grass prairies. Bison and elk disappeared from tall-grass regions by 1833. Bison were exceptionally numerous on short-grass prairies prior to 1821 but dropped off sharply thereafter. Elk abundance was highest on tall-grass prairies during the earliest historical periods. Pronghorn were most abundant on short-grass prairies during 1806-1820 and again during the 1850s, and most abundant on mixed-grass prairies between those periods. Human influences were likely responsible for the paucity of bison on tall-grass prairies. The persistence of all three species on mixed-grass prairies was influenced by that biome’s distance from centers of human populations encroaching from both east and west.
Chapter
The defining period of coevolution among Great Plains plant and ungulate species occurred during the past 12,000 years (Mack and Thompson 1982, Axelrod 1985). In the late Pleistocene and early Holocene, a diverse array of large grazers and browsers were reduced to a much smaller group of ungulate species represented by bison (Bison bison), pronghorn (Antilocapra americana), deer (Odocoileus hemionus and O. virginianus), and elk (Cervus canadensis). These changes occurred in the presence of nomadic humans from the Asian steppe who were immigrating to the Great Plains during the same time. The landscape was characterized by gently rolling interfluvial surfaces covered with perennial herbaceous vegetation. These exposed grasslands were periodically interrupted by more protected wetland, riparian woodland, or scarp woodland habitats. Although wetlands and woodlands occupied less than 7 and less than 3% of the Great Plains, respectively (National Wetlands Inventory, and Nebraska Natural Heritage Program data bases), the heterogeneity that they created at landscape scales played a major role in determining the distribution and abundance of native ungulates. Extreme cold and heat, drought, flood, fire, wind, and countless biotic interactions caused locally short-term fluctuations in ungulate populations and long-term shifts in landscape features. These dynamic temporal changes were overlayed on a multi-scale spatial mosaic. Native ungulates were adapted to this landscape.
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Seven different SPOT satellite scenes of the Konza Prairie Research Natural Area were analyzed to assess the potential of using textural algorithms as a quantitative measure of seasonal variation in heterogeneity. Unburned watersheds usually have greater heterogeneity than annually burned watersheds. However, the greatest amount of heterogeneity as measured by textural analysis occurs in those areas with a mixture of forest and upland tallgrass prairie. -from Authors
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Comments on annual rates of consumption; herbivore effects on primary producers and primary production (including discussion of changes in species composition, herbivore-induced changes in plant morphology and population structure, and the grazing optimization hypothesis); and alteration of nutrient cycling by herbivores. Grassland herbivores typically consume 15-60% of the annual aboveground net primary production and 5-15% of belowground production. Light to moderate grazing may enhance NPP, particularly in the case of large ungulate grazing in tropical African grasslands, but there are few well-documented cases of this, and data from temperate North American grassland indicate that there is usually a decrease in NPP. Defoliation results in an increase in the proportion of carbon and nutrients to aboveground structures. Aboveground grazers tend to feed preferentially in previously grazed areas; root-feeding invertebrates are often more abundant in the rooting zone of plants which have received moderate grazing. In both cases, increased nutrient concentrations (particularly N) in shoots and roots may be implicated as possible partial causal factors. Grazing may keep nutrients in a relatively available, rapidly cycling pool near the soil surface, and it may reduced ammonia volatilization losses from leaf surfaces. -from Author
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The dominant tallgrass prairie species, Andropogon gerardii, and a less common (more mesic) grass, Panicum virgatum, were studied at the Konza Prairie Research Natural Area, NE Kansas. Early in the growing season in a burned plot, leaves of A. gerardii exhibited greater photosynthesis (maximum CO2 uptake 41.6mu mol.m-2.s-1), leaf conductance, leaf N content, N use efficiency, leaf thickness, and shoot biomass compared to shoots from an unburned plot. Postburn differences in P. virgatum were less pronounced, and CO2 uptake rates (maximum 46.0mu mol.m-2.s-1) were not significantly different between burned and unburned sites for this grass. Both grasses had broad temperature optima for photosynthesis, and neither was light-saturated at 2.2mmol.m-2.s-1 quantum flux. The response of A. gerardii to burning reflects the documented postfire vigor of this grass, and is indicative of a substantial shift in the water, energy, and nutrient dynamics of tallgrass prairie following fire. Attributes of A. gerardii that may contribute to its dominance in tallgrass prairie were the ability of this grass to maintain high rates of carbon gain over a greater range of leaf temperatures and at lower leaf water potential than P. virgatum. -from Author
Article
Grazed and ungrazed sites subjected to different fire frequencies were sampled on the Konza Prairie Research Natural Area in northeast Kansas after 4 years of bison grazing (1987-1991). The objective was to study effects of bison grazing on plant species composition and diversity components (plant species richness, equitability, and spatial heterogeneity) in sites of contrasting fire frequency. Cover and frequency of cool-season graminoids (e.g. Poa pratensis L., Agropyron smithii Rydb., Carex spp.) and some forbs (e.g. Aster ericoides [A. Gray] Howell, and Oxalis stricta L.) were consistently higher in sites grazed by bison than in ungrazed exclosures, whereas the dominant warm-season grasses (Andropogon gerardii Vitman, Sorghastrum nutans [L.] Nash, Panicurn virgatum L., Schizachyrium scoparium [Michx.] Nash) and other forbs (e.g. Solidago missouriensis Nutt.) decreased in response to bison. Plant species diversity (H') and spatial heterogeneity in all areas sampled were significantly increased by bison. Increased heterogeneity and mean species richness in grazed prairie (40 species per sample site) compared to unglazed prairie (29 species per site) were likely a result of greater microsite diversity generated by bison, whereas preferential grazing of the dominant grasses and concomitant increases in subordinate species resulted in an increase in equitability of species abundances. Species/area relationships indicated greater effects of bison on plant species richness with increasing sample area. Increases in plant diversity components associated with bison grazing were generally greater in annually burned than in 4-year burned sites. Effects of ungulate grazers on floristic diversity have important implications given recent evidence that plant species diversity and the compositional and production stability of grassland plant communities are positively related.
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Field data came from Wind Cave National Park, South Dakota. Laboratory estimates of net nitrogen mineralization were highest in soils from the more altered areas of prairie dog colonies (Cynomys ludovicianus) and lowest in adjacent, lightly grazed, uncolonized grassland. The ratio of CO2:net N mineralized, an index of immobilization, was highest in the uncolonized grassland, lowest in the altered core areas. Soil moisture was an important modifier of in situ field estimates of net N mineralization. Root biomass, an important C source for decomposers in perennial grasslands, was lowest in the altered core area and highest in adjacent uncolonized grassland. Decreased N immobilization and increased net N mineralization in laboratory incubations likely resulted from decreased root C inputs in grazer areas, which limited C availability to decomposers. -from Authors
Article
On tallgrass prairie vegetation, in the Konza Prairie Research Natural Area, defoliation history largely controlled whether or not defoliated plants overcompensated (exhibited enhanced production compared to undefoliated controls) for tissue removal. Plants on chronically grazed sites only compensated for foliage removed by grazers. Production on plots mowed prior to the year of measurement was similar to that on chronically grazed sites, while previously unmowed plots exhibited substantial aboveground overcompensation. Aboveground production was maximized by the most frequent mowing treatment and by intermediate mowing heights. Nitrogen and P concentrations and amounts in aboveground tissues were increased by mowing and grazing. Current mowing regime was more important than mowing history in determining N concentrations except very early in the growing season. Frequent mowing appeared to limit accumulation of belowground N reserves and biomass. In North American grasslands, overcompensation is a nonequilibrium plant response to grazing. Photosynthate that would be stored as reserves and used for root growth and flower and seed production instead is used to replace lost leaf area, resulting in higher foliage productivity. However, under chronic grazing or mowing, vegetation is prevented from maintaining high nutrient and water uptake capacity (large root biomass) and accumulating reserves that allow overcompensation responses. -Authors
Article
(1) Using the results of diet selection studies and two wild and two domestic species, we compare some aspects of ecology in relation to body size, the recent evolutionary history of the species and current forage conditions. (2) Food niche breadth and mter-species diet overlap seemed dependent upon recent evolutionary history as well as upon body size, but values were strongly influenced by forage quantity and quality. (3) Dietary selectivity appears especially sensitive to seasonal changes in forage quality, e.g. large as well as small animals pursued relatively selective strategies when forage conditions permitted, but body size and related nutritional-energetic demands appeared to set the limits where switches from selective to non-selective tactics took place. (4) Sensitivity to diet composition and quality increased with decreasing size except in the domestic sheep. It is likely that anatomical-physiological adaptations, including a relatively large rumeno-reticulum allow domestic sheep to utilize more forage plant species and mhabit a wider variety of niches and ecosystems than most ungulates. Human selection has made the sheep food and habitat generalists despite their relatively small size.
Article
Investigated the response of Schizachyrium scoparium (C4 photosynthetic pathway) and Poa pratensis (C3) to natural and simulated bison urine deposition in a northern, mixed prairie in South Dakota. Total aboveground biomass and root mass were higher and root:shoot ratios were lower on urine patches. Higher total aboveground biomass on urine patches resulted primarily from increased aboveground P. pratensis production. Urine deposition in May had little effect on aboveground production of S. scoparium except during July when S. scoparium was most active. Urine deposition date and plant phenology appear important in determining changes in species composition. Following urine deposition, aboveground N concentrations of P. pratensis and S. scoparium were higher on patches relative to conspecifics off patches, an increase greater in P. pratensis. The large increase in P. pratensis biomass following urine deposition is probably related to its relatively large response to increased soil N availability and its rhizomatous habit. Root N concentrations were higher on urine patches. Poa pratensis on urine patches initiated growth earlier in the season and postponed senescence relative to plants off patches. Aboveground production following clipping was greater on urine patches and N concentrations in regrowth of both species were higher than concentrations in plants not previously clipped. Aboveground herbivore utilization was greater on urine patches than on adjacent vegetation. Although urine patches covered only 2% of the study site, they provided 7% of the biomass and 14% of the N consumed by aboveground herbivores from June through August. Urine patches probably provided an even greater source of forage and N for herbivores earlier and later in the growing season when surrounding vegetation was mostly quiescent. -from Authors
Article
(1) Seasonal information on dietary composition, forage digestibility and selectivity was collected for bison, cattle and sheep from two treatments representing lightly grazed and heavily grazed pasture. (2) Bison have a greater preference for warm-season grasses and appear to feed less selectively than cattle and in different areas within shortgrass vegetation. (3) Sheep consume fewer grasses than either species. (4) Bison appear to have a greater digestive power than cattle when consuming low protein, poor quality forage, and may also consume greater quantities of forage as compared to cattle. (5) These two mechanisms of feeding strategies may permit bison to exploit more fully than cattle the herbage resources on shortgrass plains.