25 research outputs found
Adjustment of Riparian Vegetation to River Regulation in the Great Plains, USA
No full textThe Missouri River and the Platte River provide opposite examples of the way riparian vegetation responds and adjusts to regulation by dams and diversions.Populus-Salix woodland has expanded rapidly into Platte River channels, while it has failed to regenerate in gaps between reservoirs along the upper Missouri River. This divergent response is the result of different geomorphologies and water-use patterns. The Platte River is a braided-type stream with a significant portion of its flow diverted for cropland irrigation. The Missouri is a meandering-type stream with low irrigation usage. I developed a graphical model that characterizes the different ways that riparian vegetation has adjusted to regulation. The model identifies two time periods: pre-regulation and post-regulation adjustment, with the latter divided into phase 1 and phase 2 subperiods. In the pre-regulation period, woodland composition shifts according to weather extremes and climate change. During phase 1, braided rivers adjust by channel-narrowing and expansion of pioneer woodland (Populus-Salix), while meandering rivers cease meandering. During phase 2, after major geomorphic adjustments are complete, both types of rivers, show sharp declines in pioneer woodland Replacement communities in the new equilibrium (post-adjustment period) will be dominated by later successional woodland or grassland species. Geomorphic factors of importance to vegetation establishment adjust relatively quickly (decades), but the subsequent adjustment of vegetation through succession is relatively slow (century or more)
Riparian Vegetation Diversity Along Regulated Rivers: Contribution of Novel and Relict Habitats
No full text1. The creation and maintenance of spatial and temporal heterogeneity by rivers flowing through floodplain landscapes has been disrupted worldwide by dams and water diversions. Large reservoirs (novel ecosystems) now separate and isolate remnant floodplains (relict ecosystems). From above, these appear as a string of beads, with beads of different sizes and string connections of varying lengths. 2. Numerous studies have documented or forecast sharp declines in riparian biodiversity in relict ecosystems downstream from dams. Concurrently, novel ecosystems containing species and communities of the former predam ecosystems have arisen along all regulated rivers. These result from the creation of new environments caused by upper reservoir sedimentation, tributary sedimentation and the formation of reservoir shorelines. 3. The contribution of novel habitats to the overall biodiversity of regulated rivers has been poorly studied. Novel ecosystems may become relatively more important in supporting riverine biodiversity if relict ecosystems are not restored to predam levels. The Missouri River of the north-central U.S.A. is used to illustrate existing conditions on a large, regulated river system with a mixture of relict and novel ecosystems
Cattle and Wooded Draws: A Second Look
No full textWooded draws or “coulees” in the western Dakotas are associated with the steeper portions of large river valleys such as the Missouri, Cheyenne, and White and their main tributaries. These woodlands are a mixture of green ash, hackberry, American elm, cottonwood, and Rocky Mountain juniper. All but juniper also dominate nearby riparian habitats. Shrub species usually outnumber tree species and are dominated by chokecherry, Saskatoon serviceberry, wild plum, buffalo currant, fragrant sumac, and western snowberry
Non-linear Responses of Glaciated Prairie Wetlands to Climate Warming
No full textThe response of ecosystems to climate warming is likely to include threshold events when small changes in key environmental drivers produce large changes in an ecosystem. Wetlands of the Prairie Pothole Region (PPR) are especially sensitive to climate variability, yet the possibility that functional changes may occur more rapidly with warming than expected has not been examined or modeled. The productivity and biodiversity of these wetlands are strongly controlled by the speed and completeness of a vegetation cover cycle driven by the wet and dry extremes of climate. Two thresholds involving duration and depth of standing water must be exceeded every few decades or so to complete the cycle and to produce highly functional wetlands. Model experiments at 19 weather stations employing incremental warming scenarios determined that wetland function across most of the PPR would be diminished beyond a climate warming of about 1.5–2.0 °C, a critical temperature threshold range identified in other climate change studies
Prairie Wetlands and Climate Change - Droughts and Ducks on the Prairies
No full textThe Prairie Pothole Region (PPR) contains 5-8 million small wetlands and is one of the most ecologically valuable freshwater resources of the Nation. These wetlands provide abundant ecosystem services, including groundwater recharge, water for agriculture, water purification, and recreation. The PPR is best known as the “duck factory” of North America. By some estimates, this region produces over 50% of the ducks in North America
Effects of Weevil Larvae on Acorn Use by Blue Jays
No full textBlue jays (Cyanocitta cristata L.) are important consumers and dispersers of the nuts of oaks and other fagaceous trees in eastern North America. Acorns compose much of the jay diet, especially during the autumn when jays may consume or cache a significant portion of an acorn crop. However, jays do not appear to possess physiological adaptations for countering the protein-binding properties of secondary compounds (tannins) found in acorns. We offered captive blue jays a mixture of infested and uninfested pin oak (Quercus palustris Muenchh.) acorns to see if the birds would selectively consume nuts containing weevil larvae (Coleoptera: Curculionidae) as a protein supplement to a high-tannin, all-acorn diet. Acorns were X-rayed to determine infestation status and then offered to individual jays in an outdoor aviary. Jays handled, opened, and consumed uninfested nuts significantly more often than infested nuts, and use of infested nuts did not increase during continued exposure to a high-tannin diet
Strategic Use of Native Species on Environmental Gradients Increases Diversity and Biomass Relative to Switchgrass Monocultures
No full textSwitchgrass (Panicum virgatum) monocultures are a leading feedstock choice for producing cellulosic biofuels. However, in natural stands, switchgrass is only dominant in a narrow ecological niche of the Tallgrass Prairie. This suggests that strategically selected monocultures or binary mixtures of species, adapted to particular ecological niches, might outyield switchgrass monocultures while increasing biodiversity at the field and landscape scales. To test this hypothesis, we planted monocultures of switchgrass and three alternative species at each of three landscape positions (shoulderslope, midslope, and footslope). Alternative species were also mixed with switchgrass such that they composed 33 or 67% of the total number of plants in each plot. Alternative species at each position included a C3 grass, a C4 grass, and a forb. Biomass data were collected in autumn during each of the two consecutive years following the establishment year. (see more in article
Climate Trends of the North American Prairie Pothole Region 1906-2000
No full textThe Prairie Pothole Region (PPR) is unique to North America. Its millions of wetlands and abundant ecosystem goods and services are highly sensitive to wide variations of temperature and precipitation in time and space characteristic of a strongly continental climate. Precipitation and temperature gradients across the PPR are orthogonal to each other. Precipitation nearly triples from west to east from approximately 300 mm/year to 900 mm/year, while mean annual temperature ranges from approximately 1◦C in the north to nearly 10◦C in the south. Twentieth-century weather records for 18 PPR weather stations representing 6 ecoregions revealed several trends. The climate generally has been getting warmer and wetter and the diurnal temperature range has decreased. Minimum daily temperatures warmed by 1.0◦C, while maximum daily temperatures cooled by 0.15◦C. Minimum temperature warmed more in winter than in summer, while maximum temperature cooled in summer and warmed in winter. Average annual precipitation increased by 49 mm or 9%. Palmer Drought Severity Index (PDSI) trends reflected increasing moisture availability for most weather stations; however, several stations in the western Canadian Prairies recorded effectively drier conditions. The east-west moisture gradient steepened during the twentieth century with stations in the west becoming drier and stations in the east becoming wetter. If the moisture gradient continues to steepen,
the area of productive wetland ecosystems will shrink. Consequences for wetlands would be especially severe if the future climate does not provide supplemental moisture to offset higher evaporative demand
Forty Years of Vegetation Change on the Missouri River Floodplain
No full textComparative inventories in 1969 and 1970 and in 2008 of vegetation from 30 forest stands downstream of Garrison Dam on the Missouri River in central North Dakota showed (a) a sharp decline in cottonwood regeneration; (b) a strong compositional shift toward dominance by green ash; and (c) large increases in invasive understory species, such as smooth brome, reed canary grass, and Canada thistle. These changes, and others discovered during re-measurement, have been caused by a complex of factors, some related to damming (altered hydrologic and sediment regimes, delta formation, and associated wet–dry cycles) and some not (diseases and expansion of invasive plants). Dominance of green ash, however, may be short lived, given the likelihood that the emerald ash borer will arrive in the Dakotas in 5–10 years, with potentially devastating effects. The prospects for recovery of this valuable ecosystem, rich in ecosystem goods and services and in American history, are daunting
The Dammed Missouri: Prospects for Recovering Lewis and Clark\u27s River
No full textThe world’s dams and reservoirs are aging. The ecological effects of a half-century or more of flow regulation and sediment alteration are becoming apparent. What remains of the highly dynamic channel and riparian ecosystem of the Missouri River described by Lewis and Clark has become static. Recent long-term studies have determined that some of the impacts on the Missouri River ecosystem turned out as predicted, such as the failure of cottonwood-dominated riparian forests to successfully establish and survive on a broad scale. Other changes were surprises, such as the effect of disease eliminating a formerly dominant tree species and the appearance of mainstem and tributary deltas affecting channel slope, floodplain hydrology, and vegetation. Restoration of the river’s hydrologic and sediment regime has been delayed long enough that the chances of functional ecosystem restoration have been greatly reduced and complicated. Two phases are now needed to attempt to restore the riparian ecosystem: one to repair the effects of post-dam changes (channel incision, bank stabilization) and another to reestablish pre-dam flow and sediment regimes. The prospects for restoration of this valuable ecosystem, rich in history and in goods and services provided to the public, are dim. Time has diminished the chances that restoration or even rehabilitation can be achieved
