Determining the best strategy for allocating weed management resources across and between landscapes is challenging because of the uncertainties and large temporal and spatial scales involved. Ecological models of invasive plant spread and control provide a practical tool with which to evaluate alternative management strategies at landscape scales. We developed a spatially explicit model for the spread and control of spotted knapweed and leafy spurge across three Montana landscapes. The objective of the model was to determine the ecological and economic costs and benefits of alternative strategies across landscapes of varying size and stages of infestation. Our results indicate that (1) in the absence of management the area infested will continue to increase exponentially leading to a substantial cost in foregone grazing revenues; (2) even though the costs of management actions are substantial, there is a net economic benefit associated with a broad range of management strategies; (3) strategies a that prioritize targeting small new infestations consistently outperform strategies that target large established patches; and (4) inconsistent treatment and short-term delays can greatly reduce the economic and ecological benefits of management.
Beaver dam mimicry is an emergent conservation practice. We evaluated the influence of constructed riffles, a unique type of beaver mimicry aimed to store water and allow fish passage, on habitat for fishes in one control reach and one manipulated reach with mimicry structures added. The beaver mimicry reach had deeper pool habitats and deeper and wider riffle habitats compared to an unmanipulated control reach.Dissolved oxygen was similar among reaches, averaging 8.7 ± 0.2 and 8.9 mg/L in the beaver mimicry and control reaches, respectively. Sediment size was also similar among reaches, with a D 50 of 8.1 and 10.6 mm in the beaver mimicry and control reaches, respectively. The beaver mimicry reach had little to no overhanging bank vegetation or riparian vegetation shade cover, while the control had 38% of its bank covered by canopy and 56% overhung by vegetation. These riparian characteristics result from a legacy of livestock grazing and lack of consistent vegetation planting during restoration. Longnose dace (Rhinichthys cataractae) and white sucker (Catostomus commersonii) dominated in the beaver mimicry reach, together comprising 70% of the fish assemblage post-structure installation. Arctic grayling (Thymallus arcticus) was not found in the beaver mimicry reach but was present in the control, albeit in small numbers of only 3% of the assemblage post-structure installation. These results highlight the need to consider both in-stream and riparian habitat features for fishes, as well as timescales of both hydrological and ecological outcomes in restoration design.
Juniper expansion across the western United States has the potential to alter watershed hydrology, especially within riparian areas. Given the uncertainties in the ecohydrological response to the expansion, this study focused on examining the water use strategies between two woody species co-occurring in a riparian area in south central Montana-Salix exigua (sandbar willows) and Juniperus scopulorum (rocky mountain junipers)-in order to address three questions: (1) Are junipers and willows using the same soil moisture pool that contributes to streamflow? (2) Are junipers transpiring more water than willows on a per tree or per sapwood area basis? (3) Are the seasonal transpiration rates between junipers and willows different? To determine the differences in water use strategies between willows and junipers, we used stable isotope analyses to trace different sources of water, water potential to determine seasonal water stress patterns and transpiration rates to quantify water loss.Our isotopic analyses suggest that junipers and willows in the riparian area were not directly using stream water but relied on different pools of soil water at different times of the year: shallow soil water in spring when soils were wet and deeper soil water in late summer. We also found that junipers transpired more than willows during the spring and late fall, but that both species had similar transpiration rates during periods of low streamflow. However, higher juniper transpiration rates in spring and late fall can potentially lead to soil moisture deficits if winter snowpack is low, suggesting that the additional water loss through transpiration by junipers may be mitigated under wet winters but exacerbated under dry winters.
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