Thus, the preservation of avian biodiversity has numerous positive benefits to society. Birds are important culturally in arts and literature; recreationally to birdwatchers and hunters; and economically as pollinators, pest predators, seed dispersers, and nutrient cyclers [ 2 ]. However, for over two decades, ornithologists have been raising the alarm about the precipitous decline of grassland birds, driven primarily by the loss and degradation of habitat by anthropogenic means [ 3 , 4 ]. Despite acknowledgment of the issue, grassland-bird habitat continues to be lost and degraded [ 5 — 7 ], and avian populations continue to decline [ 8 ].
However, most of the grasslands that these species rely upon for habitat have been converted to alternate uses [ 5 ]. Two primary causes of contemporary habitat loss are crop production and energy development that result in grassland conversion and fragmentation [ 6 , 9 , 10 ].
Neither of these drivers, i.
Lark et al. The largest regional crude-oil-production growth through in the United States is expected to come from the Bakken formation in North Dakota, USA [ 11 ]. The International Energy Agency [ 12 ] forecasts that the largest growth in world power-generating capacity will be from renewable energies, with the United States the second-biggest market after China. Regionally, the states of North Dakota and South Dakota have abundant wind resources, routinely ranking in the top 20 wind-producing states [ 13 , 14 ].
A primary cause of habitat degradation is the fragmentation of remaining expanses of grassland habitat. Habitat fragmentation refers to the reduction in area of some original habitat, a change in spatial configuration that is, spatial arrangement , and an increasing distance between the patches of what remains, through the subdivision of continuous habitat into smaller pieces [ 15 , 16 ].
Fragmentation, while increasing overall heterogeneity within a landscape, can decrease the heterogeneity of individual habitat types within blocks of remaining grasslands. With the loss of heterogeneity within grasslands comes an associated loss of biodiversity. Fragmentation also lowers habitat quality because of edge effects, such as lower avian reproductive success near the edge than the interior of remaining habitat [ 17 ].
The indirect effects on habitat quality can be much larger than the direct effects of habitat loss. For example, McDonald et al. Thus, any evaluation of grassland-bird habitats should include an assessment of the indirect effects on the quality of remaining habitats.
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To offset the loss and degradation of native habitats, and the services they provide, both governmental and nongovernmental organizations have made significant monetary investments to restore and protect grassland habitats in the PPR. Given the prominence of agriculture throughout the PPR, the most wide-reaching conservation efforts have been associated with various programs of the U. These conservation grasslands provide numerous ecosystem services, including climate regulation, water purification, and erosion regulation [ 20 ]. Habitat created by the conservation grasslands is important in maintaining populations of wildlife, including grassland-bird species [ 21 — 24 ].
These conservation grasslands can also buffer other adjacent grasslands from the indirect effects of crop production and energy development activities. However, payments to agricultural producers participating in the CRP and other conservation programs have often failed to keep pace with rising values of agricultural commodities and land-rental rates [ 25 ].
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The disparity of profits between participation in a conservation program versus production of agricultural commodities or the rental of land for crop production has resulted in a recent exodus of agricultural producers from conservation programs [ 6 , 20 , 26 ]. Since peak enrollment of Additionally, new varieties of pesticide-tolerant and drought-resistant crops, as well as the rising popularity of corn Zea mays and soy Glycine max as biofuels, have resulted in the production of row crops in many areas previously dominated by small-grain production and conservation grasslands [ 27 ].
In addition to the current loss of conservation grasslands to crop production, increasing demand for domestic energy sources will likely have a negative impact on grassland quantity and quality. McDonald et al. The most intact grassland landscapes in the PPR are generally located on high-elevation geological features that are too rugged for mechanized agricultural equipment or too dry for row-crop agriculture, but even these grasslands are threatened due to their potential as sites for wind facilities or for oil and gas development [ 9 , 10 ]. We did not attempt to quantify the impact of historic habitat losses in the PPR on grassland birds.
Instead, we focused on the contemporary impacts that crop production and energy development activities have on remaining habitats and the role of conservation grasslands in mitigating these impacts. Our specific research objectives were to: 1 quantify the current grassland-bird habitat within the PPR using a modeling approach that incorporates indirect impacts to habitat integrity, 2 verify that the resultant habitat-quality rankings are related to grassland-bird abundance, 3 quantify the contribution of oil, natural gas, and wind development to the degradation of the remaining grassland habitat, and 4 quantify the habitat degradation that would occur if various percentages of CRP conservation grasslands in the PPR were returned to row-crop production.
Recognizing that crop production and energy development will likely continue to cause loss and degradation of the remaining grassland-bird habitats, and that CRP grasslands continue to decline across the PPR, we provide a baseline scenario against which future habitat projections can be compared. Glacial processes shaped the region and created a landscape consisting of millions of palustrine wetlands often termed prairie potholes interspersed within a grassland matrix [ 29 , 30 ].
It is a globally important ecosystem for a wide variety of flora and fauna including grassland and wetland plants [ 32 ], grassland birds [ 33 ], shorebirds [ 34 ], waterbirds [ 35 ], waterfowl [ 36 ], small mammals [ 37 ], amphibians [ 38 ], and aquatic and terrestrial invertebrates, including pollinators [ 30 , 39 , 40 ]. Despite the biological value of the PPR, grassland loss continues, and conservation efforts are not keeping pace [ 5 , 6 , 40 , 41 ].
I n VEST is a suite of spatially based modeling tools that quantify services derived from ecosystems, including the maintenance of wildlife habitats [ 45 ]. We chose because it is the most current year for which we could obtain both energy-development and CRP data layers. Weights were assigned relative to one another, with higher weights representing the most suitable habitat. Suitable grassland-bird habitat was defined as any land-cover category of grassland i. For example, native prairie and CRP grassland were equally highly weighted i. InVEST takes habitat models one step beyond relative habitat-suitability rankings by incorporating threats to habitat integrity, weighting those threats relative to one another, incorporating the linear distance that those threats influence adjacent habitats, and ranking the sensitivity of habitats to each threat.
We identified threats to grassland-bird habitat as the primary causes of fragmentation and degradation of large tracts of grasslands. The primary habitat threats identified were: 1 woodland, 2 urbanization, 3 cropland, 4 roads, and 5 energy development [ 5 , 46 — 54 ]. We weighted each threat from 0—1 by expected impact to grassland-bird habitat, with higher weights representing greater habitat degradation S4 Table. We determined the distance that threats acted upon nearby habitats based on published literature [ 9 , 10 , 47 , 48 , 50 , 51 , 55 , 56 ].
We used InVEST to apply these threats to our baseline habitat raster to account for their degradation of nearby habitat. We assigned the greatest threat value to woodland and urbanized areas because grassland birds find these land-cover types virtually unsuitable for all aspects of their life cycle and they harbor predators and nest parasites that affect quality of nearby habitats [ 17 ]. Cropland can serve as habitat, e. Roads, well pads and turbine pads accompanying energy development generally have a small relative footprint on a landscape level, and species show varying degrees of tolerance to these types of disturbances [ 9 , 10 ].
Subsequently, we chose to isolate and examine the impact of two of our five threats, cropland and energy development, because cropland has the greatest footprint in the PPR Fig 1A and is the traditional and ongoing major cause of habitat loss for grassland birds, whereas energy development is a more recent, but still developing, threat, and its impact is more localized. We developed cropland and woodland threat layers through a reclassification process of land-cover layers using R version 3.
Geological Survey S2 Table. We buffered the turbine locations by 30 m [ 59 ] and the gas and oil well locations by m [ 9 ] to represent surface impact.
To verify that habitat-quality scores are positively associated to grassland-bird abundance, we related the habitat-quality scores output by the model to breeding-bird abundance data using negative binomial regression due to the over-dispersed nature of the count data [ 60 ]. We based our bird-abundance estimates on ten avian species that represent mixed-grass prairie endemics and that are considered grassland birds as categorized by Sauer et al.
We acquired count data for these species from the North American Breeding Bird Survey BBS , a continental, road-side survey conducted annually since [ 8 , 61 ]. We included the years on either side of to capture the full temporal shift in bird response to disturbance caused by initial development of threats as well as potential temporal lags in grassland-bird responses to threat establishment, respectively. We buffered each survey stop by m, the distance at which birds are assumed to be detected in the surveys and calculated the mean habitat quality within this buffer from our InVEST output and compared these values to the grassland-bird abundance estimate for that point.
Using each set of polygons as a mask, these fields were converted to row crops in our baseline land-use layer to simulate the conversion of CRP grassland habitat to agriculture. By removing percentages of fields rather than total area in our baseline data layer, we followed the assumption that if an agricultural producer decided to remove land from a conservation program, this decision would be made on a field-by-field basis rather than on an unrealistic pixel-by-pixel basis.
We used an output cell size of 30 m. A half-saturation constant of 0. In each run i. Output data layers from the model were used to create maps depicting changes in grassland-bird habitat quality among scenarios of CRP loss.
1.7 million acres of grasslands lost to cultivation in 2017
From our habitat quality maps, we produced summary tables quantifying changes in suitable-habitat quantity ha by ecoregions. The relationship between abundance estimates from BBS surveys and our modeled bird abundance was significantly different from zero C.
We calculated a pseudo R-squared of 0. Thus, while points with high habitat-quality ratings were associated with both low and high bird abundance, points with low quality ratings were almost always associated with low bird abundance Fig 2. From our baseline model and our definition of suitable habitat as any land-cover type with a habitat-quality ranking higher than 0. Availability of suitable grassland-bird habitat was lowest in the Des Moines Lobe ecoregion. The area of cropland 8. Our application of the InVEST model to quantify effects of cropland and energy development demonstrated low impact 65, ha in causing original habitat-quality rankings to become unsuitable, i.
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However, cropland and energy development had a much greater impact in terms of degrading the quality of habitat when habitats that did not drop below a score of 0. Among ecoregions, remaining grassland-bird habitats in the Northern Glaciated Plains and the Des Moines Lobe were degraded the most by cropland and the Northwestern Glaciated Plains the least, whereas the Northern Glaciated Plains and the Northwestern Glaciated Plains were degraded the most and the Des Moines Lobe the least by energy development.
Although not nearly as ubiquitous in distribution as cropland, where energy development occurs, its localized impact can be significant S1 Fig. Land within the PPR is surveyed according to the Public Land Survey System of dividing land into parcels, one division of which is a township comprised of thirty-six 1-mi 2 ha sections [ 64 ]. We found entire townships were rendered unsuitable habitat by the clustering of oil wells in close proximity S1 Fig. The largest decline in habitat quality occurred in the Northern Glaciated Plains and the least in the Des Moines Lobe.
Lost habitat indicates suitable habitat that fell below the relative habitat-quality rating of 0. Degraded habitat indicates suitable habitat that dropped in habitat-quality ranking but stayed above 0. Values in parentheses represent the percentage of current suitable habitat degraded under the different scenarios.
Values in parentheses represent the percentage of current suitable habitat lost under the different scenarios of CRP conversion. We demonstrated both the utility of applying the InVEST-modeling approach to quantifying habitat suitability for grassland birds and for estimating the effects of land-cover conversion scenarios on these habitats.
This allows for more robust quantifications of how matrices of land cover, some of which are suitable habitat for birds and some of which are habitat threats, interact to affect overall landscape integrity, in our case for grassland birds. We did not attempt to forecast grassland-bird population sizes, but rather quantified habitat quality as influenced by threats and susceptibility to those threats. Multiple factors in addition to summertime nesting habitat affect grassland-bird populations; some e.
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Thus, prediction of population sizes was beyond the scope of our work. However, habitat-quality information derived from the methodology described here could play an important role in the development and improvement of grassland-bird population models. We also did not attempt to quantify a monetary aspect to the losses in grassland-bird habitat. While the estimation of monetary gains or losses associated with loss or degradation of habitats and effects on ecosystem services is useful in guiding decisions, such quantifications were well beyond the scope of our research effort.
Rather, we focused on the preliminary step necessary to calculate the monetary effects of losses and degradation, that being the quantification of habitat losses and degradation itself. We provide methodology to obtain such quantifications.
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To illustrate our method, we chose to quantify the degree to which one traditional and widespread threat, cropland, and one nascent but more localized threat, energy development, influenced the availability of suitable grassland-bird habitat in the current matrix of land cover in the PPR.