Outleasing of areas for agriculture affects biodiversity directly by converting natural habitats to cultivation, grazing, or other manipulation, and through the associated repeated disturbances that accompany conversion. Agriculture affects biodiversity indirectly through water management practices for irrigation and drainage, soil erosion and sedimentation, and elevated nutrient and pollutant discharges into the environment.
Agroecosystems (agricultural ecosystems) can be mosaics of pasture, cropland, woodland, and wetlands, and this patchiness may benefit some species. Agricultural lands may provide more suitable habitat for native wildlife and birds than do fragmented and extensively modified urban or suburban lands. When developing agriculture management plans, it is important that the resource manager consider the compatibility between biodiversity and agriculture, with key considerations being habitat availability, species at risk, as well as the potential for economic damage to agriculture caused by wildlife. At the landscape level, agriculture can best preserve biodiversity when it incorporated as part of a matrix of habitats connecting natural areas. In agroecosystems, the conservation of aquatic biodiversity requires consideration of impacts to aquatic systems from agricultural nonpoint source pollution and the potential effects on aquatic ecosystem structure and function from altered hydrology (Blann 2006).
Habitat and threats from non-native and invasive species in agricultural lands directly compete with biodiversity goals. Approximately 46 percent of the plants and animals federally listed as endangered have been negatively impacted by invasive species (USDA 2006). The significant threat of invasive species to biodiversity increasingly is being recognized both internationally and domestically. Biodiversity goals and objectives outlined in the INRMP should include contingencies for impacts resulting from invasive and non-native species. Early warning of possible negative impacts is possible when biodiversity management includes monitoring and adaptive management measures.65
Grazing and rangeland
Rangeland and pasture management has typically focused on simplifying ecosystem structure and achieving uniform disturbances across a landscape. Most rangeland and grazing management techniques were developed under the model of increasing and sustaining livestock production by decreasing the rangeland diversity. This approach is obviously incompatible with biodiversity management and prevents development of an ecological framework for alternative management objectives. Maintaining biodiversity and preserving habitats for many individual species is contrary to the typical range management model and depends on the interspersion of diverse habitat types throughout a heterogeneous rather than a homogeneous landscape (Fuhlendorf and Engle 2001).
Grazing management includes fencing needs, water development, seeding, brush control, fertilizing, salt distribution, and intensified animal husbandry (Laycock 1983). Management can be aimed at improving range biodiversity with careful study of the desired plant species, their phenological characteristics, how they respond to grazing pressures during each annual season, and annual re-seeding (Gayaldo 1996). For example, light to moderate grazing of grasslands, oak forests and savanna habitats can potentially promote plant and associated vertebrate wildlife diversity (EBMUD 2001).
Many of the biological-physical-management interactions associated with rangeland biodiversity are only beginning to be understood (West 1993). However, a number of studies have shown that grazing does affect the vegetational composition of a community (Gayaldo 1996). Long periods of time (several decades) are required for significant vegetational changes to occur in rangelands, and are dependent on soil and climatic conditions, competing species, and available native seed sources. Also, it is documented that more time is required for a site to progress from a poor to fair condition than from a fair to good condition (Gayaldo 1996). Livestock grazing and rangeland practices that pertain to water quality protection are also applicable to habitat protection, and the maintenance and enhancement of biodiversity. This is particularly true for riparian and aquatic habitats when livestock access is excluded by establishing buffer zones, and by providing alternate water supplies for livestock. Prescribed grazing, livestock exclusion, fencing and control location and timing of livestock impacts, are commonly used to protect and enhance plant and wildlife diversity. Also, establishment of proper stocking rates and judicious monitoring form the basis for biodiversity management on outleased watershed lands that are grazed.
Biodiversity guidelines that may be applicable to grazing management at some military installations include the following (taken from the East Bay Range Resource Management Plan ):
- Identify high-priority sites for habitat restoration based primarily on water quality protection and on the value of restored habitats and locations relative to important wildlife use areas and corridors.
- Monitor listed species populations and conduct site surveys.
- Identify key habitat areas necessary for protection and management of special-status plants and animals. Provide buffer areas to reduce disruption of nesting and roosting areas for sensitive wildlife species.
- Recognize the ecological value and likely permanence of certain non-native species and habitats (e.g., annual grassland), and incorporate the management of these species and habitats into biodiversity planning efforts.
- Use prescribed fire, periodic grazing, mastication (chipping trees on site with either a mulcher head or hydro-axe), or other means to discourage shrub encroachment and maintain grassland conditions where annual grazing has been eliminated from grassland habitats and grassland retention is a biodiversity priority.
In the United States there have been substantial changes in the mix of cropland and pastureland over the past century (Blann 2006). The expansion of crop production over hay and pasture production has been accompanied by more intensive farming practices, increased farm size, and reductions in shelter belts, field borders, wetlands, and remnant habitat areas that were previously inconvenient to farm. Fencerow-to-fencerow farming has reduced biodiversity by eliminating much nesting, feeding, and winter cover for wildlife (Blann 2006), and croplands do not provide the stubble fields and harvested grassland habitats important to many invertebrate, bird and small mammal species.
The influence of agriculture on biodiversity often goes beyond farmed land itself, as the majority of semi-natural habitats are linked to the surrounding agricultural land and may be fragmented or isolated within the larger agricultural landscape. Cropland practices which may impact biodiversity include fertilizer use; monoculture; abandonment of farmland; removal of field margins such as hedges, ditches, and fencerows; poor drainage and irrigation, and soil erosion.
It is possible to provide a balanced environment, sustained yields, biologically mediated soil fertility, and natural pest regulation through the design of diversified agroecosystems and the use of low-input technologies (Altieri 1995). Different types of habitats in agricultural landscapes, depending upon their size, shape, and location, may support different types of biodiversity. Non-farmed areas can be used to provide patches of certain habitat types, or to form corridors linking protected areas and enabling species to maintain genetic contact between otherwise isolated populations. Such benefits can be achieved on outleases via lease agreement language and through programs such as the ACUB process. Agricultural areas can make a positive contribution to diversity when the surrounding matrix is managed with biodiversity in mind.
Blann (2006) offers the following cropland practices for biodiversity management (adapted from Granatstein  and Bird et al. ). These practices could readily be implemented on outleased lands through the lease agreements and enforcement procedures.
- Practice soil conservation measures. Increase protective cover on the soil surface, using no-till, cover crops, windbreaks, contour strip cropping, and grass waterways.
- Eliminate or minimize intensive row-cropping and tillage on highly erodible land, and on sensitive lands such as floodplains, riparian areas, wetlands, and steep slopes.
- Use a greater variety of crops grown in more complex rotations. This breaks weed and disease cycles.
- Enhance habitat quality to encourage and enhance wildlife diversity. Use cover crops and soil-building crops like legumes, clover, and grass. Integrate crops and livestock production with intensively managed grazing and recycling of manure to build soils.
- Use integrated pest management, in which pest levels are monitored, biological controls are used wherever available, and chemicals used only when an economic threshold is reached.
- Nutrient inputs should be managed to maximize efficiency and minimize nutrient movement to surface water and groundwater.
- Properly store and apply animal manures. Compost manures and other wastes.
- In arid regions and other areas relying heavily on irrigation, develop and implement management systems for efficient water use. Water-intensive crops that compete with instream uses often impose high costs on local ecosystems. Cropping systems should be matched to local and regional climatic and environmental conditions.
Dorothy M. Gibb,, Technical Director
A.H. Environmental Consultants
Joseph S. Ferris, Principal Environmental Consultant