Grasslands, Shrublands, Savannas, and Deserts

Grasslands, also known as prairies, steppes, or savannas, exhibit naturally dominant grass vegetation, typically in areas where there is not enough rainfall to support the growth of a forest but not so little as to form a desert. Deserts are biomes characterized by small amounts of moisture – typically less than 250mm of annual precipitation.

Characteristics of Grasslands, Shrublands, Savannas, and Deserts  

Grasslands account for slightly more than one-third of U.S. land uses. Landscapes with vegetation predominantly consisting of grasses and/or shrubs are often characterized as grasslands, savannas, and shrublands. These biomes can include steppes, tallgrass, and shortgrass prairies. Typically grasslands contain only grasses, such as swordgrass, whereas savannas support both grasses and widely dispersed trees; trees in these landscapes do not form a canopy as they do in forests.  While the temperature of these land types can range from semi-arid to semi-humid, these systems often share characteristics of fertile, nutrient rich soils, with a warm to hot season in the summer and a cold to freezing season in the winter.

In the United States, grasslands, savannas, and shrublands of the Great Plains region are typically considered to be temperate. Bioregions of the Southwestern United States such as the Sonoran and Mojave include mild-winter to cold-winter deserts and xeric shrublands, which are shrublands that persist on little moisture.  Similarly, deserts are biomes characterized by small amounts of moisture – typically less than 250mm of annual precipitation. In the Rocky Mountain region and along the Pacific Coast and Northern California, intermountain deserts and xeric shrublands, as well as temperate grasslands and shrublands are present. Alaska’s landscape includes frozen tundra, a type of steppe system where tree growth is limited by cold temperatures and short growing seasons. These bioregions face unique management challenges due to impacts from climate change.

Challenges Presented By Climate Change to Grasslands, Shrublands, Savannas, and Deserts

The National Wildlife Foundation reports that climate change impacts such as shifts in temperature and precipitation will have direct effects on grasslands and shrublands and may exacerbate existing stressors to these systems. Impacts to these extraordinarily varied habitats—from frozen Alaskan tundra to arid Southwestern grasslands—will differ considerably by region and ecosystem type. Nonetheless, climate change is already effecting the health and vitality of these important natural systems, threatening not only their many benefits to people and wildlife, but also undermining their ability to help cleanse the air of the greenhouse gases that are the underlying cause of climate change.

In a report called Climate Change in Grasslands, Shrublands, and Deserts of the Interior American West: A Review and Needs Assessment, scientists summarized current research on climate change and its potential effects on grasslands, shrublands and desert ecosystems. The report addresses animal, plant, and invasive species models and responses, as well as vulnerabilities, genetic adaption and habitats.

Some key findings of the report include:

• By the turn of the century, climate in the western United States may be incompatible with current vegetation types, resulting in shifting distribution patterns of terrestrial ecosystems.
• In arid and semi-arid shrublands and deserts, invasive grass species with higher flammability, like cheatgrass, will spread and increase fire frequency and range.
• Increased temperatures can affect insect development time and may result in significant increases in generations per year/per habitat and expose new environments to colonization.
• Drying rivers and wetlands, which currently support a wide range of flora and fauna, are exceptionally vulnerable to changing climate and weather trends, presenting conservation challenges and opportunities.

Additionally, this report concluded that there is an immediate need for improved tools and approaches for assessing vulnerabilities and conserving diversity of all lands.

Best Management Practices: What Land Trusts Are Doing

Climate change threatens the biodiversity of grasslands, shrublands, and deserts at scales ranging from the gene to complex ecosystems. The USDA reports that rate of climate change may overcome normal ecosystem resilience, disrupting ecosystem functioning and provision of critical services. Guidelines for identifying and conserving at-risk species through a variety of experimental methods are available and being utilized. Although these approaches and models for predicting future risks are evolving and not universally ac­cepted or applicable, grasslands and shrublands are increasingly being assessed for both their vulnerability to climate change as well as their potential to mitigate increasing emissions.

Elements used to identify species or systems vulnerable to climate change include effects of exposure to climate change, sensitivity or the level to which the organism or system is altered, and its capacity to adjust to the change. Vulnerability assessments focus on unique variables or combinations of variables for comparison of organisms, natural systems, or human systems and range widely in their objectives; all rely on projections of future conditions. These assessments aid in planning adaptation strategies and prioritizing management. Available assessment tools include: vulnerability indices, process simulations, evaluation of shifts in species or community distribution, and integrated models. Research must focus on improved climate change predictions, species and habitat response models, identification of new community compositions, and management options.
The American Carbon Registry highlights the mitigation potential of grassland systems – in 2010, the 636 million acres of grasslands in the United States sequestered approximately 8.3 million metric tons of CO2 emissions equivalent. Despite their importance as a carbon sink, high commodity prices, increasing demand for biofuels and feedstock, as well as decreases in conservation funding have contributed to a net loss of about 9% of the nation’s grasslands since 1949. Today, several federal incentive programs are available to avoid conversion and preserve ecosystem services of grassland systems, and voluntary carbon offset programs are beginning to consider avoided-conversion projects.
While there is no one-size-fits-all approach to address climate impacts, conservation organizations are working with their communities to identify opportunities to reduce vulnerabilities and build resilience to prepare for changing temperatures. Agencies are making similar strides to implement projects that reduce risks and plan for resilience by incorporating adaptation, mitigation, and engagement into their strategic goals and objectives. Working together, land managers can identify vulnerabilities and implement adaptation projects, as well as support efforts to reduce greenhouse gas emissions through improved resource stewardship practices.

Learn More

• Climate Change in Grasslands, Shrublands, and Deserts of the Interior American West: A Review and Needs Assessment, USDA / US Forest Service
• Evaluation of Avoided Grassland Conversion and Cropland Conversion to Grassland as Potential Carbon Offset Projects, Climate Action Reserve
• Projecting Future Effects of Land Management, Natural Disturbance, and CO2 on Woody Encroachment in the Northern Great Plains in a Changing Climate, USGS
• Safeguarding Grasslands and Shrublands: Ecosystem Adaptation to Global Warming, National Wildlife Federation
• United States Grasslands and Related Resources: An Economic and Biological Trends Assessment, Conner et al.
• 2010 U.S. Climate Action Report, U.S. Department of State