Grassland Biodiversity: Importance, Threats, and Protection

Grasslands cover roughly a quarter of Earth’s land surface and rank among the most biologically rich ecosystems on the planet, yet they receive a fraction of the conservation attention directed at forests or coral reefs. Their biodiversity supplies services ranging from pollination to carbon storage and soil stability, and the threats bearing down on them—cropland conversion, woody plant invasion, intensifying drought—are moving faster than protection efforts can keep up. What makes grassland conservation so challenging is that these ecosystems depend on disturbance, particularly fire and grazing, to stay grasslands at all.

What Grassland Biodiversity Provides

The most visible service grasslands offer is habitat for pollinators. Wild bees, butterflies, and other flower-visiting insects rely on the flowering plants in grasslands for nectar and pollen. Research across the United States has shown that native wildflower plantings embedded in agricultural landscapes attract greater abundance and richness of wild bees, and that maintaining continuous bloom throughout the growing season is critical to supporting the greatest pollinator species richness.¹ This matters well beyond the grasslands themselves: pollinator populations sustained in grassland patches radiate outward to service surrounding crop fields.

Below the surface, grassland soils store enormous quantities of carbon. Most of a grassland’s biomass sits underground in dense root networks, and this below-ground carbon is less vulnerable to wildfire than the above-ground carbon stored in forests. Grassland soils also regulate water movement. Native grassland vegetation builds soil structure that promotes infiltration and slows runoff, reducing both flooding and erosion. When that vegetation disappears, the soil’s ability to absorb rainfall can degrade rapidly.

Animal Engineers That Shape Grassland Life

Grassland biodiversity is not simply a product of the plants growing there. Burrowing mammals act as ecosystem engineers, physically reshaping the landscape in ways that create niches for other organisms. In semi-arid California grasslands, the giant kangaroo rat increases the diversity and abundance of other species through both engineering and non-engineering pathways. Burrow construction is the primary factor structuring plant and small mammal communities, while the rats’ other activities—seed caching, soil disturbance, selective foraging—shape invertebrate communities and boost lizard populations.²

A parallel story plays out across Eurasian grasslands with the steppe marmot. Marmots maintain small-grass meadows by grazing dominant grasses, which allows less competitive species to gain a foothold. Their burrow mounds expose bare substrate that seeds need for germination, and their foraging areas create a shifting mosaic of vegetation patches that keeps plant communities diverse.³ Remove marmots, and the meadows tend to simplify into a few dominant grass species.

Invertebrate engineers matter too. Dung beetles relocate and bury livestock and wildlife dung, and in doing so they cycle nitrogen into forms that plants can absorb, reduce soil compaction, improve aeration, and connect above-ground and below-ground microbial communities.⁴ These small-scale soil improvements accumulate across landscapes, keeping grassland soils productive.

Fire and Grazing as Ecological Partners

Grasslands evolved with two powerful forces acting on them simultaneously: fire and herbivory. Grasses are unusual among plants in that many species tolerate, and even benefit from, being burned or eaten. A broad framework examining grass life-history strategies shows that flammability, fire tolerance, palatability, and grazing tolerance traits have been shaped together by long exposure to these disturbances, alongside pressure from aridity.⁵ Some species invest in flammable, upright foliage that carries fire and eliminates competitors. Others invest in palatability and regrowth after grazing. This diversity of strategies is part of what makes grasslands species-rich.

Long-term data from a tallgrass prairie in North America, spanning more than two decades, reveals that fire and grazing push grassland plant communities in different directions depending on fire frequency, and that the functional traits of those communities shift accordingly.⁶ When either fire or grazing is removed from a grassland that evolved with both, the plant community loses diversity. The disturbance itself is not the enemy of biodiversity—it is a prerequisite.

One reason grasses bounce back so well from fire and grazing is that they maintain underground bud banks: dense reservoirs of dormant buds in the soil that can rapidly regenerate shoots when conditions allow. Research on alpine meadows of the Tibetan Plateau has found that appropriate rest from grazing during spring soil thawing promotes the buildup of these bud banks, increasing the grassland’s capacity for self-renewal.⁷

Agricultural Conversion and Habitat Fragmentation

The single largest threat to grassland biodiversity worldwide is conversion to cropland. When a grassland is plowed, the change extends below the surface. A global analysis found that converting grassland to cropland significantly reduces the diversity of soil microbial communities, homogenizing the bacteria and fungi that drive nutrient cycling.⁸ Even abandoning converted grassland does not restore the original microbial community: research on China’s Loess Plateau showed that converting grassland to abandoned land significantly altered the relative abundance of major bacterial groups, with some phyla increasing and others declining compared to intact grassland.⁹

What remains after large-scale conversion is often a patchwork of small grassland fragments surrounded by cropland. These fragments lose species in predictable ways. A study on the Swedish island of Öland measured plant diversity across hundreds of small plots in semi-natural grasslands and found that species richness was relatively sensitive to grassland isolation: the more cut off a fragment was from other grassland patches, the fewer plant species it contained.¹⁰ Fragmentation also blocks species from tracking suitable climate as temperatures shift, particularly in heavily developed regions.¹¹

Where intensive grassland management persists without outright conversion, biodiversity still suffers. A survey of intensively managed temperate wet grasslands found severely impoverished plant communities, with a median of just 15 species per plot in field interiors. Edge habitats held significantly more diversity—a median of 23 species per plot—and 38 species were found only at field edges, making these margins critical refugia.¹²

Woody Encroachment

Even where grasslands have not been plowed, they can be lost from the inside out. Woody encroachment—the gradual spread of shrubs and trees into open grassland—is happening across every continent and is one of the most pervasive threats to grassland biodiversity. A meta-analysis of 29 studies across 13 different North American grassland and savanna communities found that species richness declined in every single community as woody plants expanded, with an average decline of roughly 45%.¹³ The losses were steepest in wetter grasslands, where woody plants experience the greatest release from water limitation once they get established.

The primary driver behind this encroachment is suppression of fire. When domestic livestock graze continuously, they remove the fine grass fuels that carry fire across the landscape. Without regular fire, woody seedlings survive and grow into thickets that shade out the grasses and herbs beneath them. As woody plant cover increases, grass biomass, density, and cover all decline, and the location of a grassland’s biomass flips from mostly below ground to mostly above ground.¹⁴

That said, the relationship is not strictly linear. Research on loess steppe grassland fragments found that plant diversity showed relatively high resistance to moderate levels of woody encroachment, with the sharpest declines in diversity appearing only above about 52% woody cover.¹⁵ This suggests a window of opportunity: intervening early, before woody cover crosses a threshold, can prevent the worst biodiversity losses.

Drought, Climate Change, and Invasive Species

Climate change threatens grasslands on multiple fronts, but drought may be the most immediate. A global experiment that imposed drought conditions across grasslands and shrublands found that losses of plant productivity were about 60% greater at sites experiencing statistically extreme drought compared to sites with more typical dry years. Drier ecosystems and those with fewer plant species were most vulnerable.¹⁶ The researchers concluded that the global impacts of increasingly severe droughts have been significantly underestimated.

Landscape features can buffer some of this damage. A study of a dominant Australian grassland species found that during extreme drought, populations collapsed across flat, uniform terrain but persisted in topographically varied areas with wetter microhabitats. Population modeling suggested that protecting these topographically heterogeneous environments, even at small spatial scales, could play a key role in conserving biodiversity under this century’s projected climate shifts.¹⁷

Invasive plants compound the problem. When exotic annual grasses invade grasslands, they can outcompete native perennials, particularly if the natives have been thinned by overgrazing or drought. However, healthy stands of native perennial grasses have a built-in defense: established natives limit the space available for exotic seeds to germinate and shade out exotic seedlings, shifting competitive interactions in favor of residents.¹⁸ This finding underscores a recurring theme in grassland ecology: intact, diverse communities are more resistant to invasion than degraded ones.

Reuniting Fire and Grazing

If grassland biodiversity depends on the interplay between fire and grazing, then restoration must rebuild that interplay rather than manage fire and grazing as separate, unrelated tools. This idea—called pyric herbivory—has been tested most thoroughly at the Tallgrass Prairie Preserve in Oklahoma, where free-roaming bison interact with random fires. The combination promotes landscape-scale heterogeneity: recently burned patches attract grazers, which crop the vegetation short, while unburned patches grow tall and accumulate fuel for the next fire. This shifting mosaic creates habitat for a wide range of species with different requirements.¹⁹

The approach works beyond tallgrass prairie. A comparison across five rangelands managed with pyric herbivory, spanning a broad range of rainfall levels and plant community types, found that fire-driven grazing created consistent patch contrast in vegetation, provided that fire was the primary driver of where grazers chose to feed.²⁰ When fencing or supplemental feeding overrode fire as the magnet for grazers, the heterogeneity benefit disappeared.

Managed Grazing for Diversity

Where prescribed fire is impractical—on small landholdings, near urban areas, or in regions where fire is culturally or legally discouraged—rotational grazing alone can still improve grassland biodiversity compared to continuous grazing. A study in the steppe zone compared continuous grazing plots to rotationally grazed pastures and found that species diversity was consistently higher on the rotational plots across every season measured. The highest Shannon diversity values were recorded on the rotational plots that had the most rest between grazing bouts.²¹

Timing matters as much as rotation pattern. In desert steppe, delaying the start of grazing in warm seasons promoted the growth of grasses and legumes that form the structural backbone of the community, reducing the proportion of weedy forbs and improving the importance value of dominant native species compared to other grazing treatments.²² Getting the timing right lets land managers encourage the plant species they want without excluding grazing entirely.

Rebuilding Soil Biology

One of the less obvious obstacles to grassland restoration is that degraded soils often lack the microbial communities that native plants need to establish and thrive. Arbuscular mycorrhizal fungi, in particular, form partnerships with grass roots that enhance nutrient uptake and drought tolerance. When grasslands are heavily invaded or repeatedly tilled, those fungal networks collapse.

Inoculating restoration sites with native soil microbes is emerging as a practical tool. In one experiment, adding native mycorrhizal fungi to ex-arable soil produced the highest native plant abundance, greatest total diversity, and the strongest suppression of a non-native grass.²³ A separate study tracked outcomes for seven years after inoculating restoration plots with old-growth prairie soil microbes. By the seventh growing season, inoculated plots had greater cover of late-successional native plants and higher floristic quality scores, and combining soil inoculation with site preparation accelerated the recovery of invaded grasslands.²⁴

Even simpler approaches work. Adding whole native soil—not processed fungi, just shovelfuls of soil from an intact grassland—significantly improved native species survival and cut reinvasion by an aggressive non-native grass by roughly two-thirds in one trial. Plots that received native soil ended a growing season with about 30% cover of the invasive Caucasian bluestem, compared to about 80% in untreated plots.²⁵ The implication for practitioners is straightforward: when restoring grasslands, pay attention to what is happening below the soil surface, not just what you are seeding above it.

Indigenous Fire Stewardship

Long before modern conservation science existed, Indigenous peoples managed grasslands with fire. A comprehensive review of studies published from 1900 to the present found that 79% of applicable studies reported increases in biodiversity as a result of Indigenous fire stewardship, and 63% concluded that habitat heterogeneity was increased by the use of fire.²⁶ The displacement of Indigenous peoples from their lands has been directly linked to declines in biodiversity and in the functional role of people in maintaining fire-dependent ecosystems.

The mechanism is what ecologists call pyrodiversity: varying the timing, size, and frequency of burns creates a patchwork of differently aged vegetation, which in turn supports a wider range of species. Research linking Indigenous burning to pyrodiversity and then to plant outcomes found evidence that this kind of fire stewardship promotes plant richness and diversity in fire-prone ecosystems.²⁷ Despite this evidence, significant barriers remain for re-engaging in cultural burning, including colonial-era fire suppression policies, land tenure issues, and regulatory frameworks that treat all fire as inherently destructive.²⁸

Rewilding with Large Herbivores

A growing body of work argues that restoring large, wild-living herbivores to grasslands could be one of the most effective long-term biodiversity strategies available. The idea, called trophic rewilding, rests on the observation that diverse megafauna promote vegetation heterogeneity, seed dispersal, nutrient cycling, and the creation of biotic microhabitats—all fundamental drivers of biodiversity that are expected to become even more important as ecosystems face increasingly novel conditions under climate change.²⁹

In practice, rewilding unfolds differently depending on the landscape. On the high-altitude Puna plateau of the Andes, reducing livestock numbers was accompanied by a rapid recovery of native camelid populations—species that had been driven close to extinction—within just a few decades.³⁰ Native grazers interact with the landscape differently than domestic cattle and sheep: they tend to be more mobile, graze more selectively, and have co-evolved with the local vegetation. This means that simply swapping one grazer for another can reshape the plant community toward greater diversity, even without changes to fire management or other active interventions. Rewilding is not a substitute for the other tools described here, but it addresses a structural deficit that no amount of rotational grazing or prescribed burning can fully compensate for: the absence of the animals that built these ecosystems in the first place.