Temperate Grassland Biodiversity: Life, Value & Threats

Temperate grasslands rank among the most biologically rich ecosystems on Earth, yet they are also among the most endangered. These landscapes, stretching across the North American Great Plains, the Eurasian steppe, the South American Pampas, and scattered remnants across Europe and East Asia, harbor extraordinary diversity both above and below the soil surface. Much of that diversity is invisible at first glance: the bulk of a grassland’s living biomass is underground, and the interactions between roots, fungi, soil microbes, burrowing mammals, and grazing animals create a web of relationships that sustains services humans depend on every day. Understanding what lives in these systems, why it matters, and what is pushing it toward collapse requires looking past the surface.

Most of the Action Happens Underground

A visitor standing in a tallgrass prairie sees waist-high stems and a scattering of wildflowers. What they cannot see is that the root network beneath their feet may outweigh everything visible above the soil by a factor of three or more. Seasonal measurements in a central Missouri prairie found root biomass ranging from roughly 1,450 grams per square meter in early spring to about 1,900 grams per square meter by the end of the growing season, with over 80 percent of that mass packed into the top ten inches of soil.¹ This dense, shallow root mat is not uniform. Different plant species divide up soil resources in distinct ways: legumes pull water evenly from the full soil profile, rhizomatous cool-season grasses concentrate their fine roots in shallow layers, and tallgrass species send dense, low-nitrogen roots deep into the soil column to scavenge nutrients from a large volume.²

This belowground partitioning of space and nutrients is one reason grasslands can pack so many plant species into a small area. Different root strategies reduce direct competition and allow species to coexist in the same patch of soil. But plants are not working alone down there. Arbuscular mycorrhizal (AM) fungi form ancient symbiotic partnerships with most land plants, trading soil nutrients like phosphorus and nitrogen in exchange for carbon from the plant. A study across four North American grassland types found that ecosystem type, not nutrient levels, was the main driver of AM fungal colonization, diversity, and community composition, with aridity, temperature, root moisture, and soil pH all playing roles.³ Even within a single grassland plot, AM fungal communities shift rapidly in both space and time, and their diversity tracks plant species richness and root biomass more closely than it tracks soil chemistry.⁴ Lose plant diversity above ground, and you lose fungal diversity below it.

Keystone Animals That Reshape the Landscape

Temperate grasslands are not shaped by plants and microbes alone. Social, burrowing, herbivorous mammals form a functional group that profoundly alters habitat across the world’s grasslands. Through grazing and digging, these animals create distinctive microhabitats for many other species, increasing biodiversity and habitat variety at the landscape scale.⁵ In North America, prairie dogs are a classic example. A systematic review of over 100 studies found consistent support for three patterns: prairie dogs boost the abundance of early-successional grassland birds by keeping vegetation short, they reshape bird community composition by adding heterogeneity to the landscape at large spatial scales, and they increase raptor abundance by serving as a prey base.⁶

The interplay between prairie dogs and large grazers like bison adds another layer of complexity. Research in mixed-grass prairie found that areas with active prairie dog colonies were dominated by several forb species and supported higher plant diversity, while areas without colonies were dominated by a few grass species with lower diversity overall.⁷ Remove prairie dogs, bison, or both from a grassland, and you lose not just two species but the structural complexity that supports dozens of others.

How Grasses Coevolved with Fire and Grazers

Temperate grasslands exist in a dynamic tension between fire, grazing, and climate. Grasses have evolved distinct strategies to cope with these pressures. A trait-based analysis of Texas savanna grasses identified three functional groups. “Fire grasses” were tall, thick-stemmed, and upright, with high carbon-to-nitrogen leaf ratios that promote burning and discourage grazing. “Grazer grasses” were short, horizontal, and leafy, with nutrient-rich foliage that attracts herbivores but does not carry fire well. A third group of generalists sat somewhere between these extremes.⁸ These are not rigid categories but endpoints on a spectrum. The same grassland can include species from all three groups, and the balance between them shifts depending on the frequency of fire and the intensity of grazing.

This interplay between fire tolerance, palatability, and grazing tolerance has deep evolutionary roots. In grasslands exposed to both fire and herbivory, plants face a trade-off: traits that help survive one consumer often increase vulnerability to the other.⁹ The result is a mosaic of strategies that keeps the community diverse. When both fire and grazing are present at moderate levels, no single strategy dominates, and the grassland supports the widest range of species.

Carbon, Soil, and Water

The dense root systems and microbial networks described above do more than support biodiversity. They store carbon on a massive scale. Grasslands hold roughly a third of the world’s terrestrial carbon stocks, and recent research shows that plant diversity actively increases soil organic carbon storage by driving more carbon into belowground biomass and promoting the accumulation of microbial residues in stable soil pools.¹⁰ Unlike forests, where most carbon is locked in above-ground wood that releases its carbon when it burns, grassland carbon is mostly underground, insulated from fire. That makes grassland carbon storage more durable in fire-prone landscapes.

Grasslands also regulate water. Experiments with simulated rainfall on different grass types showed that dense, fibrous-rooted grasses achieved sediment reduction rates above 98 percent while maintaining or slightly increasing surface runoff retention.¹¹ Those fibrous roots bind soil particles, and the biological soil crusts that form in healthy grasslands act like a sponge, slowing runoff and trapping sediment that would otherwise wash into waterways. Convert grassland to row crops, and you lose both functions simultaneously.

Pollinators and Forage

Grasslands are critical habitat for pollinators, and the relationship runs on floral resources. Research in productive agricultural grasslands found that both the abundance and species richness of pollinators correlated strongly with the density of legume and forb flower heads. Bees, butterflies, and hoverflies all responded positively to greater floral diversity.¹² Even grasslands enrolled in general conservation programs, without any pollinator-specific management, supported robust pollinator communities. A multi-year survey of U.S. Conservation Reserve Program (CRP) grasslands sampled over 13,000 pollinators from 375 taxa and found only marginal differences in diversity between fields with and without specialized pollinator habitat enhancements.¹³ The grassland itself was doing most of the work.

Diverse grasslands also produce better forage. A study of semi-natural grasslands found a positive relationship between plant diversity and economic performance measured as potential milk production revenue. On average, increasing plant diversity from one to 16 species raised revenues by about 1,400 euros per hectare per year, and increasing to 60 species raised revenues by about 3,100 euros per hectare per year, regardless of management intensity.¹⁴ The economic case for grassland biodiversity is straightforward: more diverse pastures feed livestock better.

Cropland Conversion, the Biggest Threat

The single largest driver of temperate grassland loss is conversion to cropland. Across the United States, grasslands, including those used for pasture and hay, made up about 88 percent of land converted to crop production.¹⁵ Between 2008 and 2016, more than two million hectares of grassland in the U.S. Midwest were plowed up for crops, with far less cropland being retired or abandoned during the same period.¹⁶ In the Prairie Pothole Region of North America, native grasslands that support diverse bird populations are being converted at an increasing rate, with over 36,000 hectares lost during one study period alone.¹⁷

What makes this trend so damaging is that it is often irreversible on any practical timeline. When a grassland is plowed, the root mat that took decades or centuries to build is destroyed in a season. The soil carbon accumulated over thousands of years begins to oxidize. The mycorrhizal networks fragment. The seed bank of native species thins out. Even if the cropland is later abandoned, what grows back is rarely the diverse community that was there before, at least not without active restoration over many years.

Overgrazing Unravels Soil Biology

Moderate grazing is natural and beneficial in most temperate grasslands. Overgrazing is a different story. Long-term experiments across grasslands of varying aridity found that grazing had no measurable negative effect on biodiversity or ecosystem function in wetter meadow steppes, but it reduced both in more arid desert steppes, with the damage worsening as aridity increased.¹⁸ Drier grasslands are simply more fragile: heavy grazing strips the soil surface, exposing it to wind erosion, and the ecosystem lacks the moisture to bounce back quickly.

The damage goes deeper than visible erosion. Overgrazing disrupts the relationship between soil fungal diversity and nitrogen availability. In ungrazed grasslands, researchers found a positive link between fungal diversity and the soil’s capacity to make nitrogen available to plants. In overgrazed grasslands, that link disappeared. The microbial community reorganized in ways that reduced the soil’s ability to cycle nitrogen and support plant production.¹⁹ In other words, overgrazing does not just remove the plants you can see. It degrades the underground biological machinery that would otherwise help the system recover.

Nitrogen Deposition and Invasive Species

Air pollution delivers a less visible but pervasive threat. Nitrogen compounds from vehicle exhaust, power plants, and agricultural ammonia drift settle onto grasslands far from their source. A large-scale analysis found that high levels of atmospheric nitrogen deposition were associated with lower plant species richness at every scale examined, from individual plots to entire regions. About 39 percent of plant species were negatively associated with increasing nitrogen deposition at the site scale, while only about 1.5 percent benefited, and some of the “loser” species are already listed as threatened in parts of Europe.²⁰ Excess nitrogen favors fast-growing, nutrient-hungry species at the expense of the slower-growing specialists that make grasslands diverse.

Invasive grasses compound the problem. In the western U.S., cheatgrass has invaded vast areas of sagebrush steppe and other semi-arid grasslands, creating a self-reinforcing cycle: cheatgrass produces fine fuel that carries fire easily, fire kills native shrubs and perennials, and the burned landscape regrows as more cheatgrass.²¹ The U.S. federal government has committed significant resources to slowing this invasive grass-fire cycle, which threatens property, livelihoods, and entire ecosystems.²² Breaking the cycle is difficult precisely because the invader has rewritten the fire regime to favor itself.

Drought, Climate Extremes, and Grassland Resilience

Grasslands are often described as resilient, and there is truth to that, but the picture is nuanced. Global analysis shows a clear positive relationship between drought severity and reductions in grassland productivity, with non-woody grasslands and closed shrublands among the types most sensitive to drought.²³ Experimental work in a Kansas tallgrass prairie found that extreme drought reduced above-ground productivity below the lowest level measured in nearly 30 years, yet the system recovered rapidly once the drought ended.²⁴ Low resistance did not preclude high resilience, in other words.

But there is a catch: grasses and forbs do not respond equally. In a multi-year extreme drought experiment, grass productivity held steady across all four years of drought, showing high resistance. Forb productivity, however, declined progressively: 38 percent in year one, 43 percent in year two, 70 percent in year three, and 87 percent by year four.²⁵ Forbs are the wildflowers that feed pollinators and add nutritional diversity to forage. If prolonged droughts become more common under climate change, grasslands may persist as grasslands but lose the forb component that underpins much of their biodiversity and ecological value. Habitat fragmentation makes this worse: as climate zones shift, species need to move, and near-continuous regions of cropland and urban development block their dispersal routes.²⁶

Restoration Tools That Actually Work

Restoring a degraded grassland is not as simple as scattering seeds and walking away. Trials in Pacific Northwest prairies tested combinations of herbicide application, prescribed fire, mowing, and native seed addition. Disturbance treatments reduced non-native plant cover, but native diversity increased only when native seeds were also added.²⁷ Killing invasive competitors is necessary but not sufficient; native species often cannot recolonize on their own because their seed banks are depleted and their dispersal distances are short.

Fire and large herbivores remain among the most powerful restoration tools. In restored tallgrass prairies, bison presence increased seed removal by granivorous animals by about 2.5 times, and unburned areas saw about four times as much seed removal as recently burned ones, suggesting that these management tools reshape food webs in ways that favor native plant recruitment.²⁸ Prescribed fire also strengthens pollinator networks: burning increased the abundance and diversity of floral resources, which in turn increased pollinator visitation and built networks more resilient to the loss of rare native forbs.²⁹

Even in intensively managed grasslands where the interior has been simplified, edge habitats can serve as refugia. A study of temperate wet grasslands found that plant diversity dropped from a median of 23 species per 200 square meters at the field edge to 15 species in the interior, with 38 species found only at edges.³⁰ Protecting and widening these edges can preserve diversity even where full restoration is not economically feasible.

Paying Herders to Protect Grassland

Conservation in working landscapes often requires financial incentives. Payment-for-ecosystem-services programs have been tried in several countries with temperate grasslands. In China’s Inner Mongolia, where grassland degradation from overgrazing and cropland expansion has been severe, researchers found that compensation levels significantly influenced herders’ willingness to participate in conservation programs, and identified a payment threshold that could achieve a 95 percent compliance rate.³¹ On the northeastern Tibetan Plateau, a similar program led to increased grassland area, higher forage yields, and greater net primary production in project regions compared to non-project regions.³² In Europe, agri-environmental payments helped maintain grazing management and preserve habitat biodiversity and function by encouraging a more even distribution of grazing intensity across the landscape.³³

Traditional Knowledge as a Conservation Model

Some of the most species-rich grasslands in the world have been managed by smallholders for centuries. In the Carpathian region of Romania, communities manage over 40,000 hectares of meadows and pastures using traditional practices including mowing-date rotation, hayseed scattering, manual thinning of unwanted plants, and targeted manuring. These grasslands support roughly 32 to 52 vascular plant species on just 16 square meters. The farmers’ goal is not biodiversity conservation per se, but keeping their grasslands productive over the long run, and the result is a management system that achieves both.³⁴ In Japan’s Kiso region, interviews documenting traditional ecological knowledge recorded 103 useful plant species in semi-natural grasslands, with significantly higher useful-plant diversity in traditionally managed sites than in other sites.³⁵

These examples are not quaint relics. They are working demonstrations of a principle that modern restoration science keeps rediscovering: grassland diversity is maintained by moderate, varied disturbance, whether from fire, grazing, mowing, or some combination. The communities that developed these practices did so through centuries of trial and feedback, and they tend to produce grasslands more diverse than anything a single industrial management approach can maintain. Supporting the survival of these traditional systems, through subsidies, land-tenure protections, and recognition of their ecological value, may be among the most cost-effective conservation strategies available for temperate grasslands worldwide.