Grasses are the headline producers of grassland ecosystems, but they share the stage with a wider cast than most people realize. Forbs, legumes, scattered trees and shrubs, and even crust-forming cyanobacteria on bare soil all photosynthesize and funnel energy into grassland food webs. Which of these producers dominates depends heavily on climate, soil, fire history, and rainfall timing, and the mix shifts more dramatically than it does in most forests.
Grasses and Their Two Photosynthetic Strategies
Grasses themselves are not one uniform group. The most consequential split among grassland grasses is between species that use the C3 photosynthetic pathway and those that use C4. C3 grasses tend to grow actively during cooler, wetter parts of the year. C4 grasses are warm-season specialists that handle heat and limited water more efficiently. Whether a grassland is dominated by one type or the other, or a mix of both, depends largely on latitude, temperature, and when rain falls during the year.
C4 natural grass hotspots, meaning areas where C4 species account for more than about 30% of the vegetation, span several continents: the Great Plains of North America, southern Brazilian savannas, African savannas, Central Asian grasslands, and northern Australia.1Nature Communications. Mapping the global distribution of C4 vegetation using observations and optimality theory In North America’s Great Plains, the tallgrass prairie of the eastern portion features C4 powerhouses like big bluestem (Andropogon gerardii), little bluestem (Schizachyrium scoparium), and indiangrass (Sorghastrum nutans). These are the species that once grew shoulder-high across vast stretches of the Midwest.
C3 grasses hold their ground in cooler or more northern grasslands and often green up in spring before C4 species have emerged from dormancy. Research across grasslands with mixed C3 and C4 cover found that C4 grasses responded more dramatically to rainfall extremes, both gaining and losing cover to a greater degree than C3 grasses during very dry or wet consecutive years. C3 grasses in places where they dominated were shaped by longer-term climate patterns, while C3 grasses that shared space with C4 species were surprisingly unresponsive to climate swings.2Ecosphere. Effects of climate and water balance across grasslands of varying C3 and C4 grass cover That difference matters because it means a grassland’s producer community is not static. Shift the rainfall pattern, and the balance between C3 and C4 grasses can rearrange.
How Moisture Sorts the Dominant Grasses
Even among C4 grasses that coexist in the same prairie, individual species sort themselves along moisture gradients. In tallgrass prairie, flooding tolerance varies enormously. Big bluestem can survive roughly a month of continuous flooding, while the shortgrass species Bouteloua (blue grama and its relatives) is far more sensitive, with a lethal flooding duration around 11 days.3American Journal of Botany. Flood‐driven survival and growth of dominant C4 grasses helps set their distributions along tallgrass prairie moisture gradients After an extremely wet late summer in Wisconsin, cordgrass (Spartina) produced the highest biomass, followed by big bluestem, while Bouteloua lagged far behind.3American Journal of Botany. Flood‐driven survival and growth of dominant C4 grasses helps set their distributions along tallgrass prairie moisture gradients
This means the producer lineup you encounter in a grassland tells you something about that site’s water regime. Wet swales host cordgrass and big bluestem. Upland ridges with drier soils favor little bluestem and grama grasses. The species are all “grassland producers,” but they carve up the landscape according to how much water they can tolerate or how little they can survive on.
Forbs and Legumes
Grasses get top billing, but forbs, the broad-leaved herbaceous plants growing among the grasses, contribute substantially to grassland productivity and plant diversity. Wildflowers like coneflowers, goldenrods, asters, and wild indigos are all producers in their own right. In many tallgrass prairies, forbs can make up a third or more of the plant species present, even if grasses account for most of the biomass.
Among forbs, legumes deserve special attention because they do double duty. Like all green plants they photosynthesize, but they also host nitrogen-fixing bacteria in their root nodules, pulling nitrogen out of the atmosphere and adding it to the soil. This makes legumes a keystone functional group in nitrogen-poor grasslands, where their contribution of fixed nitrogen benefits surrounding grasses and other forbs too. Species like prairie clovers, vetches, and wild lupines are common grassland legumes. Research on the legume Medicago ruthenica, native to Asian grasslands, shows the kind of resilience some grassland legumes have evolved: it tolerates multiple stresses through changes in growth form, metabolic adjustments, and partnerships with soil microbes like rhizobia.4PubMed Central. From “Omics” to Field: Deciphering the Stress Adaptation Networks and Breeding Potential of Medicago ruthenica L.
Legume abundance is sensitive to soil fertility in ways that might seem counterintuitive. Adding nitrogen to grasslands consistently reduces legume cover, richness, and biomass, particularly in soils that were nitrogen-poor to begin with, while non-nitrogen-fixing plants increase.5PubMed Central. Negative effects of nitrogen override positive effects of phosphorus on grassland legumes worldwide In a multi-continent study, nitrogen addition alone slashed legume aboveground biomass by about 65% compared to untreated plots.6Plant and Soil. Nitrogen but not phosphorus addition affects symbiotic N2 fixation by legumes in natural and semi-natural grasslands located on four continents Even adding phosphorus alongside nitrogen failed to rescue legumes; in one alpine grassland experiment, combined nitrogen and phosphorus suppressed legume biomass by more than half.7Journal of Plant Ecology. Phosphorus does not alleviate the negative effect of nitrogen enrichment on legume performance in an alpine grassland The practical upshot is that nitrogen pollution from agriculture and fossil fuel emissions threatens one of the most functionally important groups of grassland producers.
Trees and Shrubs in Savanna Grasslands
Tropical and subtropical savannas blur the line between grassland and woodland. In these systems, scattered trees coexist with a ground layer dominated by C4 grasses, and both are producers. How trees and grasses share the same space has been debated for decades.8PubMed. Linking resource- and disturbance-based models to explain tree-grass coexistence in savannas Fire, herbivory, and competition for water and light all play roles in preventing trees from simply shading out the grasses.
Australian savannas illustrate the diversity of producer life forms well. They include evergreen trees, deciduous trees, and a mix of annual and perennial grasses, creating a boom-bust seasonal productivity pattern that tracks the wet-dry rainfall cycle.9Biogeosciences. Tree–grass phenology information improves light use efficiency modelling of gross primary productivity for an Australian tropical savanna During the wet season, grasses green up fast and dominate production at the ground level, while trees maintain steady but lower photosynthetic output year-round. When the dry season hits, the grasses cure to straw and the trees carry most of the system’s remaining productivity. This complementary timing means the total producer output of a savanna is spread across a longer growing window than a pure grassland’s would be.
Biological Soil Crusts
Not every grassland producer is a vascular plant. In drier grasslands and the transitions between grassland and desert, biological soil crusts (biocrusts) form a living skin on bare soil. These crusts are assemblages of cyanobacteria, mosses, lichens, and other microorganisms that photosynthesize and fix carbon, making them genuine producers even though they stand only millimeters tall. Biocrusts are particularly important in arid and semiarid grasslands, where vascular plant cover is sparse and large patches of bare soil would otherwise be exposed to erosion.
The crust-forming cyanobacteria in these communities are slow growers. Restoration efforts have shown that it takes about four months of careful nursery conditions to produce enough biocrust biomass to treat roughly 6,000 square meters of degraded dryland soil, starting from a natural crust remnant as small as a few dozen square centimeters.10PubMed Central. Microbial Nursery Production of High-Quality Biological Soil Crust Biomass for Restoration of Degraded Dryland Soils That gives a sense of how fragile these producers are. A single pass of a vehicle or heavy trampling can destroy crusts that took years to develop naturally.
Wet Grasslands and Their Distinct Producer Communities
At the other end of the moisture spectrum from dryland crusts sit wet grasslands, transitional wetlands defined by an abundance of grasses and periodic flooding. These systems support producers adapted to waterlogged soils: sedges, rushes, moisture-loving grasses, and aquatic or semi-aquatic forbs. Wet grasslands provide livelihoods for millions of people through grazing and hay production, but they are threatened by climate change, drainage for agriculture, and altered flooding regimes.11Ecosystem Health and Sustainability. Future wet grasslands: ecological implications of climate change
The producers in wet grasslands often include species you would not find on a dry hilltop prairie: cattails, bulrushes, various Carex sedges, and reed canary grass. These plants bridge the ecological gap between upland grasslands and true marshes, and their productivity can be high because water is rarely the limiting factor. Instead, nutrient availability and the depth and duration of flooding determine which species dominate.
What Happens Below Ground
A feature that sets grassland producers apart from forest producers is how much of their biomass sits underground. Grassland plants invest heavily in roots, rhizomes, and belowground bud banks. In some grasslands, the proportion of biomass below ground dwarfs what you see above the surface. Alpine meadows, for instance, allocate a significantly higher share of biomass below ground compared to desert steppes, and that allocation pattern shifts with temperature, rainfall, and soil nutrient levels.12PubMed Central. Climate Factors Influence Above- and Belowground Biomass Allocations in Alpine Meadows and Desert Steppes through Alterations in Soil Nutrient Availability
This root-heavy strategy is partly why grasslands persist under fire and grazing. When a fire sweeps through or a bison herd strips the aboveground foliage, the plants regenerate from meristems and buds safely insulated below the soil surface. Annual burning in tallgrass prairie increased grass bud banks by about 25%, while forb bud banks declined substantially, and the size of the underground grass bud bank turned out to be an excellent predictor of the prairie’s aboveground productivity in both the long and short term.13Plant Ecology. The effects of fire frequency and grazing on tallgrass prairie productivity and plant composition are mediated through bud bank demography The real engine of a grassland’s production, in other words, is underground.
Rainfall Patterns Drive Producer Output
Grassland productivity is famously tied to precipitation, but total annual rainfall tells only part of the story. Across Eurasian temperate grasslands, aboveground productivity increased with mean annual precipitation, but the seasonal distribution of that rain explained nearly as much of the variation, accounting for about 39% of the spatial differences in productivity compared to 40% for total precipitation.14Global Change Biology. Spatial variations in aboveground net primary productivity along a climate gradient in Eurasian temperate grassland: effects of mean annual precipitation and its seasonal distribution For mid-range grasslands like the typical steppe, when rain fell mattered more than how much fell over the whole year.
The size of individual rain events matters too. In a semi-arid grassland experiment, plots that received fewer but larger rain events produced nearly 80% more aboveground biomass than plots receiving the same total water in smaller, more frequent doses. Larger events pushed moisture deeper into the soil profile, where it stayed available to roots longer.15PubMed. Increasing precipitation event size increases aboveground net primary productivity in a semi-arid grassland Climate projections suggest storms will become less frequent but heavier in many regions, which may actually boost production in drier grasslands while creating new stress for wetter ones.
The response is not symmetrical, either. Modeling work across different steppe types found that the impact of decreased precipitation was more pronounced than the impact of the same magnitude increase, and the most arid grasslands were hit hardest by drying.16PubMed Central. Divergent response of grassland aboveground net primary productivity and precipitation utilization efficiency to altered precipitation patterns by process-based model So while grassland producers broadly track rainfall, the relationship has kinks and thresholds that make simple predictions unreliable.
Drought Resilience and Phenological Flexibility
How producers respond to drought reveals another layer of their adaptations. On the Colorado Plateau, researchers imposed seasonal drought on two common perennial grasses, one C3 and one C4, for four years and then tracked two years of recovery. The C4 grass, Pleuraphis jamesii, showed flexible timing of its growth stages in response to drought, adjusting when it flowered and set seed. The C3 grass, Achnatherum hymenoides, was more rigid in its phenology and experienced high mortality, with recovery lagging behind.17PubMed Central. Flexible Phenology of a C4 Grass Linked to Resiliency to Seasonal and Multiyear Drought Events in the American Southwest The implication is that under increasingly variable rainfall, C3 grass populations in some dryland systems could decline and give way to warm-season C4 species, reshaping the producer community.
Mycorrhizal Fungi as Hidden Partners
Most grassland producers do not work alone belowground. Arbuscular mycorrhizal (AM) fungi colonize the roots of the majority of grassland plants, extending thread-like hyphae far beyond the root zone to scavenge nutrients, especially phosphorus. In grassland microcosms, the presence of AM fungi reduced phosphorus loss during simulated rain events by about 60% and ammonium loss by roughly 7.5%, effectively tightening the nutrient cycle and keeping more resources available for plant growth.18PubMed. Mycorrhizal fungi reduce nutrient loss from model grassland ecosystems
AM fungi also boosted plant nutrient stocks and aboveground biomass in experiments simulating future climate conditions, though the benefit was most apparent when plants were competing for a limited nutrient pool. When nutrients were abundant, the fungi’s contribution was less obvious.19Environmental and Experimental Botany. Effects of arbuscular mycorrhizal fungi on grassland productivity are altered by future climate and below-ground resource availability This suggests mycorrhizal partnerships are most critical exactly where grassland producers need them most: in nutrient-poor soils under environmental stress.
Rising CO₂ and Invasive Producers
Elevated atmospheric carbon dioxide tends to boost plant growth, and grassland producers are no exception. But the benefits are not evenly distributed. In a long-running prairie experiment, elevated CO₂ initially produced moderate increases in both biomass and plant diversity. Over time, though, an invasive forb (Centaurea diffusa, diffuse knapweed) responded so aggressively to the extra CO₂ in disturbed plots that biomass gains in those areas were ten times larger than in intact prairie, while diversity dropped by about 17%.20PubMed. Soil disturbance and invasion magnify CO2 effects on grassland productivity, reducing diversity Intact, undisturbed grassland saw a more modest productivity boost alongside a slight increase in diversity. The lesson is that rising CO₂ does not lift all producers equally; it can supercharge invasive species in disturbed grasslands and squeeze out native producers.
Sown Pastures Versus Semi-Natural Grasslands
People often assume that replacing native grassland producers with improved pasture grasses will raise productivity. Research in seasonally dry climates tells a more nuanced story. Sown pastures did produce higher peak productivity during the rainy season, but semi-natural grasslands maintained more stable production across the full year, including the dry season when livestock still need forage. Over a whole annual cycle, replacing semi-natural grasslands with sown pastures did not actually increase total production under prevailing management practices, while the temporal distribution of that production became less even.21PubMed Central. More stable productivity of semi natural grasslands than sown pastures in a seasonally dry climate The native mix of producers, it turns out, hedges its bets across the seasons in a way monoculture pastures do not.
Restoring Grassland Producer Communities
Where grasslands have been converted to cropland or degraded by overgrazing, restoration typically starts with reintroducing the producers. That means sowing seeds of native grasses, forbs, and legumes. One of the trickier challenges is controlling invasive grasses that colonize degraded ground. Researchers have explored designing seed mixes using functional traits to create communities that overlap with and outcompete invasive species, an approach called limiting similarity.22Applied Vegetation Science. Exploring seed density and limiting similarity to reduce invasive grass performance for grassland restoration purposes In long-term restoration experiments, sowing native species and tracking how diversity develops under altered rainfall conditions has shown that restored grasslands can reassemble functional producer communities, though the trajectory depends on which founding species are chosen and what the climate does next.23PubMed Central. Effects of Manipulated Rainfall and Intraspecific Variation Within Dominant Species on Community Assembly: Insights From a Long-Term Grassland Restoration Experiment Getting the producer community right is not just an ecological nicety; it determines whether the restored grassland will function as habitat, hold soil, cycle nutrients, and support the food web that depends on it.