Bird’s-foot trefoil (Lotus corniculatus) is a perennial legume commonly used as a forage crop for livestock. Native to Europe and parts of Asia, it has been widely introduced around the world and is now present on six continents. Bird’s-foot trefoil is valued for its high nutritional quality and non-bloating properties. However, there are concerns that it may become invasive and crowd out native plants in areas where it has been introduced. This article will examine the evidence on both sides of this debate.
What is bird’s-foot trefoil?
Bird’s-foot trefoil is a low-growing legume, typically reaching 1-2 feet in height. It has yellow pea-like flowers and seed pods that resemble a bird’s foot, giving rise to its common name. It is a member of the bean family Fabaceae. There are both annual and perennial varieties, with the perennial types being most common. Perennial bird’s-foot trefoil is long-lived, with individual plants surviving for 3-4 years or more. It spreads through both seed dispersal and vegetative propagation via stolons (runners along the ground).
Bird’s-foot trefoil thrives in cool, moist environments and does well on marginal land. It can tolerate acidic and low fertility soils. For these reasons, it has been widely planted for livestock forage, especially in areas with heavy or poorly drained soils. It is high in protein and non-bloating, making it a valuable component of pasture mixes. Bird’s-foot trefoil contains condensed tannins, which helps prevent intestinal parasites in grazing animals.
Native range and introduction history
Bird’s-foot trefoil is native to Europe, including the British Isles, Scandinavia, and parts of the Mediterranean. It is also native to parts of northern Africa and western Asia. Within its native range, it occurs in meadows, pastures, roadsides, and other open areas.
Bird’s-foot trefoil was introduced to North America in the late 19th century. It was first planted experimentally at the Ontario Agricultural College in 1886. Early introductions were aimed at providing high-quality forage for livestock. It was soon after planted for soil improvement and erosion control.
Bird’s-foot trefoil is now naturalized across much of the United States and Canada. It has also been introduced to South America, Australia, New Zealand, and other regions with temperate climates suitable for its persistence. It has become an important component of pastures in many parts of the world.
Evidence for invasiveness
There are several lines of evidence suggesting that bird’s-foot trefoil may be invasive or weedy in parts of its introduced range:
– It can spread aggressively via stolons once established. Bird’s-foot trefoil produces many thin horizontal runners along the soil surface. These stolons allow it to colonize open ground rapidly.
– It produces abundant seed. A single bird’s-foot trefoil plant can produce 2000-13,000 seeds per year. This high reproductive rate facilitates dispersal and establishment in new areas.
– It exhibits allelopathy. Bird’s-foot trefoil releases biochemicals that suppress the growth of competing plant species. This allelopathic effect gives it an advantage over native plants.
– It has few natural predators outside of its native range. Deer often avoid eating it due to its tannins. It lacks specialist herbivores that help check its spread in its native Europe and Asia.
– It can push out and replace native plants over time. Studies have shown declines in native plant diversity and altered plant community structure where bird’s-foot trefoil has invaded.
– It forms dense monocultures. Bird’s-foot trefoil can produce thick stands that crowd and shade out other species. This has been observed in parts of North America and New Zealand.
Evidence against invasiveness
However, there are also reasons to think bird’s-foot trefoil poses a low risk of becoming invasive:
– It has a relatively short life span. Individual plants only live 3-4 years on average. Thus stands need to be reseeded periodically.
– It does not spread rapidly in undisturbed areas. Bird’s-foot trefoil spreads primarily in areas of soil disturbance like along roadsides or in overgrazed pastures. It does not easily invade intact prairies and rangelands.
– It has specific habitat requirements. Bird’s-foot trefoil grows best in cool, moist areas with full or partial sun. It struggles in hot, arid climates. This limits the areas where it thrives.
– It does not reproduce vegetatively over long distances. The stolons only allow for local spread of a few feet per year. Long-distance colonization relies on seed dispersal.
– Seed dispersal is limited. The seed pods do not have structures promoting animal dispersal. Seeds mostly fall passively around the parent plant. Long-distance spread via wind, water, or animals is minimal.
– It does not thrive in dense shade. While bird’s-foot trefoil can tolerate moderate shade, it grows best in full sunlight. It cannot easily invade intact forests and shady understories.
– Native species can provide biotic resistance. In areas with diverse plant communities, competition and herbivory help check bird’s-foot trefoil spread. It becomes weedy primarily where diversity is already reduced.
Evidence Summary
Evidence for Invasiveness | Evidence Against Invasiveness |
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Management implications
The mixed evidence suggests that bird’s-foot trefoil has the potential to become invasive, but that this depends heavily on the ecosystem and conditions where it is introduced. A few management implications include:
– Avoid introducing bird’s-foot trefoil adjacent to high quality native habitats. Focus planting in areas already degraded or dominated by exotic species.
– Monitor plant community changes after introduction. Quickly detect any declines in native species diversity or habitat quality.
– Limit use in regions with Mediterranean climates favoring its persistence. It poses the most risk in areas with cool, wet winters and warm, dry summers.
– Maintain healthy native plant communities. Diverse, intact ecosystems resist invasion better than simplified, degraded ones.
– Consider native forage alternatives. Where feasible, choose native legumes and forbs to improve pasture quality while avoiding risks of invasion.
– Prevent seed production and vegetative spread along roads and waterways. These act as conduits for bird’s-foot trefoil to colonize new areas.
Conclusion
Bird’s-foot trefoil is valued as a forage crop worldwide thanks to its agricultural utility and nutritional qualities. However, its aggressive spreading ability means that it could become problematic in regions where it is not native. The risk of invasiveness depends on the specifics of the local habitat and plant community. With prudent management, the benefits of bird’s-foot trefoil can be captured while minimizing unintended harms to native biodiversity and ecosystems. Continued monitoring of its long-term impacts will be important as this species continues to spread to new areas via both intentional introductions and accidental spread.