Invasive Weeds - Weeping and Lehmann's Lovegrass

Eragrostis curvula & E. Lehmanniana

Although there is a native lovegrass species (E. intermedia), these 2 species of Eragrostis are introduced from South Africa.

These plants were introduced as part of range restoration/soil conservation programs in the southwest, and thousands of acres were planted with them in the 1930’s (Moser & Crisp 2003). In the mid to late 1900’s, these species were commonly included in seed mixes used after fires, highway construction/reconstruction, and other ground-disturbing activities, such as powerline road construction. Lehmann’s lovegrass has thrived the best at elevations from 3000 to 4500 feet; weeping lovegrass grows in Arizona from 4900 to 6500 feet. They were planted with forage value in mind, however, they are not as palatable as native perennial grasses, and tend to out-compete them. Although they are classified as warm-season growers, they produce more green herbage in the winter and early spring than native grasses. This active growth during a time when native warm-season grasses are still dormant is key to their dominance in a grassland community years after planting (Moser & Crisp 2003, Uchytil 1992, Walsh 1994).

When native grassland and pastures seeded to Lehmann’s and weeping lovegrass were compared, the two site types differed consistently in that the planted exotics grew in monospecific stands and native grasses did not. Total native herbaceous canopy, species richness, shrub density and shrub canopy were significantly reduced on plots seeded to the lovegrasses. Small birds that nest in grasslands will use Lehmann’s lovegrass, but nest more frequently in native grassland if it is available. (Uchytil 1992)

Lehmann’s lovegrass reseeds itself quickly after disturbance, and tends to replace native grasses where it has been planted. It has replaced Arizona cottontop, threeawn grasses, and grama grasses over much of the Santa Rita Experimental Range in Arizona (Cable 1971). Weeping lovegrass produces up to 1000 seeds per seedhead, but rate of spread by seeds is very slow, and this plant does not actively colonize adjacent nonplanted sites. Weeping lovegrass should not be planted after wildfires for restoration if management objectives are to maintain native plant communities. Although weeping lovegrass is not particularly invasive, once it is planted, it remains in place for a very long time (Walsh 1994).

Desert shrublands that have been invaded by Lehmann’s lovegrass experience much more intense burning during wildfires. Most native desert plants and cryptogams are not adapted to intense and frequent fires; species composition changes over time in sites that have been invaded by this and other exotic perennial grasses such as buffelgrass.

Lehmann’s lovegrass seeds are initially dormant, requiring 6 to 9 months of afterripening. They need some type of dry heat to scarify their seedcoat and increase water uptake by the seed to be able to germinate. Shading inhibits germination, as the seeds also require exposure to red light to germinate (Uchytil 1992). Weeping lovegrass exhibits facultative apomyxis; that is, seeds do not have to be fertilized to grow into new plants. Weeping lovegrass seedlings must have dependable moisture after they germinate. Less than 20% of newly germinated seedlings survived one day of dessication, and none survived 3 days of dessication (Uchytil 1992).

On the Tonto, these grasses have been extensively seeded along highways, powerline corridors, and even aerially seeded after fires. In 1951, weeping lovegrass was aerially seeded in the Pinal Mountains after a wildfire (Walsh 1994).

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Weeping lovegrass

Lehmann’s lovegrass