Anthoxanthum odoratum

ANTHOXANTHUM ODORATUM can be distinguished from other grass species by its perennial habit and sweet, vanilla scent, especially when dry.

Sweet vernal grass is a native of Eurasia (Hitchcock 1971, Munz and Keck 1973). It occurs on poorer soils in dry fields, lawns, meadows, and waste places (Muenscher 1955).

GROWTH AND COMPETITION

When grown with other common pasture grasses, ANTHOXANTHUM ODORATUM is highly competitive. In a North Carolina study, it generally dominated mixtures that included PLANTAGO LANCEOLATA, POA PRATENSIS, SALVIA LYRATA, and RUMEX ACETOSELLA (Fowler 1982).

In a study of competition with LOLIUM PERENNE, DACTYLIS GLOMERATA, and HOLCUS LANATUS (Remison and Snaydon 1978), sweet vernal grass proved highly competitive in the early spring due to its rapid growth and early flowering. Later in the summer it declines in aggressiveness. Among these species, sweet vernal grass is the most highly competitive for potassium (Remison and Snaydon 1978). A Dutch study revealed similar results (Berendse 1983). Even at low densities, competition between ANTHOXANTHUM ODORATUM and PLANTAGO LANCEOLATA is very strong. ANTHOXANTHUM's competitive ability is highest in early spring.

In competition experiments (Remison 1978) with HOLCUS LANATUS and DACTYLIS GLOMERATA, ANTHOXANTHUM ODORATUM had the lowest yield, especially at low densities. It proved most competitive at intermediate densities. Again, however, sweet vernal grass was most competitive early in the growing season, due to its rapid spring growth.

ANTHOXANTHUM ODORATUM roots are quite shallow, absorbing nutrients mainly from the upper 10 cm of soil (Berendse 1982). It commonly occurs on soils that are low in phosphorus (Roberts 1982). On fertilized soils, sweet vernal grass develops a dense surface root mat (Remison and Snaydon 1978). Although ANTHOXANTHUM tillers profusely, its poor root growth reduces its competitive ability (Remison 1978). The ratio of roots to shoots is therefore quite low at 0.(55) (Remison and Snaydon 1978).

In mixed species plots, intraspecific competition is more important than interspecific competition (Berendse 1983). Like many other grasses, sweet vernal grass contains allelopathic chemicals that suppress the growth of other plant species (Scott 1975). It is "allo-inhibited," growing better with exudate from its own and similar species in permanent grasslands (Newman and Rovira 1975).

The decomposing roots of ANTHOXANTHUM ODORATUM have an effect opposite that of the allelopathic leachate. Old roots appear to enhance the growth of other grass species, while decreasing the growth of new ANTHOXANTHUM plants. Phosphorus content in the roots averaged 0.155%, a relatively high level. This is probably one of the factors leading to the increased growth of other species on sites with decomposing sweet vernal grass roots (Newberry 1979).

ANTHOXANTHUM ODORATUM plants average 3.5 leaves per shoot. The individual leaves are unusually short-lived, with a mean survival of only 19 days. Only a few leaves survive for three months. This rapid turnover of leaves is probably a reflection of the plant's rapid growth rate (Sydes 1984).

POPULATION DYNAMICS

The biology of ANTHOXANTHUM ODORATUM populations is complex and depends upon the particular habitat. Different character complexes are favored by different habitat types leading to substantial phenetic differences between ecologically marginal and central populations. Ecologically marginal populations have higher turnover rates than central ones. Individual life expectancy is shorter in marginal populations, while central populations contain a skewed age distribution in favor of older individuals, making them potentially less stable (Grant and Antonovics 1978).

In response to contrasting environments, sweet vernal grass can rapidly differentiate, even without geographic barriers. In one study (Kiang 1982), significant differences in morphology, flowering date, and pollen fertility developed in less than 40 years. Such differences among populations were genetic adaptations to contrasting soil environments. Similar results are reported by Snaydon and Davies (1972, 1976) for populations at distances of less than 30 m apart.

When environmental boundaries are distinct, ANTHOXANTHUM ODORATUM populations can exhibit sharp differences. Plants growing only 0.1 m apart across a sharp environmental boundary that had existed for less than 120 years showed significant differences in height, yield, flowering date, and morphology (Snaydon and Davies 1976).

ANTHOXANTHUM ODORATUM reproduces from seeds, flowering early in the spring and forming distinct, identifiable clumps that do not spread vegetatively (Grant and Antonovics 1978). The plants are generally self-incompatible (Antonovics 1972). Plants in North Carolina were reported to produce from 58 to 1,257 seeds per plant (Grant and Antonovics 1978).

SEED DISPERSAL AND GERMINATION

Seeds with awns are able to move further along the soil surface than awnless seeds. ANTHOXANTHUM ODORATUM seeds have awns that wind and unwind with changes in atmospheric humidity. The movement of seeds by this mechanism is not great, averaging 1.6 cm on dry soil and 1.3 cm on wet soil over a 5-day period, but it may give the seeds a slight advantage in reaching suitable germination sites (Schonfeld and Chancellor 1983).

Harris (1961) found some dormancy in ANTHOXANTHUM ODORATUM seeds. Most germination began the 4th week after sowing and ceased by the 8th week, but a few seeds germinated more than a year later. In experimental studies in England (Williams 1983a), A. ODORATUM seeds stored for 48 weeks in dry storage resulted in 86% germination. There is thus indirect evidence of seed dormancy, which may increase a seed's chance of being incorporated into the soil while still viable. For seeds sown on moist soil, however, emergence occurred rapidly (within three months). Those seeds that did not emerge within 10 months were not viable. Emergence was highest for seeds sown at a depth of 1 cm (75% viable) and decreased to 52% for seeds sown at a depth of 5 cm.

In another British study (Williams 1983b), ANTHOXANTHUM ODORATUM was compared with eight other grassland species. It showed a greater ability to germinate under constant conditions than when conditions were varied. When A. ODORATUM seeds were stored for 28 weeks, a much higher percentage of the seeds germinated when stored at constant temperatures.