Holcus lanatus

HOLCUS LANATUS is rarely mistaken for any other species with the possible exception of H. MOLLIS. H. LANATUS can be distinguished by the purplish coloration on the panicles and veins of the sheaths, soft hairs all over, and lack of rhizomes. The two species may be able to hybridize (Jones 1954).

HOLCUS LANATUS exhibits a wide climatic tolerance of temperate regimes over a wide range of altitudes (0-1500m). It is killed by severe frost (Watt 1978b). Optimal growth occurs under moist conditions; however, it grows well in very wet conditions and can survive moderate periods of drought (Watt 1978a).

In Britain H. LANATUS occurs on a wide range of soil types including those of rich-fen and fen-meadow communities, poorly drained, waterlogged, low to moderately fertile, and nutrient-rich soils. It occurs independent of soil phosphorous content and grows well in potassium- and/or nitrogen-poor soils. It tolerates a wide range of soil pH, growing best between pH 5.0 and 7.5 (Thompson and Turkington 1988). Studies in Oregon (Hart and McGuire 1963) indicate an increase in the abundance of velvet grass under mildly acidic conditions.

Little research has been done on HOLCUS LANATUS in North America. In Europe, it is an adaptable, competitive species that tolerates a wide range of habitats, particularly acidic, low nutrient sites (Watt 1977).

GROWTH, PRODUCTIVITY, AND COMPETITION

In the Soviet Union, Trapaidze and Gogiya (1981) report that HOLCUS species have an exceptionally long growing season. Germination occurs from seed or as sprouts from roots in late autumn, with flowering between May and July. In a Dutch experiment (van Andel and Jager 1981), velvet grass leaf area peaked 15 weeks after sowing, and maximum dry weight was attained two weeks later. In the later stages of growth, root mass increased dramatically, reaching half of the total plant weight. Nitrogen levels also showed a marked increase after 15 weeks of growth. Nitrogen availability may be the limiting factor in HOLCUS LANATUS growth (Watt 1978). HOLCUS LANATUS normally occurs on soils of moderate to low fertility, but fertilization appears to improve its competitive ability (Remison and Snaydon 1980).

High water table levels reduce the productivity of velvet grass. HOLCUS manages to persist on these wet sites by producing a large number of fine roots on the soil surface where aeration and nutrient levels are higher (Watt and Haggar 1980b). Grootjans (1979) noted that a lowered water table increase the N-mineraliza- tion rate and the nitrate content leading to a strong site dominance by HOLCUS LANATUS. Severe winter weather and high ground water can kill the grass, perhaps by lowering the N-mineralization rate (Bakker et al. 1980). Velvet grass can tolerate soils with a pH range of 3 to 8.1 (Grime and Lloyd 1973) but does best on sites with a pH of 4.5 to 5.5 (Roberts 1982).

Like other weeds from disturbed but productive habitats, HOLCUS LANATUS is able to grow rapidly. The mean recorded growth rate is 1.56 g/g.week while the maximum growth rate exceeds 2 g/g.week (Redosevich and Holt 1984). This rapid growth may indicate a high potential competitive ability among crop and weed species (Redosevich and Holt 1984). This aggressiveness is shown in the dominance of velvet grass in English pastures (Turkington et al. 1979). HOLCUS also does well in both high and low levels of light (Anonymous 1976).

In an English study, Remison and Snaydon (1980) found that HOLCUS LANATUS outcompeted DACTYLIS GLOMERATA (orchard grass) under a wide variety of conditions. Velvet grass yield increased by 50% on sites with competition over sites where it was grown alone. Similar results are reported for competition between HOLCUS LANATUS and LOLIUM PERENNE (ryegrass). Velvet grass is particularly aggressive in root competition due to its higher proportion of roots than other British pasture species (Watt and Haggar 1980a).

In a Dutch grassland study (Bakker et al. 1980), HOLCUS LANATUS became dominant when the grass was mowed following maturation and seed dispersal. When earlier cuts were made, HOLCUS LANATUS survived but became less dominant. HOLCUS LANATUS responds well to cutting, even when cut back to only 2 cm above the ground. On unharvested sites, velvet grass gradually forces other plants out, reducing species diversity. This process is particularly apparent on unfertilized sites. Allelopathy may also play a role in the dominance of HOLCUS LANATUS over other grasses (Remison and Snaydon 1978).

FLORAL BIOLOGY

In North America, flowering occurs June through August (Septem- ber). H. LANATUS is wind pollinated and predominantly an outcrossing species. Successful self-fertilization occurs only occasionally and is impossible in some plants (Beddows 1931). During anthesis the panicle opens from the apex down and closes likewise (Tutin et al. 1964).

SEED PRODUCTION

In England, HOLCUS LANATUS seeds are shed from June to September (Mortimer 1976). The plants require vernalization to flower, but this process is enhanced and, to a small extent, replaced by short- day treatment (Watt 1977). It flowers and produces seeds from the second year onwards and behaves as a "paucennial." In places with reduced competition, the plant will often die after a few years, particularly following luxuriant flowering. In southern Europe, very short-lived races that flower the first year are found in dry habitats. In northern races, the plants require a period of vegetative growth prior to flowering in the second year (Bocher and Larsen 1958). HOLCUS LANATUS also exhibits variation in culm length and growth habit. In exposed maritime habitats, it grows as a low plant, while farther inland, the plants are more erect with tall culms (Bocher and Larsen 1958).

Trapaidze and Gogiya (1981) report up to 850 wind-dispersed seeds per plant in the Soviet Union. In England, Watt (1976) found production of up to 240,000 seeds per plant, most of which germinated shortly after landing on moist soils.

SEED GERMINATION

Williams (1983) found that when stored under dry, shaded conditions, velvet grass seeds remained viable for at least 48 weeks with 90-99% germination. Trapaidze and Gogiya (1981) found a germination rate of 95% for the first two years after seed harvest. Both vertebrates and earthworms appear to significantly reduce velvet grass populations by their burial or consumption of seeds (Mortimer 1976). When the seeds were buried, only 3% of them were still viable after a year. Seeds buried at a depth of 1-2 cm had a much higher chance of emergence than those at a depth of 3 cm (Williams 1983). In the Soviet Union, HOLCUS seeds showed 87% germination rate on the ground surface, 76% at a depth of 1 cm, and only 5% germination at 2 cm (Trapaidze and Gogiya 1981). HOLCUS LANATUS seeds are thus apparently not innately dormant, though certain field conditions may enforce dormancy (Williams 1983). Even though most of the seeds are nondormant, the potential number of seeds produced by each plant is so high that even a 1% level of innate or enforced dormancy would result in a large amount of buried viable seed (Watt 1976). The species can thus exist in large numbers in a seed bank, even if it is not an important plant on a given site (Roberts 1982).

Seed germination can occur at 7-8 C (Trapaidze and Gogiya 1981). Thompson and Whatley (1984) suggest that burying the seeds may induce a requirement for fluctuating temperatures of greater than 19 C. The result is that HOLCUS LANATUS seeds germinate more readily in larger canopy gaps (wider than 25 cm) where their survival chances are improved (Thompson 1977). Mortimer (1976) estimates that when various mortality factors are taken into consideration, each HOLCUS LANATUS plant can produce 9.9 adult plants the following year.

HOLCUS LANATUS is not usually considered a stoloniferous species, but regeneration can occur by the formation of decumbent tillers in late summer that subsequently produce roots and shoots at the nodes. Growth of these shoots may be enhanced by grazing or mowing, but root growth does not appear to be affected (Watt and Haggar 1980a).