The following information is derived largely from monitoring records of the Illinois Department of Natural Resources but some may come from the literature and other sources. It relates to the biology of the species in Illinois.
Species: Dalea foliosa, Leafy Prairie Clover
Compilers: Bill Glass & John Schwegman, Illinois Department of Natural Resources and Marcella Demauro, Will County Forest Preserve District.
Date of Most Recent Update: January 31, 1992
Location and Description of Monitored Populations: The entire population at Romeoville Prairie Nature Preserve in Will County was censused for flowering plants annually. This population occupies a linear tract of habitat some 1,875 feet long and about 300 feet wide occupying about 13 acres. A demographic plot of 14.13 sq. meters was established in part of the overall population to follow individuals of all age and reproductive classes through time. Seedlings and juveniles were followed only in half of the plot. Data here represent findings from 1986 through 1991. Monitoring was about August 1 annually.
Variations from Normal while Monitoring: Severe drought occurred in the summer of 1988 through the spring of 1989 and in the summer of 1991. An exceptional low temperature of -20 F occurred in December 1989. 1990 had a cooler than normal spring followed by a wetter than normal summer. The plot was burned in the spring of 1985, the fall of 1987 and spring of 1989.
Range of Natural Communities: Dolomite prairie, a prairie community developed in relatively thin soil over dolomite bedrock.
Range of Plant Communities: Vegetation in the demographic plot is dominated by Poa compressa-Aster ericoides-Ambrosia artemisiifolia. Dominants at other sites were not noted.
Range of Soil and Substrate: Sandy loam with dolomite bedrock at or near the surface.
Range of Slope and Aspect: Level.
Range of Shading or Crown Cover: Full sun for plot, but other censused plants were observed growing in partial shade of shrubs such as sandbar willow and smooth sumac.
Flowering Dates in Illinois: July 14 to August 14. Flowering was delayed after the cool wet spring and summer of 1990. There were lots of plants in bud but none in flower on August 1, 1990. No flowering was observed during the 1988 drought. Stems grazed by rabbits frequentlyset on new flowering heads that bloom much later than ungrazed branches and heads.
Fruiting Dates in Illinois: Mature fruits observed August 14 until after frost.
Known Phenotypic Variation: None noted.
Known Pollinators in Illinois: Small bees visit to collect pollen and seem to be effective pollinators. Syphid flies were also noted on the flowers.
Reproductive Mode: Seed.
Known Conditions for sexual Reproduction: Numerous seedlings (small single stemmed plants < 5 Cm high) were present in the demographic plot in 1986 after a spring burn in 1985 followed by normal temperatures and moisture. There were 305 seedlings in a plot of 7.06 Sq. Meters or 43 per Sq. Meter. These seedlings were in the lower (more moist?) part of a thinly vegetated short grass (about 15 cm tall) rocky open area in full sun. Seedlings were also noted as abundant in deep shade of a willow thicket in 1986. Both areas apparently had mulch from the 1985 vegetation. Forty one seedlings were in the demographic plot in 1987. Although fall burned in 1987, no seedlings were found in the severe drought of 1988 that persisted through spring 1989 or in subsequent years. A spring burn in 1989 under drought conditions did not result in any seedlings even though moisture increased by the summer of 1989 and 1990 was very wet. Thus, the combination of a spring burn followed by adequate moisture during the growing season has produced the only natural reproduction noted.
Known Diseases: None observed.
Known Grazers and Parasites: The larger plants are often heavily grazed, apparently by rabbits. Grazing is most severe in drought years. By late July in drought years, most vegetation growing with this species is withered and brown, but the Dalea remains conspicuously green. Its green and succulent leaves seem to draw more attention to it during drought. During the drought year of 1991, 86% of 161 stems present in the plot were grazed. In the very wet year of 1990, 42% of 136 stems were grazed. This species compensates for grazing by regenerating multiple flower heads (usually 2) on some grazed stems. Ungrazed flowering stems only have a single flower head (inflorescence).
Known Problems with Exotic Species: It grows with Poa compressa and Daucus carota in the plot, but these seem to have no detrimental effect on it.
Response to Fire: Spring fire stimulates seedling germination if followed by normal moisture. It apparently accomplishes this through scarification of seed. Frost heave mortality was high in 1988 following the fall burn of 1987. It appears that frost heave was enhanced by removal of the mulch by the fall burn. Six plants went dormant in 1988 after the fall burn in 1987. After the 1989 spring burn, only 1 plant went dormant. There were 2 dormant in 1987 and again in 1990 not associated with burns. 1988 was a severe drought year which may have caused the dormancy of 6 plants, but the fall burn of 1987 may have influenced the high dormancy rate by addingstress. Possible stress factors include colder soil temperatures due to mulch removal, increased frost heave and moisture loss through increased runoff of winter rains.
Mortality: One large plant that died between 1989 and 1990 had its root crown elevated 2 cm above the soil due to frost heave. This was interpreted as its cause of death. Frost heave was credited with killing some of the seedling/juveniles lost in 1987 and 1988. In 1988 one large plant leafed out and then died in late July apparently from drought. Another large plant had apparently just died in early August from severe grazing by rabbits in conjunction with drought. In the severe drought year of 1991 a large plant had just turned brown at monitoring time and had 7 of 10 stems grazed by rabbits. It appeared to be dying. Some of the juvenile/seedling mortality of 1987 and 1988 was attributed to drought.
Known Shifts in Plant Vigor: During the severe drought of 1988 there was no flowering at all in the plot and only 10 flowering plants were found in the entire Romeoville Prairie population. This is considered a shift in vigor in response to drought. Average maximum stem height was cm and cm in the drought years of 1988 and 1991 respectively. It was cm in the very wet year of 1990. Plants have gone from flowering one year to sterile the next and back to flowering. The number of stems an individual plant has can vary with moisture conditions and in response to dormancy and vigorous growth. One plant had 2 stems in '86, 13 in '87, was dormant in '88 then had 48 stems in '89, 4 in the wet year of '90 and was dead or dormant in '91. These shifts indicate increased vegetative growth after dormancy and decreased vigor after an exceptionally vigorous growth year. Six year stem counts for some plants indicate there may be a decline in stems with age, but more monitoring is needed to determine this.
Known Dormancy (of Perennial Herbs): As many as 6 plants have remained dormant in the plot one year and then emerged the following year or later. One plant was dormant for two consecutive years (the drought years of 1988 and 1989) and then returned. Many formerly vigorous plants were missing in the drought year of 1991 and some of these are surely dormant rather than dead.
Summary of Apparent Factors Regulating Size and Health of Populations:
Moisture restricts mature plant vigor and can cause mortality, especially of young plants. Spring burns and adequate moisture are needed for seedling establishment. Frost heave can kill plants, especially young ones, and is increased in severity by fall burning. Severe rabbit grazing in conjunction with drought can kill plants and reduces seed production.