BLOOM, THOMAS C.1, JERRY M. BASKIN2*, and CAROL C. BASKIN2,3. 11209 Glade Street, College Station, TX 77840; 2School of Biological Sciences, University of Kentucky, Lexington, KY 40506; 3Department of Agronomy, University of Kentucky, Lexington, KY 40546. - Ecological life history of the facultative biennial Arabis laevigata var. laevigata (Brassicaceae).
The ecological life history of Arabis laevigata, a facultative
biennial native to e. North America, was studied in a rocky deciduous
woodland in nc. Kentucky from 1985-1994. Its woodland rock outcrop
habitat is stable and thus differs from the ruderal habitat of many
other facultative biennials. Seeds of A. laevigata mature in
June and dispersal lasts >1 yr; most fall within 0.5m of parents.
Seeds have nondeep physiological dormancy, which is broken during
winter. Germination occurs in March and April, and seeds that fail to
germinate become part of a persistent seed bank. Plants form a rosette
the first year and flower in their second or a later year. There was
no consistent pattern of transition between size intervals.
Vernalization is required for bolting/flowering, but plants are
day-neutral. Bolting occurs in March, and anthesis peaks in mid-April.
Arabis laevigata is capable of both self- and
cross-fertilization and is not agamospermous. Probability of survival
and of bolting increased with rosette size, which was highly
correlated with number of seeds produced. Low leaf litter cover, low
herbivory, and a rock/moss substrate were associated with increased
bolting. Flower stalk herbivory was the primary reason many plants
that bolted did not produce seeds. Less than 5% of 3,083 plants marked
in the seedling stage survived 1 yr, and <1% of them reproduced.
Cohorts exhibited a Deevey Type III survivorship curve.
Pre-establishment mortality corresponded positively with no (vs
partial) leaf litter cover and negatively with increased
precipitation. Greater mortality in established plants generally was
associated with small (vs. large) size, moderate (vs. low) leaf litter
cover, a soil (vs. rock/moss) substrate, herbivory, and low
precipitation. We conclude that A. laevigata exhibits a
stress-tolerant ruderal (SR) strategy (sensu J.P. Grime's
Key words: ecological life history, facultative biennial, reproductive biology, survivorship