Summary
Southern Quebec (Canada) represents the northern limit of wild leek (ail des bois) Allium tricoccum, a deciduous forest perennial herb of eastern North America. In Quebec in 1989 it was designated ‘vulnerable’ (due to over-collecting of its edible bulbs) and it became illegal to commercially harvest the species. To conserve wild populations and assess the feasibility of undertaking reintroductions, experimental transplanting of bulbs and sowing of seeds were undertaken, investigating how environmental factors influence growth and survival.
Study sites comprised seven ‘natural’ sites situated in and around Gatineau Park (45°31'N, 75°55'W) within 15 km of the donor population (within sugar maple Acer saccharum forest). The eighth was at the Montreal Botanical Garden.
At the Botanical Garden, soil moisture and nutrient levels were maintained at a relatively high level (plants watered and fertilized regularly). At each natural site (six in deciduous woodland, one in an abandoned field), in 1985 light availability, soil moisture and major soil nutrient concentrations were recorded every 3-weeks during the growing season (May-end October) using standard techniques.
Seds: In autumn 1984 about 800 seeds were collected and stratified over-winter. In spring 1985, 100 were sown at each site. Wire cages were used to exclude small mammals. Fifty seeds were also sown at each site in spring 1986,
Bulbs: Bulbs were selected in spring1985. Total leaf width (TLW) of each plant was measured (to determine size without having to dig up the bulb; TLW is correlated size). Individuals of four different size classes (1-2 years old; intermediate-sized; non-reproductive large plants; reproductive plants that had flowered) were marked. Approximately 20 bulbs of each size-class were transplanted into each of the eight sites in October (when dormant) 1985.
Each spring (1986-1990) mortality, seedling emergence, growth, sexual reproduction and TLW was recorded. Analyses were performed to determine how light availability, soil moisture and nutrient levels affected survival and growth.
Seeds: Seedling emergence was site-specific and mostly influenced by soil moisture, with emergence best at the (watered) garden site (90%) in 1985, with similarly high levels at this and one of the natural sites in 1986. Summer drought prolonged dormancy.
Bulbs: Bulb of the three larger sizes in the first year (1986) had high survival (average 99%; range 87-100%) but survival of young plants was lower (average 71%; range 54-88%). Survival over subsequent years and over sites varied greatly but three populations maintained high survival. In spring 1987, most transplants at one site were harvested by collectors; tree-fall killed many atanother; and flooding killed many at a third.
Overall, maintenance of adequate soil moisture was the most important factor governing survival and growth; light availability had little influence. High soil nutrient levels appeared to help maintain bulb growth. These results suggest that A.tricoccum may grow under open conditions for propagation purposes, unlike wild populations which grow under forest canopies.
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