PS 66-105
The effect of microhabitat conditions on the growth and flowering of Listera australis
The biology of the Orchidaceae family of vascular plants is particularly compelling due to the reliance of orchids on both above- and belowground interactions with other species. This characteristic makes orchids an excellent indicator of ecosystem condition yet a challenging group to conserve and manage effectively. The present study focuses on the habitat and ecology of Listera australis, Southern Twayblade. L. australis is distributed across Texas and the Southeast United States, the Mid-Atlantic and Northeast, and into Quebec and Ontario. The plant is listed as rare in New Jersey and as threatened or endangered in many other states. Though the number of occurrences of L. australis is low, the plant is often locally abundant. Little is known about its ecology beyond a general sense of plant community type. To establish baseline data about the species and begin to consider larger questions about its population dynamics, the current habitat of the orchid in NJ was considered in terms of: forest cover, herbaceous species cover, and midday light conditions (PAR, photosynthetically active radiation) at the time of flowering. The number of individual plants, the number of flowers per stalk, and plant height were compared between three distinct communities.
Results/Conclusions
L. australis grows in moist, acidic soils and in sparsely to densely forested areas. Three habitat types were identified: peat bogs dominated by Atlantic white cedar (Chamaecyparis thyoides); transitional shrub lands dominated by mountain laurel (Kalmia latifolia); and pitch pine (Pinus rigida) uplands. Though the number of plants in peat bog plots was 6 times higher than that in shrub land and 2.5 times higher than the number in uplands, plant height and flower number followed a different pattern. Average plant height was 11.7 ±1.2 cm in shrub lands, 11.1 ±2.9 cm in pine forests, and 10.5 ±2.1 cm in cedar swamps. The average number of flowers per plant was 13 in pine forests and 10 in both shrub lands and cedar swamps. L. australis prefers partly to mostly shady locations. No orchids were found in locations where mid-day PAR exceeded 600 µMol/m2/s. In partly shady locations – 1-4 orchids per point – PAR ranged from 173 to 480 µMol/m2/s, with an average of 308 µMol/m2/s. PAR in mostly shady locations – 3-5 individual plants – ranged from 75 to 229 µMol/m2/s, and averaged 158 µMol/m2/s. The tolerance of L. australis for variable microhabitat conditions may influence short-term population dynamics in NJ.