Observations on the understory climbing fern, Polybotrya pubens (Dryopteridaceae) in a Peruvian rain forest
American Fern Journal
1991
Journal Article
81
2
63-67
Parque Nacional del Manu Plants Vascular plants Pteridophytes ferns abundance Polybotrya pubens Pteridophyta vines distributions Madre de Dios Bibliography
The abundance of Polybotrya pubens measured in this study was the same as that found on a 10 by 20 m plot located about 0.5 km away (0.5 plants/m-2; Young and Leon, 1989). The percentage of climbing individuals found during the present study, however, was even less than that found previously (15% versus the 25% of Young and Leon, 1989). Only rarely do P. pubens individuals in the study area reach situations where they can potentially produce spores. The availability of suitable support elements for climbing was a limiting resource for the studied population, as was the case for lianas in Panama (Putz, 1984). The great number of individuals with short rhizomes suggests high mortality or slow growth during the terrestrial phase of the sporophyte's life. Only a few of the climbing individuals clearly reached their trees after begining growth on the ground, and these apparently germinated by chance much closer to a tree than the average nonclimber. Rhizome growth of Polybotrya pubens, as inferred by examination of rhizome form and characterized by extension in unpredictable directions, seemed well suited to help nonclimbers encounter a support. However, once the fern was climbing, it often doubled back on itself. Vines locating trees by growing towards dark forms (i.e., skototropism; see Strong and Ray, 1975) might face a similar dilemma in that growth that helps to locate a climbing support might act to prevent further upward growth once the support is located. Despite the ability of Polybotrya pubens' rhizome to change its angle and orientation of growth, it appears that the potential for reproductive success was due mostly to unpredictable factors, such as the germination site of the spore and local tree spatial patterns and dimeters. Polybotrya pubens is restricted to mature forest, perhaps because it requires large trees to climb, in addition to requiring the relatively stable microenvironment of the tropical rainforest understory. Treefalls and regrowth vegetation have much more extreme environmental conditions (e.g., Chazdon & Fetcher, 1984) and offer an array of smaller-diameter support elements to climbing plants. To expand upon these observations, data are needed on the rates of growth of climbing and nonclimbing P. pubens, and the length of time nonclimbers can persist on the forest floow without reaching suitable trees to climb.