Bioethics@

Pitcher plant

by E.W. Tollner, Kelly Cain, Jim Spain and Roy Dodd

The pitcher plant is an exotic endangered species found in the Georgia and North Carolina mountains. The Nature Conservancy is considering purchase of selected sites for preservation purposes.

Background

The site is on the shore of Lake Chatuge. The pitcher plant thrives in a nitrogen poor soil and needs reasonably open canopy affording some exposure to direct sunlight. The pitcher plant thrives in areas with much sunlight and humidity coupled with protection from high winds. The soil appeared to have a high clay fraction. The plant's competitive advantage stems from an ability to capture and use N from entrapped insects. The plant community is within a zone owned by two property owners ("A" and "C"), shown on the attached sketch. Property "A" is now up for sale. Property "C" has agreed not further to develop the tract and will also not apply nutrients. The canopy is open. A rock outcrop may indicate the presence of an aquitard or aquiclude. The aquiclude limits the deep-rooted species and provide steady water via seepage from nearby hills and mountains (not shown on the sketch). A flowing spring at the drain tile outlet suggested an underlying clay aquitard. The 4 ft deep clay tile drain was installed on this aquitard. The rock feature did not seem to extend over to the drainage ditch, based on quick observation.

Many questions remain about how the plant community arrived at its present state. Ecologists have advanced three theories about how the pitcher plant survived in the site in years past: 1) Burning and cultivation by the native Indian population; 2) native beaver populations and 3) burning by lightning. These theories were tentative at best. The property owner burned the site annually in the recent past. The site was apparently not plowed or otherwise disturbed. This fortuitous burning worked to the competitive advantage of the pitcher plant community. Sorting it out the spatial-temporal scale effects from hydrologic disturbance effects is hard.

There is another pitcher plant community nearby. This community was in a bog type area also. This area was either plowed in the past (by mule) or very near land plowed based on recollection by local people.

Past hydrological alterations: The hydrological alterations began 1941-42 with TVA construction of Lake Chatuge. The plant community lies within the TVA 500 yr easement. The lake to date has never reached this level.

The second major hydrological alteration was the construction of the tile drainage line (depth estimated at 4 ft) and a drainage ditch in 1965 on property "A.." This ditch was recently cleaned. The 30 to 40 ft high trees along the ditch showed it was functional over the period. It is about 150 to 200 ft from the plant community. Assuming the clayey soils in the region have a low Ksat value, the influence of the drain is probably not too great. Capillary fringe would probably add 1 ft or so to the piezometric level. There was a low flow in the ditch welling up from a spring near the tile drain outlet. This spring may indicate a break in the aquitard on which the clay tile was installed, with positive piezometric head underlying the near surface aquitard. The 1965 tile drain was not discharging. If the spring is a recent development, the effect on the surface moisture regime was unknown. The spring could reduce upward water movement through the aquitard by functioning as a pressure relief. A 30 to 40 ft growth of mixed hardwoods exists along the ditch, suggesting a constant presence of water in the ditch. Since the drain installation, owners have managed the adjacent field as an improved pasture, implying occasional N applications.

The third major hydrological alteration was the construction of the 1997 perforated tube drain (estimated depth of 2 ft), coupled with cleanout of the 1965 drain channel. The owner evidently not deepened the channel during cleanout. The 1997 tile was not discharging.

Potential hydrological alterations: An infrequent rising of Lake Chatuge is possible. Climatologists estimated that a 1994 rainfall event was a 500 to 1000-yr rainfall event. The impact of short time (e.g., 1 month or less) flooding on the pitcher plant community is unknown.

Land values in the area indicate the potential of development all around the site. With development will come the possibility of aquifer drawdown due to well installation. More significantly, N levels in the soil may increase due to increased numbers of septic systems. Surface runoff may also increase due to reduced infiltration due to development.

The management of another adjacent property (property "B") is a major unknown. This property seems to exert the dominant up-elevation influence on the pitcher plant community. If the area persists in pasture, surface runoff probably would not substantially increase. An intensification of cattle production could increase surface runoff and N concentrations to the disadvantage of the pitcher plant. It could also increase the groundwater N concentrations.

Questions

  1. Has the hydrology of the lands surrounding the pitcher plant (Sarracenia oreophila) community been altered as to jeopardize the continued viability of the pitcher plant community?
  2. What, if anything, ought to be done to save the pitcher plant? Defend your answer by appealing to normative principles.

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Published by: Office of Biotechnology, Bioethics Outreach
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Last Update 06/06/03