The challenges of restoring rare and endangered plants...

Pyne's ground plum in Rutherford County, Tennessee.A new study in the journal Restoration Ecology explores some of the challenges of restoring rare and endangered plants. When a plant species faces extinction risk, conservationists sometimes take the extraordinary step of trying to establish new self-sustaining populations in the wild. This can ward off extinction by increasing population numbers, promoting genetic variability and restoring population dynamics.

But restoring rare and endangered plants is very challenging and prone to failure. The study looked at a seven-year effort to establish self-sustaining populations of Pyne's ground plum (Astragulus bibulatus) a federally endangered forb endemic to cedar glades underlain by limestone bedrock in the central basin of Tennessee. The researchers wanted to shed light on best practices for restoring Astragulus bibulatus and endangered plant species in general. Establishing new populations of Pyne's ground plum in protected areas is considered crucial to the continued existence of the species. Scientists know of only three populations of the species left in the wild - all on private property within a 20 square kilometer area in Rutherford County.

Project Methods

• Given that the remnant populations of Astragulus bibulatus have very little genetic difference, the project collected seeds from all 3 remaining populations to promote genetic variability in the species.

• Seedlings of Astragulus bibulatus were grown in a greenhouse in 2000.

• Stones River National Battlefield was chosen as the restoration site based on its similar physical and biological characteristics to existing population sites. Five glade areas measuring 200 to 1200 square meters were chosen as the trasplant sites.

•  The seedlings were transplanted in March and September 2001 to test for differences in transplant survival and growth based on season.

Results

The project was able to successfully establish populations in the wild. But ultimately the project failed to establish populations that were self-sustaining. Nevertheless the results will help inform future efforts:

• After 7 years, only 4% of transplants introduced in spring survived compared to 33% survival for transplants introduced in the fall.

•  Transplant survival and growth varied widely among glade sites, despite their close proximity and apparent similarity in habitat suitability.

• Transplants introduced in the spring remained nonreproductive across all years, whereas 18% of transplants introduced in the fall transitioned into reproductive adults.

• Despite the initial success, no transplants flowered after 2004, and no new seedling recruits were observed at any sites after 2005.

• At the end of 7 years, the introduced population consisted of 11 individuals from eight different maternal families that were distributed across four sites. 

 Recommendations for Conservation Practice

 Based on these results, the study offers the following recommendations for future introduction efforts of Astragulus bibullatus and other rare and endangered plant species:

• Transplanting across multiple sites is recommended to hedge against environmental stochasticity.

• The study supports using mixed population sources when introducing a narrowly endemic species into apparently suitable but unoccupied habitat.

• Proper timing of introductions with seasonal climatic conditions is necessary when restoring Astragalus bibullatus, and probably other rare species native to habitats that experience obvious wet and dry seasons.

• Repeated introductions may be needed to buffer new populations from local extinction due to demographic stochasticity.

• Given the dramatic difference between short-term success and long-term viability of the introduced population, sustained monitoring is needed to draw appropriate conclusions on the project success.

 --Reviewed by Rob Goldstein

Source:	Restoration Ecology
Title:	Changes in demographic processes over long time scales reveal the challenge of restoring an endangered plant
Authors:	a) Matthew Albrecht and b) Kimberlie McCue
	a) Missouri Botanical Gardens, Saint Louis, Missouri b) Vanderbilt University, Nashville, Tennesee