Successful reintroductions of the endangered long-lived Sargent's cherry palm, Pseudophoenix sargentii, in the Florida Keys

Published source details Maschinski J. & Duquesnel J. (2007) Successful reintroductions of the endangered long-lived Sargent's cherry palm, Pseudophoenix sargentii, in the Florida Keys. Biological Conservation, 134, 122-129.
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Summary

Sargent's cherry palm Pseudophoenix sargentii is a slow-growing, long-lived palm native to the Caribbean Basin. The species is listed as Florida endangered, and as Caribbean populations are also declining, it is IUCN listed as regionally endangered and globally vulnerable. Throughout its restricted range it grows predominantly on coastal limestone or dune sand over limestone in seasonally dry forest, tropical hammock, and coastal scrub. P.sargentii has reached reproductive maturity in cultivation (where supplemented with water and/or fertilizer) within 14 years, but wild individuals take much longer to reproduce. The 1991-1994 reintroductions to 13 Florida Keys sites and subsequent monitoring represent a long-term effort to conserve the species. To assess reintroduction success, population demographics were compared at sites with and without reintroduced plants.

Study areas and palm surveys in the Florida Keys: In the USA, historically, Sargent's cherry palm populations (a few to 200 plants) were known from three islands (Sands, Long and Elliot) in the Florida Keys. In 1950, 28 adult palms were found on Elliott Key, and in 1958 three were discovered on Long Key. A 1991 survey revealed that the palm was extirpated from Sands and Long Keys; on Elliott Key 47 plants persisted, all in Biscayne National Park.

Reintroductions: In an attempt to ensure survival of the US population of the palm, Fairchild Tropical Botanic Garden (FTBG) and Florida Department of Environmental Protection (FDEP) scientists conducted reintroductions using nursery grown plants (1991-1993) to 13 locations on these three Keys. Introduced plants were propagated at FTBG from seeds collected from Elliott Key. A total of 265 palms were transplanted:

Elliott Key - rockland hammock, 6 sites, 63 palms planted 1991-93;

Long Key - top of coastal berm, 2 sites, 102 palms planted 1991-94; landward side of coastal berm, 3 sites, 21 palms planted in 1991; rockland hammock, 2 sites, 79 palms planted 1991/94;

Sands Key - landward side of coastal berm, 3 palms planted in 1991.

There were no descriptions of specific microsites were palms grew historically at Elliott or Sands Keys, but palm stumps revealed some locations on Long Key. In addition, populations in the Yucatan Peninsula (Mexico) grow in all microhabitat types selected.

Planting took place in May through July (i.e. wet season with rain fell daily). Rockland hammock planting required picks, shovels and steel bars to dig holes. A 50:50 mix of high organic nursery soil and native soil and leaves was used to back-fill holes for the largest transplants (in 3 or 10-gallon containers). All plants were watered at time of transplanting, but not thereafter. After observing heavy herbivory on plants <1.5 m tall on Elliott and Long Key, transplants on Long Key <4-years old were caged. Cages were removed as individuals reached 1.5 m in height. After 1991, no planting on the landward side of berms was undertaken due to 100% mortality of transplants in this microhabitat.

Monitoring: Prior to and following introductions all palms were monitored. The following were recorded: height to tallest rachis (main stem); diameter at breast or crown height; number of leaves; presence/absence of growth spike; survival; health; presence of herbivory; chlorosis and/or overgrowth by surrounding vegetation. In some years not all individuals were visited and measured on Elliott Key, on Long Key all individuals were monitored yearly. The three palms introduced to Sands Key all died in the year of planting.

Wild palm population: In 1991, 47 individuals were recorded at the wild Elliott Key locality; in 2000, there were 221 plants; by January 2004, 302 plants, mostly small juveniles. The wild population has had good survival from 2000–2004 (93%). Growth was also positive (λ = 1.013). Recent wild population growth is attributed to good seedling recruitment and removing the greatest threats (e.g. herbivory; no details given in original paper).

Reintroductions: Of the 265 palms planted from 1991-1994, 115 (43%) were still alive in 2004, thus increasing total plants in the wild by 27%. Reintroduced plants had faster maturation rates, improved population age structure, and enhanced population growth (λ = 1.032).

Survival varied with transplant year (e.g. 1991 was a poor year due to a hurricane), microsite (all 24 palms planted on the landward side of berms quickly died; rockland hammocks and the tops of berms had greatest plant growth and survival), and transplant size (large plants survived better).

Failures in 1991 and in some habitats indicate a need for a continued multi-site approach to reintroductions, which will also serve to buffer against stochastic losses (e.g. due to hurricanes). No reintroduced plants are yet reproductive (plants may require >30 years to mature) thus continued long-term monitoring is required to assess whether the populations are self-sustaining.

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http://www.sciencedirect.com/science/journal/00063207