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Estimating the magnitude of decline of the Florida torreya (Torreya taxifolia Arn.)

Biological Conservation

By:
, , and
DOI:10.1016/S0006-3207(00)00008-2

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Abstract

Torreya taxifolia is a coniferous tree that is endemic to the 35 km stretch of bluffs and ravines along the east side of the Apalachicola River in northern Florida and adjacent southern Georgia. This formerly locally abundant tree declined during the 1950s and 1960s as a result of disease and is currently on the US Endangered Species list. For sparsely distributed species it can often be difficult to determine both current and historic population sizes. Historical descriptions of the distribution (203 km2) and relative abundance (14.2% of dominant ravine trees) of T. taxifolia are used along with current measures of forest structure to estimate the pre-decline population density (30 trees/ha) and size (∼0.3–0.65 million individuals). Survey information from five extant stands is used to estimate current population size (∼500–4000 individuals). The surveys were conducted in areas with known high tree densities such that a simple extrapolation to the entire distribution would produce a gross over-estimate of population size. We therefore use a variety of assumptions to produce a range of estimates for total population sizes. Regardless of the particular model, our estimates suggest that T. taxifolia has lost at least 98.5% of its total population size since the early 1900s. We discuss these results in relation to the potential difficulties likely of restoring sustainable populations of this species.

Additional publication details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Estimating the magnitude of decline of the Florida torreya (Torreya taxifolia Arn.)
Series title:
Biological Conservation
DOI:
10.1016/S0006-3207(00)00008-2
Volume:
95
Issue:
1
Year Published:
2000
Language:
English
Publisher:
Elsevier
Contributing office(s):
Western Ecological Research Center
Description:
8 p.
First page:
77
Last page:
84