At the Brink of Extinction
"Paleoecology and the Assisted Migration Debate: Why a Deep-Time Perspective Is Vital" online essay by Torreya Guardian Connie Barlow, February 2011.Connie Barlow (with assistance from Russell Regnery) has posted a short, 11-point summary essay that aggregates the data and develops strong scientific reasoning in favor of assisted migration for Torreya taxifolia. The essay also advocates a shift in the foundational paradigm from assuming 1491 is the proper time-standard for assessing native range to a "deep-time" perspective grounded in a paleoecological understanding that native ranges for all plants in temperate latitudes of the Northern Hemisphere have undergone substantial altitudinal and/or latitudinal migrations that have tracked changes in climate during the past several million years of Pleistocene glacial and interglacial cycles.
In the 1950s, Torreya taxifolia suffered a catastrophic decline, the ultimate cause of which is still unexplained. By the mid-1960s, no large adult specimens which once measured more than a meter in circumference and perhaps 20 meters tall remained in the wild, felled by what seemed to be a variety of fungal pathogens.
Today, the wild population persists as mere stump sprouts, along the Apalachicola River of the Florida panhandle, cyclically dying back at the sapling stage, such that seeds are rarely, if ever, produced. T. tax thus joins American chestnut in maintaining only a juvenile and diminishing presence in its current range.
Access in PDF the official USFWS ESA plan (updated summer 2010) for managing this endangered species.
Access in PDF a 2013 paper (by L. Vargas and V. Negron-Ortiz) on soil fungi and potential root pathogens of T. taxifolia in its historically native range.
LEFT: The Apalachicola River in Florida's Torreya State Park (January)
The International Union for the Conservation of Nature (IUCN) monitors endangered species via its IUCN Red List of Threatened Species. An update of its "critically endangered" Torreya taxifolia IUCN listing in 2011 includes these entries:The estimated 98% decline in mature individuals within the last three generations means that Torreya taxifolia meets the criteria for Critically Endangered under Criterion A2. The actual causes of the decline (the death of individuals and the reproductive failure associated with infection from a range of pathogens) is not well understood: recent surveys indicate it is continuing. The decline may be reversible in the future if those causes can be identified and controlled.
Restricted to a few ravines along the east side of the Appalachicola River in northern Florida and southern Georgia. Its total extent of occurrence is estimated to be about 200 km2 with an area of occupancy under 50 km2.
The current population is estimated to be between 500 and 600 trees. Of these, less than 10 are known to produce male or female cones (this species is dioecious). Individuals persist as stump sprouts. Before the start of the decline in the early 1950s, the population was estimated to have been more than 600,000. Since then there has been a decline of more than 98%.
Torreya taxifolia occurs along limestone bluffs on the Appalachicola River in a region with a warm and humid climate, occasionally influenced in winter by cold waves from the north that dip temperatures below the freezing point. It grows mostly in the shade of wooded ravines and steep, N-facing slopes under canopy of Fagus grandifolia, Liriodendron tulipifera, Acer barbatum, Liquidambar styraciflua, Quercus alba, and occasionally pines (Pinus taeda, P. glabra). Often these woods are hung with vines (e.g. Smilax spp., Bignonia capreolata). Another rare conifer, Taxus floridana, occasionally grows with Torreya taxifolia.
The most significant current threat to T. taxifolia is the continued reproductive failure associated with fungal pathogens. Individuals do not reach reproductive size before being top-killed. Recent research has identified a previously unknown species of Fusarium that may be the cause (J.A. Smith pers. comm. September 2010). Rubbing by deer is an additional problem as it causes physical damage and may also be a vector for disease transmission. Changes in landuse and fire regimes in surrounding areas along with changes in hydrology and soil chemistry linked to the construction of dams may also be implicated in its historical decline. Augmentation plantings within the natural range have proved to be susceptible to infection: no naturally resistant clones have been identified to date. Population viability analyses indicate that extinction within its native range is inevitable. Below: Sample graphic from the IUCN Red List page for Florida Torreya.
Jason Smith at the University of Florida is lead author of several papers probing the pathology of disease organisms contributing to the demise of Torreya taxifolia in its historically native range. Click the image right for a pdf of a detailed analysis of fungal pathogens (published in 2010).
In 2013, Smith was one of 5 coauthors, publishing in the journal Mycologia about the newly identified and named pathogen Fusarium torreyae. ABSTRACT: During a survey for pathogens of Florida torreya (Torreya taxifolia) conducted in 2009, a novel Fusarium species was isolated from cankers affecting this critically endangered conifer whose current range is restricted to northern Florida and southwestern Georgia. Published multilocus molecular phylogenetic analyses indicated that this pathogen represented a genealogically exclusive, phylogenetically distinct species representing one of the earliest divergences within the Gibberella clade of Fusarium. Furthermore, completion of Koch's postulates established that this novel species was the causal agent of Florida torreya canker disease. Here, we formally describe this pathogen as a new species, Fusarium torreyae.
Editor's note: Investigations of soil and root microbes, fungi, and potential pathogens sampled from distressed T. taxifolia specimens in this tree's climatically challenged "native" range will almost surely be devoid of beneficial mycorrhizal root fungi that would have supported healthy populations in the early 20th century. Urgently recommended are studies of mutualistic root fungi discovered in seedlings sprouting under healthy mature T. taxifolia trees in North Carolina. In 2013, Torreya Guardians serendipitously made that discovery; click here for Torreya Guardians observations of beneficial mychorrhizal fungi on NC seedling roots of T. taxifolia.
Elizabeth A. Atchley in 2004 wrote her master's thesis on this topic: "The Effects of Habitat Alterations on Growth and Vitality of Torreya taxifolia Arnott in Northern Florida, U.S.A". It is an excellent background document, and can be accessed online in PDF. Page 12 includes,"It is also possible that current populations are climatic relicts that once had a more northerly range, but during the last glacial the advancing ice pushed them south where they mixed with the temperate deciduous forest species. It is possible that when the ice retreated, the Torreya did not reoccupy their northern range and could only survive in cool, moist refuges such as evergreen mountain forests, ravines, and some riverbanks. This is believed to be the case for Torreya taxifolia.
Torreya expert Mark Schwartz observes:"There are probably fewer than 1000 individuals extant in the current distribution and the numbers are dwindling. At last count, there is a single known individual that is producing seeds in the wild (personal observation). Aside from this one individual and the approximately 8 seeds it has produced, there has been no observed seedling recruitment for at least 20, and probably 40 years."
In June 2009, a paper published in the Proceedings of the National Academy of Sciences contained supplementary information that detailed the plight of Florida Torreya. Richardson et al. 10.1073/pnas.0902327106 wrote:
Torreya taxifolia (Cephalotaxaceae) is a dioecious coniferous tree that is endemic to the bluffs that extend 5Ð10 km eastward from the Apalachicola River for approximately 35 km in northern Florida, extending less than a kilometer into Georgia. During the late 1950s and early 1960s, all adult trees throughout its range were killed as a consequence of a pathogen outbreak. The current population is likely not 1,500 individuals, likely seeds and seedlings that were viable at the time of the decline. During the past 40 years, there has been a single tree that has been observed to have matured into a seed-bearing adult. It produced 2 seeds. This individual is now dead, and the seeds produced are presumed dead as well. The agent of the decline is unknown but is thought to be a fungal pathogen. The current rate of decline is slow. Estimates of growth and mortality data suggest that it will be at least a century before the population goes extinct in the wild. Cuttings from 150 trees are currently grown in botanic gardens.
More recently, 2 efforts have begun for the conservation of this species. Torreya taxifolia has been planted in North Carolina in an attempt to establish populations in that region (http:// www.torreyaguardians.org/). This effort was done as an indirect response to climate change. The species is in declining in its native range with no sign of recovery. Proponents felt that this species 'belongs' in the region where they relocated it. They also feel that this intervention is the best chance for the species to survive, given its condition in its native range.
Specimen No. 1
Reclining Specimen #1 at Torreya State Park in northern Florida
Bark damage near base of Specimen No. 1. (Notice browsed suckers to right.) Specimen No. 2
Specimen #2 near creek (with bald cypress knees visible), amid American holly tree, beech, evergreen magnolia), January.
Evidence of pathogens on foliage (left) and stem (right) on Specimen No. 2
Access a webpage for a PHOTO-ESSAY BY GLENN RILKE of his periodic visits to surviving Torreya trees in historically native range in Torreya State Park (panhandle of Florida).
"Coevolution of Cycads and Dinosaurs" paper by George E. Mustoe, The Cycad newsletter, March 2007.Barlow and Martin 2004 proposed that Torreya taxifolia might have gotten trapped in its peak-glacial pocket reserve (in northern Florida) for lack of its coevolved seed disperser, and thus was unable to geographically respond to the warming interglacial climate. The above paper suggests that another taxon of gymnosperm that thrived (along with genus Torreya) in the Jurassic period might have suffered from an inability to easily track climate change when the seed-dispersing dinosaurs died out.
Download in PDF two articles, for and against assisted
migration of Torreya taxifolia, published as the featured
Forum in the Winter 2005 issue of Wild Earth. Download
the pro and con articles separately for printing on standard
size paper. Or, for viewing the 2-article Forum as it
appeared in publication (wide-screen, with all illustrations),
download the "Forum."
FOR assisted migration, by Connie Barlow & Paul Martin
ANTI assisted migration by Mark Schwartz
FORUM (both articles for wide screen)
"Rewilding North America" The 18 August 2005 issue
of the prestigious science journal, Nature contains an advocacy
article that proposes "rewilding" close-kin of some of the
large mammals that went extinct in North America at the
end of the Pleistocene, 13 thousand years ago. By comparison,
the proposal to "Rewilding Torreya taxifolia" looks mild! To access
this amazing article, you can view or download it at
Learn about efforts to SAVE Torreya taxifolia from extinction. Explore a photo-essay of Torreya Guardians REWILDING ACTION in North Carolina (2008).
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