Torreya taxifolia : case study of an endangered tree species

1. Torreya taxifolia: case study of an endangered tree species Dr. Sharon Hermann hermasm@auburn.edu

2. Primary interest lecture: Case History of endangered tree Torreya taxifolia • Time line • Issues suggested to be related to decline • Associated research • Secondaryinterests: • Rewilding • Assisted migration

3. Torreya taxifolia • Common name Florida Torreya • Also Stinking Cedar, Stinking Yew, Gopherwood, Polecat wood, Savin • Evergreen, dioecious, mid-size (15m) • 7 species in genus (1 in California) • Pre-pleistocene range large, (based on fossil evidence) • Recent range: one of the smallest for a tree • ~ 200-400 sq km • ~ 35 km stretch east side of Apalachicola River • Portions of 2 counties in Florida & 1 in Georgia

4. Range of Torreya taxifolia Florida torreya described as the most endangered tree species in continental United States. Today, number in wild = ~ 1,500; none* reproductive.

5. Hot spots of biodiversity Range of Florida torreya

6. At torreya sites, hills rise 50+ m above small streams (over time, streams result in formation of steepheads) Tallest bluffs in torreya range rise ~ 100 m from the Apalachicola River. Low hardwood forest is beech, magnolia, and oak with mesic species (needle palm). Upland habitat is drier, open canopied longleaf pine forest (naturally maintained by fire).

7. TORREYA TIME LINE From European settlement time, trees cut for shingles, fence posts, Christmas trees (tops), fuel for boats, etc. 1840 HB Croom “discovers” Florida Torreya 1870s Pilgrimages & reminiscences (Asa Gray paper) 1884 Gov report suggests that species could go extinct (based on range?) 1900’s Observations reported on species habitat and distribution 1914 Harper estimates tree densities

8. TORREYA TIME LINE Prior to ~ 1950 • Many adult Florida torreya have been cut in ravines • All longleaf pine have been clearcut in uplands • Extensive site preparation have occurred • Planting of loblolly pine plantations attempted • Most wildland fires in uplands suppressed • Apalachicola River dammed for a reservoir • Torreya trees planted at Biltmore Estate (NC) & McClay Gardens (FL)

9. TORREYA TIME LINE 1954 no obvious problems noted by Kurz 1955-60? presumed dramatic decline but no data 1962 “destined for extinction” says Godfrey and Kurz in Science (1962) 1967 Stem and needle blight pathogensreported by Alfieri et al. (1967) 1970s no wild adults (fruiting) observed 1984 federally listed as endangered

10. TORREYA TIME LINE 1987 Arnold Arboretum initiated growing trees from cuttings (takes 5+ yrs to grow upright) 1993 1st field data published 1998 Georgia PCA out- planting in “Safeguard Program” 2004 “Torreya Guardians” formed;considering rewilding and assisted migration

11. Field research begun in 1988 (Schwartz and Hermann) • Estimate populations prior to decline • Examine status of populations on public land • Model population extinction • Consider pathogen data: biotic • Decide hypotheses valid but has little support • Environmental induction hypotheses: abiotic • Moisture and/or temperature stress (dam, climate) • soil moisture, temperature, rel humidity, light • Changes in soil chemistry (forestry site prep) • Fire suppression (effect of smoke)

12. Populations on public land (Schwartz & Hermann 1993a, 1993b; Schwartz et al 2000a, 2000b) • Estimate current numbers • Monitor change over time (<10yr) • Estimate historic numbers (Harper 1914 & witness tree data) • Project population changes

13. Need to determine amount of area in suitable habitat. Field data indicate torreya currently not found in ravines >3.5 km from river By 2000, > 1% of original number Estimates based in part on relative densities extracted from Harper (1914).

14. In Apalachicola ravines, < 100 years ago adult Florida torreya trees were • As common as beech • ~ ½ density of American magnolia • 7th most abundant tree in ravine forests  locally Florida torreya was NOT RARE

16. Model population changes based on various measures of survivorship and growth

17. Results: modeling time to population extinction

18. Assumption has been pathogen(s) caused decline but need to review previous data (identifications) • Until recently, most (all?) identified fungal pathogens associated with secondary infections • Decide hypotheses valid but little past support • Recently, have done challenge tests on cuttings in the shadehouse • Resulting symptoms are consistent with Pestalotiopsis sp. infections on conifers • Begun to fulfill requirements of Koch’s postulate …. but need more work!

19. Explored environmental induction hypotheses • Changes in soil chemistry (forestry site prep) • Moisture and/or temperature stress (dam, climate) • soil moisture, temperature, relative humidity, light • Fire suppression (effect of smoke) No temporal changes: • Soil chemistry or moisture factors • Temperature or relative humidity

20. Light ? • No information on canopy structure or light environment prior to decline • Physiological research suggests that Florida torreya not totally the shade-loving tree that was described in early literature • Field research VERY preliminary Fire ? Preliminary indications of effect of lack of fire: experimental treatments demonstrated that smoke could decrease the number of fungal spores on juvenile torreya

21. Climate change is still viewed as major factors in the decline of Florida torreya by some conservation groups, although to date, no data support the idea • Research on pathogens suggests that many types associated with torreya are likely to be secondary infections. However preliminary studies have identified a likely pathogen. • Decrease light may play a role

22. Lack of recovery from decline may be unrelated to what triggered decline • May be multiple reasonable hypotheses that help explain why Florida torreya has yet to recover from 1950’s crash • Stressors may prevent recovery • Change (decrease) in light needs study • Genetic bottle neck may also play a role

23. Does disease and/or climate change explain what caused the death of all reproductive adults??? • Tree ring work underway • But preliminary examination hasn’t indicated growth pattern differences • Stress related to changes in uplands and local decrease in light coupled with other factors (pathogen?) may be plausible hypothesis • “Garden” tree seed are viable • Additional research much needed but funding limited

24. “Rewilding” • Reconstituting “natural” landscapes • New term that seems to encompass and summarize many previous ideas • Major focus is often on recreating natural processes and landscape structure • Rewilding America by D. Foreman (2004)

25. “Ecological Wounds”(Rewilding America by D. Foreman, 2004) • Direct killing • Habitat destruction • Habitat fragmentation • Introduction of exotic species (including diseases) • Pollution • Loss of natural processes (ecological & evolutionary) • Climate change

26. “Assisted Migration”(term coined by Keel 2004) “… problems of rapid human-caused climate change, landscape fragmentation, and habitat destruction will put many plant species at risk of extinction. For plants to survive climate change they must either adapt … or track suitable habitats as the climate changes, that is migrate. For plant species that can not adapt, landscape fragmentation and habitat destruction may prevent migration, and human intervention in the form of assisted migration will be necessary to prevent extinction.” (Keel 2004)

27. Georgia Plant Conservation Alliance Project “Safeguarding Torreya taxifolia” • Initiative to rescue and/or maintain Georgia Torreya • Some concerns that prompted the initiative include: • Originally probably small proportion of range in Georgia • Current natural site is public but without much protection • Belief that climate of new far north sites would be more beneficial for growth and/or resistance to disease • Cuttings of Georgia-only genotypes grown at ABG • However no indication that GA plants differ from FL ones • Recent out-planting in North Georgia on state land

28. Note: Georgia project moves Florida torreya north of it’s natural (recent) range • Atlanta Botanical Garden • State wildlife management lands* • Keel (2004) formally proposed concept of assisted migration for some orchid species • There are individuals and informal groups who have carried out similar, but unofficial, assisted migration actions for their favorite species (cf. Venus-flytrap)

29. Barlow et al. (2004) and “Torreya Guardians” (torreyaguaridians.org) have expanded idea • Consider distribution of Florida Torreya in “near time” (< 15,000 YBP, human influence) as well as “deep time” (> 15,000 YBP, pre-human influence) • Relocation becomes “repatriation of a once-native” • Propose considering assisted migration “a form of rewilding that uses near-time or deep-time baseline for determining native range” (Barlow et al. 2004)

30. Some adult trees in NC gardens regularly produce fruit … used to promote idea of assisted migration Why conservation efforts for Florida Torreya should not include assisted migration(ideas developed in collaboration with Schwartz 2004) A need to escape disease not fully supported by data • Little support that extant plants are overly susceptible to a specific disease • Agent for original decline (pre-1960) not determined • Some plant NC Torreya have died or appear sick

31. More ideas on why conservation for Florida Torreya shouldn’t include assisted migration • Unknown effects of new species on recipient ecosystems … all exotic species are native somewhere (granted, Torreya doesn’t have traits that suggest it is likely to be a problem) • Don’t plantings in botanical gardens have most (all?) of the benefits of assisted migration without most (all?) of the potential negative side effects?

32. !!! NEWS FLASH !!! • Not all in situ remediation actions tried for torreya • thinning to improve light conditions for in situ planting • Idea of rewilding (assisted re-introduction) has been dramatically expanded; has been suggested for some large vertebrates once “native” to N America • Donlan et al. (2005) propose “restoring animals that disappeared 13,000 years ago from Pleistocene NA” • Commentary in Nature suggests using species of wild horses, camels, cheetahs, elephants, lions and tortoises • See Barlow and Martin 2005 and Schwartz 2005 for two views on “assisted migration” for Torreya