Ecology and Post-Fire Recovery of Cladonia Perforata, an Endangered Florida-Scrub Lichen

For. Snow Landsc. Res. 75, 3: 339–356 (2000) 339 Ecology and post-fire recovery of Cladonia perforata, an endangered Florida-scrub lichen Rebecca Yahr1 Archbold Biological Station, PO Box 2057, Lake Placid, FL 33862, USA 1 Current address: Duke University, Department of Biology, Box 90338, Durham, NC 27708, USA [email protected] Abstract Cladonia perforata is an endangered terrestrial lichen which co-occurs with many fire-adapted species in central Florida scrub. Prescribed fire is a common tool in the maintenance of natural landscapes and of high diversity within some plant communities, but its role in lichen communities is little studied. A prescribed fire at Archbold Biological Station on the southern end of the Lake Wales Ridge impacted three separate populations of C. perforata in July 1993, leaving only remnant unburned patches scattered among completely burned areas. This study was undertaken to investigate the rate and mode of post-fire recovery of C. perforata in comparison with co-occurring lichens.Detailed GPS maps of individual patches of this lichen were made in January 1997 and com- pared with those made in August 1999. In addition, abundance of all lichen species was monitored yearly during the winters of 1997–1999. Although all of the other terrestrial species in the same habitat recovered from juvenile stages, no juvenile forms of C. perforata were recorded. The area occupied by C. perforata increased by more than 200% , on average, over the three sites. However, population growth (for all species) has so far been too slow to be documented and has not changed markedly over this period.Therefore, dispersal of unburned C. perforata into burned areas may be the primary method of short-term population recovery. Keywords: fire, recovery, Cladonia, ecology, Florida scrub, endemic 1 Introduction Fire is a widely studied natural disturbance that is critical in defining plant and animal communities (CHRISTENSEN 1985) since it reduces ground cover, spurs productivity and repro- duction, and maintains open space suitable for colonization (PICKETT and WHITE 1985, WHELAN 1995, MENGES and HAWKES 1998). Changes in plant community composition and species distribution patterns are known to vary with fire intensity, scale of disturbance,and time since disturbance (WHITE 1979, CHRISTENSEN 1985, MENGES and HAWKES 1998). In fire-maintained Florida scrub, post-fire vegetation recovery patterns vary with scrub type (MENGES and HAWKES 1998) and with species (MENGES and KOHFELDT 1995),although most vascular species recover pre-fire abundance after only a few years following fire. Cladonia perforata A. Evans (Cladoniaceae) is an endangered terrestrial lichen which occurs in this fire-prone and fire-managed landscape. Florida scrub is populated by other more common Cladonia species and by many other endemic species with specific and varying niches in relation to fire.Historically in the south-eastern United States,fire has been an important part of the ecosystem process in scrub (MYERS 1990) and is increasingly used as a management tool for restoration and habitat maintenance. Yet, the post-fire rate and mode of recovery of these lichen species is unknown. 340 Rebecca Yahr Many members of Florida scrub communities, ranging from Florida Scrub-Jays (FITZPATRICK et al. 1994) to invertebrates (DEYRUP 1989) to herbaceous plants, are dependent on periodic fire for habitat maintenance (reviewed in MENGES 1999). In the Florida scrub, many endemic herbaceous species rely on fire for the creation and maintenance of open sand gaps (JOHNSON and ABRAHAMSON 1990, HAWKES and MENGES 1996), though optimal fire- return intervals vary with species (MENGES 1999). In scrub dominated by Florida rosemary (Ceratiola ericoides Michx.), at least three of these species, Hypericum cumulicola (Small) P. Adams, Eryngium cuneifolium Small, and Polygonella basiramia (Small) G.L. Nelson & V.M. Bates have peak population sizes within the first ten years following fire.These species recover from seedbanks or occasionally resprout (HAWKES andMENGES 1995,MENGES andKIMMICH 1996, QUINTANA-ASCENCIO et al. 1998). They decline more or less rapidly in the following years as favorable microhabitats change, with open gaps giving way to increasing shrub cover. In contrast,the dominant shrub,Ceratiola ericoides, does not reach reproductive maturity until at least seven years after fire (JOHNSON 1982), so that it is lost from sites with rapid fire-return intervals. The life-history of lichens in relation to fire has been little studied. Lichens have no perennating underground structures or other mechanisms which allow them to tolerate fire, which means fire either kills or severely damages them (JOHNSON and ABRAHAMSON 1990, SCHULTEN 1985), and recolonization is solely via dispersal from unburned sources. In addition, vegetative growth is quite slow (TOPHAM 1977), and the development of dense, dominant lichen mats probably takes several decades. The post-fire recovery of lichen populations has been investigated in boreal and north-temperate areas and can be generalized as follows: appearance of Cladonia species within the first five years, becoming dominant approx.20–25 years following fire and followed by replacement with per- sistent, stable Cladina mats (AHTI 1959, MAIKAWA and KERSHAW 1976, MORNEAU and PAYETTE 1989). In Florida scrub, MENGES and HAWKES (1998) have noted elements of a similar progression. Cladonia perforata occurs in a smaller percentage of available habitats than do other terrestrial Cladonia species of Florida scrub. It is patchily distributed in open gaps in rosemary scrub, a xeric vegetation type characterized by abundant open space (“sand pine scrub, rosemary phase” sensu ABRAHAMSON et al. 1984). Fires in the southern Florida peninsula, as well as hurricanes along the Gulf Coast,represent natural periodic disturbances that may be important in maintaining this open habitat structure for C. perforata and other species dependent upon gaps in the shrub canopy. Natural openings in rosemary scrub can persist for decades in some sites, though shrub and tree canopies and litter tend to slowly increase, eliminating the xeric bare sand gaps important for herbs and some lichens (HAWKES and MENGES 1996, MENGES and KOHFELDT 1995). Natural fire return intervals are estimated at between 10–100 years in this habitat (MAIN and MENGES 1997). During recent decades, natural fire has been replaced by either fire suppression or prescribed burning. The consequences of fire suppression include the loss of open spaces,which presumably results in the loss of this lichen.In addition, the effects of habitat fragmentation can compound changes due to fire suppression by altering fire frequency or intensity.Where prescribed fires replace natural fires,land managers must determine how to implement fire as a landscape-scale management tool to maintain diversity and encourage persistence of species and communities of interest. Three of the known populations of C. perforata were burned in recent years, and, in all cases, small remnant populations of the lichen have been found. For this study, populations are defined as discrete occurrences of C. perforata, limited by the extent of local habitat.The boundaries of each are easily discerned in the field. For. Snow Landsc. Res. 75, 3 (2000) 341 2 Objectives This project was undertaken to characterize post-fire population recovery and growth, inter- specific interactions, and microsite preferences of the terrestrial Cladoniaceae in central Florida, especially C. perforata. Post-fire population recovery includes the mechanisms of establishment or the recolonization of burned sites and rate of population growth. A combination of the data on population spread and on dispersal limitations can be used to refine habitat requirements and to estimate the relative threats and risks of local extirpations.These insights will offer confidence in the use of prescribed fire or other management tools to promote the species in a landscape. In addition, abundance estimates measured only a few years after a fire will provide a baseline for studies of population growth. 3 Methods 3.1 Species studied Cladonia perforata, an endemic lichen of Florida sand pine scrub (BUCKLEY and HENDRICKSON 1986, EVANS 1952), is listed by the U.S. Fish and Wildlife Service (1989) as endangered.About 30 populations are distributed across three distinct regions,the north Gulf Coast, the Atlantic Coastal Ridge, and the Lake Wales Ridge. The latter probably supports about two thirds of all known sites. Only a few sites throughout its range are protected, while the rest are threatened by some combination of habitat loss due to development or agricultural conversion, human disturbance, improper management, and hurricane washover (USFWS, 1989, Ann F. Johnson and Dennis Teague, pers. comm.). Discrete populations are typically found as isolated patches on knoll tops of rosemary scrub patches, which form discrete habitat islands separated by intervening dense oak and palmet- to scrub.As vegetation develops after fire on these rosemary scrub patches,the shrubs become more dense, and bare sand gives way to increased litter and lichen cover. Nevertheless, roughly 30% of the bare sand persists for more than 25 years (HAWKES and MENGES 1996). In the surrounding lower-elevation vegetation, the open space drops to less than 10% in less than three years after fire (YOUNG and MENGES 1999). In addition to the rarity imposed by temporal variation in the availability of colonizable sites, dispersal

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