UCI Papers & Posters

Prescribed Burning Impacts on Late Successional Species

Peter A. Bowler, Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697-2525, and Richard E. Riefner, Jr., 17554 Vandenberg #14, Tustin, CA 92680.

Abstract. Prescribed burning of coastal sage scrub is often proposed primarily to relieve fire hazard to human property from large fuel loads in old stands. Many academic researchers have made the point that prescribed burning may serve human ends but has little to no to negative "benefit" to the habitat; most say just leave it alone. Westman suggested that the more open canopy of sage scrub could serve as a refuge for understory taxa excluded by closed canopy chaparral, but similarly old stands of coastal sage scrub act as refugia for late successional species such as lichens. In several papers we have recommended preserving old fire cycle stands to act as refuges and sites of inocula to perpetuate late successional epiphytes, many of which qualify for federal and state protection.

The lichen flora of southern California is diminishing and becoming simplified due to many reasons including air pollution, habitat loss, and the effects of increasing isolation and diminishment in occurrence of lichen-rich stands in coastal sage scrub (Bowler and Riefner, 1990; Bowler and Riefner, 1995). These stands are old in terms of the fire cycle, allowing colonization by late successional epiphytes such as lichens. Bratt (1987) documented species losses in fruticose lichens at Point Loma comparing historic with current species richness, and Herre (1936) called for the conservation of lichen habitat which even then was becoming reduced along the coast in a poignant paper entitled "Our vanishing lichen flora." Herre described the loss to development of site after site in a diversity of coastal habitats with which he had direct botanical experience since 1912. While long distance dispersal in lichens occurs, it happens slowly over a far longer time period than inter-fire cycle colonization. The dependency of lichen colonization and species richness upon mosaics of differing age class stands can be seen at age class burn interfaces, where lichens from old stands leak into the edges of adjacent younger (more recently burned) stands. This effect is particularly evident in exceptionally species rich sites such as those along coastal northwestern Baja California, but occur throughout the sage scrub community. Lichens are notoriously patchy, so that not all old stands have good representations of them - thus underscoring the significance of those which do. Sites like San Clemente Island where historic grazing effectively eliminated most corticolous substrates exhibit a depauperate corticolous flora (Bowler and Riefner, 1996), and it is clear that a similar fate awaits late successional lichen species in Southern California coastal sage scrub. Areas which have experienced large burns, such as the Laguna Beach fires of 1993 that created a 40,000 acre "lichen free" hole in distributions, will likely not recover historic lichen species richness. Prescribed burning of remnant lichen-rich old growth would eliminate near neighbor sources of inoculum - and realistically it is not likely that they will persist. Local southern California floras are not well known, and it should be understood that saxicolous (rock inhabiting) and terricolous (soil dwelling) taxa also require local sources from which to draw for colonization. If these are lost, so is the species richness, though it may take many years for a species to actually perish, even in the face of a lack of recolonization. In a sense, death is incremental, and an isolated rock outcrop is like a fragment of a former constellation of subpopulations. An example of a primarily saxicolous local flora in a maritime chaparral stand (Cneoridium dumosa, Salvia mellifera dominants) in Laguna Beach is presented below (Table 1). Maritime chaparral is itself a candidate threatened habitat. At this site thirty-six species of lichens were recorded, including a first record for southern California(Thelomma californicum; Riefner, Bowler and Ryan, 1995).

Table 1. The lichen flora of an old stand of maritime chaparral in Laguna Beach. The site, known as Diamond Crestview, is a relict stand of Cneoridium dumosa, Salvia mellifera, Rhamnus crocea and other characteristic taxa. Voucher collections of nearly all of these taxa are in IRVC.

Acarospora obpallens (Nyl.) Zahlbr. Acarospora schleicheri (Ach.) A. Massal. Aspicilia sp. Buellia halonia (Ach.) Tuck. Buellia oidalea (Nyl.) Tuck. Buellia retrovertens Tuck. Caloplaca bolacina (Tuck.) Herre Caloplaca luteominia (Tuc,) Zahlbr. var. luteominia Caloplaca saxicola (Hoffm.) Nordin Chrysothrix candelaris (L.) J.R. Laundon Cladonia fimbriata (L.) Fr. Cladonia furcata (Hudson) Schrader Cladonia macilenta Hoffm. Cladonia sp. Dimelaena radiata (Tuck.) Hale & Culb. Diploicia canescens (Dickson) A. Massal. Diploschistes muscorum (Scop.) R. Sant. subsp. muscorum Diploschistes scruposus (Schreber) Norman Flavoparmelia caperata (L.) Hale Flavopunctelia flaventior (Stirton) Hale Lecania sp. Lecanora sp. Lecanora caesiorubella Ach. ssp. merrillii Imshaug & Brodo Lecanora campestris (Schaerer) Hue Lecanora muralis (Schreber) Rabenh. Lecanora varia (Hoffm.) Ach. Lecidella stigmatea (Ach.) Hertel & Leuckert Leprocaulon microscopicum (Vill.) Gams ex D. Hawksw. Leproloma membranaceum (Dickson) Vainio Pertusaria sp. Physconia sp. Rinodina bolanderi H. Magn. Thelomma californicum (Tuck.) Tibell Thelomma mammosum (Hepp) A. Massal. Trapeliopsis wallrothii (Florke) Hertel & Gotth. Xanthoparmelia mexicana (Gyelnik) Hale

Examples of late successional epiphytic taxa (Table 2) are such fruticose genera/species as Alectoria, Bryoria, Usnea, Ramalina, Ramalina lacera, Teloschistes exilis, Niebla ceruchis, - as well as many foliose species. N. ceruchoides and N. polymorpha (both saxicolous) are other species with limited occurrences in these coastal habitats. As Bowler and Reifner (1995) reported, conspicuous species present in historic lichen collections from sage scrub such as Ramalina lacera are now rare or extinct in southern California.

Table 2. Late successional indicator species, most becoming increasingly rare, for soil, rock outcrop, and shrub habitats in coastal sage scrub habitats. This list is by no means comprehensive, they are merely indicator species; there are many other species also associated with and characteristic of such habitats.

Terricolous (soil dwelling) Acarospora thelococcoides (Nyl.) Zahlbr. Cladonia thiersii S. Hammer Endocarpon subnitescens Nyl. Mobergia calculiformis (W.A. Weber) H. Mayrh. & Sheard

Saxicolous (rock outcrops) Cypheliuim brunneum W.A. Weber Punctelia punctilla (Hale) Krog Niebla ceruchoides Rundel & Bowler Niebla polymorpha Bowler, Marsh, T. Nash, & Riefner Xanthoparmelia angustiphylla (Gyelnik) Hale

Corticolous (shrubs) Heterodermia erinacea (Ach.) W.A. Weber Heterodermia cf. galactophylla (Tuck.) Culb. Niebla cephalota (Tuck.) Rundel & Bowler Niebla ceruchis (Ach.) Rundel & Bowler Ramalina lacera (With.) J.R. Laundon Schizopelte californica Th. Fr. Teloschistes californicus Sipman Teloschistes exilis (Michaux) Vainio Trichoramalina crinita (Tuck.) Rundel & Bowler Xanthoria ramulosa (Tuck.) Herre

As Belsky (1996) and we have recommended (Bowler and Reifner, 1990; 1995), careful consideration needs to be made before prescribed burning is used, so that the natural mosaic of adjacent age classes is not lost. Many academic researchers question the need and rationales for prescribed burning sage scrub, and dispute the concept of "senescent stands" (Zedler, 1995) as "needing burning" for ecological or any other reason. Fuel modification by removal of canopy plants in lichen rich sites such as Buck Gully in Irvine California, and postfire hydroseeding on soil and rock are additional fire-related anthropogenic practices which damage lichen communities (Bowler, 1995). If old stands which have rich lichen and other epiphyte floras (not all do) are burned to reduce fuel loads, there will no near neighbor source from which recolonization will originate. If colonization is dependent upon long distance dispersal alone, species richness will be dramatically reduced in a short time period. While air pollution does have a significant contribution in reducing species richness of lichens in many areas of California, as has been noted since Herre's (1936) times, direct loss of habitat has had an enormous impact as the primary contributor to the diminishment of the lichen flora. Relict pockets of old growth sage scrub which are "dripping" with lichens still occur in increasingly rarity. The presence of these remnant micro-sites suggests that habitat loss, including old growth stands, plays a strong role in local species losses - whatever the background of air pollution may or may not be. The magnitude of habitat loss, including disruption of fire cycles and historic survival of old growth sage scrub stands, far outweighs air pollution impacts in many areas along coastal southern California. There may be a synergism between these two contributors to lichen decline in terms of slowing the extent of recolonization after fires.

Conclusion

As habitat becomes more and more reduced in southern California, prescribed burning concepts should not disregard historic age class mosaics and the absolute dependency of late successional species like lichens upon them. Lichen rich stands should be identified, valued for their ecological significance, and protected. If these stands are sacrificed for anthropogenic purposes, there is little likelihood of even eventual recovery of species richness. Burning such sites contributes to the endangerment of now rare species and guarantees local extinctions and continued loss of species in southern California.

Acknowledgments

The University of California Natural Reserve System provided computer support for the project, which was sponsored in part by a grant from the Transportation Corridor Agencies.

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Bowler, P.A. 1995. Impact of Postfire Hydroseeding on Sensitive Plant Communities in Laguna Canyon, California. Pp. 193-194 in Keeley, J.E. and T. Scott (eds.). Brushfires in California Wildlands: Ecology and Resource Management. International Association of Wildland Fire, Fairfield, WA.

Bowler, P.A. 1997. Species Richness and Coastal Sage Scrub Restoration. in Bowler, P.A. and E. Read (eds.). Coastal Sage Scrub Restoration: Proceedings of the Coastal Sage Scrub Restoration Symposium held at the Fifth Annual Conference of the Society for Ecological Restoration. Published by Society for Ecological Restoration, California Chapter (in press).

Bowler, P.A. and R. Riefner. 1990. A preliminary lichen checklist for the University of California, Irvine, campus and the San Joaquin wetlands. Crossosoma 16: 1-10.

Bowler, P.A. and R.E. Riefner, Jr. 1995. Notes on the Ramalinaceae and Current Related Research in California, U.S.A. Bulletin of the California Lichen Society 2(1): 1-5.

Bowler, P.A., W.A. Weber, and R.E. Riefner, Jr. 1996. A Checklist of the Lichens of San Clemente Island, California. Bulletin of the California Lichen Society 3(2): 1-8.

Bratt, C. 1987. Point Loma lichens - now and then. Pp. 289-293 in Elias, T.S. (ed.). Conservation and Management of Rare and Endangered Plants. California Native Plant Society, Sacramento.

Herre, A.W.C.T. 1936. Our vanishing lichen flora. Madrono 3: 198-200.

Riefner, R.E., Jr., P.A. Bowler, and B. D. Ryan. 1995. New and interesting records of lichens from California. Bulletin of the California Lichen Society 2(2): 1-11.

Zedler, P.H. 1995. Fire frequency in Southern California Shrublands: Biological Effects and Management Options. pp. 101-112. In Keeley, J.E. and T. Scott (eds.). Brushfires in California Wildlands: Ecology and resource Management. International Association of Wildland Fire, Fairfield, WA.