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MANAGEMENT OF HABITAT Daniel H. Janzen2FRAGMENTS IN A TROPICALDRY FOREST: GROWTH'ABSTRACT Tropical conservation biology is inescapably the biology of habitat fragments and has been focused on habitatdecay. Habitat restoration is primarily the initiation, growth, and coalescence of habitat fragments. Managementof a tropical wildland will become the art and science ofarresting the decomposition of habitat fragments andpromoting their growth and coalescence. Forces that determine accumulation of structure and species aresignificantly within human control. Today's management actions will determine the nature ofwildland habitatsfor centuries to come. Tropical dry forest is the most threatened of all the major lowland tropical forest habitats,simply because it has always occupied some of the lands most easily farmed in the tropics, and because it is sosusceptible tofire. When dry forest and fields are abandoned and therefore allowed to return to dry forest, thereare two principal kinds offorest initiation (assuming that there are nearby seed sources). a. When large pasturesare downwind of a relatively intact forest, the initial invasion is primarily by individuals of large wind-dispersedtrees that will persist and characterize the site for hundreds ofyears. However, these tree species are a minorityof the total fora. Such forests of wind-dispersed trees are relatively inhospitable to animais, highly deciduous,and relatively species-poor. b. When there is any kind of attraction for animals in an abandoned open area,they may perch in it or rest below it while crossing the open area. This results in accumulation of an entirelyvertebrate-dispersed forest patch. Such patches may grow and coalesce to form a forest type as artificial as isa wind-generated forest. Vertebrate-generated forests contain more food items of interest to animais, are morespecies rich, and are more evergreen than are wind-generated forests. As large areas of abandoned low-gradefarm and ranch land are returned to dry forest, the manager of national parks or other wildlands is confrontedwith the dificult decision of just which of the above, or other, forest types is to be promoted. The same willapply to rainforest when its restoration becomes a focus of concern. Tropical conservation biology is inescap-ably the biology of habitat fragments. Thereare two kinds of fragments. First, much ofwhat is worthy of conservation has alreadybeen broken into decomposing habitat frag-ments that are refugia and remnants. Evena large national park that is a solid block ofpristine forest is a fragment. The biology ofthe decomposition process of these fragmentsis of intense contemporary interest to con-servation planners and managers (e.g., Love-joy et al., 1986; Diamond, 1986; Janzen,1986a, c; Wilcove et al., 1986; Uhl & Busch-bacher, 1985; Newmark, 1987). Second,habitat restoration is primarily the initiationand coalescence of growing habitat frag-ments. Management of a tropical wildlandtherefore becomes the art and science of ar-resting decomposition of habitat fragmentsand promoting their growth and coalescence.In such an arena, today's management ac-tions will determine the nature of wildlandhabitats for centuries to come; forces thatdetermine accumulation of structure andspecies are significantly within human control. Here I examine the biology of habitat ini-tiation and growth in a Costa Rican tropicaldry forest. Dry forest is the most threatenedof ail the major lowland tropical forest habi-tats. It once covered more than half of theworld's tropics (e.g., Brown & Lugo, 1982;Murphy & Lugo, 1986) but now supports adiverse array of breadbaskets, cotton fields,and pastures. In Pacific Mesoamerica, forexample, less than 0.1% of the original trop-ical dry forest, which once covered an areathe size of France (equal to five Guatemalasin area), has conservation status, and there This study was supported by NSF BSR 83-07887, BSR 84-03531, BSR 83-08388, and DEB 80-11558,and by the Servicio de Parques Nacionales de Costa Rica. The manuscript has been constructively reviewed byW. Hallwachs. 2 Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, U.S.A. ANN. MISSOURI BOT. GARD. 75: 105-116. 1988.



Management of Habitat Fragments in a Tropical Dry Forest: Growth

Daniel H Janzen
Annals of the Missouri Botanical Garden 75: 105-116 (1988)

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