BlOTROPlCA 29(4): 384-395 1997 Stand Characteristics and Leaf Litter Composition of a Dry Forest Hectare in Santa Rosa National Park, Costa Rica’ Robyn J. Burnham Museum of Paleontology, University of Michigan, Ann Arbor, Michigan 48109-1 079, U.S.A. ABSTRACT zyxwvuts One hectare of tropical dry forest in Guanacaste Conservation Area, Cosra Rica was mapped and all trees larger than 10 cm diameter at breast heighr (DBH) identified. The same hectare was sampled for leaf litter and the zy two data sets, forest and litter, were compared. Dominant and subdominant species of the forest are represented in the leaf litter, whereas rare tree species are highly variable in their representation in the leaf litter. Relative abundance of dominant and subdominant tree species is represented well by the litter although absolute rank-order is nor identical between source forest basal area and leaf litter mass. The litter adds a significant component to the source forest data owing to the presence of vines and lianas, and more rarely small trees or shrubs. This indicates that litter studies may be able to add depth to forest diversity surveys. The source forest also was used to test foliar physiognomic recon- structions of climate that have been proposed recently by paleobotanists as an alternative to taxonomic affinities methods. The observed climate of the area does not conform to the climatic values that were predicted by application of these new methods. RESUMEN Una hectirea de bosque seco tropical en el Area de Conservaci6n de Guanacaste, Costa Rica fue mapeada, y todos 10s irboles mayores de 10 cm de dap fueron identificados. En la misma hectirea, se tomaron muestras de hojarasca y 10s dos colecciones de datos. bosque y hojarasca, fueron comparadas. Se encontr6 que las especies dominantes y subdominantes del bosque estaban representadas en las muestras de hojarasca, mientras que la presencia de especias arb6reas raras en las muestras de mojarasca fue muy variable. La abundancia relativa de especies arbbreas dominantes esti bien representada en la hojarasca aunque el Area basal del bosque de origen y la masa de hojarasca no heron idtnticos en rangos absolutos. La hojarasca afiade un componente significativo a 10s datos del bosque de origen debido a la presencia de bejucos y lianas en la hojarasca, y zyxwvuts mis raramente irboles pequefios y arbustos. Estos datos indican que 10s estudios de hojarasca pueden incrementar la precisi6n de las estimaciones de la diversidad de 10s bosques. El bosque de origen fue usado tarnbien para examinar reconstrucciones del clima basados en la fisiognomia foliar re- cientemenre propuesras por paleobotinicas como una alternativa a mttodos de afinidad raxon6micas. El clima obser- vado en el Area no corresponde con 10s valores climiricos que heron predecidos por la aplicaci6n de estos nuevos mttodos. zyxwvutsrqp Ktywordr: biodiversity; conservation;fDssil phnts; Guanacaste; leaf litter; lianas; palPobotany; tropical dy firest. TROPICAL DRY FOREST HAS BEEN CITED as one of the most threatened forest ecosystems on earth today Uanzen 1988a, b) yet only recently has the phe- nology of dry forest been addressed by studies car- ried out in a variety of seasonally dry forests (Koel- meyer 1960, Janzen 1967, Daubenmire 1972, Frankie et zyxwvutsrq al. 1974, Lieberman 1982, Reich zyxwvu & Borchert 1984, Murphy & Lug0 1986, Lott et a[. 1987, Bullock et al. 1995, Martinez-Yrizar 1995, Murphy & Lug0 1995). Tropical dry forest has been estimated to have covered as much as 500,000 h2 on the Pacific Coast of Central America as recently as 400 years ago Uanzen 1 9 8 8 ~ ) . The rel- ative ease of clearing dry tropical forest and its ’ Received 23 October 1995; revision accepted 16 May 1996. adaptability to many forms of land use has resulted in its accelerated loss in the past two centuries (Maas 1995). The forest and leaf litter characteristics of one hectare of forest in Santa Rosa National Park (SRNP), Costa Rica which represents a remnant of semi-deciduous dry tropical forest are described here. The objectives were to compare the compo- sition and distribution of trees on the hectare to the identifiable leaf litter accumulating in the cen- tral part of the hectare, to determine whether a reasonable reconstruction of the forest could be made using leaf litter alone, and to use the forest as a test of regression analyses that are currently used to reconstruct paleoclimate. The leaf litter collections and their comparison to the source forest can be used in two very differ- 384