Anthropogenic change in subtropical dry forest during a century of settlement in Jaiquí Picado, Santiago Province, Dominican Republic

Summary AimThe dry forests of the tropics have received little scholarly attention relative to their significance and their rate of disappearance. This study aimed to characterize the structure and composition of two intermingled Antillean subtropical dry forest types and shed light upon their origins, development, and possible future conditions. LocationJaiqui Picado, Santiago Province, Dominican Republic (19° 26′ N, 70° 54′ W). MethodsBiophysical data from quadrat sampling of vegetation, soils, and site characteristics were subjected to cluster analysis, means comparisons, discriminant analysis, and linear regression. Extensive interviews with local land users provided information on early forests as well as present and historical land use practices. ResultsSpatial patterning of the area's two main forest types relates closely to past land use but not to any observed differences in the physical characteristics of their sites. ‘Old-growth’ stands found on land never placed in cultivation resemble the forests encountered by late-nineteenth-century settlers of the area in their wealth of woody plant taxa and relative abundance of endemic and other native species. In the ‘scrub’ stands growing on land abandoned from grazing, fully 70% of stems belong to one native (Acacia macracantha Willd.) and two exotic (Haematoxylon campechianum L. and Prosopis juliflora (Sw.) DC.) woody legumes that contribute to the markedly greater representation of deciduous and thorn-bearing individuals in this type. The two forest types do not differ significantly in average bole dimensions, but the canopies of scrub stands are concentrated in a narrower layer, their understories are more open, and they contain more multiple stems of apparent sprout origin. A chronosequence of scrub stands covering a range in age of three decades indicates a moderate increment in species diversity over time and gradual disappearance of some of the more abundant invasive shrubs; but such stands continue to be dominated throughout this period by the same three scrub trees, while most species characteristic of old-growth forests, including many of the least abundant, fail to appear among the regeneration in their understories. Main conclusionsAntillean forests classified as thorn scrub may include a form of ‘disclimax’ created through past land use activities in areas once bearing more diverse tropical dry forest. Whether they will ever develop into stands similar to the previous forests is uncertain, given the present state of fragmentation and other processes taking place within these ecosystems. Resumen En una zona seca de la Republica Dominicana, coexisten extensiones de ‘brena’, o ‘monte de espinas’, entremezcladas con fragmentos de un bosque subtropical seco de mayor diversidad, formando patrones espaciales que no pueden ser atribuidos a ninguna diferencia aparente entre las condiciones fisicas de los sitios. Se aplico una variedad de metodos, incluyendo el muestreo de parcelas de vegetacion y suelos asi como entrevistas con los residentes locales, para caracterizar estos dos tipos de bosque e investigar su posible origen. Los rodales del bosque maduro, los cuales se encuentran en terrenos nunca cultivados, se asemejan en su riqueza de especies lenosas y la abundancia de especies endemicas y nativas a los bosques encontrados por los pobladores que llegaron al area a finales del siglo diecinueve. En la brena que nace en terrenos abandonados del pastoreo, el 70% de los tallos pertenece a tres especies leguminosas lenosas – una nativa (cAcacia macracantha Willd.) y dos exoticas (Haematoxylon campechianum L. y Prosopis juliflora (Sw.) DC.) – que contribuyen a una representacion notablemente mayor de arboles caducifolios y espinosos en esta vegetacion. Los dos tipos de bosque no difieren significativamente en las dimensiones medias de sus troncos, pero el dosel del monte espinoso se concentra en un estrato mas angosto; su sotobosque se mantiene mas abierto; y contiene una proporcion mayor de tallos multiples aparentemente nacidos de rebrotes. La comparacion de una secuencia de rodales de monte espinoso, cuyas edades cubren un rango de tres decadas, indica que la diversidad de especies lenosas aumenta paulatinamente durante tal periodo y que se van desapareciendo algunos de los arbustos invasivos mas abundantes; pero el monte sigue dominado por los mismos tres arboles espinosos, y la mayoria de las especies caracteristicas del bosque maduro, incluyendo muchas de las mas escasas, no llegan a aparecer entre la regeneracion en su sotobosque. Entre los bosques antillanos ahora clasificados como ‘monte espinoso’ puede haberse incluido una especie de ‘disclimax’ ocasionado por las actividades humanas en terrenos anteriormente cubiertos de un bosque seco mas diverso; el desarrollo futuro de estos montes – en particular su posibilidad de aproximarse a la composicion de los bosques maduros – es aun impredecible.