Cambios en la estructura y composición de la vegetación relacionados con los años de abandono de tierras agropecuarias en la selva baja caducifolia espinosa de la reserva de Dzilam, Yucatán

The dry forests in the northern Yucatan Peninsula are highly important not only for science but also for the conservation of biodiversity because of their unique biogeographical and ecological characteristics. The combination of arid climate, stony soil and relative isolation from other biogeographical regions, has resulted in their sheltering an important proportion of the peninsula's endemic taxa. Nevertheless, this region suffers from such human pressures as cattle ranches and the exploitation of limestone banks. This scenario makes it necessary to describe the ecological changes on the land once it has been abandoned after being used for agriculture, because there is no pristine forest in Yucatan. We compared the structure and composition of trees and shrubs on abandoned agricultural land of different ages. All sites were derived from tropical dry forest, a vegetation type which contains several endangered species. The changes in composition and relative abundance of the subfamilies belonging to the Leguminosae (Papilonoideae, Mimosoideae and Caesalpinoideae) were also reported, since this family was the most abundant at the study site. Average tree height and density and shrub richness showed larger changes with increasing number of years without management (ANOVA, P< 0.05). Younger plots (1-5 years and currently in use) were more similar among themselves than to older sites (more than five and more than ten years). The Leguminosae were the richest family in species in all the plots and one of the most abundant, possibly indicating a history of intense use. Agriculture tends to deplete nitrogen from the soil, which gives a competitive advantage to legumes. Papilonoideae were the most abundant in older sites (more than five and more than ten years), whereas Mimosoideae dominated recently abandoned sites (five years or less) and those currently in use. Metopium brownei, Bursera simaruba and Plumeria rubra were the most abundant species in the oldest site. The first two are found in almost all types of terrestrial vegetation on the Yucatan Peninsula, and all three are reported as being very resistant to disturbance, such as fire or damage associated with wood harvest, and to regenerate readily. Their presence may indicate a history of intense use of this region.Las selvas bajas del norte de Yucatán son de gran importancia científica y conservacionista; sus condiciones de aridez, pedregosidad del suelo y su relativo aislamiento de otras regiones biogeográficas le permiten albergar una importante proporción de los endemismos de la península. No obstante lo anterior, esta área sufre de presiones por actividades humanas, principalmente la ganadería, agricultura y la extracción de piedra caliza. Por esta razón se hace necesario estudiar los cambios en la vegetación en las tierras agropecuarias después de su abandono. Se comparó la estructura y composición de árboles y arbustos de potreros derivados de selva baja caducifolia espinosa en Dzilam, Yucatán con diferentes tiempos de abandono. Se reportan los cambios en la composición y abundancia de las tres subfamilias pertenecientes a la familia Leguminosae (Papilonoideae, Mimosoideae y Caesalpinoideae) ya que es una familia muy importante en los trópicos secos y fue la más abundante y rica en nuestra área de estudio. Se encontró que la altura y la abundancia de individuos del estrato arbóreo y la riqueza del estrato arbustivo fueron las variables que cambiaron de manera más intensa con la edad de abandono (ANOVA, P < 0.05). Los sitios de pasto en uso y sitios con menos de cinco años de abandono mostraron una mayor semejanza en la composición de especies entre ellos que con los más antiguos. Las parcelas con más de 10 y 5 años de abandono formaron otro grupo, aunque con un bajo valor de similitud (Sorensen < 0.2). La familia Leguminosae fue la más rica en especies en los estratos arbustivo y arbóreo. Las leguminosas también se encontraron entre las más abundantes. Esto se explica por un suelo pobre en nutrientes y la historia de manejo intenso, ya que su capacidad de establecer simbiosis con microorganismos fijadores de nitrógeno les confiere una ventaja competitiva. Las abundancias relativas de las mimosoideas fueron las más altas en los sitios de reciente abandono, en tanto que las de papilonoideas dominaron en los sitios más antiguos. Las especies más abundantes en el sitio de más de 10 años resultaron ser Bursera simaruba, Metopium brownei y Plumeria rubra. Las primeras dos se encuentran en casi todos los tipos de vegetación terrestre de la Península de Yucatán. Las tres especies son resistentes a disturbios, como incendios o destrucción asociada a la explotación maderera y poseen una alta capacidad de regeneración, lo que puede indicar una historia de uso intenso de este tipo de vegetación

Data from: Genetic variation and structure in the neotropical tree, Manilkara zapota (L) P. Royen (Sapotaceae) used by the ancient Maya

Manilkara zapota is a tropical tree species that was used by the ancient Maya in construction of their temples and as a source for fruit. Although this has been supported by ethnographic and paleoethnobotanical data, we used genetic approaches to estimate variation and structure in modern populations of this neotropical tree species to discern if genetic patterns were consistent with earlier influences of ancient Maya management or if they could be explained by the natural history of the species. Nine microsatellite markers, consisting of seven novel markers and two markers identified in a related species, were used to characterize the genetic diversity and population genetic structure in three populations of M. zapota collected from reforested, historically urbanized ancient Maya ceremonial centers in Guatemala and Belize, from home gardens in Guatemala, and from a number of cultivars. Levels of genetic variation were slightly higher in forest populations (H O = 0.447) than in gardens (0.430) and cultivated varieties of M. zapota (0.351). We observed low but significant population substructuring (θ = 0.01) between sites 90 km apart, and minimal evidence of inbreeding. Substantial levels of genetic diversity with minimal genetic structure in M. zapota are consistent with movement of the ancient Maya as they possibly carried fruits and seedlings during immigration, but they may more likely reflect natural processes such as seed and pollen being dispersed widely throughout the tropical forest