3 research outputs found
Descripci贸n de una coenoclina en el SW del Chubut
p.163-171El presente trabajo se orienta a la determinaci贸n de la influencia de las precipitaciones sobre la composici贸n de las comunidades vegetales en el SW del Chubut. Estas forman un continuum de vegetaci贸n o coenoclina, determinada por un gradiente de precipitaciones crecientes de E a W. Dentro de la misma se trat贸 de determinar rangos intr铆nsecamente homog茅neos, con el fin de poder estudiar dentro de cada uno de ellos caracteres de la comunidad vegetal, especialmente los relacionados con el uso pasturil, sin interferencias del factor humedad. Con ese objetivo se realizaron en la regi贸n 43 censos en clausuras y en potreros que no presentan signos de deterioro. Estos censos se ordenaron en forma directa a trav茅s del m茅todo de los 铆ndices de ponderaci贸n de las especies. El ordenamiento as铆 obtenido permiti贸 la partici贸n de la coenoclina en 7 segmentos, dentro de los cuales no se aprecia variaciones flor铆sticas importantes. Result贸 evidente la relaci贸n entre los cambios flor铆sticos y el gradiente de precipitaciones en los sectores occidental y central, mientras que en el oriental no se observ贸 tal relaci贸n por lo que se supuso que son otros los factores ambientales que condicionan la composici贸n de las comunidades
Regeneration niche of the Canarian juniper: the role of adults, shrubs and environmental conditions
Canarian Juniper woodlands, now very scarce, are rich in endemic and endangered plants. However,
many aspects of juniper regeneration are almost unknown.
This paper relates occurrence and abundance of recruits of Juniperus turbinata ssp. canariensis to
(1) small-scale soil characteristics; (2) vegetation cover; and (3) distance to conspecific adults in two
contrasting juniper stands in the eastern mountains of Tenerife.We used non-parametric classification
trees and generalised linear models (GLM) to evaluate the effect and importance of each explanatory
variable on the occurrence of juniper saplings.
Sapling density, vitality and growth rate, as well as fruit production by adult trees, but neither cone
density on the ground nor sapling size, varied significantly with respect to slope orientation, representing
environmental stress. Within each stand, distance to nearest adult tree was the most important
variable explaining the spatial distribution of juniper saplings and availability of seeds in cones. Additionally,
saplings were positively associated with shrub cover at the microsite-level, but not with
spiny shrub cover. Soil depth and rock cover had a weak negative effect on sapling establishment, but
only at the south-facing site and in the open space microhabitat.
Results suggest that recruitment of Canarian juniper is facilitated by microhabitats offered by
adults and shrubs. The key factors affecting recruitment are thought to be (1) favourable microenvironmental
conditions and (2) high ambient seed availability. Browsing intensity in recent decades
was very low. The presence of spiny shrubs did not favour juniper establishment. Facilitation therefore
appears to result from amelioration of abiotic conditions rather than from protection against
herbivory.Comunidad Europe