INVESTIGADORES
DEFOSSE Guillermo Emilio
capítulos de libros
Título:
Seedling dynamics in an environmental gradient of Andean Patagonia, Argentina
Autor/es:
LÓPEZ BERNAL, P.M.,. M. F. URRETAVIZCAYA, AND G. E. DEFOSSÉ
Libro:
From seed germination to young plants: ecology, Growth and Environmental influences.
Editorial:
Nova Science Publishers
Referencias:
Año: 2012;
Resumen:
In this chapter, we analyze the most important
environmental and biotic factors that influence seedling dynamics of three of
the most conspicuous species grown in a forest-steppe gradient of Patagonia in
Argentina. In a short distance of about 80 km in this gradient, vegetation abruptly
changes from pure Nothofagus pumilio
forests (grown from the timberline down to altitudes of about 1,200 m a.s.l., with
2,000 to 3,000 mm/yr of precipitation), to mixed Austrocedrus chilensis-Nothofagus
dombeyi forests and pure A. chilensis
forests towards the east, and isolated A.
chilensis forests in the ecotone with the steppe (at altitudes from 900 to
500 m a.s.l. and 1,200 to 500 mm/yr of precipitation), and then to a grassland steppe
zone, located at about 400 to 600
m a.s.l., and in which precipitation barely reaches 300
to 400 mm/yr. Although precipitation
values greatly differ, all areas share the same Mediterranean climate, with
rains concentrated during late fall and winter followed by a marked dry spring
and summer period. The most important native species in this gradient are the
trees, Nothofagus pumilio (lenga), in
the higher slopes of the Andes, Austrocedrus
chilensis (cypress or ciprés de la cordillera) at mid slope and in the
forest-steppe ecotone, and the grass Festuca
pallecens (coirón blanco), in the steppe zone. All three species reproduce
by seed, and form transient soil seed banks.
In the case of Festuca pallescens this
bank is annually replenished, while
for A. chilensis and N. pumilio seed production occurs during
favorable periods every that may vary from two to several years. Among the
environmental factors that affect seedling dynamics, water stress during the
summer dry period appear to be of paramount importance for Festuca and A. chilensis seedlings, and less important for N. pumilio. For the latter species, and after
germination, light availability appears to be crucial for further sapling
growth. Right after germination, young Festuca
or A. chilensis seedlings appear to
grow better under protected microsites provided by either an adult Festuca plant or a nurse shrub in the
case of A. chilensis. This facilitation effects seems to change as
seedlings become older, shifting this interaction to competition as secondary
succession progresses. Apart from the environmental conditions, seedling dynamics
of all three species are also affected by natural (fires, earthquakes,
avalanches, falling out of senescent trees in the case of N. pumilio) and anthropogenic disturbances (fire, grazing, browsing,
and logging). Although the inferences
made here about seedling dynamics may be valid for the whole area of
distribution of A. chilensis and F. pallescens, for N. pumilio, by instance, will be constrained to continental
Patagonia (excluding Tierra del Fuego), in which Mediterranean climatic
conditions prevail.