INVESTIGADORES
GRAU Hector Ricardo
artículos
Título:
Rainfall variability, fire, and vegetation dynamics in neotropical montane ecosystems in northwestern Argentina
Autor/es:
GRAU, HR; VEBLEN, TT
Revista:
JOURNAL OF BIOGEOGRAPHY
Editorial:
Blackwell
Referencias:
Año: 2000 vol. 27 p. 1107 - 1121
ISSN:
0305-0270
Resumen:
Aim
We explored the relationships among rainfall, fire and tree population dynamics during
the twentieth century. Relationships were analysed on seasonal, interannual and multiannual
time scales.
Location
The study was conducted at ecotones between Andean grasslands and montane
forests in north-western Argentina. In this area of subtropical monsoonal climate (wet
summers, dry winters), annual rainfall has increased and forests have expanded into grasslands
and shrublands during the 20th century.
Methods
We used annual tree-rings of alder (
Alnus acuminata
H. B. K.), the dominant
tree species, to date fire scars on 265 trees and determine establishment dates of 455 trees
dispersed over areas > 100 ha at five sites. We also sampled tree establishment and resprouting
in 21 plots of 0.15 ha and determined mortality patterns in one recently burnt stand.
Results
Fire occurrence during the winter dry season tends to lag by 1 year after years of
above-average moisture availability. This pattern is probably due to enhanced production
of fine fuels during the growing season of the preceding years. Over 5-year periods, higher
fire frequency is associated with greater variability in rainfall. On a 5-year time scale, tree
establishment is also associated with higher rainfall variability. Tree age structures suggest
that a decades-long trend towards increased rainfall may also promote forest expansion.
By the age of 1020 years,
Alnus acuminata
attains a large enough size to survive
the low-intensity fires typical of these open woodland sites. Recovery of
A. acuminata
after
fire is also assured by vigorous resprouting and seedling establishment after fire removes or
reduces the herbaceous understorey. During relatively wet periods or at relatively wet sites,
fire appears to favour forest expansion by reducing competition between tree juveniles and
non-forest vegetation.
Main conclusions
These results demonstrate the importance of variability in interannual
rainfall as an influence on the dynamics that control ecotones between high Andean grasslands
and subtropical montane forest.
Keywords
Alnus
, climate change, climate variability, ecotone, fire ecology, forest dynamics, tropical
montane forests.