Patterns of tree seedling mortality in a temperate-mediterranean transition zone forest in Chile

Abstract

Seedling mortality in forests is the net result of an array of processes that vary spatially and temporally. We quantified emergence and mortality of seedlings at monthly intervals for two years, in a forest situated in the transition zone between the Mediterranean and temperate regions of Chile. We aimed to determine if survival of species responded differentially to seasonal water availability, to the spatial variation in light availability and to seedling density. The commonest species in the seedling bank were the Mediterranean-climate species Cryptocarya alba (61%) and the temperate-climate species Aextoxicon punctatum (29%). 279 of the 504 new seedlings that emerged during the two-year study died during the same period, corresponding to 55,4% mortality. Four of the less common species (Persea lingue, Peumus boldus, Nothofagus obliqua and Luma apiculata) suffered 100 % mortality of new recruits. Mortality of A. punctatum showed a marked seasonal pattern, with high mortality during the dry summer months. In contrast, mortality of the Mediterranean-climate species C. alba was more evenly distributed throughout the year. Multiple regressions showed that light availability had no significant effect on mortality of A. punctatum or C. alba. The same analysis revealed that survival of A. punctatum was negatively affected by conspecific seedling density, but this density-dependent effect was not found for C. alba. Heterospecific density-dependent effects were not found, i.e. mortality of neither species was affected by local density of seedlings of other species. This study shows that spatial and temporal variation in critical factors shapes interspecific variation in seedling mortality in this forest. KEYWORDS:Aextoxicon punctatum, Cryptocarya alba, density-dependent mortality, drought tolerance, shade tolerance. RESUMENLa mortalidad de las plántulas es el resultado de una gama de procesos y agentes que pueden variar espacial y temporalmente en los ecosistemas forestales. En este estudio cuantificamos la emergencia y mortalidad de plántulas mes a mes, por un período de dos años en un bosque situado en la zona de transición entre la región mediterránea y templada de Chile. Pretendimos dilucidar si las especies sobreviven en forma diferencial a la disminución estacional en la disponibilidad de agua, a la variación espacial en la disponibilidad de luz y a la densidad local de plántulas. Las especies más abundantes en el banco de plántulas son la esclerófila Cryptocarya alba (61%) y la especie templada Aextoxicon punctatum (29%). Del total de 504 plántulas emergidas durante el estudio, murieron 279, lo que corresponde a un 55,4 %. Cuatro de las especies menos abundantes (Persea lingue, Peumus boldus, Nothofagus obliqua y Luma apiculata) sufrieron un 100 % de mortalidad de plántulas emergidas durante los dos años. La mortalidad de A. punctatum evidenció una marcada estacionalidad, con tasas elevadas durante la estación más seca (verano), pero este patrón fue mucho menos evidente en C. alba. Un análisis de regre...

Factors Affecting Natural Regeneration of Tropical Forests across a Precipitation Gradient in Myanmar

“…This finding supported the research by Galiano et al [45] and Parada and Lusk [46], which explored how drought or reduced rainfall limited the survival of plants at the seedling stage. In comparison with other studies, the density of natural regeneration at our study sites was lower than that of semi-evergreen forests in Myanmar studied by Oo [47], and higher than that of the secondary forests in Vietnam studied by Woo et al [48].…”

Patterns of carbon storage in relation to shade tolerance in southern South American species

“…High levels of C storage could be advantageous to recover from drought and fire, which are main causes of seedling mortality in Mediterranean forests. Furthermore, drought and shade tolerance were found to be unrelated in Mediterranean forests (Sánchez‐Gómez et al, 2006), even with similar climate and physiognomy to the one I studied (Parada and Lusk, 2011). Likewise, shade tolerance and fire resistance are not apparently related in the Mediterranean species studied here, because resprouting has been reported in both highly shade tolerant and intolerant species (Veblen et al, 1979; González et al, 2002; Donoso, 2006).…”

Temperate rain forest species partition fine-scale gradients in light availability based on their leaf mass per area (LMA)

“…In contrast to the temperate rain forest sites, we found that woody species in the Mediterranean forest we surveyed did not partition the fine-scale gradient in light availability. This is most probably because, unlike temperate rain forests, regeneration in Mediterranean forests is most strongly limited by water rather than light availability (Parada and Lusk, 2011), or perhaps regeneration here is mediated by traits other than LMA. In fact, the range of GLI values found in this Mediterranean forest (50 %) was considerably lower than in the temperate rain forests (80 %).…”