Temporal progression trends of cypress mortality at permanent plots in a National forest reserve of Austrocedrus chilensis (Patagonia, Argentina)

Abstract

Longevity is a characteristic of forest trees that influences their responses to challenges by biotic and abiotic stresses and the temporal development of symptoms. Monitoring programs have been extensively used to detect the impact of climatic change, air pollution and outbreaks of pathogens on forest health, growth and dynamics. In Argentina, forests of Patagonian cypress are affected since mid twenty century by a mortality process called «mal del ciprés» (cypress mortality), but information about their temporal progression is scarce. In the present work we used a database from a program of dasometric permanent plots to analyse the temporal development of cypress mortality on plot and tree level, and determine qualitatively the spatial distribution of affected trees. Particular pulses of appearance of affected trees shared by all plots, rapid or slow progress of mortality at tree level and a homogeneous distribution of affected trees without a clear pattern of expansion from a central point were determined. The results indicate that the episodic appearance of affected trees can be related with warm and dry climatic periods and suggest that the individuals affected by cypress mortality share some special characteristics such as genetic background, developmental conditions or physiological mechanisms for drought responses.Key words: symptoms development; monitoring; spatial distribution; drought; mortality pattern. ResumenTendencias en el desarrollo temporal del mal del ciprés en parcelas permanentes de una Reserva Forestal Nacional de Austrocedrus chilensis (Patagonia, Argentina)La longevidad de las especies arbóreas afecta la respuesta a estreses bióticos o abióticos y, en gran medida, determina el desarrollo temporal de los síntomas. Por tal motivo, los programas de monitoreo se han empleado para detectar el impacto del cambio climático, la polución ambiental o estallidos de patógenos en la sanidad y dinámica de los bosques. En Argentina, los bosques de Austrocedrus chilensis sufren desde 1945 una mortalidad masiva conocida como «mal del ciprés»; sin embargo, hay escasa información sobre su progresión temporal. En el presente trabajo una base de datos de un programa de parcelas permanentes se empleó para analizar el desarrollo temporal de la mortalidad a nivel de parcela e individuo y la distribución espacial de los árboles afectados. Se determinó que la aparición de síntomas sigue un patrón de pulsos compartido por todas las parcelas, con mortalidad rápida o lenta a nivel de individuo y una distribución homogénea de la mortalidad sin un patrón de expansión desde un punto central. Los resultados indican que los episodios de afectación pueden ser relacionados con períodos climáticos cálidos y secos, sugiriendo que los individuos afectados comparten características tales como background genético, condiciones de sitio o respuesta a la sequía.Palabras clave: desarrollo temporal de síntomas; monitoreo; distribución espacial; sequía; patrón de mortalidad.

Temporal patterns of radial growth in declining Austrocedrus chilensis forests in Northern Patagonia: The use of tree-rings as an indicator of forest decline

“…Specifically, 67 trees exhibited a decline in radial growth and were classified as overstory trees at the onset of decline, but had asymptomatic crowns at the time of sampling. As living symptomatic and dead trees can undergo long periods of radial growth decline but the transition from asymptomatic to symptomatic crowns and from symptomatic to dead trees occurs over short intervals of 1-3 years (Havrylenko et al, 1989;Rosso et al, 1994;El Mujtar et al, 2011), we infer that the decline in radial growth can precede the manifestation of symptoms in the crown of at least some A. chilensis trees. This inference assumes that the observed trees with radial growth decline will develop crown symptoms over time, which can be verified or refuted by monitoring our sample sites through time.…”

Does drought incite tree decline and death in Austrocedrus chilensis forests?

“…; El Mujtar et al. ) highlight the role of climatic variability on the decline and death of trees in these forests, here we present a framework for interpreting mortality of A. chilensis as a forest decline process driven by multiple factors (sensu Manion ; Manion & Lachance ). Complex interactions between abiotic and biotic factors acting at different spatial and temporal scales predispose trees, and incite and contribute to the development of the symptoms leading to the subsequent death of trees over large areas.…”

“…; El Mujtar et al. ). Short duration droughts might weaken individuals, making them more susceptible to subsequent factors, including biotic agents.…”