Abstract Climate projections predict shifts in environmental conditions, with cascade effects on forest growth dynamics. As such, Pinus pinea L., an ecologically important low-elevation Mediterranean tree, can be threatened by drought events. The occurrence of negative stem growth anomalies (“negative pointer years”, or NPY) and its relation to climatic conditions were analyzed, as well as the influence of extreme dry spells upon the species growth. NPY were temporally independent among the analyzed forest stands, likely due to local factors. We observed that NPY depended on dry and hot conditions during the spring-summer period at both sites, while differences in the NPY-climate reflected the species medium term dendroclimatological signal. Extremely dry years directly reduced stem growth rates. Water stress differentially affected growth at each site, likely reflecting local adaptation to droughts. Because of the increasing drought trend expected for the Mediterranean basin, our findings must be considered regarding the conservation and management of these forests.

SUMMARY: An increase in drought conditions over the last century has been documented in Central Chile, a fact that could affect the Mediterranean forests, especially the northernmost Nothofagus populations from South America (Nothofagus macrocarpa). For this reason, it is key to study the climate influence on radial growth and trees establishment to design strategies of conservation and mitigation in the face of a climate change situation. In this study, 10 trees populations of N. macrocarpa were selected across natural distribution for a dendroecological analysis. The relationship between droughts and radial growth was analyzed annually, while the influence of water favorable conditions in trees establishment was evaluated in periods of 10 years. Results identified three growth patterns: (i) most degraded populations of the Coastal Mountains (young trees predominate), (ii) low-intervened forests found at a higher altitude in the Coastal Mountains and (iii) low-intervened forests of the Andes Mountains. All populations showed positive correlations with the SPEI-drought index during winter-spring, being sensitive up to 36 months after a dry period. More than 64% of the years with lowest growth are associated with historical droughts in all the chronologies, whereas trees establishment linked to humid periods was found especially in the less degraded forests (37-41% trees). These results provide an ecological vision of the climatic sensitivity of the Chilean Mediterranean forest and can contribute to the design restoration, conservation and mitigation actions in situations of global warming.

RESUMEN: Se ha documentado un aumento de las condiciones de sequía durante el último siglo en Chile central, que estaría afectando al bosque mediterráneo, especialmente a los bosques septentrionales del género Nothofagus en América (Nothofagus macrocarpa). Por esta razón resulta imprescindible estudiar la influencia del clima en el crecimiento radial y establecimiento de árboles a fin de diseñar estrategias de conservación y mitigación al cambio climático. Diez poblaciones de N. macrocarpa fueron seleccionadas para analizar la relación entre las sequías y el crecimiento radial anual y la influencia de condiciones hídricas en el establecimiento. Se identificaron tres patrones de crecimiento: (i) poblaciones más degradadas de la Cordillera de la Costa, (ii) bosques poco intervenidos y que se encuentran a una mayor altitud de la Cordillera de la Costa, y (iii) poblaciones poco intervenidas de la Cordillera de Los Andes. Todas las poblaciones presentaron correlaciones positivas con el índice de sequía SPEI (índice estandarizado de precipitación-evapotranspiración) durante invierno-primavera, siendo sensibles hasta 36 meses después de un período seco. Más del 64 % de los años con bajo crecimiento en todas las cronologías fue asociado a sequías históricas. Se observó mayor establecimiento de N. macrocarpa vinculado a períodos húmedos especialmente en los bosques poco degradados. Estos resultados entregan una visión ecológica sobre la sensibilidad climática del bosque mediterráneo de Chile y pueden contribuir en el diseño de proyectos de restauración, conservación y mitigación frente al calentamiento global.

RESUMO Em uma área da Floresta Ombrófila Mista Aluvial impactada por vazamento de óleo bruto no município de Araucária - PR, Brasil, conduziu-se o estudo dendroecológico de Sebastiania commersoniana (Baill.) L.B.Sm. & Downs (Euphorbiaceae) e da espécie exótica Hovenia dulcis Thunb. (Rhamnaceae). Os objetivos do estudo foram avaliar o efeito do alagamento da área a partir da construção de diques como medida de descontaminação de petróleo e de fatores meteorológicos no crescimento em diâmetro do tronco de ambas as espécies. Foram coletadas três séries temporais radiais do lenho de cada indivíduo adulto selecionado com uso de sondas de incremento, em duas condições, ambas com solo hidromórfico (Gleissolo Háplico), tendo como diferença a altura do lençol freático: SHT - saturação hídrica temporária (Sebastiania commersoniana n=12; Hovenia dulcis n= 10) e SHP - saturação hídrica permanente (Sebastiania commersoniana n=6; Hovenia dulcis n= 0). Séries cronológicas foram desenvolvidas, correlacionando-as com dados meteorológicos da região. Os resultados demonstraram que os indivíduos da espécie nativa em ambas as condições apresentaram padrão semelhante de crescimento, com tendência de diminuição ao longo dos anos; diferentemente dos indivíduos da espécie exótica, com tendência de aumento do incremento ao longo dos anos. Os indivíduos da condição SHP tiveram taxas menores de incremento após o ano do derramamento, o que mostra que o alagamento da área a partir da construção de diques como tentativa de descontaminação afetou o crescimento dos indivíduos. O crescimento das espécies correlacionou-se com a precipitação apenas na condição SHT. A temperatura mínima representou ser fator limitante ao crescimento de Sebastiania commersoniana, mostrando que temperaturas mais elevadas são importantes para o crescimento, principalmente no início do período deste. Entretanto, a ocorrência de temperaturas muito altas nos meses mais quentes pode ser limitante ao crescimento. Para Hovenia dulcis, nenhuma correlação significativa foi observada com a temperatura, porém, a precipitação mostrou-se fundamental nos meses em que a espécie mais cresce, sendo, no entanto, prejudicial em meses subsequentes às fortes chuvas devido ao efeito de saturação hídrica do solo.

ABSTRACT In a forest remnant of the Alluvial Mixed Rain Forest impacted by crude oil spill in the district of Araucaria in Paraná, Brazil, we conducted a dendroecological study of Sebastiania commersoniana (Baill.) L.B.Sm. & Downs (Euphorbiaceae) and the exotic species Hovenia dulcis Thunb. (Rhamnaceae). The study objectives were to evaluate the effect of the flooding area by dyke construction as way to decontamination petroleum and the meteorological factors in the tree diameter growth of both species. Wood samples were collected using increment borer, from two conditions, both on hydromorphic soils (Haplic Gleisol), but at two sites differing in the depth of the water table: SHT - temporary water saturation (Sebastiania commersoniana n=12; Hovenia dulcis n= 10) and SHP - Permanent water saturation (Sebastiania commersoniana n=6; Hovenia dulcis n= 0). Radial time series were developed and correlated with the meteorological data from the region. Results show that individuals of native species at both soil conditions experienced similar inter-annual growth patterns with decreasing trend over the years; differently individuals of exotic species, with increase of increment over the years. Individuals of SHP condition had lower rates of growth after the year of the spill, which shows that the flooding of the area by construction of dykes as attempt to decontaminate, affected the growth of individuals. The construction of dykes as attempt to decontaminate the area affected de individual growth. Precipitation showed a direct link with tree growth, only at sites with temporary water saturation. Moreover, minimum air temperature is a factor limiting the growth of Sebastiania commersoniana, showing that high temperatures stimulate growth, particularly at the early stages of the growth period while warmer months may depress the growth. Hovenia dulcis showed no significant correlation with temperature, but precipitation arises as crucial factor for growth, but the effect of soil saturation in the subsequent months may limit tree growth.

Dendroclimatological methods represent one of the most useful tools in analyzing the influence of climate upon the radial growth dynamics and morphology of woody species. In the Central Monte Desert, Prosopis flexuosa DC (algarrobo dulce), grows as one-stemmed as well as multi-stemmed tree. Previous researches showed the utility of the species ring widths as a proxy of climate variability. Nevertheless, these researches differed methodologically, by considering or rejecting the multi-stemmed trees. This work analyzed if the variability in the tree growth habit express differences in the algarrobo dulce dendroclimatological signal. Two tree-ring chronologies, one derived from the one-stemmed (UF) and the other from the multi-stemmed trees (MF) growing under the same ecological environment, were developed. The MF chronology showed higher sensibility than the UF to climate extremes and oscillation. This suggested that multi-stemmed trees represent a good proxy for explaining local climatic variability. Due to the widespread spatial distribution of this species, further works are needed to a deeper understanding of the presented results.

Los métodos dendroclimatológicos representan una de las herramientas más valiosas para analizar la influencia del clima sobre la dinámica del incremento radial y la morfología de las plantas leñosas. En el Desierto del Monte Central, Prosopis flexuosa DC (algarrobo dulce), crece como árbol uni-fustal pero también como multi-fustal. Investigaciones anteriores han evidenciado la utilidad del ancho de anillo de esta especie como registro de eventos climáticos. Sin embargo, estas investigaciones han diferido metodológicamente, considerando o descartando los individuos multi-fustales. Este trabajo analizó si la variabilidad en el hábito de crecimiento expresa diferencias en la señal dendroclimática del algarrobo dulce. Dos cronologías de ancho de anillos, una derivada de individuos uni-fustales (UF) y otra de multi-fustales (MF) presentes en un mismo ambiente ecológico fueron desarrolladas. Se observó que hay una mayor sensibilidad de la cronología MF respecto de la UF en relación a la incidencia en el crecimiento de eventos climáticos extremos y del clima en general en el largo plazo. Esto sugiere que los individuos multi-fustales constituyen una buena representación de la variabilidad del clima local. Debido a la gran extensión territorial de especie, otros estudios que abarquen la extensión geográfica de P. flexuosa son deseables para profundizar los resultados logrados.

In this work we report the phenological response experienced by the foliage of A. araucana seedlings to four levels of freezing temperatures (-2 °C, -6 °C, -10 °C and -15°C) induced during the active plant growth season. Nursery seedlings were exposed to different frost levels in a freezer under computer control. The results showed that after three weeks of the thermal treatments, 90% of the A. araucana seedlings remained with living leaves at temperatures up to -6°C, whereas when the temperature decreased to -10°C or lower, the seedlings showed a variable percentage of dead leaves and even total death of the foliage. Under natural conditions, late frosts in northern Patagonia may expose seedlings of A. araucana to potentially lethal consequences. Therefore, a better understanding of the response of A. araucana to extreme low temperatures is particularly useful for interpreting forest dynamics processes and for management and conservation guidelines in relation to future climate change scenarios.

En este trabajo se comunica la respuesta fenológica que experimenta el follaje de plantines de Araucaria araucana sometidos a cuatro niveles de temperaturas de congelamiento (-2°C, -6°C, -10°C y -15°C), inducidas durante la temporada de activo crecimiento vegetal. Para ello se utilizaron plantines de vivero y los distintos niveles de congelamiento fueron producidos en freezer mediante control por computador. Los resultados mostraron que, a tres semanas del tratamiento térmico, el 90% de los plantines de A. araucana mantuvieron vivas todas sus hojas hasta -6°C, mientras que al descender la temperatura del aire a -10°C o menos, los plantines presentaron porcentajes variables de hojas necrosadas hasta muerte total del follaje. En condiciones naturales, heladas tardías en el norte de Patagonia expondrían los plantines de A. araucana a consecuencias potencialmente letales. Por ello, un mayor conocimiento de la respuesta de A. araucana a extremos de frío resulta de particular utilidad para interpretar procesos de dinámica forestal y establecer pautas de manejo y conservación frente a escenarios de cambio climático.

Frost rings are defined as anatomically abnormal and ecophysiologically pathological structures. We studied frost injuries in tree-rings of Araucaria araucana trees growing at the northern limit of its natural distribution. We recorded 121 frost injuries at two sites in the northern xeric distribution of A. Araucana forests. Frost rings at both sites were primarily restricted to the middle frost ring section of the rings. These results represent the first attempt to report and describe the occurrence of these events for this species and region. These proxy records represent important indicators of extreme temperature conditions.

Las lesiones de heladas en los anillos de crecimiento de árboles son definidas como estructuras anatómicamente anómalas y ecofisiológicamente patológicas. En este trabajo se estudiaron estos anillos de heladas en árboles de Araucaria araucana creciendo al límite norte de su distribución natural. Se registraron 121 marcas de heladas para los dos sitios estudiados. En ambos sitios el mayor porcentaje de heladas se ubicaron en la mitad del anillo. Estos resultados representan un primer intento de informar y describir la ocurrencia de marcas de heladas en anillos de crecimiento para esta especie y la región. Registros de esta naturaleza representan importantes indicadores de eventos extremos en la temperatura.