Mariano M. Amoroso

The influence of climate change, site type, and disturbance on stand dynamics in northwest British Columbia, Canada

Stand and disturbance dynamics are key processes that need to be assessed along with climate-species interactions if we are to better understand the impacts of climate change on species. In this study we investigated the biotic interactions (competition) between species, the influence of disturbance type, and changes in resource availability (moisture and light) on the response of six tree species to climate change in the northwest region of central British Columbia, Canada. Two ecological models were parameterized, linked together and coupled to climate change scenarios to explore the interactions between: (1) the response of species in the regeneration phase and (2) the role of disturbance, resource availability and competition on determining stand composition and productivity. Climate change was found to reduce soil moisture availability which resulted in a decline in regeneration potential for all species on dry sites and negative to neutral responses on sites with higher water availability. Following fire, stand dynamics and composition were modeled to undergo significant changes under the 2080s climate compared to current climate conditions on dry and mesic sites. Changes in stand dynamics under climate change were marginal following bark beetle disturbances. While significant changes to stand dynamics were found on dry sites, the presented results suggest that the sites with the highest moisture availability maintain the same general stand dynamics and composition following disturbances under climate change. This study highlights the need to consider species response to climate change in interaction with existing stand conditions, disturbance type, competition, resource availability, not just temperature and precipitation.

Can a natural experiment be used as a tool to design partial cutting regimes? The decline of Austrocedrus chilensis forests, an example

The forests of Austrocedrus chilensis in Argentina suffer mortality from what is locally known as ‘mal del ciprés’. This disturbance usually appears as aggregations of dead trees of varying sizes. The mortality process seems unpredictable, and regeneration establishment is variable under these conditions. The highly variable mortality rates results in a natural experiment that allows the correlation of overstory mortality with regeneration rate. This correlation should then make it possible to estimate the regeneration success which would follow after different levels of partial cutting, allowing the purposeful direction of the regeneration process. We collected data from eight Austrocedrus chilensis-dominated stands and reconstructed overstory mortality over time and correlated it to the regeneration recruitment. Mortality showed two patterns: increasing ‘continuous’ mortality over time, and ‘pulses’ of important basal area loss in short periods. Overstory mortality had an effect on the recruitment and composition of the regeneration by allowing different species establishment depending on the degree of mortality. By quantifying mortality basal area and recruitment over time, we calculated estimates that can provide partial cutting guidance. Partial cuttings would then allow the purposeful direction of the regeneration process. Stand reconstruction studies provided a useful tool to help designing regeneration systems using a natural experiment. Some specific management implications for symptomatic A. chilensis forests are given.

Frost ring distribution in Araucaria araucana trees from the xeric forests of Patagonia, Argentina

Resumen en: Frost rings are defined as anatomically abnormal and ecophysiologically pathological structures. We studied frost injuries in tree-rings of Araucaria ara...

Establishment of Nothofagus pumilio at Upper Treelines Across a Precipitation Gradient in the Northern Patagonian Andes

ABSTRACT Trees at upper treelines are exposed to more extreme environmental conditions than those at lower elevations. Climate changes at the upper treeline facilitate the establishment or intensify the mortality of trees and, consequently, affect species distributions. The structure and density of individuals of Nothofagus pumilio above the upper treeline, together with their temporal patterns of establishment, were determined in three sites located along a west-east precipitation gradient across the Patagonian Andes. Patterns of tree establishment were compared to regional variations in temperature and precipitation, as well as to indexes of atmospheric circulation that modulate northern Patagonian climate. Mesic and dry sites along the moisture gradient have a lower density of newly established trees; however, individuals show larger basal diameters and greater annual growth rates, heights, and number of branches than those established in humid sites. In wet areas, the high density of individuals reflects the higher rates of N. pumilio establishment and survival. At drier treelines, low snow persistence, associated with longer growing seasons, appears to be related to the larger size of individuals. At all sites, patterns of tree establishment are characterized by an abrupt increase in recruitment starting in the mid-1970s and a marked decrease in the late 1990s. The onset of tree establishment above the treeline coincides with an increase in regional spring-summer temperature in the year 1977, concurrent with the negative-to-positive shift in the phase of the Pacific Decadal Oscillation (PDO). In contrast, the decrease in N. pumilio establishment since the late 1990s coincides with an opposite shift (positive to negative) in the PDO. This recent change in the PDO phase did not significantly modify the mean values but increased the interannual variability of the spring-summer temperatures in the region. Changes in the PDO, which encompasses complex variations in environmental conditions at the upper treeline, are more closely related to N. pumilio establishment than are variations in temperature or precipitation alone. In addition, the distinction between the effects of changes in mean values versus the effects of climate variability is crucial for properly predicting forest responses to climate changes.

Land‐use intensity indirectly affects ecosystem services mainly through plant functional identity in a temperate forest

1CONICET, Argentina; 2Instituto de Investigaciones en Recursos Naturales, Agroecología y Desarrollo Rural, Universidad Nacional de Río Negro Sede Andina, Mendoza, Argentina; 3Instituto Argentino de Investigaciones de Zonas Áridas, Mendoza, Argentina; 4Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Cuyo, Mendoza, Argentina; 5Freiburg Institute for Advanced Studies, University of Freiburg, Freiburg im Breisgau, Germany and 6Department of Natural Resource Sciences and McGill School of Environment, McGill University, Montreal, QC, Canada

South American Dendroecological Fieldweek 2016: Exploring Dendrochronological Research in Northern Patagonia

Abstract The South American Dendroecological Fieldweek (SADEF) associated with the Third American Dendrochronology Conference was held in El Bolsón, Argentina, in March 2016. The main objective of the SADEF was to teach the basics of dendrochronology while applying specific knowledge to selected research questions. The course included participants and instructors from six different countries. This report describes activities of the course and briefly summarizes exploratory group projects. The Introductory Group developed an Austrocedrus chilensis chronology from 1629–2015 and documented a persistent decline in growth since 1977 which supports the fact that the current severe drought is the most severe in the 386-year record. Based on regional A. chilensis chronologies from 32° to 39°S Latitude, the Stream Flow Reconstruction Group developed a regional 525 year-long reconstruction from Río Chubut and found the most severe drought episodes from 1490 to the present occurred from 1680–1705, 1813–1828, 1900–1920, 1993–2002, and from 2011 to the present. The Drought Reconstruction Group used A. chilensis annual tree-ring width chronologies to develop preliminary spatial field reconstructions of the Palmer Drought Severity Index spanning the Central Andes region. The reconstructions explain up to 81% of the 1907–1975 PDSI variance, indicating this tree species is powerful for informing on historical drought especially in very arid domains. The Dendroecology Group documented three spreading fires since the 1850s with a 12-year return interval but lack of fire for the last 94 years; they also documented a persistent decline in their chronologies in recent years, dating back to 1965.

Climate and Nothofagus pumilio Establishment at Upper Treelines in the Patagonian Andes

Due to its climate sensitivity, the upper treeline offers a unique opportunity to document variations in forest dynamics in response to current climate change. It is generally accepted that the expansion of the upper treeline is limited by cold temperatures. Consequently, warmer conditions in the context of global warming are expected to induce an advance of forests into alpine vegetation. To complement previous studies in the North Patagonia treeline, we conducted a study in the southern Patagonian Andes to: 1) characterize the temporal patterns of Nothofagus pumilio establishment in the upper treeline along a precipitation gradient, 2) establish the relationship between variations in regional climate and tree establishment, and 3) determine the influence of continental and hemispheric-scale climatic forcing on tree establishment at regional scale. At El Chalten-Laguna del Desierto area, the N. pumilio establishment above the upper treelines started at the mid-1970s and reached two peaks in the late 1980s-early 1990s and around the year 2000. Although tree establishment followed similar patterns along the precipitation gradient, we noted some differences between wet and dry forests. Whereas at the wettest sites the largest establishment peak occurred in the most recent, relatively-dry period, tree recruitment was more abundant in the earliest humid period at the driest treelines. Our studies suggest that the location of the N. pumilio upper treeline in the Patagonian Andes is sensitive to changes in climate. The increment in temperature during the past decades has facilitated tree recruitment; however, the rate of seedling establishment appears to be modulated by interactions between the temperature increase and variations in precipitation. The expansion of the upper treeline is mostly limited to 5-10 m from the abrupt treeline suggesting that seed dispersal and winds modulate the rate of spatial advance. While the recent expansion of the upper treeline in northern Patagonia was regulated by temperature and precipitation variations associated with the different phases of the Pacific Decadal Oscillation, the climatic variations induced by the positive trend of the Southern Annular Mode during the last decades have facilitated the establishment above the upper treeline in the southern Patagonian Andes.

Dendroecology: Lessons Learned and Future Frontiers

Over the past four decades dendroecology has been instrumental in shaping contemporary understanding of how forests around the world change over time. Dendroecological research has provided important new insights into the functioning of temperate, boreal, and tropical forests at sub-annual, annual, decadal, and centennial time scales. Importantly, dendroecological research has provided the empirical framework for our current understanding of how individual trees respond to their environment, whether background climatic conditions, the effects of local competition, the impacts of biotic (e.g., herbivory by insects and vertebrates, disease) or abiotic (e.g., fire, wind, floods, drought) disturbances, or interactions among multiple environmental factors. The fundamental strength of dendroecology is in providing a universal framework for interpreting individualistic responses of trees to their environment.

Forest Decline in Northern Patagonia: The Role of Climatic Variability

Forest decline is driven by several factors interacting in complex ways, and it is often exacerbated by climate, adding complexity to the process and making it more difficult to identify the causing factors. The long-term perspective provided by tree rings has proven to be successful for disentangling the causes of forest decline worldwide. We present recent dendroecological studies developed to determine the influences of climatic variation on the radial growth patterns and death of trees in declining Austrocedrus chilensis and Nothofagus pumilio forests in northern Patagonia, Argentina. These results were used to distinguish between possible causes and interactions of abiotic and biotic stress factors versus stand dynamics processes in the development of the forest declines. For our study forests, we found complex interactions between abiotic and biotic factors acting at different spatial and temporal scales that predispose trees, then incite and contribute to the development of the symptoms leading to their subsequent death. We summarize our findings in a conceptual model presenting forest decline as a spiral of processes driven by interactions between abiotic and biotic stress factors that predispose, incite and contribute to stand-level decline in these forests. Our framework formalizes an alternate hypothesis to single causal agents of decline in Patagonian forests by emphasizing the role and importance of climatic variability as a driver of decline.