Fidel Alejandro Roig

Tree-Ring Formation, Radial Increment Periodicity, and Phenology of Tree Species from a Seasonal Semi-Deciduous Forest in Southeast Brazil

Many tropical tree species produce growth rings in response to seasonal environmental factors that influence the activity of the vascular cambium. We applied the following methods to analyze the annual nature of treering formation of 24 tree species from a seasonal semi-deciduous forest of southeast Brazil: describing wood anatomy and phenology, counting tree rings after cambium markings, and using permanent dendrometer bands. After 7 years of systematic observations and measurements, we found the following: the trees lost their leaves during the dry season and grew new leaves at the end of the same season; trunk increment dynamics corresponded to seasonal changes in precipitation, with higher increment (active period) during the rainy season (October–April) and lower increment (dormant period) during the dry season (May–September); the number of tree rings formed after injuries to the cambium coincided with the number of years since the extraction of the wood samples. As a result of these observations, it was concluded that most study trees formed one growth ring per year. This suggests that tree species from the seasonal semi-deciduous forests of Brazil have an annual cycle of wood formation. Therefore, these trees have potential for use in future studies of tree age and radial growth rates, as well as to infer ecological and regional climatic conditions. These future studies can provide important information for the management and conservation of these endangered forests.

Seasonal cambium activity in the subtropical rain forest tree Araucaria angustifolia

Information on the timing and dynamics of tree ring formation is essential to assess the seasonal behavior of secondary wood growth and its associated environmental influences. Araucaria angustifolia is a dominant species in highland pluvial ecosystems of southeastern South America. Previous investigations indicated that their growth rings are formed annually, but no information exists about the timing of growth ring formation and the environmental triggers influencing cambium activity. In this paper we examine inter- and intra-annual cambial activity in A. angustifolia, through anatomical and dendrochronological evidence at two study sites, and model the relationships between regional climate variation and intra-annual tree ring formation. The results confirm the annual growth ring formation in A. angustifolia and indicate that its growth season extends from October to April. Day length and temperature were the main environmental factors influencing the seasonal cambium activity. Our results evidence the dendrochronological potential of A. angustifolia for ecological and climatological studies in southeastern South America.

Interdecadal climatic variations in millennial temperature reconstructions from southern South America

Two millennial reconstructions of mean summer temperature departures from the eastern and western slopes of the southern Andes (1120 and 3620 years, respectively) have been spectrally analyzed to determine the most significant modes of climate variations in southern South America during the last millennia. Blackman-Tukey and Maximum Entropy spectral analyses of these reconstructions identify temperature oscillations with periods of 35.8, 23.9, 9.5, 6.0–6.9, 5.4–5.7, 4.5–4.8, and 3.4–3.7 years. Because of the relatively flexible standardization used to derive the temperature reconstructions, a large part of the variance (related to the oscillations of summer temperature) is concentrated in short-term periods. A new set of eight long tree-ring chronologies from Fitzroya cupressoides (ranging from 1120 to 3620 years in length), has been used to develop a regional record of tree-ring variations during recent millennia in the southern Andes. A more conservative detrending than that used for developing the temperature reconstructions has been employed here to preserve the low frequency components in the tree-ring series. Maximum Entropy spectral analyses for different filter orders indicate prominent peaks at around 250, 77, 50, 33, 21, 17, 15, and 11 years. Some power is also seen at 4–7 years, probably associated with El Nino-Southern Oscillation events. The 11, 21 and 77-year terms may be related to long-term solar variations or long-term circulation of the Southern Oceans. Ocean-atmosphere model predictions suggest the possibility of using the South American tree-ring records to reconstruct past changes of the thermohaline circulation in the Atlantic Ocean.

Fuegian floating tree-ring chronology from subfossil Nothofagus wood

The discovery of subfossil Nothofagus wood buried in several peat bogs of Argentine Tierra del Fuego is reported. A provisional, fragmented-floating tree-ring width chronology covering the last 1400 years has been obtained. Statistical and spectral analysis revealed no significant differences between the present and floating Tierra del Fuego tree-ring chronologies. Some cyclical growth peculiarities found in both modern and floating chronologies are discussed.

CAMBIAL GROWTH PERIODICITY STUDIES OF SOUTH AMERICAN WOODY SPECIES – A REVIEW

This paper reviews histological studies of cambium activity in South American woody species and provides future research prospects. The majority of the studies almost exclusively describe radial increment and/or its periodicity. There are 15 papers concerning the cambial activity of 17 woody species from the South American flora and 3 exotic species in 4 countries that were published to date. Despite endogenous factors affecting the radial meristem, the seasonality of rains has been identified as the main factor influencing cambial activity in the tropics and subtropics. There is a lack of standardization and a need for improvement and discussion concerning the methods used. Moreover, radial growth studies conducted by monitoring cambium cell production are still scarce in South America, especially when considering the high diversity of the continent’s flora and ecosystems.

Dendroclimatology from Regional to Continental Scales: Understanding Regional Processes to Reconstruct Large-Scale Climatic Variations Across the Western Americas

Common patterns of climatic variability across the Western Americas are modulated by tropical and extra-tropical oscillatory modes operating at different temporal scales. Interannual climatic variations in the tropics and subtropics of the Western Americas are largely regulated by El Nino-Southern Oscillation (ENSO), whereas decadal-scale variations are induced by long-term Pacific modes of climate variability such as the Pacific Decadal Oscillation (PDO). At higher latitudes, climate variations are dominated by oscillations in the Annular Modes (the Arctic and Antarctic Oscillations) which show both interannual and longer-scale temporal oscillations. Here we use a recently-developed network of tree-ring chronologies to document past climatic variations along the length of the Western Cordilleras. The local and regional characterization of the relationships between climate and tree-growth provide the basis to compare climatic variations in temperature- and precipitation-sensitive records in the Western Americas over the past 3–4 centuries. Upper-elevation records from tree-ring sites in the Gulf of Alaska and Patagonia reveal the occurrence of concurrent decade-scale oscillations in temperature during the last 400 years modulated by PDO. The most recent fluctuation from the cold- to the warm-phase of the PDO in the mid 1970s induced marked changes in tree growth in most extratropical temperature-sensitive chronologies in the Western Cordilleras of both Hemispheres. Common patterns of interannual variations in tree-ring chronologies from the relatively-dry subtropics in western North and South America are largely modulated by ENSO. We used an independent reconstruction of Nino-3 sea surface temperature (SST) to document relationships to tree growth in the southwestern US, the Bolivian Altiplano and Central Chile and also to show strong correlations between these regions. These results further document the strong influence of SSTs in the tropical Pacific as a common forcing of precipitation variations in the subtropical Western America during the past 3–4 centuries. Common patterns of interdecadal or longer-scale variability in tree-ring chronologies from the subarctic and subantarctic regions also suggest common forcings for the annular modes of high-latitude climate variability. A clear separation of the relative influence of tropical versus high-latitude modes of variability is currently difficult to establish: discriminating between tropical and extra-tropical influences on tree growth still remains elusive, particularly in subtropical and temperate regions along our transect. We still need independent reconstructions of tropical and polar modes of climate variability to gain insight into past forcing interactions and the combined effect on climates of the Western Americas. Finally, we also include a series of brief examples (as ‘boxes’) illustrating some of the major regional developments in dendrochronology over this global transect in the last 10 years.

Clues for dendrochronology from studies of wood structure and function

Summary Dendrochronological interpretation relies on the existence of relationships between data recorded in the plant, and the environment. Studies of wood structure and function can provide information that will clarify the relationships, including the ranges of conditions over which they are valid, and the probabilities associated with the relationships. Descriptive studies describe patterns. They can summarize short or long time scales, and can document phenotypic, genotypic, community, population, or evolutionary responses. Mechanistic studies attempt to show the causes of the patterns, either through plausible explanations or through duplication of stimuli to show that they cause the expected effect. We need more studies of both types. Our knowledge about physiology of wood formation will benefit especially from research on the stimuli and processes of wood development; on wood patterns in more ecosystems, plant parts, and growth forms; and on which factors within a plant can compensate for, and interact with, other factors. We need more techniques for rapid assessment of plant structure. Process-based models can be used more fully to highlight which areas of structure/function/environment we understand well and which areas we do not. Lastly, we need to continue working in multi-disciplinary groups and becoming cross-trained in a wide range of scientific and technological areas. The more clues we have to the relationships between plant structure function and the environment, and the better the collective knowledge and cross-communication that exists within a research group, the better that group will be at interpreting their dendrochronological data not only to propose the most likely scenarios, but also the range of possible scenarios and their likelihoods.

Understanding Climate from Patagonian Tree Rings

Publisher Summary This chapter focuses on recent dendroclimatic research in southwestern South America by using tree rings from subantarctic species as proxy for climate. The paleoclimate background for different time-window scales are deduced from new tree ring data sets interpreted in a context of large-scale climate dynamics or forcings. Compared to the large diversity of tree species and even shrubby plants in the Patagonian region, there is only a short list of species that are appropriate for growth ring studies. Nothofagus is the most diverse and widespread tree genus in the Patagonian Andes forests. Tree rings formed in N. pumilio have proved to be high-quality material for dendrochronological research. The proof of the strong effects of the physical environment on the development of the annual wood increments is the high interseries correlation at any latitudinal site . The factor that influences more growth, temperature or precipitation, appears to depend on the ecological characteristics of the forest environment. Tree ring chronologies from trees growing in more xeric environments indicate that precipitation is the main limiting factor, while chronologies from trees growing in more humid or altitudinal sites indicate that temperature is the more determining factor for growth. These growth/climate models have been the baseline for ecological and dendroclimatic reconstructions in the southern Andes.

North Atlantic oscillation signatures in Western Iberian tree-rings

Abstract. Exactly dated ring‐width chronologies derived from Pyrenean oak and sweet chestnut trees growing in northern Extremadura, Spain, were evaluated for their potential as proxies for regional precipitation and North Atlantic Oscillation variability. The relationships among tree‐rings, instrumental climatic records, and three versions of the NAO index were computed for different time subperiods over the last century. The results indicate that tree‐ring records reflect, with variable intensity, both short‐term and long‐term variations in climate. Multiple correlation and regression analysis revealed that summer precipitation appeared to be the major factor affecting tree growth at inter‐annual timescales. Moreover, since fluctuations in accumulated variability in annual rainfall over southwest Iberia are controlled by winter precipitation, the accumulated rainfall (August of the year n‐1 to July of year n) and winter NAO indices are also strongly correlated with tree‐ring records at interdecadal timescales. This relationship appears to be especially strong during the second half of the 20th century, which is consistent with an increase of the NAO signal in the annual precipitation during the later part of the century. These results indicate that tree‐rings from western Iberia are potential proxies of the NAO variability, useful to be included in palaeoclimatic model studies.

Sensitivity of tree ring growth to local and large-scale climate variability in a region of Southeastern Brazil

We explored the relationship between tree growth in two tropical species and local and large-scale climate variability in Southeastern Brazil. Tree ring width chronologies of Tectona grandis (teak) and Pinus caribaea (Caribbean pine) trees were compared with local (Water Requirement Satisfaction Index—WRSI, Standardized Precipitation Index—SPI, and Palmer Drought Severity Index—PDSI) and large-scale climate indices that analyze the equatorial pacific sea surface temperature (Trans-Niño Index-TNI and Niño-3.4-N3.4) and atmospheric circulation variations in the Southern Hemisphere (Antarctic Oscillation-AAO). Teak trees showed positive correlation with three indices in the current summer and fall. A significant correlation between WRSI index and Caribbean pine was observed in the dry season preceding tree ring formation. The influence of large-scale climate patterns was observed only for TNI and AAO, where there was a radial growth reduction in months preceding the growing season with positive values of the TNI in teak trees and radial growth increase (decrease) during December (March) to February (May) of the previous (current) growing season with positive phase of the AAO in teak (Caribbean pine) trees. The development of a new dendroclimatological study in Southeastern Brazil sheds light to local and large-scale climate influence on tree growth in recent decades, contributing in future climate change studies.