Tree-ring based climate reconstructions have been critical for understanding past variability and recent trends in climate worldwide, but they are scarce in Australia. This is particularly the case for temperature: only one tree-ring width based temperature reconstruction – based on Huon Pine trees from Mt Read, Tasmania – exists for Australia. Here, we investigate whether additional tree- ring parameters derived from Athrotaxis cupressoides trees growing in the same region have potential to provide robust proxy records of past temperature variability. We measured wood properties, including tree-ring width (TRW), mean density, mean cell wall thickness (CWT), and tracheid radial diameter (TRD) of annual growth rings in Athrotaxis cupressoides, a long-lived, high-elevation conifer in central Tasmania, Australia. Mean density and CWT were strongly and negatively correlated with summer temperatures. In contrast, the summer temperature signal in TRW was weakly positive. The strongest climate signal in any of the tree-ring parameters was maximum temperature in January (mid-summer; JanTmax) and we chose this as the target climate variable for reconstruction. The model that explained most of the variance in JanTmax was based on TRW and mean density as predictors. TRW and mean density provided complementary proxies with mean density showing greater high-frequency (inter-annual to multi-year) variability and TRW showing more low-frequency (decadal to centennial-scale) variability. The final reconstruction model is robust, explaining 55% of the variance in JanTmax, and was used to reconstruct JanTmax for the last five centuries (1530–2010 C.E.). The reconstruction suggests that the most recent 60 years have been warmer than average in the context of the last ca. 500 years. This unusually warm period is likely linked to a coincident increase in the intensity of the subtropical ridge and dominance of the positive phase of the Southern Annular Mode in summer, which weaken the influence of the band of prevailing westerly winds and storms on Tasmanian climate. Our findings indicate that wood properties, such as mean density, are likely to provide significant contributions toward the development of robust climate reconstructions in the Southern Hemisphere and thus toward an improved understanding of past climate in Australasia.

Female and male plants often differ in reproductive effort and habitat requirements. The aim of this study was to analyze these differences between the sexes and the effect of climate on tree-ring width in European yew (Taxus baccata). The study was conducted in five yew populations in western Poland. Wood samples were taken from 196 trees (98 females and 98 males) and subjected to the standard procedure of dendrochronological dating. Mean tree-ring width was significantly higher in males since about the beginning of sexual maturity. No such relationship was observed in the youngest population, which is the most distant from the current geographic limit for this species. In most of the analyzed populations, width of tree rings in female individuals, in contrast to males, was negatively correlated with high temperatures in August and September in the year prior to the formation of the tree ring, and correlated positively with precipitation in June and July in the current year. The differentiation of tree-ring width between males and females likely began when the yew trees reached sexual maturity, probably because of the assumed greater reproductive effort of females in comparison with males. The lack of difference in the youngest population may result from a short time since the beginning of sexual maturity or from a milder climate in that region. Different reactions of the two sexes to climate indicate that this may affect the range and viability of populations at the limits of the range.

Changes in the productivity of temperate forests have important implications for atmospheric carbon dioxide (CO2) concentrations, and many efforts have focused on methods to monitor both gross and net primary productivity in temperate forests. Remotely sensed vegetation indices provide spatially extensive measures of vegetation activity, and the Enhanced Vegetation Index (EVI) has been widely linked to photosynthetic activity of vegetation. Networks of tree ring width (TRW) chronologies provide ground-based estimates of annual net carbon (C) uptake in forests, and time series of EVI and TRW may capture common productivity signals. Robust correlations between mean TRW and EVI may enhance spatial extrapolations of TRW-based productivity estimates, ultimately improving understanding of spatio-temporal variability in forest productivity. The research presented in this thesis investigates potential empirical relationships between networks of TRW chronologies and time series of Landsat EVI and Landsat-based phenological metrics in the Northeast United States. We hypothesized that mean TRW is positively correlated with mean monthly EVI during the growing season, EVI integrated over the growing season, and growing season length. Results indicate that correlations between TRW and EVI are largely not significant in this region. The complex response of tree growth to a variety of limiting climatic factors in temperate forests may decouple measures of TRW growth and canopy reflectance. However, results also indicate that there may be important lag effects in which EVI affects mean TRW during the following year. These findings may improve understanding of links between C uptake and growth of tree stems over large spatial scales.

Long-duration records are necessary to understand and assess the long-term dynamics of natural systems. The purpose of this research was to use dendrochronologic modelling to construct proxy histories of hydroclimatic conditions and Pacific salmon abundance in west central British Columbia. A multi-species regional network of tree ring-width and ring-density measurements was established from new and archived tree-ring chronologies. These chronologies were then used in multivariate linear regression models to construct proxy records of nival river discharge, summer temperature, end-of-winter snow-water equivalent (SWE), the winter Pacific North America pattern (PNA) and Pacific salmon abundance. All proxy hydroclimate records provide information back to 1660 AD. Reconstructions of July-August mean runoff for the Skeena and Atnarko rivers describe below average conditions during the early- to mid-1700s and parts of the early-, mid- and late-1900s. Models describe intervals of above average river discharge during the late-1600s, the early-1700s and 1800s, and parts of the early- and mid-1900s. Fluctuations in proxy reconstructions of July-August mean temperature for Wistaria and Tatlayoko Lake, May 1 SWE at Mount Cronin and Tatlayoko Lake and October-February PNA occurred in near synchrony with the shifts described in runoff records. Episodes of above average runoff were typically associated with periods of enhanced end-of-winter SWE, below average summer temperature and positive winter PNA. A history of Pacific salmon abundance was reconstructed for four species of salmon (chinook, sockeye, chum and pink) that migrate to coastal watersheds of west central British Columbia. Proxy records vary in length and extend from 1400 AD, 1536 AD and 1638 AD to present. Salmon abundance reconstructions varied throughout the past six centuries and described significant collapse in population levels during the early-1400s, the late-1500s, the mid-1600s, the early-1700s, the early-1800s and parts of the 1900s. Wavelet analyses of reconstructed hydroclimate and salmon population records revealed low- and high-frequency cycles in the data. Correlation analyses related reconstructions to atmospheric teleconnection indices describing variability in North Pacific sea surface temperatures and the Aleutian Low pressure centre. To a lesser degree, relationships were also established between reconstructions and the El Niño-Southern Oscillation. Results thus confirm the long-term influence of large-scale ocean and atmospheric circulation patterns on hydroclimate and Pacific salmon abundance in west central British Columbia. The reconstructions introduced in this thesis provide insights about the long-term dynamics of the west central British Columbia environment. Several reconstructions presented in this thesis provide novel contributions to dendrohydroclimatic and paleoecologic research in Pacific North America. Proxy runoff records for the Skeena and Atnarko rivers are the first to be constructed for nival-regime basins in British Columbia. The models of Skeena River runoff and Mount Cronin SWE are additionally the first reconstructions of runoff and snowpack in Pacific North America based on a ring-density chronology, demonstrating the significant contribution that wood density measurements can make to dendrohydroclimate research. The models of Pacific salmon stocks are the first to utilize climate-sensitive tree-ring records to construct a history of regional salmon abundance and thus represent a significant advancement to paleoecological modelling. / Graduate

No description available.

I arbetet har jag samlat in borrprovkärnor från 21st levande träd 218-27år gamla från en lokal nära Torneträsk, behandlat och analyserat borrprovkärnorna vad gäller ringvidd (TRW), eng. tree ring width, och densitet (MXD), eng. maximum density, samt studerat hur väl resulterande kronologier följer sommarmedeltemperaturerna från Abisko väderstation. I arbetet ges kort bakgrundsfakta om det valda geografiska områdets, Torneträsk, roll och betydelse i det aktuella forskningsområdet, dendroklimatologi, och beskrivningar av några för uppgiften viktiga aspekter och metoder och problematiken med fenomenet divergence phenomena (DP). Datat är förberett för att användas som en förlängning till den existerande kronologin. Dendrokronologin vid Torneträsk innehåller innan detta; TRW som sträcker sig över 7 400år (år 5704 f.kr. – år 2004) och MXD som sträcker sig över 1 563år (åren 441 – 2004). Vid insamlandet har unga träd inkluderats i proverna för att undvika DP vid skapandet av kronologin. / In this project I have sampled 21 living trees in the age range of 218-27years old in the Torneträsk area, northern Sweden. I have prepared and analysed the samples regarding ring width (TRW) and maximum density (MXD) and investigated the correlation to summertemperatures from the nearby wheather station in Abisko. The data has been prepared as an update for the now existing chronology from the area which up until this contains TRW data spanning over 7 400years (BC 5704 – AD 2004) and MXD data over 1 563years (AD 441 – 2004). Young trees as well as older were sampled in an attempt to avoid creating divergence phenomena (DP) from the update.