A Changing Temperature Response with Elevation for Lagarostrobos Franklinii in Tasmania, Australia

A network of seven Huon pine ring-width chronologies is constructed from sites ranging in elevation from 200 to 950 metres above sea level in western Tasmania. The chronologies are analysed individually and collectively to explore Huon pine’s response to climate as a function of elevation. Three chronologies from greater than 700 metres in elevation exhibit a strong, direct response to temperature for most growing season months (p < 0:05), while three from below 700 metres exhibit a weaker, direct response to growing-season temperature, and a strong, inverse relationship with temperature of the prior season of growth, also significant at the 0.05 level. Moisture availability at these temperate rainforest sites is less growth-limiting than temperature, and significant correlations for January (inverse) and April (direct) of the year of growth largely reflect the inter-relationships between temperature, precipitation and cloudiness, and their combined influence on photosynthesis, particularly at higher-elevation sites. A rotated Principal Component Analysis reveals a clear grouping of the high and low-elevation chronologies, represented by the first and second eigenvectors, respectively. The 700 metre Lake Marilyn Low chronology is revealed to be a transitional site between the two groupings, and likely reflects an important climatic ecotone where both temperature and photosynthetically-active radiation drop below optimum levels for the species, and begin to directly inhibit growth. Tasmania’s west coast climate has been shown to exhibit a distinct vertical structure, exemplified by a subsidence-inversion layer above 900 metres. Temperature increases slightly with altitude above 930 metres (the elevation at which a peak in daily minimum and maximum humidity levels is observed) before decreasing again. A dense, orographically-generated cloud-zone of reduced light and temperature has a mean altitude between 700 and 900 metres, with the steepest drop in both air and soil temperature exhibited between 850 and 930 metres. This structure can account for Huon pine’s changing response to climate with elevation as described in this paper, and reinforces the importance of careful site selection for dendroclimatic research. In the case of reconstructing warm-season temperature from Tasmanian Huon pine, the desired signal might be maximised through sampling at the few rare, subalpine stands which have been located in western Tasmania. The great length afforded by the low-elevation Huon pine resource may ultimately yield a far more detailed reconstruction of regional climate throughout the Holocene, with respect to a vertical profile, following the development of more sound, mechanistically-based response models.