Finally: My Research Results

Treeline

The aim of my research was to investigate the Victorian treeline physiognomy (i.e. the general position, form and appearance of the treeline) after a major disturbance, building on a previous data set collected shortly after wildfire. This research investigated the key questions that might indicate permanent change over the medium to long term. It was assessed by evaluating seedling elevation, density and key factors driving seedling establishment at treeline ecotones burned during the 2003 wildfires, and then re-examining the specific locations initially measured.

Locations

Seedlings found in the Victorian Alps after fire are establishing themselves in the alpine zone at higher elevations than the current treeline, and in greater numbers in the subalpine zone in locations where competition is constrained, litter is minimised, and there are adequate amounts of original trees with girths of approximately 50cm. Subsequently, the models suggest that the Victorian treeline physiognomy has slightly changed due to the 2003 alpine fires.

Model1

The analysis of increase in treeline elevation after fire was limited by few seedlings establishing above the current treeline. Despite this, a comparison of the burnt and unburnt transect models indicates that seedling establishment probabilities above the treeline are greater after fire compared to locations long absent of fire. This implies an increase in seedlings at elevations higher than the treeline after fire. The model calculates that there is a 31% chance of seedling establishment two metres above the treeline, and an 18% chance five metres above the treeline. Even higher elevations estimate much smaller probabilities. Subsequently, it is likely that only single trees will sparingly establish within the tree species zone, and consequently become outpost trees.

Model 2

An increase in treeline density after fire is supported by modelling, as seedling numbers are predicted to reach a maximum when fire is a recent occurrence. However, the Time Since Fire predictor variable was found to have 25% less influence than Litter, and 20% less influence than Evenness in maximising seedling numbers as calculated during sensitivity analysis. This suggests that fire may initially facilitate additional seedling numbers, however the magnitude of the density change is more dependent on the amount of competition in the area coupled with the quantity of litter cover. Locations that exhibit evenness across quadrat features are much more likely to support multiple seedlings, most likely due to a reduction in competition, and where a niche space can be realised. Secondly, a reduction in the amount of litter coverage within a location increases the number of seedlings. This is probably because litter acts as a barrier to seedling germination and emergence. In contrast, a decrease in litter allows greater seedling numbers to establish.

Model 3

Modelling of factors that influence seedling establishment after fire determined that apart from competition and litter, the amount of trees and their age are significant macro level factors influencing subalpine seedling establishment. Seedling counts were highest due to significant influences of competition and litter, and this was verified by models which determined a 91% probability of seedling establishment when competition and litter was minimised.
Tree characteristics were found to be imperative to seedling establishment. Tree girths between 20cm and 50cm are the only circumferences that can result in seedling probabilities above 90%, with substantial probability decreases above and below these girths. By relating girth to the age of the tree, this outcome ultimately defines the optimal reproductive age of the stand to facilitate seedling establishment after fire. Using previously created models that evaluate the relationship of Eucalyptus pauciflora subsp. Niphophila, tree girths of 20cm to 50cm correspond to tree ages of approximately 24 years to 42 years.
Finally, the quadrat must have a sufficient amount of trees to facilitate seedling success. A seedling establishment probability of above 90% was modelled to occur in locations where tree coverage ranges between 45% and 50% of the total area of the quadrat.

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