Laboratory flammability experiments

Flammability experiments were undertaken on the fresh leaf material collected from the live plants, and surface litter, which consisted of woody branch and bark material. All leaf material was excluded from the litter samples as leaves of varying dryness were examined separately.

3.2.2.1 Laboratory procedures

The samples of fresh leaf material were processed as soon as possible on return to the laboratory, which was generally about two hours after collection. For each species, 10 leaf samples were randomly selected from the original pool of material. From the same pool of material a pair was then selected for each of the original 10 samples which was of near identical size and shape. The duplicate leaves were weighed as a batch and placed in the drying oven at 105 °C for 48 hours, while the original leaves were used in the flammability experiments. This was done in order to determine an estimate of foliar moisture content from samples that were to be destroyed in the flammability experiments. The dried batch was then re-weighed to determine an estimate of percent foliar moisture content using equation 3.1.

For each single leaf sample the weight, length, area and thickness were measured. However, not all species had leaves of sufficient size to be studied individually. In cases in which the leaf was judged too small to provide sufficient data, a branchlet of leaves was examined. This was the case for Nothofagus gunnii, N. cunninghamii and Bauera rubioides. Length of all leaf and branchlet samples was measured to the nearest millimetre with a scale ruler. For N. gunnii, N. cunninghamii and B. rubioides length was considered to be from the apex of the highest leaf on the branchlet to the base of the lowest leaf. Weight was measured to the nearest gram on an electronic scale. Leaf thickness was measured to the nearest millimetre with callipers and standardised by taking a

25 thickness two-thirds of the way to the midrib, near the midpoint of the lamina (Gill and Moore 1996). For N. gunnii and N. cunninghamii the leaf thickness was measured as the thickness of the leading leaf two-thirds of the way to the midrib. For B. rubioides, thickness was recorded as the thickness of the stem, half way along the length of the branchlet. Area of each leaf was

determined by scanning the samples, calculating the number of pixels and converting this number to millimetres squared. For N. gunnii and N. cunninghamii branchlets, the area was calculated individually for each sample. For all other leaf material the average area was calculated from between 18 and 77 randomly selected samples, depending on the size of the leaves, with a greater number of samples taken from smaller leaves. Area was not calculated for B. rubioides. The volume of each leaf was determined for Anodopetalum biglandulosum, Atherosperma moschatum,

Banksia marginata, Eucryphia lucida, Eucalyptus nitida and Orites diversifolius using the following equation:

Volume = (SA * 2) * t

Equation 3.2 where SA is the mean surface area for each species and t is the thickness of the leaf sample, measured two-thirds of the way to the midrib.

Branch litter was divided into the following diameter size classes: 0-3 mm, 3.1-6 mm, and 6.1-25 mm, modified from Brown et al. (1982). Fresh weight, diameter and length were recorded as for the leaf samples. Volume was determined for each branch by assuming a cylindrical shape and applying the formula for a cylinder, with diameter measured from the mid-length of each sample. In addition, bark litter was prominent in the litter at the Eucalyptus coccifera woodland and this was used as an additional sample, with weight and length of individual pieces being recorded.

3.2.2.2 Flammability

Ten samples of each species (leaf material) or class (litter material) were measured by exposing them to an ignition source, in the form of a gas flame of constant height burning vertically within the still air of a fume cabinet (Dickinson and Kirkpatrick 1985). Leaf material was held in a natural position with tongs, with the tip of the vegetation being subjected to the flame. Woody material was held at a slight angle to the horizontal, with the end of the branch exposed to the flame. For all samples, the rate of spread and time to ignition were recorded with a stopwatch.

26 Time to ignition was defined as the amount of time required until flames appeared on the leaves. Flaming was not necessarily sustained. Where ignition was not sustained, the time to full

combustion whilst being subjected to the flame was recorded (“time to consumption”). The nature of burning (sparking, spitting, smoking, smouldering) was noted.

3.2.2.3 Moisture content

The effect of moisture content on the flammability of the fresh leaf samples was tested by repeating the above procedures on samples of varying moisture content. Samples were dried slowly by being placed in a plant press with samples then subjected to the flammability tests described above every 18, 24, 42, 48, 72 and 120 hours. At each sampling time, paired samples were taken to determine the percent foliar moisture content using the oven drying method described above and equation 3.1.

The woody litter samples were air dried on a drying rack in the laboratory, where the daily air temperature was an average of 23.5 °C and the mean relative humidity was 44%. Ten samples of each diameter size class were tested periodically for time to sustained ignition, which was

recorded with a stopwatch. The bark sample was only tested once as 100% of the samples ignited. After each test the weight, length and diameter were measured for each sample as well as the combined weight of all samples in each size class. This was used to determine the moisture content for each size class sample after oven drying for 48 hours at 105 °C and using Equation 3.1. Once woody litter samples had been oven-dried to determine moisture content, 10 samples of each size class were tested for rate of spread, using the same methods as for leaves. This provided the rate of spread at zero percent moisture content.

The woody litter samples generally consisted of the branch material of the dominant tree in each habitat; however there was also some branch litter from two additional identifiable species. These were A. moschatum, in the callidendrous forest, and B. rubioides, from the deciduous beech scrub. Notes were made when samples came from one of these two species.

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