Other Effects

Tea trees are harvested by cutting the main stem near ground level, leaving a bare stump that will produce the coppice regrowth. However it takes time to produce a new canopy and during the first 3 months after harvest, the growth rate was 46% of that during months 4-6, the most efficient stage (Murtagh 1996). After 6 months, new shoots were less vigorous than before and the growth rate declined to 71% of the stage two rate. The relative rates were calculated with all other conditions remaining constant. The best yields of biomass were obtained by timing harvests so that the second and third regrowth stages coincided with the best environmental conditions for growth. The analysis of the effect of water stress on yield provided a good example of the gains from following this approach. Across all harvest times, water stress reduced biomass yields by an average of 24%. However, an October harvest that matched the first stage of regrowth to the driest period, had only a 7% reduction in yield due to water stress. This result reflected in part the assumption, supported by the functional analyses, that there is no water stress soon after harvesting because of the large root to shoot ratio (Blake and Tschaplinski 1986).

Melaleuca species are reputed to be very tolerant of water logging. Gomes and Kozlowski (1980) found no effect of 30 days flooding in stagnant water on the growth of M. quinquenervia, but longer periods did reduce growth. Bolton and Greenway (1996) obtained good growth from M. alternifolia growing in 100-150mm deep, flowing sewage effluent over 20 months, but it is unlikely if the same tolerance would be present in stagnant water with a higher oxygen tension. Colton and Murtagh (1990) noted that growth was depressed on waterlogged soil.


Because the two are not closely related, the combined effect of oil concentration and leaf yield gives a wide range in potential oil yield. Colton and Murtagh (1990) indicated that the oil yield could range from a low of 43kg/ha/yr to a high of 392kg/ha/yr, with a yield of 150-200kg/ha/yr representing a realistic target for most plantations in northern NSW.

Since these projections were recorded in 1990, there has been no confirmed advance in the potential oil concentration on a plantation scale, but the situation could change in the near future. Doran et al. (1996) recorded a 60% increase in oil concentration in plants grown from seed from a selected provenance, over the concentration in plants from selected lines used in commercial nurseries. Williams (1995) has developed clones that produced more than twice the oil yield of unselected trees. Efforts are proceeding to confirm that these gains can be achieved in commercial plantations, but at this stage it would be premature to use either set of work to adjust the projected oil yields. Apart from the use of genetic improvement to increase the oil concentration, it might be possible to use preharvest treatments to increase the concentration, but little work has been done in this regard.

Some progress has been made since 1990 towards producing higher leaf yields by fine-tuning the agronomic procedures in growing a crop (Murtagh 1998). The expected yields in Table 3 were obtained by increasing the previous estimates of leaf yield (Colton and Murtagh 1990) by 5%, and using the leaf: twig and twig: biomass ratios in Murtagh (1996), and a mean dry matter content of 40% to calculate the other plant yields. In addition to the above gain, more growers are producing crops in the higher yielding categories, so the industry average has increased by more than 5%. A realistic yield target would be 170-220kg oil/ha.

Table 3 Typical yields of tea tree under three growing conditions

Growing Conditions

Growing Conditions

Table 3 Typical yields of tea tree under three growing conditions




Leaf yield (t DM/ha)




Twig yield (t DM/ha)




Biomass yield (t DM/ha)




Biomass yield (t GW/ha)




Oil yield (kg/ha) @ low cone.*




@ medium conc.




@ high conc.




*Representative oil concentrations are 30mg/g (low), 55mg/g (medium), and 80mg/ g (high). See text for explanation of plant fractions.

*Representative oil concentrations are 30mg/g (low), 55mg/g (medium), and 80mg/ g (high). See text for explanation of plant fractions.


Tea tree oil is produced from trees grown as a row crop. The cultural aim is to maximise the oil concentration in leaves and the yield of leaf at harvest time.

The oil concentration follows a seasonal trend, with the highest concentration in summer and the greatest amplitude between seasons in the cooler localities. Additional short-term variation is superimposed on the seasonal trend and is more marked in plants with a high oil concentration. The rapid recovery in concentration following a short-term loss indicates that new oil is obtained either from direct synthesis or interconversion from another chemical form. The oil concentration increases with increasing temperature and humidity, but was not altered by irrigation on a site with subsoil moisture. The observed changes in oil concentration are consistent with a double pool conceptual model where some oil is held in a stable storage, and the remainder in an organ that is subject to gains and losses of oil.

The yield of leaf is primarily determined by the total biomass yield of a tree. Trees grow best at high temperatures, and the effect of water stress on growth is most marked in the post-flush stage of growth. Growth is most efficient during 4-6 months after harvest when a new canopy has developed and the shoots are relatively young. Timing a harvest to synchronise this optimum growth stage with the best seasonal conditions for growth gave the highest biomass yields.


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