Dailan Pugh, North East Forest Alliance, January 2022
Why are forest transects worthwhile? With enough replicates they can be extrapolated across the whole of, or part of, a logging area to quantify:
- Current carbon storage and future sequestration potential (with application of an appropriate formulae basal area can be converted into above and below ground biomass volumes, and thus carbon storage, growth data can be applied to quantify CO2 sequestration)
- Densities of hollow-bearing and recruitment trees (for comparison to retention requirements (are there enough, will some be cut down?), including NRC recommendations for enhanced protection)
- Densities of special trees, ie Koala feed trees (for comparison to retention requirements, in Cherry Tree they can be used to determine whether the forest would constitute core Koala habitat if it was on private land in accordance with the Koala SEPP, and for determining whether the EEC Grey Gum-Grey Box WSF is more widespread where there is a rainforest understorey)
- Basal areas (which is the basic regulatory tool, ie requirements to retain 10-12m2)
These results can be compared to the logging protocols to identify potential logging impacts.
Conducting another survey in Doubleduke State Forest Feb 2021
The methodology can also be applied to logged forests to identify tree removal, damage to retained trees, and test compliance with CIFOA requirements. With diameters of stumps (adjusted for taper to estimate dbhob) a variety of other comparisons can be made.
For the Sandy Creek Koala Park we did plots in a patch of oldgrowth which enabled me to contrast this with the logged-over forests to assess the effects of a century of logging on biomass, carbon storage, tree hollows and nectar production.
On Sunday Andrew Murray and myself trialled undertaking a forest transect in Cherry Tree SF. We concluded that best would be a 100x20 m transect within which every tree >10 cm diameter (diameter at breast height (1.3m)) is measured (preferably with a dbh tape). For each tree identify: species, dbh, whether it is a canopy tree (estimate canopy height, ie 25-35m), presence of hollows (small, medium, large), signs of animal usage (such as distinctive Koala scratches, Koala scats, Yellow-bellied Glider notches), and logging damage (ie stumps, logging damage - if in logged area).
We broke the transect into 2x50m transects, ran a 50m tape out and marked points 10m each side at each end to sight outside edges. Where the understorey restricts sighting along the edges of the transect, more tags may be required. Each 50x20m transect is 1,000m2. You could combine 2 50x20m plots as we did to make a 100x20m plot to better sample overstorey, or you could also do some stand alone 50x20m plots to better sample variation. You need to GPS each end of transect. I also took GPS locations for each Koala feed tree (ie scratched trees).
You need to have someone who can identify tree species. A dbh tape is best to measure tree diameters, otherwise the most accurate way is probably to measure tree circumference with a normal tape and later convert to diameters. Also you need a GPS (or another means of identifying each end of the transect), a 50m tape, and a 10m tape. Transects could take a few hours each.
Transects need to be spread throughout the proposed harvest area and located randomly in an area of interest – the aim is to sample the range of variation that occurs. The more the better, with numbers depending on the area. For Sandy Creek we did 12-29 x 500m2 plots in each of 5 State Forests, and even 12 plots (ie 6,000 m2) seemed sufficient to provide a reasonable estimate of structure – so I reckon 6 x 100m transects is probably enough to reasonably sample Cherry Tree. For Sandy Creek we did 12.6m radius circular plots at 50m spacings, though I think 100x20m (or 50x20) will be more useful for characterising overstorey.
Download the representative data sheet here - one page is likely to be needed for each 50x20m transect.