Farm Forestry New ZealandHow Old Before You Can Harvest?
Northland Totara Working Group newsletter, August 2019.
Ring counts of harvested tōtara trees reveal age
Scion scientists have studied discs from farm-tōtara trees harvested as part of the Tōtara Industry Pilot (TIP) project. The median age of the trees harvested was 83 years old.
Discs from a random sample of 33 trees harvested from the Cookson property at Kawakawa, were analysed by forest ecologist, Dejan Firm, at Scion.
Key findings are:
- The mean diameter at breast height (DBH) was 50cm (49.8)
- The median age was 83 years
- The majority (around 75%), was less than 90 years old
- The mean annual increment for DBH was 0.59cm
- DBH is a poor predictor of tree age –
i.e. similar-sized tōtara trees can differ markedly in their age. (For example; two trees that had almost identical diameters of 35.6 and 35.8cm DBH, were aged at 86 versus 48 years respectively)
These results are in line with age estimates based on ring counts from an earlier harvest off the McGee property in Kaeo, which indicated the same mean DBH of 50cm and mean age of 85 years.
These trees were all selectively harvested from stands that have naturally regenerated on farms but have not been tended or managed for timber production. Under continuous cover forest management a range of tree sizes and ages are involved.
These results suggest that in managed plantations of planted trees, on similar sites, harvesting could start well-within 80 years.
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