Acting Facilities Manager Russ Drewry replies:
We do indeed have Pinus radiata (Californian/Monterey pine) which are approximately 46 years old covering about 40ha within the valley, mostly on the eastern side. They were planted as a crop for lumber. The recommended harvesting age for these is between 25 – 40 years.
The three main reasons why we haven’t removed them are:
Until the native bush regenerating beneath the pines takes a firmer hold, clearfelling them would have serious implications on the stability of the already fairly fractured friable ground that makes up the valley and could cause slips and soil erosion.
Because of what is below the trees (tracks, kiwi burrows, transect lines, nesting boxes, tuatara burrows & the fence) straight felling and removal, which would be the most cost effective solution, is out of the question. We already have to meticulously search around a felling site to identify & remove anything which may be at risk from a dropped tree and because of access issues have to leave the fallen trunks in situ which is not always ideal (although as they break down they can provide biodiversity benefits). Removal programs similar to the ones undertaken by the council to clear trees from the town belt using helicopters would be the best all round solution but this is extremely costly and time consuming.
Our natives need time to catch up
Some of our birds (kākā, kārearea, kererū, etc) like to perch in & use tall trees for various reasons. The tall native trees which these birds would naturally have used (kahikatea, rimu, miro, mataī, pukatea, rātā, etc) are few and far between and most are quite small because they have only been planted here since about 2000 and it will take many years (hundreds in some cases) to reach their magnificent full heights of 60m+ and become the emergent layer of the bush. Until this happens, removing the exotic pines would leave few emergent trees for our birds to use; this might encourage birds to venture beyond the safety of our pest-exclusion fence to find suitable alternatives, opening them up to predation by mammals.
BUT some of the things we are doing are:
- Replanting under them so as they begin to naturally senesce and “dismantle” themselves there will be regenerating bush beneath them to take their place and maintain soil integrity. We have to close the valley view track from time to time because some of the pine trees, exposed to high winds, drop branches or even fall over.
- Removing any juvenile pine trees.
- Planting the aforementioned natives so that over time they will reach the stature of tall emergent trees, making the exotic pines redundant!