Belief that native trees grow slowly is wrong say experts

Foresters wanting to plant woodlots of native trees for commercial production in New Zealand have been hampered by a lack of scientific information and a perception they are slow growing.
Two Forest Research scientists working on indigenous forests part time are trying to put that right.
Rotorua-based David Bergin and Greg Steward spoke to about 40 members of the Bay of Plenty Farm Forestry Association in Te Puke about the planting and management of native trees as crops.
Dr Bergin gave an example of a typical commercial planting of kauri. In 1935 40ha of kauri was planted in Waitangi Forest. After a high mortality rate over the first few years, major replanting took place.
A few years later most of the 40ha of kauri was destroyed to plant pine and in 1979 a fire went through the area, leaving 0.3 ha of kauri.
"Like many other early plantings of native trees, there was little care given to managing plantations after planting and hence most have failed," he said.
It was a sad tale of exploitation of native forests from the 1820s to the present day. In fact, clear felling of native podocarp forest continued until 1975 and native timbers have contributed to New Zealand's wealth, as a nation.
The two scientists shared their preliminary findings into growing totara and kauri, as well as other softwoods such as rimu and kahikatea along with hardwood species such as puriri, beech, rewarewa and kohekohe.
Dr Bergin said they thought the single biggest problem with native trees was they needed "releasing" (freeing from weeds) more than once in their growth.
"They need about five years of releasing. Another problem is poor site selection. The nursery stock quality is often variable and seedlings are often planted out when they are too small," Dr Bergin said.
Seed selection from areas where there were a good number of native trees was needed.
"Sometimes seedlings can fail because seed collected from a single tree growing alone lacks the level of cross pollination needed for healthy growth and can become inbred," Mr Steward said.
It was also hard to get commercially grown seedlings of good enough quality to form the basis of a woodlot.
Site selection was tricky, the scientists said, because foresters wanting to plant natives often relied on bush remnants when selecting sites. They were also planted in difficult exposed areas after the best sites have been used for pasture and pine forestry.
"They're being planted where native bush has been left - usually on steep and relatively inaccessible areas, which is not necessarily where they grow well," Mr Steward said.
There were examples of totara being planted close together, producing straight, clear boles up to 15 metres on 90-year-old trees planted at 1.2 to 1.5 m spacings.
There are other examples of 30 and 50-year-old totara trees growing well in Hawke's Bay forests.
Dr Bergin said totara and kahikatea established more successfully on open sites than other podocarp species but the use of a cover of hardy shrubs improved survival and growth.
"Manuka, kanuka, pittosporum and even gorse make good nurse species, reducing the risk of frost and wind damage. Totara could be planted in cleared lines through the scrub.
"Without side shelter, stem form is likely to be poor and a large proportion of totara will be multi-leadered if planted at more than 1.2 to 1.5m," Dr Bergin said.
The more successful totara plantations on open, fertile sites had a mean annual height increment of up to 55cm and a mean annual diameter increment of 10mm.
"The relationship of growth with age is more direct for diameter than for height. In a study of 13 planted stands, ranging between 10 and 100 years old, it was found that less than one third of the potential growth rate could be expected on poor sites with poor husbandry."
With fertile sites, fertiliser applications, good releasing and seedling shelter a tree rotation of 60 years was predicted with an average volume of 470 cubic metres a hectare.
The rotation was twice as long as for radiata pine which had volumes of 400 to 900 cubic metres a hectare.
However, European foresters commonly had rotation periods from 40 to more than 100 years, on trees.
Dr Bergin and Mr Steward said the reasons for planting and managing native forests were many despite a longer production period. They would supply high value, specialised timbers greatly sought after for furniture and other building requirements.
Native trees improved the aesthetic qualities of the landscape and gave better scope for recreation, such as walking. Plantations supplied good shelter and screens and became a fertile seed source as well as controlling erosion.
It was a way of extending forest remnants in a culturally significant way and riparian plantings protected water quality and supplied a better food source for native birds. Dr Bergin said many people had planted large areas of natives which had not done well because they did not have the resources to tend them properly.
"Don't bite off more than you can chew."
The two said they would rather see one hectare go into indigenous forest and be well looked after than a large area lacking care which would grow into a disappointment.
David Bergin has written a bulletin, Totara, Establishment, Growth and Management and can be contacted at the New Zealand Forest Research Institute Ltd at Private Bag 3020, Rotorua.
Email: David Bergen