A 60 metre high redwood stand near Taumarunui. Photo / Supplied
A 60 metre high redwood stand near Taumarunui. Photo / Supplied
Pinus radiata has been the go-to species for New Zealand's vast plantation forest estate for well over 100 years, but another Californian import - coastal redwood - is gaining ground.
The species, also known as Sequoia sempervirens, has risen in popularity to the point where seedlings are now in shortsupply.
Most redwood is concentrated in the North Island, with some large plantations in the King Country.
Michael Watt, Principal Scientist at Scion - a Crown Research Institute - said there has been a sustained planting effort since 2000 and about 10,000ha of redwood has been established since this time.
With the current emphasis on planting forest for carbon, Watt says the potential is there for redwood to make up much more of the estate than the current 1 per cent, which compares with 90 per cent for radiata.
Watt says there is "virtually no wilding risk" with redwood and it is a healthy species with no major insect or disease problems.
It's also resistant to fire and wind damage.
He says redwood is a good choice for erosion control because the species' roots lock together, which helps to stabilise soil.
Watt admits that radiata pine ticks a lot of boxes for foresters because of its high growth rate.
"However, the growth rate of radiata pine declines after 30 years, which may limit our ability to build enduring carbon stocks if we establish large areas of this species as permanent carbon forests," he says.
"Establishment of native forests has been widely advocated and these species provide important ecosystem services and cultural value.
"However, as native trees grow a lot slower than exotic species, particularly over the short term, it will be difficult to reach net-zero emissions by 2050 using a high proportion of planted native species."
Redwood is known as an "appearance grade" timber. Photo / Grant Bradley
Although the current debate around reaching net-zero emissions is polarised around the establishment of radiata pine or natives, there are other options that could rapidly sequester carbon over both the short and long term.
Watt says redwood is one of the most promising of these options.
Redwood has been found to store more carbon than forests dominated by any other species and is able to maintain high growth rates over hundreds of years.
Individuals within this species include some of the oldest and tallest living trees on earth that have reached ages exceeding 2,200 years and heights of 115m.
A peer-reviewed paper written by Watt and consultant Mark Kimberley compares the amount of carbon sequestered by redwood with that of radiata pine throughout New Zealand.
Growth rates of redwood were found to be highest in warm, wet areas with optimal regions for the species including Waikato, Bay of Plenty and Taranaki.
By age 40 average carbon for redwood within the North Island exceeded that of radiata pine for stands growing at medium to high density.
Predictions of carbon at age 40 for redwood were very high within the Bay of Plenty and Waikato where they reached 4,000 tonnes CO2 per hectare at some locations - far exceeding the 1,750–2,500 tonnes CO2/ha reached by radiata pine at these sites.
"As redwood grows faster than radiata pine at older ages, the species difference in carbon becomes even more pronounced at age 50 for sites that are suited to redwood," the paper says.
A high productivity 12-year-old redwood forest stand growing in the Kauaeranga Valley, near Thames, with a measured mean height of 14.4 metres. Photo / Supplied
Redwood was found to grow relatively slowly on cold and/or dry sites and the species had lower carbon productivity than radiata pine at age 40 throughout most of the eastern South Island.
But Watt says when the siting is right, it will outperform radiata.
The species also has a number of other advantages as a stable appearance-grade timber with high value and market potential in both domestic and export markets.
As redwoods are shade-enduring, they can be managed as a continuous cover crop with selective felling which makes the species an ideal candidate for permanent forests that can continuously supply timber and sequester carbon, he says.
Redwood was once a serious contender for plantation forestry along with radiata and other species, but radiata won out in the end.
"Radiata was a species that the early foresters started with, although redwood was also on the cards as well back then," he said.
"The two were moving forward but radiata got on the front foot because some redwood stands were put in the wrong spots, and didn't do as well".
Watt says that since then much has been learned about the optimal conditions for redwood and establishment practices.
The genetic material has greatly improved over the last two decades.
He said the latest research was likely to further help with correct siting of high productivity redwood stands.
