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Alders and Redwoods Together - by Ben Gaia, www.dialatree.co.nz


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Alders and Redwoods together, by Ben Gaia, June 2023





In the bad old days when the logging companies strip-mined California and Oregon for their Redwood timber, Cedars and Douglas firs, the giant trees were removed leaving bare open scrub. It regenerated fast in Red alder and other broadleaf light loving trees.

Initially there was panic that these big fast things would suppress the regrowth of any young redwoods on the forest floor. Forests of alder were sprayed with herbicide to give the slower growing conifers a chance.

But as time went by observations showed that the alders in reality, sheltered the new young trees with shade in summer, gave them winter light, and leaf fall for soil, as well as essential wind shelter from any drying winds from all directions. The red alders were helping the cleared forest recover more quickly, as it might from a forest fire or destructive storm.

So now, with the new interest in growing Redwood stands for timber, shelter and carbon capture in New Zealand/Aotearoa, there has been some experimentation with using alder species as a companion to redwoods in plantation forests. They provide useful side and overhead shelter which helps the young, vulnerable redwoods establish. As a bonus, alders supply soil nitrogen naturally through their root nodules. This is like applying nitrogen fertiliser all year round, without any leaching from chemical application. So they help feed both the establishing timber forest and the nearby soils.

A combination of broadleaf species can boost the success of a young redwood forest or other conifer stand. You can match the planting density tree for tree, eg 400 of each per hectare, and later, harvest the alder as a bonus timber or charcoal crop. Or sprinkle alders through the stand and around the outside edges for wind shelter. This should result in a "gold standard" Redwood stand.

Red alder, Alnus rubra, grows very fast and large in NZ. The favoured alder at the moment is the Italian alder, Alnus cordata. This alder species has an excellent quality hardwood timber product after thirty years, as well as one of the world's finest charcoals on a ten year coppice cycle.







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