Planting poplars and willows for soil conservation
Support for landowners - subsidised poplar and willow poles
Northland Regional Council grows and supplies poplar and willow material for the planting of erosion prone land from our nursery in Mata south of Whangārei.
Poplars and willows grow readily from cuttings so our trees are supplied as bare stems with no roots or branches. These are commonly referred to as ‘poles’ or ‘stakes’ depending upon their age and length . The regional council is also trialing the use of rooted cuttings but supply is currently limited.
To learn more about the multiple benefits of using poplars and willows to stabilise your land, check out the Poplar and Willow Trust website at: poplarandwillow.org.nz
For many years, NRC’s main tool to manage erosion in pasture has been planting poplar trees. This is because poplars are fast growing and have extensive root systems that help hold the soil in place, allowing erosion prone farmland to stay in pastoral production.
Extreme weather events such as Cyclone Gabrielle can have severe impacts on our environment and the event in February took its toll on some poplar plantings. Land Management staff at NRC toured some areas of Northland where Cyclone Gabrielle caused the most extensive damage to poplar trees, to try to gain a better understanding of why those particular trees were more impacted than others.
Key points noted were that Cyclone Gabrielle was an extreme wind event that came after an unusually wet summer, so the combination of severe winds with highly saturated soil conditions resulted in localised windthrow of poplar. Because poplars grow fast, tend to be planted in wetter areas and were in full leaf at the time the cyclone hit, they appear to have suffered more windthrow than other tree species in Northland.
As Kawa has been the main poplar variety planted in Northland since the 1980s, the majority of windthrow was Kawa. Levels of windthrow varied across the region, but we only visited locations that were extensively damaged. In many locations, Kawa was unaffected by the cyclone.
Cyclones are unpredictable as to where they land and the direction of wind. While localised wind severity and turbulence can’t be planned for, some broad-brush contingencies will increase windthrow resilience, including:
- Poplar forest design should prioritise the main need e.g., erosion control, shade and shelter etc, with timber production secondary.
- Avoid planting Kawa in poorly drained areas with weak soil strength, especially if a plantation crop.
- Set poplar back from drain and stream edges (at least 3-5m from the top edge of the bank).
- When growing poplar for timber, rooted cuttings are planted at up to 1,000 stems per hectare (STP). However, at this stocking trees are tall and thin which increases their vulnerability to windthrow. To reduce the risk of this happening, poplar stands should be thinned down to a final spacing of 250-300 STP (6m x 6m), similar to a radiata regime.
Kawa has been a proven performer for Northland conditions. However, it appears Kawa is more vulnerable to cyclones than other clones such as Veronese. One reason for this may be smaller root plates compared to other poplar varieties. Northland Regional Council is conducting field trials on a range of poplar varieties to determine their suitability for Northland conditions. In addition to rust resistance, possum resistance, quality timber and good form, resistance to windthrow is an important selection criterion for future breeding and selection programmes.