Sandy slopes can be a death trap for tree seedlings, especially if the season turns dry. That’s what Boyup Brook tree growers David Singe and Natalie Kuser found in 2015 when they received just 150mm of rain in the six months after planting. But as luck would have it, the planting was part of a trial looking to improve seedling survival, and one trial-treatment has helped to significantly limit the losses.
David and Natalie own 45 hectares on the Blackwood River south of Boyup Brook, part of which was previously cleared for pasture.
“We’re not farmers. This is a lifestyle block”
“We could lease it out for sheep but it seemed like a lost opportunity not to utilise it ourselves and create something for our family.” David says.
In 2013 they approached South West Catchments Council (SWCC) with a proposal to demonstrate the establishment of eight local South West species in two woodlots with the aim of producing high value timber. The proposal was accepted, but with a condition that the planting incorporate a trial aimed at minimising the exposure of soils to wind and rainfall.
Trial plots tested swales, mulch, soil wetter and summer watering
With help from SWCC, David designed a woodlot that included trial plots to test the effect of four treatments—swales (furrow lining), mulch, soil wetter and summer watering—on tree survival and growth. Swales were cut along alternating rows across the whole site. Three replicate plots for the remaining treatments and two control plots, each consisting of about 100 seedlings, were positioned on the site, which consisted of sandy soils with slopes ranging between 3-15%
Average survival of seedlings on swales was 80% compared to 47% without swales, a significant difference (P<0.001). From visual inspection, David thought the effect of swales increased with increasing slope, and became obvious on slopes greater than 5%, and also increased with increasing soil-sandiness
Survival on swales was 80% compared to 47% without swales
Of the other treatments (mulch and granular soil wetter), only mulching seemed to make a difference in survival, and only on non-swale rows, where survival was 67% compared to 46% without mulch (P<0.05). However, David thought mulching was also improving growth and assisted with watering. “When we were watering we were able to get about twice as much water on the mulched plants before it began to run away.
An issue with swaling that SWAN Committee member Bob Hingston raised is the increased erosion risk due to the concentration of water flow along the swale or where water concentrates at the end of swales. This risk can be reduced by swaling on the contour, limiting the length of the swale and ending the swale on a level sill with established groundcover and no wheel ruts. Erosion was a potential risk at David’s woodlot, which received over 100mm of rainfall during one week in January. The risk was reduced by swaling as close to the contour line as possible and also by having the first swale close to the top of slope so the catchment above it was small. Mulching may also have minimised erosion by reducing the velocity of water flow along the swale.
David and Natalie own 45 hectares on the Blackwood River south of Boyup Brook, part of which was previously cleared for pasture.
“We’re not farmers. This is a lifestyle block”
“We could lease it out for sheep but it seemed like a lost opportunity not to utilise it ourselves and create something for our family.” David says.
In 2013 they approached South West Catchments Council (SWCC) with a proposal to demonstrate the establishment of eight local South West species in two woodlots with the aim of producing high value timber. The proposal was accepted, but with a condition that the planting incorporate a trial aimed at minimising the exposure of soils to wind and rainfall.
Trial plots tested swales, mulch, soil wetter and summer watering
With help from SWCC, David designed a woodlot that included trial plots to test the effect of four treatments—swales (furrow lining), mulch, soil wetter and summer watering—on tree survival and growth. Swales were cut along alternating rows across the whole site. Three replicate plots for the remaining treatments and two control plots, each consisting of about 100 seedlings, were positioned on the site, which consisted of sandy soils with slopes ranging between 3-15%
Average survival of seedlings on swales was 80% compared to 47% without swales, a significant difference (P<0.001). From visual inspection, David thought the effect of swales increased with increasing slope, and became obvious on slopes greater than 5%, and also increased with increasing soil-sandiness
Survival on swales was 80% compared to 47% without swales
Of the other treatments (mulch and granular soil wetter), only mulching seemed to make a difference in survival, and only on non-swale rows, where survival was 67% compared to 46% without mulch (P<0.05). However, David thought mulching was also improving growth and assisted with watering. “When we were watering we were able to get about twice as much water on the mulched plants before it began to run away.
An issue with swaling that SWAN Committee member Bob Hingston raised is the increased erosion risk due to the concentration of water flow along the swale or where water concentrates at the end of swales. This risk can be reduced by swaling on the contour, limiting the length of the swale and ending the swale on a level sill with established groundcover and no wheel ruts. Erosion was a potential risk at David’s woodlot, which received over 100mm of rainfall during one week in January. The risk was reduced by swaling as close to the contour line as possible and also by having the first swale close to the top of slope so the catchment above it was small. Mulching may also have minimised erosion by reducing the velocity of water flow along the swale.
