Tuesday, April 23, 2024

Green shoots of hope on post-cyclone land

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Clear signs that orchards, arable and pastoral properties are starting to regenerate.
This paddock has recovered well from the sediment left by Cyclone Gabrielle.
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“Green shoots” is an idiom often roped in to describe a return to life after a traumatic event, but it is one that is taken literally for scientists studying how East Coast land is recovering from Cyclone Gabrielle.

Based in Hawke’s Bay with environmental company LandWISE, project manager Alex Dickson said there are clear signs that orchards, arable and pastoral properties are starting to regenerate after Gabrielle’s devastating blow. 

LandWISE has partnered with AgResearch, Massey University and others on a project hoping to provide longitudinal insights into how land can be remediated after such an event.

“What was really unique about Gabrielle was the fact it affected so much of New Zealand’s high value cropping land and not only pastoral country. As a country we have never been in a situation where such a vast area and range of crops have been affected. So, the challenge is how to get back to producing those crops,” Dickson said.

Understanding of pastoral systems’ remediation has been relatively well informed by past events, including Manawatū’s 2004 event. But Dickson’s hope is that the decision support tools available for pastoral will soon be enhanced as better understanding of crop and orchard systems’ recovery is added in.

Five months post-Gabrielle, Dickson and her colleagues are returning to sites they and others initially visited, stretching from Northland to Hawke’s Bay, gathering baseline data on soil recovery.

They are finding sediment depth and coarseness are major determinants of the rate of recovery, and if a crop can even be grown again in the same area.

“In some areas of Esk Valley there are  pockets of really coarse, deep, sandy silt with low organic matter. In some of the deposits that are finer, the fertility is okay.” 

The researchers found Wairoa has suffered particularly coarse sediment while Gisborne’s silt has tended to be finer.

Response after the event by growers has also offered some insights. 

“We have been working with a proactive grower who only four weeks after Gabrielle flew ryegrass seed onto their cropping and cattle property. You can graze cattle there now, and the cattle seem to also be helping mix in the silt. We are seeing plant roots extending through the 20cm of silt, earthworms are moving in and structure is improving.”

Sampling taken by Dickson and colleagues is showing earthworm populations are not completely wiped out, and even increasing in some areas with finer silt deposits.

Some growers have viewed the event as an opportunity to reset their management, improving their environmental approach while also getting back to full production as soon as possible.

Perennial crops such as grapes, apples and kiwifruit require some careful thought on the silt’s depth, orchard’s age, profitability, and recovery percentage when deciding whether to continue or start again.

Younger apple orchards established in the modern layout may have the economic robustness to remain, with silt removal. An older orchard with the same silt levels may be best suited to removal and replanting in the modern design.

“For some growers it is moving them to make a decision sooner than they may have before.”

Kiwifruit are complicated by heavy silt deposition lowering the picking height under the vines.

The team are also analysing soil nutrient status prior to springtime so they can discuss “where to” with growers prior to spring planting.
Funding was provided for the initial baseline work; now Dickson and colleagues are hoping further funding can be found to extend the work out over five years.

“The challenge is how do we go about returning our most versatile, productive soils back to being our most versatile, productive soils?”

The study also provides valuable psychological support for growers worn down by months of wet weather and the cyclones themselves.

“Seeing what they have done, it is a nice reminder to growers from us that they have made some progress, especially when it has felt so much like Groundhog Day.”

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