However that wasn't Shirley's initial concern. Her family has had a bach on the river for years and it was during trips up from Wellington in the early 2000s with partner Karen 'Ardy' Ardin, that Shirley decided something needed to be done about the possums eating all the walnuts off the bach's tree.
The pair started started trapping possums in 2007 in a bid to win the walnuts for themselves. They were amazed at how many they got. Then they noticed a clutch of piwakawaka (fantails) fall prey to pests. Possum trapping morphed into trapping for stoats, rats and weasels and, Shirley says, "it just kind of grew from there".
When Shirley and Ardy moved up to the Tūrangi area permanently six years ago, their programme extended to the goal of providing more bird habitat along the river banks.
The wall of weeds in the riverbank reserve was formidable. But Shirley set to it in sections. Her technique is first to spray the weeds with weedkiller.
Once the weeds have been sprayed, hay contractor Bryan Lawrance comes in with his machinery, clears and mulches the weeds and leaves bare ground ready for planting.
It's a technique that is transformational. Five years later, the first area Shirley started is now a patch of thriving native plants.
"These kāhikatea went in at about knee height and now some of them are up to two metres so we're lucky that we've got beautiful fertile ground here."
As well as spending 25 to 50 volunteer hours a week planting, weeding, spraying and trapping, Shirley is a Project Tongariro board member and works with community and school groups to educate them about conservation. Earlier this year Project Tongariro nominated her for Volunteering Waikato's Volunteer of the Year Award, saying "Shirley lives and breathes conservation and is one of our volunteer role models. She has the ability to "infect" others and motivate them to join the cause. Her efforts have brought bird song back to the Tauranga-Taupō region".
From the original section of reserve Shirley, Ardy and Bryan and other volunteers have worked their way outwards, with more ground planted. Weed control and restoration planting has been done on approximately 2ha, with another 14ha in the next five to seven years if money can be found. Funding so far has come from the Waikato Regional Council's small scale initiatives fund, the Waikato Catchment Ecological Enhancement Trust, and Matariki Tu Rakau which is creating commemorative forests to honour past and present New Zealand Defence Force members.
Shirley says Bryan's involvement in the project is key, along with ecologist Nick Singers.
Tongariro Prison supplies eco-sourced trees and Ian and Frances Jenkins of Tūrangi donate hundreds of trees every year. Stella and Mark Usherwood, Sarah and Mike O'Sullivan and Collette Taylor all lend a hand, and more people are getting involved with Project Tongariro.
The planting is the easy bit. The weeds need to be kept at bay, and native seedlings protected from being smothered. It would be wonderful to have more people help because there are now so many plants, she says.
"We have to hand-release a margin around the base of them but we're lucky that contractors
Protecting their own patch
deliver mulch to us or we put carpet squares around which suppresses the weeds and I can spray around and protect the trees. Rabbits are also a bit of a problem," says Shirley.
"We've got problem [weed] species: flowering cherry which is a major problem and hawthorne, cotoneaster, berberis, wilding pines, broom. Weeding is an ongoing issue for three to five years."
Shirley and Ardy trap all through the reserve.
"A couple of my dreams are to have [nationally critical native plant] kakabeak growing here and we've got the possums to very low numbers." For Shirley and Ardy, the reward is seeing the increase in bird life — since 2007 it's just gone off.
"Now, instead of just having birds flying across this woody mess, we have birds living in there.
"Korimako (bellbird), tui, whiteheads. I saw a male riroriro and we have heard a robin on three occasions over the last six years so that's really encouraging. Last weekend we had a flock of approximately 60 tui which was mind-boggling. It was amazing.
"When the toutouwai (robins) arrive, it will be a champagne day."