TOSSI – Measuring the success of creating a forest

At Tāwharanui Open Sanctuary, two decades of planting native flora have been planned and evolved into a philosophy to establish foundation bush that enables natural re-forestation. Our volunteers are well-versed in monitoring germination rates in the on site nursery, predator controls and even the number of Duvaucel’s geckos scampering around in the bush. However, there has been little more than anecdotal monitoring of the long-term success of winter planting days undertaken by hundreds of people every year.

We gaze at the patches of regenerating bush, pat ourselves on the back and say isn’t it doing well or alternatively, curse bare patches where rabbits have chewed seedlings to the ground. To achieve a more analytical understanding of the progress of native plantings, Steve Burgess and David Bowden, from Auckland Council’s Ngahere (Forest) programme, visited Tāwharanui in January.

The Council initiative has progressed from urban reforestation to investigating the success of current native planting schemes at Auckland regional parks. The results will help determine the potential for greater carbon sequestration in sections of regional parks that are already, or could be, retired from grazing. TOSSI volunteers were keen to learn more and armed with measuring tools, clipboards and enthusiasm, they joined Burgess and Bowden at last year’s planting site at Slip Gully.

Six patches within the gully were selected and each provided samples of the diverse growing conditions at Tāwharanui. There were ridgelines exposed to salt-laden winds, a formerly barren clay slip, sheltered gullies beside more established plantings, damp creek beds and open patches halfway up the hillside. TOSSI recruits and Council researchers marked each spot with a central post, attached a five-metre line to it and manoeuvred around in a circle to collect plant data. Every plant was identified, measured to the nearest 10 centimetres with a bamboo rod and given a health score, from zero (dead) to five (thriving).With good teamwork, TOSSI inductees quickly picked up the methodology, ensured plants were not missed and data was accurately recorded.

On the ridgeline, where the wind and salt create tough conditions, it was heartening to see kānuka and mānuka doing well, some planted six months ago were already about 1.4 metres tall. However, tasty karamu (Coprosma robusta) were devoured by rabbits and some tōtara had turned up their toes where rabbits burrowed under the roots. Needless to say, the rabbit situation is being addressed at the sanctuary.

Interestingly, the seemingly inhospitable patch of barren slip already has some self-seeded natives. The same six sites will be monitored annually until a forest canopy is formed and the data will determine the effectiveness of planting methods and what changes, if any, are required. Understanding how nature works and trying to emulate the interwoven processes is significantly more difficult than most of us realise.

A seemingly small change can impact on planting economics and may also affect the survival rate of maturing trees, for example, simply altering the planting space between seedlings by half a metre. The Ngahere (Forest) programme wants to know the revegetation process is translating into carbon sink forest and TOSSI wants to know its hard mahi is working.

Now our volunteers have the know-how, they can use the methodology to track future community plantings at Tāwharanui and they will have irrefutable stories to share with their grandkids.