Performance of Indigenous Species Three Years after Planting on a Backdune, Ohwia Spit, Eastern Bay of Plenty

An indigenous species coastal planting trial was established at Ohiwa Spit, eastern Bay of Plenty in mid-2005 by the the Ohiwa Beach Coast Care group, Whakatohea Trust, Environment Bay of Plenty and Opotiki District Council. The aim of the trial was to evaluate the performance of a range of local indigenous ground cover and shrub species planted within three demarcated zones on a relatively stable backdune site and to compare the relative performance of seedlings raised in Tinus rootrainers with those raised in PB planter bags. Three years after planting there were significant differences in plant performance between front, mid and back zones. While overall survival was high, growth was poor for most species especially on the exposed front and mid zones compared to the more sheltered back zone that comprised a cover of vegetation dominated by exotic species. There were few differences in survival and growth for most species 3-years after planting between seedlings raised in root trainers and PB2 planter bags. Degree of exposure is considered to be a major factor in limiting performance of planted indigenous species; most plants on the open sites had lost height and plant spread probably due to severe exposure to onshore winds and salt spray. While increased shelter in the landward backzone contributed to improved growth and plant vigour, competition from exotic vegetation had resulted in higher early mortality for some species. Care is required in selecting the appropriate zone for the planting of coastal backdune species and to avoid planting a wide range of indigenous species too far seaward in exposed zones. It is recommended that existing vegetation cover on backdunes should be used wherever possible to provide shelter for assisting in establishment of indigenous shrub species. Ground cover plant species are more likely to succeed on open dune sites rather than taller shrub species. The trial indicates that a small selection of hardy indigenous coastal shrub species can be successfully established within the shelter of existing back dune vegetation.