Threats to pīkao
Pīkao's disappearance from the coastal environment can be attributed to a wide range of influences and events.
The greatest threat to pīkao is considered to be marram grass which was introduced at the turn of the 20th century to stabilise areas that had been protected by pīkao but had been burnt from around the 1880s onwards. Marram's nitrogen fixing companion plant, the yellow tree lupin, arrived around the same time. Together they literally smother the smaller and far less competitive pīkao.
Marram grass, Spit Island
Because of its invasive qualities, marram has been used a lot on reclamation and development projects, often at the expense of pīkao remnants. One of the reasons that marram is so competitive is that it turns more mobile dune habitats (pīkao's preference) into a much more stable evironment. As a result pīkao succumbs to the invader's pressure.
Burning by early settlers was a major reason for pīkao's decline along with land development for agriculture and forestry. Many dune areas that were once covered in pīkao are now stablised by pinus radiata plantations. Several plantations along the Horowhenua-Wanganui coastline are good examples.
Grazing is also a major problem. Originally the damage on coastal properties was done by sheep and cattle, but rabbits and possums have also developed a taste for pīkao. This can be a major problem in areas with high rabbit numbers where the plant is being re-established.
Other threats to the plant include sand mining and indiscriminate use of vehicles in dune areas.