kowhai grown to an impossible size

Size
Height: 10–12 m
Lifespan
100–200 years
Diet
Herbivorous – absorbed nutrients through extensive root system gripping floodplain soils. A kōwhai built for the river – tall, broad-canopied, with roots that gripped shingle and branches that spread across water. Burst into golden flower each spring.
Habitat
Riversides, alluvial terraces, and seasonally flooded lowlands of Canterbury's braided rivers and North Island's east coast. A kōwhai built for the river – tall, broad-canopied, with roots that gripped shingle and branches that spread across water. Then the floodplains were drained.
Range
Found on riversides, alluvial terraces, and seasonally flooded lowlands of Canterbury's braided rivers and North Island's east coast. Described from subfossil remains found in floodplain deposits. Last reliably recorded in the 1880s.
Endemism
Endemic
Main Threats
Floodplain conversion to pasture was the primary threat. Also threatened by river straightening and browsing by introduced mammals. Last reliably recorded in the 1880s. A few pressed specimens remain in herbarium drawers – their golden flowers faded, their seed pods cracked.
Population
An extinct mainland giant form, related to Hall's kōwhai but vastly larger. Estimated height 10–12 metres (the living Sophora hallii reaches 1–2 metres). Trunk diameter 40–50 centimetres. Last reliably recorded in the 1880s, crushed by floodplain conversion to pasture and river straightening.
Conservation Status
Extinct
Golden-flowered trees light up the spring landscape. But there is a kōwhai you may not know – Hall's kōwhai, a small, tangled shrub from the Chatham Islands, a survivor of windswept coasts and poor soils. It is modest, unassuming, a divaricating mess of twigs. But there was once a giant relative that grew on the mainland, along the great braided rivers of Canterbury and the floodplains of the east coast. It was not a shrub. It was a tree. A tall, spreading, golden-flowered tree that turned the riverbanks into a blaze of gold each spring. It was the giant Hall's kōwhai, and it is gone. The living Hall's kōwhai is a shrub of poor soils and harsh winds. The giant form was a tree of abundance – tall enough to compete with the cabbage trees, broad enough to shade the riverbank. Its roots gripped the shifting shingle of the braided riverbed, holding the stones together. Its branches stretched out over the water, dropping flowers and leaves into the current. It was the king of the river edge. It fed the birds. Its golden flowers – larger and more abundant than any living riverbank kōwhai – produced nectar that fuelled the tūī, the kākā, the bellbird, and the piopio. Its seed pods fed the parrots and the ground birds. Its branches provided nesting sites for the river birds – the black-fronted tern, the wrybill, the banded dotterel. It also stabilised the riverbanks. Its roots held the shingle together, preventing erosion. Its canopy shaded the water, keeping it cool for the fish – the kōura, the galaxiids, the eels. It was the bridge between the land and the water. It flowered prolifically each spring. Its seeds were hard and required scarification – passing through a bird's gut or being tumbled in floodwaters – to germinate. That strategy worked when the rivers were wild and the birds were abundant. It failed when the rivers were tamed and the birds were gone. Floodplain conversion and herbivore pressure destroyed it. When Europeans arrived, they converted the floodplains to pasture. They planted grass, drained wetlands, fenced the riverbanks. The giant kōwhai, which needed open shingle and seasonal flooding to regenerate, could no longer reproduce. Its seedlings could not establish in grass. Its seeds washed down rivers that no longer spilled over their banks. Introduced grazing mammals – cattle, sheep, deer, rabbits – ate the seedlings and stripped the bark from the mature trees. The old trees died, one by one, with no young trees to replace them. By the 1910s, it was gone. The last trees were probably felled by a river flood, undermined by erosion, or simply died of old age with no seedlings to carry on. The living Hall's kōwhai survived on the Chatham Islands – smaller, tougher, more wind-resistant. It is the survivor, the divaricating shrub, the plant that refused to give up. But the giant mainland form is extinct. A few pressed specimens in a herbarium, a few fragments of wood in a river terrace, and the memory of a tree that used to turn the riverbanks gold each spring. We converted its world. Then we wondered why the river felt so empty.