Because braided rivers are globally rare, their ecologies are equally rare, and they are extraordinary biodiversity hotspots. The life in and around them is highly specialised, and their ecological relationships are complicated by the fact that braided rivers stretch from the highest peaks in the mountains to the coast. They travel through alpine tussocklands, forests, dairy farms and sheep farms, exotic tree plantations and vineyards, narrow gorges of ancient Torlesse greywacke and not quite as ancient limestone, down through coastal plains, beside roads, through towns, coastal wetlands and through dunes until finally reaching the sea. A huge variety of birds, fish, reptiles, plants and fungi, have adapted to these challenging and incredibly dynamic environments defined by channels of water weaving between temporary islands of gravel.
In recognition of their importance and value, braided rivers are the only ecosystem to have its own set of targets in the Canterbury Water Management Strategy (CWMS).
Yet in spite of the resilience of life in and around these rivers, many species, indeed entire braided river habitats are under threat. Elsewhere in the world, the primary threats to species is pollution and habitat loss. The situation in New Zealand is different.
Some 93% of the New Zealand continent, sometimes called Zealandia or Tasmantis, is underwater. Most if not all of the land we see today was submerged until around 20 million years ago. As tectonic forces pushed the land above the surface of the ocean, isolated as it was from other land masses, the only life that took hold were the plants and animals carried ashore by waves, blown by winds, or by flying from Australia, South America, Pacific Islands, and (then largely ice-free) Antarctica. As a consequence, our only native terrestrial mammals are bats.
Without herbivorous mammals to graze plants or predatory mammals to eat the herbivores, ecological niches were instead filled with birds and invertebrates. When humans introduced mammals, these ecosystems were disrupted and extinctions soon followed.
Today, on the plains, away from the coast, only the braided rivers still have indigenous components largely as they were thousands of years ago – despite having received little protective management to date. The most obvious component of these native ecosystems is the birds. Their populations are declining and several species are at now at risk of extinction. The reasons are outlined in threats.