Big Population of Water Brome (Amphibromus Fluitans) Discovered At Arohaki Lagoon, Whirinaki
Several weeks ago members of the Rotorua Botanical Society were delighted to discover a very large population of water brome (Amphibromus fluitans) in the Arohaki Lagoon, Whirinaki Forest. The lagoon, a large ephemeral wetland complex located within dense Podocarp forest is at the end of a very popular bush walk. Water levels within the lagoon vary from season to season, reaching a maximum depth of almost 2 m in wet years and virtually nothing during dry spells. Consequently much of the “lagoon” is given over to a dense turf dominated by Hypsela rivalis, Pratia angulata, P. perpusilla, and swards of Baumea arthrophylla.On the margins of the wetland, the wind grasses Lachnagrostis filiformis, L. elata and L. striata are common, and as it turns out so is water brome. However, the first plants of this cryptic, somewhat elusive species were found by Rotorua Botanical Society member and Department of Conservation, Bay of Plenty Conservancy botanist Mr. Paul Cashmore, near the centre of the lagoon partially submerged in 0.3 m of water. The plants were immediately recognized by their distinctive inflorescences bearing green, narrow, awned spikelets. These, as is typical of species occur partially obscured within the very long leaf-sheaths, until fully mature, when they rapidly elongate to drop their seed.
Last week a follow up survey by Department of Conservation staff and President of the Rotorua Botanical Society Mr John Hobbs, found an estimated 1000 plants encircling the lagoon and also in several smaller ephemeral systems adjacent to the main wetland system. Mr Hobbs was delighted with the find which surprised Botanical Society members as the wetland had been thought to have been very well explored by botanists in the past.
This find is the second for the Bay of Plenty Region, the first, made last year by Ms Sarah Beadel - founder, and director of Wildlands Ecological Consultancy, and a New Zealand Plant Conservation Committee member - was on the margins of Lake Rerewhakaaitu, where at least 1000 plants grow along the edge of the lake within a popular camping ground.
Outside the Bay of Plenty, water brome still occurs in large populations near Lake Wairarapa and at Waihora Lagoon west of Lake Taupo. There are scattered records from elsewhere in the North Island. In the South Island it has been recorded twice, from Lake Tekapo in the 1940’s and from Maher Swamp, North Westland in 1991.
Internationally water brome occurs also in Australia, where it is believed to be at risk, and may even be already extinct in several of the states including Tasmania.
Posted: 20/03/2006