Gumlands

Gumland with cemented pan visible at the surface, Lake Ohia, Northland (Susan Wiser)

Gumlands are shrub-covered, flat to rolling land in northern New Zealand, which have deposits of kauri gum. Most remaining ones are centred on Kaitaia or Kaikohe. Soils are strongly leached (mostly podzols), derived from deeply weathered old consolidated sands, sandstones, and claystones. They are very infertile, acidic, seasonally waterlogged, and mostly have a thin siliceous topsoil (sometimes with peat) above a slowly permeable or cemented horizon. They have become more widespread since human settlement as a result of repeated fires. The vegetation is typically heathland, comprising low-growing manuka (Leptospermum scoparium), Dracophyllum lessonianum and other shrubs, sedges, especially Schoenus brevifolius, and ferns, especially tangle fern (Gleichenia dicarpa). Manuka dominates drier gumlands (better drained sites under lower rainfall), and tangle fern wetter ones (poorly drained sites under higher rainfall), with mixed communities occurring on intermediate sites. Sedges (Schoenus brevifolius) dominate recently burnt sites, with shrubs becoming dominant again over time.

Gumlands are a subset of heathlands, which can occupy a much wider range of soils, altitudes and hydrological conditions.

Synonyms

Notable flora and fauna

Threatened plants include the nationally critical Phylloglossum drummondii, copper beard orchid (Calochilus herbaceous), spiral sun orchid (Thelymitra matthewsii) and sun orchid (Thelymitra sanscilia); the nationally endangered king fern (Todea barbara), tauhinu (Pomaderris phylicifolia), plumed greenhood (Pterostylis tasmanica) and swamp hibiscus (Hibiscus diversifolius subsp. diversifolius); the nationally vulnerable bog clubmoss (Lycopodiella serpentina), Machaerina complanata and pygmy sundew (Drosera pygmaea); the declining rawiri (Kunzea linearis) and swamp blueberry (Dianella haematica); the relict bladderwort (Utricularia delicatula); the naturally uncommon Centrolepis strigosa, dwarf mistletoe (Korthalsella salicornioides), helmet orchid (Corybas rotundifolius), bearded orchid (Calochilus paludosus), yellow gumland leek orchid (Corunastylis pumila), fan fern (Schizaea dichotoma), Caladenia bartlettii and short-hair plume grass (Dichelachne inaequiglumis). Colonisers are the mauve sun orchid (Thelymitra malvina) and large tongue orchid (Cryptostylis subulata).

There are also undescribed orchids, an undescribed Prasophyllum, and several undescribed Thelymitra species with the tag names 'Ahipara', 'Rough leaf', 'Sky', and 'Darkie'. Gumlands are the only known habitat for some of these. Their abundance has decreased in recent times as disturbances needed for their establishment have declined and woody species have increased.

Notable fauna include black mudfish (Neochanna diversus), endemic Northland mudfish (Neochanna heleios), nationally vulnerable North Island brown kiwi (Apteryx mantelli), declining Northland green gecko (Naultinus grayii), and North Island fernbird (Bowdleria punctata vealeae).

Worldwide, gumlands are known to be important habitats for Lepidoptera, and NZ gumlands are no exception; they harbour more than 160 species. It is unlikely that any Lepidoptera species are restricted to gumlands, but two undescribed species in the genera Megacraspedus and Paramorpha have never been collected elsewhere.

Threat status

Critically endangered (Holdaway et al. 2012)

Threats

Most gumlands have been lost to agricultural and urban development, both of which are continuing. Remaining sites are vulnerable to a suite of woody weed species, such as Hakea sericea, H. gibbosa, and gorse (Ulex europaeus). In some areas, there are problems with off-road drivers, motorcyclists, and dumping of rubbish and fertiliser drift from adjacent agriculture is a likely threat. Wind farm development may pose a future threat.