Some notes about Mabi Forest

From: Newsletter Storm Season October - December 2003

By Tony Irvine

A one line description of Mabi Forest is a tall vine forest with a dense shrub zone below. Mabi Forest is a structural classification of a type of vine forest (= rain forest in the tropics) and the key thing about Mabi Forest structure, even in its most pristine state, is that it has mostly tall canopy trees, many vines and a dense shrub layer. This forest structure is similar to the forest structure that develops after a cyclone has hit a rain forest or when a rain forest has been heavily selectively logged.

Why is the structure of pristine Mabi Forest equivalent to a disturbed rain forest? It is because Mabi Forest occurs in the driest region (1,300- 1,600 mm per annum, on porous volcanic soils) where rain forest canopy trees can still obtain 45m in height. To survive in such conditions, many of the canopy trees are semi-deciduous or deciduous. Consequently there is seasonally a high amount of light that reaches the forest floor and this enables a dense shrub zone to be formed. This is exactly what happens when an evergreen canopy is opened up by a cyclone or heavy selective logging. The understorey species, shrubs, tree seedlings, and vines, particularly lawyer vines respond to the increased light and temporarily form a dense understorey layer which is equivalent to a dense shrub zone.

The description of the forest structure at Shiptons Flat near Rossville that occurs on volcanic soil, does not conform to a Mabi Forest structure as Geoff Tracey (1982) states the forest is tall but is quite open below. Hence this forest structurally lacks the essential ingredient of a dense shrub zone below and cannot be equated with Mabi Forest structure. Pristine Mabi Forest will have mosaics of evergreen and deciduous trees in the canopy. Where there is a high cluster of evergreen trees, correspondingly the shrub zone will be less dense below but overall in Mabi Forest the lower vegetation will be dominated by mid dense to dense shrub zones.

Other features also come into play in the description of Mabi Forest structure. The fact that it occurs on deep, nutrient rich volcanic soils enables the trees to grow tall but in some areas, the canopy can be as low as 14 m high as in areas at Thomas Rd and parts of Halloran's Hill where the depth of the volcanic soil has shallowed. The influence of these nutrient rich soils results in a complex type of rain forest, technically described by Tracey and Webb as Complex Notophyll Vine Forest and designated the number Type 5b to distinguish it.

Complex rain forests are associated with nutrient-rich sites. An immediate conspicuous feature of a complex forest is the high presence of trees with plank buttresses which are triangular sharply keeled buttresses as against the more rounded spur buttresses that may be present in some species. Another feature is that large woody lianes (vines) are readily noticeable. Fern epiphytes and flowering plant epiphytes as well as fleshy herbs are also very common.

Notophyll refers to the leaf size and a normal general leaf shape which is between 7.5 cm and 12.5 cm long is classed as a notophyll-sized leaf. To classify a forest as a notophyll forest means that overwhelmingly, the main leaf size of the canopy trees is notophyll. Factors such as precipitation, soil-moisture retention, fertility, wind exposure and Mabi Forest temperature can all influence canopy leaf-size. The wetter, warmer, more humid, nutrient-rich sites will tend to have the greatest development of large-leaf species (i.e. mesophylls and macrophylls).

Back to Mabi Forest. Its development is strongly influenced by the severe seasonal dry that is experienced on the Tablelands which usually becomes most severe in October. This is accentuated by the very porous, well-aerated nature of the volcanic soils, resulting in a high amount of dry air. circulating around the root zones of plants. The likelihood of significant rainfall occurring in October decreases rapidly on a SE-NW gradient on the Tablelands and an October rainfall event of 25 mm at Topaz usually decreases to 10-12 mm at Malanda and 2-4 mm at Atherton. The species that dominate the forest are those that can survive the dry conditions but there are some species that exist in the Mabi forest canopy and subcanopy today which must have established in much wetter times when dry seasons were less severe.

Key diagnostic features of Mabi forest are:

The forest may have up to six layers of vegetation. The canopy is uneven and consists of:

  1. Scattered emergent trees, 40-45m tall
  2. A main canopy, 25-40m tall but occasionally as low as 14-20m (At Thomas Road and parts of Halloran's Hill).
  3. A subcanopy, 12-20m tall which will be lower at Thomas Rd and parts of Halloran's Hill.
  4. A lower layer, 6-8m tall. This layer tends to be absent in areas with lower upper canopies.
  5. A predominantly dense shrub and scrambling lawyer vine zone 1-5m tall.
  6. A zone of seedling trees, shrubs, vines and herbs 0-1m tall.

In the next newsletter I will discuss the distribution of Mabi Forest, the origin of the name and if room permits some of the characteristic species of Mabi Forest.

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More about Mabi Forests

From: TREAT Newsletter Wet Season January - March 2004

By Tony Irvine

Remember the definition, Mabi Forest is a tall nutrient-rich, vine forest with a dense shrub zone below. It is associated with a rainfall regime of 1300-1600 mm per annum and occurs on a seasonally-dry upland (700-850 m altitude) in rich, volcanic soil. The name "Mabi Forest" arises from the fact that the forest supports high populations of Lumholtz Tree Kangaroos (Dendrolagus lumholtzi) and both the Dyirbal and Yidiny Aboriginal Languages call the tree kangaroo, "mabi".

Mabi Forest is confined entirely to the Atherton Tablelands and today remnants consist of Curtain Fig including Thomas Road, Picnic Crossing, Kairi Research Station, Cullamungie Pocket (slightly south of Pelican Point but on the eastern side of Tinaroo Dam), Halloran's Hill, Nasser's Property (Wongabel), Wongabel State Forest, Nicholas Creek, Tolga Scrub and other small scattered areas of less than 0.5 ha on private property. Curtain Fig is the largest remnant, roughly consisting of slightly less than 4 square kilometres in area.

There are six characteristic species that dominate the shrub zone. Atherton Turkey Bush (Hodgkinsonia frutescens), Dwarf Phaleria (Phaleria octandra), Moluccan Codiaeum (Codiaeum variegatum var. moluccanum), Atherton Sauropus (Sauropus macranthus), only known in Mabi Forest and margins, Green Mackinlaya (Mackinlaya macrosciadea) and the shrub form of the vine Papuan Dichapetalum (Dichapetalum papuanum). Usually Atherton Turkey Bush is dominant, but combinations and presence vary within and between fragments. Generally at least four of the shrub species can be readily observed.

Scrambling vines are dominated by Fishtail Lawyer Vine (Calamus caryotoides) and to a lesser extent Hairy Mary (C. australis) and Vicious Hairy Mary (C. radicalis). Other conspicuous vines are Dichapetalum papuanum, Millaa Millaa Vine (Elaeagnus triflora), Leichhardt's Vine (Melodorum leichhardtii), Broad-leafed Parsonsia (Parsonsia latifolia), Headache Vine (Clematis glycinoides) and New Holland Pepper (Piper novae-hollandiae). Large lianes are Black's Blood Vine (Austrosteenisia blackii), Cockspur Vine (Maclura cochinchinensis) and Antarctic Grape (Cissus antarctica).

The forest is rich in fig species - there are some 12 species and two varieties that may be present - Green Fig (Ficus virens var. virens), Light Green Fig (F. virens var. sublanceolata), Superb Fig (F. superba), Small Leaf Fig (F. obliqua var. obliqua), Watkin's Fig (F. watkinsiana), Gabi Fig (F. pleurocarpa), Fraser's Fig (F. fraseri), Plentiful Fig (F. copiosa), Hairy Fig (F. hispida), Septic Fig (F. septica), Sandpaper Fig (F. opposita), Red Leaf Fig (F. congesta) usually on stream banks, as is Riparian Fig, (F. adenosperma) and Cluster Fig (F. racemosa).

There are more than 200 species of trees in the forest but if one walked into a Mabi Forest one is very likely to see Candle Nut (Aleurites rockinghamensis), Black Bean (Castanospermum australe), Red Cedar (Toona ciliata), Red Tulip Oak (Argryodendron peralatum) and/ or substitutes Brown Tulip Oak (A. trifoliolata), Boonjie Tulip Oak (A. sp.), Floppy Leaf Ash (Flindersia schottiana), Queensland Maple (F. brayleyana), Bollywood (Litsea leefeana), Northern Laurel (Cryptocarya hypospodia), White Cedar (Melia azedarach), Brown Tamarind (Castanospora alphandii), Rose Tamarind (Arytera divaricata), Northern Tamarind (Diploglottis diphyllostegia), Damson (Terminalia sericocarpa) and Lemon Aspen (Acronychia acidula).

One could go on but suffice to say that because the forest occurs on rich soils it has a rich array of animals. Birds can be heard in the forest throughout the year whereas in wetter forests and nutrient poor forests, birds appear to be seasonally prominent.

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