Ecology of the Newnes Plateau plants

• Life-forms, longevity and community strata
• Plant speceis longevity and persistence
• Prominent families and species richness
• Exotic species
• General abundance of populations
• General soil / nutrient status
• Species distribution patterns
• Flowering
• Fruit types
• Seed dispersal
• Seed dormancy
• Recruitment
• Fire ecology
• Soil / canopy physical disturbance ecology
• Drought / rainfall ecology

Life-forms, longevity and community strata

Trees dominate the woodland and forest vegetation canopy but are absent from swamp vegetation, and generally of low-growing or multi-stemmed mallee form in heath vegetation. Eucalyptus species (23 species) are the main vegetation dominants.

On the Newnes Plateau, as in other sandstone landscapes, much of the plant biodiversity is in the shrub layer - 40% of the plant species on the Newnes Plateau are shrubs, with a further 32% in the herbs, small shrubs and graminoids class (see table below). This latter class are mainly hard-leaved sclerophyllous species with leaves present all year.

Despite the cold winters the only deciduous species are the terrestrial orchid species (about 86% of the Orchidaceae species).

Number of species by life-form for Newnes Plateau flora

Plant species longevity / persistence

Most Newnes Plateau species are perennial; there are few if any annual species. In terms of longevity most species are likely to be long-lived (20-50 years) with some very long-lived. Many have underground rootstocks lignotubers enabling longterm persistence or rhizomes and tubers probably allowing almost indefinlte longevity.

There are very few short-lived species. Possibly Platysace lanceolata, Coronidium wadellii, Wahlenbergia and Actinotus forsythii.

Actinotus forsythii is one of the few annual species on the Newnes Plateau.

Prominent families and species richness

Over 500 (593) native species have been recorded from the Newnes Plateau representing at least 95 plant families.

Prominent families are sclerophyllous families that are important in low nutrient ecosystems including Myrtaceae, Proteaceae, Fabaceae, and Cyperaceae.

Some families are widespread, and frequently dominant across vegetation types on the Newnes Plateau, particularly Myrtaceae, Fabaceae and Cyperaceae, others are more localised such as Rutaceae and Santalaceae. Common families in other areas such as Asteraceae are rare or localised.

Exotic species

Untill more recently, few weeds were found on the Newnes Plateau due to low nutrient conditions . Changes to water flow in creeks and swamps, such as prolonged flows lead to the introduction and spread of weeds such as Cirsium vulgare and Conyza when flows drop.

The pine plantations growing alongside the native forests have also resulted in the spread of pine seedlings in some areas of the Plateau.

General abundance of populations

While the distribution of many species are widespread on the Plateau, such as many Myrtaceae, populations of many species are localised, despite their often being large areas of apparently similar habitat. For example many species, but not all, in Rutaceae, Santalaceae, Orchidaceae and Asteraceae. This may be due to local variations in the soil and drainage factors that are not readily discernible, but are critical during the recruitment and establishment phase of the species. The limited dispersal ranges of many species is likely to reinforce these patterns.

General ecological characteristics

General soil / nutrient status

The Newnes Plateau landscape is a sandstone landscape and has many features in common with other low nutrient ecosystems particularly other areas of sandstone in the Blue Mountains. However it is the highest extensive sandstone area in the Blue Mountains with an extensive areas of deep loamy soils. The margins of the Plateau are distinguished by sandstone forming characteristic pagoda formations as a result of weathering and movement of iron rich strata. Soils here are extremely shallow to skeletal with extensive areas of bare rock, in contrast to the deeper upper Plateau soils. Peaty sandy soils have formed in the valley swamps, permanently moist but also very low in nutrients. Forest occurs in sheltered gullies which provide maximum protection and good drainage and moisture conditions but there are virtually no areas with high nutrient soils, the closest being the basalt caps such as Mount Cameron to the north east. Climatically it has high rainfall and cold winters with severe frosts and occasional snowfalls.

Species distribution patterns

Species adapted to low nutrient conditions and closely follow soil, geology and moisture features, with forest, woodland and heath following a decreasing soil nutrient-depth gradient, and shrub swamp on permanently wet sites. Small valley systems generally contain a suite of habitats with woodland on the upper plateaus, heath and pagoda rock formations on ridges, perched valley side and valley floor swamps, and forest further downstream These patterns and habitats are repeated across the Plateau providing replication of relatively localised habitats for plant and animal species. As a result many species have narrow habitats but are relatively widespread across the Plateau, depending on extent of their habitat. Many of the habitats are restricted to the Plateau particularly those depending on permanent moisture and consistently cooler temperatures.

Flowering

For most of the species on the Newnes Plateau flowering is related to season and temperatures. Following winter when there is virtually nothing in flower, a strong succession of flowering begins. Some examples are:

• August  Acacia terminalis 
• September - October many of the peas - Daviesia, Mirbelia, other Acacia species, Leucopogon, Boronia deanei
• November - December Leptospermum species, Patersonia species, orchids - Thelymitra
• January - February Persoonia species, Platysace lanceolata, Banksia serrata, Banksia cunninghamia
• March - April - May  Platysace linearifolia, Eucalyptus pauciflora
• June - July minimal flowering
  

Many species flower over a relatively short time, but some flower for many months e.g. Pimelea linifolia and Phyllota squarrosa.

Little is known about the pollination mechanisms of most of the Newnes Plateau species. Bird and insect vectors are likely to be important. Large inflorescences such as Banksia and Telopea are likely to be pollinated by birds (honeyeaters are important). Genetic studies of Telopea are showing that despite the disjunct occurrences of populations of this species, significant gene flow is taking place over long distances between coast and mountains, presumably as a result of bird pollination. 

Acacia kybeanensis in flower

Pollination of the orchid Spiranthes australis.

Fruit types

The largest fruits are probably the distinctive woody fruits of Hakea, or the long capsules of Telopea speciosissima. Fruits of most species are small and dry. A few are fleshy - Persoonia have the largest fleshy fruits with Persoonia chamaespitys up to 15 mm. Some of the Santalaceae have fleshy fruits. Some of these were important aboriginal foods.

Seed sizes range from very small - orchid seed, fern spores and Juncus, to large winged seeds of some of the Proteaceae (Hakea, Telopea)

Timing of seed maturity varies depending on the species, peas take about 2 months from flowering to maturity. Many Acacia species mature in summer during December - January, though flowering times may vary.

Seed dispersal

Unlike many of the species in higher nutrient ecosystems such as the Grassy Woodlands of the Cumberland Plain, very few species are dispersed by animals by adhesion.

Most of the Newnes Plateau species do not appear to have specialised structures for distance dispersal of their seed, and we assume that most are dispersed locally, essentially by gravity and downslope wash. Such distances are likely to be of the order of 1 - 20 m, allowing seed to remain in the same habitat as the parent plant.

Many species particularly in the Fabaceae have seeds with foodbodies that are attractive to ants, which move the seeds to different sites. Though this movement is still only a matter of metres it may leave the seed in a better place for germinating such as more deeply buried.

Seeds with wings, or seed held high up in canopy species might be dispersed during catastrophic events such as storms or updraughts in major fires. Eucalypt capsules may possibly be dispersed long distances under such conditions.

The fleshy fruits of some species, Persoonia, Santalaceae, might be dispersed further by birds or mammals; we don’t know.

Though exotic weed species are relatively rare on the Newnes Plateau, those that do occur have better dispersal than most native species e.g. backberry seeds are spread in fox scats, spear thistle, Cirsium vulgare and fleabane, Conyza are efficient wind-dispersed Asteraceae species.

Fleshy fruit of Persoonia oblongata.

Capsule of Oxalis sp.

Seed Dormancy

Most seed enters a soil-stored seedbank where dormancy features allow it to remain until conditions for germination are suitable. Fire is an important trigger for many species. Many Fabaceae species (peas and acacias) have hard coated seeds which are cracked by fire temperatures, allowing germination to occur following rain. In some species dormancy may be triggered by smoke, or smoke and heat. Dormancy mechanisms in families such as  Rutaceae, Ericaceae and Cyperaceae, and genera such as Persoonia, is poorly understood.

A feature of some of the distinctive sclerophyllous species of low-nutrient habitats is to have seeds retained on the parent plant for long periods after maturity. This feature is known as serotiny. Species of Banksia, Hakea, Petrophile, Isopogon and Lambertia in the Proteaceae have woody fruits which hold mature seeds for many years, until released by the heat of a fire or in some cases death of the stem. Similarly species of Eucalyptus, Leptospermum and Callistemon in the Myrtaceae have woody fruits which may be retained for up to a year, sometimes longer, though some such as Leptospermum blakelyi and Leptospermum trinervium are not retained. Generally once seed is shed from the woody fruit there is no dormancy mechanism and the seed germinates or dies.

As in many aspects of ecology it is difficult to extrapolate from one species to another.

Seed of Acacias have physical dormancy and are often seen germinating after fire

Woody fruit of Hakea salicifolia

Recruitment

Many of the Newnes Plateau species are long-lived, and with mechanisms such as resprouting from rootstocks, rhizomes and lignotubers are able to survive conditions of fire and extended drought. In existing vegetation occupant plants are strongly persistent e.g. Isopogon prostratus may survive at least 30 years.

Seedling recruitment of many species appears to be episodic and related to disturbance events such as periodic fire or drought, which provide open conditions necessary for germinating seeds. We have characterised the ecology of the main plant species as being fire, disturbance or drought-rainfall driven depending on how it appears to recruit in relation to these conditions. For example Grevillea acanthifolia seedlings noted in drying swamp conditions in Murrays Swamp in 2008 indicate disturbance or drought-rainfall ecology rather than fire-related.

Fire ecology

Fire has a major influence on the ecology of the shrub-dominated sclerophyllous vegetation of the sandstone plateaus of the Sydney area. Fire frequency and intensity are important factors in the impact on the vegetation at any particular site. Because of its relatively high rainfall and generally cool conditions, fire events on the Newnes Plateau are probably less frequent than lower elevation sites, but may be of high intensity when they occur. Low intensity hazard reduction burns and accidental fires may also occur.

On the Newnes Plateau many species are able to cope with fire, and positively benefit from it. Many species survive fire as adults by regrowing from rootstocks, lignotubers or  rhizomes. Many eucalypts can regrow from epicormic shoots on their trunks. Such regrowth happens almost immediately after fire and extensive growth will have been achieved within 2 - 4 years after fire.

Some species however are killed by fire (fire-sensitive species), with the recruitment of the next generation taking place by germination of seeds in the nutrient enriched ashbed of the fire, aided by the increased light conditions and lack of insect predators that may occur after major fire. The seeds of many species in the family Fabaceae (peas and wattles), Rutaceae and Ericaceae may be in the pre-fire soil-stored seedbank, but seeds from species with woody fruits (serotinous fruits) in the Proteaceae familiy such as Banksia, Hakea, Petrophile and Isopogon, as well as from the Myrtaceae family like Eucalyptus and Leptospermum, will be released from capsules after the fire to be shed onto the burnt soil. Successful germination and establishment will depend on weather conditions, rainfall and time of year, as well as the impact of grazing and predation.

Fire

Many species resprout after fire.

Soil / canopy physical disturbance ecology

Disturbances other than fire may impact on vegetation, for example erosion or land slips may expose bare soil. Some species are adapted to colonise such sites; their ecology may include long term seed dormancy triggered by exposure, followed by quick growth/ short life-spans in the open conditions. Many weed species have these traits. Coloniser species of disturbed sites on the Newnes Plateau include Cirsium vulgare and Hypochaeris radicata.

Drought / rainfall ecology

In drier inland parts of Australia, where rainfall is low, fire is relatively infrequent and limited by the lack of biomass to sustain an extensive burn. Extended dry periods are normal and longterm survival during severe droughts depends on long-lived trees and rootstock regrowth, evolved in response to periodic dryness. Short-lived species however may die out in dry conditions but remain as dormant seeds in the soil-stored seedbank. Recruitment of new individuals may occur only after periodic high rainfall events. Species with a drought / rainfall responding ecology are rare on the Newnes Plateau (mainly Asteraceae species) but are frequent in woodlands on higher nutrient soils such as the Cumberland Plain Woodland in western Sydney.