Characteristics

Subtropical rainforests of the Illawarra-Shoalhaven

Lesson delivery

Teacher/student led

Lesson description

The characteristics of the ecosystem, including its spatial pattern and the nature of its biodiversity

The lesson focuses on the subtropical rainforests of the Illawarra-Shoalhaven region, exploring their spatial and ecological characteristics through interactive activities. Students begin by learning what subtropical rainforests are and examining subtropical zones worldwide. Using Google Earth, they create a slideshow highlighting the rainforests of NSW and explore the elevation and extent of the region’s rainforests through topographic maps and satellite imagery. Key topics include the landscape characteristics of the Illawarra escarpment, orographic rainfall, and the biodiversity of the ecosystem, with attention to prominent flora and indicator species. Fieldwork skills are employed through practical tasks such as constructing an elevation profile and learning how quadrats and transects are used to assess biodiversity. The lesson integrates geographic tools and spatial data to deepen students' understanding of the subtropical rainforest ecosystems in the Illawarra-Shoalhaven.

Duration

100 minutes

Supporting materials

Lesson 1 worksheet - Characteristics of the subtropical rainforests of the Illawarra-Shoalhaven

What is subtropical rainforest?

Subtropical rainforests are dense, lush forests found in regions with warm, humid climates and distinct wet and dry seasons. They are characterised by a high diversity of plant species, including tall trees, ferns, and vines, along with rich animal life.

Subtropical rainforests typically occur between tropical and temperate zones, and they are found in various parts of the world, including parts of Asia, Africa, South America, and Australia. The most well-known subtropical rainforests in Australia are the World Heritage listed Gondwana Rainforests of New South Wales and Queensland including Lamington National Park, and Dorrigo National Park. Further south in NSW are the Illawarra-Shoalhaven rainforests, which reach the geographical southern limit for this ecosystem.

These rainforests play a crucial role in biodiversity conservation and are considered highly vulnerable to climate change and human-induced modifications.

Subtropical zones of the world

Source: Meteoblue

The range of subtropical rainforests in NSW

Visit Google Earth to view the subtropical rainforests of NSW listed below. Follow the instructions provided in question 2 of your worksheet to create a Google Earth Slide Show of the rainforests featured in the pictures below.

Lamington Rainforest

Dorrigo Rainforest

Mt Keira Rainforest

Minnamurra Rainforest

Milton Rainforest

Spatial characteristics of the subtropical rainforests of the Illawarra-Shoalhaven

Elevation

Subtropical rainforest in the Illawarra-Shoalhaven is usually found below 350m above sea level (ASL), but there are occurrences up to around 550 – 600 m ASL, for example around Cambewarra Mountain.
Use the following topographic maps to investigate the elevation of the escarpment at Minnamurra Rainforest and Illawarra Escarpment State Conservation Area.

Location and distribution

View satellite imagery of the Illawarra-Shoalhaven area on Google Earth to observe the location, range, extent of the subtropical rainforests of the Illawarra-Shoalhaven.

Extent

Use the choropleth / topographic map on the NSW SEED map website to:
- Use scale to calculate area of subtropical rainforest
- Observe the presence of subtropical rainforest predominantly east of the escarpment and on
southeast facing gullies.
- Observe the extent of habitat fragmentation throughout its range.

SEED map instructions:
1. In the basemaps options, select ‘NSW Topo Map’.
2. Click ‘Add layers from catalogue’ / Vegetation / Vegetation classes of NSW (Version 3.30 - 200m Raster)
3. Close the catalogue window to reveal map.
4. Switch view to from ‘layers’ to ‘legend’.

Landscape characteristics

Escarpment profile

The Illawarra escarpment has a steep landscape profile with cliffs and deep valleys that create a sheltered environment for subtropical rainforest growth. This topography protects the area from prevailing westerly winds, leading to a microclimate that supports diverse plant and animal life.

Chemical weathering, physical weathering, and erosion continually reshape the landform, shifting the profile landward while maintaining its overall shape.

Orographic rainfall

In the Illawarra-Shoalhaven region, orographic rainfall plays a key role in sustaining the rainforest's water cycle. As moist air rises over the escarpment, it cools and condenses, delivering consistent rainfall that nourishes the forest and supports its rich biodiversity. The steep topography also ensures efficient drainage, preventing waterlogging while allowing roots to access both moisture and oxygen.

The dense rainforest canopy intercepts this rainfall, reducing runoff and promoting gradual water infiltration into the soil. This process not only supports plant growth but also stabilises the soil, preventing erosion and enhancing groundwater recharge. These mechanisms ensure a stable water supply for the rainforest.

🧭 Fieldwork skill - calculate relief and slope

Elevation Profiles

Optimum rainforest development occurs in locations with good topographic shelter from the west, and usually in sites with a south-easterly aspect. Under these conditions moisture loss through desiccation by dry westerly winds is minimised, as is their mechanically destructive effect upon the rainforests' closed canopies.

View the selected map regions, with associated scale bars, to complete an elevation profile from the summit of Mt Keira to Dumfries Ave, either as an excel file or hand drawn graph in question 6. of the Lesson 1 worksheet.

Lesson 1 - Mt Keira Elevation Profile

Ecological characteristics of the subtropical rainforests of the Illawarra-Shoalhaven

Climate

The warm, humid coastal climate in this region marks the southern limit for many subtropical rainforest species, benefiting from milder temperatures with minimal frost.

Rainfall

The subtropical rainforests of the Illawarra and Shoalhaven regions receive 1,200 to 2,000 millimeters of rainfall annually. Rainfall is fairly consistent throughout the year, peaking in warmer months. This moisture is vital for ensuring the sustainability of the rainforest.

Soil

The volcanic soils in the Illawarra and Shoalhaven regions are nutrient-rich, supporting a variety of tall trees and plants. These soils also retain moisture well, creating ideal conditions for the rainforest ecosystem and supporting a rich diversity of plant and animal life.

Canopy

The canopy of the Illawarra and Shoalhaven subtropical rainforests consists of 10 to 16 species and is multilayered, with an upper layer of emergent trees, a dense rainforest canopy, and a subcanopy. Emergent trees can exceed 35m in height, while non-rainforest species like eucalypts make up less than 30% of the emergents.

The nature of its biodiversity

The subtropical rainforests of the Illawarra and Shoalhaven are renowned for their rich biodiversity, hosting a diverse array of plant and animal species. This unique ecosystem supports a wide variety of flora, including towering trees, ferns, and epiphytes, which create complex layers of habitat. Additionally, the rainforests are home to numerous endemic species and provide critical habitats for wildlife, including birds, mammals, and reptiles.

Species Diversity

Illawarra-Shoalhaven ecosystems species numbers

The Illawarra-Shoalhaven subtropical rainforest is relatively biodiverse, supporting 577 plant species and 140 animal species. While it has greater species diversity than local ecosystems like coastal dunes, it is slightly less biodiverse compared to dry sclerophyll forests (eucalypt forests), which host around 700 plant species and 180 animal species. Despite this difference in overall species numbers, the subtropical rainforest remains a vital and ecologically rich habitat within the region, particularly noted for its diversity of reptiles, birds, and invertebrates. It plays an essential role in maintaining regional biodiversity.

Amazon and Illawarra-Shoalhaven Subtropical Rainforest vertebrate species

The Amazon rainforest is one of the most biodiverse ecosystems on Earth, supporting around 40,000 plant species and an estimated 2.5 million animal species, including 427 mammals, 1,500 bird species, 378 reptiles, and 400 amphibians. In comparison, the Illawarra-Shoalhaven subtropical rainforest hosts 577 plant species and 140 animal species, with 23 mammals, 73 bird species, 33 reptiles, and 12 amphibians.

While the subtropical rainforest is highly biodiverse for its region, the sheer scale and variety of life in the Amazon are incomparable, especially in terms of plant diversity and the vast number of species in each vertebrate group. Nonetheless, the Illawarra-Shoalhaven rainforest remains a crucial habitat for many species, playing a significant role in regional biodiversity and ecological stability.

Prominent flora types

Stranglers

Hemi-epiphytes, such as strangler figs, begin their life high in the canopy and send roots downwards to envelop host trees. Over time, they can kill their hosts, forming hollow trunks. These figs create intricate structures and significantly alter the forest's composition.

Palms

Palms such as the Cabbage Tree Palm are characteristic of NSW subtropical in the Illawarra-Shoalhaven. They dominate the understorey, providing habitat for wildlife and enhancing the forest's layered structure.

Woody vines

Woody vines, or lianas, are common in subtropical rainforests, climbing trees to reach sunlight. These vines form complex networks between trees, increasing forest connectivity and providing pathways for animals.

Epiphytes

Epiphytes, including Bird's Nest Ferns and orchids, grow on other plants without drawing nutrients from them. They capture moisture from the air and absorb nutrients that are washed down from the trees above.

Plank buttresses

Plank buttresses are wide, flat extensions at the base of tree trunks that offer stability in shallow soils, anchoring the trees in soft, moist ground while also aiding in the absorption of nutrients from the forest floor.

Ground Ferns

Ground ferns cover the forest floor in dense layers, thriving in the shaded, moist environment of the subtropical rainforest. They play a crucial role in soil conservation and provide a habitat for small animals and insects.

Mosses

Mosses cover tree trunks and rocks in subtropical rainforests, forming dense, spongy carpets. They help retain moisture and contribute to nutrient cycling by breaking down organic material, maintaining the rainforest’s high humidity.

Fungi

Fungi play a crucial role in subtropical rainforests, breaking down organic matter and recycling nutrients. They form symbiotic relationships with trees, aiding in water and nutrient absorption while enhancing the ecosystem's biodiversity.

Key species - subtropical rainforests of the Illawarra and Shoalhaven

The following species are regarded as key species because they are commonly and typically found in the Illawarra-Shoalhaven subtropical rainforest.

Giant Stinging Tree

Red Cedar

Strangler Fig

Illawarra Flame

Perons Tree Frog

Swamp Wallaby

Superb Lyrebird

Diamond Python

🧭 Fieldwork skill - use fieldwork methods to assess biodiversity

Quadrats

(click picture for instructional video, 5.31 min)

Quadrats are used as a tool in ecological fieldwork to estimate the abundance and distribution of plant and animal species within a specific area. A quadrat is typically a square frame of a known size (e.g., 1m² or 5m²) that is placed randomly or systematically within the study site. Researchers then count or record the species found within the quadrat, allowing them to estimate population density and abundance over a larger area.

For plant species, in addition to counting individuals, quadrats are also used to estimate percentage cover, which refers to the proportion of the ground within the quadrat that is covered by each plant species. This method provides a more accurate representation of the dominance of certain plant species, particularly in densely vegetated areas.

By sampling multiple quadrats across a habitat, ecologists can estimate species abundance, distribution patterns, percentage cover, and overall biodiversity.

Belt transects

(click picture for instructional video, 5.10 min)

Belt transects are used in ecological fieldwork to measure the distribution, abundance, and changes in species across a gradient or environmental zone. A belt transect involves laying out a long line (transect) across a habitat, and then placing quadrats at regular intervals along the line to sample the area. This allows researchers to study how species composition and abundance vary along the transect.

Unlike a single quadrat, which captures data from one spot, a belt transect provides a more comprehensive view by sampling a continuous strip of the habitat. Within each quadrat along the transect, researchers count individual species and, for plant species, estimate percentage cover. This method is particularly useful in detecting changes in species distribution that correlate with environmental gradients, such as changes in elevation, soil type, or moisture levels.

By using belt transects, ecologists can track species abundance, diversity, and spatial patterns, offering insight into how ecosystems respond to environmental factors and human impacts.

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