Vulnerability and resilience

Subtropical rainforests of the Illawarra-Shoalhaven

Lesson delivery

Teacher/student led

Lesson description

The dynamics of ecosystem functioning, including vulnerability, resilience and ecological disturbance

This lesson explores the key components of subtropical rainforest ecosystems, focusing on their interactions and contributions to overall ecosystem health and resilience. Students will examine the roles of the canopy, understory, epiphytes, and forest floor, understanding how these layers contribute to processes like nutrient cycling, water regulation, and habitat creation. Additionally, the lesson will cover the impacts of disturbances and the concepts of vulnerability and resilience, emphasising the importance of maintaining biodiversity and ecosystem stability in the subtropical rainforests of the Illawarra-Shoalhaven region.

Duration

40 minutes

Supporting materials

Lesson 2 worksheet - The dynamics of ecosystem functioning, including vulnerability, resilience and ecological disturbance.
Illawarra-Shoalhaven subtropical rainforest in the Sydney Basin Bioregion (map)
Illawarra Climate Change Snapshot (2014)
NSW SEED map website

Dynamics of ecosystem functioning

Examining the dynamics of ecosystem functioning involves studying how different components of an ecosystem interact and contribute to its overall health and resilience. In the subtropical rainforests of the Illawarra and Shoalhaven, this includes understanding the relationships between plant species, such as the roles of canopy trees, understory plants, and epiphytes, as well as the interactions with fauna, including pollinators and seed dispersers. It also encompasses nutrient cycling, water regulation, and the impact of disturbances, helping to identify factors that maintain biodiversity and ecosystem stability.

The canopy

The canopy is the uppermost layer of the rainforest, formed by tall, mature trees. These trees perform several critical functions:

Primary Productivity - Canopy trees are responsible for capturing most of the sunlight and conducting photosynthesis on a large scale, producing energy that supports the entire ecosystem.
Water Regulation - By intercepting rainfall, canopy trees reduce soil erosion, control runoff, and contribute to the gradual infiltration of water into the soil.
Habitat Creation - The canopy provides shelter and nesting sites for a variety of animals, including birds, insects, and mammals. The structure also supports a wide range of epiphytes that grow on their branches and trunks.

The understorey

The understory consists of shrubs, small trees, and herbaceous plants that grow beneath the canopy. Their role in the ecosystem includes:

Light Utilisation - Understory plants thrive in low-light conditions, making efficient use of the dappled sunlight that filters through the canopy.
Nutrient Cycling - These plants contribute to the decomposition process, enriching the soil with organic matter as their leaves and branches fall and decay.
Species Diversity - The understory supports a high level of biodiversity by providing habitats for smaller species that rely on the shelter and food sources offered by these plants.

Epiphytes

Epiphytes are plants that grow on the surface of other plants, particularly on canopy trees, without taking nutrients from them directly. They play several important roles:

Nutrient Capture - Epiphytes collect nutrients from the air, rainwater, and debris that accumulate around their roots. This helps in nutrient cycling within the ecosystem.
Microhabitats - Epiphytes create small ecosystems on canopy branches, providing habitats for insects, birds, and small mammals.
Moisture Regulation - By trapping water in their structures, epiphytes help maintain humidity within the canopy, which is vital for many species' survival.

Forest floor

The forest floor is the lowest layer and plays a foundational role in ecosystem functioning:

Decomposition and nutrient recycling - The forest floor is home to decomposers, such as fungi and bacteria, which break down dead organic matter like fallen leaves and branches, returning vital nutrients to the soil.
Moisture retention - The leaf litter and organic matter on the forest floor help retain moisture, creating a damp environment that supports plant roots and soil organisms.
Soil stabilisation - The plant roots and organic debris stabilize the soil, preventing erosion and maintaining the integrity of the forest’s foundation.
Habitat - The forest floor supports a diverse range of species, including ground-dwelling mammals, reptiles, and invertebrates, which rely on the cover and food provided by the dense litter.

Cycles in the rainforest

The dynamics of ecosystem functioning in the subtropical rainforests of the Illawarra-Shoalhaven rely heavily on intricate water and nutrient cycling systems, which are essential for sustaining biodiversity and ecosystem health.

Water regulation

In the Illawarra-Shoalhaven subtropical rainforest, vegetation is crucial for water regulation within the ecosystem. The dense canopy captures rainfall, reducing soil erosion and allowing water to gradually infiltrate the ground. Trees with deep root systems store water in the soil, replenishing groundwater reserves and maintaining moisture levels, especially during dry spells.

Through the process of transpiration, trees release water vapor into the atmosphere, contributing to cloud formation and subsequent rainfall. This interplay between vegetation and the water cycle helps sustain the rainforest’s biodiversity, regulates local water cycles, and minimizes surface runoff, ultimately ensuring a stable water supply for the diverse plant and animal life that inhabit the ecosystem.

Nutrient cycling

Nutrient cycling is tightly controlled to prevent nutrient loss due to the high rainfall, which could otherwise lead to leaching. Rainforest plants have evolved mechanisms such as nutrient extraction from leaves before they are shed, shallow root systems for rapid nutrient uptake, and symbiotic relationships with fungi to break down organic matter in leaf litter. These processes allow the rainforest to conserve nutrients, even on nutrient-poor soils, making the ecosystem highly efficient in recycling essential elements.

Understanding vulnerability and resilience in ecosystem functioning

The concepts of vulnerability and resilience are central to understanding how ecosystems function and respond to disturbances. Ecosystems are dynamic systems composed of interactions between species, the physical environment, and ecological processes like nutrient cycling and energy flow. When stressors such as habitat loss, climate change, or invasive species disrupt these systems, they affect the balance of ecosystem functioning. The degree to which an ecosystem is endangered depends on the balance between its vulnerability and resilience, which in turn shapes its ability to maintain its essential functions.

The Illawarra-Shoalhaven subtropical rainforest is classified as an Endangered Ecological Community under the New South Wales Threatened Species Conservation Act.

Vulnerability of the Illawarra-Shoalhaven Subtropical Rainforests

Vulnerability refers to an ecosystem's susceptibility to disruptions that can undermine its ability to function. These factors directly affect the stability and balance of species interactions, nutrient cycles, and energy flows:

Extent of decline
Habitat fragmentation
Intensity of threats
Loss of key species
Climate sensitivity

Extent of decline

When ecosystems are significantly reduced in size, their capacity to support complex interactions and biodiversity diminishes. This loss impacts food webs and energy transfer, making ecosystems more vulnerable to collapse.

The subtropical rainforest in the Illawarra-Shoalhaven region has experienced significant decline since European settlement. Historically, this ecosystem stretched across large areas of the Illawarra escarpment and coastal lowlands. However, land clearing for agriculture, urban expansion, coal mining and the logging of valuable timber species like red cedar dramatically reduced its extent. Today, only about 25% of the original subtropical rainforest remains. Subtropical rainforest habitat has been impacted more than any other rainforest type in the Illawarra district.

Landuse and ecosystem change

View the spatial map viewer of the Illawarra-Shoalhaven region to observe the variety of land uses present in the Illawarra-Shoalhaven, eg. farmland, urban, forested areas.

Habitat Fragmentation

This map represents possible occurrences of the Illawarra-Shoalhaven subtropical rainforest and the consequent habitat fragmentation which has occurred.

The subtropical rainforests of the Illawarra-Shoalhaven have been extensively fragmented due to a combination of natural topography and human activities. Once vast, continuous stretches along the Illawarra Escarpment and coastal lowlands, these rainforests now exist in scattered and isolated patches. Habitat fragmentation plays a significant role in the vulnerability of these ecosystems. The continuous forest has been broken into smaller, isolated patches, particularly along the steep escarpment and remote areas like Kangaroo Valley. This fragmentation disrupts connectivity between patches, affecting species movement, gene flow, and the ecosystem's ability to sustain viable populations. Species like the powerful owl, which require large territories, are confined to these small fragments, heightening their risk of local extinction.

Loss of key species

a) Indicator species

Indicator species in the subtropical rainforests of the Illawarra-Shoalhaven are plants and animals that signal the health and functioning of the ecosystem. These species are particularly sensitive to changes in environmental conditions such as moisture levels, habitat quality, and biodiversity, making them useful for assessing ecosystem stability and vulnerability. One prominent indicator species is the Illawarra Socketwood (Daphnandra johnsonii), an endemic tree that is highly sensitive to habitat loss and fragmentation. Its presence indicates a relatively intact and healthy rainforest ecosystem, while its decline can signal increased vulnerability due to human disturbance.

Other key indicator species include powerful owls (Ninox strenua), which require large tracts of undisturbed forest to thrive, and their presence suggests a well-connected and functional habitat.

b) Endemic species

Endemic species, which are restricted to a specific geographical area, are particularly vulnerable to extinction due to their limited range. Since they exist only in one location, any environmental changes, such as habitat destruction, climate change, or the introduction of invasive species, can have devastating effects on their survival. The smaller and more isolated their habitat, the greater their risk, as they often lack the flexibility to adapt or relocate.

Click on the pictures below to learn more

Illawarra Socketwood

(Daphnandra johnsonii)

Endangered

White Flowered Wax Plant

(Cynanchum elegans)

Endangered

Illawarra
Zieria

(Zieria granulata)

Endangered

Scrub
Turpentine
(Rhodamnia rubescens)

Critically Endangered

c) Interdependent species

When interdependence is disrupted in an ecosystem, such as the subtropical rainforests of the Illawarra-Shoalhaven, the overall resilience of the system decreases. In highly interconnected environments, the loss of one species can trigger a chain reaction, affecting multiple species that rely on each other for food, shelter, or other ecological functions. This weakening of mutual dependencies can undermine critical processes like nutrient cycling, reproduction, and habitat stability. Without alternative species to fulfill similar ecological roles, the system’s ability to recover from disturbances is diminished, making the ecosystem more vulnerable to additional threats like climate change, habitat fragmentation, or invasive species. This highlights how interdependence plays a crucial role in maintaining the balance and resilience of rainforest ecosystems.

Strangler Figs
and Fig Wasps

Strangler figs depend heavily on specific pollinating fig wasps for reproduction, as these wasps are the only species that can pollinate the fig trees, ensuring the survival of both species. This near-exclusive relationship illustrates a high degree of interdependence.

Blue Triangle Butterflies and Sassafras

The Blue Triangle Butterfly relies on the native Sassafras tree as a host plant for its larvae. The butterflies lay their eggs on the leaves, and the larvae feed on them, establishing a strong plant-insect connection crucial for the butterfly's life cycle and the pollination of forest plants.

Grey-headed Flying Fox and fruit trees

The Grey-headed Flying Fox is vital to subtropical rainforests as it pollinates trees and disperses seeds while feeding on nectar, pollen, and fruit. This process supports plant reproduction and diversity, while the flying fox relies on these plants for food. This mutual relationship sustains the health and biodiversity of the forest ecosystem.

Noisy Pitta
and snails

The Noisy Pitta, a colorful ground-dwelling bird, plays a key role in controlling snail populations. It uses stones as "anvils" to crack open snail shells, which is essential for its diet. This interaction helps regulate snail populations, which could otherwise overconsume plant matter and damage the forest floor vegetation.

Climate sensitivity

The subtropical rainforests of the Illawarra-Shoalhaven are particularly vulnerable to the various impacts of climate change, which could significantly alter their structure and function. This vulnerability stems from increasing temperatures, which can stress native flora and fauna, and changing precipitation patterns that disrupt the water cycle essential for maintaining ecosystem health. Additionally, the anticipated rise in extreme weather events can lead to habitat destruction and loss of biodiversity, further compromising the resilience of these ecosystems. As species decline, the ecological interactions that sustain forest health and productivity may falter, ultimately diminishing the ecosystem services these rainforests provide.

Threatened species list

Click on the picture for a list of the threatened plants and animals of the Illawarra-Shoalhaven subtropical rainforests

Resilience of the Illawarra-Shoalhaven subtropical rainforest

Ecosystem resilience is the ability of an ecosystem to absorb disturbances and maintain its core functions and structures. It reflects how well an ecosystem can endure stress without shifting into a different state with new processes. Rather than aiming for stability, resilience acknowledges that ecosystems are dynamic, constantly cycling between disturbance and recovery.

Forms of disturbance in the rainforest

In the Illawarra-Shoalhaven subtropical rainforests, several natural disturbances occur, each affecting the ecosystem in different ways. The resilience of the rainforest to these disturbances varies depending on the nature and severity of the event. Key natural disturbances include:

Drought

While the rainforest can withstand short dry periods, prolonged drought stresses both plant and animal species, disrupting nutrient cycling and reducing biodiversity. Resilience is low during long-term droughts, particularly as climate change increases their frequency.

Bushfires

Subtropical rainforests are not fire-adapted, and fires can cause severe damage to vegetation and biodiversity. Fires destroy the canopy and understorey, significantly hindering recovery. This disturbance has low resilience, especially as it opens opportunities for invasive species to spread.

Storms and wind events

The steep Illawarra Escarpment makes the rainforest vulnerable to strong winds and intense storms. However, the rainforest is generally protected from damaging hot, dry westerly winds due to the barrier provided by the escarpment. Instead, it is more exposed to southerly winds and storms, which can create canopy gaps. These gaps allow light to penetrate, promoting biodiversity by encouraging the growth of lower vegetation. The rainforest shows moderate resilience to storms, as many species can regenerate quickly after minor disturbances, helping to maintain the ecosystem's health and diversity.

Flooding and landslides

East Coast Lows (ECLs) are the primary drivers of heavy rainfall in the Illawarra-Shoalhaven region. These intense low-pressure systems bring significant rainfall and can cause extreme weather events, such as localised flooding and landslides, especially when interacting with the steep escarpment. This combination of intense rainfall and topography strips both vegetation and topsoil, severely affecting the rainforest's ability to recover. With limited resilience, the ecosystem’s regeneration is slow, and affected areas often become vulnerable to invasive species during this recovery period.

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