Coastal Plants: A Guide to the Identification and Restoration of Plants of the Greater Perth Coast

By Kingsley Dixon

The greater Perth coast is a biodiverse and ecologically vulnerable region, with its unique native plant species threatened by clearing, invasive species, fire and climate change. This second edition of Coastal Plants has been updated and expanded to provide a definitive guide to 128 of the most common plants of the Perth coastal region. It includes the key species used in coastal restoration, along with important weeds. The description of each species is accompanied by a distribution map and diagnostic photographs of the whole plant, flowers, seeds and fruits. The book also contains introductory chapters on the biology and ecology of the coastal plants, their biogeography, and practical approaches to the restoration of coastal dune vegetation.

Coastal Plants is distinctive in its focus on restoration, which makes it valuable for community groups and individuals interested or involved in coastal natural history or restoration activities.

• Language: English
• Publisher: CSIRO PUBLISHING
• Release date: May 1, 2020
• ISBN: 9781486311392

Book preview

Part 1

Ecology and biology of plants of the west coast

Australia is more biodiverse than 98% of other countries. As one of the 19 mega-biodiverse countries on Earth, Australia, through its 65 million years of evolutionary isolation as the island continent, developed species and ecosystems that are world-class and unique – 80% of our plant and animal species are found only in Australia. For the biodiversity hotspot of south-west Australia, the uniqueness of the biodiversity is even higher with 99% of species found here and nowhere else.

As the island continent, these long periods of genetic isolation have meant that Australia’s biodiversity has adapted in remarkable ways to some of the world’s poorest soils and most hostile environments. Understanding how Australian species operate ecologically presents challenges, particularly where conservation of biodiversity is involved.

A consequence of our unique species and ecosystems is that adopting conservation, restoration and management approaches from other regions of the world and applying them in the Australian context is simply not feasible and rarely appropriate. Such practices ignore the complex and unique ecological processes that drive diversity and function in Australian, and particularly the south-west Australian native ecosystems, Australia’s primary biodiversity hotspot, now complemented by the east coast rainforest ecosystems.

Resolving effective means for developing the knowledge base to protect, manage and rehabilitate Australia’s unique species and ecosystems represents a significant challenge for conservation and restoration scientists and practitioners. Nowhere else is this more evident than for the fragile coastal fringe of south-west Australia where the intersection between human activities and ecological disruption pervade the marine and coastal environments. And with more than 80% of Australians now living within 80 km of the coast, the impacts of human activity on coastal biodiversity is resulting in loss of ecological integrity with many areas particularly adjacent to urban environments facing continued degradation processes.

The Western Australian coast

The Western Australian coastline hosts a remarkable 1227 vascular plant species, about the same number of species as found in the British Isles, of which 10% (166 species) are weeds (adapted from Beard 1990 and FloraBase online information).* This equates to the richest and most diverse native biodiversity of any mediterranean coastal region. The reasons for such richness are unclear, but are possibly linked to the extraordinary diversity of the coastal hinterland that acted as the potential donor for many coastal species.

Species richness can be looked at in other ways. For example, the number of species that are unique to an ecosystem (endemic) reflects soil qualities, evolutionary processes (e.g. ecological isolation, geological stability, phylogeny, breeding biology) and continental/regional isolation. Figure 1 shows the uniqueness values for coastal species at the Western Australian and Australian levels (from Beard 1990). Aquatic species have a more cosmopolitan distribution followed by species of the littoral zone (i.e. near-coastal environments) with dune species (those of consolidated or moderately mobile sediments) having the highest local endemism of the coastal zone.

The terrestrial component of the Perth coast is a rich resource of biodiversity. With 147 species of native plants found in the dunes of the Perth metropolitan coast, the plants provide almost year-round flowering, fruiting, seeding and habitat opportunities for insect, reptile and bird life.

Although the number of species in the Perth coastal dunes is low compared to the hyperdiverse inland vegetation of the Swan Coastal Plain or the Mt Lesueur National Park (860 native flowering plant species), coastal dune plants exhibit remarkable diversity in growth form with remarkable adaptability to the stringencies of life on the coast. For example, the 10 major plant families (in terms of species number and abundance) found in Western Australia retain representative species in the dune vegetation, including the Myrtaceae, Proteaceae, Fabaceae/Mimosaceae, Goodeniaceae, Ericaceae, Asteraceae, Poaceae, Orchidaceae, Chenopodiaceae and Liliaceae (sens. lat.).

Why, in comparison to hinterland floras, are coastal dune ecosystems relatively species poor? A key factor relates to the long periods of time necessary for inheritable adaptive traits to develop and resolve new species on new soil types and substrates. Since the coastal soils of the west coast are geologically recent (hundreds to tens of thousands of years compared to the more ancient (tens of millions of years) substrates of the species-rich hinterland), insufficient time has elapsed for the evolution of species adapted to the unique alkaline pH and structure of coastal soils and substrates (i.e. limestone). The ecological volatility of the coastal environment also means that only species with fast-growing attributes are likely to survive.

Similarly, plants of coastal environments have ecological attributes reminiscent of plants from other ‘young landscapes’ such as post-glacial regions, including North America and northern Europe. Though geographically large, post-glacial and coastal ecosystems are relatively species poor (in comparison to more inland areas of south-west Australia, for example) with many species possessing high growth rates with seed that moves long-distances that is often reflected in low genetic variation.

Figure 1. Percentage endemism of coastal species for Western Australia and Australia based on the three key ecosystems: aquatic (plants living in water including emergent species); littoral zone (between high water and low water mark often on margins of estuaries, lakes and rivers); and coastal dunes including consolidated and mobile sands.

Conservation planning

Protecting the diversity of plants and animals in coastal dunes is complex, long-term and resource intensive, though easier to rehabilitate and restore in comparison to the geologically older ecosystems such as banksia woodland or jarrah forest.

The ecological footprint of humans along the Western Australian coast is most pronounced in the extensive metropolitan sprawl of Perth where it is estimated that less than 5% of Quindalup Dune ecosystems remain (Figure 2).

Direct impacts through infrastructure developments (e.g. housing, roads, beach development, groynes) and indirect impacts (such as invasive plants, feral animals, fire, erosion and pests and diseases) have contributed to a rapid decline in the ecological integrity of dune ecosystems. For example, most metropolitan coastal dunes that retain natural plant cover have some form of ecological disturbance, through tracks (formal or informal), weed incursion, feral animals or development. Weeds exploit both natural and artificial disturbances in dune communities with highly invasive species such as the South African rose pelargonium (Pelargonium capitatum) and the diminutive annual Crassula glomerata being unbiquitous in dunes along much of the west coast.

Figure 2. Digital terrain image showing pre-European and current extent of the Quindalup Dune System (red) along the Swan Coastal Plain with insert images highlighting how remnant areas are now surrounded in urban development.

Maps from Google Earth.

As with many other ecosystems in the south-west Australian biodiversity hotspot (an area south-west of a line from Shark Bay to Eucla), disturbance and weeds represent major ecological perturbations that result in significant degradation and ecological dysfunction. Once a disturbance cycle is established, the degradation process will continue unless intervention occurs. Dedicated and well-resourced management over the long term is necessary to return disturbed coastal areas to a level of natural ecological resilience; however, monitoring and remedial actions may be required on very long time frames.

Degradation of coastal dune habitats outstrips restoration efforts by orders of magnitude. Redressing this imbalance and creating coastal environments where there is a zero net impact on native biodiversity values remains a significant challenge for planning agencies and land management organisations. Significantly, cumulative impacts in coastal ecosystems are rarely considered in making even the most modest of planning decisions. The walkway, carpark extension, building or exercise area that is constructed today is a permanent loss of coastal habitat, and each and every development adds to the cumulative loss of coastal ecosystems.

Unlike most other Australian capital cities, Perth has a number of significant coastal assets that retain a moderate to high level of ecological integrity. The most significant and intact coastal ecosystems include Warnbro Sound, Garden Island, Rottnest Island, Point Peron and Woodman Point, margins of Cockburn Sound, Campbell Barracks (Dept. of Defence), Bold Park, Whitford Nodes, coastal precincts in the Town of Cambridge, City of Stirling, and the City of Joondalup including Ocean Reef marina northwards.

Planning efforts along the coast have resulted in a number of studies* that attempt to balance development with conservation. However, on-ground activities for protection and enhancement of biodiversity values rely on local authority planning and management plans. Importantly, local government plays a critical role in protection and management of coastal environments, often with direct management responsibilities. Thus it is important that there are technically competent staff to manage the conservation and social complexities of coastal management.

Coastal management must be guided by well-considered coastal management plans that are locally relevant to the protection of biodiversity and ecological values while providing necessary guidelines for coastal restoration activities. Generic restoration guides are provided through the Western Australian Planning Commission, Natural Resource Management groups and Coastwest (e.g. the Coastal Planning and Management Manual**); however, rehabilitation and restoration activities should be aligned with the principles in the National Standards for the Practice of Ecological Restoration in Australia published by the Society for Ecological Restoration Australasia (see the next box with information on the recovery wheel that is a useful means to assessing the success and trajectory of restoration and rehabilitation projects). By incorporating the guiding principles in the National Standards with locally developed management plans, it is possible to achieve a sustainable balance between protection, restoration, conservation and use of the coastal strip as well as addressing locally unique issues such as access and use of coastal resources, erosion control, and protection of locally endemic biodiversity and unique ecological communities.

A good example of a local coastal planning document is the Town of Cambridge Coastal Natural Areas Management Plan, which guides coastal management. This document was adapted to local issues yet is both regionally and nationally benchmarked. Though out-of-print, the document contains the components needed in locally relevant plans. Importantly, coastal management plans require a social licence, and early, informed engagement with the community is necessary to ensure the plan has broad community support. Amongst other things, such engagement ensures volunteer support for restoration activities through local volunteer organisations such as Coastcare. However, constant vigilance is still required to ensure practices and principles that put protection of coastal environments ahead of development are enshrined in decision making. For example, in October 2016, a 1 ha coastal site in the Town of Cambridge restored by dedicated local coastcare volunteers for 10 years was converted into a car park.

National Standards for the Practice of Ecological Restoration in Australia

The National Standards* are the most comprehensive guide to the principles and practices to achieve sustainable and resilient rehabilitation and restoration of Australian ecosystems. Designed to be applicable to terrestrial, aquatic and marine environments, the Standards provide clear guidance as to what constitutes a scientifically robust and ecologically sustainable restoration program. The Standards outline the steps required to plan, implement and monitor a restoration project. The six key principles that underpin all restoration programs are:

1. An appropriate native reference site (natural or an analog that approximates the altered state of the site) is used to set restoration goals and targets and to assess the success of an ecological restoration project – locate an area where there are intact dune and coastal areas remaining to provide reference points in terms of species diversity, density and pattern.

2. The techniques used to restore a site are appropriate to the condition of the site and the ability of the ecosystem to recover naturally – for coastal communities some level of ‘autogenic recovery’ may be possible if militating factors such as weeds, wind erosion, grazing and disturbance are controlled.

3. Restoration success is guided by clear goals and objectives, using measurable indicators of success – this may involve staging a restoration program (site weed control in 1 year, planting in another and follow-up enrichment plantings in subsequent years). Key attributes to set goal and objectives include site physical state; species composition; community structure (appropriate numbers of key life forms); ecosystem function (pollinators, indicator fauna, evidence of natural regeneration in plants and animals, nutrient and water status stable and representative); and absence of threats.

4. Ecological restoration should aim for full recovery – for coastal ecosystems where species numbers are low and ecological resilience is high, it is tech nically feasible to achieve full restoration . Measures of progression towards full recovery can be mapped onto a ‘recovery wheel’ (see below) that provides a graphic visualisation of progression of a restoration program towards full recovery (5-star restoration).

5. Restoration uses the best available knowledge that, where appropriate, links to scientists and research programs . Many coastal restoration programs use the principle of ‘adaptive management’ (see later section) where restoration is planned to test principles that are under development, such as use of a new weed-matting material or changes to planting methodologies. It is critical that where an approach is recommended, it is validated through testing that involves the use of a control treatment.

6. Communities are informed, engaged and, where appropriate, contribute to the achievement of the restoration outcomes . The lack of a ‘social licence’ can lead to poor community buy-in and, in some situations, open suspicion of a restoration program. A local Coastcare group is a useful means for building community engagement.

* Standards Reference Group (2017) National Standards for the Practice of Ecological Restoration in Australia. Society for Ecological Restoration Australasia.

Measuring outcomes and success using the SERA recovery wheel

The Society for Ecological Restoration Australasia (SERA) has developed the restoration recovery wheel as an interactive tool that visualises the progression of restoration program towards 5-star recovery (Figure 3). Using six key indicators, the wheel provides a graphic representation of where extra effort might be required to achieve successful restoration (Figure 3). Available online (go to https://www.seraustralasia.org and scroll down to the section on Standards to download the menu instructions under recovery wheel) or as a phone app for android or iPhone – go to iTunes or the Android store and search for ‘Recovery Wheel’.

Figure 3. Blank recovery wheel template

Using the recovery wheel to gauge ecological trajectory in coastal restoration

Three examples where the recovery wheel has been applied to coastal restoration sites (Figure 4). The sites are being managed to achieve 5-star restoration. The first site has some plantings and attempts at weed control, but the restoration trajectory is uncertain and that site is likely to return to a weedy state without considerable additional inputs and management (i.e. intensive weed control and further plantings). The second example is a newly planted site where plants and diversity are representative of a reference state, but this site is lacking ecological connections and functional maturity due to its developing state. Though rated as 3-star, the site is to be managed towards a 5-star recovery state. The third example is a 20-year restoration site that has been progressively managed and is rated as 4+ star. This site was the location of a surf club building and, following demolition, the site remained in an abandoned state until a local Coastcare group commenced work to restore a native dune communuity. This involved scalping of contaminated and weed-infested soil, jute matting (due to risks of wind erosion) and progressive plantings, weed control and fence management over a 15-year period. Today the site is a representative assemblage of local species with evidence of faunal connections with nearby natural areas.

Figure 4. Three sites at various stages of recovery towards a 5-star rated restoration site. Top-left: 2-star site with some native species, substantial weed cover, limited evidence of recruitment of native species and little evidence of desirable animals. It is stable but would degrade substantially if disturbed. Top-right: 2.5-star site undergoing restoration and, though open with limited cover and structural development, has the higher star rating as the prospect of full recovery is likely due to the input of a local coastal group. Bottom: 4.5-star site that has been undergoing intensive restoration for 20 years and has evidence of natural recruitment of native species with limited weed impacts in addition to good structural development of plants and no evidence of erosion. The site was originally a building site.

The Perth coast

Perth’s coastline is world-renowned. Expanses of white sandy beaches interspersed with limestone headlands and promontories, reefs and dune vegetation create natural coastal landscapes that are world-class, but are also fragile.

Equal to the beauty of the Perth coastline are the abundance and diversity of marine and coastal life that is among the most biodiverse of any temperate coastal environment. For example, 14 species of seagrass, including the most southerly distribution of the tropical species Syringodium isoetifolium (Figure 5), occur in coastal waters, making it a global hotspot for seagrass diversity. These rich assemblages of seagrass species in turn have led to extensive seagrass meadows along the coast that provide stabilisation of beaches and important habitat and nursery sites for marine life.

The dynamic action of successive geological sea-level changes give the Perth coast its distinctive swale-based lake systems (such as near Warnboro Sound), extensive protective offshore reef systems and islands that provide refuge habitats for marine birds and mammals (Figure 6).

Figure 5. Syringodium isoetifolium on a reef near Perth

John Statton

Figure 6. Southern metropolitan coastline at Rockingham showing the submerged marine reef systems and offshore islands that play a role in protecting in-shore marine and coastal environments and contribute to the geomorphological development of the coast. For example, accreting sediments and changes in sea level have impounded lake systems that are a feature of the Quindalup and Spearwood systems.

Google Earth

The pH of coastal substrates ranges from neutral to slightly acidic on the most leached eastern parts, becoming progressively more alkaline in the adjacent Spearwood Dunes with highly alkaline soils found in the youngest geomorphological element, the Quindalup Dunes. It is the plant species of the Quindalup Dunes, coastal sands and associated limestone outcrops that form the basis for this book as these plant communities are subjected to high levels of human impact and population pressure.

The Swan Coastal Plain

The Swan Coastal Plain is an extensive depositional, mostly sandy plain extending from Eneabba to Dunsborough. Up to 30 km wide, the Swan Coastal Plain is bounded on the east by the Darling Range, an escarpment that forms the western edge of the continental bedrock of the pre-Cambrian Australian Shield and abruptly ends in the west with the young coastal dunes and limestones of the Quindalup complex. The Swan Coastal Plain is a low-lying (rarely above 80 m high), undulating region largely composed of shoreline deposits and alluvium from erosion of the continental materials with deposits in some parts up to 15 km deep. Whereas the Australian Shield is 3.5 billion years old, the Swan Coastal Plain is relatively young, ranging from > 120 000 years old (the Bassendean Dunes) to the 2000–10 000-year-old Quindalup Dunes.

The Swan Coastal Plain has accreted in a westerly direction with repeated marine incursions and repositioning of the coast leading to a system of roughly parallel terrestrial dunes and, offshore, submerged marine reefs and islands. Rises and falls in sea level, particularly in the last 10 000 years, have given Perth much of its distinctive coastal geomorphology. For example, the north–south linearity of offshore islands in the Perth region reflects past beachfronts.

Sea-level change has been a key factor in the formation of the topography and local geomorphology of the Swan Coastal Plain. The dynamic interplay of increasing and subsiding sea levels over thousands of years has provided the Perth coast with diverse geomorphological features.

The most prominent part of the coastal system are the Quindalup Dunes, which give the coastline the distinctive mounded coastal dune vegetation comprising low heath and swale thickets interspersed with patches of white sand.

Quindalup Dune geomorphology is characterised by an extensive series of linear, north–south dunes up to several kilometres wide, accreted from successive depositions of marine shoreline deposits resulting from sea-level changes often over