SOIL SEED BANK DYNAMICS IN TRANSFERRED TOPSOIL
EVALUATING RESTORATION POTENTIALS
William M. Fowler
Bachelor of Science in Environmental Science and Environmental Restoration
School of Environmental Science
October 2012
Acknowledgements
Thanks to my supervisors Dr. Joe Fontaine and Prof. Neal Enright for all the advice and support given over the last year. I would also like to thank the members of the Murdoch University, Terrestrial Ecology Research Group (TERG) for their valuable assistance and guidance, especially Willa Veber and Dr. Philip Ladd, as well as the Murdoch University Environmental Science Association (MUEnSA) for helping find enthusiastic volunteer field assistants. I wish to thank the Department of Environment and Conservation (DEC) for providing technical and financial assistance in addition to information and resources that were vital to this projects success. Finally I would like to thank the Environmental Weeds Action Network (EWAN) for awarding me a scholarship to help me complete this valuable research.
DECLARATION
I declare that this thesis is my own original work and has not been submitted for any other unit for academic credit.
William Michael Fowler
Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
ABSTRACT
Global change, increasing human population growth and urbanisation represent increasing pressures on biodiversity and ecosystem function. It is now widely recognised that conservation of existing natural fragments will not be sufficient to maintain extant biodiversity or meet conservation goals. Thus there is a major and rapidly expanding need for the practice of ecological restoration whereby degraded lands are managed to increase and maintain indigenous species.
A soil seed bank germination experiment was conducted over a period of 13 weeks. This aimed to evaluate restoration values of topsoil transfer, by investigating soil seed bank similarity to standing vegetation, and exploring mechanisms to improve restoration outcomes on the Swan Coastal Plain, Western Australia. This was experimentally designed to make comparisons between the soil seed bank pre and post- transfer, an aspect of topsoil transfer that has not been looked at previously. In addition sampling was conducted at two depths, with treated (smoke and heat) and non-treated trials. This study examined the similarity of the soil seed bank to standing vegetation, the effect of soil transfer, and the influence of soil spreading depth and fire related germination cues.
Seventy-three per cent of germinants were found in the top 5 cm of natural (pre- transfer), soil transfer leading to mixing (no depth effect) and a reduction in germinant densities (-2472.00 germinants m-2). Treatment with germination cues (heat and smoke in concert) increased germinant densities by 1537.80 germinants m-2, however no increase in transferred soils was observed. Native annuals dominated species composition of transferred soils, contributing 68% of observed richness, with woody species only accounting for 9% overall. The similarity of the soil seed bank to the standing vegetation ranged from 15% to 19%, the higher similarity found when treatment was used. Overall topsoil transfer is a useful tool for restoration; however it must be used in conjunction with other methods, such as planting and direct seeding, to return a representative set of species to a site.
iii Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
TABLE OF CONTENTS
DECLARATION ...... II
ABSTRACT ...... III
TABLE OF CONTENTS ...... IV
LIST OF FIGURES ...... VI
LIST OF TABLES ...... VII
CHAPTER 1 – INTRODUCTION ...... 1
1.1 RESEARCH AIMS ...... 5
1.2 THESIS OUTLINE ...... 6
CHAPTER 2 – STUDY AREA AND METHODS ...... 7
2.1 STUDY SETTING ...... 7
2.2 FIELD SAMPLING AND DATA COLLECTION ...... 9
CHAPTER 3 – RESULTS ...... 18
3.1 SEED BANK DYNAMICS ...... 18
3.2 SIMILARITY ...... 27
3.3 COMMUNITY ANALYSIS ...... 27
CHAPTER 4 - DISCUSSION ...... 31
4.1 INFLUENCE OF DEPTH OF TOPSOIL ON RESTORATION OUTCOMES ...... 31
4.2 THE EFFECT OF TOPSOIL TRANSFER ON GERMINANT COMPOSITION ...... 34
4.3 GERMINATION SIMULATION WITH COMMON GERMINATION CUES ...... 34
4.4 SOIL SEED BANK AND ITS RELATIONSHIP TO THE STANDING VEGETATION ...... 35
CHAPTER 5 – CONCLUSIONS AND RECOMMENDATIONS ...... 38
iv Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
5.1 CONCLUSIONS ...... 38
5.2 RECOMMENDATIONS FOR MANAGEMENT OF TOPSOIL TRANSFER ON THE SWAN COASTAL PLAIN ...... 38
5.3 RECOMMENDATIONS FOR FUTURE RESEARCH ...... 39
REFERENCES ...... 40
APPENDICES ...... 50
APPENDIX A – STATISTICAL SUMMARIES OF ALL NORMAL PARAMETRIC ANALYSIS ...... 50
APPENDIX B – SPECIES LISTS ...... 51
v Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
LIST OF FIGURES
Figure 1 – Diagramatic representation of the change in seed gradient as a result of mixing due to the transfer process...... 5 Figure 2 – Site locations relative to Perth, Western Australia. The cross indicating the location of Jandakot Airport from which soil was striped. Triangles indicating the recipient sites of Forrestdale Lake and Anketell RD. Adapted from the Nokia map service (Nokia 2012)...... 8 Figure 3 - Position of transects and plots at Jandakot Airport. The area which soil was stripped from is enclosed by the solid black lines. Plots are represented by the dots; with series of dots forming transects which are labelled accordingly...... 10 Figure 4 - Main: Image of the loader used to harvest topsoil from Jandakot Airport by Urban Resources. Insert: side view of the wing-like bucket modifications used to prevent over harvesting of topsoil...... 11 Figure 5 – Site and plot locations at Forrestdale Lake. Dots representing plots, clustered in the deep areas of transferred soil at the three smaller sites within the greater area of Forrestdale Lake (Nature Reserve)...... 11 Figure 6 – Site and plot locations and Anketell Road. Dots representing plots, clustered in the deep areas of transferred soil at the three smaller sites within the greater Anketell Rd site...... 12 Figure 7 - Diagram of the soil sampling tube (not to scale) used for sampling topsoil in this study. . 12 Figure 8 – Sampling arangement within each plot (not to scale), the circles representing the locations of soil samples which were composited...... 12 Figure 9 – Diagram of seeding marking procedure, bands indicating colour code progression as identification became more developed...... 15 Figure 10 – Proportion of total germinants the study over time (weeks)...... 18 Figure 11 – Mean germinants m-2 by treatment across depth and site...... 19 Figure 12 – Mean species richness by treatment across depth and site...... 20 Figure 13 – Diversity using the Shannon-Wiener index, by treatment across depth and site...... 21 Figure 14 – Mean germinants m-2 by treatment, across depth and site, comparing growth forms. .. 22 Figure 15 – Mean germinants m-2 of invasive species and native species split into longevity categories, across treatment and depth (unknown species removed)...... 23 Figure 16 – Density of native perennial species and their proportion of woody and non-woody. .... 25 Figure 17 – Density of germinants m-2 of seeders and resprouters across treatments, depths and sites...... 26 Figure 18 – Mean density germinants m-2 of categories of Proteoid roots (0=0, 1=0-25%, 2=25-50%, 3=50-75%, 4=75-100%)...... 26 Figure 19 – Ordination of all trays using NMS. Axis 1 correlated with site, from transfer to natural. Axis 2 correlated with depth, 5-10cm to 0-5cm...... 28 Figure 20 – Panel of three joint plot analyses, with correlations. A – Growth form and invasive status, B – Richness and diversity, C – species. Only those vectors with r2 values > 0.20 are displayed...... 29 Figure 21 – Graphical representation of the potential influence of compaction in the soil stripping process. Effect of over harvesting is for illustrative purposes only...... 32 Figure 22 – Photo of proteoid roots on site at Jandakot Airport...... 33
vi Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
LIST OF TABLES
Table 1 – Criteria used by DEC and their relative importance in recipient site selection. Adapted from Brundrett (2012)...... 9 Table 2 – Ranking system for the allocation of cover rankings consistent with Braun-Blanquet (1932)...... 10 Table 3 - Top 5 species by abundance for each treatment on natural and transferred soils. Blanks indicate that the species was not in the top 5 most abundant for that treatment...... 24 Table 4 – Average number of species found in the soil seed bank (SSB) and above ground vegetation (AGV), and the average similarity between the SSB and AGV, using Sorenson’s similarity index...... 27
vii Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
CHAPTER 1 – INTRODUCTION
Ecological restoration is of vital importance in a world of rapid human population growth and development, and consequent degradation of the natural environment. Simply conserving the remaining natural areas is no longer sufficient to meet current goals (Grimm et al. 2008; McCarthy et al. 2012). Ecological restoration can be defined broadly as the process of assisting the recovery of an ecosystem that has been degraded, damaged or destroyed (SER 2004). As biodiversity conservation becomes ever more important on a global scale, restoration is being used increasingly as a tool to offset the ecological impacts of development (CBD 2010; Hobbs et al. 2011; McCarthy et al. 2012). Offsets in restoration may occur through physically restoring an area to its pre-disturbance state, or by securing and restoring new areas for conservation (Gardner and Bell 2007; Hobbs et al. 2011). Restoration has the potential to be misguided, under the expectation that ecosystems can be completely restored, which may not always be a realistic goal (Gardner and Bell 2007; Hobbs 2007; Hobbs et al. 2011). Ecological restoration is a relatively new science, and thus requires more research in order to understand its complexities, and to create better outcomes for biodiversity conservation in the future.
Increasing pressure on natural areas drives the need for ecological restoration. Expansion of the built environment is having detrimental effects on natural areas, through bushland clearing and fragmentation, altering of chemical and physical dynamics and loss of biodiversity (Folke et al. 2004). It is these natural areas which are vital for species as either habitat, feeding grounds, for ecological linkages and to provide ecosystem services (Loreau et al. 2001; Grimm et al. 2008; Palmer and Filoso 2009). Restoring biodiversity can also create greater resilience to future disturbance as well as enhance ecosystem function (Loreau et al. 2001; Folke et al. 2004). In addition to ecological benefits, restoration can return many other values to the landscape, including personal, socioeconomic and cultural values (Clewell and Aronson 2007).
A broad range of techniques are used to restore areas of degraded vegetation, most often involving two distinct methods, the planting of nursery-raised seedlings and direct seeding using seed mixes of desired native species. Topsoil transfer, the process of moving topsoil containing dormant but viable soil stored seeds of native plants – potentially in high quantities – is a relatively recent method employed to enhance restoration success, and is playing an increasing role in the restoration of ecosystems
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Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
(Tacey, Olsen, and Watson 1977; Engel and Parrotta 2001; Skrindo and Pedersen 2004; Ralph 2006; Tozer et al. 2012). Direct planting is characterised by relatively high survivorship but can be expensive and is limited to those species available from commercial nurseries (Engel and Parrotta 2001; Viani and Rodrigues 2009). Direct seeding can be done mechanically on a large scale or by hand, but is generally considered to have a high mortality compared to planting, and is most feasible in areas receiving over 250 mm rainfall per year (Ackzell 1993; Knight, Beale, and Dalton 1998; Engel and Parrotta 2001). It is also expensive, since seeds must be collected for each species, which may vary in their timing and abundance of seeding, and in their germination requirements, so that their ability to be restored via these methods is limited (Ralph 2006; Sweedman and Brand 2006; Koch 2007b). Topsoil transfer has several benefits over these methods, in particular over direct seeding (Fry 2011). The soil itself can suppress the potential weedy underlying soil which could limit the success of planting and seeding. Moving topsoil can also transfer beneficial soil microbes and other propagules of species not able to be restored readily by other methods (Jasper 2007; Koch 2007b). The use of soil seed banks through topsoil transfer is increasingly common in restoration because of its benefits over other methods (Howard and Samuel 1979; Koch 2007b; Tozer et al. 2012).
Most of the world’s plant communities produce some form of soil seed bank, and it is these seed banks that are an important part of a functioning ecosystem (Harper 1977; Bell 1999). Mature seed is shed from the parent plant to the soil surface, and accumulation of these seeds over time develops a soil seed bank comprising seeds which may be able to remain dormant for many years (Bell, Plummer, and Taylor 1993; Baskin and Baskin 1998; Fenner and Thompson 2005; Keith 2012).
There are two broad categories of soil stored seed, transient seed banks, those that persist for less than a year, and persistent seed banks, which persist for longer periods of time (Fenner and Thompson 2005). This is an important distinction because transient seed banks tend to be those that germinate immediately or seasonally, while those that persist for longer periods are dormant until they receive an appropriate trigger (Merritt and Rokich 2006). Triggers are related to disturbance or opportunity, whereby either light is received to the understory or a more widespread disturbance such as fire enables plant propagules stored in the soil to take advantage of a lack in competition. However, not all species contribute equally to the soil seed bank. For example, serotiny (canopy stored seed) is used by some species, and is commonly seen in the Mediterranean regions of Western Australia and South Africa (Lamont et al.
2 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
1991). Resprouting (tending not to produce high amounts of seed) is also a trait exhibited in species which results in little contribution to the soil seed bank (Lamont et al. 1991). Soil seed banks as a result are highly variable in composition and seed density both locally and globally depending on the ecosystem type, species present and time since disturbance (Hopfensperger 2007).
Depth, heat and smoke cues are important factors in enabling germination from soil seed banks in fire-prone environments. Seed density in soil declines with depth, with most seeds close to the soil surface, those buried at depths greater than a few centimetres generally failing to germinate (Bellairs and Bell 1993; Brown, Enright, and Miller 2003; Fenner and Thompson 2005; Luzuriaga et al. 2005; Merritt and Rokich 2006; Fisher et al. 2009). Many seeds in the soil seed bank lie dormant until a germination cue such as smoke and/or heat occurs. Without such a cue to stimulate germination, many seeds will not germinate easily (Bell, Plummer, and Taylor 1993; Bell 1999). In fire-prone environments, the chemicals in smoke have been found to be a key component in triggering germination (Keeley and Keeley 1987; De lange and Boucher 1990; Dixon, Roche, and Pate 1995; Roche, Koch, and Dixon 1997; Smith, Bell, and Loneragan 1999; Rokich and Dixon 2007; Tozer et al. 2012). Heat is also a common trigger in many hard-seeded species, due to scarification, or damage of the seed coat that results from heat exposure (Bell, Plummer, and Taylor 1993; Baskin and Baskin 1998; Enright and Kintrup 2001; Merritt and Rokich 2006). The combination of heat and smoke together is increasingly seen as the most effective means to illicit germination across a range of species in such environments (Keith 1997; Blank and Young 1998; Smith, Bell, and Loneragan 1999; Thomas, Morris, and Auld 2003; Merritt and Rokich 2006; Lindon and Menges 2008).
Seed density is one of the defining characteristics of soil seed banks. Variations in density can be found between regions and ecosystem types, and are also influenced by the ecology of the system, including plant functional traits. Much of the global research into soil seed banks has been undertaken in temperate Mediterranean environments. For example: the soil seed banks of the Fynbos shrublands of South Africa range from 1100-1900 seeds m-2 (Holmes and Cowling 1997). Densities of 1050- 1802 seeds m-2 are reported from a heathland environment in Spain (Valbuena and Trabaud 2001). The northern Jarrah forest of South-West Australia has been seen to have seed densities of between 377-1579 seeds m-2 (Vlahos and Bell 1986). Tropical Rainforests in comparison have generally lower densities 88-694 seeds m-2 (Martins and Engel 2007; Dainou et al. 2011). Soil seed stores in Mediterranean environments thus
3 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials tend to contain higher amounts of seed that can be utilised for restoration by methods such as topsoil transfer. However, even within Mediterranean environments plant functional traits can influence seed density. For instance a vegetation community near Eneabba, Western Australia, is dominated by serotinous and resprouter species, as such much lower soil seed densities of 140-174 seeds m-2 (Bellairs and Bell 1993) have been observed.
Banksia woodland of South Western Australia is a high biodiversity ecosystem and represents an ecosystem of serious conservation concern (Myers et al. 2000; Rokich and Dixon 2007). This research project focuses on topsoil transfer as a method for restoration of Banksia woodland on the Swan Coastal Plain (SCP) of Western Australia. The Banksia woodlands sit within a biodiversity hotspot, characterised by high richness and endemism, with 79.2% of the vascular plant species and 21.9% of animal species endemic to the region (Myers et al. 2000; Paczkowska and Chapman 2000). Within this hotspot, Perth is a rapidly expanding city resulting in the fragmentation and degradation of the natural landscape (Ramalho and Hobbs 2012). Continued land clearing, fragmentation, and degradation results in increased pressure on species requiring natural vegetation for feeding and roosting habitat, such as Carnaby’s Cockatoo (Calyptorhynchus latirostris) which is listed as ‘Endangered’ under the Environmental Protection and Biodiversity Conservation Act 1999 (Cwlth) (Valentine et al. 2011). As a whole, the South West of WA now only retains 10.8% of its original extant of vegetation. Within this, the Banksia woodland ecological community is listed as endangered, making restoration important in this setting to help conserve this community type (Myers et al. 2000; SEWPC 2009).
As the process of topsoil transfer is likely to be used increasingly as an offset to clearing established vegetation communities for urban development or mining, it is important for research of this kind to be conducted. Little published, peer-reviewed research exists on the optimisation of topsoil transfer for restoration purposes throughout the world. What little research has been carried out has predominantly been undertaken in Western Australia (Vlahos and Bell 1986; Koch et al. 1996; Ward, Koch, and Ainsworth 1996; Koch, Ruschmann, and Morald 2009). Alcoa World Alumina (Alcoa) are the primary drivers of this research for mine site rehabilitation on the lateritic soils of the Darling Plateau, east of Perth (Koch 2007a). This study on the SCP is therefore innovative in that it tests the impacts of the transfer process on soil seed bank properties relating to Banksia woodlands, and the value this process may hold for restoration and management in the future. Potential applications of this study include
4 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials the optimisation of procedures and practices of restoration using topsoil transfer, while also adding to our knowledge of the world’s soil seed banks in different environments. It is vitally important for the preservation of Western Australia’s unique but threatened native vegetation that this process is examined in detail, as many of our native plant species are not currently able to be propagated by any other means (Rokich et al. 2000).
1.1 RESEARCH AIMS
This thesis examines the soil seed bank composition of undisturbed topsoil from a natural bushland and compares it with the same soil after it has been removed, transported, and spread at another site in the topsoil transfer process. The aim is to establish in general terms how successful topsoil transfer is and how it could be more successful through examining the following specific questions:
1. HOW DOES DEPTH OF TOPSOIL APPLICATION INFLUENCE RESTORATION OUTCOMES?
This research question examines the seed density by depth in the soil seed bank both pre and post-transfer. Transfer involves stripping a depth of soil greater than where the bulk of seeds are situated, therefore this may cause dilution of the seed density of the soil that has been transferred (Figure 1). This may affect the germination within the transfer sites when compared to the undisturbed bushland since many seeds previously near the soil surface will now be buried too deep for germinants to grow through the soil surface. This is important to potentially maximise restoration outcomes, and because the amount of soil transferred affects the cost of transportation. Alcoa for instance has used sieving of seed from soil to concentrate seed density and so reduce the transportation component, however this does also remove small seeded species (Rokich and Dixon 2007).
Figure 1 – Diagramatic representation of the change in seed gradient as a result of mixing due to the transfer process.
5 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
2. WHAT EFFECT DOES THE TRANSFER PROCESS HAVE ON GERMINANT COMPOSITION?
The effects of the soil transfer process need to be examined more closely. In this study trials are conducted both pre-transfer and post-transfer; this is an aspect that has not been researched elsewhere. The rationale of this part of the study is that the physical act of transferring the soil may have an influence on the germination ability of the soil in either a positive or negative way. The process of topsoil transfer may lead to the physical scarification of seeds within the seed bank, which could mitigate the need for other germination treatments. Scarification, a physical germination trigger, combined with smoke and heat treatment should provide enhanced germination of hard seeded species, as a result the above procedure will be duplicated at the transfer site to examine the effects of transfer (Baskin and Baskin 1998; Merritt and Rokich 2006).
3. DOES TREATMENT WITH FIRE RELATED CUES ENHANCE GERMINATION SUCCESS?
Treatments with heat and smoke in combination have been conducted to replicate fire disturbance, considered a vital trigger for seed germination in many species, especially in SW Australia (Wills and Read 2002). Smoke and heat treatments together maximise the dormancy breaking effect and subsequent germination response. A control treatment using watering only was conducted for comparison purposes (Pierce, Esler, and Cowling 1995; Read et al. 2000; Merritt and Rokich 2006).
4. HOW REPRESENTATIVE IS THE SOIL SEED BANK TO STANDING VEGETATION?
Certain species of the Banksia woodland community will not be present in the soil seed bank due to being resprouters or serotinous in nature; this includes the dominant canopy genus, the Banksias (Wills and Read 2007). Previously it has been found that 60- 80% of the species of the Banksia woodland can store their seed in the soil (Rokich and Dixon 2007). It is important to examine the species composition of the species that are present in the soil seed bank, and how these relate to the standing vegetation of high quality bushland sites, as this is the reference for restoration.
1.2 THESIS OUTLINE
This thesis is organised into 5 chapters. Chapter 2 provides details of the study area and the methods used to answer the stated research questions. Chapter 3 presents the results. An in depth discussion of these results is provided in Chapter 4, and conclusions and recommendations for future topsoil transfer projects are presented in Chapter 5.
6 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
CHAPTER 2 – STUDY AREA AND METHODS
2.1 STUDY SETTING
The climate of SW Australia is Mediterranean with hot, dry summers and mild, wet winters (BOM 2012). Annual mean rainfall is 869 mm, 80% of this falling between May and September, with the summer (December through February) average being 36 mm. Temperatures in summer average 31°C maximum and 17°C minimum, while over winter, maximum and minimum temperatures average 18°C and 8°C respectively (BOM 2012). A sustained decrease in annual rainfall has been documented since the mid- 1960s with a 23 mm drop per decade (based on 1950-2005 records) (Timbal, Arblaster, and Power 2006; Gallant, Hennessy, and Risbey 2007). Since the 1970s mean annual temperature has increased by an average of 0.15°C per decade (Bates et al. 2008). Climate predictions include continued drying of 15-160 mm and warming of 0.4-2.0°C by 2030, relative to 1990 (Hughes 2003).
Study sites, Jandakot Airport (from which the topsoil was taken), Forrestdale Lake and Anketell Rd (where topsoil from Jandakot Airport was received), were located approximately 20 km south of Perth, Western Australia on the SCP (Figure 2). The SCP is characterised by sandy soils of varying ages with north-south strips of similarly aged soils, increasingly old and leached at increasing distances from the Indian Ocean (Powell 2009). Soils at the study sites are classified as Bassendean sands; Aeolian in origin and pale grey to faint yellow in colour. These are the oldest soils on the SCP, originating in the middle Pleistocene, around 800,000 years ago (McArthur 1991; Bolland 1998). Due to their age, minerals and nutrients have been largely been leached, making these soils quite infertile (Powell 2009).
The extant vegetation of the Jandakot Airport site was remnant Banksia woodland, a unique vegetation community to the SCP. This vegetation type is dominated by a tree layer comprising of Banksia attenuata, B. menziesii, B. ilicifolia, Eucalyptus marginata, E. todtiana and Nuytsia floribunda, with a dense understory of shrubs, herbs, sedges and rushes (JAH 2009). As with many of Perth’s remnant bushland areas, the site at Jandakot airport has been isolated by urbanisation, and as such there has been little influence of fire in the recent past and there is evidence of weed invasion, especially concentrated at the edges (Fowler pers. obs.).
7 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Perth
Jandakot Airport
Forrestdale Lake
Anketell Rd
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Figure 2 – Site locations relative to Perth, Western Australia. The cross indicating the location of Jandakot Airport from which soil was striped. Triangles indicating the recipient sites of Forrestdale Lake (Nature Reserve) and Anketell Rd. Adapted from the Nokia map service (Nokia 2012).
Transfer sites, Forrestdale Lake and Anketell Rd, were selected by the Department of Environment and Conservation (DEC) based on a variety of priorities related to restoration and offset objectives (Table 1). These sites are now contained within nature reserves; however they have had a rich history of disturbance since European settlement. The study sites at these locations are areas of former agricultural activity and have been cleared for several decades. Whilst the land in these areas in recent times was predominantly used for grazing of sheep and other livestock, in the earlier years of European settlement vegetable crops were the main activity, especially within the area around Forrestdale Lake, and these areas were held in private ownership until being assimilated into the reserve (DEC 2005). Historically, cleared areas at both sites have become highly degraded and are now dominated by weeds (CCWA et al. 2010). Adjacent areas at both Anketell and Forrestdale have had recent restoration projects, both by topsoil transfer and other means, with mixed success (Brundrett, pers. com.).
8 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Table 1 – Criteria used by DEC and their relative importance in recipient site selection. Adapted from Brundrett (2012).
Criteria Importance Carnaby’s Cockatoo feeding habitat high Bush Forever Site high Within 45 km of Jandakot Airport on Swan Coastal Plain high Site with secure tenure high Carnaby’s cockatoo breeding site proximity high Carnaby’s cockatoo night roost proximity high Site containing Caladenia huegelii high Banksia woodland similar to Jandakot Airport (i.e. Bassendean sands) Very high Proximity to Jandakot Airport Very high Total area of remnant vegetation high Declared rare or priority flora: WA State listings medium Threatened ecological Community or Priority Ecological Community: WA State medium listings Rare or priority fauna: WA State listings medium
2.2 FIELD SAMPLING AND DATA COLLECTION
Field work was conducted in two phases, first the sampling of soils prior to transfer and second, the sampling of soils at the two recipient sites following transfer of topsoil. Sampling prior to transfer occurred during the period 24-29 February 2012 and post-transfer at Anketell Rd and Forrestdale Lake on 23 May 2012. Following field collection, soil samples were stored in dry paper bags until 1st June when glasshouse work was initiated. Assessment of the soil seed bank was conducted through mass germination. This method was chosen due to its practicality over sieve removal of seeds from soil (which can miss small seeds), and that it excludes seeds that are not viable (Gross 1990; Baskin and Baskin 1998).
Sampling at Jandakot Airport consisted of four 200 m transects situated throughout the area designated for clearing and topsoil transfer. Transects were made up of six 10x10 m plots spaced at ~10 m increments for a total of 24 plots. Extant vegetation was sampled at all 24 plots, half by DEC in December 2011 and the remaining half as part of this study. Vegetation data collected by DEC was percentage cover per species in 10% increments, whereas the subsequent vegetation data collected used the Braun-Blanquet (1932) cover abundance method, with ranks assigned as shown in Table 2. The two data sets were rationalised to be comparable for assessment of extant vegetation and the soil seed bank.
9 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Table 2 – Ranking system for the allocation of cover rankings consistent with Braun-Blanquet (1932).
Ranking Percentage cover 0.1 <1% 1 1-5% 2 5-25% 3 25-50% 4 50-75% 5 75-100%
Vegetation clearing and soil transfer at Jandakot Airport commenced in late February and transfer was completed by mid-May. Although a large area of Banksia woodland was cleared, a smaller proportion, approximately 17 ha, had topsoil removed and transferred (Figure 3) (Brundrett 2012; DEC 2012). Soil stripping from Jandakot Airport was specified as 70 mm (limits: 50 mm to 100 mm). A converted loader was used for this process, with wing-like bucket attachments (Figure 4) to prevent harvesting of soil at greater depths. Topsoil was then transferred to recipient sites, Anketell Rd (10-12 ha) and Forrestdale Lake (5-6 ha). Where applicable, existing weedy soil present at recipient sites was removed using a grader, to a depth of 30 mm (limits: 20 mm to 50 mm). Transferred topsoil was then spread over the top at two depths, 50 mm (limits: 40 mm to 60 mm) and 100 mm (limits: 80 mm to 120 mm) (DEC 2012). Two spreading depths were used to enable further research to be conducted on this project.
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Figure 3 - Position of transects and plots at Jandakot Airport. The area which soil was stripped from is enclosed by the solid black lines. Plots are represented by the dots; with series of dots forming transects which are labelled accordingly.
10 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Wing-like modifications
Figure 4 - Main: Image of the loader used to harvest topsoil from Jandakot Airport by Urban Resources. Insert: Side view of the wing-like bucket modifications used to prevent over harvesting of topsoil.
Transfer of soil from Jandakot Airport was received at Lake Forestdale (Figure 5) and at Anketell Rd (Figure 6). An equal number of plots were set up (n=24) to match the Jandakot site. These were allocated proportionally amongst the recipient sites based on the extent of the area, with seven plots at Anketell East, four at Anketell West, five at Forrestdale SW, five at Forrestdale NW and three at Forrestdale SE. These were randomly positioned within the deep areas of transferred topsoil (~10 cm deep), to
ensure depth of sampling did not penetrate into the underlying, former soil surface.
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Figure 5 – Site and plot locations at Forrestdale Lake. Dots representing plots, clustered in the deep areas of transferred soil at the three smaller sites within the greater area of Forrestdale Lake (Nature Reserve).
11 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
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Figure 6 – Site and plot locations and Anketell Road. Dots representing plots, clustered in the deep areas of transferred soil at the three smaller sites within the greater Anketell Rd site.
Soil samples were required to give inference to the area as a whole. Soil sampling tubes made from PVC pipe, 15.5 cm in diameter, 10 cm length were used (Figure 7). Five subsamples per 10x10 m plot were taken and composited (Figure 8) for each of two depths: 0-5 cm and 5-10 cm. This method was chosen as it provides a consistent volume sample from which further calculations of density can be made and is similar to the methods employed in other studies of soil seed banks (Bekker et al. 1997; Fisher et al. 2009).
Figure 7 - Diagram of the soil sampling tube (not to Figure 8 – Sampling arangement within each plot scale) used for sampling topsoil in this study. (not to scale), the circles representing the locations of soil samples which were composited.
12 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
2.2.1 GLASSHOUSE PREPARATION
Following final field sampling, soil samples were prepared in trays and placed in the glasshouse for germination trials to assess seed bank composition. Trials were initiated on 31 May – 01 June, 2012. To maximise germination rates, soil samples were treated with heat and smoke together, as treatments are known to enhance germination (Dixon, Roche, and Pate 1995; Keith 1997; Roche, Koch, and Dixon 1997; Keeley and Fotheringham 1998; Tieu et al. 2001), and another set of soil samples prepared as controls. The initial step was to prepare germination trays (35.5 cm x 29.5 cm x 5 cm); 192 trays were required for 96 soil samples (48 from pre-transfer site and 48 from post- transfer sites). Germination trays were cleaned to remove any soil, seeds and pathogens possibly present from past use. Trays were lined with Chux® cloth and filled with 1500 ml of vermiculite mixed with 500 ml of clean white sand, and the topsoil placed on top of the sand-vermiculite mix.
Samples varied widely in their bulk densities due to the presence of high levels of organic matter in some (especially proteoid roots). To make samples consistent, topsoil samples were poured into a bucket and mixed. The weight of the total sample was then taken before a quantity of this sample was put into two aluminium trays (29 cm x 19 cm x 5 cm) and weighed to be ~2100 g, with the aim to keep the quantity of soil treated constant. This was not always possible due to some samples containing a high proportion of proteoid roots, as these made large volume/low weight samples. All trays were numbered and labelled as completed, as well assigned a score between 0 and 4 for the amount of proteoid roots present in the tray, 0 being not present, 4 being 75-100%. By recording mass used and total sample mass, a correction factor could be applied to data later. Once trays were filled, half were treated with heat and smoke. Heat treatment consisted of boiling water poured to fill the tray and left to cool, before being spread evenly in a germination tray. Control trays were treated with an equal amount of cool water.
Once all trays were prepared and located in the glasshouse, smoke treatment was applied to samples that had previously been heat treated. This was done with aqueous smoke solution REGEN 2000 SMOKEMASTER, a commercially available product that has been found to replicate the effects of natural smoke associated with bushfires (Thomas and Davies 2002; Wills and Read 2002). The solution was diluted 10 to 1 as recommended by the suppliers, and 400 ml lots of the diluted solution were applied by watering can to each germination tray that required treatment.
13 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
To ensure possible contamination events of plant propagules entering the glasshouse were identified, five clean seed-free sand trays were prepared in the same manner as the other germination trays, but contained sterile sand instead of topsoil. This was designed to indicate if experimental contamination had occurred from seed entering the glasshouse through the air conditioning system or other means.
The glasshouse was air-conditioned to prevent excessive temperatures from occurring, with settings designed not to exceed 24°C (range: 7-24°C). Watering was maintained by automatic table reticulation, using misters set to run for 10 mins every second day. Nevertheless, watering rates were found to be variable depending on table position (range: 15-91 ml). Trays were monitored to evaluate if extra watering was necessary, and every four weeks trays were re-randomised within the glasshouse to mitigate any possible effects on germination among trays.
2.2.2 GERMINATION TRACKING
To quantify germination timing and identify species, emergence was checked weekly and germinants marked with a series of colour-coded toothpicks. Each germinant was marked with a toothpick consisting of a colour code (up to 4 bands of colour) to identify germinants of the same species. Over time this identification was changed as necessary, since germinants that appeared to be the same in early stages of growth sometimes developed into several distinct species (Figure 9). Due to the very high density of emerging seedlings, from time to time advanced individuals needed to be pulled out to prevent too much competition for space in the trays; numbers and identifications of plants pulled were recorded. Representative plants for each identification code were potted up and grown on for identification purposes.
14 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Figure 9 – Diagram of seeding marking procedure, bands indicating colour code progression as identification became more developed.
2.2.3 DATA ANALYSIS
Normal parametric statistics were used to analyse overall patterns of density, richness, and diversity, native and invasive species, growth habit and certain functional traits. Data were analysed using multi-way ANOVA for density, richness and diversity on a per tray basis to assess the potential effect of depth and treatment, plant functional traits and other grouping factors, among and between sites. Linear regression was also conducted to gain a measure of estimate, as well as to determine R-squared values. The statistical analysis program R’ 2.14.2, published by The R Foundation for Statistical Computing was used for these analysis (R 2012).
Density, richness and diversity are used in this study to investigate how topsoil transfer influences the soil seed bank, and for overall comparisons between the various treatments. Density was calculated (Equation 1) to provide a comparable measure of germination across trays, while species richness, the average number of species in a given sample, quantified biodiversity, and was important for ecological comparisons (Gotelli and Colwell 2001). The Shannon-Wiener index of diversity (SWI) was used as the measure of diversity (Equation 2). This index incorporates both richness and evenness of the population (Sax 2002). All data was assessed on the groupings of site (natural/transfer), depth (0-5 cm, 5-10 cm) and treatment (control, treated). All means were graphed with 95% confidence intervals, to aid the interpretation of figures (Cumming 2005, 2009). Unknown species were removed from graphical displays as they represented less than 2% of the data on all occasions, most being less than 1%.
15 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Sorensen’s similarity index (Equation 3) was used to determine the percentage of species in common between the soil seed bank and the standing vegetation (Sorensen 1948). Some species had to be removed from this analysis due to being unidentified, to prevent skewed results. Analysis was conducted with annual and serotinous species, and with these species removed, for each treatment.
Equation 1 – density
( )
Equation 2 – Shannon-wiener index of diversity
∑
Equation 3 – Sorensen’s index of similarity
Multivariate community analysis methods were used to explore compositional changes in the data. Ordination analysis of community composition was done using PC- ORD version 6.08 (McCune and Mefford 2011). Nonmetric Multidimensional Scaling (NMS) was used based on the Sorensen distance measure, which performs well in demonstrating ecological gradients with complex data sets (Culman et al. 2008; Peck 2010). Stress values should ideally be under 20 for this type of ordination, however values from 20 to 35 can still yield useful interpretations, as stress tends to increase with sample size (McCune and Grace 2002).
Multi-response permutation procedures (MRPP) were used to assess the evidence for differences between groups at the community level, evaluating differences between two or more groups based on within-group similarities (McCune and Grace 2002; Peck 2010). MMRP has the advantages over other multivariate analysis techniques in that it does not require distribution assumptions, which are rarely met in ecological situations (Biondini, Bonham, and Redente 1985; Zimmerman, Goetz, and Mielke 1985; McCune and Grace 2002). The Euclidean (Pythagorean) distance measure was used for the MRPP due to its better representation of outliers in such an analysis (McCune and Grace 2002). Rare species were removed from the ordination dataset if only present once, resulting in 25 species being removed. Outlier analysis was then
16 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials conducted; tray 96 was removed from the dataset on this basis. A random starting configuration was used, and a thorough NMS was conducted with 250 runs. NMS ordination was also run with native perennials only, however a useful ordination was not found using PC-ORD.
17 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
CHAPTER 3 – RESULTS
The results from this study from sampling conducted prior to topsoil removal and post-transfer, subsequently examined in the glasshouse are presented and statistically analysed in three main themes: seed bank dynamics, similarity, and community analysis.
3.1 SEED BANK DYNAMICS
Seed bank dynamics were examined during germination trials lasting 13 weeks. Emergence of seedlings peaking around week 8, with a total of 11,551 germinants recorded over the entire period, belonging to 127 species (Figure 10).
Figure 10 – Proportion of total germinants the study over time (weeks).
Mean density of germinants found in this study was 1935 germinants m-2 this ranged between 1692-4239 germinants m-2 in natural soils and 795-1016 germinants m- 2 in transferred soils. In total 79% of all germination occurred in the natural soils (0-5 cm: 73%, 5-10 cm: 27%). Transfer (post-transfer) soils on average contributed to 21% of overall germination (0-5 cm: 54%, 5-10 cm: 46%) (Figure 11).
18 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
There is a significant depth effect between 0-5 cm and 5-10 cm (F1, 185 = 47.3, p <0.001), with an average difference of 2347.9 ± 348.7 germinants m-2. However this depth effect is not the same between sites, indicated by the significant interaction between depth and site (F1, 185 = 33.4, p <0.001). The overlap of confidence intervals in transferred soil suggests that there is no depth effect in these soils. These transfer sites had significantly lower densities than the natural sites (F1, 185 = 104.7, p <0.001), with an average difference of 2472 ± 348.70 germinants m-2. Treatment had a significant influence (F1, 185 = 8.5, p =0.003), increasing germination by an average 1537.8 ± 348 germinants m-2, but again this was only apparent in the natural soils, with a significant interaction between site and treatment (F1, 185 =13.9, p <0.001), the transfer soils showing no significant influence of treatment.
Figure 11 – Mean germinants m-2 by treatment across depth and site.
A total of 127 species were recorded in the study, with species richness patterns found to be similar to those of density (Figure 12). A significant depth effect is present
(F1, 185 = 80.9, p <0.001), with on average 7.13 ± 0.90 more species being located in the 0- 5cm region. The depth response is different between the natural and transfer soils, as indicated by the significant interaction between depth and site (F1, 185 = 26.2, p <0.001).
A significant difference between sites is also apparent (F1, 185 = 80.9, p <0.001) between natural and transferred soils. Transferred soils contained an average of 7.04 ± 0.90 less
19 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
species than the natural soils. Treatment has a significant influence on richness (F1, 185 = 7.4, p =0.007). Treatment effect between sites is not the same, with a strong interaction influence (F1, 185 = 13.2, p <0.001), no significant response of treatment in the transfer soils.
Figure 12 – Mean species richness by treatment across depth and site.
The mean Shannon-Wiener diversity (SWI) was 2.01, with natural 0-5 cm being highest at 2.34. A somewhat different pattern to the density and richness plots can be observed (Figure 13). There is a significant depth effect among both sites (F1, 185 = 34.8, p
<0.001), and a significant difference between sites (F1, 185 = 28.8, p <0.001). There are no significant interactions of treatments.
20 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Figure 13 – Diversity using the Shannon-Wiener index, by treatment across depth and site.
Overall, grassy species (including grasses and grass-like species) contributed 812.58 germinants m-2 or 41.98%. Herbs accounted for 676.84 germinants m-2 or 34.97%, both the grassy and herbaceous species represented the majority of germinants found within the seed bank (76.95%) (Figure 14). The remainder was filled by the shrubs (166.53 germinants m-2, 8.60%), succulents (274.85 germinants m-2, 14.2%).
Grassy species were significantly influenced by depth (F1, 185 = 20.6, p <0.001), representing a reduction between 0-5 cm and 5-10 cm of an average of 699.57 ± 166.58.
A significant site effect is also supported (F1, 185 = 106.2, p <0.001) and although treatment is not significant for grassy species overall, there is a significant interaction here, suggesting a shift in the pattern generated by treatment between sites (F1, 185 = 14.9, p <0.001).
The density of herbaceous species follows a similar trend to that of the grassy species, having a depth effect (F1, 185 = 45.1, p <0.001), a site effect (F1, 185 = 73.0, p
<0.001), and significant treatment effect (F1, 185 = 3.9, p =0.05). Significant interactions are seen between depth and site (F1, 185 = 38.1, p <0.001), also between site and treatment (F1, 185 =4.4, p =0.04).
21 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
The density attributed to shrub species, significant depth (F1, 185 =7.2, p =0.008), site (F1, 185 =129.8, p <0.001), treatment (F1, 185 =20.3, p <0.001), interaction between depth and treatment (F1, 185 = 5.0, p = 0.03) and interaction between site and treatment
(F1, 185 =8.4, p =0.004).
Succulent species has significant depth effect (F1, 185 = 5.6, p = 0.02) this differing between sites (F1, 185 = 10.1, p = 0.002), significant site effect (F1, 185 = 5.2, p = 0.02), with an increased representation in the transferred soils.
Figure 14 – Mean germinants m-2 by treatment, across depth and site, comparing growth forms.
Across all treatments and depths, invasive species represent on average 8%, native annuals 68% and native perennials 17% (Figure 15).
Significant depth effect can be seen for invasive species is observed (F1, 185 = 26.8, p <0.001), with an estimated reduction of 421.64 ± 59.75 germinants m-2. There is a significant difference between sites (F1, 185 = 23.6, p <0.001), 412.70 ± 59.75. Treatment has a negative effect on invasive species (F1, 185 = 5.6, p = 0.02), a difference of 187.02 germinants m-2. A significant interaction is present between depth and site (F1, 185 = 30.9, p <0.001), indicating the depth effect was not the same among.
22 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Native annual species have a significant depth factor (F1, 185 = 33.9, p <0.001),
1592.80 ± 283.2 germinants m-2, significant site effect, (F1, 185 = 62.9, p <0.001), resulting in a difference of 1506.50 ± 283.20 germinants m-2, and significant effect of treatment
(F1, 185 = 6.4, p = 0.01) resulting in an increase of 1149.40 ± 283.20. Significant interactions can also be seen between depth and site (F1, 185 = 23.5, p <0.001), and between site and treatment (F1, 185 = 12.7, p <0.001).
Native perennial species, have a significant depth effect (F1, 185 = 14.5, p <0.001),
184.34 ± 59.98 germinants m-2. Significant site effect is also present (F1, 185 = 175.2, p
<0.001) a difference of 417.61 ±59.98 germinant m-2. Treatment effect is significant (F1,
185 = 14.6, p <0.001), resulting in an increase of 304.52 germinants m-2. Significant interactions of depth and site (F1, 185 = 7.0, p = 0.009) and site and treatment (F1, 185 =14.7, p <0.001).
Figure 15 – Mean germinants m-2 of invasive species and native species split into longevity categories, across treatment and depth (unknown species removed).
23 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
The top 5 species contributed 47% to 65% of the overall germination in each grouping (Table 3). All of the species represented in the high dominance categories are native species. Native annuals are most dominant in the soil seed bank, with Crassula colorata, Isolepis marginata and Centrolepis glabra occurring in the top 5 abundant species across all groupings. Crassula colorata became most dominant in the transferred soils.
Table 3 - Top 5 species by abundance for each treatment on natural and transferred soils. Blanks indicate that the species was not in the top 5 most abundant for that treatment.
Germinants (Percentage of grouping) Species Natural Natural Transfer Transfer (control) (treated) (control) (treated) Centrolepis alepyroides - - 57 (4%) - Centrolepis glabra 249 (7%) 566 (10%) 116 (9%) 67 (6%) Crassula colorata 244 (7%) 329 (6%) 466 (36%) 336 (31%) Gnephosis angianthoides - - 64 (5%) - Isolepis marginata 617 (17%) 1257 (23%) 145 (11%) 136 (13%) Isotoma hypocrateriformis - - - 40 (4%) Leucopogon conostephioides 262 (7%) - - - Poranthera microphylla - 346 (6%) - - Trachymene pilosa 341 (9%) - - - Unknown_24 - 345 (6%) - 55 (5%) Totals 1713 (47%) 2843 (51%) 848 (65%) 634 (59%)
24 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Native perennial (discussed previously), is made up of woody and non-woody species
(Figure 16). They differ in that woody species are effected by treatment (F1,185 = 20.1, p <0.001), increasing density by 201.09 ± 36.24 germinants m-2, where as this is not significant in non-woody species. Woody species also have a significant interaction of depth and treatment (F1,185 = 4.9, p = 0.03). Non-woody have a significant interaction of depth and site (F1,185 = 5.7, p = 0.02), where woody species do not.
Figure 16 – Density of native perennial species and their proportion of woody and non-woody.
Overall seeders contributed to 87% of the composition, a further 11% were resprouting species. Seeder and resprouter species, despite being different in abundance, both followed a similar trend to each other, both having significant depth
(F1, 185 = 44.6, p < 0.001; F1, 185 =9.5, p = 0.002), site (F1, 185 =87.2, p <0.001; F1, 185 =89.1, p
<0.001), and treatment (F1, 185 = 8.1, p 0.005; F1, 185 =7.0, p = 0.009) effect. Interactions are seen between depth and site (F1, 185 = 32.2, p <0.001; F1, 185 = 4.1, p = 0.04), as well as site and treatment (F1, 185 = 12.3, p <0.001; F1, 185 = 15.5, p <0.001), indicating the depth and treatment effects are not the same between sites.
25 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Figure 17 – Density of germinants m-2 of seeders and resprouters across treatments, depths and sites.
Overall the highest densities of germinants are associated with the mid-range of proteoid root score >0 to 75%, the highest category of root matter (75% to 100%) resulted in reduced germination.
Figure 18 – Mean density germinants m-2 of categories of Proteoid roots (0=0, 1=0-25%, 2=25-50%, 3=50-75%, 4=75-100%).
26 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
3.2 SIMILARITY
Similarity between the soil seed bank and the extant vegetation, without excluding species such as annuals and serotinous species, is 19% ± 2.8. With serotinous species excluded from the standing vegetation and annuals removed from the soil seed bank results from control (not treated soil seed bank), similarity then reduced to 15% ± 2.5. Treated soil seed banks result in the highest similarity of 19% ± 3.3.
Table 4 – Average number of species found in the soil seed bank (SSB) and above ground vegetation (AGV), and the average similarity between the SSB and AGV, using Sorenson’s similarity index.
Average ± 95CI SSB AGV Sorenson’s similarity (%) SSB and AGV (full)† 27 ± 2.2 33 ± 1.8 19 ± 2.8 SSB and AGV (control)* 5 ± 0.7 26 ± 1.4 15 ± 2.5 SSB and AGV (treated)* 9 ± 0.9 26 ± 1.4 19 ± 3.3
† Only unidentified species were removed.
* All serotinous species and annuals were removed from the standing vegetation. All annuals and unidentified species were removed from the soil seed bank data. These would not have been consistently present between sampling.
3.3 COMMUNITY ANALYSIS
The NMS ordination of species abundance in all trays, using the Sorenson distance measure, yielded a 2-dimentional solution with a final stress of 20.52, and instability of 0.000 over 58 iterations (Figure 19). Axis 1 (capturing 44% of the variability) is associated with a site based gradient, axis 2 (capturing 27% of the variability) a depth gradient (cumulative r2 = 0.71). MRPP analysis was conducted on several combinations of groups; distinct variations in community structure could be seen between depth and site (A=0.14, p<0.001) and between natural and transferred soils (A=0.10, p<0.001), however treatment showed no significant difference (A=0.01, p<0.002).
The panel of joint plot comparisons, and associated correlation tables (Figure 20, A, B and C) visually show the relationship of variables with the ordination axes. Only vectors with an r2 > 0.20 are displayed. All growth forms are associated with depth (Figure 20, A). Succulents are correlated with site, however they are the only growth form negatively correlated with axis 1. All growth forms are correlated negatively with axis 2, suggesting 0-5 cm natural soils are more important.
27 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Diversity, richness and proteoid score (Figure 20, B) show density and richness correlated strongly with site, the negative correlation with axis 2 suggesting these factors are also correlated with 0-5 cm natural soils. Proteoid score has a strong correlation with natural sites as a whole.
Species, (Figure 20, C) show the most highly correlated species. Crassula colorata is the only species negatively correlated with axis 1 (site), having a greater correlation with depth. All other species here are correlated with the natural site.
Figure 19 – Ordination of all trays using NMS. Axis 1 correlated with site, from transfer to natural. Axis 2 correlated with depth, 5-10cm to 0-5cm.
28
A. Joint plot analysis of growth form and invasive status. B. Joint plot analysis of richness and diversity. C. Joint plot analysis of species.
Axis 1 (r) Axis 2 (r) Axis 1 (r) Axis 2 (r) Axis 1(r) Axis 2(r) Grassy .727 -.353 Proteoid .625 .021 Austrostipa compressa .451 -.133 Herb .528 -.404 score (austcomp) Centrolepis glabra .485 -.102 Shrub .654 -.043 Richness .673 -.334 (centglab) Succulent -.096 -.649 Density .624 -.503 Crassula colorata -.100 -.641 (crascolo) Woody . .654 -.043 Isolepis marginata .577 -.292 Native .648 -.474 (isolmarg) Invasive .335 -.438 Laxmannia sessiliflora .464 -.039 (laxmSP) Annual .566 -.544 Leucopogon conostephioides .452 .017 Perennial .727 -.038 (leuccono)
Figure 20 – Panel of three joint plot analyses, with correlations. A – Growth form and invasive status, B – Richness and diversity, C – species. Only those vectors with r2 values > 0.20 are displayed.
Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
CHAPTER 4 - DISCUSSION
4.1 INFLUENCE OF DEPTH OF TOPSOIL ON RESTORATION OUTCOMES
4.1.1 THE SOIL SEED GRADIENT
Consistent with previous work (Bellairs and Bell 1993; Read et al. 2000; Rokich et al. 2000; Brown, Enright, and Miller 2003; Pickup, McDougall, and Whelan 2003; Fenner and Thompson 2005; Merritt and Rokich 2006; Fisher et al. 2009), natural soils had a strong depth gradient with most (73%) seeds in the top 5 cm. In transferred soils there was no evidence of this depth gradient, although few studies have looked at this aspect. Koch et al. (1996) found evidence of a mixed profile after the topsoil transfer process had been conducted, finding only 15% of the seed within the top 5 cm (diluted from 20 cm) of transferred soil, compared the results of this study which found 54% (diluted from 7 cm, range: 5-10 cm) of the seed in this depth zone after transfer. A study into soil seed banks affected by intense disturbance by Luzuriaga et al. (2005) demonstrated a similar effect from the disturbance of ploughing.
It would be expected that transferred soils, after a mixing effect during the transfer process, would be an average between the 0-5 cm and 5-10 cm depths of the undisturbed soils. However, transferred soils produced less germinants than even the undisturbed 5-10 cm from Jandakot Airport. Alcoa found in its mining operations within the Jarrah forest of Western Australia that compaction had caused a 5% reduction in the profile by up to 75 cm in depth (Croton and Watson 1987). Compaction occurring during the clearing and to a lesser extent during the soil stripping process may have resulted in a greater proportion of topsoil being removed from the soil source site (Figure 21). Thus this would have a dilution effect reducing germination in the transferred samples.
31 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Figure 21 – Graphical representation of the potential influence of compaction in the soil stripping process. Effect of over harvesting is for illustrative purposes only.
Although this study anticipated that the physical abrasion of transfer could be beneficial by being a physical germination trigger, this was not the case, as germination was less in transferred soils. The transfer process and compaction may have caused damage to seeds within the soil seed bank, contributing to reduced germination (Chambers and MacMahon 1994; Koch et al. 1996). Compaction is generally considered a hindrance to in situ emergence of seedlings (Thill, Schirman, and Appleby 1979; Kozlowski 1999; Botta et al. 2006), but no previous work has examined compaction specifically for physical seed damage. In one of the few studies of the transfer process, Koch et al. (1996) observed decreases in the germinable seed throughout the process, with 31% of the original density found after respread of soil. Physical abrasion from topsoil handling may destroy seed, especially smaller seeded species (Koch et al. 1996). This trend is mirrored in this study, as it was observed that transferred soils were 26% of the density of the pre-transfer soils.
4.1.2 LOSS OF ORGANIC MATTER (PROTEOID ROOTS)
The results show evidence that a dilution effect also occurs with the proteoid organic matter within the soil. Proteoid roots are an adaption of the flora of south Western Australia to low nutrient environments (Watt and Evans 1999; Neumann and Martinoia 2002). Due to the rapid turnover of active roots, they add much organic material to an otherwise impoverished soil structure, and therefore increase the nutrient and water holding capacity of the soil (Neumann and Martinoia 2002). In this
32 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials study, the highest proteoid root scores are correlated with natural soils, and were highly visible on site at Jandakot Airport (Figure 22). Therefore, as organic matter was less prevalent in the transferred soils, this may have had implications on the success of certain species that are adapted to the conditions provided by proteoid roots. DeFalco et al. (2009) found a consistent positive relationship between cover of litter and the viable soil density, proposing that litter is an indicator of degradation in arid lands. This may have played some role in the high densities observed with root scores of >0 to 75%. Organic material located in the top few centimetres of soil results in seedlings that are more likely to establish successfully (Canham and Marks 1985; Baskin and Baskin 1998). Homogenization of the soil profile due to transfer can therefore create a loss of stratification, seed dilution and loss of organic material that helps provide soil structure needed for successful establishment.
Figure 22 – Photo of proteoid roots on site at Jandakot Airport.
4.1.3 IMPLICATIONS FOR THE TRANSFER PROCESS
From these results it can be seen that the mixing process that occurs when transferring topsoil results in around 50% of the germinants lying beyond a germinable depth. To maximise potential for restoration, soil stripping ideally needs to be a maximum of 5 cm to retain high density, richness and structure in the transferred soil. In order to take advantage of the seed store, its attributes, and the weed suppression qualities of transferred topsoil, double stripping is a possible alternative to the single stripping process conducted. Alcoa currently practices this, removing a shallow top layer separately from underlying material, and subsequently returning soil in the same order in which it was removed in, thus providing concentration of seed, suppression of weeds, and maximisation of structural and biological attributes (Koch 2007a).
33 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
4.2 THE EFFECT OF TOPSOIL TRANSFER ON GERMINANT COMPOSITION
All growth forms were reduced in abundance in the transfer process. Community analysis shows that there is a significant difference between natural and transferred soils. The highest densities, richness, and most plant functional types were correlated with 0-5 cm in natural soils. A greater proportion of succulents can be seen in transferred soils. The abundance of these is still equal or less than those of natural soils, therefore the seeds of the succulents, predominately Crassula, were likely less negatively affected by the process of transfer. Interestingly shrubs and woody species are of a greater proportion in 5-10 cm natural samples than the 0-5 cm natural samples, whilst there is a reduced proportion of grassy and herbaceous species. Several factors could lead to such a difference between natural and transferred soils. Koch et al. (1996) flagged damage to seed during the process as being influential of low establishment. Therefore, those species with more durable seeds could be less diminished than those smaller seeded species. Timing of topsoil transfer has previously been found to effect outcomes for restoration and germination (Ward, Koch, and Ainsworth 1996; Rokich et al. 2000; Merritt and Rokich 2006). The time which topsoil transfer occurred (late autumn) may have had some influence on the soil seed bank viability. Transfer that occurs earlier in a year offers improved seedling recruitment, due to the greater time available for establishment while appropriate conditions are present (Merritt and Rokich 2006). Other studies have produced similar recommendations, such as Rokich et al. (2000) who demonstrated autumn transfer produced better results than winter and spring.
4.3 GERMINATION SIMULATION WITH COMMON GERMINATION CUES
This study has found that smoke and heat treatment (in combination) offered an enhanced density and richness in natural soils and no impact on diversity. Previous literature has found smoke and heat in combination to be important in enhancing germination of the soil seed bank (Dixon, Roche, and Pate 1995; Enright et al. 1997; Morris 2000; Read et al. 2000; Merritt et al. 2007). More recently there has been increasing literature on smoke and heat in combination being the best method in which to induce germination of seed in a broader range of species (Read et al. 2000; Thomas, Morris, and Auld 2003; Merritt and Rokich 2006). Although abundance did increase, composition seems to have not been significantly altered. Overall only native species were affected positively by treatment, invasive species were found to decline. Not all species respond to heat and/or smoke treatment (Thomas, Morris, and Auld 2003;
34 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Clarke and French 2005). Studies have also previously shown that invasive species are more vulnerable to heat and smoke exposure (Smith, Bell, and Loneragan 1999; Read et al. 2000), and therefore may decline in abundance with such a treatment.
Heat and smoke treatment of transferred soil samples did not significantly alter the soil seed bank composition, although woody species showed a response to treatment in transferred soils. In this study, soil of the transfer sites were damp due to recent rains, and this may have negated the effect of the treatment. However, being damp alone is unlikely to be the cause as all treated samples were wet due to the application of boiling water for heat treatments . Alternatively seasonality is more likely to have played an influence. Several studies, such as that by Roche, Dixon and Pate (1998) and De Lange and Boucher (1993), found that the season of smoke application had an effect on germination response, summer having a greater response than late autumn or winter. As a result of damp soil, the sampled transfer topsoil may have already started germinating. However, due to the vulnerability of seed being damaged, the movement of transfer/sampling could consequently reduce germination. Losses of presence and abundance of species have been observed after ripping in autumn and winter, compared with summer (Ward, Koch, and Ainsworth 1996). This is evidence that disturbance after rains damages the viability or physically damages the early emerging seed, and therefore effects the perceived results, although it is likely that this would only affect the early responders (weeds and annuals) (Fisher et al. 2009).
4.4 SOIL SEED BANK AND ITS RELATIONSHIP TO THE STANDING VEGETATION
4.4.1 SEED BANK COMPOSITION
The soil seed bank is not representative of standing vegetation, even though invasive species had a surprisingly little impact on the soil seed bank (accounting for only 7% of overall germination). The species present in high abundance across all treatments, namely Crassula colorata, Isolepis marginata, and Centrolepis glabra, were all native annuals, with this group representing 68% of the soil seed bank composition. Native perennials are an important group and are the focus of restoration efforts. Without these species restoration is unlikely to be successful; however this group only represented a fraction of the composition (17%).
There is also little similarity to the standing vegetation on a plot by plot basis. This study found the seed bank – extant vegetation similarity ranged between 15% and 19% (excluding serotinous and annual species). This is less than the value that
35 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Hopfensperger (2007) reported in a review of similarity, finding 31% similarity for forest ecosystems over 31 separate studies. However, these forest ecosystems were found to be the least similar, being most similar in grasslands (Hopfensperger 2007).
The results of Hopfensperger (2007) suggests the idea that grasslands invoke high similarity due to grasses having a similar (prolific) seeding habit. This is further supported by Odgers’ (1994) study in Eucalypt forests where grass species have a similarity of 82-93%, and De Villiers (2001) who reported a similarity of 75% of annuals in the South African Karoo. With a mixed community such as a woodland or forest system, the prolific seeders, such as the grasses and herbs, will be disproportionate in number compared to the other functional types, as they have a higher degree of similarity within the soil seed bank. In Mediterranean fire prone environments, similarity is likely to be lower; Enright et al. (2007) reported values of 26-43% in an area with a high degree of serotiny. Furthermore, this region has a high abundance of resprouter species which do not produce high quantities of seed. Although it is the standing vegetation that drives the assemblage of the soil seed bank, due to disproportionate seeding and dormancy mechanisms amongst species, the soil seed bank alone is not capable of restoring many of the species required to achieve restoration goals.
4.4.2 SYSTEM RE-ASSEMBLAGE
Results suggest that the system after topsoil transfer is in the early stages of re- assemblage. Overall 77% of the soil seed bank studied was comprised of grassy and herbaceous species, and although there is a high proportion of native species (91%), 68% of these are annual species. This is suggestive of early re-assemblage through secondary succession. It is not well documented if the early composition after topsoil transfer adjusts over time to become more similar to that of the original vegetation. A natural part of recovery from disturbance is the rapid recovery from the pioneer species, as these species are generally short-lived annual species such as grasses and herbs (predominately seeders) (Enright and Cameron 1988; Hobbs and Atkins 1990). The low numbers of woody species recruitment (8.6% shrubs, 0% trees) found in this study was likely due to the soil seed bank not being the only source of recruitment (the seed bank alone excludes resprouter and serotinous species). It is important to consider that some species may not germinate in the early stages, or require specific conditions to initiate germination that may have not been met (e.g. repeated drying and wetting)(Lush, Kaye, and Groves 1984; Hobbs and Atkins 1990; Pickup, McDougall, and
36 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Whelan 2003; Fenner and Thompson 2005). But, as governed by the concept of complete initial floristics (Egler 1954), the climax community of woodland is unlikely to be achieved with topsoil transfer alone.
4.4.3 IMPLICATIONS OF THE SIMILARITY OF THE SOIL SEED BANK TO THE STANDING VEGETATION.
The soil seed bank is not representative of the standing vegetation, even with removal of annual and serotinous species. This is likely due to many of this category being resprouter species and therefore not producing much seed in relation to seeder species (87% seeders, 11% resprouters). Similarity is higher with treatment of smoke and heat in combination. Although disproportionate (seeders vs. resprouters), density of woody species overall is reasonable (47-166 germinants m-2), and structural regeneration of shrubs is possible over time through succession.
The study timeframe of thirteen weeks may not have been long enough to fully establish the longer term composition of the soil seed bank. A longer timeframe to observe the germination and compositional profile for Banksia woodland species after topsoil transfer may be useful to examine the richness and compositional trends further. Furthermore, factors such as repeated wetting and drying were not demonstrated in this experiment, it has been recognised to aid seeding emergence in some species (Lush, Kaye, and Groves 1984; Pickup, McDougall, and Whelan 2003; Fenner and Thompson 2005).
37 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
CHAPTER 5 – CONCLUSIONS AND RECOMMENDATIONS
5.1 CONCLUSIONS
Topsoil transfer is a useful tool for restoring degraded lands, especially where other restoration options are not practical due to weed infestations or degraded soil physical or chemical properties. This practice also aids to restore portions of the vegetation community usually neglected by other forms of restoration due to germination difficulties or technical restraints with these species. Furthermore, restoring these species and a soil seed bank will aid future disturbance resilience of the regenerated landscape. However, in the Banksia woodland of the SCP, topsoil transfer alone may not adequately re-establish the structure and species composition required for full recovery as many resprouter and serotinous species are often not representative. Further ecological interventions through planting or direct seeding are required for this to become a functioning Banksia woodland system.
The results of this project are highly useful for the optimization of the topsoil transfer process. There is a dilution effect associated with the process of topsoil transfer, which resulted in a loss of germinant density, richness and changes in the composition of the soil seed bank. Timing is important in how effective treatment will be; treating before rainfall while soil is still dry, being the key to successful results across all native species groups. Treatment with germination cues (heat and smoke in combination) resulted in an increase in density and species richness, overall improving the similarity to the standing vegetation, but not influencing the relative proportions of growth forms.
Although there were some limitations to this study, mainly its length, these results have several implications for topsoil transfer. The main findings suggest that the transfer process needs rethinking due to the dramatic decrease in the germinable seed bank post-transfer. The following section provides recommendations for future studies and management of topsoil transfer.
5.2 RECOMMENDATIONS FOR MANAGEMENT OF TOPSOIL TRANSFER ON THE SWAN COASTAL PLAIN
From this study, it is suggested that the soil seed bank does not highly resemble the standing vegetation. Therefore, topsoil transfer should be conducted alongside other means of restoration, such as planting or direct seeding, to make the post-restoration community more resemblant of the original remnant bushland. There is supportive
38 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials evidence to suggest that topsoil transfer should be conducted in the summer months while seeds are at their maximum dormancy. Once it becomes cooler and wetter, there is a greater possibility of loss of seeds due to damage in the transfer process. Ideally, treatment with smoke and heat should be conducted; a possible method could be the application and subsequent burning of woody debris applied to the transfer areas, therefore increasing the potential of serotinous species in restoration by releasing them from the canopy.
Concentration of seed density is important to maximise the potential for restoration using topsoil transfer. Stripping at a shallower depth will help increase seed density by minimising the dilution effect seen with greater depth, enabling adjustment for a potential compaction effect Alternatively, a form of double stripping could be conducted to help retain other benefits associated with the soil, such as suppression of weeds from underlying degraded soils, beneficial soil associations and chemical properties that are also being transferred.
5.3 RECOMMENDATIONS FOR FUTURE RESEARCH
This research has raised questions of the topsoil transfer process, as well as suggested ways that this process could be more successful. Continued monitoring of past and present transfer projects is important for developing a full picture of topsoil transfer and how these re-assembling communities change over time. Several areas can be researched further to gain greater knowledge of the processes and the interactions present to further develop solutions.
Soil stripping may have been inaccurate due to compaction; further research is required on the influence of compaction and how much of an influence this plays. This needs to be quantified in terms of measurable depth of compaction, so procedures can be altered accordingly. Additionally the influence of compaction and other soil disturbances involved need to be studied in regards to seed mortality in these environments.
A small-scale simulated topsoil transfer (under controlled conditions) may be of benefit to gain a detailed understanding of topsoil transfer, providing valuable insights into the process by minimising potential variables. The simulation of topsoil transfer could be achieved by gathering set-depth samples from remnant bushland and mixing them together to simulate transfer, taking subsequent samples from this mixed soil, thus removing potential contamination and compaction effects.
39 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
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49
APPENDICES
APPENDIX A – STATISTICAL SUMMARIES OF ALL NORMAL PARAMETRIC ANALYSIS
Table A1 – Statistical summaries of all normal parametric analysis. “NS” denotes non-significant values.
Density Richness Diversity Invasive Native Grassy Herb Shrub Succulent Native Native Woody Non-woody Seeder Resprouter Density Density Species Species Species Species Annual Perennial Depth P-Value <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.008 0.02 <0.001 <0.001 0.009 0.002 <0.001 0.002 F-Value 47.3 80.9 34.8 26.8 43.6 20.6 45.1 7.1 5.6 33.9 14.5 7.0 10.3 44.6 9.5 Estimate -2347.90 -7.13 (0.90) -0.42 (0.09) -421.64 -1933.70 -699.57 -1331.5 -43.83 -280.14 -1592.8 -184.34 -44.26 -140.08 -2091.20 -147.39 (SE) (348.70) (59.75) (315.30) (166.58) (195.1) (36.24) (98.62) (283.2) (59.98) (36.24) (41.20) (321.40) (48.38) Site P-Value <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.02 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 F-Value 104.7 144.8 28.8 23.6 109.4 106.2 73.0 129.8 5.2 62.9 175.2 130.3 85.2 87.2 89.1 Estimate -2472.00 -7.04 (0.90) -0.35 (0.09) -412.70 -2076.60 -874.88 -1421.6 -212.40 33.09 -1506.5 -417.61 -212.82 -204.79 -2135.30 -210.37 (SE) (348.70) (59.75) (315.30) (166.58) (195.1) (36.24) (98.62) (283.2) (59.98) 36.24 (41.20) (321.40) (48.38) Treatment P-Value 0.003 0.007 0.02 <0.001 0.008 <0.001 <0.001 0.01 <0.001 <0.001 0.005 0.009 F-Value 8.5 7.4 5.6 13.6 7.1 3.9 20.3 6.4 14.6 20.1 8.1 7.0 NS NS NS Estimate 1537.80 3.54 (0.90) -187.02 1720.00 619.25 578.0 201.52 1149.4 304.52 201.09 1379.30 179.38 (SE) (348.70) (59.75) (315.30) (166.58) (195.1) (36.24) (283.2) (59.98) (36.24) (321.40) (48.38) Depth:site P-Value <0.001 <0.001 <0.001 <0.001 0.009 <0.001 0.002 <0.001 0.009 0.02 <0.001 0.04 F-Value 33.4 26.2 30.9 28.8 7.0 38.1 10.1 23.5 7.0 5.7 32.2 4.1 NS NS NS Estimate 2326.40 5.33 (1.04) 383.30 1953.20 509.33 1390.0 361.53 1585.9 183.78 113.75 2106.0 113.32 (SE) (402.60) (68.99) (364.10) (192.35) (225.2) (113.87) (327.0) (69.26) (47.57) 371.20 55.86 Depth:Treatment P-Value 0.03 0.03 F-Value 5.0 4.9 NS NS NS NS NS NS NS NS NS NS NS NS NS Estimate -93.43 -92.59 (SE) (41.85) (41.85) Site:Treatment P-Value <0.001 <0.001 <0.001 <0.001 0.04 0.004 <0.001 <0.001 0.004 0.003 <0.001 <0.001 F-Value 13.9 13.2 19.5 14.9 4.4 8.4 12.7 14.7 8.5 9.1 12.3 15.5 NS NS NS Estimate -1502.50 -3.79 (1.04) -1608.70 -742.11 -471.3 -121.13 -1165.6 -265.26 -121.97 -143.29 -1301.80 -219.82 (SE) (402.60) (364.10) (192.35) (225.2) (41.85) (327.0) (69.26) (41.85) (47.57) (371.20) (55.86) Adjusted R-Squared 0.51 0.58 0.25 0.31 0.52 0.44 0.45 0.47 0.08 0.41 0.54 0.47 0.36 0.48 0.38
Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
APPENDIX B – SPECIES LISTS
Table B1 - List of species recorded in plant surveys conducted at Jandakot Airport, with invasive status.
Genus species Status Acacia pulchella native Acacia saligna native Acacia willdenowiana native Adenanthos cygnorum native Allocasuarina humilis native Amphipogon turbinatus native Arnocrinum preissii native Austrostipa compressa native Banksia attenuata native Banksia ilicifolia native Banksia menziesii native Baumea vaginata native Beaufortia elegans native Bossiaea eriocarpa native Briza maxima invasive Burchardia congesta native Caladenia flava native Caladenia sp. native Calectasia narragara native Calytrix flavescens native Calytrix fraseri native Carpobrotus edulis invasive Cassytha sp. native Chamaescilla corymbosa native Chordifex sinuosus native Conostephium pendulum native Conostephium preissii native Conostylis aculeata native Conostylis juncea native Conostylis setigera native Croninia kingiana native Dampiera linearis native Dasypogon bromeliifolius native Daviesia triflora native Desmocladus fasciculatus native Desmocladus flexuosus native Ehrharta calycina invasive Eremaea asterocarpa native Eremaea pauciflora native
51 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Eucalyptus marginata native Eucalyptus todtiana native Gastrolobium capitatum native Gladiolus caryophyllaceus invasive Gompholobium tomentosum native Haemodorum spicatum native Hardenbergia comptoniana native Hemiandra pungens native Hensmania turbinata native Hibbertia huegelii native Hibbertia hypericoides native Hibbertia subvaginata native Hypocalymma robustum native Hypochaeris glabra invasive Hypolaena exsulca native Jacksonia furcellata native Lasiopetalum drummondii native Laxmannia squarrosa native Lechenaultia floribunda native Lepidosperma drummondii native Lepidosperma squamatum native Lepidosperma tenue native Leucopogon conostephioides native Leucopogon insularis native Leucopogon sp. native Levenhookia stipitata native Lomandra caespitosa native Lomandra hermaphrodita native Lomandra micrantha native Lomandra preissii native Lomandra sp. native Lomandra suaveolens native Lyginia barbata native Lysimachia arvensis invasive Melaleuca ryeae native Melaleuca systena native Melaleuca thymoides native Nuytsia floribunda native Patersonia occidentalis native Persoonia saccata native Petrophile linearis native Philotheca spicata native Phlebocarya ciliata native Phlebocarya filifolia native Pimelea sulphurea native Podolepis gracilis native
52 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Rhytidosperma occidentale native Scaevola repens native Schoenus curvifolius native Schoenus efoliatus native Scholtzia involucrata native Solanum nigrum invasive Sonchus oleraceus invasive Stirlingia latifolia native Stylidium piliferum native Stylidium repens native Stylidium sp. native Tetraria octandra native Thysanotus thyrsoideus native Thysanotus triandrus native Trachymene pilosa native Ursinia anthemoides invasive Wahlenbergia preissii native Xanthorrhoea preissii native Xanthosia candida native
Table B2 – List of species germinated in glasshouse experiment, with invasive status, and number of germinants observed across treatments.
Natural Transfer Genus species Status control treated control treated Acacia pulchella native 0 4 0 1 Aira caryophyllea invasive 31 11 6 1 Aira cupaniana invasive 1 1 3 0 Anigozanthos humilis native 5 26 2 5 Anigozanthos manglesii native 0 20 0 0 Arctotheca calendula invasive 1 0 5 11 Austrostipa compressa native 126 91 7 3 Bossiaea eriocarpa native 3 8 1 3 Briza maxima invasive 89 33 2 1 Briza minor invasive 1 0 0 0 Bromus diandrus invasive 2 1 14 20 Calandrinia granulifera native 3 0 5 1 Calandrinia corrigioloides native 13 31 0 2 Cardamine hirsuta invasive 0 0 2 0 Carpobrotus edulis invasive 1 7 10 16 Cassytha sp. native 0 2 0 0 Centrolepis alepyroides native 152 202 57 31 Centrolepis aristata native 0 0 5 2 Centrolepis glabra native 249 566 116 67 Chamaescilla corymbosa native 116 38 17 2 Conostephium pendulum native 0 2 0 0
53 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Conostylis aculeata native 0 40 0 1 Conostylis juncea native 4 20 0 0 Conostylis setigera native 0 3 0 0 Conyza bonariensis invasive 34 10 12 2 Crassula colorata native 244 329 466 336 Cynodon dactylon invasive 0 0 0 1 Dasypogon bromeliifolius native 1 1 0 0 Daviesia pedunculata native 1 0 0 0 Daviesia triflora native 0 1 0 0 Desmocladus flexuosus native 6 6 2 0 Drosera erythrorhiza native 0 1 0 0 Drosera menziesii native 0 3 0 0 Drosera platypoda native 2 1 1 0 Drosera platypoda native 3 5 1 0 Ehrharta calycina invasive 0 1 0 5 Euphorbia peplus invasive 1 0 0 1 Gamochaeta coarctata invasive 1 0 1 1 Gladiolus caryophyllaceus invasive 48 13 12 0 Gnaphalium indutum native 0 0 0 1 Gnephosis angianthoides native 2 0 64 26 Gompholobium tomentosum native 5 62 6 20 Hensmania turbinata native 1 0 0 0 Hibbertia hypericoides native 1 0 4 0 Hibbertia sp. native 0 1 0 0 Hibbertia sp. native 2 1 0 0 Hibbertia subvaginata native 8 7 3 1 Homalosciadium homalocarpum native 21 26 1 4 Hypocalymma angustifolium native 1 1 0 0 Hypochaeris glabra invasive 66 60 13 9 Isolepis marginata native 617 1257 145 136 Isotoma hypocrateriformis native 1 37 1 40 Jacksonia furcellata native 1 3 0 0 Juncus sp. unknown 1 8 13 17 Laxmannia ramosa native 1 5 1 0 Laxmannia sessiliflora native 164 152 57 29 Lechenaultia floribunda native 8 169 3 12 Lepidosperma drummondii native 1 0 0 0 Leucopogon conostephioides native 262 173 19 28 Leucopogon sp. native 14 4 1 3 Levenhookia pusilla native 15 3 0 3 Levenhookia stipitata native 68 85 6 4 Lolium sp. invasive 42 14 2 3 Lomandra caespitosa native 1 2 0 0 Lomandra hermaphrodita native 0 3 0 0 Lomandra preissii native 0 0 0 1 Lomandra sp. native 1 0 0 0
54 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Lotus sp. invasive 0 0 1 1 Lyginia barbata native 3 1 0 0 Lysimachia arvensis invasive 1 0 0 0 Medicago sp. invasive 0 0 1 0 Microtis sp. native 5 1 1 0 Patersonia occidentalis native 1 3 2 0 Phlebocarya ciliata native 2 2 0 0 Phlebocarya filifolia native 0 1 0 1 Podolepis lessonii native 23 74 0 0 Podotheca chrysantha native 0 0 1 0 Podotheca gnaphalioides native 9 14 6 4 Poranthera microphylla native 21 46 3 4 Poranthera microphylla native 75 346 35 21 Rhodanthe corymbosa native 60 47 2 1 Rhodanthe laevis native 6 3 0 0 Romulea rosea invasive 0 2 11 1 Sagina apetala invasive 0 0 1 0 Sagina apetala invasive 0 0 2 0 Schoenus curvifolius native 1 1 0 0 Solanum americanum invasive 1 0 0 0 Solanum nigrum invasive 3 2 3 1 Sonchus oleraceus invasive 1 1 5 0 Spergula arvensis invasive 0 0 1 0 Stylidium brunonianum native 3 141 1 4 Stylidium emarginatum native 132 204 15 26 Thysanotus manglesianus native 4 1 2 0 Thysanotus sp. native 3 2 0 1 Thysanotus triandrus native 1 1 1 0 Trachymene pilosa native 341 179 21 32 Trifolium campestre invasive 4 5 2 0 Unknown_01 invasive 8 5 1 1 Unknown_02 native 0 1 1 0 Unknown_03 native 1 4 1 4 Unknown_04 native 0 1 0 0 Unknown_05 native 127 93 2 0 Unknown_06 unknown 0 0 0 1 Unknown_07 native 4 4 0 0 Unknown_08 native 1 0 0 0 Unknown_09 native 0 0 1 0 Unknown_10 native 4 10 22 19 Unknown_11 native 1 14 1 5 Unknown_12 unknown 2 0 2 1 Unknown_13 unknown 1 2 0 0 Unknown_14 native 0 0 0 2 Unknown_15 native 0 0 1 0 Unknown_16 native 0 19 0 0
55 Soil seed bank dynamics of transferred topsoil: evaluating restoration potentials
Unknown_17 unknown 0 0 2 1 Unknown_18 native 2 3 1 1 Unknown_19 native 0 0 0 1 Unknown_20 native 7 73 1 10 Unknown_21 native 0 2 20 3 Unknown_22 native 1 3 0 0 Unknown_23 native 0 1 0 0 Unknown_24 native 4 345 5 55 Unknown_25 unknown 6 0 9 4 Ursinia anthemoides invasive 86 56 0 8 Vulpia sp. invasive 65 25 7 2 Wahlenbergia capensis invasive 13 32 9 2 Wahlenbergia preissii native 147 222 7 15 Xanthosia candida native 2 5 1 1 Totals 3624 5547 1297 1083
56