4.2. Spinifex Trials and Primary Planting
After two to three months of crest/swale formation on the newly constructed dunes, planting of early dune colonizing species was trialled (
Figure 9). For the more than 1 km of reconstructed dune, a rapid and efficient method to re-establish the native colonizing species Spinifex was required.
The methods trialled at Magenta Shores had previously been used successfully on the New South Wales coast. These included harvesting and planting stolons (used at Casuarina and Salt developments in northern New South Wales); burial of Spinifex seed heads [
9] (used at Budgewoi) [
7]; and planting nursery grown plants (used by the first author at Kurnell in southern Sydney).
Figure 9.
Bush regenerators carrying out preliminary planting below coastal tea-tree windrows.
Figure 9.
Bush regenerators carrying out preliminary planting below coastal tea-tree windrows.
Five methods of Spinifex introduction, at three different planting densities, were trialled in the southern dune section from 11 November 2004. By 10 January 2005, a clear trend was evident. Final data was collected in November 2005.
A split plot design was applied to a 550 × 25 metre stretch of the CPZ with the sampling area consisting of twenty-two 20 × 20 metre quadrats each divided into four 10 × 10 metre subquadrats. The 20 × 20 metre quadrats were separated by 5 metre intervals (
Figure 10).
Figure 10.
Spinifex planting trial layout with four subquadrats per treatment cell.
Figure 10.
Spinifex planting trial layout with four subquadrats per treatment cell.
The methods trialled were firstly, Spinifex stolons planted upright at 2 metre and 5 metre intervals; secondly, Pigface and Spinifex stolons co-planted horizontally at 0.8 metre intervals; thirdly, well-rooted nursery grown plants of Spinifex planted at 2 metre intervals; fourthly, Spinifex seed head buried at up to 30 cm depth in naturally occurring moist sand at 0.8 metre and 2 metre intervals; and fifthly, no planting or seeding (control). Depth of seed burial was increased due to the sand being highly mobile.
All of the plant material used was local provenance, with the majority from the re-constructed Budgewoi Beach dune and a small amount from the development area at Magenta Shores. The original source of Budgewoi plant material was from 3 km north of Magenta Shores on Tuggerah Beach. Stolons collected consisted of cut sections with two to three rooting nodes. No whole plants were dug up. The donor site was assessed prior to and post the collection to ensure that adequate cover was maintained. To avoid moisture loss, all stolons were collected in early morning, and transplanted on site during the day; and all stolons collected for propagation were transported to the nursery within four hours of collection.
Fresh seed was planted as split seed heads at up to 30 cm depth. Spinifex seed ripens quickly with ripeness indicated by the presence of Galah (Cacatua roseicapilla). The Galah arrives in flocks to eat the carbohydrate rich grass seed. About one third of the ripe fertile seed heads were harvested, packed into large open weaved bags and stored for planting.
The trial plantings occurred between 11 November and 9 December 2004. Apart from about 15 mm of rain falling between 16 and 19 November 2004 when Pigface and Spinifex stolons from Budgewoi beach were planted, most planting days had little to no rain. There were five days with > 1 mm rain during planting in November and December 2004 which was lower than the long term average of 9 rain days in November and 7 rain days in December. The daily temperatures ranged from 16.5 to 25 degrees Celsius [
18].
By 10 January 2005, all of the vertically planted Spinifex stolons had died regardless of planting density and the unplanted cells remained bare, except for weed growth (
Figure 11). These cells were criss-crossed with long Spinifex runners planted in the naturally occurring moist subsurface sand, with only a small part of the foliage emerging.
Figure 11.
January 2005 and June 2005 survival.
Figure 11.
January 2005 and June 2005 survival.
By June 2005, planting seed-head at 0.8 metre density appeared to have better establishment than planting it at 2 metre density (
Figure 11). By November 2005, there was higher Spinifex cover for the 2 metre interval planting density (average of 19.3 percent cover) than for the 0.8 metre interval planting density (average of 12.5 percent cover) (
Figure 12).
Figure 12.
Surface cover by Spinifex achieved by 8 November 2005.
Figure 12.
Surface cover by Spinifex achieved by 8 November 2005.
Germination and establishment of Spinifex from buried seed resulted in two to eleven runners per subquadrat within three of the nine seed trial cells at 19 May 2005; and germination in all seed trial cells by 8 November 2005, with between 14 to 60 percent surface cover in seven out of nine cells, and a mean cover of 14 to 17 percent (
Figure 12 and
Figure 13).
Figure 13.
Buried Spinifex seed resulting in long runners by November 2005.
Figure 13.
Buried Spinifex seed resulting in long runners by November 2005.
Cover for Pigface stolons and planted seed head of Spinifex was similar to the 2 metre interval Spinifex seed head planting density and was a very cost effective and satisfactory method for achieving initial cover. The results of planting a mix of Pigface and Spinifex showed no significant difference in contribution to establishment and survival of the Spinifex planted with the Pigface. However, it was observed that Pigface would establish cover rapidly and then die back, providing soil nutrient that in turn would promote growth of more complex species (
Figure 14).
Figure 14.
Pigface dying back and native diversity and cover increasing in 2007.
Figure 14.
Pigface dying back and native diversity and cover increasing in 2007.
The nursery grown stolons had well developed runners at the time of planting. At 19 May 2005, one to 13 long runners were present within 38 percent of the nursery plant trial subquadrats; and by November 2005 between 20 to 90 percent surface cover had been achieved in half of the nursery plant subquadrats, with an overall mean cover of >30 percent at 8 November 2005 (
Figure 12). The nursery grown stolons were the most effective in achieving rapid cover (
Figure 11), but expensive (
Table 1).
Table 1.
Cost of each revegetation method.
Table 1.
Cost of each revegetation method.
Method | Cost per plant | Cost at 5 m density per 20 m × 20 m quadrat | Cost at 2 m density per 20 m × 20 m quadrat | Cost at 0.8 m density per 20 m × 20 m quadrat |
---|
Nursery grown stolons | $2.33 | NA—not trialled | $233 | NA—not trialled |
Seed head | $1.60 | NA—not trialled | $160 | $1,000 |
Direct planted stolons (including mixed planting) | $3.39 | $ 54.24 | $339 | $2,118.75 |
The planted Spinifex seed head was a successful technique for achieving cover within a 12 month period. Spinifex germination in the spikelet is inhibited by slow rate of gas exchange between embryo and atmosphere when whole spikes are planted rather than seed that has been removed from the spikelet [
19]. Planting single seed into the moist sand horizon may achieve cover more quickly than burying whole spikelets, however removal of the seed from the spike would be more time consuming.
Relative cost of each method
Nursery stolons cost one dollar each plus initial stolon collection and planting labour costs, which worked out to a total of $2.33 per nursery stolon planted. Seed heads and transplanted stolons had no buying cost, but had both collection and planting labour costs; with seed heads costing $1.60 per seed head planted and planted stolons costing $3.39 per stolon planted. This cost increased with increasing density of planting (
Table 1). Nursery stolons worked out to be cheaper than collecting and directly planting stolons because more plants could be grown and planted for each stolon length collected.
The most cost effective method proved to be burial of Spinifex seed head in moist sand at 0.2 metre density. This method mimicked the natural process of seed blown on shore and buried by mobile sand. Following the Spinifex trials, the remainder of the shaped seaward facing dune was extensively planted and seeded with the primary colonizing species Pigface and Spinifex to provide early rapid cover and promote establishment of sand holding fungal hyphae and organic content prior to re-introduction of secondary native species.
4.3. Soil Fungi Testing
Fungi are important for colonisation and survival of plants [
20]. Mycorrhizal fungi increases nutrient uptake by plants growing in nutrient poor environments [
16]. Plants with no pre-existing root colonisation by mycorrhizal fungi will become colonised by mycorrhizal fungi if planted into sand containing mycorrhizal fungi, however area of root colonised will be lower than in that of plants with existing mycorrhiza prior to planting in sand containing mycorrhiza [
16].
Seed of secondary native colonising species, including
Acacia longifolia subsp.
sophorae, Kennedia rubicunda, Ficinia nodosa, Leucopogon parviflorus, Lomandra longifolia, Imperata cylindrica and
Scaevola calendulacea (all known to have mycorrhizal associations) [
15,
21,
22], was distributed heavily mainly on the crests of the reconstructed dunes, annually from 2005 to 2008, during late Spring to early Autumn when rains are expected. The seed was buried under a shallow layer of sand to prevent birds eating it and to promote sand burial and natural abrasion of the seed coat by sand movement. Seed was not pretreated to break dormancy, as natural germination under favourable conditions such as rain was more likely to favour plant survival than instant germination. Although germinations occurred during the first year, they did not begin to survive and flourish until 2006. The earlier germinations died, usually as a result of being swamped by the highly mobile sands. There was insufficient cover by Spinifex, and presumed corresponding inadequate levels of fungal hyphae present throughout the sand to hold the sands and also to colonise the roots of and assist in sustaining the growth of secondary colonising species.
It was surmised that there were low levels of fungi owing to the disturbed nature of the habitat, with very low levels of organic and carbon content following previous mining and ensuing domination by bitou bush. Development of fungi may be dependent on the presence of sufficient and appropriate nutrients [
16,
23]. Sudden addition of nutrient in the form of fertilizer, although of possible benefit to the growth of some native species [
23], was not desirable, as addition of Phosphorus could have a detrimental impact on fungi growth [
24]. Inoculation of roots of nursery propagated plants prior to planting in the field has been used successfully in revegetation, especially of woodland ecosystems [
23,
25,
26], but less is known about using this practice in restoration of dune ecosystems [
15]. It is possible that to be effective, mycorrhizal strains used need to be compatible with the provenance of the host species [
23,
27,
28].
Introduction of fungi via inoculation of local native species prior to planting was not used because Magenta Shores was a conservation site with existing local native vegetation within 10 m of the dune reconstruction. Time was allowed for sufficient organic and carbon content to develop naturally in the soil, following recolonisation by Spinifex and Pigface, for natural colonisation of fungi from the present low levels in the reconstructed area; and from existing adjacent native vegetated areas in the hind dune. The more resilient northern area and the incipient dune were preserved and carefully weeded throughout the reconstruction.
From May 2005 to September 2006, studies were undertaken to assess the presence/absence of sand binding fungal hyphae along the reconstructed dunes, as an indicator of the progress of the dune stabilisation. On 19 May 2005, 12 fine root samples were collected from four plant species Spinifex,
Leucopogon parviflorus (Coast Beard Heath), bitou bush and
Scaevola calendulacea (Fan Flower) along the Coastal Protection Zone (
Figure 15 and
Table 2). All specimens were found to have hyphae present on or near the roots, however, only
Leucopogon parviflorus (Ericaceae) had frequent intracellular hyphae. There was evidence of hyphae penetrating cell walls and growing within the root cells of bitou bush and
Scaevola calendulacea, although they did not form well defined structures and could not be considered as mycorrhizal.
Table 2.
Observations of root samples at May 2005.
Table 2.
Observations of root samples at May 2005.
Specimen No. | Plant Species | Hyphae present | Observations |
---|
1 | Chrysanthemoides monilifera subsp. rotunda | Yes | Some hyphal penetration. Intracellular hyphae. |
2 | Scaevola calendulacea | Yes | Some penetration, no mycorrhizal structures. |
3 | Chrysanthemoides monilifera subsp. rotunda | Yes | Possible some penetration |
4 | Leucopogon parviflorus | Yes | Cell penetration, some hyphae coiling. |
5 | Leucopogon parviflorus | Yes | Cell penetration, some hyphae coiling, early ericoid mycorrhizal structures. |
6 | Chrysanthemoides monilifera subsp. rotunda | Yes | Possible some penetration. No mycorrhizal structures. |
7 | Spinifex sericeus | Yes | Possible some penetration. No mycorrhizal structures. |
8 | Spinifex sericeus | Yes | No penetration. |
9 | Unknown, near
Leucopogon parviflorus | Yes | Root heavily colonised by hyphae. |
10 | Spinifex sericeus | Yes | Possible some penetration. No mycorrhizal structures. |
11 | Spinifex sericeus | Yes | Possible some penetration. No mycorrhizal structures. |
12 | Spinifex sericeus | Yes | Possible some penetration. No mycorrhizal structures. |
Figure 15.
Fungi sampling locations.
Figure 15.
Fungi sampling locations.
Further sampling was undertaken from 12 to 18 July 2005, with 88 soil samples collected at a depth of between 2 and 5 cm, from three treatment types located in incipient, lower, upper and hind dune areas of 22 transects (
Figure 15). Samples were taken from the bitou bush dominated area immediately south of the Magenta Shores site (Treatment 1); areas previously invaded by bitou bush that were reshaped and then revegetated (Treatment 2); and dunes that were not reshaped and had minor infestations of bitou bush that were being controlled via spraying of herbicide and cut and paint methods (Treatment 3).
All three treatments suggested a trend of increasing hyphal abundance along the dune gradient from incipient foredune to hind dune, and a substantially higher abundance of hyphae in Treatment 3 that had more native vegetation and less bitou bush (
Figure 16).
In September 2006, approximately 22 months after commencement of dune restoration, the fungal status was reviewed. Root samples were collected from the Magenta Shores reconstructed foredunes in the south, more intact foredune in the north and Budgewoi revegetation site. At each site a total of twelve samples were collected from three 50m transects. Samples were taken from the hind dune (small trees and shrubs, coastal tea-tree and Acacia species); dune crest (Spinifex); middle (Spinifex); and incipient dune (Spinifex and bitou bush). Additional root samples from bitou bush were also collected from the bitou bush infested dune south of Magenta Shores. The root samples were inspected and the extent of fungi present in each sample was recorded as a percentage of the total root length.
Figure 16.
Average fungal hyphae counts for three dune treatment areas at July 2005.
Figure 16.
Average fungal hyphae counts for three dune treatment areas at July 2005.
The results showed that the reconstructed dunes at Magenta Shores had levels of fungal hyphae comparable to the native dune and restored Budgewoi dune areas (
Figure 17), (however one relatively high fungal count in the incipient area of the reconstructed Magenta Shores dune was mainly due to the presence of pathogenic species, possibly
Pithium or
Phytophthora, rather than AM fungi). The native dune with the lowest disturbance had high occurrence of fungal hyphae within the incipient and middle dune areas. Both ectomycorrhizal fungi (EM) and some endomycorrhizal (AM) fungi were recorded. The bitou bush root samples showed consistently lower occurrence of fungal hyphae (
Figure 17).
Figure 17.
Mean rates of fungal hyphae recorded at three sites in September 2006.
Figure 17.
Mean rates of fungal hyphae recorded at three sites in September 2006.
Most of the mycorrhizal infection observed in the roots of Leptospermum in the hind dune was made up of ectomycorrhizal fungi (EM) (80%). However, some endomycorrhizal (AM) fungi were also present. Spinifex roots collected at Budgewoi harboured at least three fungal species, including EM. Gigaspora was the main AM genus found in these roots. In addition, Ascomycetes and other fungi were found on the root surface. Roots collected on the incipient dune at Magenta showed signs of pathogenic infection, however were also colonized by AM fungi, including Archeospora. The confirmed presence of hyphae growing on the constructed dune at rates comparable to more stable sites indicated that the constructed dune sands were stabilising.