Monitoring the vegetation of the vernal pools and their immediate upland rim

Vegetation transects are undertaken each November or December across:

• the constructed pool,
• two remediated degraded pools (which were weeded and had their seed banks augmented),
• two reference pools (which were high quality pools that were not treated in any way) and
• two control pools (which were degraded pools that were not treated, to act as controls for measuring the success of the remediation efforts in degraded pools)

Where mixed species occur together, the VPS (vernal pool species) cover has been calculated as a percentage for that section of the vegetation transect. Graphs showing the progress of the mitigation pools against reference and control pools are presented here.

Vegetated cover as a percentage of the total length of the transect

Graphs of vernal pool species (VPS) as a percentage of transect length (absolute cover) and of vegetated transect length (relative cover)

The shortness of the wet seasons in 2006 through 2008 allowed upland plants such as clover to infiltrate right across most of the pools. The upland plants grew over areas that would have contained open mud in wetter years, and into sparser stands of VPS. The average rains of 2009 were sufficent to drown invading upland plants across some of the deeper parts of Reference Pools 2 and 6 where dense growth of VPS was observed. The dead annual biomass from the invading upland plants has contributed to the peaty organic layer at the bottom of these pools. Annual upland plants appear less able to outcompete VPS in the shallower pools when statstically wet years occur, causing VPS to return to dominance..

Perennial upland plants such as couch, curly dock and kikuyu have a longer term influence on pool species dominance. In 2010 and 2011 it was noted that couch was still dominant in the southern part of Reference Pool 6 and the northern part of Reference Pool 2. It is likely that perennial invaders will need a series of wet years and/or treatment with herbicide once the pools dry up each year. Couch and kikuyu are both summer growing so they remain green and growing after the pools dry up, providing a window of opportunity for control.

Weed control in the remediated pools (Pools 4 & 10) was aimed at controlling perennial weeds. Pool 4 was the weediest of the degraded pools, being overgrown with Rumex crispus which was controlled in autumn of 2006. By 2008 the vegetation in the pool was dominated by brassicas, but the average rains of 2009 gave the Rumex a chance to return and it once again dominates the vegetation of this pool, along with Solanum eleagnifolium. It is recommended that these plants be controlled again before they become thoroughly established.

In contrast, Pool 10 was infested with couch and kikuyu. These are only slowly returning since they were treated in 2006 and VPS have now expanded to cover a significant portion of the pond transect.

In 2009 a new invasive species was recorded in the vicinity of Reference Pool 2. The plant is Coolatai Grass (Hyparrhenia hirta). It is recommended that this grass be controlled immediately. The plant currently forms a single clump at AMG 282703E, 6145413N (datum GDA, zone 54).

In 2009 the pools held water long enough for Amphibromus nervosus (regionally listed as extinct, but occurring in the vernal pools) to set seed in the constructed pool and in Pools 2 and 9. This was the first year since the mitigation works were undertaken (2006) that this had been observed. Amphibromus flowered again in 2010 and in 2011, but the seed set was poor, and few fertile seeds were observed. It seems that a hydroperiod of more than 100 days is necessary for this grass to reproduce.

The last few years has seen an increasing cover of vernal pool species recorded in the Constructed Pool, and the initiation of a layer of dead plant material on the base of the pool. The high value Reference Pools (2 and 6) retain the highest abundance of vernal pool species. The Remediated Pools (Pools 4 and 10) were subject to weed control and seedbank augementation. They show quite different responses with Pool 10 gradually increasing abundance and maintaining its diversity of vernal pool species while Pool 4 appears to be returning to its weed infested state. The low value Control Pools (Pools 9 and 11) have not improved spontaneously - both still have very low cover (abundance) of VPS although the two pools have widely differing diversity values.

The vegetation of the upland grassland with emergent Sclerolaena muricata var villosa that surrounds the vernal pools has become overgrown with blanket weed and bearded oat in the last few seasons. As a result the site may pose a fire hazard unless it is slashed or grazed. The blanket weed appears to be outcompeting Sclerolaena in the upland areas and is becoming common around the edges of the vernal pools. It appears the smaller amphibious plants edging the pools (including Wilsonia rotundifolia and Cressa cretica) may struggle to maintain their niche in the face of this invasive species.

The management plan for the vernal pools suggests slashing be conducted of the upland areas in mid to late Summer (or slightly earlier in years when the site dries off quickly. There is no need to mow through the dried vernal pools, which are recognisably vegetated with different plant species to the upland areas. As an alternative, light grazing may have the same benefits but should only occur after all Amphibromus nervosus in the vernal pools have finished flowering (after earlyJanuary).

If grazing is considered, it should be restricted to sheep as they are not known to eat the poisonous Chincherinchee (Ornithogalum thyrsoides) that grows on the site, whereas horses and cattle do. Chincherinchees are a South African bulb species that grows aroung 'vleis' (similar to vernal pools) in its native land. As a weed in the Adelaide area it appears largely restricted to grasslands on heavy clay with gilgai-type hollows.

During 2011, as part of Parafield Airport's environmental planning, the airport environment managers and consultants determined that sufficent information had been obtained from the monitoring program to support the hypothesis that weed control is an effective mitigation tool within the vernal pools. As a result, weed control will in future be undertaken site-wide, including the degraded control pools (Pools 9 and 11).

The success of seed bank augmentation, whether by the introduction of seed, tubestock or inoculum into the vernal pools, is still undetermined. Therefore, while additional augmentation can occur in the constructed pool, the remediated pools (pools 4 & 10) and all pools not forming part of this monitoring program, augmentation with vernal pool species should not occur in the reference and degraded control pools (Pools 2, 6, 9 and 11).

Augmentation of upland plantings across the higher parts of the entire site will also occur, using upland species native to the site.

Species lists

Native plant lists for all the pools and their immediate uplands, with specialist vernal pool species (VPS) marked with #. Some specialist vernal pool exotics are recorded in the table but are marked with #*. Other exotics have not been recorded here but are listed in several studies of the pools. The lists on this page are updated as new species are noted during monitoring.

Number of vernal pool species (VPS) present along transect line only (others may be present off the transect line)

Photographs of plants found in the vernal pools and around them in the upland buffer zone

Eleocharis acuta (vernal pool)	Muehlenbeckia florulenta (upland buffer)
Lythrum hyssopifolia (vernal pool)	Rumex tenax (vernal pool)
Maireana decalvans (upland buffer)	Marsilea spp. (vernal pool)
Wilsonia rotundifolia (vernal pool)	Austrostipa scabra (upland buffer)
Limosella australis (vernal pool)	Lotus australis (upland buffer)

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