3 Plant species and sites 1 Target species



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3 Plant species and sites

3.1 Target species


Priority species for sampling were determined with stakeholders. These species were identified as important species for minesite revegetation success and included native framework species, weeds of the wet/dry tropics and species that increase the risk of fire due to fuel load. Species of concern at the Ranger Project Area (RPA) and/or the rehabilitated Nabarlek minesite were also targeted for sampling and these included species that may potentially threaten the ecosystems of the country surrounding minesites.

3.1.1 Weeds


Declared Weeds of the Northern Territory, which must be managed according to NT legislation, were identified as important target species and include the following:

Herbs:

Hyptis suaveolens (Hyptis)

Grasses:

Pennisetum polystachion (Mission grass)

Themeda quadrivalvis (Grader grass)

Shrubs:

Lantana camara (Common lantana)

Senna alata (Candle bush)

Senna obtusifolia (Sicklepod)

Senna occidentalis (Coffee senna)

Sida acuta (Spinyhead sida)

Sida cordifolia (Flannel weed)

Stachytarpheta spp (Snake weeds)

While focus was not on aquatic forms of weeds, it is envisaged that the project will expand to include aquatic plants in the future. Declared aquatic species of weeds affecting the NT include Hymenachne amplexicaulis (Olive hymenachne) and Salvinia molesta (Salvinia) which are species particularly relevant to the rehabilitation of Ranger uranium mine that may contain water features post rehabilitation.


Further weeds of concern


Further weeds of the Wet/Dry tropics that are found in the Alligator Rivers Region and have the potential to impact minesites in the region include those outlined by Smith (1995 & 2002):

Vines:

Calopognium mucunoides (Calopo vine)

Centrosema molle (Centro vine)

Ipomoea spp (Morning glory vine)

Macroptilium atropurpureum (Siratro vine) and M. lathyroides (Phasey bean vine)

Merremia aegyptia (Hairy merremia vine) and M. dissecta (White convolvulus creeper)

Passiflora foetida (Wild passionfruit vine)

Herbs:

Acanthospermum hispidum (Goat’s head, Starburr)

Crotalaria goreensis (Gambia pea or Rattlepod)

Hibiscus sabdariffa (Rosella)

Hyptis sauveolens (Hyptis, Horehound)

Stylosanthes hamata (Carribean stylo)

Stylosanthes humilis (Townsville stylo)

Stylosanthes scabra (Shrubby stylo)

Grasses:

Andropogon gayanus (Gamba grass)

Cenchrus cilaris (Buffel grass)

Cenchrus echinatus (Mossman River grass)

Chloris inflata (Purple top chloris)

Chloris virgata (Feathertop rhodes grass)

Cynodon dactylon (Couch grass)

Hymenachne amplexicaulis (Olive hymenachne)

Melinis repens (Red Natal grass)

Pennisetum polystachion (perennial Mission grass)

Pennisetum pedillatum (annual Mission grass)

Themeda quadrivalvis (Grader grass)

Urochloa humidicola (Brachiara humidicola) (Tully grass)

Urochloa mutica (NT/WA) (Para grass)

Urochloa maxima (NT/WA) (Guinea grass)

Shrubs:

Aeschynomene americana

3.1.2 Species of the Ranger Project Area


The Primary Environmental Objectives for rehabilitation of the RPA are to revegetate the disturbed sites of the RPA using local native species similar in density and abundance to those existing in adjacent areas of Kakadu National Park to form an ecosystem of long-term viability which would not require a maintenance regime significantly different from that appropriate to adjacent areas of the Park.1 Further to the RPA requirements, the Environmental Requirements of the Commonwealth of Australia for the Operation of Ranger Uranium Mine (1999) state that operations should not result in change to biodiversity, or impairment of ecosystem health, outside of the RPA, and that the operations at Ranger will not result in any adverse impact on Kakadu National Park through the introduction of exotic fauna or flora.

Hollingsworth and Meek (2003) describe six vegetation communities, comprising Eucalypt savanna woodlands and a Melaleuca sedge/grassland as analogue descriptions for the ecosystem reconstruction for the RPA. They recommend a list of 60 candidate species (including overstorey, midstorey and understorey species) for restoration of the landform based on their commonness, dominance and similarity to community structure in similar adjacent areas in Kakadu National Park. The ground covers, or understory described included 40 species, and these species are ranked with importance values across habitats. In order of importance for ground covers, they list the following grasses: Sorghum intrans, Aristida holathera, Heteropogon triticeus, Sehima nervosum, Dicanthium fecundum, Alloteropsis semialata, Thaumastochloa major and Ectrosia agrostoides.

Brennan (2005) undertook a quantitative description of native plant communities for potential use in revegetation at Ranger uranium mine. His research was undertaken on natural plant communities on hills (both schists and sandstones) in the region and those on the Koolpinyah surface on the Ranger lease. He measured herbaceous plants quantitatively at 13 sites. For the herbaceous component, he found that there were natural plant communities on hills in the region that were very similar floristically to the vegetation in eucalypt woodlands on the Ranger lease. A summary of the herbaceous flora findings by Brennan (2005) include:


  • Ranger sites and all sandstone hills were dominated by Sorghum brachypodum. Sorghum accounted for almost 60% of the total seasonal production of herbaceous biomass at the Ranger sites. The species was absent on schist hills.

  • A further 20% of the total annual productivity (at the Ranger sites) was added by other grasses (22 species). Of these Heteropogon triticeus and Alloteropsis semialata were ‘high biomass’ species, but the short grasses, Schizachyrium fragile, Eriachne agrostidea, Eriachne ciliata, Thaumastochloa major, Digitaria gibbosa, Aristida holathera, Brachiaria holosericea, Mnesithea formosa, Sporobolus pulchellus Pseudopogonatherum irritans and Yakirra nulla each had high site frequencies.

  • There were several herbaceous species with high frequency amongst the Ranger sites and the schist sites eg Heteropogon triticeus, Schizachrium fragile, Mnesithea formosa, Alloteropsis semialata and Ipomoea graminea. However, only Heteropogon triticeus was noted as having high biomass on both site types.

The differences in species identified by Hollingsworth and Meek (2003) with Brennan (2005) can be attributed to the sites surveyed, and more importantly, the method of data reporting. For example, Hollingsworth and Meek (2003) identified many of the same grass species as Brennan (2005), but many of these grass species do not feature as a candidate species because of the criteria used to determine a candidate (ie those that occur in more than one replicate plot).

Species important for the rehabilitation of the RPA can be derived from the Ranger revegetation strategy of the trial landform, which include the following understory species (Daws et al 2008):



Aristida hygrometrica

Aristida holathera

Eragrostis sp

Eriachne shultziana

Psuedopogonantherum irritans

Schizachyrium fragile

Spermacoce sp

Daws et al (2008) probably deliberately exclude high biomass covers like Sorghum spp and Heteropogon spp in an attempt to reduce fire on the landform. Species may also have been selected for ease of germination and seed collection. In addition, Energy Resources of Australia (ERA) held a workshop on the Weeds at Ranger and defined those weeds of most concern to the Ranger Site, important weed species to the Ranger site and weed species not present, but important if found (EWL Sciences 2005):

Weeds of most concern to the Ranger site:

Andropogon gayanus (Gamba grass)

Calopognium mucunoides (Calopo vine)

Pennisetum polystachion (perennial Mission grass)

Pennisetum pedillatum (annual Mission grass)

Themeda quadrivalvis (Grader grass)

Other important species at RUM are:



Crotalaria goreensis (Gambia pea or Rattlepod)

Stachytarpheta spp (Snake weeds)

Sida acuta (Spinyhead sida)

Hyptis suaveolens (Hyptis)

Ipomoea spp (Morning glory vine)

Macroptilium atropurpureum (Siratro vine) and M. lathyroides (Phasey bean vine)

Senna alata (Candle bush)

Senna obtusifolia (Sicklepod)

Senna occidentalis (Coffee senna)

Passiflora foetida (Wild passionfruit vine)

Stylosanthes hamata (Carribean stylo)

Stylosanthes humilis (Townsville stylo)

Stylosanthes scabra (Shrubby stylo)

Cenchrus cilaris (Buffel grass)

Important species if found at RUM are:



Cenchrus echinatus (Mossman River grass)

Urochloa mutica (NT/WA) (Para grass)

Urochloa maxima (NT/WA) (Guinea grass)

3.1.3 Species of the Nabarlek area


A project was commenced by eriss in mid-2003 at the Nabarlek minesite to quantitatively assess revegetation performance since 1995, and to develop survey methodologies applicable to the future rehabilitation of the RPA. Canopy cover and ground cover vegetation were characterised on sample transects located on rehabilitated areas of the minesite and on adjacent natural reference sites, and compared. The results of the surveys conducted during a dry and wet season (Bayliss et al 2004b) are summarised in Table 1 and below.

Table 1 Plant species found on transects in the late wet season, May 2004 (Source Bayliss et al 2004b)



A total of 121 ground cover species were recorded during the wet season survey. Of these 34 (28%) were grasses, 73 herbs (60%) and 14 (12%) sedges. There were 11 (32%) weed grasses and 17 (23%) weed herbs.

Weeds comprised 48% of all species on the minesite.

Twice as many native grass species were found on reference sites than minesites Overall, five times more weed herb species were found on minesites compared with reference sites. However, there were three times more (native) sedge species on reference sites compared with minesites in both seasons.

Reference sites remain largely free of grass weeds that typify the minesite. The cover of native grasses on reference sites was about five times that of minesites and the cover of native grasses approximately doubled in both locations.

Similar dominance ratios for biomass were found as for percentage ground cover (ie grasses>>herbs>>sedges).

There was 5.5 times more native grass biomass on reference sites compared with minesites and, in contrast, 318 times more weed grass biomass on minesites compared with reference sites.

3.1.4 Priority target species


A summary of declared weeds, weeds of concern and ground covers of importance to RUM and Nabarlek are outlined in Table 2a–c. The list focuses on weeds and native grasses only, and further information on native herbs and sedges can be found in Hollingsworth and Meek (2003), Brennan (2005) and Bayliss et al (2004a & b).

Table 2a Summary of target weedy grass species important for Ranger, Nabarlek and weeds (declared/of concern)






Genus

Species

Ranger**

Nabarlek*

Weeds (declared/of concern)

Weedy grasses

Andropogon

gayanus







Cenchrus

cilaris









Cenchrus

echinatus









Chloris

inflata








Chloris

gayana









Chloris

virgata








Cynodon

dactylon








Echinochloa

colona









Melinis

repens








Paspalum

plicatulum









Pennisetum

pedicellatum







Pennisetum

polystachion







Setaria

sp









Sporobulus

sp









Themeda

quadrivalvis








Urochloa

humidicola









Urochloa

maxima








Urochloa

mutica








** identified by Brennan (2005), Hollingsworth and Meek (2003), EWLS (2005) and Daws et al (2008)

* identified by Bayliss (2004a & b)



Table 2b Summary of target weedy herb and vine species important for Ranger, Nabarlek and weeds (declared/of concern)




Genus

Species

Ranger**

Nabarlek*

Weeds (declared/of concern)

Weedy herbs and vines

Acanthospermum

hispidum









Aeschynomene

americana








Alysicarpus

vaginalis









Calopognium

mucunoides (vine)








Centrosema

molle (vine)









Crotalaria

goreensis








Euphorbia

heterophylla









Euphorbia

hirta









Hibiscus

sabdariffa









Hyptis

suaveolens







Ipomoea

graminea









Ipomoea

spp (vine)







Macroptilium

atropurpureum







Macroptilium

lathyroides







Passiflora

foetida (vine)







Senna

alata








Senna

obtusifolia








Senna

occidentalis








Senna

alata









Sida

acuta







Sida

cordifolia









Sida

rhombifolia









Stachytarpheta

spp








Stylosanthes

hamata







Stylosanthes

humilis








Stylosanthes

scabra








Stylosanthes

viscose









Tridax

procumbens









** identified by Brennan (2005), Hollingsworth and Meek (2003), EWLS (2005) and Daws et al (2008)

* identified by Bayliss (2004a & b)

Weedy ground covers, with an emphasis on grasses, were identified by stakeholders as the priority species for spectral measurement. The spectral identification and discrimination of these species is important to minesite applications because declared weeds in any location must be managed, weedy covers do not feature in the surrounding ecosystem of the RPA and the expanse of weedy covers at Nabarlek has hampered revegetation attempts and increased the threat of fire affecting framework species. The spectral identification and discrimination of weedy covers maybe relevant to other landscape applications. Native species that were co-located with dense and homogenous patches were targeted opportunistically. Native species will be more thoroughly addressed during the Ranger Trial Landform research.

Table 2c Summary of target native grass species important for Ranger and Nabarlek






Genus

Species

Ranger**

Nabarlek*

Native grasses

Alloteropsis

semialata






Aristida

holathera





Aristida

hygrometrica






Aristida

ingrate






Bothriochloa

bladhii






Brachiaria

holosericea






Chrysopogon

fallax






Dicanthium

fecundum






Digitaria

bicornis






Digitaria

gibbosa





Dimeria

ornithopoda






Ectrosia

agrostoides






Eragrostis

potamophila






Eragrostis

spartinoides






Eragrostis

sp






Eriachne

agrostidea






Eriachne

burkittii






Eriachne

ciliata






Eriachne

major






Eriachne

shultziana






Heteropogon

contortus






Heteropogon

triticeus





Imperata

cylindrical






Mnesithea

formosa






Pseudopogonatherum

contortum






Pseudopogonatherum

irritans





Pseudoraphis

spinescnes






Rottbeollia

cochinchinensis






Schizachyrium

fragile





Sehima

nervosum






Sorghum

brachypodum






Sorghum

intrans






Sorghum

plumosum






Sorghum

stipodeum







Spermacoce

sp






Sporobolus

pulchellus






Thaumastochloa

major






Yakirra

nulla





** identified by Brennan (2005), Hollingsworth and Meek (2003), EWLS (2005) and Daws et al (2008)

* identified by Bayliss (2004a & b)

Four pastoral grasses, with potential to become weeds, were identified at the Darwin Berrimah Research Farm. These grasses were represented as dense and homogenous patches and were located within a short walking distance making spectra of these species easily obtainable in a few hours of sampling. The opportunity to obtain temporal readings of these following four pastoral species was taken: Brachiaria humidicola (Tully grass), Digitaria eriantha (Pangola grass), Digitaria milanjiana (Jarra grass) and Digitaria swynnertonii (Arnhem grass).



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