Rehabilitation of open cut coal mines using native grasses

Rehabilitation of open cut coal mines using native grasses: Management guidelines

Prepared by Charles Huxtable

D e p a r t m e n t o f S u s t a i n a b l e N a t u r a l R e s o u r c e s

Cover illustrations, from left to right: • The spikelet of the native pasture grass,

Austrodanthania setacea. • A good stand of Taranna wallaby grass

(Austrodanthonia richardsonii) at Ravensworth mine, 1 year after sowing.

• A brush harvester for native grass seed built for the rehabilitation trials, and designed by J. Ryan of Cooma.

Acknowledgments Funded by the Australian Coal Association Research Program

(ACARP). Initiated by the Hunter Coal Environment Group. Thanks to Chris Nadolny and Ian Cole for reviewing the contents. Thanks to Evelyn Roberts for editing.

Published by: Centre for Natural Resources

Department of Sustainable Natural Resources

Parramatta

April 2003

© NSW Government ISBN 0 7347 5291 1 CNR2002.021

Contents

Page

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Why use native grasses? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Options for vegetation including native grasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Where to use native grasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Choosing suitable native grasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Selecting and sowing seed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Controlling weeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Managing native grasses on rehabilitation sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Further reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Table

Table 1. Recommended species for rehabilitation of coal mine spoil in the Hunter Valley . . . . . . 8


3


INTRODUCTION

These guidelines provide a brief summary of the species of Australian native grasses and their management that are recommended for rehabilitation of open cut coal mines in the Hunter Valley. The information is based on the results of 5 years of research carried out on mine sites during 1994–1999.

WHY USE NATIVE GRASSES?

Native grasses are a diverse group of plants with a range of attributes which make them important components of vegetation in the landscape. Because of their diversity, native grasses play an important role in mine rehabilitation as components of reconstructed vegetation communities and for a range of post-mining landuses. Native grasses are environmentally friendly, contribute to overall biodiversity and can be grown in association with native trees, shrubs and forbs (small broad-leaved plants) on minesites.

Some native grasses have a high forage value for livestock and can tolerate low soil fertility and drought. These attributes make them a desirable choice where land is intended for grazing after mining.

Introduced pasture species have been used for mine rehabilitation in the past, but compared to native grasses they have the following disadvantages:

• They can be costly to maintain. • They tend to need more fertile soil and to be less drought tolerant. • A pasture containing only Rhodes grass tends to develop when introduced pastures (which

usually include Rhodes grass) are not managed properly.

A trial of mixed species at Howick mine, 2 years after sowing. After 1 year, 17 native grasses and 7 native forbs were established at this site.


4


OPTIONS FOR VEGETATION INCLUDING NATIVE GRASSES

To rehabilitate land, native grasses can be grown alone or with trees and/or shrubs. Native forbs can also be included in pastures containing native grasses.

WHERE TO USE NATIVE GRASSES

• On topsoil that has been taken from pre-strip areas dominated by native grasses. • On areas with raw spoil, where topsoil is not available. • On areas of low fertility topsoil that contains few seeds from introduced plants.

These situations give native grasses a competitive advantage because the soil has one or more of the following features:

• few seeds of introduced plants • many seeds of native plants • low fertility.

Where there is a risk of soil erosion, other soil conservation measures may be necessary.

Although it was not sown, the native species blown grass (Lachnagrostis filiformis), was growing on a trial site at Ravensworth mine, in the spring of 1998. Native grasses can establish from reserves of seed in topsoil used for a rehabilitation site.

CHOOSING SUITABLE NATIVE GRASSES

Native grasses should be selected mainly for their ability to survive the local soil and climatic conditions on the mine sites. Species that originally grew locally are desirable, but are not essential.


5


Recommended species

Table 1 lists recommended species, their seasonal growth patterns, recommended sowing times and special attributes.

As many suitable species as possible should be sown, with a minimum of three warm season perennial (WSP) species and two year-long green perennial (YGP) species. Cool season perennial (CSP) and cool season annual (CSA) species can be added if they are available.

For raw spoil, the best YGP species are wallaby grasses and plains grass. The best WSP species is windmill grass. (Table 1 lists the scientific names.)

For saline, alkaline dispersible topsoil, the best YGP variety is Taranna wallaby grass; the best WSP species are Queensland bluegrass, native millet, windmill grass and couch.

For better quality topsoil (loam to loamy clays with slightly acid to neutral pH and low salinity), the best YGP species are wallaby grasses and plains grass. The best WSP species are Queensland bluegrass, pitted bluegrass, native millet, windmill grass, blown grass, umbrella grass and early spring grass. For highly acidic, sodic loamy sand, the best WSP species are wiregrass, pitted bluegrass, couch, slender rat’s tail and tall windmill grass.

Yanganbil grass (Austrostipa bigeniculata), a native, growing on raw spoil at Howick mine, 2 years after sowing.

Windmill grass (Chloris truncata) growing at Ravensworth mine, showing the level of groundcover 4½ years after sowing.

SELECTING AND SOWING SEED

When selecting and sowing native grass seed, consider:

• dormancy • viability • form of seed sown (degree of cleaning) • sowing depth • soil moisture • temperature.


6


Taranna wallaby grass growing on good topsoil at Preparation of a rehabilitation site at Howick Ravensworth mine. Mine, October 1997.

Pitted bluegrass (Bothriochloa decipiens) seed in it’s uncleaned form, as harvested by a brush harvester.

Diamond harrows were used to rake in wallaby grass seed after sowing at Howick mine.

To maximise establishment, consider:

• seed source and quality • sowing rate • sowing technique • multi-phase sowings and species diversity • fertiliser application at the time of sowing.

CONTROLLING WEEDS

Weed control is absolutely essential during the first year, and probably later also.

A herbicide with the active ingredients picloram and triclopyr (for example Grazon®*) can be used to control galenia, because that type of herbicide has little adverse effect on native grasses. Competition from Rhodes grass and couch is a major threat to establishment of sown native grasses. These plants can be spot sprayed with a post-emergent herbicide containing the active ingredients glyphosate, diuron or atrazine (for example Roundup®) or another post-emergent herbicide.

* Other suitable herbicides include 4Farmers Tri-Pick®, Generex Trichloram®, Picker® and Grass-Up®. Mention of the product names given in this brochure is not intended to imply endorsement of one product over another equivalent product. Herbicides should be used only as instructed by the directions on the container label.


7

Tabl

e 1.

Rec

omm

ende

d sp

ecie

s for

reh

abili

tatio

n of

coa

l min

e sp

oil i

n th

e H

unte

r Va

lley

Com

mon

nam

e Sc

ient

ific

nam

e#

Gro

wth

Sp

ecia

l fea

ture

s pa

ttern

Bun

derr

a w

alla

by g

rass

* Au

stro

dant

honi

a

YG

P G

ood

colo

nise

r, to

lera

tes

raw

spo

il, g

ood

fora

ge v

alue

, pre

fers

hea

vier

soils

, tol

erat

es g

razi

ng.

ringe

d w

alla

by g

rass

* A.

cae

spito

sa

YG

P G

ood

colo

nise

r, to

lera

tes

raw

spo

il, g

ood

fora

ge v

alue

, tol

erat

es g

razi

ng.

Hum

e w

alla

by g

rass

* A.

ric

hard

soni

i cv.

Hum

e Y

GP

Goo

d co

loni

ser,

tole

rate

s ra

w s

poil,

goo

d fo

rage

val

ue, t

oler

ates

gra

zing

. Ta

rann

a w

alla

by g

rass

* A.

ric

hard

soni

i cv.

Tar

anna

Y

GP

Goo

d co

loni

ser,

wid

e so

il to

lera

nce,

tole

rate

s ra

w s

poil,

goo

d fo

rage

valu

e, to

lera

tes

graz

ing.

smal

lflow

er w

alla

by g

rass

* A.

set

acea

Y

GP

Goo

d co

loni

ser,

tole

rate

s ra

w s

poil,

goo

d fo

rage

val

ue, t

oler

ates

gra

zing

. pl

ains

gra

ss*

Aust

rost

ipa

aris

tiglu

mis

or

YG

P G

ood

colo

nise

r, to

lera

tes

alka

linity

and

raw

spo

il, m

oder

ate

fora

ge v

alue

,A.

big

enic

ulat

a to

lera

tes

graz

ing.

spea

rgra

ss

A. s

cabr

a Y

GP

Goo

d fo

rage

val

ue w

hen

in g

reen

leaf

, dro

ught

tole

rant

, tol

erat

es g

razi

ng.

slen

der b

ambo

o gr

ass

A. v

ertic

illat

a Y

GP

Goo

d fo

rage

val

ue w

hen

in g

reen

leaf

, dro

ught

tole

rant

, tol

erat

es g

razi

ng.

shor

thai

r plu

meg

rass

D

iche

lach

ne m

icra

ntha

C

SP

Goo

d fo

rage

val

ue, g

erm

inat

es fr

om to

psoi

l see

d ba

nk.

com

mon

whe

atgr

ass

Elym

us sc

aber

C

SP

Very

hig

h fo

rage

val

ue, g

erm

inat

es fr

om to

psoi

l see

d ba

nk.

blow

n gr

ass

Lach

nagr

ostis

filif

orm

is

CSA

G

ood

colo

nise

r, go

od fo

rage

val

ue, g

erm

inat

es fr

om to

psoi

l see

d ba

nk.

wire

gras

s*

Aris

tida

ram

osa

WSP

Pr

efer

s lo

w fe

rtilit

y so

ils, p

oor f

orag

e va

lue,

dro

ught

tole

rant

, goo

dco

loni

ser.

re

dgra

ss/p

itted

blu

egra

ss*

Both

rioc

hloa

W

SP

Goo

d co

loni

ser,

smal

l pla

nt b

asal

are

a bu

t sur

vive

s dr

ough

t wel

l.

mac

ra/d

ecip

iens

win

dmill

gra

ss*

Chl

oris

trun

cata

W

SP

Goo

d co

loni

ser,

low

fora

ge v

alue

, dro

ught

tole

rant

, tol

eran

t of v

ery

poor

tops

oil a

nd ra

w s

poil,

sho

rt-liv

ed p

eren

nial

.ta

ll w

indm

ill g

rass

* C

hlor

is v

entr

icos

a W

SP

Goo

d co

loni

ser,

low

fora

ge v

alue

, dro

ught

tole

rant

, tol

eran

t of v

ery

poor

tops

oil a

nd ra

w s

poil,

long

-live

d pe

renn

ial.

barb

ed w

ire g

rass

C

ymbo

pogo

n re

frac

tus

WSP

Pr

efer

s po

or s

oils

, low

fora

ge v

alue

, sen

sitiv

e to

gra

zing

, ver

y dr

ough

tto

lera

nt.



8


Que

ensl

and

blue

gras

s*

Dic

hant

hium

seri

ceum

W

SP

Req

uire

s be

tter q

ualit

y to

psoi

l, pr

efer

s he

avie

r bla

ck s

oils

, mod

erat

efo

rage

val

ue, d

roug

ht to

lera

nt.

cotto

n pa

nic

gras

s D

igita

ria

brow

nii

WSP

G

ood

fora

ge v

alue

, pre

fers

bet

ter s

oils

, ger

min

ates

from

tops

oil s

eed

bank

. um

brel

la g

rass

D

igita

ria

diva

rica

tissi

ma

WSP

M

oder

ate

fora

ge v

alue

, pre

fers

bet

ter s

oils

, ger

min

ates

from

tops

oil s

eed

bank

. ea

rly s

prin

g gr

ass

Erio

chlo

a ps

eudo

acro

tric

ha

WSP

N

atur

ally

col

onis

es to

psoi

l and

raw

spo

il fr

om s

eedb

ank

or s

urro

unds

.M

ay b

e sa

lt-to

lera

nt. C

an fo

rm e

xten

sive

sta

nds

with

goo

d gr

ound

cove

ran

d go

od fo

rage

val

ue.

nativ

e m

illet

Pa

nicu

m d

ecom

posi

tum

W

SP

Mod

erat

e fo

rage

val

ue, p

refe

rs h

eavi

er s

oils

, may

be

salt

tole

rant

.ha

iry p

anic

Pa

nicu

m e

ffusu

m

WSP

G

ood

fora

ge v

alue

, ger

min

ates

from

tops

oil s

eed

bank

.

# Sc

ient

ific

plan

t nam

es a

ccor

ding

to W

heel

er, J

acob

s an

d W

halle

y 20

02.

CSP

=

cool

sea

son

pere

nnia

l. M

ost g

row

th a

nd s

eedi

ng o

ccur

s du

ring

cool

mon

ths.

The

plan

t liv

es fo

r mor

e th

an 1

yea

r.Y

GP

= ye

ar-lo

ng g

reen

per

enni

al. M

ost g

row

th a

nd s

eedi

ng o

ccur

s in

the

cool

er m

onth

s, bu

t the

pla

nt g

row

s th

roug

hout

the

year

, in

resp

onse

to ra

in. T

he p

lant

live

s fo

r m

ore

than

1 y

ear.

CSA

=

cool

sea

son

annu

al. T

he p

lant

ger

min

ates

, gro

ws,

seed

s an

d di

es d

urin

g th

e co

oler

mon

ths.

It liv

es fo

r onl

y 1

year

.W

SP

= w

arm

sea

son

pere

nnia

l. M

ost g

row

th a

nd s

eedi

ng o

ccur

s du

ring

war

m m

onth

s. Th

e pl

ant l

ives

for m

ore

than

1 y

ear.

An

aste

risk

(*) i

ndic

ates

spe

cies

whi

ch w

ere

sow

n du

ring

thes

e pr

ojec

ts.

Coo

l sea

son

pere

nnia

ls, y

ear-l

ong

gree

n pe

renn

ials

and

coo

l sea

son

annu

als

shou

ld b

e so

wn

in e

arly

to m

id-a

utum

n (M

arch

to A

pril)

.W

arm

sea

son

pere

nnia

ls s

houl

d be

sow

n in

ear

ly to

mid

-aut

umn

(Mar

ch to

Apr

il) o

r ear

ly s

prin

g (S

epte

mbe

r).


9

Cereal rye


MANAGING NATIVE GRASSES ON REHABILITATION SITES

Different species of native grasses respond differently to a variety of management techniques. Grazing, slashing burning and fertiliser application can be used to maintain the desired pasture composition and diversity, and minimise invasion by weeds and exotic grasses.

Grazing favours some species such as redgrass, Queensland bluegrass and wallaby grasses. However, grazing is harmful to other grasses such as barbed wire grass, kangaroo grass and native sorghum. High intensity grazing for short periods (such as in time-control cell grazing) provides the most uniform defoliation, forcing animals to eat both palatable and unpalatable species.

Slashing has similar effects, but lacks the selectivity of low intensity grazing. Compared to grazing, slashing also lacks the effects of addition of urine and manure, and soil disturbance by hoofs.

BBuunnddeerrrraa

Cereal rye

Bunderra wallaby grass 6 months after it was sown with a cover crop of cereal rye at Rix’s Creek mine.

GGaalleenniiaa SSaallssoollaa

A severe infestation of the weeds galenia (Galenia pubescens) and soft roly poly (Salsola tragus) at a rehabilitation trial site.

Burning was one of the methods used to control Rhodes grass (Chloris gayana) before native grasses were sown in a rehabilitation trial at Warkworth mine in October 1998.

Some native grasses are able to compete with vigorous introduced grasses such as this self-sown slender bamboo grass (Austrostipa verticillata) growing amongst phalaris and Rhodes grass sown at Howick mine 5 years earlier.


10


Low intensity burning benefits kangaroo grass by reducing the amount of dead material and stimulating new leaf growth and seed germination.

FURTHER READING

Huxtable, C. H. A. 1999, Rehabilitation of open-cut coal mines using native grasses: Management guidelines, final report to the Australian Coal Association Research Project (ACARP), ACARP Report No. C6004. AMIRA. Melbourne.

Huxtable, C. H. A., Sawicki, A. J. and Streat, J. 1997, Rehabilitation of open-cut coal mines using native grasses, final report to the Australian Coal Association Research Project (ACARP), ACARP Report No. C3054. AMIRA. Melbourne.

Waters, C., Whalley, W. and Huxtable, C. 2000, Grassed-up: Guidelines for revegetating with Australian native grasses, NSW Agriculture.

Wheeler, D. J. B., Jacobs, S. W. L. and Whalley, R. D. B. 2002, Grasses of New South Wales, 3rd edn, Botany, School of Environmental Sciences and Natural Resource Management, University of New England, Armidale NSW, 2351.


11

Documents

Rehabilitation of open cut coal mines using native grasses