03-056 - corella research project - final report

Appendix H

Tree health surveys by Arbortech Pty Ltd, December

2002 and April 2003

Dr Andrew Fisher Senior Ecologist QED Pty Ltd PO Box 7088 Hutt Street Adelaide5000

18th February 2003

Re: Corella Research Project: Impacts on selected trees.

INTRODUCTION:

Damage to significant trees by Corellas on the Fleurieu Peninsula and elsewhere in South Australia has raised community concerns that the destructive habits of these native birds may adversely impact long-term tree viability.

At the request of Dr Andrew Fisher of QED, I visited three locations in mid December 2002 to make Arboricultural assessments of 14 selected trees. The intention of this work is to return late in autumn and make a follow-up assessment of the same trees.

The chosen sites were:

Old Noarlunga:1.Market Square Reserve. (4 trees)

2.Hutchinson Reserve. (2 Trees)

Strathalbyn:3.Soldiers Memorial Gardens and Rotary Park. (10 trees)

FINDINGS:

The full survey results are detailed at the end of this report. The survey included information on:

• Reference and location.

• Age & life expectancy.

• Tree dimensions.

• Present health and structural condition.

• Corella impacts on tree health.

• Maintenance recommendations.

Accompanying the survey is a spreadsheet with information used to calculate an amenity value for each tree in the survey, using the Draft Australian Standard, DR 99307.

Amenity tree values range from $1,200 for a poor condition Sugar Gum to $76,800 for the Moreton Bay Fig in the swimming pool grounds at Soldiers Memorial Park in Strathalbyn.

The average tree value was $26,142.

Of the 14 trees assessed, none are immediately endangered by Corella damage at this time.

The type of injury inflicted by the birds may impact on tree health over time, but is highly unlikely to cause tree death regardless of the severity of the attack in any one season. See ‘Discussion’ for further information.

Four trees carry symptoms of stress associated with previous root system damage or root zone degradation. These include:

• The Moreton Bay Fig in the swimming pool enclosure at Soldiers Memorial Gardens.

• The Canary Island Pine in the Soldiers Memorial Gardens.

• The Aleppo Pine in the Soldiers Memorial Gardens.

• The Sugar Gum in the traffic island adjacent to Soldiers Memorial Gardens.

Separating the impact of previous injury/s from decline caused by Corella injury alone will be difficult in these cases.

Of the remaining 10 trees assessed, only the aesthetic viability of the Norfolk Island Pine

and the short-term viability of the Stone Pine in the Solders Memorial Gardens are directly threatened by bird damage. Repeated defoliation and bark chewing by Corella’s has killed many limbs in both trees. The steady decline in their condition will continue while the impact of Corella injury on tree crowns persists.

The existing damage to the Norfolk Island Pine is not serious enough to result in the death of this specimen. However the impact of foliage stripping by the birds on the trees form is perilously close to being permanent. The top of the tree and much of the eastern side are dead or dying. Once the dead limbs are removed, the tree will be disfigured and will not regain its original shape, regardless of circumstance.

The Stone Pine on the other hand has no capacity to regenerate from dormant buds beneath the bark and limited energy reserves with which to produce new foliage from the areas that remain alive. The tree is also approaching the limit of its safe useful life expectancy in the reserve. It has dubious structure and therefore the potential for major structural collapse will increase as tree condition deteriorates. Regardless of circumstance, the Stone Pine has at best 20 years remaining before it will have to be removed on safety grounds. If the Corella damage continues unabated at the same levels, the tree will most likely be dead within 5-10 years as it runs out of energy and the root system degenerates to the point of no return.

DISCUSSION:

The level of Corella damage being sustained by the majority of the survey trees is not life threatening and is likely to vary with the seasons, depending upon factors influencing their movement patterns.

The bird damage is occurring in combination with other growth limiting factors, such as root zone degradation, root competition, increasing age, site disturbance, pests and disease etc.

A feature of many adverse tree growth influences is the variation in the degree or extent of the problem over time.

As an example, one of the most prominent growth-limiting factors for many tree species in South Australia is moisture availability.

Each year the majority of trees experience dry periods of varying severity and duration. Most commonly used park species have some level of drought tolerance and can adapt to the fluctuating moisture conditions and summer temperature extremes with relative certainty of survival into better times. The symptoms of prolonged moisture stress become increasingly obvious with the length of drought conditions. However trees will recover within a few years depending upon the severity of conditions.

The predation of Eucalypts by the River Red Gum Basket Lerp, Cardiaspina retator is another factor that varies enormously with the seasons, inflicting large-scale defoliations of many Eucalyptus species across great swathes of southeastern Australia. In the vast majority of cases the trees survive repeated attacks over several years in concurrence with few ill effects.

It is only where trees are weakened by other factors such as drought, or repeat annual defoliation occurs over extended periods without respite, that Lerps can be a catalyst for tree decline.

Damage by Corellas is another seasonal factor, impacting upon trees to varying degrees depending upon the season and this problem should be viewed in a similar light to drought or Lerp attack.

• Most healthy trees will be able to withstand partial or total defoliation and some degree of bark damage and still recover sufficiently in the intervening period between seasonal events. Trees must maintain their energy reserves at a level sufficient to ensure adequate resources are available for all metabolic and growth needs.

• All of the trees in the survey not affected by soil level changes or root system damage have the capacity to recover from the damage, with the possible exception of the Stone Pine in the Soldiers Memorial Gardens. Given respite from the damage they would regain their vigour over time despite previous bird injury over many years.

• Rarely if ever will bird damage result in outright tree death. Where trees do die, one or more other factors, such as old age, root system damage or dysfunction, disease, drought, etc, will reduce the trees ability to respond to the demand for new growth as a result of defoliation or bark injury by animals.

• The death of individual branches is more common. ‘Stag headed’ specimens of Sugar Gum, Eucalyptus cladocalyx and occasionally River Red Gum,Eucalyptus camaldulensis do occur where bird numbers are great. The branch extremities of Norfolk Island Pine, Araucaria heterophylla are commonly killed by repeated Corella attack.

• Species with no capacity to regenerate new growth from epicormic buds beneath the bark are at greater risk of individual branch death as a result of defoliation. The majority of limbs that are ringbarked by birds will die regardless of the species affected.

The long-term impact of bird or animal damage will depend upon the individual species growth characteristics, general tree health and vigour, the duration and severity of attack, the level of carbohydrate reserves in the tree and how often the defoliation or injury cycle is repeated.

RECOMMENDATIONS:

Tree Health:

The preservation of tree vigour (the ability of a tree to respond to good conditions) is a vital component of tree management, enabling trees to recover from the ongoing impacts of bird, animal, root system, disease, insect or other damage.

Acceptable tree vigour also provides the regenerative and protective capacity to enable the effective management of tree crowns for safety.

Maintaining and improving tree vigour requires specific management actions in line with best practice Arboriculture, involving:

1. Irrigation management tailored to the needs of individual trees.

• The operation of the irrigation systems in all three locations should be appraised for their necessity, suitability and effectiveness.

• No water should come into direct contact with tree trunks during irrigation under any circumstances.

2. Where possible and practical, the surrounding growing areas should be managed for minimum root system competition and improved to encourage further root growth. In most cases this will require changes to existing circumstances.

• Turf areas around trees should be examined for opportunities to create low maintenance garden beds or mulched zones over all or part of the root zone.

3. Preventing adverse changes within the root zone of mature trees is another important factor in preserving long-term tree health. Any disturbance within the root zone such as trenching for irrigation installation or repairs, or soil level changes should be appraised carefully for their impact on root systems and tree health prior to the work taking place. Site disturbance or root system damage once every decade or two may cause sufficient injury to impact on the long-term health and vigour of trees

4. Yearly monitoring of trees by an Arborist should be undertaken to determine their health and safety needs. This will facilitate proactive intervention in declining health and vigour, tree structure or pest and disease issues where they occur, to minimise health impacts.

In my view the moderate to low vigour of trees in the majority of areas examined reflected increasing tree age and growing environments not conducive to good root growth. There are also deficiencies in the provision of stable growing environments and good quality Arboricultural care. The bird damage adds to the stress levels, compounding the negative outcomes of other issues.

This broadly based problem could be addressed through the development of more comprehensive tree management strategies for all public parks to improve the whole spectrum of amenity tree care practices, resulting in improved tree condition.

Tree Replacements:

Replacement trees should be established in two of the sites surveyed.

1. In Market Square the Pinus halepensis are aging and have short useful life expectancies.

2. Several trees in the Soldiers Memorial Gardens are declining and other trees should be established to take their place.

Their replacement with species of the same stature should be a priority.

Prospective species with similar characteristics and tolerances could include:

• Pinus canariensisCanary Island Pine

• Pinus pineaStone Pine

• Araucaria heterophyllaNorfolk Island Pine

• Araucaria cunninghamiana Hoop Pine

• Cupressus macrocarpaMonterey Cypress

• Ficus macrophyllaMoreton Bay Fig

• Ficus rubiginosaPort Jackson Fig

• Ficus microcarpa ‘Hillii’Hill’s Weeping Fig

• Eucalyptus camaldulensisRiver Red Gum

• Eucalyptus maculataSpotted Gum

• Quercus ilexHolm Oak

• Quercus suberCork Oak

A word of caution: If new trees are to establish rapidly and

succeed in the medium to long-term a number of common tree

establishment pitfalls must be avoided. These relate to the quality

of stock purchased, site preparation and planting detail as well as

follow-up management practices. I would urge those persons

concerned to contact either myself or another qualified Arborist

for specific tree establishment advice prior to taking any action.

Minimising Tree Damage by Corellas:

A range of monitoring, disruption and deterrent strategies could be undertaken to minimise the long-term health impacts to trees by seasonal bird damage.

These may include but are not limited to:

1. Regular culling. (various methods)

2. The use of bird scarers.

Gas Guns.

Predatory Bird Call Systems.

Some degree of damage to trees by birds must be accepted in the circumstances.

Finding a combination of measures that can prevent the annual bird damage from exceeding a tolerance threshold is desirable.

Establishing a local council officer to monitor and record bird numbers will enable predetermined action/s to be taken when the threshold is reached.

Determining the threshold for action will require careful monitoring of the relationship between tree damage, bird numbers and their destructive behaviour for at least one full season. Realistically, this could only be accomplished by a person with the appropriate skills, training and time for such an intensive task, in cooperation with Arboricultural and Environmental professionals.

When the collected data is evaluated, a tolerance threshold could be determined that will provide a basis for the future management of problem.

Meanwhile, the establishment of many more trees in all areas affected by tree decline issues should be a priority.

Such a program is essential to help minimise the visual impact of tree losses on the landscape over time, whatever the cause of tree decline.

A broad range of suitable species, successfully established in multi-aged stands should be the intended long-term outcome of the planting program.

If you have any further queries regarding issues raised in this report please feel free to contact me on 82542905 in the office during work hours, or on 0418831445.

Yours sincerely

Kym Knight Adv. Dip. of Arboriculture, Adv. Cert. of Arboriculture, Adv. Cert of Horticulture. MAIH Principal Consulting Arborist, Arbortech Tree Services Pty Ltd.

NB: Assessments and surveys completed by Arbortech Tree Services staff, aim to represent the site circumstances, conditions of trees and property, as well as any inter-relationships between these factor, objectively and to the best of our ability.

Tree 1. River Red Gum: Hutchinson Reserve, Old Noarlunga. 17/12/02

Tree 2. River Red Gum: Hutchinson Reserve, Old Noarlunga. 17/12/02.

Tree 3. River Red Gum: Old Noarlunga, Market Square Reserve. 17/12/02

Tree 4. River Red Gum: Market Square Reserve, Old Noarlunga. 17/12/02

Tree 5. Aleppo Pine: Market Square Reserve, Old Noarlunga. 17/12/02

Tree 6. Aleppo Pine: Market Square Reserve, Old Noarlunga. 17/12/02

Tree 7. White Poplar: Soldiers Memorial Gardens, Strathalbyn. 17/12/02

Tree 8. Aleppo Pine: Soldiers Memorial Gardens, Strathalbyn. 17/12/02

Tree 9. Moreton Bay Fig: Soldiers Memorial Gardens, Strathalbyn. 17/12/02

Tree 10. Lilly Pilly: Soldiers Memorial Gardens, Strathalbyn. 17/12/02

Tree 11. Stone Pine: Soldiers Memorial Gardens, Strathalbyn. 17/12/02

Tree 12. Canary Island Pine: Soldiers Memorial Gardens, Strathalbyn. 17/12/02

Tree 13. Norfolk Island Pine (right): Soldiers Memorial Gardens, Strathalbyn. 17/12/02

Tree 14: Sugar Gum: On traffic island adjacent to Soldiers Memorial Gardens, Strathalbyn. 26/1/03

Tre

e R

ef.

S

pecie

s

Ag

e

Lif

e e

xp

. Y

rs.

Tru

nk

cir

c.

Cro

wn

d

ia.

Tre

e

he

igh

t T

ree H

ealt

h

Tre

e s

tru

ctu

re

Co

rell

a Im

pacts

B

asic

main

t. r

eq

S

pecif

ic

main

t. r

eq

T

ime

1.

Hutc

hin

son

Res.

Euc

alyp

tus

cam

aldu

lens

is

120+

61-1

00

4m

21m

20m

Ave

rage.

Modera

te

vigour.

Som

e d

ead

limbs.

Thin

nin

g c

row

n.

Bore

rs in m

ain

tru

nk

to

west.

New

gro

wth

flu

sh

initia

ted.

Sin

gle

tru

nk.

Multip

le leaders

fr

om

4m

.

Dead b

ranch e

nds

in c

entr

al

& w

este

rn c

anopy.

Part

ially

defo

liate

d. Low

Im

pact

on

health a

nd v

igour.

Cro

wn lift ove

r ro

ad.

Rem

ove

dead w

ood

ove

r 40m

m.

Reduce

horizo

nta

l lim

bs

x 20%

fo

r safe

ty.

Impro

ve s

ite

managem

ent.

4

2.

Hutc

hin

son

Res.

Euc

alyp

tus

cam

aldu

lens

is

120+

61-1

00

2.9

15m

14m

21m

Good.

Modera

te

vigour.

M

odera

te

leve

ls o

f dead w

ood.

New

gro

wth

flu

sh

initia

ted.

Sin

gle

tru

nk.

Tw

in

leaders

.

Low

Im

pact on h

ealth a

nd

vigour.

P

art

ially

defo

liate

d

to e

ast

.

Rem

ove

dead w

ood

ove

r 50m

m.

None.

2

3.

Mark

et

square

res.

Euc

alyp

tus

cam

aldu

lens

is

100

21-4

0

4.8

m

24m

26m

Ave

rage.

Modera

te

vigour

in m

ost

part

s.

Low

er

on t

he w

este

rn

& n

ort

hern

sid

es.

Mundulla

Yello

ws lik

e

sym

pto

ms

pre

sent

to

NE

.

Sin

gle

tru

nk.

Multip

le leaders

. P

revi

ous h

ist. o

f fa

ilure

. Lim

b o

ver-

ext

ensio

n.

A f

ew

dead b

ranch e

nds.

Min

or

health im

pacts

. P

art

ially

defo

liate

d in

weste

rn h

alf.

New

flu

sh o

f gro

wth

occ

urr

ing.

Conve

rt s

ect

ion o

f car

park

and t

urf

to

mulc

hed g

ard

en b

ed.

Rem

ove

dead w

ood.

Contr

ol lim

b

weig

ht

2yr

ly x

15%

re

ductions.

R

educe

horizo

nta

l lim

bs

x 20%

.

6

4.

Mark

et

Square

R

es.

Euc

alyp

tus

cam

aldu

lens

is

100

61-1

00

4.0

5m

28m

N

S.

20m

E

W.

26m

Good.

Modera

te

vigour.

Larg

e

dead

wood.

Inte

rnal

epic

orm

ic r

egro

wth

. O

ld b

ore

r w

ounds o

n

low

er

trunk.

Sin

gle

tru

nk.

Multip

le leaders

. Low

bark

in

clu

sio

n.

Pre

viously

lopped

at

4m

.

Min

or

health im

pact. S

mall

term

inal dead w

ood.

Lots

of

epic

orm

ic r

egro

wth

on

bra

nch e

xtre

miti

es.

Good

folia

ge c

ove

r.

Mulc

h a

rea. R

em

ove

dead w

ood.

Reduce

horizo

nta

l lim

bs

x 20%

5

5.

Mark

et

Square

R

es.

Pin

us

hale

pens

is

100+

10 t

o 2

0

1.7

3m

15m

16m

B

elo

w A

vera

ge L

ow

vi

gour.

Sin

gle

tru

nk.

Larg

e

sid

e li

mbs. H

igh

cro

wn.

Modera

te h

ealth im

pacts

. P

art

ially

defo

liate

d lim

bs.

D

am

age to w

este

rn s

ide

most

notic

eable

. A

ffect

ed

bra

nches u

nlik

ely

to

recove

r.

Rem

ove

larg

er

dead

wood t

o im

pro

ve

appeara

nce.

Nearing t

he

end o

f its

usefu

l life.

Pla

n to

repla

ce.

3

6.

M

ark

et

Square

R

es.

Pin

us

hale

pens

is

100+

10 t

o 2

0

2.1

5m

17m

17m

B

elo

w A

vera

ge L

ow

vi

gour.

S

ingle

tru

nk.

Larg

e

sid

e li

mbs.

Part

ially

defo

liate

d.

Dead

bra

nch e

nds

thro

ughout

cro

wn.

Reasonably

serious

health im

pacts

thro

ugh

ongoin

g p

redation.

Rem

ain

ing f

olia

ge t

hin

.

Rem

ove

dead w

ood

and b

ranch s

tubs t

o

impro

ve a

esth

etics

.

Nearing t

he

end o

f its

usefu

l life.

Pla

n to

repla

ce.

3

7.

Mem

orial

Gard

ens

Pop

ulus

alb

a 60

41-6

0

2.2

8m

13m

13m

G

ood.

Modera

te

vigour.

New

gro

wth

flush.

Sin

gle

tru

nk.

Larg

e

sid

e li

mbs.

Larg

e

dead w

ood in

upper

cro

wn.

Sm

all

dead b

ranch e

nds

ove

r m

ost of

the c

row

n.

Min

or

health im

pact.

Part

ially

defo

liate

d b

ut

recove

ring w

ell.

Sum

mer

irrigation.

Main

tain

sta

ble

gro

win

g c

onditio

ns in

root

zone.

Rem

ove

dead w

ood.

2

8.

Mem

orial

Gard

ens

Pin

us

hale

pens

is

100

10 t

o 2

0

2.4

7m

12.5

m

20m

A

vera

ge.

Low

vig

our.

R

oot

sys

tem

buried b

y la

ndscapin

g.

Sin

gle

tru

nk w

ith

heavy

cro

wn b

ias

to w

est.

Sm

all

needle

s, thin

upper

cro

wn.

Min

or

health im

pact.

A f

ew

dead b

ranch e

nds.

Short

usefu

l life

-span.

Pote

ntial fo

r w

hole

tre

e

failu

re a

s la

rger

str

uctu

ral ro

ots

decay.

Pla

n to

repla

ce.

_

9.

Mem

orial

Gard

ens

Ficu

s m

acro

phyl

la

130

10 t

o 2

0

6.5

m

23.5

m

23m

Belo

w A

vera

ge.

Low

vi

gour

in m

ost

part

s of

the c

row

n.

Epic

orm

ic

regro

wth

form

s m

uch

of

the f

olia

ge. P

revi

ous

root

sys

tem

dam

age.

Bark

inclu

sio

ns

betw

een leaders

and m

ultip

le

leaders

form

a

weakened

str

uctu

re.

Som

e d

ead b

ranch e

nds.

Modera

te h

ealth im

pact

resultin

g fro

m p

revi

ous r

oot

sys

tem

dam

age c

om

bin

ed

with b

ird d

am

age. P

art

ially

defo

liate

d in

east

ern

upper

half. T

he tre

e h

as

limited

capacity

to r

ecove

r.

Rem

ove

dead w

ood.

Sta

bili

ze c

onditi

ons

within

the r

oot

zone.

Reduce c

row

n m

ass

by

20%

where

vig

our

perm

its

Pla

nt a

repla

cem

ent

tree A

SA

P.

6

10.

Mem

orial

Gard

ens

Ara

ucar

ia

hete

roph

ylla

120+

10 t

o 2

0

3.7

m

15m

29m

Poor.

Low

vig

our.

Very

th

in c

row

n.

Sm

all

leave

s. E

pic

orm

ic

spro

uting.

Sin

gle

str

aig

ht

trunk.

Larg

e d

ead

wood.

Majo

r health im

pacts

. B

ranches

alm

ost bare

on

easte

rn h

alf.

Sm

all

tuft

ed

epic

orm

ic r

egro

wth

on m

ost

limbs.

T

erm

inal is

dead.

30%

folia

ge c

ove

r.

Sym

metr

ical t

ree form

is

lost. L

imited c

apacity

to

recove

r am

enity

valu

e.

Rem

ove

tota

lly d

ead

limbs

Pla

n to

repla

ce.

4

11.

Mem

orial

Gard

ens

Syz

gium

pa

nicu

latu

m

100

21-4

0

1.4

7m

7

11m

G

ood.

Low

vig

our.

S

om

e n

ew

gro

wth

.

Sin

gle

tru

nk.

Bark

in

clu

sio

n a

t base

of

low

lim

b.

Dead b

ranch e

nds

mostly

to

east .

Modera

te to h

igh

health im

pact. H

eavi

ly

defo

liate

d in

upper

cro

wn.

Good c

apaci

ty to r

ecove

r.

Rem

ove

dead li

mbs.

Reduce

horizo

nta

l lo

w

limb x

25%

. 2.5

12.

Mem

orial

Gard

ens

Pin

us p

inea

120+

<10 w

ith

birds.

15-2

0w

ithout.

5m

26m

22m

P

oor.

Low

vig

our.

Sin

gle

tru

nk.

Bark

in

clu

sio

ns.

Multip

le

leaders

. Larg

e

dead w

ood

Many

dead b

ranches &

dead b

ranch e

nds.

Majo

r health im

pacts

. T

ota

lly

defo

liate

d o

n t

he e

aste

rn

sid

e.

Spars

e f

olia

ge o

ver

the

rem

ain

ing c

row

n.

Litt

le o

r no

capacity

to r

ecove

r.

Rem

ove

larg

e d

ead

wood f

or

safe

ty.

Pla

n to

repla

ce.

8

13.

Mem

orial

Gard

ens

Pin

us

cana

riens

is

120+

21-4

0

2.4

m

13m

25m

B

elo

w a

vera

ge.

Low

vi

gour.

Fill

ove

r ro

ot

sys

tem

.

Sin

gle

tru

nk.

Larg

e

dead w

ood

Dead b

ranch t

ips.

Min

or-

modera

te h

ealth im

pact.

Thin

nin

g f

olia

ge o

n e

aste

rn

& s

outh

ern

sid

es.

Rem

ove

dead w

ood.

2

14.

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orial

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ARBORTECH Tree Services P/L

SOUTH AUSTRALIANSOCIETY OFARBORICULTURE

Founding Member 1998

ASSA

Arboricultural contractors and consultants

PO Box 25, Cockatoo Valley, 5351. Tel./Fax 08 82542905 Mobile 0418 831445 E-mail: [email protected]

A.B.N. 85 050 167 470

CORELLAS & TREE DAMAGE ON THE FLEURIEU

PENINSULA

Final report on Corella damage inStrathalbyn and Old Noarlunga.

Additional information ontree condition at selected sites in Willunga.

April 2003

Report Prepared by:

Kym Knight. Adv. Dip. of Arboriculture, Adv. Cert. of Arboriculture, Adv. Cert of Horticulture. MAIH. Principal Consulting Arborist, Arbortech Tree Services Pty Ltd.

Arbortech Tree Services Pty Ltd – Corella Tree Damage Assessment: April 2003


List of Contents:

Page No.

Introduction. 3

Findings. 4

Comparative Photographs of study Trees 1-14.4-10

Outcome of the Corella Tree Impact Study.11

Amenity Tree Valuations. 12

Tree Health Assessments, Reserves:

Soldiers Memorial Gardens. 14

Market Square Reserve. 15

Hutchinson Reserve. 16

Willunga Recreation Reserve. 16

Willunga Park: West of Railway Terrace. 17

Station Road & Main Road adjacent to Willunga Primary School. 17



INTRODUCTION:

In Mid December 2002 I carried out a survey of Corella damage to 14 selected trees at 3 sites on the Fleurieu Peninsula. Refer to our report dated 18th February 2003 for additional details.

I made follow-up assessments of tree health and Corella impacts for the same specimens in mid April 2003.

Site locations included:

Old Noarlunga:1.Market Square Reserve. (4 trees)

2.Hutchinson Reserve. (2 Trees)

Strathalbyn:3.Soldiers Memorial Gardens and Rotary Park. (10 trees)

In addition to assessing the specific trees in these areas, I have also been requested to comment on the general health of trees in these reserves, as well as in three reserves not previously assessed at the nearby township of Willunga.



FINDINGS:

Corella numbers at the originally selected locations in Strathalbyn and Old Noarlunga must have been reduced significantly compared to previous years, judging by the lack of tree impacts recorded during my second assessment.

The extent of bird damage has not been as high as anticipated and in most cases tree condition was unchanged or slightly better in the follow-up assessment than in the first. While this might seem to have negated the value of the study to some degree, there are also very positive outcomes for tree and Corella management.

The following photographs demonstrate the limited changes that have occurred in the selected trees between December (left) and April (right).

Tree 1: Minimal changes in tree appearance were perceivable. The apparent greater foliage density in the photo is attributed to the light conditions. No obvious change in tree appearance has taken place due to Corella damage.



Tree 2: Also with minimal changes in appearance. The apparent foliage density differences in the photo are attributed to the light conditions at the time the photo was taken. No negative changes in tree appearance or health could be noted or attributed to Corella’s.

Tree 3: This specimen also had no obvious change to tree appearance or health that could be attributed to Corella’s.



Tree 4: A minor change in tree appearance was notable in the River Red Gums assessed in Market Square Reserve. However the tree had been pruned between assessments. There was no noticeable Corella damage.

Tree 5: No change in appearance or health status was evident as a result of Corella predation in the pines at Market Square Reserve, Old Noarlunga.



Tree 6: No change in the appearance or health status was evident in the large Aleppo Pine in the photo at Market Square Reserve as a result of Corella activity.

Tree 8: No change in appearance or health status could be seen in the White Poplar at Soldiers Memorial Gardens as a result of Corella predation.



Tree 9: There was a significant improvement in the appearance of the Moreton Bay Fig at the Soldiers Memorial Gardens, with thicker foliage in higher sections of the crown and considerable epicormic regrowth along many stems. No Corella damage could be noted.

Tree 10: Few positive changes were noted for the Norfolk Island Pines in the Soldiers Memorial Gardens. The remaining foliage is responding very slowly to the reduced predation levels. It was very marginally thicker than noted during the first assessment in December.



Tree 11: There were positive changes in appearance of the Lilly Pilly, with significantly greater foliage density in higher section of the crown and little sign of recent Corella damage.

Tree 12: There were minor positive changes in appearance of the Stone Pine in the Soldiers Memorial Gardens. The tree had slightly improved foliage density in those areas still living. The prognosis for the future this tree remains poor.



Tree 13: The Canary Island Pine at the Soldiers Memorial Gardens remains essentially unchanged from the original assessment. No Corella damage could be noted.

Tree 14: The health and appearance of the Sugar Gum in the study had declined during the assessment period. This was due to the impact of recent earthworks around the tree and its declining overall condition resulting from previous poor pruning and inappropriate root zone treatments.



STUDY OUTCOME:

The respite from Corella damage over the past summer experienced by the trees in Old Noarlunga and Strathalbyn has made several factors abundantly clear:

1. It is difficult to anticipate with any degree of accuracy the location and extent of damage to trees caused by Corella’s. This factor means the plans for any future Corella impact assessments should be flexible.

2. The majority of trees affected by Corella’s have the capacity to recover relatively quickly, provided other over-riding health limiting elements are not contributing to reduced tree condition.

3. Where serious health limiting factors are impacting on trees, such as previous or ongoing root system damage, soil level changes, excessive soil compaction or excessive/poor quality pruning, the combined effects of Corella’s can contribute to a further decline in overall tree condition.

4. Long-term repeat Corella damage may adversely affect the health and chances of recovery of highly favoured species in prominent locations. i.e. Norfolk Island Pines. These trees are the exception to the rule and specific strategies should be devised to minimise the effect of Corella damage to them where warranted.

My examination of trees affected by Corella’s at the survey sites and many others recently has led me to the conclusion that Corella’s are a people problem rather than a tree problem. The effects on trees are but a small part of a much wider issue.

Corella’s cause considerable angst in the community for many reasons including:

• Noise pollution • Faecal pollution • Localised large amounts of leaf litter • Localised blocked gutters and drains • Adverse aesthetic tree impacts • Perceived adverse tree health impacts • Damage to houses, covered cables, ovals and other public spaces and property.

I believe the resolution of the communities concerns over the Corella issue can only be successful through a multi-faceted approach to the problem, combining a broad community education program with other more specific strategies to limit damage to trees and infrastructure where needed.

As stated in my previous report, further work is required to monitor bird numbers relative to tree, infrastructure or other damage and assess the broader community impacts before an effective strategy could be devised to limit the scale and consequences of urban Corella populations.



AMENITY TREE VALUATIONS:

I included a tree valuation for each specimen in the study in my previous report, using the Draft Australian Standard DR 99307, Amenity Trees-Guide to Valuation, non-replacement method (a) to community.

The details of how the value is arrived at is as follows:

Points Factor

1 2 3 4 1. Size of Tree Small Medium Large Very

Large 2. Useful Life Expectancy 10-20 yrs 20-40 yrs 40-100 yrs 100+ yrs 3. Importance of position in the landscape

Little Some Considerable Great

4. Presence of other Trees Many Some Few None 5. Relation to Setting Barely Suitable Fairly Suitable Very Suitable Especially

Suitable 6. Form Poor Fair Very Suitable Especially

Good 7. Special Factors None One Two Three

The amenity value of a tree is calculated by selecting the appropriate values from each category and multiplying them together. 1 point represents $50 AUS.

Information used to determine the appropriate value in each category is as follows:

1. The tree height multiplied by its crown diameter (in metres) provides the value used to determine which size category the tree falls into, with values from 1-4, from the smallest to the largest tree.

2. The useful life expectancy must be determined by a competent Arborist. It takes a wide range of factors into account, such as tree age, tree location, structure, safety, pruning tolerance, species longevity etc, to arrive at a figure that falls into one of the four categories.



3. The importance of a trees position in the landscape is determined by the following.

Little Importance Some trees in rural areas, or in groups of trees etc.

Some Importance Individual roadside trees in urban areas, back yards, trees close to busy roads, trees in public parks, pseudo-street trees, etc.

Considerable Importance Prominent individual trees in well frequented places such as town centres, shopping centres, etc.

Great Importance Trees which are of crucial importance to well known places.

4. Presence of other trees.

Many More than 30% of the visual area covered by trees and at least 10-20 trees in total.

Some More than 10% of the visual area covered by trees, and at least 4-9 trees in total.

Few Less than 10% of the visual area covered with trees but at least 1-3 other trees present.

None No other trees present in the visual area

5. The relation of species to the setting is more difficult to define. As a general rule one should have the largest and densest tree, or group of trees, that the available space will conveniently contain. Small trees in large spaces or large trees in small spaces reduce the value. The requirements for light and suitability of form within the context of the space and its function also need to be considered.

6. Tree form is based on a structural judgement relative to tree genetics, and the previous impacts of pruning, storm damage etc.

7. This is a special category that takes into account unusual or other important factors. It is only used if required. Trees can deserve additional points for rarity, historical associations, exceptional landscape merit, unusual botanical interest, or where they are important to screen unpleasant views, or where a tree is planted in a composition and is vital to that landscape.



RESERVE TREE HEALTH ASSESSMENTS:

Soldiers Memorial Gardens:

This is a large area with many inter-connected sections.

The majority of trees on the site are affected by long-term stress as a result of soil compaction and root competition with turf.

Many of the prominent trees are old and in decline.

• The south-western corner of the gardens is of particular concern, with few healthy trees. The larger trees present are in poor condition. This area needs substantial replanting input. The existing newly planted trees have little chance of establishing successfully for a variety of reasons.

• The River Red Gum at the corner of the site is an eyesore with no chance of recovery. It should be removed ASAP.

• The Corella impact on the Norfolk Island Pines over the years has been dramatic. They will almost certainly have to be removed eventually. Establish new trees first.

• The performance of replacement trees throughout the park is generally poor. Improved planting and establishment techniques are vital for the success of future plantings and good tree cover in the gardens.

• The poor condition of Pinus halepensis by the bridge is due to the presence of soil fill over the root system. It is not due to Corella damage. This tree will not recover.

• Other Pinus halepensis in the park are old and in the final years of life. They should be progressively removed over the next 10-15 years and replaced with more ormamental species.

• The Aleppo Pines either side of the new road works should be removed ASAP.

• The Lagunaria patersonii in the traffic Island will need summer irrigation if they are to survive this change in circumstance.

• The smaller Elms adjacent to the creek are in poor condition. They have been planted too deep. Replacement is the best option.

• The SA Blue Gums and River Red Gums throughout the area are in average to good condition.

• The big Sugar Gums in the lower park area have fill over the root system and are in poor condition with no chance of recovery. Plan to remove.



• Many other trees in this area are highly stressed as a result of compacted soil conditions but are surviving.

• A detailed tree assessment and management plan is needed for the park.

• Tree cover in the future is not assured by existing new plantings and greater attention to providing the fundamental growth requirements is needed.

Market Square Reserve:

• The River Red Gums at this reserve are in relatively good condition and are not threatened by Corella damage.

• The Sugar Gum by the creek is also in good condition.

• Recent pruning of the Sugar Gum and the River Red Gums has been carried out. This work was of a very low standard and will contribute to increased tree hazards and reduced aesthetics in the future.

• It should be ensured that any pruning complies with the Australian Standard, AS 4373 1996, ‘Pruning Amenity Trees’, and is carried out by adequately trained Tree Workers, preferably qualified Arborist’s.

• The condition of a group of Eucalyptus saligna by the playground has improved significantly since my last assessment. The terminal growth in particular is much improved.

• The yellowing Sugar Gum by the road to the east is in decline and should be removed within the next 2 years.

• The Peppercorns are in average to good condition and are very suitable for the site, with high recreations values.

• The large Aleppo Pines in the reserve are all nearing the end of their useful lives and those at the western end will also need to be included in a replacement program, preferable within the next 10 years.

• There are no new trees within the reserve. An ongoing planting and replacement program is essential preserve tree cover for the future.



Hutchinson Reserve:

• Tree health and vigour at this site is generally good, despite Corella impacts in recent years.

• Existing mulched garden beds are helping to improve tree condition over time.

• The expansion of the mulched areas would ensure continued improvements in tree health over time.

• Mundulla Yellows Syndrome symptoms are present at the entrance to the reserve at the corner of Paringa Parade in the River Red Gums and the Lemon Scented Gums. There is no accepted strategy for dealing with this disease at this time. Substantial Council contribution to the research fund for MY is clearly in their best interests.

• A number of smaller trees between the larger individuals are in poor condition. These trees are unlikely to recover and may need to be removed in time.

• The presence of large turf areas in close proximity to native trees is in conflict with their needs. Minimising the area of turf in close proximity and maximising the distance of turf to trees is recommended as the most successful long term strategy for improving the health of River Red Gums.

Willunga Recreation Reserve:

• Avenues of Ash, Fraxinus oxycarpa on the southern, northern and western sides are under stress as a result of high levels of soil compaction. The condition of these trees varies considerably from tree to tree.

• Most are suffering Corella damage, though the taller trees are more favoured and therefore sustain greater damage. This species is capable of surviving the site conditions and the Corella damage, however they would benefit in time from the restriction of vehicle traffic over the root systems (beneath the crowns).

• The Cupressus macrocarpa at the playground are in good health and not impacted adversely by Corella’s at the time of inspection.

• The River Rd Gums at the southern end of the parking area have sustained greater levels of damage caused by the Corella’s. This is similar to other trees elsewhere in the township.

• The trees are affected are in a variety of ages and conditions. The root zone of the older trees is adversely affected by soil fill, impermeable surface capping and is heavily compacted. This is a poor environment for root growth and the long-term consequences are clearly visible in the tree crowns. The larger older specimens are weakened, with thin poorly coloured foliage. Trunk wounding is also a problem.



• The trees at this site will continue to decline while the area is open to vehicles. It will have to be modified to encourage new root growth if the present decline of older trees is to be halted and possibly reversed.

• The younger trees are tolerating the conditions though they too would benefit from improved conditions.

• Any improvements to the site will assist the trees to withstand future Corella damage.

Willunga Park, west of Railway Terrace: Rose Garden to Public Toilet Block

The reserve comprises mostly older River Red Gums and a few younger trees, including a Lemon Scented Gum.

• All specimens are equally affected by extensive defoliation caused by Corella’s.

• At the time of inspection masses of small twigs and leaves were on the ground beneath the trees.

• Tree appearance is significantly affected by defoliation.

• Removal of the leaves and small twigs exposes existing dead wood and makes it stand out, particularly in the older trees.

• The older trees are carrying a legacy of Corella damage caused during previous intensive predation periods, as well as that caused by changes within their root zone. In these circumstances it is impossible to separate them.

• Tree response following the birds leaving will be the best gauge of their health. If they respond with a major flush of new growth in early spring, then all is well.

• I believe they do have the capacity to respond and the damage is short term and cosmetic.

Station Road & Main Road, adjacent to Willunga Primary School:

At the time of assessment there were large numbers of birds in the trees at this location.

Trees present are predominantly River Red Gums of varying ages from mature to over-mature.



• Damage caused by the Corella’s is the same here as other locations in the township.

• Defoliation, bark damage, small twig and branch death.

• Recent medium sized horizontal limb failures have occurred.

• The high use of the surrounding area, reduced tree health and large size of overhanging trees pose substantial risks to the public. Formulating a risk management strategy for the trees in this area should be a high priority.

• Individual tree assessments are required to determine the level of risk and action required to minimise the risk to the public by falling limbs.

• The main issues affecting tree health are not damage caused by Corella’s. Bird damage is a small factor in the overall tree health picture.

• Root system damage as a result of changes within the root zone for road upgrades, combined with diminishing root space, are the primary factors influencing tree health at this site.

• The yellowing of foliage in some trees may also indicate the presence of the Mundulla Yellows syndrome. This cannot be confirmed.

• There are few options available to improve tree health in these circumstances other than maintain root zone stability over long periods of time, manage tree crowns with the minimum of intervention possible and provide new or improved zones for root growth in adjacent areas where possible.

03-056 - corella research project - final report

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