IJ 2J~!I~

BOTANY DIVISION REPORT

VEGETATION OF THE HEAD OF THE HARBOUR SALT MARSHES, LYTTLETON HARBOUR, CANTERBURY

rr.R. PARTRIDGE

IAPRIL 1989 661

VEGETATION OF THE HEAD OF THE HARBOUR SALT MARSHES , LYTTE LTON HAR BO!JR,

CANTERBURY.

A report prepared for the Department of Conservat i on.

T . R. Partridge

Botany Division, DSIR

Lincoln

SUMMARY AND RECOMMENDATIONS

Apr .i l 1 9B ~l

The salt marshes of the Head of the Harbour , Ly t t e l t o11 ar t~ of con s i de r ah I c

botanical value, especially as they are one of the bes t e xa mp .les t' ema ining

within the Canterbury region. They are di vers e a nd i 11 good c on cU t i u n .

They comprise lower and upper marsh zones, ea ch lwv .i.ng l> o t h s il ,H't tu r f

vegetation and taller rushes or shrubs . Spartina is p1' c :S ~! 11I lrnt c; onfi11 P d

to a smal 1 area. Much of the former area of salt ma r s h ha s howe 'Je1· bee n

reclaimed by empoldering . It is recommended t hC:lt til e rema inin g area of

salt marsh be protected from reclamat .ion a nd g 1·az .ing , a 111l th ut a ny s pr·e rt d

of Spartina be controlled .

List of plant communities

Lower marsh - glasswort

- sea rush

Upper marsh - turf

- coastal ribbonwood

- leptocarpus

Spartina

2

INTRODUCTION

Unlike·Otago, Marlborough and Nelson provinces, ~vil.11 lhr!i1· 1!xl1~nsivl! <11·c!dS

of estuarine salt marsh, Canterbury has only sma.l I fragments of tlws1~

speciaJ plant communities. Even in the many shelt.1;rerl bays or Ba11ks

Peninsula there is little of this kind of vegetation. Furthermore, many (Jt

the areas described as salt marsh occur in .lagoons and have pec11l iar

vegetation patterns unrelated to the regular tidal inundation cycle, l>u1

determined by salinity patterns related to irreguJar flood1ne. Mo~;t

important of those is Lake Ellesmere. Of the areas of true sa It mar·sh.

many have been extensively reclaimed, such as in the Avon Hea Ll1co t(~

estuary, and the area under examination here. Others are highly modified

by naturaJ processes that have promoted invasion by in trod11ced l•H!l!ds, or

are heavily grazed, such as at the Ashley River mouth.

Any areas of salt marsh in Canterbury that are in r;ood condl t i 011 and h<ivv <1

representative sequence of communities, are therefore of primP lwl.i1nical

value to the region. This report examines the remnant sa I L marsl1 <11·eil~> <1 l

the Head of the Harbour, to see how they rate in view of such er· it el' ia.

Salt marsh vegetation patterns

Vegetation patterns in salt marshes are primarily determi11ed by saJ inily,

this depending upon the regular tidal regime. This results in a

distinctive sequence from the unvegetated mudflats to dry land. Fo1

conven]ence in this report, the sequence has been d.iv.idt:d j11t.o .i lu1w1·

zone, characterised by the presence of exposed mud amongst the [l L111t s, 11nd

an upper zone whet'e the vegetation is continuous. Tlle prese1H·t: of r resli

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water, such as creeks, and areas where water ponds an! .i rnpo1· 1 an l modi fie i·s

of the vegetation patterns in the upper marsh.

DESCRIPTIONS OF PLANT COMMUNITIES

A Lower Marsh

Lower marsh comprises two typical commurdties, and a small an:u that is

atypical.

Al Glasswort

This vegetation consists of glasswort (Sarcocornia q1riw11wfioru) mudflats

with little else apart from clumps of the grass Puccinellia strict11 in

certain areas. It occurs as a narrow margin below ballks or as more

extensive areas.

A2 Sea rush

Like the glasswort community, this consists of Jjttle elst! apa1·L from sc:;1

rush (Juncus maritimus). The tall rushes of this species t'oi·m de!lse sl.amls

on areas of mudflats.

A3 Spartina

There is one area of cord grass (Spart·ina angl ica) at the southern end (~we

area descriptions). This species occurs on mud, where the plants appeal'

relatively vigorous, and in upper marsh (see 83).

B Upper Marsh

This, like the lower marsh, can be divided into short turf V<!ge ta ti 011, and

that dominated by taller rushes, grasses and shrubs.

4

Bl Salt marsh turf

Dominated by glasswort, Se11iern radicans, aucl l'1rcc i.1wl. lin st.1· ict:<1, ll1i s

vegetation is short hut forms a complete cover . Rurer· assoc iat e d species

include Samo1us repens, buck's horn plantain (Plant.ago co1·01wpus), At:i-ifJL ,~ -....

prostratn, sea barley grass (Hordeum marinum), Triuloc hirt sLr' iutum and

Schoenus nitens. It occurs on small patches amongst lll e Lal ll:t· Vf:getrll i i111

or occasionally as large continuous areas, especially in the so uth of t.!11~

marshes examined. Where heav i 1 y grazed, strawbe1Ty c J ove1· ( 'fr i f'o l i nm

fragiferum) becomes important.

82 Coastal ribbonwood and associated species

B2a Coastal ribbonwood/sea rush

More common in the north, this consists primarily of s h r ubs of coas la1

ribbonwood (Plagianthus divaricatus) with clumps of sea t'11sh a 11d s il ver

tussock (Poa cita) . Glasswort and Sel1i e ra radicr.ms nrc com111011 associdl.c:d

species.

B2b Coastal ribbonwood/leptocarpus

Al though Lep tocarpus s imi l is occurs scattered throughout, it is ren l l y 0111 y

an important constituent in the south of the area. Apar L f rnm sornc~ l.<1 l l

fescue (Festuca arundinacea) there are few associated species.

B2c Coastal ribbonwood/tall fescue

The introduced, weedy, salt-tolerant grass tall fescue occurs with coast1tl

ribbonwood and occasionally sea rush over much of Uw so 11tlt or the area. .

Occasional associated species include creeping bent (Agrostis stolonifer·n)

and Atriplex prostrata.

5

83 Spartina/glasswort/sea couch

Where Spurt ina cmg l ica has invaded upper marsh, j t hil s r e s1d l t! cl i 11 it V t: 1·y

'messy' community dominated by very short Spartinu cmol ir:c.1 , sea Ct) u c h

(Elymus farctus) and remnant areas of nat:ive spec :i c~s i11 c l11tli11g i.;Jas s ~vo1 · l,

Seltiera radicans, and sea rush.

C Empoldered areas

Much of the former salt marsh is now enclosed wi tld n po 1 de rs, w.i Lit th (-:

intention of converting the land to agricultural purpos e s. Ne ar Tedding tu1 1,

this seems to have been particularly successful, wjtlt quality pasture

established, but elsewhere, especially where empolderi11g has bee n carci e d

out recently, salt marsh species persist. Glassworl survive s for a long

time, but the introduced weeds buck's horn plantain , sea barley g rass aml

creeping bent invade and tend to dominate.

AREA DESCRIPTIONS

The salt marshes can be divided up into five disU.nc l. <1rPas 1'1liicl1 r11 ·1:, f1 '0 111

north to south (see map):

l. bays in lee of hills

2. first narrow point

3. second narrow point

4. extensive wide point at Teddington

5. recently empoldered area at base of hill :in so ut.l1 ea s t.

The areas are made up as follows (communities refe 1·red to in brac ke t s ) :

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1. Bays in lee of hill s

The lower marsh here is mostly sea rush (A2) wj t.11 m.in(Jt ' <tl'(·: <1s of' l'.lc1 ssw11r· l

(Al) . The upper marsh is dense coastal ribbonwood on a s Le e p bank ( B2a)

wj th clumps of silver tussock. Behind is pasture or 1· l1t ! f1 · 1 -~s li -- w<1lt ~ 1 · 1· t1 s l 1

.Juncus effusus. Wh e re the salt marsh meets the road. l11iw•!vc r, I t11· f

vegetation (Al and Bl) dominates.

2-3 Two narrow points

The two na r row points are very similar. Most of t heir sa] t rn ;-ir·sh l1 a s IH ! t! l1

reclaimed by empoldering (C), leaving a narrow band domi11at1~ d b y v::, t;1l

ribbonwood and sea rush (B2a), and the tips of the poj nt s wlwr e l 11 cf" (Ill)

dominates . The northernmost of the two points i s notable for the abse 11 ce

of the introduced grasses creeping b e nt and tal] fescm!, whj e h tc!1Hl Lo

invade upper marsh communities that hav e been modified .

4. Extensive wide point at Teddington

This is by far the largest area, bigger than all the rest toget h e r . It

starts as a na1Tow fringe of coastal ribbonwoocl ( B2c) in th e 1101"tl1 , lw f'1 >1 ·, .

opening out to a very large area of turf (Bl) surround e d by t a ll e 1·

vegetaUon (B2a, H2 c ). This area has survived be c nus l! reclamal i o n has 111>l

extended as far out as on the other areas. The wh o l e salt 111 a 1·s h ha s <1

r e verse slope, the highest elevations being at tlw Sf!award E lld , wil t~ i ·t~ "

stee p bank mee ts the mudflats below . The turf has l ower e l eva tion , h11L

drains through a number of creeks that cut through Llw ta 11 e r ve ge l '1 t. i (i1 1.

In much of the turf however, water ponds, and in some cases, 'bad spo1 s ·

are found. TIH!se are where, under ponded wat.f!r, n! d11 c in [~ Cll111 li Lion s o c i:11 1·

killing the vegetation. They are a feature of these kinrls 1>t' s dlt m<tl' :; l1 .

Worthy of note are a small number of cl umps of Suaedll novrw - z tdu 11di.ue i 11

the north of the area .

7

:\•, I lie vei;P I ii t ion 11n n·ows nnd curves to the southeast, there are sudden

r · li;111i~r' '.'. TliP f'i1 · ~;t i11 vr1 l vP.s I.he uppP-n.rance of Spartinn. anglica (A3, R3),

1· itl1 its imp ;H:: l 1J11 . 1 Jll'f: domi.n a nl:ly turf vegetati.o n. Although q1d t 1.

.. ~; t _ r ' nsi vP wilhin thi s an~a . Spartina has not spread, and beyond this, to

1,; l1''l"' U1P- s; il 1. mur s h m Pct~; the road, is mostly upper marsh dominat e d by

~Rptocarpus similis a nd coastal ribbonwood.

:l. HecP.ntly empoldercd orea .in southeast

Th e a 1·ea to the southeast has been recently extensively empoldered (C) .

l' hJs hns J pft a narrow lower marsh outside the polders, dominated by

g lasswort (AJ) . In the base of the hill however, there is still some

c oastal l'ihbonwoocl with tall fescue (B2c), and in a small piece of

;1ss ocintecl turf was the o nly occurrence of Schoenus nitens.

110T/\NH:/\T. VJ\LllES

111 tlw r:ont1!Xf. of Cantt>rlrnry's salt marsh vegetation, the botanical values

nf the Head of the Hnrbour marshes are immense . These values remain

clcsr i tP P.x ten s i ve r ec lamation, and indeed the value of what is left is

c 11li:111 ce d for this snm e rF?ason. Al though fragmented, the communities are

EC !l eniJ l y in f~ood cond .i U on (wh e n outside polders), and there is good

rliversity nf species . Certainly, disturbanc e to some areas has encouraged

''"'~· <I .inv asion l>y ta ·1 I fe s cue, creeping bent, buck's horn plantain and salt

h <i r l RY R;rass . but there are sti 11 many areas where these are absent or

rn i nor. The> ma r·s hes c on t:;1 in a large heC1l thy "opul at ion of coastal

1· ibhonwond, n spec.i(-~S s n ofte n one of the first to succumb to reclamation

;1nd 1~1«1 z i1w . Thr! vr!W!lation patterns are of great scient .if :ic interest.

N;1t111·ill sn lt marsh prnr~e sses of accret.ion, establishment and erosion are

8

;111 taking pla ce. The djspos:i.tion of some of the communiUes demands

nnswers that cnn onJy be supplied by further clet.ajled study; some of the

p;it terns nre indeed very complex. These remaining salt marshes should

therefore be protecte d .

~1ANAGEMENT

·rhc vegeta tion of the salt marshes faces three threats; reclamation,

r,1·;1zi ng, and the spr·ea cl of Spartina.

fi f' I ; 1 i llll <I t i Oll

This p1 ·oce ss has a ·1 ready claimed vast areas of what would once have been

sa lt rnnrsl1. Although much of the reclamation is old, that in the southeast

i s rP C f'lll anrl hns all b11t destroyed the botan.ical values of that corner.

111 ord e r to pr· es erve the remaining botan.ical values, it needs to be ensured

t !1< 11 110 fu1 ·t lwr rr~ c.ln matjon takes place .

\111 1 il<r! mr-rny areas of' sa lt marsh elsewhere, those at the Head of the

. H:--it ·bour , n i·p t' e ma r·kab .ly fr ·ee from grazing damage. This is one of the

1·1~risn11s tl!iil. the VPl~elalion js in such good conditjon. Fences around

pa ddo c k s a r e in good ord e t', and there are few signs of stock being turned

1i1 1l lo 1 ~ 1 · ; 1 7:<! llir~ 111 ; 11 · s lH~s them s r! lves. Th.is r eg jmP. needs to be maintained to

[ll ' PSP l' \IP t h ~ IJnl.nnic;al va ln es nlrendy present.

9

Spnrt.ina

11· . . is rqr,reltf'd lh;it this agressive specjes :is present on an area of the

ma~she s . Tl1e botanical values of that area have been diminished, although

tlw rlyn 211nics of Spw·ti.n.n. in Uds kind of situal .ion are of scientific

interest. There ar e however two positive points; firstly, the plants are

n11t at all vigorous except perhaps when on mudflats, and secondly there is

no sign of Spctr' tirw spre;:iding elsewhere across the marshes . It is not

r,on s .idered fea~d hl e to r e move Spartina from its present. location. The best

managem e nt ther e fore would be to periodically (say once every three years)

c heck lhe s urrou11djng areas for establishing plants, and remove any that

werP found .

HEUJMMENIJJ\TJ ONS

1) That t lie remaining areas of salt marsh be protected from

recla.maU on and grazing, because of their high botanical

value and r·egi onal importnnce.

2 ) That p e riodic checks be made to ensure that Spartin.a

does not spread beyond its present distribution.

/''

G nors Bay ---·~:::-:::::·--T ddington - ove --··---·· -..:...... .. ·-e ---:..:::=.:::---- .. ---:.:--:--;:::;.::::;:--- ---

.-;:::::;:::::::::::.----- . Saline pasture )'

-<;/ ~~~2 Hills

1

Pasture

Pasture /~ 3

N 0 '

4~ Jlfudflats

' / '" \ / ) ·,, _ _) '\ ~4partina

~ I "\: l ~ c

"\ --!) c ~ ....._ /

'~~!~::a / Hills

...:;::_~- Teddington - Diamond Harbour

Map of salt marsh areas at the Head of the Harbour

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i\f'PENDIX List of Species Asterisk indicates adventive species

Agrostis stolonifero* J\ trip l. ex p r·ostl'fl t.n*

lh=:ta vu I. fJot' i. s *

c i. r s i.11.m vu/, 9nre *

Dn.ct:-1 I is 9 ! onwrnLn*

F7.ymns rnrctus*

Festuco 01'1mdinnceo*

Honlemn mm· i.num*

.luncus effusus* J . mm' i. t i mus

Le pt i.ne/, 1.o dio i.cn Lep tocnrpris s im i l i. s Lolium pererme*

/llnehlf'nheckin compl.Pxo

Pl.ogUmtlms diva1'i,ccttns l'lcmtngo cor'onopus* Pon cito Puccinel. l i.u stl'i.cl.a

Somo l us 1'epens Sm'cocorni.n quinqueflorn Schoerrn.s n i. I ens Sel I, iern ntdi.co.ns Sonchus ol.eracens* Spartirw <m9lica* Srwedn novoP zealnndine

T r· if o l i. um r 1'n9 i,f e nun*