the establishment of permanent vegetation quadrats on the ... · on the poor knight islands s by...

Tone f 19/0) 16: 45- 51 45

T H E E S T A B L I S H M E N T O F P E R M A N E N T V E G E T A T I O N Q U A D R A T S O N T H E P O O R K N I G H T S I S L A N D S

by Barbara S. P a r r i s *

A B S T R A C T The establishment of permanent vegetation quadrats on the Poor

Knights Is lands i s descr ibed and the p o s s i b l e sequence of suc cess i on in these i s d i s cussed .

I N T R O D U C T I O N

T h e Poor Knights Is lands l i e fifteen mi les off the east coast of North Auck land (35° 30'S, 174° 45 ' E ) .

In May 1969 two permanent quadrats were set up on T a w h i t i R a h i , the northernmost and largest i s l a n d (318 acres) of the Poor K n i g h t s group, in order to study the qual i tat ive and quantitat ive changes i n the vegetation on a longterm bas i s . Both quadrats are s ituated on the eastern s ide of the i s l a n d , almost due east of L a n d i n g Bay on the lowest part of the saddle between the plateau and the smal l h i l l s at the southern end of the i s l a n d ( F i g . 1).

T h e southern part of the i s l a n d contains plant communities of two d i s t inc t ages. The youngest i s a " m e a d o w " of Leptocarpus simplex, toetoe (Arundo conspicua), f lax (Phormium tenax) and several spec i e s of grass , with scattered s m a l l trees and shrubs of several spec ies between one and s i x feet h igh . T h i s probably dates from a fire about twelve years ago (W. Doak, pers. comm.). The older community conta ins the tree and shrub spec ies present i n the meadow but as a c l o s e d canopy from seven to twenty feet h igh. T h i s community has probably developed s ince a fire in about 1923 ( K i n s k y & Sibson , 1959). Both quadrats were set up in the younger community.

The vegetation cover ing most of the i s l a n d i s pohutukawa (Metrosideros excelsa) forest with kanuka (Leptospermum ericoides) l o c a l l y important i n the canopy. O c c a s i o n a l l y trees of other spec ies are found in the canopy. Nei therpohutukawa nor kanuka can regenerate under a forest canopy and these w i l l eventual ly be replaced by other spec i e s . The vegetation of T a w h i t i Rah i w i l l be d i s c u s s e d in further de ta i l elsewhere ( P a r r i s , in prep.).

It i s hoped that these quadrats, together with those of C u v i e r Is land and L i t t l e Barr ier I s land , w i l l be sampled at regular in terva l s . It would be appreciated i f the next party to examine these quadrats would take some lengths of ga lvanised pipe to mark the corners of the quadrats as only wooden pegs were ava i lab le when the quadrats were set up.

Department of Botany, University of Auckland. Present address: Plant Diseases Div. , D.S.I.R., Auckland.

FIG. 1: Location of quadrats on Tawhiti Rahi, Poor Knights Is.

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M E T H O D O F S A M P L I N G

The method of sampl ing was that used by E n g l i s h & Brock (1964) and P a r r i s & Keen (1968) on the L i t t l e Barr ier Island quadrats and P a r r i s (1969) on the Cuv ier Is land quadrats. The re lat ive abundance of seedl ings of tree and shrub s p e c i e s was a lso recorded, as has been done for C u v i e r Is land ( P a r r i s , I .e.) . The vegetation was d iv ided as f o l l o w s :

1. P o l e s . Greater than 4 inches D . B . H . (Diameter Breast Height) . 2. S a p l i n g s . Between 1 and 4 inches D . B . H . which were further sub­

d iv ided into: A . 1-2 inches D . B . H . B . 2-3 inches D . B . H . C . 3-4 inches D . B . H .

3. S tr ip l ings . L e s s than 1 inch D . B . H . and higher than 12 inches . These were further subdiv ided into height c l a s s e s :

a. 1-5 feet b. 5-10 feet c. 10-15 feet d. 15-20 feet

4. Ground cover. Phanerogams and cryptogams l e s s than 12 inches in height. Frequency and density of p lants in th i s category were not recorded because of their erratic occurrence.

E a c h quadrat i s 10 yards square and i s divided into 6 foot square p lots which were sampled separately as above. The results are expressed as frequencies and dens i t i es . The various height and D . B . H . c l a s s e s , as we l l as seed l ing occurrence, were also recorded.

Frequency and density were ca l cu la ted as fol lows: ^ _ p lots in which spec i e s occurs , „ „ F - £- ——-j 7—r—. x 1 0 0

total no. of p lo ts total no. i n d i v i d u a l s of a given spec ies

" ~ total area of quadrat in sq . yards

F e r n s and dicotyledons are as in ' F l o r a of New Z e a l a n d ' by H . H . A l l a n (1961), monocotyledons are as in 'Manual of the New Zea land F l o r a ' by T. F . Cheeseman (1925) and adventive spec ies as in 'Handbook of the Natura l i sed F l o r a of New Z e a l a n d ' by H . H . A l l a n (1941).

R E S U L T S

Quadrat 1

T h i s i s s ituated 30 yards from the eastern c l i f f edge in the lowest part of the saddle. The southeast peg stands four feet high and the

T A B L E 1: Species found in Quadrat 1 arranged in order of density.

Density Frequency Size Classes

Seedlings Density Frequency Poles Saplings Striplings Seedlings Density Frequency Poles A B C a b c

Seedlings

Metrosideros excelsa 0.17 52 15 2 none Hebe bollonsn 0.05 20 5 none Pittvsporum crassifolium 0.03 12 3 none Coprosma repens 0.01 4 1 none Cyathodes fasciculata 0.01 4 1 none

Numbers in each class as a percentage of the total number 92.6 7.4

T A B L E 2: Species found in Quadrat 2 arranged in order of density.

Density Frequency

Size Classes

Seedlings Density Frequency Poles Saplings Striplings Seedlings Density Frequency Poles A B C a b c

Seedlings

Cyathodes fasciculata 0.49 76

A

49 common

Leptospermum ericoides 0.29 60 29 common Metrosideros excelsa 0.28 60 28 common Myrsine divaricata 0.12 32 12 common

Pittosporum crassifolium 0.07 20 7 local

Cassinia retorta 0.02 8 2 rare Corokia cotoneaster 0.01 4 1 none

Numbers in each class as a percentage of the total number 100

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top is painted white; from this the northeast peg i s at 10°, the southwest at 280

The ground s lopes to the west. The vegetation here i s typ i ca l of the burn community on the exposed saddle and there i s some bare ground. Pohutukawa and Pittosporum crassilolium are the most important spec i e s here (see Tab le 1).

The ground cover with in the quadrat c o n s i s t s of Pimelea prostrata, Cyathodes lasciculata, Hypochaeris radicata, Sonchus oleraceus, Samolus repens, Lobelia anceps, Leptocarpus simplex, toetoe and Deyeuxia billardicri. No seedl ings of the tree and shrub spec ies l i s t e d i n T a b l e 1 were found within the quadrat.

Species found near but not within the quadrat are Disphyma australe, Spergularia marginata, Cassinia retorta, Centautea umbellata, Myoporvm laetum and f lax. Seedlings of a l l the spec ies l i s t e d in Tab le 1 except Coprosma repens were found c lose to the quadrat.

Quadrat 2

The northeast peg of Quadrat 2 i s 50 yards along a bearing of 200° from the southeast corner of Quadrat 1. From the northeast peg the south east corner i s at 220°, the northwest at 310°. The southwest peg i s in a s m a l l area free of vegetat ion, with a few blackened tree stumps.

The ground s lopes to the west. T h i s quadrat i s in a l e s s exposed pos i t ion than Quadrat 1, being sheltered on the east and south by the older community of trees, between 10 and 15 feet high. It i s t y p i c a l of much of the younger burn community. Pohutukawa and Pittosporum crassilolium are more important than in Quadrat 1 and there is a greater variety of tree and shrub spec i e s than in Quadrat 1 (see T a b l e 2)- With two except ions the spec ies l i s t e d in T a b l e 2, together with Catmichealia cunninghamii, ate the major constituents of this burn community. Corokia cotoneaster i s rare and l o c a l and Cassinia retorta i s l e s s common i n the middle and on the western s ide of the i s l a n d .

T h e ground cover with in the quadrat c ons i s t s of Schizaea listulosa, Pteridium aquilinum var. esculentum, Asplenium flaccidum, Haloragis procumbens, Hypochaeris radicata, Lobelia anceps, Astelia hunk si i, f lax , Scirpusnodosus, Leptocarpus simplex, toetoe, an unidenti f ied grass , Thelymitra? longifolia and Acianthus tornicatus. Seedlings of a l l the tree and shrub spec ies l i s t e d in Tab le 2 are present with the exception of Corokia cotoneaster.

Species found near the quadrat are Muehlenbeckia complexa, Carmichealia cunninghamii, Pseudopanax lessonii, Hebe bollonsii, and Xeronema callistemon.

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D I S C U S S I O N

It w i l l be of great interest to fol low the development of the vege tion in Quadrat .1. P l a n t s character i s t i c of ' s a l t spray ' and ' c l i f f com munities are present and i t i s probable that because of exposure to salt spray and strong winds the vegetation w i l l never be as d iverse as that in Quadrat 2.

Apart from Myrsine divaricata the f ive spec i e s with the greatest density i n Quadrat 2 (see T a b l e 2) are not regenerating under, their own canopy in the older burn community. Seedl ings of spec ies which are as yet rarely found as mature trees on the i s l a n d are common here. These include Dysoxylon spectabile, Corynocarpus laevigatus, Planchonella novo-zelandica, Gymnelaea apetala, Melicope ternata, Hedycarya arborea and Paratrophis banksii. T h e common shrub spec ies on the i s l a n d , Coprosma macrocarpa, Macropiper excelsum, Geniostoma ligustrifolium, and Melicytus ramiflorus, a l so occur in this community and seedl ings of these are common i n the ground cover. The ferns Phymatodes diversi-tolium, Asplenium lucidum and A. flaccidum, and the sedge Carex vacillans, are also important in the ground cover.

It seems l i k e l y that many of the spec ies now present i n the ground cover w i l l d isappear as the vegetation in Quadrat 2 grows and a c l osed canopy is formed. The i r place may be taken by the spec ies found in the ground cover of the older burn community. In time the nursery canopy may be replaced by the tree and shrub spec ies now present as seed l ings .

At present four spec i e s apart from pohutukawa are important in Quadrat 2. In comparison with areas of older vegetation on the i s lands it seems l i k e l y that Cyathodes fasciculata, Myrsine divaricata and Pittosporum crassifolium w i l l become decreas ingly important in the canopy whi le pohutukawa and kanuka w i l l become dominant.

The quadrats on Cuv ier Is land ( espec ia l ly 3 and 4) are designed to study the s u c c e s s i o n of spec ies in a coasta l d i coty lous forest at present dominated by pohutukawa ( P a r r i s , 1969). The Poor Knights quadrats provide a unique opportunity to study not only this replacement of pohutukawa forest by other spec ies but a l so the ear l ier stages of i t s development (almost from establishment) in an environment free from the effects of any introduced animals . No other offshore i s l a n d has a develop­ing pohutukawa community of such s i ze and youth, and further sampling of these quadrats w i l l give valuable information on the speed of succes ­s ion and the spec ies invo lved . The time of this success ion w i l l help evaluate the age and perhaps history of other areas, not only on the Poor Knights Is lands but a lso on the other offshore i s l a n d s .

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A C K N O W L E D G E M E N T S

The author wishes to thank M e s s r s . J . P . C r o x a l l and D. P . Gordon of A u c k l a n d U n i v e r s i t y for a s s i s t a n c e in sett ing up the quadrats, Mr. F . C o t t e r i l l of Tutukaka for prov id ing transport, and the Commissioner of Crown L a n d s , Mr. J . D. O ' B r i e n , for permiss ion to land on the i s l a n d .

R E F E R E N C E S

ENGLISH, D. A . , 1964 A further examination of the permanent quadrats on B R O C K , J . L . Little Barrier Island. Tane f0.79-83.

KINSKY, F . C , 1959 Notes on the birds of the Poor Knights Islands. SIBSON, R. B. Notornis 8 (5): 133-138.

PARRIS, Barbara S. 1969 Studies on the vegetation of Cuvier Island, III. The establishment of permanent vegetation quadrats. Tane 15: 75-85.

PARRIS, Barbara S., 1968 A further examination of the permanent quadrats on K E E N , Lynn R. Little Barrier Island. Tane 14:83-92.