al s o lacks ob jectivity (Pearsall ( 1 924: 135-39 ) )

Pearsall (1 924: 1.39 )

has c

onc

l

uded that nothing of value will be los t by the arbit rary standardization uf

minimal

areas.

For

th

e

present

work , it was decide

d

t o

use

a quadrat _{of side}

30

_{cm. ,} that is , with

an

area

of about 900

_sq.cm.

( approxim· tely

one square

foot ).

(Cain (19�3 :

243

)

, determining frequency in

fell-field

veget ati on, UH ed a

plot

area

of 1000

sq.cm.).

It was necessary to reali ze that th� inforrna-

ti on that

could be

obtained by thtl use of these

quadrats , na.IMly the

probability

that a giveri species would occur

in a random plo

t of this

si ze ,

would

_{be empirical only .}

It

would

s eem that the rrumber of quadrats must also be chosen

arb-

itrarily.

(

'rhe conc ept of the ''minimal number

cw·ve " (Cain (1943 :

2Jt.3 ) ) is analagous with t ha t

of

the 'hlnilnal area curve " ) . It ·R8.8 decidod t o

use 25

quadrat

s per

uni t area

to

dete11mine percentage frequency. Thi s number may be c ompared with the 2 C used by Cain

(1943:

243 ) at each

"stat ion " , and t he 30 to 50

per

"community "

of Weaver and Clements

( 1938 : 21 ) .

(

The degree of prt�cisiun a ttaiaed in an est imate of percent-

age

fr

equency

(

using randcm quadra ts

)

may be det�rmined as i

n

the case

of point

analysis. Thus,

for

a specie s having a fre quency of

the

stan

dard error of

the

mean

fol" aamples

of

25 quadrats

wuuld

be

namely lQ%,

o

r

2Q%

_of

t

he mean

)

.

25

quadrats were

foynd

to reprea•nt ab

o

ut one hour ' s work.

In the pres

en

t

work ,

a square wooden

frame was

used

which

had a

side of 30 cm.

( internal meas urement ) .

J:'o assist examin:tt ion ot

t

he vegetation , the

i

nternal area of thtl

frame

was

divided by

lines

into nine

6S

frame itself was not thrown about , bec ause it would have tended to slide

on steep

slopes.

The

dart that was used in

the

point analyses was thrown t o obtain the random loc_ations of the frame , t he framo itself being placed

so

that the centre c oincided wit h the point on whioh the

dart fell. The frame was ori�nted randomly when b� ing _{thus placed}

in

posi ti on.

The

recording

was carried out as

for

point analysis , in that the

species

we re listed and t

h

e number of

each

sampl

e

was _placed alongside the

names

of t he species that occurreu

in

_tr�t quadrat .

Phaneropb_ytea

were

annotated as in the

point

analyses.

(A non-phanerophytic

species was annotated with N for a given quadrat if s one or all of the plants

or

of that sp�c ies within t hat quadrat had permanently exceeded

10 inclw s in height

)

.

If a frame fell in a

mic1 ohabitat

feature ( defined as for the

transacts

)

this fac t was rec urded. Dung was not recorded within the

frame ,

but such r$cords might have serv

ed

as a check of

the

transect

records

had

they been made.

�eneral .

4.8

unit areas were sarnpled by point analysis

and

frequency .

(

This number inc lude� three unit areas of

plough-

abl e pasture , which

W6re

sampled t o ruuplifs the result s of the extensive

examin,.t ion ). Three furthEJr _{areas of swampy} grrund. were sampled by point analysis

a

lone

.

It was rec o:ni zed that ther

e

was a theoretical

need for s�asonal checks , but , as in the c ase of trans act ing , time and labour were

the l

imit_{ing factors. The}

sampling

was carri ed out in October-Dec ember

1954

(

spring arrl e8rly

summer) ,

when the vegete.tion

was mo.,;t like ly to

inc lude

annuals and

die -bac k

perennials.

(vii)

.

Treatment

of'

Data .

of Transect The _original

line

transects

c overed

a total l

e

ngth of 199, 193

feet

(about

38 miles) ,

and

pa

ssed

through

1608

tmit areas. Table II gives the _{classification of these}

1608

unit areas in terms of land-use , and the t otal lengths of the sam-

within each class of unit area.

1138

s ampling trans ects , totall

ing 163,180

fe et , were recorded

in unploughable past

ur

e

. (Of

these

1138

transec t s ,

412

were later re-

run accord

ing

t o th� �nded sampling

method).

These sampling transact s range in length from

1

to

1675

fee t , with a mean length of

about

145

feet and a standard deviation of about

165

feet. The disad­ vantage in having sampling units of varying lengths has been mentioned in connec t ion with the planning of the field method. An attempt was made to mee t thi s difficulty by dividing the tran

s

acts int o length­ groups. Comparisons of estimates of frequency or abundance wculd be more likely to be va lid it' based on sets of transacts belonging to the

same length-group or having similar length-group distributions .

(

The opinions of two bianetricians , namely Mr. A.c . Gbndq

and

Dr.

B. I.

Haymm , were obtained on the validity of comparing estimat

es

of frequency based on s ets of sampling unit s of varying size , when suoh s e ts of sampling unit s

have

_{s imilar si ze-distributi cns. 'l'b.ey c ons id­} e red that t�re are no apparent object ions t o making such comparisons , other _than the additional wo.ck involved in detezmi.ning th� simil arity of

the size-distri buti ons , _and the difficulty of determinir� the reliabi l-

ity of the result s. Neithe r of' tLt�ae ob jections would , of c ourse ,

have

arisen wi th sampline

un

it

s

of

_uniform size

)

.

It was proposed t o de limit thG length-group s in s uc h a

w�

that the midmark of e ach grou9 was roU£hly twic e the preceding midma.rk. In view

of the value of t he mean lenLrth of the transec ts , th{:l basic length-

group

was

t aken as

101

- 200

feet .

(This

range c ontains 241 transec t s

)

. The le sser groups were therefore takan as

51-100

fe et

(218

transoct

s)

,

26-50

feet

( 171 ) ,

and

13-25

feet

( 114) .

( It

was decided arbitrarilY t o disreg_ard the

107

trans ec ts le s s than

13

feet in length,

since

lllaJV'

of these repre sent ed fragment ary unit areas

)

. The transacts greater

than

200

fe et in len6th were subdi

vi

ded in a s] ightly different �' so

that the numbers of transect s in the groups would bt� roughly of the same order as t hose in the groups of lesser leneth. One grou._, was taken

aa

67

TABLE CLASSIFICATION OF T�TS OF UNIT AREAS

Classification

Number

o:f Unit

Areas

Transeoted.

Unploughable pasture

1138

Impene trable vegetati on

(

non-pasture

)

_1.45

Cliff's and. stream

banks

₃₄

Watercourses and

str

e

am b

e

ds

210

Erosion

features

( active

or

unhealed)

_4-3

Plougb.able

land u

In document A study of ecological interaction between introduced and indigenous plant species in the Manawatu district, North Island, New Zealand : a thesis presented at Massey Agricultural College for the degree of Doctor of Philosophy in the University of New Zeala (Page 72-75)