VENTAJAS

aa paesia acaberula, i

n

c

i

aa, Blechnum and

B.

I t ha s alr

e

ad

y

been not ed that vegetative spread appears to

b

e

a significant charact eristic of the indi genous species of and of most of the indigenous

sward-forming

sp

ecies.

A f'urther reason for the apparent aggressiveness of theae

species would appear to be the widespread deforestation

that

amounts to the creation

on

a largJ scale of a habitat :Juitable for them.

(

This ha a be en referre:i to by Cockayne

( 1 928 : 1 88) ) .

The

pioneer

speci es

in

th

e

regenerative process DllSt b e

light-demanding,

or at least light-tolerant, and able to tolerate the drier conditions of the open. Unless they are extremely adaptable, such species wil l no t tend to be of DllCh importance as subordinat es within the climax

forest . f

l

uvi

a

t

i

le

occurs as

a forest subordinai:e, but

this speci

e

s appears _1x>

have

a more limit ed distribution in pa sture

than most of the other species discussed in this section

)

. Conversely,

the subordinat e species

of

the forest

will

not

tend

to be of much importance aa pioneers

in

the open, except in shady and/or ahel tered p

l

ac

e

s, or

in

the rela

t

ive

l

y wet and clo

u

d

y

climat es of

highc

altitudes. Elsewhere, they

wi 11

be more likely to enter the succession

only

in the shelt er of the hardi er p

i

on

e

ers.

The

le

sser

importance

of phanerophyt

i

c

(

but not

fern)

weeds on

soil t

ypes 1

22 and 1 2J•

v.ould appear to be due to

the fact that

species of this lite-form that are suited 1x> life in the open are still only

in the process of moving on w these soils .

( 3)

NCfi-PASTURE

129

condi tion, and in the areas tha t are definit ely under human control, the watercourses and str

e

am beds

of

t

h

e s tudy area appear to be characterized by a fairly open non-phanerophy tic vegetatio�

In

view of the instability

of

th

e

soil, it is probable that the vegeta tion

of this habitat has always bee

n

of this type .

It

is the only

t;y.po

of

non-pas ture vegeta ti.on in which introduced non-pbanerophytic species may establish themselv

e

s freel

y

and persist.

Wi th the exception of wa tercours es and s tream beds

(and

the

possibl e e:�eception of areas that are subj eot to heavy g:ra.aing by wild animals

)

, the general vegeta tive tendency on tne non-�o

land within the study area

that is

not at pr esent occupied by indigenous

f

or

e

st, is towards

the regeneration of

that

forest.

Even

where idle or unused land is

far from

t

h

e nearest indigenous

c<»J11Iilnity, the tendency may be observed. On the roadsides

of

the

intensively-farmed Kairanga Plain may be seen scattered apecimer.a

or clumps

of such

speci

e

s

as Pteridium

lalehl en.beckia ArundD

k.akahc),

australis, and

um.

In general, the introduced species do not p ersist in the non­

pa sture vegetation, once succession towards forest geis

UDder

way. This would appear to be largely a matter of life-form, toget

h

e

r

wi th a t endency for most of the introduced s2ecies involved to b e l ight­

demanding rather than

shade-tolerant. If

land adjacent to p1sturo or crop land i

a

cleared and abandoned, introduce

d _{non-phaneropbytea}

may be coDIJlOn enough in the early

s

tage

s _of

succes

si

on

.

As ha s

been

shown,

a scatt ering

of

introd

u

ced non-phanerophytic species

(particularly those with

wind-borne fruits

)

may even be

found

in

damged

f

o

r

est

at some

distance from occupied land. When the succession procee

d

s

to

the phanerophytic stages,

the role

o

f

the introduced species changes. The introduced

non

-phanerophytes do no t appear to survi

v

e the e

ar

li

e

st phanerophytio stage.

(

This is

confirmed by the observations of

Croker ( 1 953 : 1 4-1 5) ) .

1.30

that Ulex

and

may be im};X)rtant

a

t the f

ir

st

phe.nerop

hy

tic stage, and may be vetry persis tent in places where few

disseiJ.Iinules of indigenous species are available.

(

The same applies to the introduced

arbo

reus and offic

i.Da

lis along the low_{er reaches of the ri.vers}

₎

_{. However, the total}

_number

_{of introduced}

phan_erop

hy

_{tic species involved is Vf!Jr'Y anall. �"'Uriher, the sp}ec_ies

that are available are ess entially nano

phan

ero_p

hy

_{tic rather than}

macrophanerophyti c (with the notable exception r'£ Pinus

ra.diata,

which is referred to later) . Even a pioneer indigenous

shrub

like is sufficiently tal l-growing to be able, to

a

large extent, to overtop the introduced species and shade them out , and they are _ce

_rt

_{ainly hardly able to survive the de'Wiiopment of the}

small-tre e layers ( characterized b y the mature forms of such s_pecies as ramiflorus

and

let a lone t:P,..; t ':If the layer charact eri zed by Beilachmiedia tawa.

It is possible, of course, tha t shade-toleran_{t introduced species} might be able to pers_is

_t

_{as subordinates in regenerating}

_forest.

However, they have yet to ent er the study ar_ea.

₍

_{Even the few}

i

ntroduced speaies that have been referred to as

en

tering damaged undergrowth in standing indigenous forest, namely the shrubby Solanum

and the herbaceous .Arotium minus

and

Tradescantia flumin ensia, rare_{ly occur tar from the forest} mar_gin).

Tlus ,

in general, the

in

tro_{duced species would appear}

_at

_present

to be imp:>rtant only

in

the earliest stages of succession in non-

pastur e vegeta tion. I:Prever, the role of Pinus

radiate. is of

interest. This s_pec_{ies is of widespread occurrence,} ev_{en it not} numer_ically

important, in the successional non-pasture vegetation of the st11dy area,

and

may

be

expected to be very persis tent. Although it resembles moat of the other introduced phanerophytes that occur in the non-pasture vegetation, in being more or leas light-de:aanding, it differs from them in being capable of BLlch t

a

l

l

er growth. Fair

l

y open successional

vegetation appears _{to be necessary for the germi}na

_t

_ion

_{and establishment}

131

survive the increasing competit

io

n for light as succession prooee da.

By the time tha t the shrubs ar e being affected by competiti

o

n from the indigen

ous species, the fast-growing plants

of

Pinus

radiata

have owrtopped the successional veg

e

tati

o

n.

(

Thus, "Northlander"

( 1 94.3: 5)

has spoken of Ulex b eing overgrown and killed

by

indigenous

s

pecies in

1 0

to

1 5

years. This could

hardly

blppen to

Pimls radiate. , which, according to Yeat�s

( 1 948 : 89 ) ,

may increase in height by three or four feet a year

after

the first year or tw

o).

Where only scatt ered

seeds reach a non-pas

tur

e area while it is at a suitable stage for the entry _of

_Pinua radiate., i solated treea

may be expected, and this is usually the case in the non-pasture vege tation of the s tudy area, except where such vegetation ia close

to a Pinus radia ta plantation.

( In

the latter case, because larger .

numbers of seeds are aviilable, the indigenous successional vegetation rray be replaced by a Pinus forest. Such a replacement

has

been

recorded by "Northlander"

(1 943 :4) .

Further, as

predict ed

by Cockayne

( 1 928 : }58) , i

t has been happening on a large scal e on the Volcanio .P lateau of the N

o

rth

Island,

where large Pinus plantations adjoin

large areas of successional

vegetation) .

The fate

of

isolated trees of Pinus radiate. when the regenera ting

indigenous

vegetation around

them at las t aohiews the forest

climx

remains

to be

seen.

(

According to Croker

( 1 95} : 20) , it

takes about 80 years

to

develop a climax

forest dom.i.na ted by Beilschmiedia

(4)

CONCWSION

(

i

)

General

'fhe paper by C»cka.yne, Simps

on

, and Sco tt-Thom.son

( 1 932) which

may be regarded as the princi pal contribu

t

ion

to

the know

ledge

ot the relationships between the introduced and the indigenous plant species of New Z ealand,

tends to

place the emphasis

on

the incompa t­ ibility of the two floras. The same approach is used in the

s

ubseque

n

t paper by .Allan

(1 9}6) ,

and imeed this is made clear in

132

due to the fac t that ooth papers are concerned with refuting earlier a llegations of the innate " superiority" of the introduced species. However, Co ckayne1 Simpson, end Scott-Thomson

( 1 9.32: 1 5-1 8, 43 )

have claimed that there are " certain funiamental differences" between the

two

floras in the

matters

of life-form

and

ha.bi ta t-preterence. Essentially, the posi ti on as described in their paper is that the exo tica are mostly

annua

l speci es,

and

the indigenous plants largely woody or semiwoody evergre en perennials; wi th the expectable result

that the exotica tend to be restricted to the ground laid bare in the process of settlement, and can only b;)ld their

ground

there

if

the regeneration of the indigenous woody vegetation is prevented.

(

In cormection with this last point, they have

observed

that the

exotica are aided by the grazing and browsing ani.rm.ls that were absent from the original indigenous vegetation

)

.

A s far as lite-form is concerned, the " fundamental

dif'ferenoe"

is to some ext ent based on ovex-genere.lization. Actually,

according

to Allan

( 1 940: 1 0)

and

Cockayne

(1 928 : 1 28-38) ,

trees

and

shrubs comprise about

1 Cl,%

of the introduced flora,

semi-abruba

about

�'

perennial t erres trial herbs about

4%,

anmals about

y"', and

others

))&,

whereaa the corresponding figures for the indigenous vascular species of the

lowlands

ahd

lower hills are approximately

3�, 4%,

4&�, �� and 1 6%.

(In

the latt er case, ferns account for more than a _{fifth of the}

combined va lue for semi-shrubs and perennial terrestrial herbs

)

. It

is true that the introduced flora may at any rat e be regarded as predominantly herbaceous, even if not "for the most part

annu

als" . Further, the result s

of

the pr esent study suggest that only a

few

of

the introduced woody species are of any numerical inq:ortance. . However, except in the case

of

the annuals, the diff erences in life-form

classification are hazdly suffici ently clear-cut to be described aa

"fundamental" . Further, al though the indigenous flora rmy have

evolved in the absence of grazing

and

b

rows

ing

mamna.

ls1 it is evident, both from previous work that ha s b een cit ed

and

from the findings of

133

of this environma:1.ta.l factor.

'ro some extent the idea of a definit e dis tinction between the

t110 floras is valid, in that most of the introduced species are economic species or weeds of long struruiing, that i s, are species of crop or pasture land, while a large proportion

of

the L�genous flora

comprises forest species. T his distinc tion i

s

perhaps m::>st applicable

to the vegetative erttremes, namely frequ ently-tilled

land and

non-

pasture. However, it is evident from the results of the present work

that there is a considerabl e overlap betwe en the indigenous

and

introduced floras in the ma tt ers of lif e-form and habitat, and tbl.t this is most noticeable in the areas of unploughable pasture.

(In

fact, this overlap may b e int erred from observations made by prnious workers. Ev en Cocka;yne, S impaon, and scott-Thomson

( 1 932) ,

while

stressing "fundamental differences" , have reco

gni

zed that "mixed"

communi ties may occur,

in

which the

in

t_roduced and indigenous species

oocupy equal positions, and indeed have given some examples

)

. For this reason, the neutral term " interaction" is prefera.ble to " compet­ ition" in a

di

scussion of the relationshi ps between the two tloraa.

(

ii

)

Ne ed for J.rurther Work

The present work can on

ly

be regarded as a preliminary study ot the su

bj

ect of intera ction. It would be very much

enhanced

by further investigations along at leas t two lines.

The first of these "WOu ld

be

a practioal determination of o.bangea in the vegetation of the study area, through the repetition of the fi eld work, and in particular of the sampling surve,ys, after a lapse of time. I t has been noted ear li er that the

sampling

surveys were

carried ou t in

1 9�,

the. t is, a t about the time when the aerial topdressing of

unploughab le

pa stures with artificial fertili zers became a normal pra ctice in t

h

e NJmB.i\'S.tu dis trict.

In view of the known eff ects of the topdres sing ot unploughe.ble

(

in conjunction, where necesary, w1 th aerial oversow

in

g,

and

possib

ly

(

Matthew& and Maclean

(1 957 : 257) )

the aerial dis tribution of herbicides

)

,

will t end to bring about an increase in the pro p>rtion of higher­

producing pasture species in the sward,

and

a consequent decJrease _in the pro];Crtion of lONer-producing and weed species, including indige-

nous spec

i

es. However, this developnent implies heavier stocking, and mre intensive s t0ck contro l , which in turn involves adequate

subdivision. The IIDre difficult the country, the more difficult will this be, even allowing for the di stribution of fencing material by air. In effect, aerial f'a.nni.ng may be expected to inerease the degree

of

human

cxmtrol over the vegetation in areas of unplougha.ble pasture,

but limiting factors will stil

l

apply.

Another possible change of some interest concems the distribution

of certain important shrubby weeds, notably

tha t nre

at

present more impl)rtant at lower altitudes. Since these

speci es appear to be spreading into the higher-a

l

titude areas,

and

since there doea not appear to be any environmental barrier, they D'IAY eventually be of equal importance at higher a lti tudes . On the other hand , the more int ensive pasture managanent just referred to, possibly in combination with biological control, may result in a considerable reduc tion in the significa..."lce as we eds of these s pe cies.

The other debirable l ine of investiga

t

ion is the development of autecological studies of the more important species among these

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