GENERAL DISCUSSION

The classification and ordination procedure was very successful in reducing the complexity of the large amount of data collected into an easily understood form. Analysis of the environmental, structural and floristic

data sets gave compatible results and the analysis of the two separate study areas demonstrated a reasonably consistent relationship between invasion patterns and patterns already existing in the native forest.

Results from the two analyses support the hypothesis that pine invasion is most common where the forest has a low basal area, is dominated by trees of poor vigour, has poor quality advance growth, and has light litter layers. Such forest is usually found on the dry exposed slopes, at low

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altitudes (below 800 m) and on sandy loam soils. Species found to be commonly associated with invaded sites were E. rossii, E. macrorhyncha, Monotoca scoparia, Brachyloma daphnoides, Acacia rubida, E. goniocalyx, Pomaderris erio- cephala, Leptospermum brevipes and L. phylicoides.

Non-invaded forest sites usually have higher basal areas, vigorous dominant trees, vigorous advance growth and heavy litter layers. They are usually found on sheltered lower slopes and gullies and on clay loam soils but can also be on exposed slopes at higher altitudes (above 800 m).

Species commonly associated with non-invaded sites are

E. robertsonii, E. viminalis, E. dives, Pteridium esculentum, Acaena anserinifolia, Dillwynia retorta var. phylicoides and Danthonia pallida.

The vegetation on both study areas consisted of a constantly varying mosaic of forest units with very few discontinuities separating these units. The invaded and

non-invaded forests described above refer to extremes within this mosaic and, therefore, forests with intermediate vigour and exposure tended to be intermediate in invasion levels.

Results from the analysis of structural data from the Bullen Range indicated a possible relationship between disturbance and invasion levels. The most heavily invaded sites are associated with areas of forest which seem to be recovering from past disturbance. These parts of the forest mosaic contain very few remnants of the old forest, and are of a more open grassy nature than the non-invaded areas which contain many remnants of the old forest and have a more closed canopy with less grass and more shrubs in the understorey. The concept that past forest disturbance is related to invasion is examined more critically in Chapter 9*

A number of factors could be important in restrict­ ing pine invasion to the poorer quality eucalypt forests.

Stronger competition for resources in the more vigorous non-invaded forests could be preventing invasion. Alter­ natively heavy litter layers and more dense undergrowth in non-invaded forests could be preventing early pine seedling establishment. The relationship between forest disturbance and invasion could indicate that disturbance by sheep and cattle graziers earlier in the century or by wildfires has left the forest in a weakened condition susceptible to invasion. The absence of invasion at altitudes much above 800 m could be related to poor survival of young P. radiata seedlings in winter, when frost and snow damage could kill them. Further experimentation is required to determine the factors which control the distribution of invasion.

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EXPERIMENTAL WORK PART II

THE ESTABLISHMENT PHASE

This section studies some of the factors respon­ sible for the patterns of invasion. Early seedling estab­ lishment is seen as the most vulnerable stage in the life cycle of P. radiata and, therefore, a series of experiments was performed on the various stages of the establishment phase. These are described in Chapter 5«

CHAPTER 3

THE ESTABLISHMENT PHASE

3.1 INTRODUCTION

The results of the pattern analysis indicate that there are distinct patterns in the distribution of pine invasion. The pattern analysis characterized the type of forest normally invaded by pines but no causative relat­ ionships could be developed because of the nature of the

techniques used.

The absence of young pine seedlings from non- invaded sites suggests that it may be in the early stages of seedling establishment that P. radiata regeneration either fails or is eliminated in some way. In this chapter various stages in the establishment of P. radiata seed­ lings are examined with the objective of identifying those

factors which control its present distribution.

In an initial experiment the possibility is examined that phytotoxins present in the eucalypt litter are preventing successful germination and early seedling development on sites not invaded by pines. The microsite requirements for germination and early seedling survival are then investigated, followed by further studies on the early establishment of seedlings on different forest sites. Finally, a study is described on the influence of browsing herbivores on early seedling survival and on the survival of well established seedlings.

The study sites

Experimental work was based on detailed studies of seedlings growing on a number of study sites. The study sites were chosen so that a wide range of invaded

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and non-invaded forest types were covered. Those sites with little or no pine invasion have been termed "non- invaded sites" and those sites which have an abundance of invasion are termed "invaded sites".

Nine study sites were chosen and their locations are given in Fig. 3*1. Not all study sites were used in every experiment. A brief description of each site is given below.

SITE 1

Not invaded; sheltered site with a southerly aspect; dominant eucalypt species E. macrorhyncha; understorey

sparse and dominated by Acacia dealbata and Bursaria spinosa with a grassy forest floor; light litter layer.

This site represents a low altitude non-invaded site.

SITE 2

Invaded; exposed site with a north-westerly aspect; dominant eucalypt species E. rossii, E. goniocalyx and

some E. macrorhyncha; understorey very sparse with Dillwynia retorta var. phylicoides, Dillwynia sericea and Danthonia pallida being the most common species; high percentage of bare ground and light litter layer.

This site is a low altitude invaded site and the most exposed of all the study sites.

SITE 3

Invaded; moderately sheltered site with a westerly aspect; dominant eucalypt species E. macrorhyncha and

E. rossii; understorey sparse with Dillwynia retorta var. phylicoides, Brachyloma daphnoides and Monotoea scoparia being the most common species; high percentage of bare

FIG. 5. 1 L o c a t i o n o f s t u d y s i t e s u s e d f o r e x p e r i m e n t s on p i n e e s t a b l i s h m e n t . J ■ / ' LEGEND Pine Plantation Study site I

1 4 1

ground; medium litter cover and light cover of grasses and herbs.

This is a very heavily invaded site. SITE 4

Invaded; moderately exposed site with north-west aspect; dominant eucalypt species E. macrorhyncha and E. rossii; understorey sparse with most common species

being Brachyloma daphnoides, Monotoca scoparia and Dodonaea viscosa; high percentage bare ground; rocky outcrops;

light cover of Poa sieberana; light litter cover. This is a heavily invaded site.

SITE 5

Not invaded; highly exposed site with a north­ west aspect; steep slopes and a heavy cover of leaf litter; dominant eucalypt species E. macrorhyncha and E. rossii;

very little understorey but with Acacia buxifolia, Dillwynia retorta var. phylicoides and Hibbertia obtusifolia present; almost no grasses or herbs.

This site is similar to an invaded site in terms of forest structure and floristics but no invasion is present.

SITE 6

Invaded; moderately exposed site with a north­ west aspect; dominant eucalypt species E. macrorhyncha

and E. rossii; sparse understorey with Brachyloma daphnoides, Monotoca scoparia, Acacia dealbata and Ac. rubida; very

little litter; high percentage of bare ground; few grasses or herbs.

This a heavily invaded site and is at a higher altitude than any of the other invaded sites.

SITE

7

Not invaded; sheltered south-easterly aspect on moderately steep slopes; dominant eucalypt species E. macrorhyncha and E. robertsonii; understorey moderately dense and dominated by Cassinia longifolia, Olearia lirata and Acacia dealbata; moderate cover of grasses and herbs including Poa sieberana and Acaena anserinifolia; moderately heavy litter layer.

This is a non-invaded site typical of many of the more mesic sites at low altitudes in the Condor Creek Valley.

SITE 8

Not invaded; sheltered flat site; dominant eucalypt species E. dives, E. robertsonii and E. mannifera subsp. maculosa; understorey sparse with Davie si. a ulici folia, Acacia melanoxylon, Monotoca scoparia and Brachyloma daph- noides; very few grasses and herbs and little bare soil; heavy litter cover.

This is a non-invaded site which is typical of those found at altitudes at around 800 m.

SITE 9

Not invaded; sheltered site with south-easterly aspect; rocky outcrops common; dominant eucalypt species E. dalrympleana and E. robertsonii; understorey moderately

dense and dominated by Coprosma hirtella, Parahebe perfol- iata and Pteridium esculentum; medium litter cover; very rocky soil; moderate percentage of bare soil.

This site at 1100 m, is located above the altitudes at which pine invasion is normally found. Some snow

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3.2 ALLELOPATHY