FREQUENTLY USED TECHNIQUES

During the studies outlined in the following chapters, several techniques were repeatedly used. Rather than repeat the descriptions of these techniques in each section, a general discussion of them is included below. The reader will be referred back to this chapter whenever the following techniques are used.

2.4.1 Measuring seedling height and diameter

Data were collected on seedling height and diameter so that daily height and diameter growth could be calculated. Seedlings were measured at the time of planting and then again at approximately six and 12 months after planting. Seedling height was measured to the nearest centimetre. Seedlings which were less than one metre tall were measured with a one metre ruler ('Sands' brand). The ruler was placed at the base of the seedling and the seedling was then held by its topmost leaves against the ruler. Care was taken not to damage the seedling. Height measurements were taken at the tallest point where the seedling touched the ruler. Seedlings which were taller than one metre were measured in the same

way except that a five metre collapsible surveyors staff ('Surmac' brand) was used. The diameter of seedlings was measured to the nearest 0.1 mm using a pair

of Vernier callipers. The callipers were placed at the base of the seedling and closed until the jaws were just touching the plant. Care was taken not to bruise the seedling itself.

2.4.2 Assessing browsing damage to seedlings

Distinguishing mammal damage from other fonns of damage

Seedlings can be damaged by a number of agents including wind, frost, insects and browsing mammals. A description of each is given below :

i) wind damage - seedlings are typically incompletely broken off part way up the main stem. Foliage may be snapped off and deposited near the base of the seedling.

ii) frost damage - some or all of the seedling's leaves may be brown and dead. Dead leaves can accumulate at the base of the seedling. Stems and branches do not appear damaged.

iii) insect damage - usually confmed to the periphery ofleaves, where relatively small circular or curved cuttings are made. Stems and branches do not appear damaged. Usually foliage has not accumulated at the base of the seedling.

iv) mammalian damage - typically foliage is partially or wholly sheared off,

leaving straight, rather than curved edges. Damage is not confmed to leaves only and may include leaf stems, shoots and branches. Usually foliage does not accumulate at the base of the seedling.

Although mammalian damage is generally quite easy to distinguish from frost and wind damage it is possible that, on occasion, insect damage was mistakenly

identified as mammal damage. This is particularly true where leaves were

damaged right back to the leaf stem, leaving little foliage by which to make an identification of the responsible agent. On these occasions it was generally assumed that mammals were responsible. Conversely, it is felt that there would have been few instances where mammal browsing was mistaken as insect damage.

Thus, the damage estimates reported in this thesis may represent a slight overestimate of mammal damage.

Assessing damage severity

Seedlings were examined for signs of vertebrate browsing at approximately six and 12 months after seedlings were planted. An assessment of the severity of damage to seedlings was carried out following Marsh (1998). Browsing damage

I

.

ii

seve�ty .was scored using a six point scale (Table 2.4 ). The scale, which ranges from 0-S, is based on a visual estimate ofthe percentage of a seedling's biomass which has been removed by mammal browsing.

Table 2.4 : The six point scale used to assess severity ofbrowsing damage to seedlings. Browse score 0 1 2 3 4 5

Estimate of the biomass removed of 0 1�29 30-49 50-69 70-89 90-100

As a guide to how the scale is used, several photo graphs of seedlings damaged to varying severities have been included along with their damage scores (Plates 4 to

9). To ensure that this relative measure of damage severity remained consistent throughout, I was the only person who ever scored browsing damage.

2.4.3 Estimating vegetation cover

During some of the following studies measures were made of the vegetation cover on each plantation and in areas of adjoining bushland The method used to assess components of ground vegetation cover was consistent throughout. Quadrats with sides 1 m x 1 m �ere the basic sampling unit used. Estimation of coverage within each quadrat was achieved using the ocular estimation of cover method outlined by Hays et. al (1981; also see Kent and Coker 1992). Briefly, this method involves visually subdividing a quadrat into 25 units with the aid of markings made on the quadrat (0.2 m apart). Given that each of these units represents 4% of the total area ofthe quadrat, the total coverage of a particular ground cover

component can be determined by estimating the number of units it occupies.

Coverage estimates were made to the nearest 10% an'd the same observer was used for all measurements.

Plate 4 : A eucalypt seedling which has not been damaged by vertebrate herbivores.

Plate 5 : A eucalypt seedling which is estimated to have had between 1 and 29% of its biomass removed by vertebrate herbivores. This seedling would be assigned a browse score of 1 .

Plate 6 : A eucalypt seedling which is estimated to have had between 30 and 49% of its biomass removed by vertebrate herbivores. This seedling would be assigned a

Plate 7 : A eucalypt seedling which is estimated to have had between 50 and 69% of its biomass removed by vertebrate herbivores. This seedling would be assigned a browse score of3.

Plate 8 : A eucalypt seedling which is estimated to have had between 70 and 89% of its biomass removed by vertebrate herbivores. This seedling would be assigned a browse score of 4.

Plate 9 : A eucalypt seedling which is estimated to have had over 90% of its

biomass removed by vertebrate herbivores. This seedling would be assigned a browse score of 5.

2.5 Statistics and notation

For each of the statistical analyses employed during this text, a brief description is given in the methods section of the chapter where it is first used. All analyses were performed using either the SAS or SYSTAT statistics packages. In all cases the level of statistical significance has been set at a<0.05 (Zar 1984). Table 2.5 outlines the notation and abbreviation associated with the techniques used. Table 2.5 : Explanation of the statistical notations and abbreviations commonly employed throughout this text.

Notation Description

'X2 the chi-squared test statistic

df degrees of freedom

F Fisher statistic for analysis of variance

n the sample size, number of observations

no. number of

ns denotes a result that is not significant (p>0.05)

p probability

r Pearson's correlation coefficient

fl coefficient of determination

adjusted r2 r adjusted for sample size

rho the Spearmann rank test statistic

se standard error

sd standard deviation

sr semi-partial correlation coefficient

t the t-test statistic

T _{the Wilcoxin signed-rank test statistic}

u the Mann-Whitney test statistic

* _{denotes a result that is significant (p<0.05)}

** _{denotes a result that is highly significant (p<O.Ol)}

CHAPTER 3

SEEDLING GROWTH AND BROWSING DAMAGE