Retos y principales discusiones planteadas sobre el periodismo judicial

INTRODUCTION

An experimental approach is most useful when examining birds and logging impacts. Management activities can be used to create experimental situations, and this approach has been used internationally (e.g., De Graaf, 1992; Keller and Anderson, 1992; Lance and Phinney, 2001) and by recent Australian studies in Western Australia (Craig, 1999; Wardell-Johnson & Williams, 2000), NSW (Huggett, 2000) and Victoria (Loyn, 1998). Therefore this investigation was originally designed as a fully replicated, integrated longitudinal study, with two years of field work in three forest areas involving bird censusing, bird behavioural observations and vegetation sampling. The field work took place between November 1992 and February 1995.

This chapter outlines and discusses theoretical and practical issues relating to the experimental design of this study, the data collection and the statistical analysis. The first section of this chapter introduces the experimental design and the study sites and discusses non-demonic influences and site-selection criteria. The chosen bird census methods are then described and justified based on a review of the relevant literature. In support of the bird census methods chosen, data is presented concerning the detectability of karri forest birds in habitats of different structure and the suitability of the chosen census cut-off distance to test the chosen census method. The three levels of data chosen for analysis - the Community level, the Guild level and the Species level are then discussed and justified.

Chapter 2 : Experimental Design and Methods

levels of analysis, statistical analysis) are relevant to several data chapters. Other methods used less widely in this thesis will be discussed in the appropriate chapters.

EXPERIMENTAL DESIGN

This study complements and extends (in both time and space) two important prior investigations - Wardell-Johnson (1984, 1985) studied the ecology of the avifauna in mature karri forest, and Wardell-Johnson and Williams (2000) examined avian edge responses in karri forest, but only in one forest block, Gray block, and only up to 3 years after logging. I examined 3-5 year old (Establishment) regrowth, and 10-15 year old (Juvenile) regrowth and so extended the ages of karri regrowth edges studied. I also chose three forest blocks, one of which was Gray, to examine the consistency of any observed Edge Effects on birds or invertebrates throughout the karri forest compared to that in Gray forest block. A further extension of the work of Wardell-Johnson and Williams (2000) was to census birds in all four seasons rather than only spring and summer. This design examined the community, guild and species-level edge responses of karri forest bird species, and looked for differences in these responses between regrowth ages, forest blocks, and over time. Rather than a BACI design (Before After Control Impact), as used by Wardell-Johnson and Williams, (2000) and Williams et al. (2001) in karri forest, and by Craig (1999) in Jarrah forest, this study used a longitudinal design of several sites of each forest age. The advantage of using a longitudinal study is

Chapter 2 : Experimental Design and Methods

Within each of the three forest blocks (Jane (34 35’, 116 18’), Sutton (34 29’, 115 17’) and Gray (34 18’, 115 49’)) (shown in Figure 1.1), three replicate transects were examined across the edges between mature forest and:

a) Establishment (3-5 year old) regrowth (hereafter referred to as Establishment transects),

b) Juvenile (10-15 year old) regrowth (hereafter referred to as Juvenile transects) and

c) Mature forest (mature trees of various ages and management history, but greater than 120m from forest/regrowth edges) with imaginary edges as controls (hereafter referred to as Mature transects).

These edge types are shown schematically in Figure 2.1. The three replicate transects for each edge age provided a random blocking factor. Each of these replicated transects consisted of a set of four points across the edge. The points were:

a) 120m from the edge into the regenerating forest b) 60m from the edge into the regenerating forest c) On the edge

d) 60m from the edge into the mature forest. There was no census point 120m from the edge into the mature forest because it was suggested from previous work that avian edge responses in Karri were restricted to within 50m of the edge on the mature side, but extend further into the regenerating forest (Wardell-Johnson, unpublished data).

Chapter 2 : Experimental Design and Methods

There were thus 108 census points in total - three transects each of four edge distances, in each of three edge ages within each of three forest blocks. The number of census points and thus replicates in the experimental design were limited by the number that one observer could census in a field season, allowing for days of bad weather which delay sampling. Figure 2.2 illustrates the field site locations, and Figures 2.3, 2.4 and 2.5 illustrate the mapped layout of transects within each of the three forest blocks.

Site selection

The most important consideration for the choice of forest blocks was the availability of regrowth coupes in the correct age classes. However, I also tried to include forest blocks as widely dispersed as logistically possible throughout the range of karri. The topographic distribution of karri within its range is related to the presence of the specific soils it depends on (McArthur and Clifton 1975, cited in Christensen, 1992). In the northern part of the Nornalup system, Karri occurs low in the profile, in the southern part of the Nornalup system and in the Denmark system, karri occurs only in the highest parts of the landscape or adjacent steep slopes, and in the central part of the Nornalup System, karri occurs throughout the landscape (Bradshaw and Lush 1981, cited in Wardell-Johnson et al., 1991). However, my sites did not extend as far south as Northcliffe and certainly did not reach the southern part of the Nornalup System or the Denmark System, so topographic issues are small. Wide dispersion should help to

Chapter 2 : Experimental Design and Methods

1) The mature forest in both control and edge transects had to be predominantly karri. Although some marri and blackbutt were allowed, sites with a predominance of jarrah were not considered suitable, although some census plots did contain jarrah trees (Chapter 10). Coupes were selected for their mature karri trees, and all mature karri were removed from a coupe. In some forest blocks and coupes, this tended to leave predominately jarrah and marri forest on the edges, because of the small natural patch size of karri-dominant forest (Bradshaw & Rayner, 1997a). This made it difficult to find edges of suitable forest that fulfilled the other criteria.

2) Easy access to the edge was essential because bird censusing is time restricted, and a number of sites had to be censused each morning. Therefore, all census sites in this study have an unsealed road or track through them. These tracks vary in width and extent of clearing. The presence of roads and tracks has been linked to changes in the density of birds (Reijnen et al., 1995; Kuitunen, Rossi & Stenroos, 1998), the bird community (Miller, Knight & Miller, 1998), habitat quality (Ortega & Capen, 1999), movements of understorey species (Develey & Stouffer, 2001) and nest predation (Yahner & Mahan, 1997), so sampling arrays paralleling roads should ideally be avoided (Thompson, 2002). However, because tracks and roads were present at all census points any influence was consistent. A passing vehicle was only observed on two occasions during two years of morning bird censuses.

3) The ages of the regenerating forest were strictly defined. Within each forest block there were only a few coupes of the correct regeneration age, and suitable edges had to be found within this restriction. Older regrowth sites could not be included in the

Chapter 2 : Experimental Design and Methods

4) The management strategy regarding fuel reduction burns at the time of the study recommended burning every seven years for karri forest. The simplest way to minimize the (unknown) effect of fire on my experiment was to use sites of differing fire age and scatter these as much as possible through the experiment so that no treatment consisted solely of one age since burning, and thus no result arose from the effect of fire rather than the effect of edge. Once the sites were chosen, liaison with Department of Conservation and Land Management (CALM) district officers meant that fuel reduction burns through the field sites could be avoided until the study was concluded. Any wildfires were likely to damage only a small number of study sites because of the distances between the forest areas. No sites were burned during the course of the study.

5) Landscape position is independent of edge in this experiment. As a result, census points are found in gullies, on hills, up slopes, near creeks and so on. The factor determining the siting of census points in the landscape is their relation to edge, not their landscape position.

Non-demonic intrusions

“By non-demonic intrusion is meant the impingement of chance events on an experiment in progress…by definition the nature, magnitude and frequency of such chance events are not predictable, nor are their

Chapter 2 : Experimental Design and Methods

Gray forest block and Sutton forest block (scrubrolling, road-building). This forced a re-design and directional change of the experiment and thesis after the first year of data collection. Consequently, the overall experimental design is neither optimal nor as complete, and this thesis considerably longer than without this ‘non-demonic intrusion’ (Hurlbert, 1984).

Stubbornly (and perhaps foolishly), rather than abandon the study, I decided to continue using salvageable portions of the original design that were still intact and which would still allow robust testing of hypotheses relating to Edge Effects. Milliken and Johnston (1984) recommend that if a design is incomplete, it is appropriate to look for hypotheses of interest that can be tested within complete subsets of the design. Risbey et al. (2000) used this approach in an ecological context. None of the three forest areas still had all replicates from all treatments intact in the second year, so intact transects in Jane and Sutton forest blocks were combined to make up the equivalent of one forest area. Jane and Sutton forest blocks were closest together geographically and were most practical to combine for logistic reasons. Two replicate transects of Mature forest and 3 transects of 10 year old edge census points from Jane block were combined with 1 transect of Mature forest and 3 transects of 3 year old edge points at Sutton block to create one data set of 36 census points. Bird banding was regrettably discontinued because of the disruption to the Jane forest block Establishment transects, and logistic difficulties caused by the distance between transects in the second year.

Because of the non-demonic intrusions, two related datasets are considered in this thesis to answer two different hypotheses about bird distribution across karri forest edges. In the first year of the study (November 1992 to August 1993), before the non-demonic intrusion, birds were censused at 108 census points distributed across 3

Chapter 2 : Experimental Design and Methods

seasons (one year). This data set enabled consideration of the consistency of bird species edge responses and distributions between forest blocks. This is the Year 1 dataset.

In the second year of this study (May 1994 to May 1995), after the non- demonic intrusions, only one forest area (an amalgamation of Jane and Sutton sites, described above) was sampled. The second dataset (the 2 year data set) used only 36 census points - three replicates of four edge distances in each of three edge ages (Establishment, Juvenile and Mature (control)), but censuses were taken in each of eight seasons. This enabled assessment of bird species distributions across karri forest edges over a longer time period to determine if changes in abundance of species are consistent over time.

Community, Guild and Species

Bird data for this thesis are analysed at three levels. The first was the community level, using the total of all species and all birds seen and heard (Chapter 3). Next, species were grouped into three broad guilds based on their diets (Chapters 4, - 6), and then the Insectivore guild into six finer guilds (Chapters 7 - 9). Finally, the bird responses to edge at the level of 24 common individual species were examined within each of the foraging guilds (Chapters 4 - 9). Sevenster (1998 p327) defined a guild as:

Chapter 2 : Experimental Design and Methods

while niches of some member species are in the centre of the guild, the niches of other species are more peripheral and/or broader, linking one guild to the next.”

This thesis uses the a-priori guild definitions of Wardell-Johnson and Williams (2000) for karri forest birds with some alterations. To create the three broad bird foraging guilds (Nectarivores, Granivore/Frugivores and Insectivores), species in Wardell-Johnson and William’s guilds were clumped according to Table 2.2. The category “Vertebrates and large invertebrates” was too small to analyse, with a total of less than 50 detections for three species in Year 1. Six insectivore sub-guilds, from the seven used by Wardell-Johnson and Williams (2000), were created by clumping their guilds “Invertebrates from bare ground” and “Invertebrates from dense understorey or damp ground below”. This was necessary because there was only one species abundant enough to analyse, the Splendid Wren, in the “Invertebrates from bare ground” guild, and the distinction between foraging on bare ground and damp ground could be ambiguous. This new guild is called the “Ground and Understorey” foraging guild. The other insectivore guilds used were the same as Wardell-Johnson and Williams (2000): “Shrub and Midstorey”, “Canopy”, “All Levels”, “Aerial”, and “Bark” foraging guilds.

BIRD CENSUSING METHODOLOGY

The principal goal of the bird census was to sample all birds within a 30m radius of the census point for comparisons of bird abundance and diversity at different distances across karri forest edges. The principal goal of bird banding was to determine,

Chapter 2 : Experimental Design and Methods

Description of the bird census methods

Censusing was carried out at each census point using the methods of Wardell-Johnson and Williams (2000), with a 5-minute count in a variable circular plot (Reynolds et al., 1980), using all birds detected within 30m of the census point for the statistical analysis. For the census, birds were recorded in six distance bands. These were 0-5m, 5-10m, 10-20m, 20-30m, >30m and >60m from the census point. Only birds detected within 30m of the census point were used for the analysis (Wardell- Johnson and Williams, 2000).

Bird censuses were taken seasonally (spring (November), summer (February), autumn (May), winter (August)). Samples were taken late in the seasons, as the karri forest is cooler and wetter than jarrah forest and the peak of each season is later (Grant Wardell-Johnson, personal communication). Field et al. (2002) found that within a season in South Australian woodland, the time span over which bird surveys were repeated on different days did not have a significant influence on species richness estimates. Census points were mainly sampled five times within each season to obtain variance estimates (Eberhardt, 1978), but some sites in some seasons (especially winter) could only be sampled three times because of inclement weather or access problems (e.g., large fallen trees, bridge closures).

Chapter 2 : Experimental Design and Methods

sampled, especially if rain had interfered with the schedule. On rainy mornings, there is a tendency for the major calling period of birds to be extended later (Keast, 1994). Censusing was continued through light, intermittent drizzle, but was never carried out during rain. Rain delays time of first singing, and birds call significantly less on rainy mornings (Keast, 1994). I did not census in high winds – birds avoid flight and there can be a marked decrease in activity in such conditions (Dawson, 1981). The census order of each point and transect were rotated through the morning so that each census point was sampled at different times in early morning, mid morning and late morning over the five samples at each point within the field season. Transect starting ends were alternated and I wore dull coloured clothing for censuses.

All birds seen and/or heard were recorded. Five core variables were always recorded for all birds or groups of birds seen and/or heard:

1) The method of detection (sight, sound, sight and sound);

2) The horizontal distance of the bird from the observer (in the six categories 0-5m, 5-10m, 10-20m, 20-30m, >30m, and >60m)

3) The direction in relation to the edge (parallel, towards, away); 4) The activity of the bird (singing, foraging, resting, flying); and 5) The number of birds in that observation.

Care was taken to avoid counting the same bird twice within the five-minute census period. If a bird counted at one census plot moved onto the next census plot and was present there during the next five-minute census period, it would be treated as an independent record and counted at that plot. The number of birds in the census plot for

Chapter 2 : Experimental Design and Methods

period. Birds flushed while approaching a census point were recorded using the distance from the point to where they were first flushed as the detection distance (Reynolds et al., 1980).

Behavioural observations were taken opportunistically during the census for birds that were seen, although the highest priority was given to detecting all birds present (the five core variables). If the bird was heard but not seen, its activity was recorded as 'singing'. Not all of the behavioural variables could be determined for each bird seen. Further variables recorded opportunistically were:

6) Activity (Forage, Call, Rest, Fly, Social, Pair, Alarm, Nest)

7) Foraging Method (if foraging) (Probe, Scratch, Pick, Flower, Fruit, Hawk, Flit, Sally, Hover),

8) Activity site (Air, Ground, Flowers, Seeds, Leaves, Twigs, Trunk, Snag, Dead Stick, Live Stick, Branch, Log)

9) Height of the bird (0-1m, 2-5m, 6-10m, 11-15m, 16-20m, 21-30m, 31- 40m, >40m),

10) Vegetation Strata (Ground, Dead Stick, Live Stick, Leaf, Midstorey, Trunk, Inner foliage, Outer Foliage, Above Canopy, Epicormic, Coppice)

11) Plant species utilized

Chapter 2 : Experimental Design and Methods

Justification of the bird census methods

In this study, I chose to use the variable circular plot method partly because it has been used in previous karri forest studies (Tingay and Tingay, 1984; Wardell- Johnson, 1984, 1985; Wardell-Johnson and Williams, 2000; Williams et al., 2001). Therefore, the results of this study can constructively increase the knowledge base for karri forest birds, without being confounded by the census method differences bemoaned by Recher (1988). However, “One should not adopt a counting technique simply because it is commonly used” (Thompson, 2002).

Of the four main methods used to census birds, transects, area searches and variable-circular plot methods are more suited to community studies than mapping or mist-netting (which is only suitable for understorey species) (Recher, 1988). The Variable-Circular Plot method was designed for tall, structurally complex vegetation types and dense vegetation (Reynolds et al., 1980; Recher, 1988) and is generally considered to be the better technique to use in these habitats (Anderson and Ohmart, 1981; but also see De Sante, 1981). In closed habitat, such as karri forest, circular plots may be the only technique logistically possible (Ralph, 1985). Although Area searches detected a significantly greater density of birds, and provided density estimates for a greater number of species than either point counts or transects in jarrah forest in south- west Western Australia (Craig, 1999), that method was not suitable for the wetter, more densely vegetated karri forest. A survey of potential biases in the variable circular plot method and how they were overcome in this study follows.

Observer Bias - By being the only observer, I effectively eliminated differences between observers, which could otherwise be a source of bias (Pyke and