Methods and sites visited

2.3.1. SAMPLING PLOTS

The members of the BIORAP team consulted together, studied previous literature and examined aerial photos to select a number of study sites that could hopefully be visited. Not all of the sites selected were visited by the whole team because the team members usually worked independently. The botanical team visited most of the study sites, nine of which were selected as suitable for the establishment of forest plots. Figure 2.3 shows the location of all sites visited by the botanical team, while Annex 2.1 gives basic information about each site. Figures 2.4 and 2.5 show some of the sites visited.

The nine selected sites are identified as follows: (1) Mt Talau secondary forest; (2) Mafana secondary forest; (3) Mo’ungalafa secondary forest; (4) Toafa disturbed lowland forest; (5) Vaka’eitu lowland forest; (6) ‘Oto lowland forest; (7) Mo’unga Lafa lowland forest; (8) ‘Euakafa lowland forest; and (9) Utula’aina lowland forest. Forest plots were sampled on these nine sites, while notes were taken on the vegetation and flora of the other sites visited.

The nine sites were visited and studied to determine the best location, orientation and size of plot to be sampled. Major considerations were accessibility and safety of establishing plots in the area, as well as the uniformity of the vegetation and the absence of signs of recent disturbance. In each of the plots, a 50 m tape measure was laid out, and if the area permitted, another one added to the end to make a 100 m centerline. Once the end points were established, their GPS coordinates were recorded so that the sites can be revisited in the future to see what changes occur there over time (see the GPS coordinates in the Results section). The boundaries were then roughly marked off 5 m on either side of the line, making the plot sizes 500 or 1,000 m².

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Figure 2.3. Location map of sites visited by the botanical team.

Figure 2.4. Utula’aina Lowland Forest (photo by J. Atherton).

Figure 2.5. Littoral Strand on ‘Umuna island (photo by J. Atherton).

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While the plots were being marked off by the field crew, the principal investigator made a checklist of all vascular plant species present in the plot and the surrounding area. Then the field team measured all trees in the plot having a minimum diameter at breast height (dbh) of 5 cm using a dbh tape. The dbh figures were recorded and were later used to calculate the relative dominance of the trees present. Figures 2.6 and 2.7 show the field work.

To present the data for the nine plots, the sum of the basal (i.e. cross-sectional) area of the individuals of each tree species was calculated. The species were then put into the right hand table column in order of their total basal area, from high to low. For each species, the number of trees sampled, the number of trees with a dbh of 15 cm or more, and the total basal area were put into the next three columns. The total basal area of all the trees was then summed at the bottom of the fourth column. The relative dominance parameter is the most important one in determining which species are the most important in the plot. This is calculated by dividing the basal area of each of the species by the sum of the basal area of all of the species, and is shown in the fifth column. The use of basal area to determine dominance is a standard vegetation ecology method. The data for the nine plots are shown in Annex 2.2.

2.3.2. RECORDING THE FLORA

In addition to the vegetation plots, the flora was also studied. Lists of species present, both native and alien species, were made for each of the sites visited, and also for other areas that were visited but not chosen for a plot. The purpose of these lists is to add to the flora additional species not found in the plots, and to see if any species might be disappearing.

A number of new native and weedy species were recorded during field work. Voucher specimens were collected for flowering or fruiting individuals found during the work, and sometimes sterile (non-flowering or non-fruiting) species if their identity was not certain. In fact, the Principal Investigator knew nearly every native and weedy species encountered, making identification more accurate. The voucher specimens were taken back to the base of operations (the Portwine Guesthouse in Neiafu), and voucher herbarium specimens were prepared. Whenever possible, an original and three duplicates were pressed. The fresh specimens were put into sections of newspaper, numbered, and put between cardboard ventilators. The two sections of a wooden plant press were then added to the ends, and the whole press with specimens was wrapped up tightly by the press straps. The press was then put onto cinderblocks, between which a space heater was placed. The whole set up was then wrapped up with a blanket-like sheet of impermeable material, and the heat turned on to dry the specimens. At first the specimens were not drying fast enough, but eventually by tinkering with the set up, most of the specimens dried in one or two days. At the end of the BIORAP, the voucher specimens in newspapers were put in numerical order and packaged up for shipment back to Samoa. In Samoa, the specimens were separated into sets to be sent to Tonga, Auckland Museum Herbarium and the University of Hawai’i Herbarium.

2.4. Results

2.4.1. FLORA

Over 180 voucher specimens, most of them with duplicates, were collected and eventually sent to the designated institutions. Nearly all of these were identified while in Tonga, but several needed further study by the Principal Investigator back in Hawai’i. The voucher specimens were then added to the list of specimens already known from Vava’u, and a comprehensive list of the flora of Vava’u was prepared (Annex 2.3). The species in the table were first arranged into five groups: (1) dicots; (2) monocots; (3) gymnosperms; (4) ferns; and (5) fern allies. The species in each group were then separated into their respective plant families arranged in alphabetical order, with the species within the families also in alphabetical order. The scientific name of each species is followed in the second column by the authors who named them.

Figure 2.6. Laying down the 50m transect tape in the Utula’aina lowland forest (photo by J. Atherton).

Figure 2.7. Hoifua measuring the diameter at breast height (dbh) of a tree (photo by J. Atherton).

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Based on the previous literature and the new collections, a total of 440 species are reported to be native or naturalised in Vava’u. This includes 262 native species, divided into 188 dicots, 39 monocots, two gymnosperms, 30 ferns and three fern allies. Tonga has 15 endemic species, eight of which are found in Vava’u, including the new record Phyllanthus amicorum.

Two species are endemic to Vava’u − Atractocarpus crosbyi and Casearia buelowii.