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The altitudinal sequence of canopy/emergent tree species of Pureora was measured and compared also the basal area and density of vegetation was sampled at two separate altitudes then compared. The basal area and density between sites was found to be slightly different although was not statistically significant (p> 0.05).
Modern biogeography is the study that attempts to document and understand the geographical variations of Genes, communities and ecosystems (Lomolino et.al. 2005). One aspect of biogeography is the study of the linkages between environmental gradients and distributions of vegetation. Botanists such as Candolle and Humbolt noted the general linkages between altitude and the composition of a species ecosystem (Lomolino et al. 2005). There are many vegetation ecosystems within New Zealand that have been found to vary according to environmental gradients such as altitude. For example, the Leathwick, et. al. (1988) study shows that the primary direction of compositional change of vegetation upon Mt. Pureora in the central North Island is highly correlated with altitude. However their research also shows the degree to which these factors can be limited when making assumptions about the link between altitude and vegetation composition "Interpretation of these floristic gradients in relation to the environment is restricted to some degree by both the limited number of environmental factors recorded during the survey, and their indirect relationship with plant growth" (Leathwick, et. al. 1988 pp).
Our study also focused on the vegetation composition upon Pureora. Our class investigated the altitudinal sequence of canopy/emergent of Pureora. Our aim was to identify any differences in vegetation composition between the two areas and to investigate the degree of change resulting from the increase in altitude. We also compared the density, basal area and specie diversity of the canopy/emergent vegetation between sample sites at different altitudes within the Pureora forest.
The sample sites were located at the north-east ridge of Pureora forest (38° 31'S, 175° 33'E Elevation 549m) area which is located 20km north-west of Taupo. The soil contains a high level of pumice and volcanic ash due to past volcanic eruptions. The Pureora forest has the remnants of the Podocarp forests that were once abundant throughout the central north island. The altitude ranges from 660m asl-1165m (Leathwick, et. al. 1988). The vegetation located in lower altitudes (660m. asl) consists of totara, mataÃ¯, miro, kahikatea, and tawa. The mid altitude forest (800m-1,000m asl.) is dominated by Hall's tötara and kamahi (Leathwick et al. 1988).
The class was split into to five separate groups to conduct sampling.
The vegetation plots were subjectively chosen along link road at approximately 50m intervals. The plots where measured at 6m in diameter. At each site the elevation was recorded and a visual estimate of the number of dominant/emergent species was conducted. Each group member recorded their results and an average was calculated for the 5 individual groups. Areas that had been affected by the track and other irregularities were not included within the results. Each group also measured the diameter breast height (dbh) of vegetation within two qualitative plots. The plots where located using a compass and the area of the plots were measured using 10m x 10m quadrates (total of 10 contiguous sub-plots). The sub-plots were chosen subjectively though we are assuming independence. We estimated the circumference of each tree within the sub-plot before actually measuring. At 1.4m above ground we measured the diameter (cm) of the tree and took into account any trees with double stems, buttressed or bulging trunks and any climbing plants that could have an effect on the result. We made sure to adjust these calculations to reduce sample error. The basal area for each tree was calculated into m². The basal area of trees found within the two altitude locations were compared using a two-sample t-test for equal variances and the density was compared using a t-test for difference in means.
The difference in basal area between two altitude locations on Pureora.
There was a difference in the mean basal area of tree species sampled at altitude 540m asl (73.3 ± 54.1 m²/ha) with 1000m asl (65.4 ± 16.6 m²/ha) (Figure 1). However the difference was relatively small (7.9 m²/ha) and was not statistically significant (P-value 0.7570).
The difference in mean density of tree species at different altitude locations on Pureora.
There was a difference in mean density of tree species at altitude 540m asl (710 ± 251 stems/ha) with 1000 asl (860 ± 320 stems/ha) (Figure 2.). The difference in mean density was 150 stems/ha although this is considered not statistically significant (p-value 0.3710).
Tree species cover abundance at increasing altitudes on Mt. Pureora
Kamahi (Weinmannia racemosa) had a large increase of cover abundance from 6.5% at 825m asl to 46% at 950m asl (figure 4.). Kamahi then rapidly decreased down to 2.5% as the altitude increased to 1050m asl (Figure 5). Hall's Totara (Podocarpus hallii) increased from 4% cover abundance up to 46.6% as the altitude increased from 825m asl up to 1000m asl (Figure 4. & Figure 5.). Hall's Totara then decreased to 11.75% cover abundance at 1100m asl. Toatoa (Phyllocladus alpinus) was found at 1000m asl with 0.2% cover abundance and increased to 23% cover abundance with an increase of 50m altitude (Figure 5.). Karamu (Comprosma foetidissima) increased from 3% to 16.9% cover abundance at 1050m asl, and then decreased to 5.75% at 1100m asl (Figure 5.). Haumakoroa (Pseudopanax simplex) increased from 0.4% cover abundance at 1050m asl to 17.5% at 1100m asl. Horopito (Pseudowintera colorata) was found through out the altitude plots on Pureora ranging from 1% at 825m asl., up to 18.85% cover abundance at 1100m asl (Figure 4 & Figure 5). Miro (Prumnopitys ferruginea) increased from 8% cover abundance at 825m asl up to 25.5% at 900m asl, and then decreased back down to 8.5% at 950m asl. Tawheowheo (Quintinia serrata) had a large cover abundance at 900m asl. 38% as the altitude increased 50m Tawheowheo decreased down to 8% (Figure 4.).
Figure 1. The mean basal area of trees sampled at Pureora lodge at 540m asl. and Mt Pureora at 900m asl. (± 95% confidence interval). N= 9 sub plots
Figure 2. The mean density of tree species found at altitude 540m asl. at Pureora lodge and 900m asl. on Mt Pureora (± 95% confidence interval). N= 9 sub plots.
Figure 4. Percentages of vegetation cover abundance on Mt Pureora form altitude (820m-950m asl.) N= 9 groups
Figure 5. Percentages of vegetation cover abundance on Mt Pureora form altitude (1000m-1165m asl.) N= 9 groups
The dominant species found on Pureora was Kamahi (Weinmannia racemosa) and Hall's Totara (Podocarpus hallii). However research conducted by (Smale 1986) found that the dominant species found within the Pureora forest over a 24 year period showed that Rimu and Matai were dominant species in various parts of the forest. This difference in dominant species found from our study to the study collected by (Smale 1986) could be due to many different factors such as the lack of skill from our observations, the number of samples we conducted or the forest could have changed overtime emerging different dominant species. Although there were similarities in results recorded in our study with the study conducted by (Leathwick et al. 1988). For example was Hall's Totara was common at mid-altitude on both samples. The species found at high altitude samples were very similar with our study as Mountain toatoa (Phyllocladus aspleniifolius var. alpines), Haumakaroa (Pseudopanax simplex) and stinkwood (Comprosma foeti) were present in both results.
The basal area of tree species sampled at two locations compared with the density of tree species shows different results (Figure 1 & 2.). The mean basal area is larger at 540m asl compared with the basal area found at 1000m asl, although the density of vegetation is higher at 1000m asl compared with 540m asl. There is only a small difference between the data though may be a result of possible biases such as some students may not have measured and record each tree's within the plots correctly. The canopy stem of multi-stemmed individuals may not have been recorded separately. Also Bulging trunks may have presented problems and this may be expressed in the data. These factors may have contributed to the difference between the basal area and density being statistically insignificant.