ASSESSMENT OF REMNANT WETLAND FORESTS: KAITUNA WETLANDS AND CLAUDELANDS BUSH

Claudelands Bush

Kaituna Wetlands (Google Maps, 2012)

JOSH COLE

1.0 INTRODUCTION

In late March 2012, Claudelands Bush in Hamilton City and Kaituna Wetlands, near Te Puke on the coastline, were surveyed. Densities and basal areas of the dominate species were calculated using DBH measurements in multiple ten by ten metre square plots (100m2). At Kaituna Wetlands there was only one dominate species, kahikatea Dacrycarpus dacrydioides. At Claudelands Bush, there was a much richer species composition and there were three main species. Along with kahikatea, there was tawa Beilschmeidia tawa and pukatea Laurelia novae-zelandiae.

2.0 METHODS

Three 10 metre by 10 metre plots were measured out with and 100 metre tap measure. The tape was left on the ground to indicate the plot boundaries. A compass bearing was taken at each corner to make sure they were 90 degrees to avoid plots that are less than 100m2. Each plant within the plot that was over 1.35 metres was measured for their DBH (diametre at breast height) at 1.35 metres off the ground. Any plant with a dbh of less than 2.5 centimetres was not recorded. A dbh tape was used, which has pre-determined diametre measurements on one side with normal centimetres on the other.

3.0 RESULTS

The total area surveyed at Kaituna was 0.18 ha (18 x 0.01 ha plots) and 0.25 ha (25 plots) at Claudelands Bush.

3.1 Density of kahikatea at Kaituna.

Table 1: Density of kahikatea at Kaituna

Total kahikatea with stems > 2.5 708 kahikateaKahikatea density (per ha) 3,933.33 per ha

Table 1 is showing that on average there are nearly 4,000 kahikatea per hectare.

3.2 Density of all tree species at Kaituna

Table 2: Density of all tree species at Kaituna

Total number of stems counted 721 stemsstems / ha 4,005.56 stems/ha

Table 2 is showing that there are on average just over 4,000 stems per hectare.

3.3 Basal area (BA) of kahikatea at Kaituna

Table 3: Basal Area of kahikatea at Kaituna

total dbh of kahikatea 9,315.00 cmtotal dbh of kahikatea 93.15 mtotal radius of kahikatea 46.58 marea of kahikatea (pi * r squared) 6,814.84 m2

metres squared per ha 37,860.22 m2/haTable 3.3 is showing that there is nearly 38,000 m2/ha of kahikatea at Kaituna.

3.4 Total BA at Kaituna

Table 4: Total Kaituna BA

total dbh of Kaituna vegetation 9,338.90 cmtotal dbh of Kaituna vegetation 93.39 mtotal radius of Kaituna vegetation 46.69 marea of vegetation (pi * r squared) 6,849.85 m2

metres squared per ha 38,054.75 m2/haTable 3.4 is showing that there is over 38,000 m2/ha of vegetation at Kaituna.

3.5 Regression analysis of kahikatea DBH and age

0 20 40 60 80 100 120 1400

20

40

60

80

100

120

140

160

f(x) = 0.000267891986246129 x³ − 0.0486072576872787 x² + 3.21083903146332 xR² = 0.976449936538085

DBH (cm)

Age

(yrs

)

Figure 1: Correlation of kahikatea DBH and age

Figure 1 is showing a Polynomial trend line (Order 3) with the y intercept set at 0. It fits the graph plots with 84.24% accuracy. The formula for the trend line is y = 0.0003x3 - 0.0486x2 + 3.2108x. According to Figure 1, kahikatea’s girth increases at a high rate until it is around 60 years old and then increases again at around age 80.

Table 5: Oldest and average age of kahikatea at Kaituna

oldest kahikatea 70.62 yrsmean age of kahikatea 32.39 yrs

Table 5 is showing the oldest (71) and average (32) age of the sampled kahikatea at Kaituna using the trend line formula in Figure 1.

3.6 Density of kahikatea, pukatea and tawa at Claudelands Bush

Table 6: Density of kahikatea, tawa and pukatea at Claudelands Bush

Kahikatea Tawa

Pukatea

Total individuals 85 40 15stems/ha  340 160 60

Table 6 is showing that at Claudelands Bush, there are 340 kahikatea per hectare, 160 tawa per hectare and 60 pukatea per hectare.

3.7 Density of all tree species at Claudelands

Table 7: Total all tree species and stems per hectare at Claudelands Bush

Species Counted stemsStems/ha

Kahikatea 85 340

Tawa 40 160Pukatea 15 60Mahoe 373 1,492Silverfern 16 64Coprosma areolata 2 8Matai 2 8Lacebark 32 128Milk tree 14 56Cabbage tree 8 32Mapou 4 16Pittosporum 4 16Hangehange 3 12Titoki 11 44Maire 1 4Pseudopanax hybrid 3 12Lemonwood 1 4Kawakawa 2 8Pigeonwood 1 4TOTALS 617 2,468

Table 7 is showing that there are 2,468 stems per hectare at Claudelands Bush.

3.8 BA of kahikatea, tawa and pukatea at Claudelands Bush

Table 8: BA of Kahikatea, tawa and pukatea at Claudelands Bush

Kahikatea Tawa

Pukatea

Total DBH (cm) 3,434.1 1,205.1 646.4total DBH (m) 34.3 12.1 6.5total radius (m) 17.2 6.0 3.2area (pi * r squared) 926.2 114.1 32.8BA (m2 /ha) 3,704.9 456.2 131.3

Table 8 is showing that at Claudelands Bush, the BA of kahikatea is 3,704.9 m2/ha and the BA of tawa is 456.2 m2/ha and the BA of pukatea is 131.3 m2/ha.

3.9 Total BA at Claudelands Bush

Table 9: All species and their BA at Claudelands Bush

Species BA (m2/ha)Kahikatea 3,704.894Tawa 456.243Pukatea 131.266Mahoe 1,958.001Silverfern 38.749Coprosma areolata 0.034Matai 1.287Lacebark 6.853Milk tree 6.587Cabbage tree 18.322Mapou 0.175Pittosporum 0.057Hangehange 0.115Titoki 15.862Maire 0.950Pseudopanax hybrid 0.546Lemonwood 0.008Kawakawa 0.019Pigeonwood 0.003TOTAL 6,339.972

Table 9 is showing that the total BA at Claudelands bush is 6,340 m2/ha.

3.10 Histogram

2.5-20 20-40 40-60 60-80 80-100 100-1200

5

10

15

20

25

30

35

40

PukateaTawaKahikatea

DBH (cm)

No.

of t

rees

(Fre

quen

cy)

Figure 2: Frequencies of DBH of Pukatea, Tawa and kahikatea at Claudelands Bush

Figure 2 is showing that the DBH frequencies for kahikatea largely follow a normal distribution curve, whereas tawa and pukatea have more trees with lower DBH’s.

3.11 T Tests

Table 10: T tests between stand 1 and stand 2 at Claudelands Bush

TreeT Test P value

Kahikatea 0.005Tawa 0.005Pukatea 0.171

Table 10 is showing the T test results when comparing the densities of three tree species between stand 1 and stand 2 at Claudelands Bush. It shows that there are significant different densities of kahikatea and tawa between the two stands but an insignificant difference in the densities of pukatea between stand 1 and stand 2.

4.0 DISCUSSION

Tables 1 and 2 show that 98% of the plants at Kaituna wetlands are kahikatea (3,933.33 out of 4,005.56 stems/ha), and tables 3 and 4 show that kahikatea represents 99% of the basal area (37860.22 m2/ha out of 38054.75 m2/ha). This indicates that although electric fences had to be hurdled before accessing the sites, grazing from stock must be occurring. The height of the pasture on the margins of the remnants was not very tall, which further indicates this.

The ecological restoration of Kaituna Wetlands is important because it may very well have the potential to house regionally and nationally rare native plants due to it being one of the only wetlands in the Bay of Plenty with its unique climate. Studies by Burns, Smale and Merrett (1999) have shown that remote, isolated patches of bush in the Waikato, not unlike Kaituna, with unique environmental conditions, house regionally and nationally rare and threatened plants with uncommon environmental requirements.

There is hope, however for the Kaituna Wetlands. Smale, Ross and Arnold (2005) reports that Dacrycarpus forests typically recover surprisingly well from under grazing like the remnant stands of kahikatea at Kaituna have been for 70 plus years (age of the oldest sampled kahikatea at Kaituna in Table 5). Twenty years of simply fencing off the remnants will see self restoration and a turning point where pasture weeds will start to lose the battle and native ground cover and understory species will start to take over. As a result, a significant recovery of population structures of major species will eventuate. In the absence of weeds, the fencing off of these remnant patches will see a recovery to near a natural state in 40 – 50 years. It is feasible to imagine the recovery of this forest to be even faster if a community group was formed to help control the weeds and to enhance the recovery by planting wetland species. This would help develop one of the only kahikatea wetland forests left in the Bay of Plenty region. It was not absolutely evident on the day if the sampled area was fenced off or not.

Figure 1 is showing a Polynomial trend line (Order 3) with the y intercept set at zero. The y intercept is set at zero because without doing so, the y intercept would be -125. This represents the age of the kahikatea and it is obviously not possible to obtain a -125 year old tree, although the R2 value is 0.9379, which is as high as it gets. The raw data comprises of only 10 graph plots, which creates this problem. To rectify this, there needs to be more data points to plot onto the graph. A linear trend line with the y intercept set at zero would give an R2 value of only 0.6139, which is fairly low as so it was not used. The trend line given in Figure 1 fits the graph plots with 84.24% accuracy, which is not very much lower than if the y intercept was not set at zero. Therefore it presents a better formula to work with to calculate an individual kahikatea’s age from its DBH. The high rate of girth increase at ages 80 plus would be due to an increase of light levels as the tree breaks through the canopy, enabling the tree to grow faster than between ages 60 and 80, when it would typically be an understory specimen. The relatively high girth increase between ages 0 and 60 is thought to be typical of juvenile kahikatea.

Tables 6 and 7 combine to give percentages of the densities (stems/ha) of the three dominant canopy species at Claudelands Bush. Kahikatea represents 14%, tawa 6% and pukatea 2% of the stems/ha at Claudelands Bush. Tables 8 and 9 also combine to give percentages of the BA of these three species. Kahikatea represents 58% of the BA, tawa 7% and pukatea 2% of the total BA at Claudelands Bush. Cornes and Clarkson (2010) reports that this species

composition will change in the near future with the changing nature of the water table and the likely further die back of kahikatea and other wetland species being replaced by more dry-land species, especially weeds unless more kahikatea is planted and weeds are controlled.

In Claudelands Bush, according to Whaley, Clarkson and Smale (1997), one third of the native vegetation of the 122 species which survived grazing from the 1860’s to the 1920’s became extinct in the 26 years between 1954 and 1980. These are mainly ground layer ferns and understory shrubs with small populations. This is mainly due to the smothering of the weed Wandering Jew, Tradescantia flumenensis, and desiccation resulting from drainage. Around half of the remaining 81 species are in small populations and further losses are likely. Adventive weed species (60 spp.) have naturalised themselves through planting and garden escapes. Seventeen of these species are regarded as problem weeds. Cornes and Clarkson (2010) reports that Claudelands Bush is changing from a wetland to a dry-land angiosperm dominated forest. This conclusion is drawn due to the comparison of species compositions from previous studies dating 1933, 1984, 1996 and 2009. From these studies it is shown that the species composition is becoming more dominated by dry-land species. For instance, a drought in 2009 initiated a major die back of fourteen kahikatea. A drain has since been installed on the western boundary of the bush and t is likely to affect the bush’s species composition again, especially of weed species.

Figure 2 shows the slow regeneration of kahikatea with not many trees found between 2.5 cm and 20 cm DBH. It is thought that tawa was logged around the time of the settlement of the early Europeans as it is used in flooring and furniture. This is supported by the low number of tawa found at Claudelands Bush between 20 cm and 40 cm DBH. There is not enough data to analyse the pukatea DBH findings.

Table 10 shows that there is a significant difference in the DBH of pukatea between stands 1 and 2. It is unclear why this is because information on the different climatic conditions (for example, hydrology and soil types) and the specific locations of stands 1 and 2 are unavailable.

5.0 RECOMMEDATIONS

It is recommended that the remnant Kaituna kahikatea wetlands be restored since there are next to none of this ecosystem type left in the Bay of Plenty, which used to be predominantly a wetland area pre 1840. The potential of this area housing regionally and nationally rare and threatened native plants is substantial. It would be highly achievable to do so.

The efficient fencing off of the areas would be a significant first step in achieving this as discussed earlier. The setting up of a voluntary community based ecological restoration group like the coastal care group that looks after Mt Maunganui and Papamoa beaches to control any non-pasture weeds like Wandering Jew would also be a major step. This is all it would take for the area to reach maturity within 50 years as discussed earlier.

To bring the area to maturity faster, the planting of wetland forest plants such as those mentioned in this report plus mahoe Melicytus ramiflorus, cabbage tree Cordyline australis and titoki Alectyron excelsa would be advantageous.

6.0 REFERENCES

Burns, B.R., Smale, M.C., and Merrett, M.F. (1999). Dynamics of kahikatea forest remnants in middle North Island: implications for threatened and local plants. Science for Conservation, 113, 1173-2946.

Cornes, T. S., Clarkson, B. D. (2010). Assessment of Vegetation Condition and Health at Claudelands Bush (Jubilee Bush; Te Papanui). Hamilton, New Zealand: University of Waikato.

Google Maps. (2012). Retrieved from www.maps.google.com.

Smale, M. C., Ross, C. W., and Arnold, G. C. (2005). Vegetation recovery in rural kahikatea (Dacrycarpus dacrydioides) forest fragments in the Waikato region, New Zealand, following retirement from grazing. New Zealand Journal of Ecology. 29(2), 261 – 269.

Whaley, P. T., Clarkson, B. D. and Smale, M. C. (1997). Claudelands Bush: Ecology of an Urban Kahikatea (Dacrycarpus dacrydioides) Forest Remnant in Hamilton, New Zealand. Tane 36, 131 – 155.