Does the biodiversity of the sand dunes at Holkham follow the expected pattern?

Question: Does the biodiversity of the sand dunes at Holkham follow the expected pattern?

Hypothesis: The sand dunes at Holkham follow the expected pattern in fig.2. This is based on the premise that forested area can be seen on fig.1, at the end of the dune. Option B: Oceans and Coastal Margins Sub-Section 2: Interactions between oceans and coastal places linked to sand dune development

Holkham: Located on the North Norfolk coast, the Holkham National Nature Reserve is England's largest national nature reserve, making it a prime location for physical geography data collection. Fig.1 shows an area of the reserve, from which data was collected

 

The variety of species found within an environment is measured by biodiversity. This is typically quantified in terms of plant species in an ecosystem of sand dunes. Biodiversity can be used to assess an area's status and gauge how favourable the circumstances are at a given time. The biodiversity of a sand dune ecosystem, in theory, rises with distance inland but falls in the late climax region. This is in line with fig. 2.

The biodiversity will increase with distance from the HWM, as conditions near the HWM are harsh, allowing a few pioneer species to survive. These species have halophytic adaptations, adaptations to reduce water loss and increase water absorption, e.g. marram grass. These species provide shelter from the conditions and release nutrients into the soil through decomposition, thus changing the conditions. They also stabilize the ground, promoting the development of soil, which retains moisture.

These factors make the environment more habitable for other species, increasing biodiversity. Away from the shoreline, the dunes increase in height, producing areas of slack (see fig.3). These areas are sheltered and are closer to freshwater stores, encouraging plant growth, and thus increasing biodiversity. Fig.3 shows this via the marked water table. Soil pH also changes, near the HWM the pH is very alkaline meaning few species can grow. Plant decomposition neutralizes the soil, meaning more species can grow, increasing biodiversity. However, biodiversity decreases in the late climax stage (see fig.2) as the area is likely to be dominated by fewer species. In the lowlands of the UK, these are expected to be oak or ash, which block sunlight to the forest floor, preventing the growth of smaller plants

Prior to data collection, a pilot study was conducted to decide on the appropriate equipment, practise data collecting, and test several clinometers, quadrants, and pH kits.

 

On March 12, 2019, a variety of data were gathered using a group sampling method. The information in fig.1 was gathered in Holkham on the North Norfolk coast.

 

 

Sadly, there were bad weather conditions, with plenty of rain and strong winds. It was decided wind speed data would not be collected as inconsistent winds would have led to unreliable results.

 

 

Data were gathered via stratified systematic sampling along a transect. Typically, data were gathered every 10 m, with the exception of the gradient, which was captured at a slope break. However, the distance was increased to 20 m if comparable results were acquired at three sites in a row. Since there were no paths for collecting the data, stratified sampling was employed. Changes could be noticed throughout the dune system thanks to the data collection method and sampling size.

 

 

A 250 m tape measure was used to measure the transect, however, only 50 m was surveyed at a time to improve accuracy. The tape was typically extended in more protected regions after being cut to 25 m owing to the weather.

 

 

There would be two ways of gathering pH data. A pH kit and probe. The probe needed to remain buried for a considerable amount of time in order to collect reliable data, according to the pilot study. Therefore, just the pH kit was utilized that day. The techniques table, fig.4, lists the precautions that must be taken while using this method to assure accuracy.

 

 

Despite data collection, the recording sheet was no longer usable because of the circumstances. As a result, data from a prior year was used; this group data is displayed in fig. 15.

 

A diversity index can be used to measure diversity. Values for the Simpson-Yule diversity index range from 0 to 1.

 

0 = Monoculture

 

 

1 = High biodiversity

 

 

The index is calculated using the equation:

 

 

\(Diversity\ =\ 1\ -\sum{(\frac{Pi}{Ni}})^2\)

 

 

Pi = Species percentage cover

 

 

Ni = Total percentage cover (excluding bare ground)

 

 

Site: 13

 

Sites 1 and 3 were not plotted on fig.17 as only bare sand was recorded. Fig.17 shows that the general trend is an increase in biodiversity with increase distance from the HWM, biodiversity at site 2 was 0 increasing to 0.501 at site 21. This agrees with the expected pattern explained in the introduction. This is due to harsh conditions near the HWM meaning only pioneer plants such as marram grass and red fescue are able to survive. These pioneer species help to retain moisture in the ground and provide nutrients via decomposition. This encourages the growth of less specialised species eg moss B, which has 88% coverage at site 10, seen in fig.18. These pioneer species also provide shelter for other flora that do not have specialised leaves to reduce transpiration

Fig.18 clearly displays the composition of percentage vegetation cover across the transect, allowing easy comparison between sites. The colour co-ordination allows easy location and identification of plant species. The changing flora along the transect can be seen in fig.18, eg dandelion which is only present after site 14. Fig.18 also shows the re-emergence of marram grass at sites 13 and 14, due to the presence of a 10 m wide path, labelled on fig.17. The changing pH from alkaline condition near the HWM to more acidic conditions, is also displayed on fig.18. Fig.18 also consists of a drawn profile of the dune, it seems to be similar to fig.3, with an obvious fore-dune and main ridge, which are followed by smaller grey dunes

However both fig.17 and 18 show a decrease in biodiversity at the late climax stage, from 0.815 at site 19 to 0.501 at site 21 on fig.17. On fig.18 it can be seen that there are fewer species present at sites 20 and 21 compared to sites 16-19. This agrees with explained predictions in the introduction. This is because the area becomes dominated by fewer larger species, which block sunlight from the forest floor, preventing growth of smaller species. It is expected that in lowland UK this would be oak or ash, however fig.18 shows, at Holkam it is mostly pine.

Therefore the pine forest at Holkam is not a natural development of the dunes. In fig.1 it can seen that there is a settlement behind the forest, which is part of the Holkham estate, the pine forest was probably planted as a wind break. Although it is not a natural species it does still fit with the model, fig.2. However it could be argued that planting these trees has meant that the model is now over a smaller area than what it would naturally have been ites 14–21 follow the trend-line, with increasing biodiversity in regular intervals (sites 14-19), then decreasing (sites 20-21). However the data at sites 2-13 fluctuated. Sites 5, 6 and 7 and biodiversity data of 0.484, 0.122 and 0.514 respectively.

These fluctuations do not seem to correlate with the changing of slope shown in fig.18. They could be due to other factors such as moisture or nutrient levels. Near the HWM the conditions are very harsh, therefore any difference in these factors can be significant, which in turn can affect growth. Marram grass is the main anomaly in fig.18. It is present at site 5 with 50% cover, then is not seen until site 13 and 15. This is due to a path that can be seen in fig.17. This caused the re-emergence of pioneer species such as marram grass, as there was a change in conditions similar to that near the HWM. However as seen in fig.17 this did not have a large negative effect on the biodiversity as many species were already established, and conditions were not harsh enough to cause then to die.

Fig.19 shows clear succession with distance from the HWM, as well as showing relatively high or low biodiversity. For example at 50 m (site 6) there was a low biodiversity, this can be seen in terms of relativity on fig.19, as few species were present at that distance. The major anomaly on fig.19 is the presence of marram grass at 170-210 m. This was previously seen on fig.18, where it was explained that this was due to the presence of a 10 m wide path, which created conditions similar to those near the HWM. Fig.19 also clearly shows that few of the species recorded were present at early sites, this is due to harsh conditions that only pioneer species with adaptations are able to survive in. Fig.19 also shows that only bare soil was recorded at sites 1 and 3.

The pH is lowering along the transect in Figs. 18 and 20, from 7.4 at site 1 (0 m) to 5.0 at site 21 (275 m), which fits the anticipated pattern described in the introduction. However, from sites 1 to 14, the pH is constant from 6.8 to 7.2. (0-190 m). The pH gradually starts to decline after site 16 (220 m). The introduction emphasised that this trend was anticipated and that it is the result of increased organic matter decomposition, which lowers soil pH.

The main anomalies occur at sites 15(190 m) with pH of 5.1 and 20(260 m) with pH of 7.4. Fig.18 shows that site 15 in on top of a slope, therefore little water will collect around the site, meaning the acidity of decomposing organic matter will not be neutralised. Fig.18 also shows that site 20(260 m) is located in an area of slack, therefore water will collect, increasing surrounding soil pH.

A reason proposed in the introduction as to why biodiversity would increase with distance from the HWM, was changing soil pH. Near the HWM the soil pH is relatively alkaline, meaning only pioneer species are able to grow. It then becomes more neutral, due to decomposing plant matter, which is a preferred pH for many plants, thus increasing biodiversity. The data in fig.18, fig.20 and fig.22, does show this trend of decreasing soil pH. However fig.21 shows there is no correlation at Holkam between pH and biodiversity. As sites with similar pH's had very different diversity index figures, eg both site9 and 13 had soil pH of 7.2, yet biodiversity recorded was 0.417 and 0.688 respectively. No statistical analysis will be carried out on the data displayed in fig21, as the scatter graph clearly shows there is no correlation. Another explanation proposed in the introduction for changing biodiversity, was dune shape, creating ares of shelter that would increase plant growth and biodiversity. Fig.17 and fig.18 show this at two points along the transect. Firstly at sites 5-7, site 6 had a much lower biodiversity of 0.122 compared to sites 5 and 6 recording biodiversity indices of 0.485 and 0.514 respectively. Fig.18 shows that site6 is very exposed to the elements whereas sites 5 and 7 are in areas of shelter. If plants are exposed to harsh conditions this increases their rate of transpiration and subjects them to physical abuse. This means that only specialised plants are able to survive in exposed conditions. Secondly at sites 18 and 19, which have diversity indices of 0.793 and 0.815. Fig.18 shows that site 19 is in an area of shelter compared to site 18 which is exposed. Although there is not a huge difference in diversity indices, it can be seen from fig 18 that site 18 recorded many more pioneering species, such as marram grass, than site 19, which instead recorded fewer specialised plants, such as Plant E.

H0 = There is no relationship between distance along the transect and soil pH Spearman’s Rank is calculated using the equation..

 

\({r_s}={1}-{6∑ d^2\over n^3-N}\)

 

\(∑ d^2 =2603\)

 

\( 6∑ d^2=15618\)

 

𝑛3 − 𝑛 = 9240

 

\({ 6∑ d^2\over n^3-n} = 1.609\)

 

Therfore we must reject H0 as the value -0.690 is higher than the critical value of 0.556 at the 0.1 range. It can be stated with 99% certainty that there is a relationship between distance along the transect and soil pH

The data gathered indicates that the hypothesis is valid. With increasing distance from the HWM, Holkham's biodiversity rises until the late climax stage, when it starts to decline. The biodiversity improves from 0 at site 2 to 0.815 at site 19, then declines to 0.501 at site 21, as shown in Fig. 17.

 

The enhanced biodiversity was discovered to be caused by the form of the dunes, which create areas of slack. These locations are better protected, creating favourable conditions for various species. Figures 15 and 16 at sites 5-7 depict this. Of the three sites, Site 6 has the least biodiversity (0.122). Sites 5 and 7 have biodiversity indices of 0.485 and 0.514, as opposed to those of those two sites. Site 6 is much more exposed, as seen in Fig. 15, thus only specialized plants, such as marram grass, may live there.

 

 

Up to the late climax stage, the introduction thought that declining pH was a cause of growing biodiversity. It was found that pH did decrease over the transect from 7.4 at site 1 to 5.0 at site 21. Figures 15 and 18 show this, and Spearmen's correlation supports it. As may be seen in fig.21, no association with biodiversity was discovered. Therefore, it is necessary to disprove this theory.

 

 

Since pH was probably not a significant influence on the plants at Holkham, no correlation was likely discovered. The pH was not severe enough to hinder the development of the vegetation. In determining the growth of the flora and hence the biodiversity, other elements like shelter and soil nutrition/moisture were probably more important.

 

When measuring gradient a problem highlighted in fig 4, was the clinometer's position, this was a particular concern due to poor conditions. To combat this another member would check the clinometer was positioned correctly. When measuring over a large distance it was difficult to see the division, so another member placed a finger across the division, clearly marking it. The same individual measured the gradient for all sites, avoiding biased results. Three measurement where taken and a mean calculated, avoiding random error. Vegetation cover data can be subjective, as highlighted in fig 4. Group decisions were made to reduce bias. When agreement could not be found, mean values were calculated. Soil pH samples were collected by the same individual, at consistent depths, avoiding unreliable results. A pH kit was used instead of a probe, because the pH kit gave more reliable results as found in the pilot study. However pH was only measured to 0.5 degree of accuracy. A different pH chart could be used, such as fig 23, giving results to a higher degree of accuracy, improving the validity of the conclusion. Soil moisture and nutrient levels, would have improved the investigation. They may have provided reasons for the changing biodiversity. The gravimetric method could have been used to measure soil moisture. Samples are weighed, then baked to remove moisture, re-weighed, and the difference calculated. This is then translated into a percentage for comparison. However due to conditions this data collection would have lacked reliability. Soil nutrients can be measured using nutrient kits, containing chemicals that measure a range of nutrients. This was not done due to equipment limitations. If collected, correlations may have been found between biodiversity and moisture/nutrient levels. Thus providing conclusive results as to why biodiversity changed at Holkham. Fig 18 is a good presentation technique, showing the vegetation cover, profile and pH along the transect. It can be used to identify patterns of changing biodiversity 21 and hypothesis reasons for them. To determine correlations, scatter graphs were used, eg fig 20. This presentation method allows conclusions to easily be made. Holkham was a good location for collecting data to test the hypothesis. It is an established sand dune and its status as a nature reserve, means it is relatively undisturbed. However the pine forest at the back of the dune is not natural, it was planted to protect residents from weather conditions. A ‘natural’ sand dune such as Morfa Harlech, may have been better. It would show how a dune’s biodiversity naturally changes, as it is unmanaged.