max adcock

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INTRODUCTION “A sand dune can simply be classified as a hill or ridge piled up with sand” (Pye et Tsoar 1987). Sand dunes are formed when a wind speed of 10 mph or stronger picks up small grain particles and deposit them when resistance is met or obstructed by an obstacle.(Cros et Serra 1993). Sand dunes are a mobile habitat; over time as vegetation colonizes an area of dune land it becomes more static. Many topographic obstacles such as boulders, escarpments and hills have the ability to induce zones of airflow acceleration, deceleration and enhanced turbulence.(Gaylord and Dawson, 1987) The formation of a sand dune is mostly related to the vegetation on the plains area and topographic Obstacles. (Cros et Serra). The process by which vegetation colonizes a sand dune is called succession. Successions can further be classified into four types – psammoseres, lithoseres, hydroseres and haloseres. A sere refers to a specific type of vegetation succession. A Psammosere is a community that started its life on exposed coastal sand. (Agate, E 2005). A Lithosere is a community that began its life on an exposed rocky surface. (Codrington, S,B. 2005). A hydrosere is a community that began its life in water. (Offwell Woodland & Wildlife Trust 1998). A halosere is a community that develops within a saline environment, for example a salt marsh. (Collard, R 1998) Succession can be further divided into primary or prisere and secondary or subsere, differentiating to when or where on a dune it occurs. Primary succession occurs first, this colonization occurs A study investigating changes in vegetation on a manmade Psammosere (Porthtowan) MAX ADCOCK Falmouth Marine School, Killigrew St, Falmouth, Cornwall, TR11 3QS. Abstract Marram grass, Ammophilaarenaria plays a very important role in stabilising dune systems. They have extensive root systems that help bind the sandy sediment together, making conditions more favourable for less ‘hardy’ plants to colonize. Porthtowan sand dune is located on the North coast of Cornwall, it is an artificial dune which was planted in the 1970’s. The dune is heavily exposed to human activity through tourism and has restricted growth from residential and commercial buildings. Fixed point photography was performed at 4 different locations using a high powered digital camera. Beach profile transects were performed at three different locations along the dunes lateral structure. Photographs taken over a period of six months were used to correlate vegetation cover into a phase 1 habitat survey. Keywords: Psammosere, Vegetation cover, Phase 1 Habitat survey

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Page 1: Max adcock

I NT RO D U CT IO N

“A sand dune can simply be classified as a hill or

ridge piled up with sand” (Pye et Tsoar 1987). Sand

dunes are formed when a wind speed of 10 mph

or stronger picks up small grain particles and

deposit them when resistance is met or obstructed

by an obstacle.(Cros et Serra 1993). Sand dunes

are a mobile habitat; over time as vegetation

colonizes an area of dune land it becomes more

static. Many topographic obstacles such as

boulders, escarpments and hills have the ability to

induce zones of airflow acceleration, deceleration

and enhanced turbulence.(Gaylord and Dawson,

1987)

The formation of a sand dune is mostly related to the vegetation on the plains

area and topographic

Obstacles. (Cros et Serra). The process by which vegetation colonizes a sand dune is called succession. Successions can further be classified into four types – psammoseres, lithoseres, hydroseres and haloseres. A sere refers to a specific type of vegetation succession. A Psammosere is a community that started its life on exposed coastal sand. (Agate, E 2005). A Lithosere is a community that began its life on an exposed rocky surface. (Codrington, S,B. 2005). A hydrosere is a community that began its life in water. (Offwell Woodland & Wildlife Trust 1998). A halosere is a community that develops within a saline environment, for example a salt marsh. (Collard, R 1998) Succession can be further divided into primary or prisere and secondary or subsere, differentiating to when or where on a dune it occurs. Primary succession occurs first, this colonization occurs

A study investigating changes in

vegetation on a manmade

Psammosere (Porthtowan)

MAX ADCOCK

Falmouth Marine School, Killigrew St, Falmouth, Cornwall, TR11 3QS.

Abstract

Marram grass, Ammophilaarenaria plays a very important role in stabilising dune systems. They have

extensive root systems that help bind the sandy sediment together, making conditions more favourable for

less ‘hardy’ plants to colonize. Porthtowan sand dune is located on the North coast of Cornwall, it is an

artificial dune which was planted in the 1970’s. The dune is heavily exposed to human activity through

tourism and has restricted growth from residential and commercial buildings. Fixed point photography was

performed at 4 different locations using a high powered digital camera. Beach profile transects were

performed at three different locations along the dunes lateral structure. Photographs taken over a period of

six months were used to correlate vegetation cover into a phase 1 habitat survey.

Keywords: Psammosere, Vegetation cover, Phase 1 Habitat survey

Page 2: Max adcock

where no soil or vegetation that has previously existed.(Bishop, V 1997).The term given to a species that is the initializing species is a pioneer species; these are usually extremely adapted organisms and are very resistant to harsh environmental and human activity. (Harper et al 1961) Succession within an ecosystem is the number of changes that occur to the ecosystems community over a period of time. Primary succession takes place on a surface where no soil or vegetation has formerly existed. (Skinner, Redfern et Farmer 2003). Marram Grass (Ammophilaarenaria) is usually one of the first species to settle on a dune system. It is highly adapted and its leaves are rolled along the vertical length of the plant. This adaptation prevents moisture loss through the underside of the leaf. Also, its long roots dig in deep to find water found far below the surface. The roots also act as a binding system, giving it grip and securing small sediment grains together.(Rae, A 2008). (Horwood 1919) states that marram grass requires algae and lichen to start the nutrient cycle off, suggesting that marram grass is not a ‘True Pioneer species’. However, marram grass is not adapted for life in stable dunes, and is easily out competed with lichens, grasses, mosses and shrubs. (Prosser, R 1997). As plants increase in number and size, sand becomes stabilized. Over time, ecological colonization leads to changes in the substrate chemical makeup allowing new species to invade.(Brooks, A 1979). As plants die off over time, they change the sandy sediment into more coarse acidic earthy sediment, making conditions more 'favourable' for more field ‘pasture’ species to colonize.(Agate, E 2005) Once succession has initiated, over time it will

develop into continuously less biologically adapted

plants. However, drifting sand can cause either

advances or retreats in the succession of dune

plants. (Kumler 1969)Dunes are also susceptible to

damage from extreme weather events and human

interaction that can also contribute to hindering

succession or accelerating it.

Sand dunes are a delicate mobile ecosystem; they

are unlike hard stable rocky shorelines. Dunes

contain hinterland shrubbery, predominantly a

coastal species that is not found in any other

location in Britain. (Brookes, A 1969). Small

changes introduced by man or the natural

environment often contribute to deterioration or

acceleration of the coastal environment. Victoria

Bishop, (1997), states that the most seaward dune

ridges are the most unstable. They are influenced

and modified by coastal storms, high tides, or

breaks in marram cover. Robert Prosser (1997),

suggests that once an area of dune is exposed to

wind, depressions called ‘blow-outs’ can occur.

Once a blow-out has occurred, wind is quick to

sweep into the fault of the dune ridge and

drastically alter its shape.

This project will focus on Porthtowan, which is a

small village located on the north coast of

Cornwall, it has a unique dune ecosystem in

comparison to its natural neighbouring dune;

Gwithian. Porthtowan is an artificial dune which

was seeded in the 1970’s. It is a small dune

ecosystem, enclosed by two cliffs running

horizontal either side of the dune border. Human

activity and the seasonal tourist activity suggest

that the dune will never meet its climatic

community. Its growth is restricted by residential

and commercial buildings. Over the past 30 years

the once healthy dune system is now retreating, it

can be classified as a declining dune ecosystem.

Figure 1 – Location of study area on google map -

Porthtowan.

Figure 2 – Location of Porthtowan.

Page 3: Max adcock

Human trampling and weather events have led to

a blowout developing, running right through the

centre of the already unstable fore-dune. Using

Carters blow-out model, you can apply the case

study of Porthtowan and evaluate that the dune is

in stage B of the blowout cycle, where the wind is

eating down until it meets resistance. In addition

to the blowout, trampling and weather conditions

have led to a decrease in the abundance of

marram grass.

Usually the typical management strategy for

restoring a dune, is to attempt to restore the dune

to its natural processes (Rooney 2010), however

this is unachievable at Porthtowan. The dune is too

restricted by human activity; it is unlikely that it

would be possible to restore the dune system by

leaving it to its natural processes, because it is an

artificial dune with far too many human inputs.

There has been some previous management put in

place at Porthtowan, (cornwall.gov.uk). The dunes

were once fenced off, sediment trapping nets

were placed to prevent sand loss, and a designated

path was established, to keep trampling to a

minimum. Unfortunately the path was destroyed

by a storm. This led to the remaining debris of the

path being bulldozed away, which could have

contributed to the large blowout that is located

near where the path once was placed.

This project will focus on vegetation change over a

6 month period, whilst my study peer Dafyd

Propert-Lewis will focus on change in topography

over a 6 month period.

M A T E R I A L S A N D M E T H O D S

The joint Nature Conservation Committee released

a guide on how best to monitor sand dune health

over a period of time in August 2004. The common

standards monitoring guidance recommends that

firstly once a site is chosen. All historical

information should be gathered and evaluated

where possible. Aerial photographs from a fixed

location over a period of time can be compared,

and plotted on GIS Software. (Dargie, 2000). The

JNCC recommends that all field studies should be

compared to the ‘Sand Dune Survey of Great

Britain’ (Radley, 1994) which contains many

records of previously surveyed dunes.

The JNCC’s recommended biodiversity assessment

is also linked in with aerial photos to give a

baseline to any scientific field study, plotting

vegetation cover onto simple GIS software which

can then be compared to survey databases such as

(Dargie, 2000).

There are varying degrees of accuracy for

measuring and mapping a dune system, ranging

from simple transects using ranging poles and a

clinometer. (Department of Education 2010) On

the other end of the scale there is extremely

accurate three dimensional laser mapping

technology. (Nagihara, S., Mulligan, K. R. and

Xiong, W. (2004)

There were two main methods used by myself and

my peer to be able to monitor successfully over

the 6 month period. Sampling was decided to fit in

with the end of the tourist season at Porthtowan

to give any indication whether the intense human

interaction with the dune in summer is having any

direct linkages with sediment movement or

vegetation development.

Fixed point photography for visual representation

of vegetation change was taken from three

different locations around the sand dune and one

was taken from the cliffs overlooking for an aerial

view. Photographic surveys were carried out in

December, February and April.

Figure 3 – Google Earth map demonstrating F.P.P

locations.

The camera used was a high powered digital

camera, photographs were taken as close to mid-

day as possible to ensure the best lighting

conditions. Photographs were then used to plot

Page 4: Max adcock

vegetation cover directly onto a gridded map, to

evaluate change over time.

Three beach transects were conducted

intersecting with the dune at three different cross

sections of the dune, to monitor sediment

movement in December, February and April.

Figure 4 – Google Earth map demonstrating three

transect locations.

Data was gathered by use of ranging poles and a

clinometer from mean low water to establish

change in height of sediment.

Data can then be correlated into graphs in order

compare change in height over the 6 month

monitoring period.

The fixed point photography showed very little

change in vegetation over the 6 months. The

communities on the dune stayed relatively stable,

however the sand movement was fairly dramatic.

The project was adapted halfway through to

examine historical aerial photography to gather

more information to suggest what activity is

occurring with the vegetation. The fixed point

photography did not show any change on the

marram grass communities on the frontal dunes,

but demonstrated an increase in the blowout, and

between February and April there is an increase in

grass communities behind the frontal dune.

R E S U L T S

Figure 5 – December Fixed Point Photograph

overlooking cliffs.

Figure 6 - February Fixed Point Photograph

overlooking cliffs.

Figure 7 – April Fixed Point Photograph

overlooking cliffs.

Page 5: Max adcock

Figure 8 – Google Earth 2001 Historical aerial view of Porthtowan Dunes. Green dot resembles vegetation present. 171

Figure 9– Google Earth 2005 Historical aerial view of Porthtowan Dunes. Green dot resembles vegetation present. 136

Page 6: Max adcock

U s i n g

Using Google Earths historical data, the

investigation was able to examine three aerial

photographs from the years 2001, 2005, and 2009.

A grid was placed over the map, and each vector

within the grid relates to an area of 8 x 8 m².

Using a marker on each grid to show an indication

of vegetation, it allows vegetation cover of the

entire dune system to be estimated and compared

to the different years.

In 2001 there were 171 squares of vegetation

cover. 8 x 171 = 1368 m².

In 2005 there were 136 squares of vegetation

cover. 8 x 136 = 1088 m².

In 2009 there were 127 squares of vegetation

cover. 8 s 127 = 1016 m².

The general trend of vegetation coverage from the

year 2001 to 2005 was a steep drop. From 2005 to

2009 the decline slows dramatically.

#

Figure 11 – Graph demonstrating the different

vegetation coverage over 8 year period.

The frontal dune was dominated by mainly

marram grass; the area behind the dune has very

stable communities of grass, in a six month period

the grass actually increases in coverage, which is

surprising considering the sand input from the

widening blowout.

0

200

400

600

800

1000

1200

1400

1600

2001 2005 2009

Me

ters

Sq

uar

ed

Year

Area

Poly. (Area)

Figure 10 – Google Earth 2001 Historical aerial view of Porthtowan Dunes. Green dot resembles vegetation present. 127

Page 7: Max adcock

D I S C U S S I O N

Sediment Characteristics

Over the 6 month monitoring period, there were

noticeable changes in the dune structure. Daffyd’s

project highlights in detail that the frontal dune is

not retreating. His investigation demonstrates the

dune is losing sediment. The dune overall is lower

down and the blowout is increasing in size. Where

the sediment is being transferred to opens up

room for a further investigation. The council runs a

sediment relocation scheme to keep access roads

clear of potentially hazardous sediment build up.

The start of the project looked at the damage done

to the dunes over the busy summer period, the

trampling cause’s sand to become dislodged and

allows it to be picked up by wind and relocated

elsewhere in the dune system. April’s photograph

demonstrates the human use on the frontal dune.

The blowout is made up purely of soft sand, and is

exposed to the sun throughout the whole day,

making it an ideal location for beach users to

sunbathe.

April’s fixed photograph clearly demonstrates that

the sediment is moving away from the frontal

dune to the colonized area of vegetation behind

the dune. There is increased % cover of sand in

comparison to grassland.

Long term Vegetation Monitoring

Visually there is a clear indication of vegetation

decline over the period of nine years. The frontal

dune shifts back by a considerable distance from

2001. The marram grass communities on the front

thin out and become very patchy. There are many

factors that may have contributed to the decline in

marram, environmental and human influence. The

lack of stable marram could explain to some extent

the lowering of the dune sediment. With no

vegetation to keep the sediment bound together,

sand is exposed to high wind speeds that have

enough energy to dramatically change the dune

topography.

The thinning vegetation on the frontal dune could

also explain the increasing amount of sand input

onto the access roads, and onto the grassland

habitat behind the dune system.

Short term Vegetation Monitoring

There was very little change in vegetation over the

6 month period of monitoring. This could have

been due to the lack of tourists over winter;

however there was still a considerable amount of

trampling. Although there was little change in

vegetation communities it is worth noting that

there was a considerable change in dune

topography.

The dune became much flatter and the blowout

had retreated further back, encouraging a build up

of sand behind the frontal dune, making it a much

more gradual decline in height leading onto the

built up grasslands.

The grasslands behind the dune in April show that

a large amount of sand had been deposited

directly onto an area of built up vegetation.

In future investigations, it would be practical to

gain access to direct aerial photographs, to directly

compare data accurately through habitat surveys,

in comparison to estimating vegetation cover and

plotting onto a rough aerial map.

Additionally it would be recommended to monitor

individual communities on the frontal dune, to see

if the microhabitats are as dynamic as the whole

artificial dune.

A K N O W L E D G E M E N T S

We would like to thank L.Hockley for her

assistance in planning this study, aiding us in

developing rigorous methodology and her

invaluable experience in the field. We would also

like to thank the Falmouth Marine School for

lending us equipment over the 6 month period to

gather our data.

Page 8: Max adcock

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F i g u r e s

Figure 1 – Google map UK

Figure 2- Google map Porthtowan

Figure 3- Google Earth map

Figure 4- Google Earth map

Figure 5- FPP Dec

Figure 6- FPP Feb

Figure 7- FPP April

Figure 8- Habitat survey Dec

Figure 9- Habitat survey Feb

Figure 10- Habitat survey April

Figure 11- Comparison graph