Habitat changes between 1983-5 and 1993 on Sutton and Hollesey Heaths, Suffolk

41

HABITAT CHANGES BETWEEN 1983-5 AND 1993 ON SUTTON AND HOLLESLEY HEATHS, SUFFOLK NICHOLAS SIBBETT The parishes of Sutton and Hollesley, a few miles east of Woodbridge, contain one of the largest remaining fragments of the once extensive Sandlings heaths on the Suffolk coast. They consist of dry acidic grassland and heathland with much bracken, self-sown pine and birch woods, and small plantations. The nature conservation value is such that the heaths have been notified as a Site of Special Scientific Interest.

Much of the heaths are under private ownership, whilst the remainder is owned by local and national government including the Ministry of Defence, Home Office, Foresty Commission and Suffolk Coastal District Council. Parts of the heaths have been managed since 1983 by the Sandlings Project which is a consortium of voluntary conservation organisations and public bodies led by the Suffolk Wildlife Trust. The intensity of management, which aims to maintain and enhance the wildlife interest, has varied over the last 10 years according to fluctuations in resources.

Management of the heaths is intended to retain all the existing heathland and acid grassland, and to restore these habitats where they have been replaced in recent years by invasive bracken and woodland. The open heath and grassland have a great number of plant and animals species, including many restricted to these habitats, which cannot survive in dense stands of bracken or under a woodland canopy. A high biodiversity is intrinsically valued for nature conservation, and also gives much pleasure to the many people who visit or work on the heaths.

Management has concentrated on manipulating Vegetation, through Operations such as bracken cutting, spraying herbicide onto bracken, removing pine and birch, cutting gorse and mowing stands of old heather to promote regeneration. Since 1989, sheep have grazed some areas to maintain the heathland Vegetation. The aim of this article is to describe the changes in areas of habitat on the Sutton and Hollesley Heaths between 1983-5 and 1993.

The 1983-5 Survey The Sutton and Hollesley Heaths were surveyed by a team of 2 - 3 biological surveyors employed by the Sandlings Project between 1983 and 1985 with different parts of the heaths surveyed once over the three-year period. They mapped habitats as 'heather', 'acid grassland', 'bracken', 'scrub and trees' and 'other'. The areas of each habitat was published in 1985 (Fitzgerald, Martin & Auld, 1985) as a separate figure for each area within the Sutton and Hollesley Heaths SSSI. The detailed methodology of the 1983-5 surveys was not recorded, and it is not clear how the areas of habitats were calculated from the maps.

The 1993 Survey I made eight visits to Sutton and Hollesley Heaths in the period mid-July to mid-August 1993, spending around 40 hours surveying. This is an average of 12 hectares surveyed per hour. With these time constraints, a detailed species

Trans. Suffolk Nat. Soc. 30 (1994)

42

Suffolk Natural History, Vol. 30

list could not be produced and mapping may not have been accurate.

Each homogeneous stand o f Vegetation seen was marked on a map by drawing a line around the edge o f the Community. Lines were drawn by eye, estimating their position rather than taking measurements from reference points. Plant species abundance was measured in up to five quadrats for each homogeneous stand to enable the Vegetation to be classifed according to the National Vegetation Classification (Rodwell, 1991; 1992). The area o f each homogeneous stand o f Vegetation was measured on the completed map with a hand-held digital planimeter, omitting the small unvegetated areas occupied by tracks, roads, etc. My 1993 survey identified some transition communities (where one habitat was changing into another) or intimate mosaics o f two habitats. For the area measurements to be comparable, I assumed that each o f the constituent communities in a discrete stand occupied 5 0 % of the area. For example, a 4 ha woodland/heathland stand would be treaxted as 2 ha o f woodland and 2 ha o f heathland. T h e figure compares the areas o f each habitat on Sutton and Hollesley Heaths in 1 9 8 3 - 5 and 1993. The table lists the area covered by each habitat on each part and the whole o f Sutton and Hollesley Heaths.

Assessment of habitat changes over the whole site In 1 9 8 3 - 5 , heathland occupied 19% o f Sutton and Hollesley Heaths, and by 1993 it had expanded to cover 3 0 % o f the area. There has been a corresponding decline o f bracken from 3 3 % to 2 2 % cover. The simple interpretation is that bracken has been replaced by heathland although the dynamic interactions are more complicated when each part o f the whole site is looked at separately.

Acid grassland appears to have increased a little, from 5 % cover in 1 9 8 3 - 5 to 8 % cover in 1993. There was a significant increase o f this habitat on the Parsnip area at the expense o f bracken, which accounts for much o f the change.

Elsewhere, acid grassland has remained at fairly constant low levels.

Woodland remains the most common habitat, with over one-third cover in both 1 9 8 3 - 5 and 1993. Gains and losses on a number o f parts o f Sutton and Hollesley Heaths show a net gain o f woodland cover.

A small area o f 'other' in 1 9 8 3 - 5 includes areas such as firebreaks, and tracks. T h e s e were not measured separately in 1993 as I feit it would be too difficult to do so accurately. This Variation o f measuring techniques means that the proportion of the site covered by semi-natural Vegetation would seem slightly higher in the 1993 survey than the 1 9 8 3 - 5 survey.

Assessment of habitat changes on each p a r t of Sutton and Hollesley Heaths (See Maps 1 and 2) Sutton C o m m o n Interpretation o f changes in each habitat is difficult, but perhaps a small increase in heathland at the expense o f bracken or woodland may have occurred.

L o w e r Hollesley C o m m o n The measured area o f heathland has increased and there may also have been a small increase in woodland cover. Bracken cover

Trans. Suffolk Nat. Soc. 30 (1994)

Trans. Suffolk Nat. Soc. 30(1994)

44

Suffolk Natural History, Vol. 30

has declined by about one-third, whereas acid grassland has remained stable.

Upper Hollesley Common The measured area of heathland has increased by about 50% with a concurrent decrease in bracken cover. Acid grassland and woodland seem to be stable. One tiny area of plantation has been felled to restore heathland.

Sutton Heath The obvious change here is an increase in woodland cover on to bracken areas. There has been no great change in the areas of heathland or acid grassland. Bracken stands occupied about one-quarter of Sutton Heath in 1983-5, but are now rnuch less abundant, occupying just 5% of the heath.

Woodland, consisting of pine plantations or recent seif sown pine, birch and oak woods, has spread to occupy most of this site.

Sutton Heath The obvious change here is an increase in woodland cover on to bracken areas. There has been no great change in the areas of heathland or acid grassland. Bracken stands occupied about one-quarter of Sutton Heath in 1983-5, but are now much less abundant, occuping just 5% of the heath. Woodland, consisting of pine plantations or recent seif sown pine, birch and oak woods, has spread to occupy most of this site.

Parsnip The areas of bracken has been reduced here by over half in the last decade, and has been replaced by acid grassland. Unlike other parts of Sutton and Hollesley Heaths, heathland has not replaced managed bracken stands perhaps because there are no heather seeds in the soil.

Hollesley Heath Much of the site is covered in plantation or secondary woodland. Woodland has expanded onto some of the heathland and has apparently also expanded onto bracken areas. As at Upper Hollesley Common, bracken glades within these woodlands (where bracken is the natural field layer) were recorded as woodland in 1993 and may have been recorded separately as a bracken Community in the 1983-5 survey. The apparent expansion of trees onto the bracken Community may be due, in part at least, to differences in interpretation.

RAF Woodbridge The 1983-5 and 1993 surveys are not directly comparable, so just the 1993 survey results are shown in the table.

Conclusions The spread of heathland and acid grassland Vegetation at the expense of bracken demonstrates that management over the last decade has succeeded in its aims of maintaining and enhancing the wildlife interest. In the early 1980s, all the Sandlings Heaths were threatened by the invasion of bracken, birch and pine woodland which by then had occupied 62% of the remaining heath area (Fitzgerald, Martin & Auld, 1985). On Sutton and Hollesley Heaths, this trend of vegetational succession has been halted and reversed.

There is a distinct difference between the publicly-owned and private parts of Sutton and Hollesley Heaths. The publicly-owned parts of Sutton Heath, Hollesley Heath, Upper Hollesley Common picnic site and Barthorps's Folly on Lower Hollesley Common all have a very high or total cover of recent selfsown or plantation woodland. The part of RAF Woodbridge is not managed at all. In contrast, the remaining privately owned parts have up to half covered by

Trans. Suffolk Nat. Soc. 30 (1994)

49.5

1993

16.0

1983-5 36.2

1993

1993

total

1983-5

1993

62.6

other habitats

63.3

89.9

117.2

1983-5

89.0

24.9

115.3

139.2

26.3

123.7

19.8

S/N

31.2

11.2

45.4

51.7

45.4

33.4

13.3

1983-5

33.1

22.6

19.7

1993

18.7

49.1

15.5

28.8 1

15.4

39.1

27.9

38.0

20.1

99.0

10.6

22.0

449.0

33.2

159.5

100.0 39.3

176.4

479.5 36.1

173.0

10.3

47.0

1983-5

15.7

S/N

S/N

37.7

S/N

1993

39.8 31.3

27.3

0 001

1983-5

25.2

Site name

17.2

Sutton Heath

Upper Hollesley Common

Sutton Common

133.7

o L/>

45.4

92.9

29.8

o

o

pL*

32.8

19.4

12.6

Percent total (excl. RAF Land)

o

to k>

o

o

On

y. bo

pK)

o

3

o

b\

b\

vO

Lower Hollesley Common

3 a u» oo

O

Hollesley Heath Parsnip

| b\ o y>

o

a•i u n n

V) 0) E" 3 a to

o

Total (excluding RAF Land)

RAF Woodbridge

bo

U fs E TO O

K 3 Q. NJ U)

a\

o

3* fz k>

N b\

EB ?

Oo b\ vo

45 HABITÄT CHANGES ON SUTTON AND HOLLESLEY HEATHS

Trans. Suffolk Nat. Soc. 30 (1994)

46

Suffolk Natural History, Vol. 30

heathland or acid grassland.

The figure shows that woodland Covers more area than any other habitat on Sutton and Hollesley Heaths. Future management could aim as a priority to reduce woodland cover to allow for the expansion of heathland and grassland.

Bracken now Covers less than one-quarter of the heaths. It is important that the bracken is managed to prevent it spreading, because it will reduce the abundance and diversity of grassland and heathland communities. However, it occupies a smaller area than the species-poor woodlands so it is now less of a problem than it has been in the past. It is essential that all existing heathland and acid grassland stands continue to be managed to conserve their wildlife and nature conservation value.

Many of the heathland sites of Special Scientific Interest in the Sandlings are now being managed for nature conservation by the Sandlings Project. Financial support from the Countryside C o m m i s s i o n ' s Countryside Stewardship Scheme and English Nature's Heathland Initiative is showing postive benefit. It would be valuable to carry out a similar re-survey on other heaths in the Sandlings to see how they have changed.

Figure - Sutton & Hollesley Heaths Change in habitat area, 1983-5 to 1993

& £

140 •

£ 120 • ' ?B 100 •' o

so •'

2 60 ' 1 •5 «•' QJ 20 '

ra

0-

Haathland

»cid graialand woodland

bracken

Ottlar

habitat t y p e

H 1983-1985

1993

Acknowledgements The help and co-operation of landowners and occupiers of the Sutton and Hollesiey Heaths is greatly appreciated.

References Fitzgerald. C.. Martin. D. & Auld, M . (1985). Report of the Sandlings Project 1983/5. Sandlings Group.

Rodwell, J. S. ed. (1991). British Plant Communities.

Vol. 1. Woodlands and Scrub. Vol. 2. Mires and Heaths. Cambridge University Press.

Rodwell, J. S. ed. (1992). British Plant Communities.

Vol. 3 Grasslands and Montane communities.

Cambridge University Press.

Nicholas Sibbett, English Nature, Norman Tower House, 1-2 Crown Street, Bury St. E d m u n d s

Trans. Suffolk Nat. Soc. 30 (1994)

HABITAT CHANGES ON SUTTON AND HOLLESLEY HEATHS

47

Trans. Suffolk Nat. Soc. 30 (1994)