Applied Geogrphy (1985), 5, 151-166

Sources for the assessment of British woodland change in the twentieth century

Charles Watkins

Department of Geography, University of Exeter, Amory Building, Rennes Drive, Exeter EX4 4RJ, England

Abstract

After a discussion of the problems of defining woodland for the purpose of survey, the paper goes on to consider the sources available to geographers and others for the study of woodland change in Britain, particularly within the 20th century. The main sources considered are Ordnance Survey maps, aerial photographs and satellite remote sensing. Forestry Commission censuses. Forestry Commission and private estate records, land utilization surveys and agricultural statistics.

Introduction

In the past decade there has been a considerable increase in interest in the study of British woodland. The research carried out has of necessity been of an interdisciplinary nature, and the work of Rackham (19SO) on the historical ecology of woodlands and Peterken (1931) on the management of woodland for nature conservation has been particularly important. Geographers have also made a number of contributions (Watkins and Wheeler 19Sl). Much of this research has been concerned with the importance of woodlands as elements of the rural landscape, refuges for wildlife and examples of an historic form of land management. Concurrent with this type of research has been a continuing debate about the importance of woodlands and forestry in the British economy (Centre for Agricultural Strategy 1980; Grove 1983; Watkins 1983).

There is no doubt that woodland is an important land use. In 1952 it was estimated that there were 2.1 x lo6 ha of woodland in Great Britain, this forming about 9 per cent of the total land area. In the same year the total number employed in forestry was estimated at 10 630. However, it must be emphasized that Britain consumes far more timber than it produces. Provisional figures for 1981 show, for example, that the volume of home produced timber (4-3 x lo6 m3) formed only 11.8 per cent of the apparent consumption (36-3 x lo6 m3) of wood and wood products (Forestry Commission 1982). Apart from the importance of woodland for the economy, for landscape, and for conservation, its importance in terms of recreation and game conservation needs to be taken into account; indeed, one of the fascinating aspects of woodland is its ability to be used for a wide variety of different purposes. Furthermore, the same piece of woodland may be used for a number of different uses. In assessing the value of a wood for these different purposes a knowledge of its historical development and the recent changes in the woodland type and species present is often important. In this paper the sources available to geographers and others for the study of British woodland change, particularly within the 20th century, are considered, and the advantages and disadvantages associated with these sources are outlined.

013~6228/85/020151-15 $03.00 0 1985 Butterworth & Co (Publishers) Ltd

12 Sources for the assessment of British ~vootllrmd chrtnge in the 20th century

Problems of definition

Before discussing the individual sources in detail it is necessary to consider some problems of definition. perhaps the most difficult of which is the definition of woo~larzd itself. Three main problems will be discussed: first, the minimum size of an area of woodland; second, the density of trees occurring in woodland. and third, the use of the term woodland to distinguish bet\veen naturally occurring trees and plantations.

The first difficulty is choosing a suitable minimum size of area covered in trees to which the term woodland should be applied. In fact, this is a purely arbitrary decision. If we take the minimum size of woodland included in the mam Forestry Commission censuses, for example, it will be seen that in 1924 the minimum size was 0.8 ha, in 194739 it was 2.0 ha, and in 1965-67 it was O-4 ha, while in the most recent census of 1979-82 the minimum size of woodland included was as low as 0.25 ha (Forestry Commission 1928, 1952, 1970, 1983). To a large extent the minimum size chosen for any particular study depends on the aims of the study and the sources used. When taking stock of the commercial importance of woodland for timber production in any particular area, for example. a minimum size of 2.0 ha or more might be quite adequate, but if a study, of the landscape importance of woodlands is contemplated a much smaller mmlmum size would be necessary. In general, a minimum size of 0.1 ha is likely to be quite adequate, this being both the minimum size within which subdivisions of different woodland type are shown on Ordnance Survey large-scale maps and the minimum area recognized by the Forestry Commission for dedication plans (Forestry Commission 1975). The choice of a minimum width of woodland is a related problem to that of minimum size. Again an arbitrary decision needs to be taken: in the last two Forestry Commission censuses a minimum width of 20 m has been used.

The second consideration that has to be taken into account when defining a woodland is the density of trees. From an ecological point of view. woodland has to be made up of trees at such a density that the habitat is characterized by, low light intensity and high humidity so that a flora and fauna characteristic of the environment can exist (Packham and Harding 1982). Also, within a wood. individual trees will tend to show certain characteristics, such as tall trunks with relatively few branches and small crowns, which differ from park or hedgerow trees. The boundary between what is woodland by these criteria and what is parkland or scattered trees is, however, sometimes difficult to define. Over much of lowland England where the land surface is firmly divided into fields, building plots or industrial sites by fixed boundaries such as hedges or fences, the boundary of woodland is usually easily drawn. It is only where natural regeneration of tree and shrub species has taken place that problems occur. In the upland areas on the other hand, it is more common to find areas of woodland, especially along the lines of rivers and streams, for which the boundaries are difficult to determine. A convenient way of dealing with this problem is to include as woodland all areas having a stocking density over a certain percentage. The minimum stocking density taken to indicate woodland will vary, as with the other criteria discussed, from study to study. In the 1947-49 Forestry Commission census, for example, this percentage was 50 per cent while in the 1979-52 census it was 20 per cent. One further point that needs to be mentioned here, is that as the most common form of woodland management in Britain at present is some form of even-aged high forest which is clear felled at the end of the rotation, one has the paradox that much woodland at some stage is devoid of trees.

Charles Watkins 153

The third point that needs to be made when considering. the definition of woodland is that, according to Rackham (1950:6), it can be divided into one of three ‘independent traditions of land-use’:

1. plantations, where the trees are all of one age and often of one species, and have been deliberately planted;

2. woods, where the trees are of different ages, or different species. or both, and have not (or not all) been intentionally planted;

3. wood-pastures, where the growing of trees is combined with grazing animals.

In general it would seem reasonable to include each of these three broad woodland types within the definition of woodland, as Ion, u as the criteria relating to woodland size and density decided upon are fulfilled.

Having considered the definition of woodland, it is necessary to define some of the important terms associated with it. As is indicated by the quotation from Rackham above, the two ways in which woodland can be established are natural regeneration and planting. Naturally regenerated woodland can be either primary or secondary. Primary woodland, although modified by management, has never been cleared and replaced by another land use, while secondary woodland has developed over areas previously used for another purpose. Areas of primary or secondary woodland which are felled and replanted become plantations. Planta- tions, if unmanaged for a considerable period, or clear felled and left to regenerate, begin to take on the characteristics of naturally regenerated woodland. It is important to note, however, that some features of primary woodlands are not re-treatable (Peterken 1974). One problem with the term primary woodland is that in practice it is difficult to prove that any woodland has never been cleared. The term ancienf woodland, meaning a woodland which has existed since before 1700 (Rackham 1980:6) is therefore more generally used. A wood may be defined as a piece of continuous vvoodland around which a continuous boundary may be drawn and which is decisively separated from any adjacent pieces of woodland. If boundaries between adjacent woods are being drawn on the ground the definition may be that there should be an intervening strip of unwooded ground of a minimum width of 20 m. If boundaries are being drawn on maps, equally arbitrary decisions have to be made. Thus on maps of a smaller scale than. say, 1:lO 000, it might be decided that surfaced roads of more than 4 m width, railways, and watercourses wide enough to demand a double blue line, would be counted as decisive breaks in continuous woodland.

Ordnance Survey maps

Although a large amount of information relating to woodland distribution, area, shape, density and type can be gathered from the various Ordnance Survey (OS) plans and maps, they are more useful for broad studies of woodland distribution and change than for detailed studies of the distribution of different woodland types and species.

OS 1:2500, 1:lO 000 and 1:lO 650

The large-scale plans and maps have been described in detail by Harley (1975) who has also outlined the development of the woodland mapping systems used by the OS (Harley 1979). On these large-scale maps and plans the minimum area of

154 Soitrces for rlze nsstmttzetzr of Bririsiz wooctlat1d clzcztzye in tlze Xrl7 cetirurj

woodland within which subdivisions of different woodland type are indicated is O-25 acreas (0.1 ha) (Harley 1975), woodland being indicated by various combinations of tree and bush symbols. There is little doubt that the representation of woodland type on these maps is accurate within the definitions employed by the OS. The surveyors of the County Series of the I:2500 (and hence in a reduced form the County Series of the 1:lO 560) were instructed that:

Although the character of the woods need not be minutely shown, yet the general character should be truthfully shown. For instance. a fir wood should not be described as mixed because it has a few forest trees on its margin. nor a large wood of forest trees be shown as mixed because it has a small clump of firs in one corner. (Johnston 1905:15.)

Since the First Series of the 1:2500 plans there has generally been a decrease in the amount of woodland information mapped. The County Series distinguished between deciduous or forest trees, firs or conifers, mixed woods and underwood, brushwood or coppice. In 1963, these vegetation types were reclassified. the main woodland types being coniferous, non-coniferous, mixed, underwood. coppice and scrub. Woodland density was shown on the County Series by varying the distance between tree symbols. In 1958, this method \vas replaced by the use of a fourfold scale from *close’, through ‘medium’ and ‘open’ to ‘scattered‘. These are represented respectively by the grouping of the coniferous, non-coniferous or scrub symbols either in groups of four, three or tkvo. or singly. This density system was also used on the Regular Series of the 1: 10 650. but on the 1: 10 000 Series a simple twofold category was applied.

One of the main advantages of the 1:2500 Series is that it shows the areas of each parcel of land. Before October 1969, these areas were in acres and since that date both acres and hectares are shown (Smith 1976). Unfortunately, the parcels of land delineated often bear little relationship to the stand boundaries within woodland.

There are three general problems associated with the use of large-scale OS maps and plans as sources of data for detailed woodland surveys. First. there is the problem of the definition of woodland for the purposes of mapping. This problem is overcome to some extent by the use of the density classification, but Coppock (1978:30) has pointed out that ‘the point at which tree cover becomes sufficiently discontinuous for the land to be regarded as primarily rough grazing can only be decided arbitrarily’. Second, there is no separate category for felled ivoodland. On the County Series, felled areas were usually shown as rough grazing. the names ‘wood’ or ‘plantation’ only being retained on the maps if there was ‘a reasonable probability of the wood being replanted’ (Harley 1979:43). As Harley points out, this was a significant instruction in view of the First World War fellinps. The third problem is that of revision dates. With the initial survey of a series of maps, such as the 1:2500 County Series which was surveyed in Nottinghamshire between 1912 and 1919, the date of survey can be accurately accounted for. The dates of later revisions are more difficult, if not impossible, to discover. In addition. after 1919, woods of less than 10 acres (4 ha) were not revised for changes in woodland types (Harley 1979:44), and the revision of some editions of the 1:lO 000 and 1: 10 560 maps only includes important changes to communications, boundaries. reservoirs and major installations. This poses a considerable danger in the use of such maps as sources for the study of woodland change. Bunce et al. (1979:3), when estimating the accuracy of 1:lO 560 maps in this context suggested that:

Chnrlrs Wutkins 155

The overall impression was that woodland symbols were not updated where deciduous woods were converted to conifers, and. consequently, the decrease in deciduous woodland area was underestimated. OS maps do not therefore provide a reliable baseline for the assessment of change . . .

This certainly underestimates the usefulness of OS maps. In this case, the reason why maps did not show changes that predated them was that the date of revision was taken to mean the date of slfrvey of the woodland.

These problems do not preclude the use of the large-scale OS plans and maps in woodland surveys, but they mean that surveys based upon them need to be carefully designed around series of maps for which the date of survey can be ascertained, and the data collected need to be based upon OS definitions and classifications (Wheeler 19%).

These map series, although useful when identifying woodlands. are not an important source of data for the detailed study of woodland type and species, The 1:25 000 maps are based on reductions from the 1: 10 650 and 1:lO 000 series, their only advantage being a greater ease in handling. The 1:63 360 maps are of considerable use when looking at changes of woodland distribution and type over large areas. The woodland types distinguished are deciduous, coniferous and mixed woodland, although the symbols are omitted for woodlands which are too smalt on the map to include one complete tree symbol. Harkness (1983) has used successive editions of the 1:63 360 maps, in conjunction with aerial photography, to investigate trends in afforestation and deforestation in the Brecon Beacons.

Significant problems are encountered when using these maps in this way. as with maps of a larger scale. It is essential, again, to check the date of revision, these maps being revised independently of the I:2500 series. Woodland felled at the time of survey is sometimes shown as another land use. Surveyors were instructed that:

If a coniferous wood has been cut down and not replanted the reviser will cancel, unless he is thoroughly satisfied, from enquiries made of responsible persons, such as Factors, Agents, or Afforestation Officers, that the area is to be planted in the immediate future. Where a wood of deciduous trees or a mixed wood has been felled, and the deciduous undergrowth is springing, the reviser must use his own judgement as to whether the area should be shown as wood, or scattered trees on [rough pasture] (Harley 197958).

However, there are instances on maps of this scale of felled woodlands, mapped as non-woodland at one survey date, regenerating, or being replanted and being reclassified as woodland at the next survey. Coppock (1978:30) notes that:

. . . since the decision to replant is one that can only be taken by the occupier, the status of [felled woodland] cannot be determined by observation until preparations for replanting begin.

It is therefore very important when making comparisons between maps to make a clear distinction between areas of woodland which have been felled prior to replanting and areas that have been cleared and converted to another land use.

The First Series of the 150 000 maps did not distinguish between different woodland types, but with the current Landranger series a broad distinction

between coniferous, broadleaved and mixed woodland has been introduced. The 150 000 maps were used by the Forest]; Commission (1983) in the census of 1979-82 to provide a samphng base for all woodlands in the country down to 0.25 ha, and to provide estimates of the total woodland area for each county,

Remotely sensed data

Aerial photographs

Many types of vegetation can be usefully mapped using aerial photographs, which are used extensively in some countries for the assessment and classification of the woodland resource. Aerial photographs have often been used because the ground survey of large areas is extremely expensive. As a result much research has been carried out and tree identification keys have been produced (Loetsch and Haller 1964; Howard 1970). Aerial photographs have been used in Britain for the mapping of non-woodland vegetation (Goodier and Grimes 1970) but their use in the determination of woodland type, species and quality has been largelv obviated by the mapping of the OS and the detailed knowledge of the character of commercial woodlands held by woodland owners and the Forestry Commission.

There has recently, however, been an increase in the use of aerial photographs in the study of British woodlands. The most widely available, and frequently used, type of photograph is black and white and at a scale of about 1: 10 000. No detailed tree keys have been worked out; they would be difficult to construct owing to the wide range of woodland types and species. However, keys aiding the interpretation of woodland type based upon the shape of the wooded area, texture, tone and associated features have been produced (Harkness 1983). Fleming (1951) notes that crown shape, shadows and texture can be used, especially in conjunction with local knowledge of the woodland concerned, to identify woodland type and. in some cases, species. Paradoxically, both one of the main advantages and one of the main disadvantages of aerial photographs stem from their availability. In the first case, aerial photographs are available for large parts of the country at a number of time horizons since the Second World War. The RAF, for example, took photographs at a scale of approximately 1:lO 000 covering most of the countrv between 1946 and 1948, and although some of these are of poor quality this set of photographs provides a most useful source of data for the assessment of post-war woodland change (Peterken and Hardin g 1974). Other sets of photographs have been taken over the years for many counties by commerical companies and Fleming (1951) notes that:

With this range of photography available it is quite feasible to monitor post-\var changes in woodland with reference to at least three and quite possibly more time horizons. Apart from providing quite different information to that provided by maps. the photographs present information at more time horizons and, very importantly. at very specific times .

Against this advantage of aerial photograph availability must be set the disadvantage that some aerial photographs are in fact quite difficult to find. National collections exist for Wales and Scotland but the equivalent collection for England, which was maintained by the Department of the Environment, has recently been closed. Usually, however, much of the aerial photograph cover for individual counties is kept by County Councils.

Charles Wutkins 157

Satellite remote sensing

Satellite remote sensing is the most recent development within aerial remote sensing. It involves the active or passive sensing of electromagnetic energy. For the study of woodlands and other land resources, the Landsat series of satellites is of great importance. Multi-spectral images are recorded for different picture elements or pixels, and reflectance is measured for a number of parts of the visible and infra-red portions of the electromagnetic spectrum. These images are stored on magnetic tape in digital form (Allan 19SO). Mather (1951) gives four advantages of satellite imagery for the study of land use: first, it provides regional-scale coverage, each image encompassing an area of IS5 X 185 km; second, the images are taken every 18 days; third, the data are cheap compared to aerial photographs; and fourth, and perhaps most important, the data are available in computer-readable form. However. a number of disadvantages have also to be taken into account. As remote sensing is a recent development (Landsat 1 was launched in 1972). satellite imagery is not an important source for the study of woodland change in the past, although this aspect will become steadily more important. Furthermore. the number of useful images is limited by the heavy cloud cover over Britain. A final point is that small-scale changes in woodland distribution and species composition are not discernible from this imagery at present. However, the technology of satellite imagery is advancing quickly and improvements in resolution are likely, especially when images are made available from Landsat IV’s ‘thematic mapper’ (Allan 1980).

Forestry Commission censuses

Forestry Commission censuses are a little used source for the study of Lvoodland distribution and change in this country. There are two main reasons for this: first. much of the original field information has been unavailable owing either to loss or restricted access under the Thirty Years Rule. Second, the censuses have not been considered suitable for such research. Thus Rackham (1976:173) suggests that:

Evidence of [ancient woodland] destruction is all around us, but to measure it Lvould require a considerable research programme. Successive Forestry Commission Cen- suses were not compiled for this purpose and are of little use to us.

These two reasons are related. The census results which Rackham and others have considered of little use for the study of woodland change have been the aggregated statistics produced for counties in the Census Reports of 1924 and 194719 and for specially defined marketing regions in 1965-67. It is only since the 1st of January 1980, that the detailed field records for the 1947-49 Census have become available for use at the Public Record Office (Watkins 1984).

Forestry Commission Census of 1924

The first census of woodlands took place in 1924 and was administered by the recently formed Forestry Commission. County organizers chosen for their local knowledge of woodlands were supplied with 1:lO 560 OS maps on which were marked all woods over two acres (0.81 ha) in extent. They sent the maps to woodland owners who were asked to show the type and age classes of their woods. As the Forestry Commission (1952:14) later pointed out:

Sources for the assessrmwt of British wootil[~t~d changr itr rl~e 2Urir cenrlrrj

This method, although it was the only practicable one at the time, contained certain inherent defects. of which the most important were variations in the fullness and accuracy of the returns submitted. and local differences in the interpretation of the instructions for classification.

However, this census does provide the first detailed description of the majority of the woodland in the country, which it is also possible to break down to county level, and it provides a picture of the country’s woodland before the planting by the Forestry Commission had made a serious impact. Owing to the age-class information which it provides. the area of tvoodland planted at different periods before 1921 can also be deduced.

Forestry Commissiott Census, 1947-49

Although a census of woodlands was started in 1938, it was not fully completed owing to the outbreak of war, and it was not until 194749 that the next complete census was carried out. The purpose of this census was to

. . . provide a detailed classification by area. based on the sis-inch Ordnance Survey maps. of all woods of five acres and over in estent (and exceeding one chain [20.1 ml in width), according to type of crop. age-class. condition. and species, and to assess the proportion of this area which could be considered suitahie for economic management. (Forestry Commission 1952: 15-17.)

In addition a sample survey was undertaken to estimate timber volume. All woods two hectares (five acres) or over, were visited by trained field staff and divided into stands which were defined as areas of woodland O-4 ha (1 acre) or more in extent which were uniform for the purposes of description. In most cases woods had to be divided into a number of separate stands, which were demarcated on the OS 1:lO 650 County Series base maps. New areas of woodland planted after the base maps had been surveyed were added to the maps. Seven main groups of data were collected:

1. ~~~0~~~~2~ type. These were coniferous high forest (CHF), broadleaved high forest (BHF), mixed high forest (MHF). coppice-with-standards (CWS), coppice, scrub, devastated, felled and lost. MHF included all mixtures of conifers and broadleaved trees where either category formed 20 per cent or more of the crop. Scrub was defined as inferior growth unlikely to develop into a utilizabie crop, while devastated stands were those from which the best timber had been removed.

2. Age chs. All even-aged high forest stands were put into one of eight age classes, a stand being considered even aged if 90 per cent or more of the trees forming a closed upper canopy were of one age class. Uneven-aged stands were put in a class of their own.

3. Sub-type. Three different sub-type classifications were used: (i) Coppice was divided into four sub-types based on species.

(ii) Naturally regenerated uneven-aged stands were distinguished from those - formed by under-planting.

(iii) Woodland felled before the outbreak of war was distinguished from wartime felling.

Charles Watkins 159

4. Stem form. All high forest and CWS stands were divided into one of four stem form classes ranging from ‘elite’ to ‘bad’.

5. Stocking. Stands were similarly put into one of four stocking categories ranging from badly overstocked to bad stocking of below 50 per cent in terms of canopy.

6. Stands were assessed as to their suitability of economic marrngemenr with regard to access, area and shape.

7. All stands were classed according to species, those comprising 90 per cent or more of a single species were classed as pure and the relevant square on the stand data form was marked. When a second species formed more than 10 per cent of the canopy the subsidiary species square was also marked. Bunce et LZI. (1979:33) have noted that ‘on a national scale this would tend to overestimate the area of the more abundant species, and underestimate the area of rarer species’.

A stand, for example, shown in the aggregated county statistics as pure or principal oak, could, although this is unlikely, be made up of only 20 per cent oak with eight other species each forming 10 per cent of the canopy. Fortunately, although the detailed species composition of individual stands is not reflected by the aggregated statistics, it is shown, to the nearest 10 per cent, on the back of the stand data form.

The original Forestry Commission Census forms, therefore, contain a large amount of detailed information which can be used as a time horizon against which post-war woodland change can be gauged (Watkins 1984). Forestry Commission woodlands were surveyed in a similar manner to private woodlands but unfortunately the original forms are not available (Locke 19S4). Coppock (1970:33) considers that ‘these data, collected by experienced surveyors in the field, are probably more accurate than most other land-use statistics . . .‘. A sample survey carried out as part of the census to determine the size distribution of woods under two hectares (five acres) showed that only 0.13 per cent (1821 ha) of the gross area surveyed had escaped inclusion in the main survey (Forestry Commission 1952:39). The Forestry Commission (1952:189) noted that:

. . a larger measure of approximation is acceptable for the purpose of a census than would be desirable in a purely local stock-taking. and sufficient latitude must be allowed in the definitions to ensure that they remain applicable to a varying range of conditions over the whole country.

As a result, compromises had to be made on three main points. First areas were computed to the nearest whole acre (0,4 ha) only. Variations of less than 0.4 ha within a woodland were therefore normally ignored. Second, stands of less than 2.0 ha (five acres) were only distinguished if important changes in description, relating to woodland type, age class or principal species, were involved; and third, intermixed stands, which would take too long to delimit, were allotted proportions of their combined area by estimation. Some information on the accuracy of the woodland type classification was obtained by a comparison between the main census results, and the results from the random volume sampling survey. From this comparison, the Forestry Commission (1952: 189) concluded that:

Taking all factors into account, it is considered that a fair representation of the degree of accuracy attained in the total classification would be given by rounding the results off to the nearest five acres in every hundred, up to a total of about 10 000 acres.

Forestry Commission Censuses 1951, 1965-67 ad 197942

The last three censuses carried out by the Forestry Commission have been made on a sample basis and are of little use as data sources for the detailed study of specific areas. The Census of 1951 had three objectives: first. to estimate the volume of hedgerow and park timber; second. to estimate the area and volume of timber in woods from 0.4 to 2.0 ha (1 to 5 acres) and third, to estimate the volume of timber in coppice and unproductive woodlands (Forestry Commission 1953). Three random sets of the quarter sheets of the OS 1: 10 650 maps were taken as the sample areas and just under I per cent of the area covered by small woods was surveyed. Results were aggregated to Forestry Commission conservancies and so direct comparison with the 1937-49 Census on a county basis is impossible.

The next Forestry Commission census was made in 196547 (Forestry Commis- sion 1970). Its objectives were rather different from those of the 193749 census and although estimates of forest type, age class and species were required they were collected on a regional basis which reflected marketing areas. Jeffers (1972) has shown that it is possible to compare results from the 191749 and 1965-67 censuses by aggregating the county results from the earlier census, thus making them comparable to the regions of the later census. It is not possible. hovvevar. to break down the 196547 results to county level as the census was not a complete survey but based on a 15 per cent sample of the total land area of the country. Even at the national level. comparison is not simple as the definitions of woodland type differ between censuses. Thus the mixed high forest category was not used in the 196547 census, high forest simply being divided into mainly coniferous and mainly broadleaved categories. Fortunately the results from the earlier census were summarized on this basis as well so a comparison can be made. Another problem ‘ is that the substantial decline in the area classed as Coppice in the last forty ye&s is due to its reallocation to other forest types and consequently makes valid comparisons difficult’ (Forestry Commission 1970:83).

The most recent Forestry Commission census (197942) is again a sample census and the results are of little use for the detailed study of specific areas (Forestry Commission 19S3). As the data are available on a county basis, comparison with the 194749 census is feasible, although a number of problems are involved in such a comparison. First, there have been many county boundary changes since 194749. Second, the 1979-Q census was based upon the OS 150 000 maps which, in turn, in many instances were based upon the OS 7th Series 1:63 360 maps which may have been surveyed as early as 1960. The Foresty Commission therefore had to make estimates of the amount of woodland cleared and planted since the survey, but unfortunately the Forestry Commission itself considers these estimates to be of low precision. Third, the 1979432 census included certain types of woodland, such as colonized gravel workings, which would not have been inctuded in the earlier census; and finally, the most recent census included all woods dovvn to O-25 ha, while the 191749 census only included woods of 2.0 ha or more.

Forestry Commission and private estate records

rjlost landowners with commercially managed ~voodland maintain records detailing its species, age class, type and quality. The Forestry Commission makes an inventory of all its woodland every 10-15 years, although records of old inventories are not normally kept. Forestry Commission woodlands are divided into compartments and sub-compartments. The former are administrative units whose

Charles Watkins 161

boundaries are formed by roads, rivers and other easily defined features. The main descriptive unit, for which information relating to woodland type, age class, species and yield class is collected when an inventory is being made, is the sub- compartment, the minimum size of which is O-5 ha. Inventories made before 1974 had only the principal species entered on the sub-compartment form. If one species occupied SO per cent or more of the sub-compartment area, this was called the principal species, and the record form would show it as covering the whole area of the sub-compartment. Thus if a sub-compartment was made up of Se5 ha of red oak, 1-O ha of sycamore and 0.5 ha of beech, red oak would appear from the record form to cover 10.0 ha. (There is a parallel here to the problems associated with the principal species system employed in the 1947-49 census.) Since 1974, this problem has been overcome by the division of sub-compartments into componenrs which may go down to 0.1 ha in area, containing trees of the same species, age and yield class.

Private woodland owners who receive grant aid under the dedication scheme (Watkins 1983) are required to manage their woodlands to a plan of operations which has been approved by the Forestry Commission. This normally includes:

a map at the scale of 1:lO 000 (or 1:lO 560) of the dedicated area showing compartments and sub-compartments; a brief written description of existing woodland and areas to be planted and a description of the methods adopted in following a specified set of management objectives; a tabular statement giving for each compartment and sub-compartment the area covered by different species and age classes and other details; an annual record of the volume of timber removed by thinning and final felling (Forestry Commission 1976: 1).

This system of mapping and recording information is very similar to that used by the Forestry Commission for their own woodlands and the records are kept at the Forestry Commission’s District Offices, but unfortunately they are considered confidential. They may, however, be consulted with the woodland owner’s permission.

Land Utilization Surveys

Woodland was included in both the Land Utilization Surveys. The First Land Utilization Survey was carried out between 1931 and 1941, although most of the fieldwork was completed in the early 1930s (Stamp 1948). Land use was mapped at the 1:lO 560 scale, and this information was then transferred to the 1:63 360 maps. Woodland was divided into high forest, coppice, scrub, and cut over land, but ‘. . . unfortunately, the information obtained was not sufficiently consistent for the subcategories to be included in either the county or the national analyses’ (Coppock 1978:56). The survey is useful, however, in mapping the distribution of woodland and the extent of new plantations.

The Second Land Utilization Survey (LUS) was inaugurated by Alice Coleman in 1960, and most of Britain was surveyed in the 1960s at a scale of 1:25 000. Only a small proportion of the sheets have been published, the unpublished sheets being available for consultation at King’s College, London. Woodland was one of the 13 land use groups surveyed and was divided into deciduous, mixed, coniferous, coppice, coppice-with-standards and woodland scrub classes. Unfortunately the

162 Sowces for the nssessment of British woodlard chinye in the 20th cermr?

woodland types are not clearly defined in the survey handbook (Coleman and Maggs 1962:14) and it is difficult to know how they compare with the Forestry Commission definitions.

There are three further problems associated with using this data source for woodland research. First, although specific symbols were alloted to each woodland type, Coleman (1961) has noted that they could only normally be applied ‘. . to the new forest areas as we shall be using Ordnance Survey base maps and will have to accept all their existing tree symbols’. The woodland type marked on the Second LUS maps is not therefore contemporaneous with the Second LUS. but with the date of survey of the OS base maps. In practice, however, certain of the LUS symbols are printed over the OS symbols. This is satisfactory, when. for example, the coppice symbol is printed over the deciduous woodland symbol of the OS. but this method of combining symbols becomes rather confusing when occasional conifer symbols are printed over a deciduous wood. Also, in larger areas of woodland it is difficult to decide whether the over-printed woodland type is meant to represent the new woodland type of the whole wood. or merely a small section. The second problem is that the handbook states that ‘recently felled woodland should be entered according to its pre-felling type . . .’ (Coleman and Maggs 1962:14) for which there is little justification. Third, as the scale upon which the survey was based was 1:25 000, the delineation of detailed stands of different woodland type was not possible.

Agricultural statistics

The Board of Trade (Board of Agriculture and Fisheries after lSS9 and later Ministry of Agriculture, Fisheries and Food) published woodland statistics in the years 1871, lSS0, lSS1, lSSS, 1891, lS95. 1905 and 1913 together with the agricultural statistics. Although considerable doubt must be placed on the accuracy of these figures, they are the first detailed national woodland statistics collected since Domesday, and Rackham (1976: 104) has used the 1905 statistics to map the distribution of coppice.

Woodland statistics were not included in the agricultural returns again until 1969. when a question was introduced relating to the area of woodland ‘ancillary to farming’. In 1974, the question was modified, and farmers were asked to include the total woodland area on the holding. This change has led to problems of interpretation and the results of a similar question in Scotland are not considered to be very accurate (Coppock 1978:31; Ministry of Agriculture, Fisheries and Food 1971:vii). Other problems associated with this source are that only those areas defined by the MAFF as agricultural holdings are included and as the data are considered confidential, information for individual holdings is not available. Recently woodland data from the agricultural returns have been quoted to show that there has been an increase in the area of woodland on farms in certain areas (Shrubb 1983). That these data must be treated carefully. however, is shown by the result of a recent study. For a single parish in Dorset, the agricultural returns showed that the area of woodland increased from 40 ha in 1970 to 89 ha in 19S0. but a ground survey showed that no change in woodland area had occurred (Marsden 1953; Peterken 1933; Essex 19S4).

Conclusions

Of the sources discussed here, the most useful for the study of woodland change are

Charles Watkins 163

undoubtedly Ordnance Survey maps, aerial photographs and Forestry Commission censuses. To what extent have these sources been used by researchers’? Until recently the study of woodland change by geographers has been relatively limited. There have been two main approaches: the Land Utilization Surveys (Stamp 1947; Coleman 1961) have provided important general information about the area of woodland, but are suspect in detail, while a small number of important papers dealing with trends in afforestation have been based largely on the Forestry Commission’s published statistics (Coppock 1960, 1964; Mather 1971, 1978). Both Clark (1982) and Proudfoot and Mitchell (1983) have noted a recent increase in the interest of rural geographers in the study of woodlands and woodland change. Research in this area is diverse and cannot be discussed without reference to work being carried out in other fields.

A number of studies have made use of the published Forestry Commission census results, but these by themselves can only be used to assess changes at the national level. Helliwell (1972) and Jeffers (1972) have used such information in conjunction with certain unpublished Forestry Commission tabulations of the area of private woodland to assess change at the county level, but Peterken and Harding (1975) have pointed out that by using such data, even disaggregated to the county level, ‘. . . evaluations of recent trends in woodland management have tended to ignore the sharp differences which exist between each area within a region’.

There are three further limitations. First, comparisons based on the published records have concentrated on change in woodland type, from which some aspects of management history can be inferred, rather than change in woodland species. Helliwell does give some species information but this refers to the areas of different species planted and does not show relative change in the areas covered by different species. Second, such studies cannot take account of the different rates of change between different sized woodland blocks; and third, no account, other than that between private and Forestry Commission categories, is taken of the effects of different types of woodland ownership.

Two recent geographical studies have made use of aerial photographs and Ordnance Survey maps to investigate changes in the distribution of woodland in specific areas during the 20th century. These are the Nottinghamshire Woodland Census (Wheeler 1984) and a study of woodland change in the Brecon Beacons (Harkness 1983). Neither of these studies have made use of field survey or Forestry Commission census material. They are essentially land use studies detailing the net and gross loss or gain of woodland between different forms of land use. Changes in the area covered by different woodland types are also shown, but, owing to the limitations of the sources used, changes in the areas covered by different tree species are not investigated.

The most fruitful interest area as regards the study of woodland change has been that of woodland historical ecology. A considerable body of research has been built up in recent years largely because the age of a woodland site and the past management of the trees are critical factors in assessing the importance of woodland for wildlife conservation. Much of the research has been based on the detailed study of individual woods using both fieldwork and estate records. Rackham (1980), by studying a large number of individual ancient woods, has, for example, been able to produce a composite picture of woodland change for eastern England.

In terms of the data collected, these conservation studies are far more comprehensive than those based on Forestry Commission published census data, taking account not only of woodland type and age, but also tree species, ground

flora and archaeological remains. Much of this work has been concerned with the pre-20th-century woodland change, but there have been a number of studies dealing with post-war woodland change, such as the work of Peterken and Harding (1975), who make use of aerial photographs taken in 1946 and a ground survey undertaken in 1972-73. Information was collected for both dates on Lvoodland type but not on tree species other than as a means of determining what constituted neglected coppice in 1972. The reason for not including species data in their studv is not given. but it is presumably because species identification from aeiial photographs is extremely difficult.

In contrast to the published Forestry Commission census material, the unpublished original census records for the 191749 census contain detailed tree species data which can be of great interest. A survey of the deciduous \\.oodlands of Scotland for the Nature Conservancy Council found that the best estimate of the decline in broadleaved woodland cover came from using the data from these original returns and comparin, 0 them with data obtained from Ordnance Survey maps (Bunce ef al. 1979). The data from the original returns of the 194749 census have also recently been used, in combination with a present-day woodland survey, to assess post-war changes in woodland type and tree species on a sample of estates and farms in Nottinghamshire (Watkins 1984).

A wide variety of sources is available for the study of British woodland change in the present century. The sources used in an,? particular study will depend upon the type of change under consideration. Thus II changes in the area of Lvoodland in a particular region or changes in the shape, size and type of individual tvoods are of interest, then Ordnance Survey maps and aerial photographs are the most useful sources. If changes in the species composition of woodland is of interest, then the original returns of the Forestry Commission 194749 census. in combination with field survey, provide a useful source of data. This paper has discussed the advantages and disadvantages of the main sources for the study of woodland change and shown that each must be used with care, and preferably m combination with other sources, in order to reduce the risk of errors of interpretation. As the afforestation of upland moors, the conversion of ancient woodland to agricultural land, the replanting of formerly broadleaved woodland with conifers or the decline of many small woodlands through neglect and grazin,. 0 become of greater concern, the study of these changes will become more important in order that they may be quantified, and policies organized to encourage or counteract them.

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(Mmtlscript receilwi 1-I August 1984)