The use of air photo interpretation for land evaluation in the Western Highlands of Scotland

CA T E NA

VOL. 4, 341 - 357

GIESSEN 1977

THE USE OF AIR PHOTO INTERPRETATION FOR LAND EVALUATION IN THE WESTERN HIGHLANDS OF SCOTLAND

C.J. Lawrance 1), R. Webster 2), P.H.T. Beckett Soil Science Laboratory, U n i v e r s i t y of Oxford J.S. Bibby & G. Hudson Macaulay I n s t i t u t e f o r Soil Research, Craigiebuckler, Aberdeen SUMMARY C l a s s i f i c a t i o n s of t e r r a i n , into land systems and land facets, r e l y i n g l a r g e l y on a i r photo i n t e r p r e t a t i o n are j u s t i f i e d in two ways: (i)

that recognition of the pattern of v a r i a t i o n w i t h i n a l a n d s y s t e m , and i t s description by means of diagrams and annotated a i r photos, f a c i l i t a t e s the i d e n t i f i c a t i o n of d i s t i n c t sub-areas w i t h i n i t (facets or elements), part i c u l a r l y by s t a f f with l i m i t e d local experience.

(ii)

that the classes are useful f o r indexing e x i s t i n g information on natural resources, including s o i l , and as s t r a t a f o r economic sampling when obtaining new data.

Such schemes have been widely used, f o r one or both reasons, but not so f a r in the i n t r i c a t e l y varying landscapes shaped by g l a c i a l and p e r i g l a c i a l processes on hard rock. This paper reports a study in which attempt was made to c l a s s i f y such t e r r a i n in the Western Highlands of Scotland using the same philosophy and procedures, and the r e s u l t checked. I t proved reasonably easy to c l a s s i f y a t r i a l area into d i s t i n c t land systems, which are mapped. Division of the land systems was more problematic since each subdivision was i t s e l f a complex, termed a "patterned f a c e t " , consisting of several elements of more or less contrasting land with d i f f e r e n t p o t e n t i a l s f o r use. Elements were not c o n s i s t e n t l y recognized c o r r e c t l y by a i r photo i n t e r p r e t a t i o n , though elements of the more s p e c i f i c a l l y s o i l complexes could be recognized by surveyors with considerable local experience.

ZUSAMMENFASSUNG Oberwiegend auf Luftbildauswertungen beruhende Landschaftsklassifikationen in "land systems" and "land facets" sind wie f o l g t g e r e c h t f e r t i g t : I

Die Kenntnis der Varianz innerhalb von "land systems" und ihre Beschreibung mit H i l f e von Diagrammen und Luftbildkommentaren e r l e i c h t e r t die I d e n t i f i z i e r u n g "facets" oder "elements" besonders fur L u f t b i l d b e a r b e i t e r mit beschr~nkten Ortskenntnissen.

i) now Transport & Road Research Laboratory, Crowthorne, Berks. 2) now Soil Survey of England & Wales, Rothamsted Experimental Station, Herts.

Harpenden,

341

I I Die Klassifikation i s t sinnvoll fur die ~rtliche Fixierung vorhandener Informationen Uber Naturressourcen einschlie~lich B~den und als Hilfsmittel erneuter Datenerhebung im Bedarfsfall. Solche Schemata werden entweder fur einen oder beide aufgefUhrten GrUnde h~ufig genutzt, allerdings nicht fur komplizierte, durch Glazial- und Periglazialprozesse geformte Gebiete in Festgesteinen. Diese Ver~ffentlichung informiert Uber eine Arbeit, in der versucht wurde, Gebiete im westlichen Hochland Schottlands nach den angezeigten Verfahren zu klassifizieren und die Ergebnisse zu UberprUfen. Es erweist sich als r e l a t i v einfach, ein Versuchsgebiet in "land systems" zu klassifizieren. Die Untergliederung der "land systems" i s t problematischer, da jede Untereinheit fur sich selbst wieder einen Komplex bildet, den wir als "patterned facet" bezeichnen, und der aus mehreren "elements" besteht, die hinsichtlich des Nutzungspotentials mehr oder weniger unterschiedlich sind. Diese "elements" konnten nicht genau genug kartiert werden, obwohl einige "elements" mit spezifischen Bodengesellschaften durch Kartierer mit guten Ortskenntnissen ausgeschieden werden konnten. 1.

INTRODUCTION

A i r photography made rapid surveys of land resources, including s o i l , f e a s i b l e . By the mid 1960s much reconnaissance s o i l survey and land evaluation, e s p e c i a l l y in A u s t r a l i a and A f r i c a , was being carried out remotely and cheaply, based on a two-tier classification of land into land systems and land facets. Land facets were the basic reasonably homogeneous classes that could be treated as uniform for practical purposes. Land systems were patterns consisting of a few land facets that recur in characteristic fashion (BRINK et al. 1966). BECKETT & WEBSTER (1965), who were developing methods for survey of remote areas, showed that i t was entirely practicable to classify land in southern England quickly in this way, and that the result was useful (eg WEBSTER & BECKETT 1968). However, a brief experience in Canada suggested that the remote surveyor would find i t more d i f f i c u l t to classify recently glaciated terrain on hard rock in this simple way. (This has since been confirmed privately by J.T. PARRYfor the Canadian Shield and by A. WELLVING in northern Sweden.) The problem obviously needed to be explored. The Soil Survey was also interested in a cheap means of surveying the Western Highlands. In this area of intricate land form and complex soil pattern maps showing conventional soil series would be very time-consuming to make. Further, the economic potential of the land there is considerably less than elsewhere in the country, and the cost of mapping conventional soil series would be quite unjustifiable. The Survey would almost certainly have to recognize complex soil mapping units of some kind, even though i t was locally based for f i e l d work. The two groups of workers, C.J.L., R.W. and P.H.T.B. at Oxford, and J.S.B. and later G.H. of the Soil Survey based in Oban, thus had a common interest. The former wished to explore the practicability of the two-tier scheme of land c l a s s i f i cation in an area of intricate terrain, the l a t t e r to evaluate this essentially physiographic approach to mapping soil in the Western Highlands. Nevertheless,the two groups we are operating under different constraints. The Oxford workers were remote from the area. They were intentionally exploring the problem of the remote surveyor. One member i f the Soil Survey (J.S.B.) had experience of West Highland conditions, gained largely outside the study area, and this influenced his approach. In the following account we make clear where this difference affected the conduct of the studyand i t s outcome. The study was planned primarily: a) to ascertain whether land system - land facet classifications could be devised for areas in the Western Highlands, and, i f so, b) whether the result could provide a basis for the acquisition of information on soil and on land capability. 342

Land use in t h a t area is most affected by c l i m a t e , land form and s o i l . To be usef u l any survey procedure must be able to provide i n f o r m a t i o n at l e a s t on land form and on s i g n i f i c a n t s o i l c h a r a c t e r i s t i c s , of which stoniness, rockiness, wetness, and the presence of a t h i c k organic h o r i z o n , are probably the most important. I.i.

Land system - land facet c l a s s i f i c a t i o n

The main.aim of these c l a s s i f i c a t i o n s is to define mapping u n i t s t h a t are as easil y recognizable on a i r photographs, and yet have as c o n s i s t e n t p r o p e r t i e s f o r a p a r t i c u l a r land use, as possible. Accordingly t h e i r d e f i n i t i o n s give considerable weight to land form and those aspects of materials and hydrology t h a t have e x t e r nal expression, and less weight to the s o i l p r o f i l e as such. The land f a c e t is the basic unit of the c l a s s i f i c a t i o n : (i) I t is a distinguishable part of the landscape, with simple and characterist i c form, rock, s o i l , and water regime; (ii) i t is recognizable on a i r photographs, and ( i i i ) i t can be managed uniformly under at least moderately intensive forms of land use. Ideally individual occurrences of land facets are of an extent that can be mapped conveniently at scales of about I : 50 000, though the mapping scale may be as large as I : 20 000 in areas of i n t r i c a t e t e r r a i n and could be as small as i : 80 000 in areas where changes are less frequent. Particular parts of a land facet, with s i g n i f i c a n t l y d i f f e r e n t effects on land use, may be distinguished and called land elements. Land systems are composite landscape u n i t s , patterns of land, distinguishable on

a i r photographs, and each consisting of a few facets that are linked together over a wide area in the same recurrent and consistent relationship to one another. Land systems are normally mapped at scales between I : 250 000 and 1 : 1 m i l l i o n , depending on the i n t r i c a c y of the t e r r a i n . Commonly, the customer or user is presented with a map of land systems, with instructions and visual aids (mainly block drawings and annotated a i r photographs) to enable him to distinguish and delineate the unmapped land facets w i t h i n each land system. The land system map is intended to serve regional or national planners, for whom the ~inimum area of interest is l i k e l y to be about 1000 ha, which covers about 2 cmL on a 1 : 250 000 map. The land facet c l a s s i f i c a t i o n is provided as a vehicle for the more detailed information required by the local planner, a g r i c u l t u r a l adviser or road engineer, for whom the smallest planning u n i t is perhaps I - 5 ha. I t is assumed that i f they want local facet maps at I : 20 000 - 50 000 such users w i l l employ the i d e n t i f i c a t i o n aids to locate the facet boundaries by a i r phDto i n t e r p r e t a t i o n . Such c l a s s i f i c a t i o n s have proved useful in many situations. But t h e i r use presupposes that most of the landscape is occupied by bodies of f a i r l y uniform s o i l , of reasonable size, which are recognizable on a i r photographs from t h e i r close association with vegetation and land form and t h e i r occurrence in a recognizable recurrent pattern. Indeed, for s t a f f with limited local experience, the recognition of the pattern of occurrence of the d i f f e r e n t facets is a s i g n i f i c a n t stage in the recognition of individual land facets. Conversely a land system c l a s s i f i cation is u n l i k e l y to be helpful where soil bodies, d i f f e r e n t enough to need d i f ferent management, are small or occur in no recognizable or definable pattern, or lack consistent external expression. 1.2.

Requirements

So t h i s study would need to ascertain, for a typical area of the Western Highlands, either i ) is i t possible to define land facets that are both recognizable, and 343

r e l a t i v e l y uniform in features that a f f e c t l a n d use? and i f so, do these occur in recognizable patterns, whose l i m i t s can be mapped as land system boundaries? i i ) are there d i s t i n g u i s h a b l e blocksof land of size comparable to land systems? and i f so, can they be subdivided into smaller recognizable u n i t s , in recurrent pattern, comparable to land facets?

or

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PROCEDURE T r i a l area

An area of Argyll was chosen f o r examination (Fig. 1), extending from Loch Creran, north of Oban, to the Mull of Kintyre. I t included the mountainous Ben Cruachan, composed of g r a n i t e s , and the andesites of the Lorne volcanic plateau in the north; the quartzites, epidiori t e s , p h y l l i t e s and slates of central Arg y l l ; the mica schists of Kintyre; and the h i l l y landscapes und e r l a i n by Old Red Sandstone and Carboniferous porphyrites South of Campbeltown. A major g l a c i a t i o n (maximum 17 000 18 000 years B.P.) had strongly eroded the landscape in north and central A r g y l l , and on i t s r e t r e a t (complete by 13 000 B.P.) had deposited t i l l widely in Kintyre. The Loch Lomond readvance (10 800 - I0 000 B.P.) was confined to the v a l l e y s of Loch Etive and parts of Loch Awe and Loch Fyne. Low areas of gravel, sand and s i l t are extens i v e l y developed near Campbeltown, Lochgilphead and at the mouth of Loch Etive and much of them are o v e r l a i n

by peat. The climate now is mild and wet. Mean annual r a i n f a l l ranges from 1250 mm near the south coast to over 2500 mm in the h i l l s . Land use is dominated by rough grazing and grassland, w i t h arable production of animal feed mainly in the south. 2.2.

Trials

Evaluati'on of a mapping procedure n e c e s s a r i l y involves making a map of a l l or parts o f an area, and then examining the t r u t h o f the map in an unbiased way. In t h i s study the t r i a l f e l l i n t o four stages: i ) to make a land system c l a s s i f i c a t i o n and map f o r the area; 2) to produce a d e t a i l e d land faCet c l a s s i f i c a t i o n f o r a r e p r e s e n t a t i v e part; 3) to s e l e c t randomly a set of t e s t s i t e s and, using only the aids provided, to i d e n t i f y the land facet at each and p r e d i c t c o n d i t i o n s there; 4) to v i s i t the s i t e s to assess the t r u t h of these p r e d i c t i o n s . The procedure and r e s u l t s are presented f o r each stage in t u r n . 2.3.

Stage one - land systems

C.J.L. and R.W. spent three weeks in the area, in the f i e l d with J.S.B., to gain local experience and to relate soils and physiography to features perceptible on a i r photographs, and to the visual patterns to which these gave rise. With this experience and general background information, and with a cover of a i r photographs at i : 10 000 and maps of solid geology at 1 : 63 360, they distinguished several landscapes on t h e i r characteristic a i r photo patterns. These appeared to exhibit reasonably d i s t i n c t i v e ranges of terrain conditions so they were mapped as tentative land systems (Fig. 1). Since many of the land system boundaries observed on the a i r photographs corresponded quite closely to boundaries on the geological maps, the boundaries of some of their smaller occurrences were taken from these. Field examination and a i r photo analysis both showed that the land systems consisted of many small areas, different enough to require different management, too small to be mapped as land facets, and some of them not consistently distinguishable on a i r photographs. They are therefore land elements. 2.3.1.

"Patterned facets"

Many of the elements appeared to occur in characteristic groups; that is the landscapes could be divided into sub-areas, each of which contained several but not a l l of i t s elements in a reasonably simple and recurrent pattern. These sub-areas were of comparable extent to the simple land facets mapped elsewhere at scales of I : 20 000 - 80 000, so we have tentatively called them "patterned facets" The pattern of elements was especially i n t r i c a t e in the andesite landscape in the northern part of the area, where several of the sub-divisions at this level contained most of the elements in the landscape, though in different proportions. Since i t is possible to describe these patterned facets more precisely than the land systems in which they occur, they convey more precise information than the land systems. Having established that i t was possible to define and map land systems, the study moved to stage 2 concentrating on Carradale land system. Although extensive in Kintyre, no soil survey had so far been conducted on i t . I t w i l l be convenient to describe i t before continuing. 2.3.2.

Carradale land system

The Kintyre peninsula is asymmetric, with an eastern zone of rounded h i l l s , up to 460 m high, penetrated by valleys, which are narrow except where close to the sea. The valleys are short and steep on the eastern flanks, but somewhat longer on the west. Between Tarbert and Campbeltown the peninsula is dominated by mica-schists, crossed by a belt of Green Beds (epidiorite, chlorite and hornblende schists) from the north east to the south west, with small Tertiary dykes, end some outcrops of schistose marble north of Campbeltown. Ground moraine or t i l l from the last glacia345

t i o n , sandy loam to f i n e sandy loam in t e x t u r e , covers most of the low ground and contains a mixture of local schistose rocks with material of Old Red Sandstone age from the Clyde basin. I t thins out on the upper slopes of the h i l l s and e x h i b i t s well marked " c r a g - a n d - t a i l " features in central Kintyre, being deeper (up to 15 m) on the west or downflow side of the h i l l s . Frost shattering above i c e - l e v e l had produced rocky debris on the h i l l crests and many such areas now display crenellated bedrock, often boulder strewn, and the shallow t i l l on the upper slopes is sandier and g r i t t i e r than that below. Outwash and a l l u v i a l deposits covered the v a l l e y f l o o r s l o c a l l y , but widespread s o l i f l u c t i o n during the i c e - r e t r e a t mantled many lower slopes and v a l l e y f l o o r s . Indurated and stony horizons were formed l o c a l l y , and d e f l a t i o n and wind deposition produced complicated patterns of stony and sandy m a t e r i a l . Some of the t i l l , p a r t i c u l a r l y that near drainage channels, has been water-modified, and patchy removal of clay has produced mosaics of loam, sandy loam and f i n e sandy loam. Following p o s t - g l a c i a l u p l i f t the drainage cut numerous g u l l i e s into s l o p e - t i l l and bedrock, and incised the v a l l e y s . Peat is now widespread. I t s depth tends to increase with a l t i t u d e , p a r t i c u l a r l y w i t h i n the range from 150 m to 450 m. In places i t is subject to local erosion, or "hagging", which leaves tabular r e l i c s on gentle slopes and s l i p features on steeper slopes. Subsurface water flow, has produced a mosaic of seepage points or "flushes" on the slopes often at the lower l i m i t s of peat patches or near the upper l i m i t s of continuous t i l l . Fig. 2 of the upper and lower extremes of the Carradale land system, and Fig. 5 a-c i l l u s t r a t e the degree of complexity that has resulted.

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topography

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i Deep till I restricted to valley bottoms. I About 2m

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346

2: Compound landscape to illustrate the extremes of Carradale

land system.

Fig.

3: D e f i n i t i v e b l o c k d i a g r a m of C a r r a d a l e T a b l e i (a).

Fig.

4: D e f i n i t i v e b l o c k d i a g r a m o f O x f o r d T a b l e 3 (a).

l a n d system:

f a c e t No.

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6. : e l e m e n t s n u m b e r e d as in

INTERPRETATIVE DIAGRAM OF SAMPLE AREA 4

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Fig. 5: a, b: I n t e r p r e t a t i v e d i a g r a m s o f s a m p l e a r e a s 4 a n d O b a n f a c e t s (Table I (b)). c: P e a t h a g g i n g .

15 to i l l u s t r a t e

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Table

i:

PATTERNED FACETS WITHIN CARRADALE LAND SYSTEM

(a) Recognized remotely

(Oxford)

i) Hill tops. Gently convex, undulating or occasionally hummocky crests. Dominated by blanket bog and gentle peaty slopes, not more than 10 ° . Rare rock outcrops. Rarely extends far down slope, though can occur as isolated patches anywhere on slope.

(b) Recognized locally

(Oban)

1) Rocky hills with peaty topsoils. very extensive, occupying up to 60 % of hill ground; mainly below 250 m: dominated by rocks but with only limited rock outcro F (Fig. 5a, 5b, 5c).

2) Areas of thin soil over rock. Smooth 2) Rocky hills with mineral topsoils. and gentle slopes of thin soils With Limited area, mainly on steep slopes mineral or peaty topsoil dominate but and low coastal hills, below 200 m are obviously underlain by bedrock at rock more prevalent than (i); mainly no great depth, of which the structure steep to moderate slopes. is often evident. Rock outcrops are frequent, but small. 3) Long smooth slopes developed on deeper 3) Crenellated, very rocky hills with solifluction or drift deposits, with peaty topsoils. Mainly on mountain mineral or peaty topsoils: smooth with tops, and above 250 m; dominated by no rock outcrops nor evidence of rock steep and moderate slopes; cofrspistructure beneath. cuous rock outcrops with peaty hollows between, often "hagged". 4) Crenellated rocky slopes many of them 4) Crenellated, very rocky hills with steep, with more than 50 % rock outmineral deposits; restricted to steep crop separating extents of mainly minslopes on the flanks of major valeral soils of variable depth; strong leys. evidence of geological structure. + 5) Floors of small valleys. 5) Rolling topography on tills with mineral topsoils, usually below 150 m; comprises most of the agricultural land in the area (Fig. 5b). + 6) Floors of major valleys. 6) Rolling topography on till, with peaty topsoils; mainly on valley hills, or on the drumlinoid ridge hills of the lower ground (Fig. 2); reclamation for agriculture may be attempted (Fig. 5a, 5b). + + 7) Coastline features. 7) Valley bottoms. + 8) Peat basins. + 9) Coastline features. + not further defined,

2.4.

except by the lists of elements

(Table 3)

Stage two - land facets in Carradale land system

When the land system map had been agreed, C.J.L. and R.W. in Oxford produced a l i s t of tentative land facets for Carradale land system. While doing so, further examination of the air photographs revealed uncertainties that their field work had not resolved. So they drew up a l i s t of questions to clarify doubtful points. J.S.B. from Oban visited the sites they had chosen to illustrate these, and answered their questions in detail, and they produced a revised facet classification. 349

Table

2: E X A M P L E O F D E S C R I P T I O N O F A P A T T E R N E D F A C E T M A D E B Y T H E RP]MOTE G R O U P (OXFORD). P A T T E R N E D F A C E T No. 2. T H I N S O I L S O V E R R O C K

R o c k o u t c r o p s are f r e q u e n t b u t small; s m o o t h a n d g e n t l e s l o p e s o f s h a l l o w s o i l s w i t h m i n e r a l or p e a t y t o p s o i l d o m i n a t e , b u t are o b v i o u s l y u n d e r l a i n b y b e d r o c k a t no g r e a t depth, of w h i c h the s t r u c t u r e is o f t e n e v i d e n t . Elements a) G e n t l e s l o p e s Smooth, g e n t l e slopes, u s u a l l y e x t e n s i v e ; the d o m i n a n t e l e m e n t of the f a c e t and o c c u p i e s m o s t o f the a r e a b e t w e e n rock o u t c r o p s . i) w i t h m i n e r a l t o p s o i l - p r o b a b l y not m u c h m o r e t h a n 1,5 m o f till o v e r bedrock. ii) w i t h p e a t y t o p s o i l - at l e a s t i m p e a t o v e r t i l l as (i); o f t e n "hagged", a n d d i f f i c u l t to d i s t i n g u i s h on a i r p h o t o g r a p h s if not. b) R o c k o u t c r o p s S o m e t i m e s b a r e rock, b u t o f t e n w i t h t h i n soil c o v e r u p to 0,5 m o v e r rock. G e n t l e a n d s t e e p slopes, up to 20 m h i g h a n d 5 0 0 m long, b u t c o m m o n l y a few m e t r e s h i g h a n d a few t e n s o f m e t r e s long: forms the m a i n p a r t o f f a c e t 2 in a l t e r n a t i o n w i t h (a). c) F l u s h e s 'Usually t r i a n g u l a r in plan, w i d e n i n g d o w n h i l l f r o m a n a r r o w source; p e r m a n e n t l y w e t w i t h w a t e r at o r n e a r surface; m a y b e a few tens o f m e t r e s long; s e v e r a l f l u s h e s m a y link up r o u n d the h i l l to f o r m a s p r i n g l i n e ; rushy. d) P e a t b a s i n s D e e p peat; u p to 1OO m across; w e t a n d p o o r l y d r a i n e d ; small.

infrequent and mostly

e) M i n o r v a l l e y f l o o r s U p to iOO m wide, i n c l u d i n g the s t r e a m itself; s o i l s as in e l e m e n t (a), b u t o f t e n w e t t e r ; w a t e r t a b l e p r o b a b l y w i t h i n I - 1,5 m; d i s c o n t i n u o u s . f) L o c h a n s P e r m a n e n t o p e n water;

up to 2 0 0 m wide;

infrequent.

The two groups agreed on the limits of the land system, and largely agreed on its major elements (once "steep slopes" proved to be rare). But not only were the land facets patterned, with 2 or 3 contrasting major elements and from 3 to 6 minor elements in each, but the elements of the land system could be grouped in d i f ferent ways and there could be no unique facet classification for Carradale land system. Patterned facets defined by the two groups (Table i ) contained d i f f e r e n t combinations of elements (Table 3). C.J.L. and R.W. followed techniques they had used already in mainly erosional and unglaciated landscapes, and depended heavily on the general appearance of the t e r rain on a i r photographs: for lack of local knowledge they probably failed to identify or draw sufficient inferences from some of the features that contributed to this general appearance. Thus their facet I was distinguished largely on its topographic position, and facets 2, 3 and 4 on t h e i r rockiness or on evidence of the underlying rock structure, and the smoothness or otherwise of their slopes, as indications of the thickness of their d r i f t cover. They supposed facet I was dominated by peaty topsoils, and facet 4 by mineral topsoils, but their facets 2 and 3 comprised both peaty of mineral topsoils. Following standard practice the land system as a whole was represented by a block diagram (Fig. 3) of a composite landscape showing the facets in their correct inter-relationships, and by a l i s t of patterned facets (Table I ( a ) ) . Two examples are included in this paper to 350

Table

3:

ELEMENTS

IN C A R R A D A L E

LAND SYSTEM

a) R e m o t e c l a s s i f i c a t i o n

Eleinents

1

a) M o d e r a t e to g e n t l e s l o p e s and blanket bog i) less t h a n 1,5 In till ii) Inore t h a n 1,5 In till b) R o c k y s l o p e s a n d r o c k outcrop c) F l u s h e s d) P e a t b a s i n s e) Sinall streains a n d g u l l y sides f) M i n o r v a l l e y f l o o r a n d bottomlands g) L o c h a n h) F l o o d p l a i n j) P e a t flat k) S m a l l m o u n d s l) H i g h t e r r a c e s In) T e r r a c e b l u f f s n) L o w e r t e r r a c e s p) A b a n d o n e d c h a n n e l s q) R i v e r r) S m a l l fans

2

Patterned 3

+p.m (25) +p,m(3)

facets 4

+m,?p +p,in(22)

+(2) +(1) +

+ + +

+

+(9)

+ + +

+

?

+(2)

?

+ +

+

+(i) +

+(2) + + + + +(5) +

+(i) +(2) + +

b) L o c a l c l a s s i f i c a t i o n a) b) c) d) e) f) g) h) i) j) k) i) In) n) p) q)

Steep slopes Moderate slopes Gentle slopes Peat basins Small peat basins Rock outcrops Boulder accumulations Flushes Small water courses Lochans Screes Banks Streain River Floodplain or alluvial Terrace Abandoned channels Peat flat

+in

+in

+p

+m +in

+in(2)

+p(3) +p(15) (i) + + +

+p +p(1) +p(23) +

+m +m +m(2) +

+p +p

+

+

+

+

+(i) + +

+ + +

+ + + +

+ +

strata

+ p (4) +

+in(4) + + + +(4) + +

+(5) +

+

+

+

+ + + +

+(4) +(6) + +

p = peaty topsoil; m = mineral topsoil; + = part of facet definition. N u m b e r s in p a r e n t h e s e s are the n u m b e r s o f t e s t s i t e s e n c o u n t e r e d in the sample.

show how the patterned facets were d e f i n e d . Table 2 describes the elements o f f a c e t 2 in d e t a i l , w h i l e Fig. 4 shows the elements o f f a c e t 6 and t h e i r r e l a t i o n ships t o one another. On the o t h e r hand J.S.B. a t Oban, w i t h more knowledge o f the Jest Highlands, was 351

c o n f i d e n t that he could d i s t i n g u i s h peaty from mineral t o p s o i l s , t i l l from nont i l l s o i l s , and three classes of slope, on a i r photographs. So his patterned facets were defined on p a r t i c u l a r combinations of t o p s o i l , slope and parent material (Table 1 ( b ) ) . Fig. 5 i l l u s t r a t e s some of t h e i r i n t e r r e l a t i o n s . The Soil Survey has used s i m i l a r c r i t e r i a to define and describe s o i l complexes in several areas of Scotland (MUIR 1956, BOWN 1973, BIBBY 1973). Soil complexes are grouped i n t o l a r g e r u n i t s , s o i l associations which d i f f e r from land systems mainly in the emphasis placed on t h e i r s o i l parent m a t e r i a l . In the lowlands one land system may comprise several s o i l a s s o c i a t i o n s , but in the uplands, where changes in physiography are often c l o s e l y a l l i e d to underlying rock type, the boundaries of s o i l associations and land systems are often the same.

i

Skipness 3x5

.

i::i

The c o n t r a s t between the two approaches is s i g n i f i c a n t . The Soil Survey approach d i s t i n g u i s h e s the elements on p a r t i c u l a r f e a t u r e s , recognizable on a i r photographs, and then defines landscape u n i t s , each to be dominated by a combination of these features. The remote c l a s s i f i c a t i o n divides the land system i n t o areas in which d i s t i n c t i v e a i r - p h o t o appearances occur in c h a r a c t e r i s t i c p a t t e r n , which can then be described in terms of the elements they cont a i n . To some extent the former could be said to recognize landscape u n i t s d i r e c t l y from t h e i r features, and the l a t t e r to depend more on the recognit i o n of t h e i r patterns and i n t e r relations. 2.5. Stage three - s e l e c t i o n of check sites

~

Arnicle

Tangy

Dippen lx5 rrisdale lx5

Glen Lussa 2x10

CA#,

~

Carradale land system

L

interpretationblocks

~

Air photo

Areasselected

•

for

detailed investigation Location of random sampleareas

C~ Fig. 6: A r e a s s e l e c t e d for f i e l d check, and r a n d o m s a m p l e a r e a s w i t h i n them. 2 x 5 indicates that 5 sites were successfully visi t e d in e a c h o f 2 s a m p l e s areas.

The f i e l d check was designed to compare the two c l a s s i f i c a t i o n s . Check s i t e s were chosen as f o l l o w s : a) Six blocks were chosen which had good cover of a i r photographs (Fig. 6), and which had not been the subject of any of the pre~ liminary investigations. b) Within each block two or four i n t e r s e c t i o n s on the 1 km national g r i d (marked on Fig. 6) were selected randomly. c), An area of 50 ha was established round each i n t e r s e c t i o n and f i v e s i t e s w i t h i n i t were selected randomly. The s i t e s were marked on the I : 10000 a i r photographs. Then w i t h o u t f u r t h e r ground check C.J.L. and J.S.B. separ a t e l y i d e n t i f i e d the facet and e l e ment present at each s i t e . T h e i r l i s t s of i d e n t i f i c a t i o n s were then put away ( " o f f i c e " l i s t s ) .

2.6.

Stage four - field check

The field check was carried out by another soil surveyor (G.H.) unfamiliar with this area and with no previous connections with the study. He was equipped with the alternative lists of facets for Carradale land system, and their definitions, and the air photographs on which the test sites were marked. He found that he could l,ocate the sites to within 5 m, but some of the sites under a dense cover of young trees planted since the air photographs were taken were omitted. Fig. 6 indicates the 75 sites that were visited. He identified the element and facet on both classifications represented at each site ("field" l i s t s ) . He examined the soil profile by spade, and peat deeper than 50 m by probe. Where possible he recorded all the features in Table 4, using the classes given there. Some records were incomplete; for example i t proved impracticable to examine the mineral soil beneath deep peat.

Table 4: Drainage class of whole profile.

P Free; PH Poor;

P - PH HP

Imperfect; Very Poor.

Texture of m i n e r a l soil

(s, is, sl, fsl, i, gravel) in Topsoil (0-20 cm); and Subsurface

(20-40 cm)

Depth of p e a t or of peat dominated horizons.

HI 0-5 cm; H2 5+-15 cm; H3 15+-50 cm; H4 50+-1OO cm; H5 >iOO cm; Soils w i t h 5-50 cm peat are 'peaty ~, with 50-1OO cm 'shallow peat', more than iOO cm 'deep peat'.

Depth of m i n e r a l soil including u n c o n s o l i d a t e d till or alluvium.

MO 0-5 cm; M1 >5 cm; M2 >15 cm; M3 >45 cm; M4 >i m; M5 • 2 m; M6 > 3 m; Each site is a l l o c a t e d to the deepest class to which the (sometimes incomplete) records a l l o w it to be a l l o c a t e d

Slope at the site

GO O-i°; GI 2-5; G2 6-9; G3 10-20; G4 >20 ° . 'Gentle' slopes are 0-9 ° , 'Moderate' 10-20 ° , 'Steep' are g r e a t e r than 20 ° .

Parent M a t e r i a l

Bedrock, Till, Head and Colluvium, Alluvium.

M a j o r Soil S u b g r o u p

Organic or Peat, P e a t y Podzol, Peaty Gley, Peaty Lithosol, Peaty F l u s h / F l u s h Gley, Podzol, B r o w n Podzolic, N o n - C a l c a r e o u s Gley, F l u s h Gley, Alluvium.

3.

RESULTS

Table 3 records the number of times each land element was encountered in this sample. The high proportion of sites of "poor" drainage (78 - 85 %), and the number of flushes encountered, confirm the prevailing wetness of the region. While facet 1 in both classifications is dominated (25/28 or 23/25) by broadly the same element and might have been presented as a simple facet, facet 3 of the remote group (Oxford) and the corresponding facets 5 and 6 of the local surveyor (Oban) are clearly patterned. Table 5 compares the success of the authors of the two classifications at identifying the elements of their land systems. The more conspicuous features of the major valley floors were easily distinguished, but minor elements of the upland facets (such as flushes, minor streams and peat basins) less so. The local surveyor 353

Table a)

5:

RECOGNITION

OF ELEMENTS:

NO.

OF

SITES

RECOGNIZED

IN

"OFFICE"

AND

"FIELD"

Oxford "Office" Facets

Facet

1 - 4

a

a

predictions

b

c

f

e

1

6

n

p

i

ii

i

25

3

28

ii

i0

ii

22

o > m

b

2

c

4

2

O 4

e

1

1

iO

2

2

o

2

f

;e

3 4

i

I 2

41

b)

20

0

1

2

3

4

2

2

75

Oban "Office"

predictions

Facets

a p

I - 6

b m

p

c m

p

Facet d

e

f

g

m

7 n

m

O

O 0

O

o

2

2

4

b >

0

2

2

o 4

o

% :~

1

26

3

5

1

42

1

6

c

1

4

d

1

e f

3

2

1

1

0

10

g

in

2

n

2 6

O

2

9

3

30

8

6

2

5

2

8

75

had considerable success in distinguishing sites with and without peaty topsoils, whereas the remote p h o t o - i n t e r p r e t e r had f e l t too uncertain to make a facet separ a t i o n . The local surveyor, however, had over-estimated gradients.

Table

6: "Office"

~redictions OBAN

OXFORD o .4 No.

of sites

No.

on

pf

sites

on

> Shallow

(facets

Till

till 1,2,6)

Shallow

(facets 3)

till

(facets 1-4)

Till (facets 5-6)

0 Shallow

till

Till

25

3

i0

11 For element

Table

7: P A R E N T

%o

Facet and Element

Bedrock

14 18 1

Oban

ib,c 5c 6b,c,f

2 8 19

8: D E P T H

SOIL OBSERVED

Facet and Element

MO

Oxford

la 3a

3 i

Oban

ib,c 5c,6b,c,f

4

9: D E P T H

a

OF M I N E R A L

OF ORGANIC

MI

For elements

M3

M4

M5

M6

i

2 i

i 6

2

6 7

i i

3

i 6

2

I

13

2

OBSERVED

HI

H2

H3

H4

H5

6 3

7 8

8 I

18 1

2

4

5

ii

I

3

6

8

2

3

Facet a n d Elelemt

-m %0

0

:

~

Oxford

la 3a

i 7

Oban

lb,c 5c 6b,c

4

a, b,

c

Table 6 compares t h e i r succes in distinguishing those elements on slopes which lay over more than I - 2 m t i l l . Again, J.S.B. had proved more successful at recognizing a p a r t i c u l a r feature on the a i r photographs.

M2

SURFACE

2

2O

Alluvium

la 3a,c 3f

Q,4J

Table

OBSERVED

Oxford

%2 ~.~

Table

MATERIAL

20

The remaining comparisons are limited to elements represented by more than one s i t e . T a b l e s 7 - 11 g ro u p the sites according to t h e i r "office" i d e n t i f i c a tion. Both c l a s s i f i c a t i o n s are reasonably successful at i d e n t i f y i n g elements on deep t i l l within the facets dominated by t i l l (Table 7) but in facet i higher up the slopes the elements i d e n t i f i e d by the local surveyor ( l b , c) were s l i g h t l y more uniform in parent material and depth (Table 8) than those ident i f i e d remotely ( l a ) . The elements i d e n t i f i e d l o c a l l y were more uniform in their.presence or absence of peaty surface horizons (Table I 0 ) , and in the depth of their.humose or peaty surfaces (Table g) than those 355

Table

iO: S O I L S U B - G R O U P O B S E R V E D I F a c e t andl Element :~=L Oxford

c

Mineral

Peaty topsoil Gley

Podzol

la 3a

24 2

9 8

1

ib,c 5c 6b,c

14

2 3 13

1 1

Lithosol

Gley

topsoil

Well-drained

5 I

14

I0

1 4

2

6 -

8 4

3

i

=c,

:3, ~

-,~ C

~

Oban

0 Q~

Table

14

ii: S O I L T E X T U R E O B S E R V E D

Facet and Element

c

5

Oxford

la 3a,c,f

Topsoil

Subsoil LS

SL

2

5

6 7

2 3

i 1

I 4

i 4 6

i 4

S

LS

SL

FSL

L

I

2 4

8 12

2

1

5

3 4 ii

S

FSL

L

D ~

~

"~

o

~

Oban

lb,c

5c 6b,c,f

interpreted remotely. C.J.L. had defined facet 1 as a h i l ~ c r e s t feature and there. by picked out the sites of more sandy topsoil (Table 11) in contrast to J.S.B. whose facet definitions make no reference to their position in the landscape. None of the elements of either group are very uniform in soil texture.

4.

CONCLUSIONS

Land systems can be defined f o r the Highlands of Scotland to serve as aids to regional planning. Also, i t i s not d i f f i c u l t to define l a n a e l e m e n t s , each to comprise a kind of t e r r a i n t h a t presents p a r t i c u l a r and f a i r l y uniform problems of management or conservation, but most of these are too small in extent to be mapped at a reasonable scale or used as a basis f o r local planning. Over much of t h i s area i t was not possible to define simple f a c e t s , l a r g e r than elements, uniform enough to be managed as s i n g l e u n i t s even i f only f o r moderately i n t e n s i v e land use. While i t was possible to define '~atterned facets", that could be d i s t i n guished on air photographs and mapped at scales of I : 20 000 - 1 : 50 000, many of these consisted of 2 or 3 major elements in recognizable pattern and several minor elements, so they are not uniform enough to be treated as single management units under moderately intensive land use. As stated e a r l i e r , land facets had to be created as units for the detailed mapping of simple landscapes in any one of which a few simple facets recurred to form a characteristic pattern. The recognition of the pattern and of the position of any site within i t is then a significant stage in the i d e n t i f i c a t i o n of the facet at any particular site, and s t a f f with l i t t l e ' l o c a l experience need not distinguish land facets on subtle or unfamiliar diagnostic features. Clearly these conditions do not apply to Central Argyll, where the landscape patterns are complex and not always clear, and several of the larger facets could not be associated with particular positions in the landscape. In such cases i t w i l l be 356

better to distinguish areas on any p a r t i c u l a r soil characteristics, such as peaty topsoil or shallowness, that are associated with specific features on a i r photographs. The mapping units that result w i l l be similar to soil complexes, already mapped in some areas, that contain two or more d i f f e r e n t kinds of s o i l . They can be grouped within soil associations, according to parent material, to f i t the c l a s s i f i c a t i o n structure already used in Scotland, and they can be mapped quickly by l o c a l l y based surveyors with good experience. Staff with l i t t l e local experience and those who must work remotely w i l l find i t d i f f i c u l t to map s p e c i f i c a l l y soil complexes from t h e i r a i r photo appearance. They can map patterned facets, and though such units may be less useful than classes defined s t r i c t l y on soil characters, they may be adequate for some forms of land evaluation. BIBLIOGRAPHY BECKETT, P.H.T. & WEBSTER, R. (1965): A c l a s s i f i c a t i o n system for t e r r a i n . Report No. 872, M i l i t a r y Engineering and Experimental Establishmen~Christchurch. BIBBY, J.S. (1973): In: Island of Mull ~ Survey and proposals for development. Special Report No. I0. Highlands and Islands Development Board, Inverness. BOWN, C.J. (1973): The soils of Carrick and the country round Girvan (Sheets 7 and 8) Mem. Soil Surv. Scotland. H.M. Stationery Office, Edinburgh. BRINK, A.B.A., MABBUTT, J.A. WEBSTER, R. & BECKETT, P.H.T. (1966): Report of the working group on land c l a s s i f i c a t i o n and data storage. Report No. 940, M i l i t a r y Engineering Experimental Establishment, Christchurch. MUIR, J.W. (1956): The s o i l s ' o f the country around Jedburgh and Morebattle (Sheets 17 and 18). Mem. Soil Surv. Scotland. H.M. Stationery Office, Edinburgh. WEBSTER, R. & BECKETT, P.H.T. (1968): Quality and usefulness of soil maps. Nature, London, 219, 680 - 682.

357