According to Cubbon the word Treen was in colloquial use long before its first appearance in written form in 1600 [Ballaugh Parish Register] or used in an 1665 Act of Tynwald.
Early derivations of the word connected it with the Latin tres (three) however later derivations connect it with Norse Tir or cheer 'land' and unga 'ounce' cognate with the Hebridean Tirunga 'ounceland' and thus clarify its use as a fiscal division paying the skett or Lord's Rent.
The most comprehensive study is that by Davies published in 1956; though the earlier, 1937, paper by Prof C Marstrander is of great value.
There are some 175 treens mentioned in the 1511 Manorial Roll each generally consisting of four farms or Quarterlands. The boundaries of some earlier, contiguous, treens are conjectured to have lost as they were merged on becoming Abbeylands (ie paying rent to Rushen Abbey) prior to 1511. Woods gives 171 treens and 752 quarterlands in his 1864 Atlas. The area of each treen varies between somewhat less than 200 acres through to little more than 600 acres of cultivatable land bounded by natural borders. The following figure taken from Davies shows the distribution.
Davies points out that the treen boundaries tend to follow natural boundaries such as streams or paths which later became roads; and that the boundaries marked by hedges or stonewalls are older than the field divisions within them. He also refers to the frequent distribution of wells (Manx Chibbyr) along these boundaries - in many cases the boundaries have been deflected from their 'natural' course to include such wells.
The number of Treens per Parish varies between 5 and 16 and does not appear to depend on the size of the parish but depend strongly on the form of the land. Davies classifies Treens as:
(a) plateau treens;
(b) valley treens;
(c) treens on the plains.
In the coastal plateau treens tend to be long strips extending from coast to hills (eg Douglas/Laxey and around Port St. Mary). A similar arrangement is also seen in the North of the Island on the northern flank of the morainic hills where the treens extend from the edges of the raised beach to the crest of the hills.
The valleys show a very different structure - here the treens
occupy the valley slopes with the valley floor providing a baseline
along which the treens terminate. The valley floor may be 'intack' as
it is (or was) boggy ground. In these regions where land aspects are
very variable the treens are arranged to provide an equitable divison
of the land each providing river meadow, arrable land on the lower
slopes and rough pasture above.
Elsewhere the treens do not appear to follow any particular pattern.
Many historians support a keeill-per-treen hypothesis in which the keeills, also associated with cultivatable land, were the 'domestic chapels' of the Christian Norse treen-holder [Marstrander 1937] and effectively replaced the pagan hofs of the earlier Norse period. In most sheadings the one keeill per treen holds good once allowance is made for possible later splittings of older treens, though Scarclowte (Scarlett) treen in Malew would appear to have 4 keeills (though one is associated with Castle Desmene, with three on the coastline). Churchyards used to allocate 20 yards of boundary wall per treen - this both demarcated burial area and responsibility for upkeep of the wall.
The word alia seen in some names is from the latin 'also'
and is used where two treens apparently share the same name -
possibly later divisions of an earlier single treen.
Some names would appear to refer to two treens (or a single treen has been split)
Baly corresponds to the modern form Balla (Farmstead), moar (large) and beg/veg (small);
In some case the names are I, II .. following Kneen
Treens are split into quarterlands - typically four as shown in the figure below:
The majority of quarterlands are between 50 and 180 acres with a fairly regular distribution around a mode of 90 acres as shown below (figure taken from Davies). Quarterlands tend to equally divide a treen but this is not always the case.
These quarterlands were the units of landholding at the beginning of the 16th century though now they may be split between two to four farms - most larger farms still approximate to quarterlands and the smaller farms are described as belonging to some particular quarterland.
The term Intack (from 'In-taken' or land 'taken into' cultivation) is first used around 1520 and is associated with enclosures of one time common land. Thus Intack is land outside of the treen and quarterland system which tended to have a boundary mostly coincident with the 600 feet contour. Above this, extending to 750 to 1000 feet and forming a fringe to the quarterlands were the intacks. Commonly these intacks are strongly linked with the owning quarterland (often referred to as 'Intacks of Ease'). In other places (especially the Curragh in the North) the intacks are separated from the quarterlands and correspond to damp meadows. The Curragh also has many smaller land holdings not associated with quarterlands.
Roscow quotes the setting quest placing a rent of between 4 to 6 pence per acre depending on fertility.
Cubbon W., Island Heritage Manchester: George Falkner & Son 1952 Chap 4 has a description of Treens
Cubbon W., Treen Divisions of Man, Coloured, based on the 1511 Manorial Roll Douglas: Manx Museum 1933
Kneen J.J., The Place-Names of the Isle of Man with their Origin and History Douglas: Manx Society 1929
Marstrander C.J.S., Treen og Keeill Norsk Tidskr. F. Sprogvidenskap,VIII, 1937 pp287-500
Bruce J.R., Manx Archaeological Survey 6th Report 1966 Douglas: Manx Museum and National Trust 1968 - see page 74
Davies E. Treens and Quarterlands: A Study of the Land System of the Isle of Man The Institute of British Geographers Publication No. 22 1956 (reprinted from 'Transactions and Papers 1956)
Roscow J. R. Dating the Beginning of Intack on the Isle of Man Proc IoMNH&AS X #4 p445 1998
Farrant R.D. Mann: Its Land Tenure etc 1937