A study of the natural conditions and of agrarian land utilization on the Karst

Abstract

The present study is the outcome of team research-work done in June
1968. Its object is to make a study of the specific karstic properties in
relation to the agrarian utilization as well as of the degree to which Karst
modifies the general deagrarization. The study has been made at the example
of the cadastrian parish of Krajna vas which is situated close to the
Yugoslav-Italian border, in the central part of the (Trieste) Karst area
from where the international geomorphological term »Karst« is taken (Sketch
No 1). The majority of the area is occupied by karst level, from 250 to 280
meters above sea-level; its basis is pure cretaceous limestone, and to a smaller
degree dolomite. There are no surface streams, and the most common karst
formations are dolines. On the basis of analyses the territory in question has
been divided into lithologic, relief, climatic, pedologic, and vegetation units
as well as into sectors of agrarian land use. Almost ali of units and sectors
are recorded in the maps No 1—8. For the most part the units ccrrespond in
the areas and as such constitute physical-geographical complexes. Their bases
are constituted by the differences in the granulation of the limestones or
rather by the degree of re-crystalization, which affects also the density of the
dolines, the thickness and properties of the soil, the vegetation, and the
utilization of land.
The morphological investigation has confuted the view that the dry
valley of the so-called Brestoviški dol (which divides the level of Krajna
vas) had been shaped by the surface stream Notranjska Reka immediately
before karstification. On the territory of Krajna vas the valley bottom
(»Draga«) is sinking in particularly quickly in places where after rainfalls
brooks come out of the dolomites and slightly permeable laddinian limestones.
When in the cold periods of the Pleistocene the ground was for a longer
period of time frozen solid, these and other local brooks could work out
Brestoviški dol.
The smallest number of the dolines is to be found in the dolomite and
the largest number in the stratified limestone with closed and gaping joints.
The medium density is 64 per 100 hectares of land. The average dimesions
of the dolines: the longer axis — 72 m, the transverse axis — 57 m, the depth
— 5.4 m, and the medium inclination of the slope — 17.6°.
Since the karst level is both in the north and in the south surrounded
by a ridge of mountains, we get a temperature inversion, a r instance of
which — for the day of June 10th, 1968, — is shown in the map No 1. The
inversion is reflected also in the average temperatures of the vegetation
period of two Iower stations and of another station (Temnica) lying 100
meters higher — ali of them having similar values. Besides, we get in the
dolines microinversion, the intensity of which was measured in two dolines
every two hours. In the dolines Ograda, which is 7—14 meters deep and
tilled, the day minima were for 2.8°, and in the almost twice as deep a
doline, but wooded Jelenov dol (— 24 m) the day minima were only for
1.4® C. lower from those in the level (see Maps No 1—3). The day
temperature course of the air at the height of 150 cm above the ground on
the sunny side of the doline overtakes the courses at the bottom or
on the shady side, and from the early afternoon until midnight the
temperaturs on the sunny side are lower (Map No 4). The reasons lies probably in the greater soil dryness and in the more intense radiation from the
earth at 150 cm above soil. But the temperatures in the layer of air immediately above the ground as well as the soil temperature remain in the sunny
areas constantly higher. At the bottom the temperature and the humidity of
the air vary rather more, and consequently some crops, notably careals,
cannot be grown in the dolines.
Dolines create just as many sunny and shady sites as the fluviatile
relief; also, they gather in the air that has been cooled during the night
but they also retain the cooled air. This is reason why level karstic surface
with dolines, covered with a thicker layer of soil is cooler than non-karstic
land of the same heights above sea-level. Krajna vas, which is only 9 km
away from the Adriatic, has during the vegetation period (april-october) a
medium temperature only between 14 and 15° C.
The territory of the village includes Volarija in the south, and Gmajna
in the north, which both have the greatest contrasts concerning the properties of soil. At Volarija, the layer of clay and loamy soil is so thick
that when the village first came into exsistence one could have here fields.
and meadows without a previous cleaning of the surface stones. At Gmajna,
on the other hand, the soil is row, shallow, and every portion of cultivated
land had first to be cleared of the stonec. Per 1 m2
of tilled soil an average of 158 kg stones has been cleared away. Originally, the land was used mostly
for pastures and when the village came into existence in the Middle Ages
usihg land for pastures spread also to the two areas in question. But in the
course of the last centuries were cleared of stones particularly at Gmajna
while fields and meadows at Volarija, where the soil is more acid (ph in
KC1 4.2—4.3) and too thick for the roots to reach the limestone ročk, were
being abandoned. In perhumid climate (1400 mm of precipitation per year)
and since during summer there is no sub-soil water on the rocky basis which
could rise during the dry period the old and thick soil has become too
acid. Although enormous amount of work has been expended in clearing
the ground of stones, most of the tilled soil is unsuitable for mechanical
treatment. Most of the dolines in which half of the village fields lie, had
been cleared from the tirne of settlement until the beginning of the second
war of not only the surface stones but also of bigger rocks below the surface
of the lower slopes of the dolines. Smoothing the slopes additional soil was
brought aut of the fissures and spread on the bottom. So the bottom of the
doline raised and fields expandes (see Map No 3, sketch a, and the photograph). In spite of this, since the bottom of the dolines is difficult to reach,
since the land property is small and scattered 82% of the peasants till the
fields in the dolines by hand (and 76% of the peasants till the meadows in
the dolines by hand). Althought most of the climatic conditions at the bottom
of dolines are less favourable (an exeception is the greater humidity), the
fields are tilled because the soil is less heavy and the number of clay
particles at the depth of 10—15 cm is for 13, and at the depth of 43 cm for
24 °/o lower from tha t on level between the dolines (se Table on the page 250).
In the post-war decreasing intensivenes of land tilling, the primary role
is played by the distance at which land lies from the village. (See Map No
12). Krajna vas has also become affected by the general process of the
population turning to non-agrarian occupations. The process of Karst being
grown over, which has now been going on for as many as one hundred
years, is felt also in the climate, with the vegetations rythm getting late
and the summer dryness milder.