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Oliver Rackham, ovvero l’ecologia storica – #2
Di seguito, il testo originale, in inglese, delle riflessioni di Oliver Rackham sui boschi di latifoglie tra Toritto, Altamura e Grumo Appula, ora nel Parco Nazionale dell’Alta Murgia.
Notes and some preliminary conclusions by Oliver Rackham
on visit of 30 March 2003
On the Murge tableland 30 km SW of Bari, close to the railway to Altamura. Thin red-brown soils overlying hard limestone which is almost horizontally bedded and has some fissures. Rock occasionally shows through, especially on hilltops.
The site is wood-pasture, with areas of trees and areas of grassland, the boundaries between which are fluid and not demarcated. It was gr azed by cattle until the late 1990s. Trees are mainly deciduous oak (mainly Quercus pubescens, some Q. brachyphylla and Q. frainetto ), with about 10% of evergreen oak (Q. coccifera ). Trees other than oak are rare, including some hawthorn (Cratægus species).
|I Boschi di Toritto in una cartografia del 1880
Oaks are mostly low, multi-stemmed and shrubby, 1 to 5 m high, like a coppice-wood. In places there are scattered big, single-stemmed, spreading oaks, which were evidently free-standing in pasture. On rocky hilltops the trees are more continuous and contain more evergreen oak (always in shrubby form). The trees have been getting bigger and encroaching on grassland.
Grassland is dominated by Dactylis glomerata and Phleum pratense, now thick and tussocky through lack of grazing. Asphodelus microcarpus is locally very abundant. At this time of year it was not possible to find out how rich the flora is, but it includes Anemone pavonina and a Serapias orchid. Many species, such as Cerinthe minor, are confined to the edges of tracks.
The site forms part of a wider area of wood-pasture, in which the tree-cover varies, including coppice-wood with patches of grassland, savanna of grassland with scattered single-stemmed or multi-stemmed trees, etc. Grazing continues. Some of the grassland has been agriculturally improved.
A massive cow-house or stable of cut-stone blocks, with a vaulted roof and stone-built mangers with stone tethering rings, dates from a period of prosperity, probably in the 18th century. Later it fell into decay: two of its three bays were demolished and the blocks taken away for reuse. The remaining bay was adapted to further use; the inscribed date 1876 may relate to this change.
|Documento del 1549 sulla reintegra di una locatione in territorio di Toritto
There is also a row of cow-houses and other buildings built and altered at various dates, probably from the 18th century onwards. The last addition, with a roof of interlocking tiles from Marseilles, would be of c. 1900 (related to the coming of the railway?). Timbers appear to be all pine, which would have to be brought from a distance.
These indicate periods of prosperity and adversity, beginning perhaps with a privatization of the land and ending with the abandonment of the farm in the 1990s.
This is a complex site affected by a number of factors:
- Browsing. Cattle have maintained the open areas. Cattle-grazing ceased a few years ago, and although there is probably some browsing by wild animals trees are rapidly spreading into the grassland. The abundant asphodel would conventionally be interpreted as the result of a period of severe grazing.
- Woodcutting. Although direct evidence of coppicing is sparse, there is probably a long history of woodcutting for firewood, ceasing 10—20 years ago.
- Burning. There is clear evidence of a fire in the oakwood c.20 years ago, which killed most of the stems down to ground level; they have since grown up again. The fuel, presumably, was dead oak-leaves and dry grass. There may well have been a long succession of fires, perhaps through occupational burning to improve the pasture.
- Fertility. The site appears to be more fertile than most Mediterranean roughland, as shown by the vigorous growth of Dactylis, Ferula, and other plants requiring nitrogen or phosphate.
- Drought. The growth-rate of the oaks is very slow (annual rings 11/2 mm or less), and the taller trees often show dieback at the top, where they have not developed extensive enough roots to withstand an unusually dry season. The site is beginning to exhibit the characteristic feature of ex-savanna, in which the continuous, infilling trees are more limited by drought than the taller original trees were. It must not be assumed that the few big, spreading oaks represent vegetation that was once continuous over the whole site.
- Snow- or ice-load, probably responsible for the breakage of some of the trees late in 2002 and for a more severe episode of breakage in the early 1990s. Occasionally this has produced trees of a pollard-like form.
Thoughts on conservation
Wood-pastures are often of great ecological value, especially if they contain ancient trees (which this site does not). Even without ancient trees, wood-pasture can easily be a richer habitat for plants and birds than either continuous forest or continuous grassland. Wood-pastures often depend on traditional management practices. A threat to such places throughout the world is the loss of traditional management, which causes savannas and other wood-pastures to infill and turn into forest.
Tree cover is rapidly increasing. If this continues, the site is likely to turn into low macchia, with even more continuous low tree cover than at present. The trees will not grow tall because of lack of moisture and possibly snow-breakage. At the same time the grasses, encouraged by the fertility of the site, will become aggressive in the remaining open spaces, and by their competition will eliminate the other herbaceous plants, except along paths and tracks. Such a habitat may still be of some value for birds, but will have lost much of its plant life.
An imponderable factor is fire. At present the fuel is increasing as dead grass accumulates. A fire would probably reset the process of succession. If a fire does not occur, however, there may come a point where the trees have gained so much over the grassland that the dead grass rots away and the site becomes relatively incombustible.
When passing through the area in 1993 I noticed signs of recent burning.