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FORESTRY POLICY SILVICULTURE AND CINEGETICS REVIEW XVII/30/2012 Occupation of forests by humans Maurice Bonneau We often tend to consider that the spaces now occupied by forests have always been like that. This is very rough estimate and recent work in mainland France and French Guiana, have shown that our forests were to a large extent, in the past, cropland or pastures. Since 1905, Henry, forest soil scientist who taught at the School of Forestry at Nancy, published a welldocumented work, "Forest soils". I read this book and was surprised to find the assertion that nitrification of ammonium in the forest was always zero. I worked at the time on nitrogen mineralization in soils of the Vosges and Massif Central and I found, for my part, an active nitrification in most cases. Taking a closer look at Henry's book, I was assured that the characterization method of nitrate that he used was perfectly correct. So there was a problem somewhere and I was puzzled for years without finding the answer. I was wondering if, since 1905, the nitrifying microorganisms were contaminating forests starting of agricultural areas and if so how. The answer was given to me in the late 1980s as part of research on forest decline. One of my collaborators, Etienne Dambrine, sought to discover the relationship that might exist between decline and the early occupation of the current forest plots. This required consulting the ancient land registers, but those of the Alsatian Vosges were written in Gothic German. Fortunately a German student, Waltraut Körner, one of the few who still know this writing, became interested in the problem and came to decipher the old records. In most cases, stands that had been spared by the decline (characterized the loss of leaves or needles, and yellowing of those who remained) were located on land parcels formerly used for agriculture, either as cropland, either as a path to the cattle. Furthermore soils of these plots were the site of active nitrification, unlike areas where there were no signs of human occupation. This was later confirmed by laboratory incubations (Jussy, 2002). So I had finally the explanation of Henry's assertion in his book turn of the century. The old agricultural plots were afforested with spruce during the second half of the nineteenth century and, as usual at the time, at planting densities of about 10,000 seedlings per hectare (I recall on this occasion that the forest of Compiegne, near Paris, very excessively exploited during the Revolution and Empire, 1920-1930 was the object of active oak reforestation and forest administration required reforestation contractors, upon receipt of the work, the existence of 50,000 live oak saplings per hectare!). Henry, who in 1905 published the results of his research, had probably collected soil samples on which he worked five to ten years earlier and, most likely, it was impossible to take samples in spruce plantations that had at the time 20 or 30 years and included 10,000 stems / ha. Therefore its results corresponded to plots that had always been in the past forest stands of beech and fir and in which, as Etienne Dambrine today, he did not find any nitrates. Etienne Dambrine did not stop here. At a meeting with a historian around Nancy, he found, in communal forests today in the form of coppice with standards of sessile oak and white beech, on limestone outcrops of the Jurassic, the remains of walls of huts, enclosures attesting that these forests were once spaces occupied by peasants. It probably dates back to the early centuries of the Christian era, when the Gallic villagers were expelled by the Romans who reserved the best land, those of the plain of the Woëvre on Callovian or Oxfordian clays, to the legionaries released after their years of service. Taking advantage then of the development of Lidar, a device that can be embarked on an aircraft and can reproduce very precisely the relief of the ground even under tree cover, he came to the conclusion that a very large part of the forest of Haye, near Nancy, had also been heavily used by farmers. This ancient occupation is confirmed by soil analyzes showing that the lands of these areas where you can now find remnants of occupation have lower C / N ratios are and richer in phosphorus than where the forest always existed. Similar findings in the Massif Central where many former pastures were afforested with spruce or Douglas fir or reclaimed spontaneously by birch or Scots pine (Prévosto, 2004) pending the return of beech and fir. Similarly, in Tronçais forest, in central France, several sites of Roman occupation were detected. The vegetation surveys carried out at increasing distances from the former agricultural buildings have shown that neutrophils or demanding nitrogen species were more and more frequent as we approached them. 11
FORESTRY POLICY SILVICULTURE AND CINEGETICS REVIEW XVII/30/2012 This requires that we recognize today that our forests have been formerly 70 or 75% occupied by farmers. We have now in metropolitan France 16 million hectares of forests, while at the end of the First Empire, the woodlands were reduced to 7 or 8 million hectares, as a result of land clearing that occurred during the Revolution, after the departure abroad of nobles loyal to the monarchy and sale as national property of the church lands. 8 million hectares of forests today are former agricultural land and half of the rest has been in the 4th or 5th century. In Guyana it is the research undertaken by INRAP (National Institute for Preventive Archaeological Research), which helped find many signs of human presence in the forest called virgin (Dambrine et Jérémie, 2010). These are very special soils, black and containing numerous fragments of pottery. These are the terra firme found mainly on river banks. They clearly confirm the first descriptions, by Francisco de Orellana who went down the Amazon in the mid sixteenth century, of large villages extending over several kilometers, but that disappeared quickly, villagers being driven out by the Spanish or Portuguese conquerors or decimated by epidemics brought by Europeans. But there are many more convincing facts. We identified over 1,800 sites within the Guyanese forest where human presence is attested by the former presence of post holes, fragments of pottery, fragments of rock, and remains of workshops of shaping tools or of game cutting. More spectacular still, barred spurs, hills or promontories around which were dug deep trenches several meters wide, defensive sites, therefore at the center of which must have existed permanently occupied villages. This leads gradually to the idea of a forest heavily inhabited by Native Americans, permanently at least in some cases. This occupation may have played a role in the distribution of tree species, some more demanding or more light-demanding coming to reoccupy plots cleared for agriculture. We must therefore conclude that, in regions where we just mentioned, forests at all times untouched by human activity are rare. The human occupation has left traces still identifiable on soil properties and composition of the herbaceous flora, probably also on the distribution of shrubs and trees. It is likely that the same applies in many areas where such signs are just waiting for the discoverers. Bibliography Dambrine E., Dupouey J.L., 2006: La mémoire des forêts. ONF, Rendez-vous techniques, n° 11, 45-50. Dambrine E. Dupouey J.L., Laut L., Humbert L., Thinon M., Beaufils T., Richard H., 2007: Present forest biodiversity patterns in France related to former roman agriculture. Ecology, 88 (6), 1430-1439. Dambrine E., Jérémie S., 2010: Groupe couac. – Une forêt vierge par nature La fin d’un mythe. In : La forêt de Guyane française. M. Bonneau, l’Harmattan, Paris, 331 p. Jussy J.H., Körner W., Dambrine E., Dupouey J.L., 2002: Benoît M. – Influence of former` agricultural land use on net nitrate production in forest soils. Euroean Journal of Soil Science, 53, 367-374. Prévosto B., Dambrine E., Moarès C., Curt T., 2004: Effects of volcanic ash chemistry and former agricultural use on the soil and vegetation of naturally regenerated woodlands. Catena, 56, 239-261. Abstract. Recent work in metropolitan France and in French Guiana shows that most of the forests were previously agricultural croplands or pastures. In the book of 1905, ‘Forest Soils’ of the pedologist Henry he states that ammonium nitrification was always zero in the forest. This statement would contradict the active nitrification found in the majority of research conducted in soils in the Vosges or the Massif Central. The answer to this problem was found in late 1980 when Etienne Dambrine discovered that stands unaffected by the drying (loss of their leaves or needles or yellowing) were located on plots of agricultural land previously used for crops or grazing animals. Moreover soils of these plots were the site of an active nitrification unlike areas where they found traces of human occupation. Subsequently, this was confirmed by laboratory incubation (Jassy, 2002). So Henry, a graduate of the Forest School of Nancy, used perfectly accurate methods to characterize the nitrates, but collected soil samples from stands of beech and fir and not spruce plantations installed on old agricultural plots in the second half of the nineteenth century with 10,000 stems per hectare, which at that time were 20-30 years old. In these forests of beech and fir Henry (1905) as well as Dambriene Etienne (1980) found no nitrates. The same author, Etienne Dambriene using a Lidar device, loaded on a plane concluded that a large part of the grove of oak and hornbeam from Haye has been used extensively in the historical past by farmers. Soil analysis reveals a lower C / N ratio and is richer in phosphorus, the forests with agricultural use traces than in forests that have always existed. 12
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