Western-Carpathian mountain spruce woodlands at their southern margin: natural or anthropogenic origin?

Origin and dynamics of spruce woodlands in central Europe is an important topic due to the current disturbances triggered by bark beetle outbreaks and extreme climatic events. We focused on the Late Holocene development of spruce-dominated woodlands at their southern margin in the Western Carpathians. We analysed eight peat profiles along an altitudinal gradient of 730&1358 m a.s.l. and evaluated the pollen spectra separately for the period before and after the start of intense medieval or post-medieval human intervention in the landscape. We focused on the relative proportions of spruce, beech, fir and noble hardwood trees. Spatial variation in the proportions of beech and spruce exceeded the temporal variation, contrary to fir that declined generally. Proportion of spruce significantly increased over time but the effect differed among sites. Proportion of beech was highest at 800&1000 m a.s.l., while that of spruce increased linearly with annual precipitation rather than altitude and reached the highest values on windward slopes and in wet valleys. Different dominant trees at the two highest altitude sites indicate that altitudinal gradient was less important in the area studied. Although foresters consider spruce woodland on the highest summits as naturally monodominant, we found an apparent admixture of fir, together with a small admixture of beech, in the period before human intervention. An exact reconstruction of the proportions of individual climax trees in past vegetation is, however, not yet possible. Based on macrofossils, spruce unlike beech, has occurred directly on peatlands. Local occurrence of spruce might increase its proportion in a pollen spectrum. Indeed, after anthropogenic deforestation, its proportion decreased. It increased again as late as the establishment of spruce monocultures either by natural succession on abandoned pastures or by forestry. In addition to the effect of local spruce occurrence, modern pollen spectra further demonstrate an over-representation of spruce relative to beech and fir pollen even in a mixed woodland on the highest summit site. We conclude that spruce is a major natural component of mountain woodlands even at its southern margin. Contrary to previous expectation, we demonstrate that the proportion of spruce was not associated with altitude but with mesoclimate and soil humidity. The natural spruce woodlands were mixed or existed as mosaics at all altitudes and the monodominant character of spruce woodlands in the area of summits is not natural.