Long-Term Responses of Mediterranean Mountain Forests to Climate Change, Fire and Human Activities in the Northern Apennines (Italy)

Abstract

Fagus sylvatica (beech) dominates the montane forests of the Apennines and builds old-growth high-conservation value stands. However, recent severe drought-induced diebacks raise concern on the future persistence of these forests and of Southern European mesophilous woodlands overall, growing at their dry edge. To explore the history of Apennine beech-dominated forests, we draw on the multiproxy paleoecological record from Lago Verdarolo, which includes a robust vegetation-independent temperature reconstruction. Numerical techniques are used to investigate the drivers of long-term Mediterranean mountain forest dynamics. Specifically, we focus on disentangling the ecological factors that caused the shift from high-diversity mixed forests to beech-dominated stands and on assessing the occurrence of legacy effects on present-day forests. Abrupt climate change largely drove vegetation dynamics during the Late Glacial and Early Holocene. Species-rich mixed Abies alba (silver fir) forests dominated about 10,500—5500 years ago, under rather dry and warmer-than-today conditions (+ 1—2 °C) and limited fire occurrence. Cooler and moister summers and increasing fire activity caused declines in several fire-sensitive temperate deciduous trees (for example, Ulmus, Tilia, Fraxinus) and favored the establishment of fir-beech forests around 5500 years ago. Further enhancement of fire activity and farming around 2000 years ago led to local Abies alba extinction and forest impoverishment. We conclude that the currently widespread monospecific Apennine beech forests are the result of multi-millennial land-use intensification superimposed on Late Holocene cooling and moistening. Given their higher drought-tolerance compared to beech stands, reviving ancient species-rich mixed fir forests represents a feasible and ‘tested’ possibility to adapt forests to climate change.

Legacies of past human activities on one of the largest old-growth forests in the south-east European mountains

“…7). Analogous expansions of beech at the expense of fir are well documented in midlate Holocene pollen records from central-southern Europe, and evidence suggests that despite the two species 16 currently sharing large parts of the ecological niche (Houston Durrant et al 2016;Mauri et al 2016), beech became more competitive after the decline of Abies alba and with the onset of cooler and moister summers and human fire disturbance (Vescovi et al 2010;Morales-Molino et al 2020). While it is difficult to disentangle the effects of climate and land-use, it seems likely that land-use and fire occurrence probably played an important role in driving the vegetation shift.…”

“…7) rather supports the hypothesis that the area of fir and spruce-dominated old-growth forest was reduced during the Middle Ages. In Central and in southern European mountains fir declined several millennia earlier (Büntgen et al 2014;Morales-Molino et al 2020) than at Biogradska Gora, and it is plausible to hypothesise that fir declined earlier in more accessible mountain areas. The higher cost of access may have prevented human activities in the old-growth forest, and land-use activities were probably limited to the outer part of the forest, as observed at Biogradska Gora (Černjavski 1937) and as is often the case for protected ecosystems (Hansen and DeFries 2007).…”

“…Thus, the factors leading to their fragmentation and the extent to which the current landscape retains legacies of past land-uses and natural components (Vale 2002;Whitlock et al 2018) are largely unknown. For instance, in the montane zone of the Apennines, monospecific beech forests established in relatively recent times following the decline of Abies alba and other mesophilous deciduous trees due to enhanced fire activity and multi-millennial land-use intensification superimposed on late-Holocene cooling and moistening (Morales-Molino et al 2020).…”

Modern pollen – vegetation – plant diversity relationships across large environmental gradients in northern Greece

“…Palaeoecology may provide such long-term perspectives on the dynamics of vegetation and plant diversity, enabling us to reconstruct changes in the past distribution of species and communities (e.g. Giesecke et al, 2017; Herring et al, 2018; Morales-Molino et al, 2020a). Moreover, palaeoecology allows assessing the roles of the different drivers of vegetation change, such as climate change or human activities (e.g.…”

“…Moreover, palaeoecology allows assessing the roles of the different drivers of vegetation change, such as climate change or human activities (e.g. Henne et al, 2013; Morales-Molino et al, 2020a). In this context, a question that might be addressed by palaeoecology would be the origin of current diversity: is it natural or has it been impacted by land use (e.g.…”