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Climate change alters forest development pathways, with consequences for ecosystem services and biodiversity. As the rate of warming increases, ecosystem change is expected to accelerate. However, ecosystem dynamics can have many causes unrelated to climate (for example, disturbance and stand development legacies). The compound effects of multiple drivers remain largely unclear. Here, we assessed forest dynamics over 28 years at Berchtesgaden National Park (BGNP), Germany, quantifying the spatiotemporal patterns and unraveling the drivers of forest change. We analyzed high-density forest inventory data, consisting of three consecutive censuses of 3759 permanent sample plots (132,866 tree records in total). We used semi-variograms to analyze spatial patterns of change, and boosted regression trees to quantify the effect of 30 covariates on changes in nine indicators of forest structure and composition. Over the 28 years investigated, the forests of BGNP were becoming denser, structurally more complex, and more species rich. Changes in forest structure were more pronounced and spatially correlated on the landscape than changes in tree species composition. Change rates of all indicators increased over time, signifying an acceleration of forest dynamics since the 1980s. Legacies and climate were the most important drivers of change, but had diverging impacts. Although forest change accelerated with increasing temperature, high legacy levels typical for late development stages dampened it. We here provide evidence for accelerating forest dynamics in mountain forests of the Alps, with potentially far-reaching consequences for biodiversity and ecosystem processes. We highlight that unmanaged forest development toward old-growth conditions could counteract climate-mediated acceleration of forest change. [ABSTRACT FROM AUTHOR]

[Display omitted] • Climate change triggers shrub encroachment into alpine grasslands and snowbeds. • Back from the future aims restore the encroached vegetation through shrub removal. • A multicriteria research protocol is proposed to assess the experiment feasibility. • The data obtained assessed the full comparability of control and manipulation zones. • The protocol allows assess the experiment feasibility and its long-term monitoring. Climate change triggers changes of vegetation floristic composition, physiognomy and even the onset of new successional pathways, requiring adequate, robust and replicable methodological approaches to properly track these changes. In tundra ecosystems woody plants are encroaching into grasslands and snowbeds, inducing their gradual regression. "Back from the Future" is a pilot project performing selective shrub removal from grasslands and snowbeds in the Italian Central Alps to contrast climate-driven shrub encroachment and promote the recovery and active conservation of vegetation communities. Here we propose a multi-criteria research protocol providing a quantitative tool for: a) the set-up of the manipulation experiment; b) the assessment of the full comparability of manipulation and control areas; c) the long-term monitoring of the efficiency of the manipulation experiment. The experiment was carried out in three study sites (Braulio, Cedec, Sforzellina) across an elevation gradient from the subalpine to the nival belts in the Italian Central Alps. At each study site we identified a control and a manipulation zone to assess the efficiency of the manipulation experiment compared to the natural ecosystem dynamics. The multi-criteria research protocol integrates different sampling approaches: mapping and morphological characterization of trees and shrubs; phytosociological survey of permanent plots; grid-point intercept survey of permanent plots; line-intercept survey along transects; allometric shrub measurements along transects. Our data show that this protocol is applicable to different vegetation types, across different elevation belts, and is suitable to match different targets and/or bioindicators of change. Indeed, the limitations of each selected method when individually applied can be overcome by their combination. Our data demonstrate the full comparability of the control and manipulation zone at each of the three study sites in terms of species richness, floristic composition, species coverage, shrub characteristics and volume. Our results supported the feasibility of this protocol as tool for the set-up of the experiment, to assess the full comparability of control and manipulation zones, and perform a detailed monitoring of the effects and the feasibility of the restoration action and the success and efficiency of this pilot project. The protocol elaborated in the frame of this pilot project could be exported beyond the local context and applied to similar mountain regions, especially in the European Alps, for the planning, set up and monitoring of good land management practices aiming to climate change mitigation. [ABSTRACT FROM AUTHOR]