Over the course of industrialization in the 20th century, vast emissions of air pollutants have occurred. The exhaust gasses contain sulfur and nitrogen oxides, which are converted to sulfuric acid and nitric acid in the atmosphere. This causes acid rain to enter aquatic and terrestrial ecosystems, the most serious consequence of which is large-scale forest dieback across Europe and North America. However, through various political measures, the exhaust gasses have been reduced and, thus, acid rain and forest dieback were stopped. Nevertheless, the lingering effects of this pollution are still present today and are reflected in hydrochemistry. More recently, fluctuating precipitation regimes are causing additional stress to ecosystems in Central Europe. Climatic extremes are becoming more pronounced with climate change. Substantial differences between drought years and years with regular precipitation are directly altering the discharge of springs. Now, two overlapping and interacting syndromes of environmental pressures can be studied in these small catchments at a landscape scale: (1) acidification and (2) climate change. In this long-term study, the waters of 102 forest springs, located in two neighboring forest landscapes in north-eastern Bavaria, Germany (Frankenwald and Fichtelgebirge), were investigated over 24 years (1996 to 2020). By linking changes in pH values with changes in precipitation and spring discharge, we found that pH increases with decreasing discharge and decreasing precipitation. This effect was strongest in the Frankenwald compared to the Fichtelgebirge. We hypothesize that this temporal pattern reflects the longer residence time and, in consequence, the increased buffering of acidic interflow in small catchments during periods of drought. However, this should not be misinterpreted as rapid recovery from acidification because this effect fades in times of enhanced precipitation. We recommend that fluctuations in weather regimes be considered when investigating biogeochemical patterns throughout forest landscapes.

Paleoclimatic changes during the late Cenozoic led to substantial losses of tree diversity in Western and Central Europe. A modern synthesis linking which taxa were lost, the timing of these losses, and their implications for the adaptation of the region’s forest ecosystems to ongoing climate change is needed. Here, we compile a dataset of fossil occurrences of tree genera from Western and Central Europe to analyze tree diversity changes during the Cenozoic (66 Ma – present). We find that tree genus richness declined 75% after its peak in the Miocene (23 – 5.3 Ma), with most losses already occurring during the Plio-Pleistocene transition (ca. 2 – 3 Ma). We then use genus-level niche models to explore how these changes unfolded within climate space. Our results show how the current regional tree flora was progressively filtered towards the colder and drier margins of climate space. This coincided with the losses of most heat-tolerant lineages, including many temperate genera that could have profited under modern climate warming (e.g., Castanea , Juglans, Aesculus ). We foresee several ways in which our analyses of paleoecological data can inform forest management to increase regional tree diversity and enhance forest resilience under climate change.

Paleoclimatic changes during the late Cenozoic led to substantial losses of tree diversity in Western and Central Europe. A complete overview of what taxa were lost, the timing of these losses, and their implications for the adaptation of the region’s forest ecosystems to ongoing climate change is needed. Here, we compiled a dataset of fossil occurrences of tree genera from Western and Central Europe to analyze tree diversity changes during the Cenozoic (66 Ma – present). We found that tree genus richness declined 75% after its peak in the Miocene (23 – 5.3 Ma), with most losses already occurring during the Plio-Pleistocene transition (ca. 2 – 3 Ma). We then used genus-level niche models to explore how these changes unfolded within climate space. Our results show how the current regional tree flora was progressively filtered towards the colder and drier margins of climate space. This coincided with the losses of most heat-tolerant lineages, including many temperate genera that could have profited under modern climate warming (e.g., Castanea, Juglans, Aesculus). We foresee several ways in which our analyses of paleoecological data can inform forest management to increase regional tree diversity and enhance forest resilience under climate change.

On oceanic islands, repeated volcanic eruptions create mosaics in which the same ecosystems occur on substrates of different ages. Long-term substrate development may therefore cause differences in the diversity, composition, and structure of plant communities, even at comparable successional stages. There are few settings in nature where such long-term ecosystem developmental effects can be observed, but La Palma (Canary Islands, Spain) provides one such setting. We used substrate age to investigate how long-term substrate development shapes plant diversity and structure in two forest ecosystems on La Palma, Canary pine forest and Fayal-Brezal. We focus on timescales of substrate development (> 10,000 years) beyond those typical of successional processes (< 100 years). We used 102 vegetation plots to characterize α- and β-diversity of plant communities and airborne laser scanning (ALS) data to quantify vertical forest structure. For each forest type, we contrasted the volcanically active southern part of the island (< 150 kya; last eruption 2021) with the older, volcanically dormant northern part of the island (last eruption > 560 kya). We found significant differences between substrate ages in Fayal-Brezal species richness, endemism, community composition, and vertical structure. In contrast, Canary pine forest showed no significant differences in plant diversity or community composition between substrate ages, although vertical forest structure differed significantly in relation to climate and elevation. These findings suggest that the developmental maturity of an ecosystem, approximated by substrate age, influences patterns of plant diversity and forest structure, but also that these effects are ecosystem specific. Ecosystem development may represent an additional dimension of conservation value, especially where older ecosystems support greater endemism, distinct plant communities, or characteristic forest structure. We encourage using oceanic islands as “natural laboratories” to test the generality of these effects and to investigate the ecological and evolutionary processes associated with long-term development of ecosystems.