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European beech (Fagus sylvatica L.) can regenerate successfully from seeds after mixed-severity fires with mid-to-long fire return intervals (>60 years). However, if fire return interval is lower than the age of sexual maturity, post-fire seeding will be limited, leaving vegetative resprouting as the only viable option for recovery. This means that the forecasted increase in fire frequency driven by climate change may erode beech forest resilience to fire. Here, we surveyed tree regeneration in a European beech forest affected by two consecutive fires, in 2003 and 2017, and applied experimental clipping of tree saplings to address the following questions: (1) What is the fire resistance and post-fire recovery via resprouting of tree saplings? (2) Which factors drive post-fire resprouting of beech saplings? (3) Does post-fire clipping of tree saplings increase the probability of survival and resprouting vigor? We monitored 2195 beech saplings and 953 saplings of other tree species during three consecutive years, from 2018 to 2020. Almost all beech saplings were top-killed by fire, and two-thirds of them died completely. However, 3 years after the second fire, 30 per cent of beech saplings survived by resprouting from the base. Post-fire resprouting was less likely in small-diameter saplings and in those more injured by fire. Overall, the second fire did not cause a major decline of beech regeneration and consequently did not alter the dominant species composition of post-fire recovery. Given the low specific resistance to fire, post-fire resprouting of saplings is therefore a key component of beech resilience to short-interval fires. The effects of clipping on post-fire survival and resprouting vigor were very limited, suggesting the unsuitability of actively clearing burned beech regeneration as a post-fire management prescription. In conclusion, basal resprouting from beech saplings after fire-induced top-kill led to a higher-than-expected resilience of beech to short-interval fires (i.e. circa 15 years). [ABSTRACT FROM AUTHOR]

We present the first high-resolution Holocene pollen, plant-macrofossil, and charcoal records from the upper-montane zone in the central Dinaric Alps. Drawing on these new records from well-dated lacustrine sediments of Zminje Jezero (ca. 1500 m a.s.l.; Montenegro) and on independent chironomid-inferred summer temperatures, we explore long-term ecosystem responses to variations in climate, fire disturbances and land use, as well as legacy effects of past environmental changes. A mixed spruce-fir forest established in the upper-montane zone around 9500 cal BP, and Fagus sylvatica became co-dominant with the two conifers after 5000 cal BP. Prehistoric land-use pressure was overall remarkably low, but increased since 2000 cal BP and was highest after the Middle Ages. We found a significant positive relationship between biomass burning and summer temperature, indicating that fires were mostly climate driven. Picea abies was insensitive to summer temperature, biomass burning and human impact, which supports the view that spruce forests may not be significantly impacted by fire. In contrast, Abies alba and other disturbance-sensitive trees (Tilia, Ulmus, Fraxinus excelsior -type) show significant negative responses to land-use pressure and positive responses to summer temperature. This supports the notion that these species may be well-adapted to warmer-than present summer temperatures and that their populations declined in recent millennia due to land-use activities. Conversely, F. sylvatica was sensitive to summer temperatures but was promoted by low biomass burning, indicating that its expansion in the spruce-fir dominated forest was enhanced by the onset of cooler and possibly also moister climatic conditions as well as by fire disturbances. [ABSTRACT FROM AUTHOR]

• Patterns of mixing effects on pine/beech growth-climate relationships were analyzed across Europe. • Tree growth-climate relationships were driven by the regional climate conditions. • Differences in climate-growth relationships between pure and mixed beech stands were evidenced in the driest climates. • On average, mixing had no significant effect on resistance to drought events. • Growth reduction during drought events was lower in mixed compared to pure pine stands in sites with higher water balance in autumn. Increasing species diversity is considered a promising strategy to mitigate the negative impacts of global change on forests. However, the interactions between regional climate conditions and species-mixing effects on climate-growth relationships and drought resistance remain poorly documented. In this study, we investigated the patterns of species-mixing effects over a large gradient of environmental conditions throughout Europe for European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.), two species with contrasted ecological traits. We hypothesized that across large geographical scales, the difference of climate-growth relationships and drought resistance between pure and mixed stands would be dependent on regional climate. We used tree ring chronologies derived from 1143 beech and 1164 pine trees sampled in 30 study sites, each composed of one mixed stand of beech and pine and of the two corresponding pure stands located in similar site conditions. For each site and stand, we used Bootstrapped Correlation Coefficients (BCCs) on standardized chronologies and growth reduction during drought years on raw chronologies to analyze the difference in climate-tree growth relationships and resistance to drought between pure and mixed stands. We found consistent large-scale spatial patterns of climate-growth relationships. Those patterns were similar for both species. With the exception of the driest climates where pure and mixed beech stands tended to display differences in growth correlation with the main climatic drivers, the mixing effects on the BCCs were highly variable, resulting in the lack of a coherent response to mixing. No consistent species-mixing effect on drought resistance was found within and across climate zones. On average, mixing had no significant effect on drought resistance for neither species, yet it increased pine resistance in sites with higher climatic water balance in autumn. Also, beech and pine most often differed in the timing of their drought response within similar sites, irrespective of the regional climate, which might increase the temporal stability of growth in mixed compared to pure stands. Our results showed that the impact of species mixing on tree response to climate did not strongly differ between groups of sites with distinct climate characteristics and climate-growth relationships, indicating the interacting influences of species identity, stand characteristics, drought events characteristics as well as local site conditions. [ABSTRACT FROM AUTHOR]