ID69: The future of mountain forest regeneration

Abstract ID 226 | Date: 2022-09-14 13:55 – 14:05 | Type: Oral Presentation | Place: THEOLOGIE – SRVI |

Maroschek, Michael (1,2); Seidl, Rupert (1,2); Poschlod, Benjamin (1,2); Senf, Cornelius (2)

Disturbances are key drivers of forest ecosystem dynamics. Under natural conditions, abiotic disturbance agents like wind, fire and avalanches, as well as biotic agents like insects, are the main causes for stand-replacing disturbances in temperate mountain forests. However, for large parts of temperate forests worldwide, the patterns of natural disturbance regimes are unknown, due to direct and indirect human influence over centuries to millennia and/or a lack of (spatially explicit) data in areas less impacted by humans – such as mountain regions. We aim to close this gap for the European Alps by quantifying the natural forest disturbance regimes of Alpine mountain forests, focusing on the distribution of patch sizes (i.e., the size of canopy gaps created by stand-replacing disturbances).

We make use of the Alparc network to identify 12 strictly protected forest landscapes (IUCN-category I or II and forest cover > 4 km²) distributed across the entire European Alps (Austria, France, Germany, Italy, Lichtenstein, Slovenia and Switzerland), with good representation of the prevailing ecological and climatic gradients. For each landscape, we derive the size of disturbance patches using satellite-based disturbance maps covering the timespan 1986 to 2020 at annual resolution. The maps depict all stand replacing disturbance patches at a spatial grain of 30 x 30 m. Focusing on the no-intervention zones of the protected areas allows us to exclude direct human impact on disturbance regimes, and thus to study the disturbance patch size distributions under natural conditions. We apply a Bayesian approach to derive the underlying distribution functions for the patch sizes of a) all observed patches and b) annual extreme events.

We show that, comparing a set of distribution functions, patch sizes in the Alps (median 0.36 ha, 10.6% > 1 ha) follow a Fréchet distribution, capable to characterize positive skewed data with heavy tails. For all observed patches, explicitly modelling mean and dispersion parameters improved model performance, whereas the inclusion of environment parameters did not. Contrastingly, environmental parameters did influence extreme events significantly. This indicates high stochasticity in realized overall patch sizes, and the importance of environmental drivers for the occurrence of extreme events.

Disturbance regimes and resulting patch sizes shape the physical template for future regeneration dynamics. Our results allow the mapping of return intervals of extreme events across the European Alps. Comparing natural and observed patch size distributions further allows for informing about naturalness of disturbance regimes outside protected areas and reveals chances and challenges for nature conservation.

Abstract ID 295 | Date: 2022-09-14 14:05 – 14:15 | Type: Oral Presentation | Place: THEOLOGIE – SRVI |

Cerioni, Matteo (1); Bače, Radek (2); Bāders, Endijs (3); Bončina, Andrej (1); Brabec, Marek (4); Brůna, Josef (2); Chećko, Ewa (5); Cordonnier, Thomas (6); Diaci, Jurij (1); Dobrowolska, Dorota (7); Dountchev, Alexander (20); Engelhart, Jeroen (8); Fidej, Gal (1); Fuhr, Marc (6); Garbarino, Matteo (9); Jansons, Āris (3); Keren, Srđan (10); Kitenberga, Māra (3); Klopčič, Matija (1); De Koning, Johannes H.c. (11); Konôpka, Bohdan (12); Kopecký, Martin (2); Köster, Kajar (13); Kucbel, Stanislav (14); Lacombe, Eric (15); Laurent, Lisa (15); Leyman, Anja (16); Lingua, Emanuele (17); Macek, Martin (2); Maciejewski, Zbigniew (18); Malandra, Francesco (19); Marzano, Raffaella (9); Metslaid, Marek (8); Panayotov, Momchil (20); Pawlak, Bogdan (7); Pittner, Ján (14); Šebeň, Vladimír (12); Socha, Jarosław (10); Svoboda, Miroslav (2); Szwagrzyk, Jerzy (21); Tsvetanov, Nickolay (20); Urbinati, Carlo (19); Vallet, Patrick (6); Van De Kerckhove, Peter (16); Vandekerkhove, Kris (16); Vencurik, Jaroslav (14); Vitali, Alessandro (19); Vodde, Floortje (8); Wild, Jan (2); Nagel, Thomas A. (1)

Large and severe disturbances may erode the resilience of temperate forest ecosystems and alter their recovery dynamics, especially under global change. Regeneration failures after stand-replacing disturbances have been documented in North America, particularly when juxtaposed with unfavourable environmental conditions (i.e. extreme droughts following the disturbances, in dry topographic positions). We examine if there are similar tree regeneration failures following large and severe disturbances in temperate forests of Europe. We investigated mid to long-term recovery after disturbances causing canopy mortality above 70 % of basal area in patches larger than 1 ha. Across a network of ≈100 sites, including various forest types and management practices, and 26 disturbance events, including wind, fire, and bark beetle, we studied regeneration density, structure, and composition, which are key indicators of forest resilience. Density of regenerating individuals was weighted according to their respective height, aggregated at plot-level, and standardized based on plot size and time since disturbance, in order to be comparable across sites. Ecological drivers of regeneration density, including disturbance characteristics (agent, size), topographic (elevation, aspect, topographic wetness), climatic (growing degree days, aridity index) and management factors (salvage logging, planting), were formally analysed using mixed models, while ungulate browsing and biotic interactions (e.g. vegetation competition) were qualitatively assessed. Separate analyses were also performed for three successional groups of tree species (pioneer, light-demanding, and shade-tolerant). We quantitatively evaluated physiognomic recovery by comparing regeneration densities with country-specific restocking targets used in forest practice, and compositional recovery by comparison with pre-disturbance stand composition or mixture management goals. Preliminary results on regeneration patterns and drivers will be presented in the context of forest resilience to large and severe disturbances.

Abstract ID 647 | Date: 2022-09-14 14:15 – 14:25 | Type: Oral Presentation | Place: THEOLOGIE – SRVI |

Stritih, Ana (1); Seidl, Rupert (1,2); Senf, Cornelius (1)

The resilience of mountain forests is a critical concern for forest management in the Alps, since disturbances can jeopardize forests’ capacity to provide essential ecosystem services, such as protection from natural hazards. In recent years, significant progress has been made in observing changes in canopy cover at the large scale, including forest disturbances and recovery, from optical satellites. However, optical satellites have a limited capacity to detect changes in forests’ three-dimensional structure, including properties such as stand height, leaf area, biomass, and vertical heterogeneity. These structural characteristics play an important role in determining forests’ resilience and their capacity to provide ecosystem services. So far, assessments of forest structure have mostly relied on airborne LiDAR data, which is not available consistently at large scales, limiting the potential for Alpine-scale analyses. In this study, we use data from GEDI, NASA’s recently launched spaceborne LiDAR mission, to assess the structural characteristics of Alpine forests. We combine plot-level GEDI data with a Landsat-based disturbance map, which allows for a space-for-time analysis of forest recovery after disturbances. Across the Alps, undisturbed forests show a similar distribution of forest structure, with two main basins of attraction in open and closed forests. Disturbances cause a shift towards open forest structures, with the lowest point of canopy cover and stand height often occurring around 10 years after a disturbance. This is followed by recovery, with consistent recovery patterns across different forest types. After 30 years, most disturbed forests regain much of their protective function, although they still show differences in structure compared to undisturbed forests. We discuss how such large-scale analyses can contribute to our understanding of forest resilience, as well as the challenges and limitations of using spaceborne LiDAR in complex mountain terrain.

Abstract ID 771 | Date: 2022-09-14 14:25 – 14:35 | Type: Oral Presentation | Place: THEOLOGIE – SRVI |

Bace, Radek; Svoboda, Miroslav

Long-term monitoring of the development of mountain spruces after large-scale and intensive bark beetle disturbance helps us to clarify the degree of adaptation of these ecosystems to disturbances. Due to the gradual breaking of dead trees, the change in the amount of light in the undergrowth is gradual with the steepest increase was in the third and fourth year after the disturbance. The peak occurred about 10 years after the disturbance. Then the understory light started locally to decline due to recruitment of new trees. Contrary to our expectations, bark beetle disturbances did not change relative proportion of the dominant herbaceous species cover. Rather, there was an increase in the total biomass of herbs. Both spruces and rowans regenerated from individuals that occurred in the undergrowth before disturbance. Only a small proportion of spruce seedling germinated in the year of the disturbance. Both spruce and rowan regeneration have a special adaptation for long-term survival in the shade of undergrowth: adventitious roots formation and root sprouts formation. The mortality of regeneration has remained very low throughout the 15 years of monitoring since disturbance, despite the fact that the numbers of individuals in the clusters are very high (exceeding 50 individuals per 1 m2). High mortality occurred only in one-year and two-year-old seedlings within two years after disturbance. The seed bed plays a minor role in the mortality rate (the most regeneration dies in vegetation and the least on dead wood). Dry years partially increase the probability of mortality in the following year. After 15 years of disturbance, the regeneration structure is heterogeneous both in height and space on several levels (from meters to kilometres). The strongly heterogeneous regeneration pattern mirrors the spatial pattern of the most preferable microhabitats (stumps, dead trees, lying dead wood). The structure of the forest tends to be passed on from generation to generation. Higher regeneration density and smaller diversity in seedling heights occur where there had been a closed canopy forest before. Measurement of the carbon balance in aboveground biomass shows the greatest carbon losses shortly after disturbance, when the fine parts (twigs, bark and foliage) decompose and the activity of wood-decomposing fungi is the fastest. At about 20 years after the disturbance, carbon release slowed and the overall carbon balance turned to higher intake due to rapid growth of regeneration. At the same time carbon stocks have reached about half of pre-disturbance levels.

Abstract ID 529 | Date: 2022-09-14 14:35 – 14:45 | Type: Oral Presentation | Place: THEOLOGIE – SRVI |

Brozova, Natalie (1,2,3); Bottero, Alessandra (1,2); Caduff, Marion (1); Bebi, Peter (1,2)

Natural disturbances are a common part of forest dynamics and may cause structural changes over large areas. They alter the functioning of forest ecosystems and affect the provisioning of ecosystem services, such as protection against natural hazards. We studied forests disturbed by bark beetle and windthrow to assess the advancing in wood decay and tree regeneration, as well as their effect on the protection capacity against snow avalanches in the three decades following disturbance.

Field data on tree regeneration and deadwood were analysed in forests disturbed by windthrow and bark beetle outbreaks. We assessed the potential drivers for the establishment of trees on deadwood and we evaluated the development of the protection capacity over the past thirty years. We used surface roughness as a proxy for protection capacity comprising the coverage of deadwood and tree regeneration. After the bark beetle disturbance, we used remote sensing data to evaluate the changing protective effect of the forest and simulated avalanches in frequent and extreme scenarios at different time steps.

Independently of the disturbance agent, over the course of three decades deadwood decomposed and moved closer to the ground, and trees grew taller and at some locations started to form a dense forest stand. Wood in advanced decay stages became a suitable seedbed for tree regeneration, especially after windthrow, as more decomposed deadwood was found compared to bark beetle-disturbed forests. Thirty years after both types of disturbances, forests showed a more diverse structure, due to secondary tree regeneration on deadwood, and a richer species composition, thanks to the higher share of broadleaves. Disturbed forests maintained sufficient protection capacity, especially in the first years after disturbance, when surface roughness was high. The protection capacity reached its minimum 10-15 years after disturbance.

Based on our analyses, unmanaged disturbed forests have the potential to recover well and are even expected to become more diverse, with higher shares of broadleaves and increased vertical structure thanks to secondary tree regeneration growing on deadwood. Such forests are potentially more resistant and resilient to the future disturbances. The protection capacity is preserved for some time, which in the case of bark beetle is mainly due to long-standing dead trees, while windthrows benefit from high surface roughness created by lying deadwood and root plates. Our results help to prioritise management after natural disturbances and to decide under which conditions the natural post-disturbance development offers sufficient protection against natural hazards.

Abstract ID 280 | Date: 2022-09-14 14:45 – 14:55 | Type: Oral Presentation | Place: THEOLOGIE – SRVI |

Manzanedo, Ruben D.; Visakorpi, Kristiina; Hillerislambers, Janneke

The environmental conditions required for generational replacement, i.e. the regeneration niche, is a key component of species responses to environmental change that remains largely understudied. Species modelling efforts still rely mostly on adult presence or performance to infer population responses to environmental change, and only recently they have started to incorporate information on multiple age classes, including the critically important juvenile phase. If juveniles and adults differ in their fundamental or realized niches, as observational and experimental data seem to suggest, inferences from models based on adult suitability may not accurately reflect future changes in distribution or habitat suitability. However, a systematic and multispecies assessment of ontogenetic niche shifts is not yet available. To adress this question, we compared the regeneration and adult niches among 43 forest species in Switzerland using data from the Swiss National Forest Inventory, to quantify the prevalence of ontogenetic niche shifts among major Swiss tree species, and whether niche shifts would generally take the shape of niche contraction or expansion. We found, niche conservatism to be the dominant pattern among all widespread species, indicating a large niche overlap across ages. Less abundant species had less consistent patterns, although detailed modelling will need to be implemented for them. As expected, regeneration niches were significantly lightly less stable than adult niche between inventories. However both adults and regeneration showed generally high temporal niche stability, supporting direct comparisons between them. Overall, our results suggest that niche stability is the most common pattern in widespread species and that ontogenetic niche contraction (niche of regeneration larger than that of adults) is more likely than niche expansion (adult regeneration larger). These represent a better scenario for tree species adaptatioon to climate change since 1) under ontogenetic niche expansion, adult occurences represent a more conservative niche assumptionand for modelling species distribution, and 2) a buffering of regeneration niche around the adult distribution may facilitate species migration with climate change via pre-established juvenile individuals.

Abstract ID 282 | Date: 2022-09-14 16:00 – 16:10 | Type: Oral Presentation | Place: THEOLOGIE – SRVI |

Gratzer, Georg; Pesendorfer, Mario

Altered disturbance regimes in forests as well as shifting bioclimatic envelops of tree species create unique challenges in terms of tree regeneration in general but particularly in mountain forests. Increased disturbance frequencies and intensities increase the demand for seeds, and changing climate influences supply and viability of tree seeds. Understanding temporal and spatial aspects of tree seed production and dispersal is thus key to sustaining adequate tree cover in future mountain forests. As the number of long-term studies and the availability of global data sets on tree seed production grow, the understanding of proximate factors driving tree seed production has strongly increased. However, to understand the effect of seed production and dispersal on long-term community dynamics and, ultimately, to evaluate the fitness consequences of different masting and dispersal strategies, it is important to link seed production and dispersal with plant establishment. This is particularly important because processes that act at different stages of dispersal, germination and seedling growth can be uncoupled and even have opposing effects. Here, we use fine scaled (a total of 162 seed traps at two one ha permanent sample plots) long-term (15 year) data on tree seed input on the forest floor of an old-growth mountain forest dominated by Fagus sylvatica and, to a lesser degree, Picea abies and Abies alba and link these to the spatial structure of established tree seedlings and saplings. Using geostatistical methods and point process modelling, we modeled 1) the relationship between annual seed crop and spatial heterogeneity of seed rain, 2) the temporal stability of seed rain hotspots and 3) the spatial relation of seed rain and recruitment into the population. Seed production in all three study species was highly variable across study years and space. Interannual variation in seed production in all three species was tightly correlated with spatial variation of seed rain, as seed crops increased, spatial variation of seed rain decreased. High spatial variability of seed rain for Fagus sylvatica was caused by distinct and stationary seed hotspots, seed input positively predicted the spatial structure of seedlings and saplings for this species. The signature of annual variation in seed rain fades with seedling mortality over time in all three focal species. We found that spatial variation in seed rain interacts with subsequent processes to shape the distribution of seedlings and saplings, but in ways that suggest decoupling of the processes between life history stages.

Abstract ID 167 | Date: 2022-09-14 16:10 – 16:20 | Type: Oral Presentation | Place: THEOLOGIE – SRVI |

Champagne, Emilie (1,2,6); Raymond, Patricia (2); Royo, Alejandro A. (3); Speed, James D. M. (4); Tremblay, Jean-Pierre (5,6); Côté, Steeve D. (5)

Climate change is modifying forest dynamics, altering the rate and composition of tree regeneration and, eventually, threatening the sustained supply of ecosystem services. In response, managers are developing climate-adapted strategies, mostly focusing on changes in abiotic conditions. Ungulate populations and their direct and indirect impacts on forest composition and productivity are likely to interact with climate change effects. This raises the issue of whether climate-adapted strategies will be compatible with abundant ungulate populations. Here, we (1) review whether climate-adapted strategies currently consider ungulates and (2) highlight how browsing could affect the success of these strategies, using a systematic mapping protocol and available knowledge of ungulate browsing. We identified 57 references discussing climate-adapted forest management that mentioned ungulates, almost exclusively in boreal and temperate forests. The majority (35/57) of these considered browsing a threat to climate adaptation. Specifically, ungulates activity could prevent the achievement of management goals for desired species composition and increased forest resilience. Our review suggests, for example, that browsing impacts will likely limit the success climate adaptive silviculture including nature-based approaches or assisted migration plantings. Potential interactions between large ungulate populations and climate-adapted forest management are sometimes considered but rarely integrated in adaptation strategies. More empirical and modelling data would be beneficial, especially on the interactive effect of climate variables and browsing on tree regeneration. Without this, the climate-adapted strategies implemented today could result in future regeneration failures and exacerbate the pressure on forests.

Abstract ID 198 | Date: 2022-09-14 16:20 – 16:30 | Type: Oral Presentation | Place: THEOLOGIE – SRVI |

Kupferschmid, Andrea Doris

Local climate and ungulate browsing are two major factors that affect tree regeneration and genetic adaptation in Central European forests. The process of regeneration is generally longer in mountain forests than at lower elevations. This is among other due to the shorter growing season and thus lower height increment. With the climate change, the process could accelerate. However, it is necessary to investigate the separate and joint effects of seed origin (and climate) and ungulate herbivory.

The aim of this study was to analyse the influence of intraspecific genetic variation on the sensitivity and resilience of tree species to stress due to frost and simulated winter browsing and the consequences regarding seedling water-use efficiency.

In a genecological experiment, we investigated quantitative genetic variation within and among 72 – 90 provenances of Abies alba, Picea abies, and Fagus sylvatica. Light and heavy ungulate browsing in spring was simulated, the growth reactions were assessed and for Abies also physiological traits.

For Abies, frost damage and clipping resulted in reduced height growth in the first year after the stress and reduced height for at least two (clipping) to four (frost) vegetation seasons. Sapling biomass and diameter increment decreased after heavy clipping. For Picea and Fagus, the effect of this single simulated browsing event disappeared over time for the growth traits. Reduced growth only persisted for Picea saplings after frost damage.

The ‘reaction type’ after browsing seems to be species specific but independent of seed origin. In contrast, the time lag between simulated browsing and formation of a clear new leader shoot increased for Abies with lower temperatures at the seed source. Differences in sapling resilience to stress enhanced the existing differences among provenances. Lowland provenances with warmer climates grew faster, and in Picea also qualitatively better, and recovered faster (Abies) or more efficiently (Picea) to leader shoot loss. From this side, here seems to be no clear evidence of a tradeoff between adaptation to climate change and resilience to stress.

However, browsing lowered seedling water-use efficiency (decreased δ¹³C) of Abies alba. Therefore, browsing could exacerbate the regeneration problem in mountain forests via two mechansim; loss of height coupled with slow/inefficient response of mountain provenances and increased risk during drought.

Abstract ID 949 | Date: 2022-09-14 16:30 – 16:40 | Type: Oral Presentation | Place: THEOLOGIE – SRVI |

Cacciatori, Cecilia (1); Gazda, Anna (1); Bodziarczyk, Jan (1); Foremnik, Kacper (1); Madalcho, Aklilu (1); Maciejewski, Zbigniew (2); Pielech, Remigiusz (1); Tomski, Andrzej (3); Zięba, Antoni (4); Zwijacz-Kozica, Tomasz (4); Szwagrzyk, Jerzy (1)

The steady growth of deer population recorded in the European forests during the last decades is causing browsing pressure on saplings to become increasingly heavy. The effects of this pressure have been studied mainly in terms of increased mortality of saplings of preferred forage species. However, still little is known about what drives selection of individual saplings within a given tree species, an issue with important implications for population genetics, forest stand structure and forestry management. Even less is known about the impact of browsing on tree architecture and, consequently on tree mechanical stability. In the first phase of a project aiming at highlighting the ecological implications of deer-sapling interaction in habitat undergoing natural disturbance and characterized by intense tree regeneration, we developed an index of browsing intensity, Bi, based on number of browsed shoots and their relative diameters per sapling, and an index of sapling vitality, Vi, based on sapling architectural parameters, and tested the correlation between the two for various tree species. The results of this first phase show no univocal pattern in the relationship between Bi and Vi, which strongly varied among different species, thus confirming that tree species identity remains the most important factor affecting browsing intensity. In the second phase, we analysed the impact of browsing, light intensity and their interaction on three architectural indices: sapling slenderness, crown slenderness and crown asymmetry. The relative importance of browsing and light on these traits was also assessed. Our results show that increasing Bi cause the saplings to become slenderer, their crowns more asymmetric and, in the case of the tall saplings, flatter, while light intensity makes saplings stouter and their crowns slenderer. Meanwhile, browsing significantly modifies the effect of light on sapling architecture, causing all tested architectural indices to decrease along with increasing light intensity. Based on these results and given the observed deer population increase we may expect to observe in the future an increasing, though slight, tendency of trees to develop asymmetric crowns and slenderer stems, which would result in a lower mechanical stability. Since extreme events such as windstorms are also expected to become more frequent and intense, browsing could ultimately expose trees to a higher risk of breakdown, with the consequent opening of forest stands and all the associated changes in understory conditions.

Abstract ID 660 | Date: 2022-09-14 16:40 – 16:50 | Type: Oral Presentation | Place: THEOLOGIE – SRVI |

Ambs, Dominik (1); Schmied, Gerhard (1); Zlatanov, Tzvetan (2); Brang, Peter (3); Kienlein, Sebastian (4); Nikolova, Petia (3)

Mixed mountain forests consisting of Norway spruce (Picea abies (L.) Karst.), European beech (Fagus sylvatica L.) and silver fir (Abies alba Mill.) are among the most productive and stable forest ecosystems in Europe. Their south-eastern geographical distribution range extends to the Western Rhodopes where they have a high economic, recreational and ecological value. During the last two decades, shelterwood cutting has been partially replaced by single-tree and group-selection systems. However, only little is known about the dynamics of the natural regeneration in these stands and its dependency on microsite and management effects.

The objective of this study is to investigate ecological factors that influence the regeneration process in mixed mountain forests in the Bulgarian Rhodopes. We focused on (1) the density of the regeneration and its main drivers and (2) the height growth of each species in dependency of light conditions.

Data on regeneration and microsite conditions were collected in four stands located in the regional forest district of Smoljan. All stands, aged 100-150 years, were similar in climate but differed in management. In randomly selected plots, we assessed stem density of fir, spruce and beech in three height classes, recorded browsing intensity, estimated the ground vegetation cover, and quantified the solar radiation. Annual height increment during the last 3-5 years was also measured.

Across all stands, fir had the highest mean stem density (18’000 N ha^-1), followed by beech (5’000 N ha^-1) and spruce (2’700 N ha^-1). Annual browsing was < 30 % in beech, < 10 % in fir, and negligible in spruce.

Generalized linear mixed models indicated microsite conditions and ground cover to control the development of fir recruitment, whereas light and proximity to canopy gaps were the most relevant factors for spruce and beech. Indirect light promoted height increment more strongly in beech than in fir and spruce regeneration. Potential practical implications to adapt the mixed mountain forests to a warming climate will be discussed.

Abstract ID 570 | Date: 2022-09-14 16:50 – 17:10 | Type: Oral Presentation | Place: THEOLOGIE – SRVI |

Bugmann, Harald

Climate change will impact forest demography, including forest regeneration. To project future changes in vegetation structure in situ as well as e.g. the upward migration of forest trees, dynamic models featuring a good representation of forest demography are needed. However, little is known on the structural complexity of the vegetation models that are in use today, nor on their behavior when benchmarked against empirical data along a broad environmental gradient. This presentation is addressing both aspects.

First, we conducted a meta-analysis of 28 models (from stand to global scales) in terms of the representation of tree demography, and found interesting historical developments since the earliest use of such models 50 years ago: model complexity has increased overall, and depending on the scope of the model the complexity of individual process formulations has increased as well. The goal, however, is not to develop “global everything models”, but models that are targeted towards specific applications. I will show that particularly landscape models and to some extent stand models have a good degree of sophistication of regeneration processes while at the same time also providing a diversity of process representations, which allows for uncertainty assessments.

Second, in the context of the COST Action PROCLIAS we conducted a systematic benchmarking of multiple dynamic vegetation models against measured forest regeneration data from 800+ stands along a wide environmental gradient in Europe. At the time of writing this abstract, it is too early to speculate about results because these will be discussed at a workshop in June 2022 only. The latest results and insights will be shared at the IMC in Innsbruck.

Overall, the conclusion is that dynamic vegetation models need a larger focus on establishment (regeneration) as well as mortality processes, because with growth processes the sophistication is already high but tree demography has not received sufficient attention to date in most models, thus rendering future projections particularly uncertain.

Abstract ID 339 | Date: 2022-09-14 17:10 – 17:20 | Type: Oral Presentation | Place: THEOLOGIE – SRVI |

Schmid, Ueli; Frehner, Monika; Bugmann, Harald

The protection of infrastructure against the impacts of natural hazards is one of the most important ecosystem services in many mountain forests. Forest management can decisively influence their current protective quality and its future development. Due to the management history and the resulting forest dynamics of many mountain forests, regular interventions are often necessary to counteract the tendency of a development towards uniform and dense stands that lack the key element of resilience: sustainable regeneration.

In practical forest management, decisions on when and how to intervene in a protection forest are usually taken on a stand-level, based on an assessment of its current state, the expected development, and the descriptions of minimal and ideal forest states according to the site type and natural hazard. However, it is not known how often interventions need to be scheduled to sustainably warrant the protective function of mountain forests. Thus, to support practical management planning, knowledge about effective long-term management strategies, i.e., the types and timing of interventions, to improve or maintain the protective function is needed.

We developed a new, spatially explicit yet simple forest stand simulation model based on empirical data with a specific focus on regeneration that includes trees as small as 10 cm in height. The model is able to depict the spatial stand structure and detailed management scenarios. This allows us to assess the protective quality of the simulated stands, including the quantity and composition of regeneration. We present the model and its validation, and apply it for deriving management strategies for typical forest types and stand structures of Swiss protection forests that increase and/or maintain the protective function against different natural hazards. We also discuss how these findings can be transferred to decision makers on different levels of forest management and planning.

Abstract ID 684 | Date: 2022-09-14 17:20 – 17:30 | Type: Oral Presentation | Place: THEOLOGIE – SRVI |

Mauri, Achille (1,2); Temperli, Christian (3); Bebi, Peter (1,2); Bottero, Alessandra (1,2)

Risks related to mass movements affect life, infrastructure and settlements in densely populated mountain regions such as the European Alps. Forests and other ecosystems provide a fundamental protective function that can strongly mitigate risks related to multiple hazards such as snow avalanches and rockfall. However, climate change and extreme climatic events, natural disturbances and management interventions may not only affect the immediate protection efficacy of the forest through stand density and stability reductions, but also regeneration dynamics and thus the long-term protection potential of forest ecosystems. The evaluation of forest dynamics under different climate, disturbance and management scenarios is thus vital to support climate-adaptive decision making in forest management.

In this contribution, we present the results of a forest landscape modelling approach (LandClim) used to simulate future forest and regeneration dynamics under a range of climate, forest management and disturbance scenarios until the end of the 21^st century in the region of Davos, Switzerland. The model was initialized with forest structure data from stand maps and high-resolution remote sensing data, current climate, management practices and disturbance regimes. Four pathways of potential forest development were included: two climate/disturbance (moderate and strong change) and two stakeholders informed management scenarios (no adaptation and adaptation to increase resilience). The climate/disturbance scenarios accounted for changes in temperature, precipitation, windthrow and bark beetles, and considered interacting effects between windthrow and beetle disturbances and their effects on forest development and its protection function.

Understanding these processes is key to identifying priority areas for targeted management interventions. Changes in tree species composition are expected particularly under the more severe climate change scenarios with an increasing share of broadleaves also at higher elevations. Although management that reduces growing stock and promotes forest regeneration may support forest resilience, and thus the long-term protective effect against gravitational natural hazards, it may need to be balanced with short-term reductions in protection efficacy.

Our findings might help identify forest communities that are more resilient to climate change and can deliver a stronger protective function against multiple hazards. Thus, our work might inform forest managers, practitioners and decision-makers to ensure the protective role of mountain forests in the long term. The presented forest landscape modelling study is part of an interdisciplinary project that evaluates natural hazard processes, cascading processes and risks for the region of Davos under the effects of extreme events and climate change.

Abstract ID 269 | Date: 2022-09-14 15:15 – 15:17 | Type: Poster Presentation | Place: SOWI – Garden |

Bottero, Alessandra (1,2); Frei, Esther R. (1,2,3); Krumm, Frank (1,2,3); Bebi, Peter (1,2)

Snow avalanches are a common disturbance in mountain forests in the Alps. The catastrophic avalanche winter of 1950/51, the so called “Winter of Terror”, damaged 2100 hectares of protective forests in Switzerland. This dramatic series of events raised questions and discussions about causes and possible measures to prevent such damages in the future.

The high elevation afforestation experiment “Stillberg” was initiated near Davos in the Swiss Alps to investigate methods to replace avalanche-damaged forests at the treeline, supporting the development of ecologically and technically sustainable measures to reduce avalanche risk. In 1975, 92’000 seedlings of Larix decidua, Pinus mugo ssp. uncinata, and Pinus cembra were planted following a gridded planting scheme along an altitudinal gradient at and above the current treeline (2075 to 2230 m a.s.l.). Trees were planted in >4000 square plots, with 25 trees in each plot placed into the original dwarf shrub community at 70 cm planting spacing. The research area also features a climate station and 400 snow stakes for the optical measurement of snow depths.

Here, we focus on the main factors driving tree regeneration, mortality and growth based on measurements and studies conducted over more than forty years of monitoring. All regeneration individuals were visited regularly from 1975 to 1995 to assess growth, health status and mortality, with further assessments in 2005 and 2015. The height of the surviving trees was recorded every 10 years. Additionally, microsite features (e.g. elevation, solar radiation, snowmelt date) were recorded for each plot.

Snowmelt date was the most important environmental factor influencing mortality of all tree species, while growth was strongly correlated with elevation during the first 30 years of the afforestation. Mortality rates were highest during the first 15 years post-establishment. Primary agents of mortality among P. cembra saplings were the pathogenic snow fungi Gremmeniella abietina and Phacidium infestans, which occurred mainly on plots with late spring snowmelt. The relative importance of different environmental variables for tree seedlings and saplings changed during the regeneration phase, and led to a forest dominated by L. decidua with participation of P. mugo and P. cembra.

Today, almost 50 years after the establishment of the Stillberg long-term research area, new questions arise about competition and facilitation processes occurring between trees at and above the treeline, and suitable management strategies to adapt high elevation forests to future climatic and environmental conditions without compromising the multiple ecosystem services they provide.

Abstract ID 712 | Date: 2022-09-14 15:17 – 15:19 | Type: Poster Presentation | Place: SOWI – Garden |

Görlich, Anna Sofia; Delgado Manzanedo, Rubén; Schiendorfer, Katja; Visakorpi, Kristiina; Bieger Altermatt, Annette; Hille Ris Lambers, Janneke

Temperate forests in the Alps are increasingly pressured by ongoing climate change and severe drought events. A trees’ ability to withstand drought and its interactions with other climate change-driven stressors are therefore crucial to understand how forests will respond to environmental change. This is especially important at the seedling stage, where strong environmental filtering on establishment influences species regeneration and thus, the structure of future mountain forest communities. However, the tolerance of seedlings to environmental extremes remains understudied for most tree species. To address this knowledge gap, we explored drought and frost tolerance across 22 widespread Central European tree species present in Swiss forests by growing them in the greenhouse and assessing their tolerance at the seedling stage. We expected that species would vary in their tolerance to these stressors, since summer drought and spring frost are two relevant extreme events affecting seedling survival, but risk varies widely across species ranges. We also expected that adaptation to these stressors might be synergistic (adaptation to one will favour adaptation to the other) or show trade-offs between them, or with other functional traits, which would ultimately affect the process of species regeneration. As expected, drought tolerance differed between species, being generally higher for needle leaved species. However, high inter- and intra-specific variability resulted in non-significant results with respect to leaf type (broadleaves vs. needles). Regardless, high inter-specific variability in tolerance suggests there will be ‘winners’ and ‘losers’ under changing climate, whereas high intra-specific variability may favour rapid adaptation of some species. We also found a positive relationship between drought and frost tolerance, which was stronger for seedlings exposed to heavier frost and for needle leaved species. Our results therefore suggest that synergies between drought and spring frost adaptation may be common across Swiss tree species in early developmental stages. This may allow cold-adapted species to have a head start to adapt to increasing drought events. However, the likelihood of this synergy benefitting specific species will depend on the difference between the current vs. future magnitude of drought and frost stress each population experiences, as well as on potential trade-offs with other traits or stress adaptations. Our results suggest that these seedling traits may play an important role in determining adaptation potential and responses to future climate change. However, further research is needed to explore adaptation trade-offs and synergies in seedlings and their role in mountain forest regeneration under climate change.

Abstract ID 901 | Date: 2022-09-14 15:19 – 15:21 | Type: Poster Presentation | Place: SOWI – Garden |

Reyes-Martín, Marino Pedro (1); Juan-Ovejero, Raquel (1); B. Leverkus, Alexandro (1); Molinas-González, Carlos R. (2); Castro, Jorge (1)

Dead wood remaining after wildfires represents a biological legacy that remains during forest regeneration, and its decay is both cause and consequence of a large set of ecological processes. As dead wood and coarse woody debris represent an important nutrient pool in forests, different degrees of forest management (e.g., clear cutting, thinning, etc.) can affect the ecosystem nutrient budget. However, the rate of wood decomposition after fires is still poorly understood, particularly for Mediterranean-type ecosystems. In this study, we estimate dead wood decomposition after a fire in a Mediterranean mountain across an elevational gradient in Sierra Nevada National Park (SE Spain). Four plots were established after the 2005 Lanjarón fire at different elevation (1477, 1750, 2053 and 2317 m a.s.l.), and standardized samples of logs of 75 cm length and variable diameters (samples, hereafter) were left on the ground for long-term monitoring. The initial wood density and nutrient content was estimated as a baseline, and thereafter a subsample of 30-50 logs per plot were harvested for analysis at different intervals (after 2, 4, 8, 10 and 15 years). The greatest density loss of the logs occurred in the last 5 years of the study. At the end of the experiment the logs had lost an overall 55% of their density, although this value ranged from an average 46% at the highest-elevation plot to 63% at an intermediate elevation. Contrary to studies in other climates, large-diameter logs decomposed faster than small-diameter logs, which might be motivated by a higher moisture content in larger logs. Nutrient content in the logs after 15 years differed sharply from the original content, supporting the promoting effect of burnt wood on soil fertility. Our results provide one of the longest time series for wood decomposition in Mediterranean ecosystems and suggest that wood decomposition is regulated by a complex interaction between moisture and temperature. Moreover, the results support that burnt wood is a key biological legacy to promote forest regeneration and restoration through its effect on habitat structure and nutrient provisioning.

This work is part of Smart EcoMountains, the Thematic Center on Mountain Ecosystems of LifeWatch-ERIC.

Abstract ID 743 | Date: 2022-09-14 15:21 – 15:23 | Type: Poster Presentation | Place: SOWI – Garden |

Meru, Lungyina Beulule

Forests across the world stand at risk due to climate change. The Eastern Himalaya region (EHR) in particular is highly vulnerable as it is considered among ‘biodiversity hotspots’,’megadiverse countries’, ‘global 200 ecoregions’ . There are 25 ecoregions within the Eastern Himalayan region alone. Thus, it is imperative that the vulnerability of the region’s forests to climate change be assessed and studied for further action. In this study, an indicator based vulnerbaility assessment has been carried out based on field study, remote sensing and Google Earth Engine. The IPCC framework of indicator based vulnerability assessment which includes exposure, sensitivity and adaptive capacity as its core elements, has been applied in the study. Indicators used include Species Richness Indices, Enhanced Vegetation Index (EVI), Palmer Drought Severity Index (PDSI), and Net Primary Productivity (NPP) in addition to climatic factors such as temperature and precipitation. Indicators such as EVI, NPP, PDSI, NPP and climatic variables were calculated through the use of Google Earth Engine. Analytical Hierarchy Process was applied to assign weightage to the indicators. The vulnerability index of the forest types was developed on a GIS platform and vulnerability maps for the same were generated. Areas of the state showcasing lower values of species richness and EVI in relation to other indicators and factors are highly vulnerable to climate change. Climate change is set to affect not only the ecosystems of the region but also the livelihoods and existence of the indigenous Naga people. This study will help in the identification of highly vulnerable areas in the state and thereby assist in key decision making for policy makers and grassroots organizations involved in protecting the local communities from climate change related impacts.