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Low mortality rates and slow growth differentiate shade-tolerant from shade-intolerant species and define the survival strategy of juvenile trees growing in deep shade. While radial stem growth has been widely used to explain mortality in juvenile trees, the leaf area ratio (LAR), known to be a key component of shade tolerance, has been neglected so far. We assessed the effects of LAR, radial stem growth and tree height on survival time and the age-specific mortality rate of juvenile Fagus sylvatica L. (European beech), Acer pseudoplatanus L. (sycamore maple) and Acer platanoides L. (Norway maple) in a primeval beech forest (Ukraine). Aboveground and belowground biomass and radial stem growth were analysed for 289 living and 179 dead seedlings and saplings. Compared with the other species, F. sylvatica featured higher LAR, slower growth and a lower mortality rate. The average survival time of F. sylvatica juveniles (72 years) allows it to reach the canopy more often than its competitors in forests with low canopy turnover rate. In contrast, a combination of lower LAR, higher growth rate and higher age-specific mortality rate of the two Acer species resulted in their shorter survival times and thus render their presence in the canopy a rare event. Overall, this study suggests that shade tolerance, commonly defined as a relationship between sapling mortality and growth, can alternatively be formulated as a relationship between survival time and the interplay of growth and LAR. [ABSTRACT FROM AUTHOR]

1 We used the forest succession model ForClim to simulate Holocene treeline dynamics along an elevational transect in the Central European Alps, in order to explore the extent and cause of changes in treeline altitude and composition. 2 A temperature reconstruction independent of vegetation proxies was used to drive the model, and the simulation results were compared with Holocene pollen and macrofossil records from a nearby site close to the present-day treeline. 3 The simulation results yielded treeline fluctuations of about ± 100 m (2375–2600 m a.s.l.), confirming earlier palaeoecological studies and quantitatively corroborating the interpretation of most palaeoecologists that decadal- to centennial-scale Holocene fluctuations of pollen and plant macrofossil frequencies reflect treeline shifts rather than productivity changes alone. 4 The simulated changes in species composition and treeline position show general agreement with palaeobotanical data between 11 000 and 4500 calibrated radiocarbon years BP. In the late Holocene, however, palaeobotanical evidence indicates a distinct lowering of the treeline, while simulation projected continuous forest cover up to an altitude of 2400 m a.s.l. 5 Our results indicate that changes in temperature alone can account for changes in treeline elevation for the first half of the Holocene. The discrepancy between simulation results and palaeobotanical records since 4500 cal. BP supports the hypothesis of a strong human influence on the Alpine treeline during the late Holocene. 6 Combining palaeoecological methods with vegetation modelling can disentangle climatic effects and early human impacts on long-term vegetation dynamics. Forest succession models may not only help palaeoecologists to achieve a better understanding of the factors driving past vegetation changes, but their validation with long-term empirical data is also an important step towards applying these models to the assessment of future vegetation dynamics in a changing climate. [ABSTRACT FROM AUTHOR]

Dynamic vegetation models (DVMs) follow a process-based approach to simulate plant population demography, and have been used to address questions about disturbances, plant succession, community composition, and provisioning of ecosystem services under climate change scenarios. Despite their potential, they have seldom been used for studying species range dynamics explicitly. In this perspective paper, we make the case that DVMs should be used to this end and can improve our understanding of the factors that influence species range expansions and contractions. We review the benefits of using process-based, dynamic models, emphasizing how DVMs can be applied specifically to questions about species range dynamics. Subsequently, we provide a critical evaluation of some of the limitations and trade-offs associated with DVMs, and we use those to guide our discussions about future model development. This includes a discussion on which processes are lacking, specifically a mechanistic representation of dispersal, inclusion of the seedling stage, trait variability, and a dynamic representation of reproduction. We also discuss upscaling techniques that offer promising solutions for being able to run these models efficiently over large spatial extents. Our aim is to provide directions for future research efforts and to illustrate the value of the DVM approach. [ABSTRACT FROM AUTHOR]

Clearcutting has been identified as a main threat to forest biodiversity. In the last few decades, alternatives to clearcutting have gained much interest. Living and dead trees are often retained after harvest to serve as structural legacies to mitigate negative effects of forestry. However, this practice is widely employed without information from systematic before-after control-impact studies to assess the processes involved in species responses after clearcutting with retention., We performed a large-scale survey of the occurrence of logging-sensitive and red-listed bryophytes and lichens before and after clearcutting with the retention approach. A methodology was adopted that, for the first time in studies on retention approaches, enabled monitoring of location-specific substrates. We used uncut stands as controls to assess the variables affecting the survival of species after a major disturbance., In total, 12 bryophyte species and 27 lichen species were analysed. All were classified as sensitive to logging, and most species are also currently red-listed. We found that living and dead trees retained after final harvest acted as refugia in which logging-sensitive species were able to survive for 3 to 7 years after logging. Depending on type of retention and organism group, between 35% and 92% of the species occurrences persisted on retained structures. Most species observed outside retention trees or patches disappeared., Larger pre-harvest population sizes of bryophytes on dead wood increased the survival probability of the species and hence buffered the negative effects of logging., Synthesis and applications. Careful spatial planning of retention structures is required to fully embrace the habitats of logging-sensitive species. Bryophytes and lichens persisted to a higher degree in retention patches compared to solitary trees or in the clearcut area. Retaining groups of trees in logged areas will help to sustain populations of species over the clearcut phase. When possible, old logs should be moved into retention patches to provide a more beneficial environment for dead wood-dependent species. Our study also highlights the need for more before-after control-impact studies of retention forestry to explore factors influencing the survival of species after logging. [ABSTRACT FROM AUTHOR]

Abstract: Forest gap models have been applied widely to examine forest development under natural conditions and to investigate the effect of climate change on forest succession. Due to the complexity and parameter requirements of such models a rigorous evaluation is required to build confidence in the simulation results. However, appropriate data for model assessment are scarce at the large spatial and temporal scales of successional dynamics. In this study, we explore a data source for the evaluation of forest gap models that has been used only little in the past, i.e., large-scale National Forest Inventory data. The key objectives of this study were (a) to examine the potentials and limitations of using large-scale forest inventory data for evaluating the performance of forest gap models and (b) to test two particular models as case studies to derive recommendations for their future improvement. We used data from the first Swiss National Forest Inventory to examine the species basal area and tree numbers in different diameter classes simulated by the gap models ForClim (version 2.9.3) and PICUS (version 1.4) for forest types that are typical of mountain forests in Switzerland. The results showed the potential of data from large-scale forest inventories for evaluating model performance. Since this type of data is typically based on a large number of samples across environmental gradients, they are particularly suited for investigations at the general level of the dominant species based on stand basal area. However, the surprisingly small variability of juvenile trees (trees <12cm diameter at breast height; dbh) indicated limitations of the data used. Insufficient representativeness due to small sample plot size and uncertainty regarding past management limit an evaluation of structural forest aspects such as species diversity, and number of small trees (dbh<12cm). The examined models reproduced the observed species composition satisfactorily. However, there were clear model deficiencies in the simulation of successional patterns and of juvenile tree numbers. We identified priorities for future model development. We conclude that large-scale forest inventory data can be valuable for model evaluation, particularly when they cover large environmental gradients and do not come from intensively managed forests. Due to their limitations, they must, however, be complemented by other data such as from a full cruise. [Copyright &y& Elsevier]

In the mountain pine (Pinus mugo subsp. uncinata (DC.) Domin) forests of the Swiss National Park in the Central Alps, disease centers associated with the root-rot fungi Heterobasidion annosum (Fr.) Bref. and Armillaria spp. are characteristic elements. We assessed the impact of these pathogens on forest dynamics by studying transects running across disease centers into the adjacent forest. Overall, mountain pine was the most abundant regenerating tree species and accounted for 84% of all seedlings (<20 cm high) and 93% of all saplings (20–130 cm high), whereas Swiss stone pine (Pinus cembra L.) was less frequent (15% seedlings : 7% saplings). The density of mountain pine seedlings did not differ significantly between the disease centers and the adjacent forest, whereas mountain pine saplings were more frequent within the disease centers, indicating that growth from the seedling to the sapling stage was favoured in disease centers. There was significantly more dead wood and a greater diversity of plant species in the disease centers than in the adjacent forest. The results suggest that root-rot fungi slow down succession towards stands with a higher proportion of P. cembra by causing premature mortality of mountain pines and creating disease centers with dense mountain pine regeneration. [ABSTRACT FROM AUTHOR]