Elsevier

Forest Ecology and Management

Volume 368, 15 May 2016, Pages 81-93
Forest Ecology and Management

What drives European beech (Fagus sylvatica L.) mortality after forest fires of varying severity?

https://doi.org/10.1016/j.foreco.2016.03.008Get rights and content

Highlights

  • Post-fire beech mortality depends on fire intensity and related severity.

  • Low fire severity results in a mortality rate comparable to the unburnt forest.

  • Moderate fire severity results in delayed mortality of smaller individuals but large seed trees survive.

  • High fire severity causes a rapid dead irrespectively of beech’s diameter.

  • Post-fire fungi infestation play a major role in triggering beech mortality.

Abstract

Predicting the timing and amount of tree mortality after a forest fire is of paramount importance for post-fire management decisions, such as salvage logging or reforestation. Such knowledge is particularly needed in mountainous regions where forest stands often serve as protection against natural hazards (e.g., snow avalanches, rockfalls, landslides). In this paper, we focus on the drivers and timing of mortality in fire-injured beech trees (Fagus sylvatica L.) in mountain regions. We studied beech forests in the southwestern European Alps, which burned between 1970 and 2012. The results show that beech trees, which lack fire-resistance traits, experience increased mortality within the first two decades post-fire with a timing and amount strongly related to the burn severity. Beech mortality is fast and ubiquitous in high severity sites, whereas small- (DBH <12 cm) and intermediate-diameter (DBH 12–36 cm) trees face a higher risk to die in moderate-severity sites. Large-diameter trees mostly survive, representing a crucial ecological legacy for beech regeneration. Mortality remains low and at a level similar to unburnt beech forests for low burn severity sites. Beech trees diameter, the presence of fungal infestation and elevation are the most significant drivers of mortality. The risk of beech to die increases toward higher elevation and is higher for small-diameter than for large-diameter trees. In case of secondary fungi infestation beech faces generally a higher risk to die. Interestingly, fungi that initiate post-fire tree mortality differ from fungi occurring after mechanical injury. From a management point of view, the insights about the controls of post-fire mortality provided by this study should help in planning post-fire silvicultural measures in montane beech forests.

Introduction

Climate change and related predictions of a warmer and drier climate (IPCC, 2014) lead to increasing concerns about the future impact of wildfires on forest resistance and resilience in forest ecosystems (Bachelet et al., 2007, Fischer et al., 2010, Schumacher and Bugmann, 2006). In many regions, the size and intensity of wildfires have already increased in recent decades (e.g., Westerling et al., 2006, Sullivan et al., 2011, Sarris et al., 2014), raising questions about how to predict the rate of fire-injured tree mortality within the framework of planning post-fire silvicultural measures such as salvage logging and reforestation (Brown et al., 2003, Ledgard and Davis, 2004, Kobziar et al., 2006, Keyser et al., 2008, Moreira et al., 2012). Models that predict post-fire mortality, as a result of various driving factors, have been developed mainly for tree species in fire-prone ecosystems, which display fire resistance traits (e.g., McHugh and Kolb, 2003, Rigolot, 2004, Kobziar et al., 2006, Sieg et al., 2006, Hood et al., 2007, Fernandes et al., 2008, Stevens-Rumann et al., 2012). Comparatively little attention has been paid to fire-sensitive species that dominate temperate deciduous forests (e.g., Catry et al., 2010). From a forest management perspective, a major problem arises from the lack of data and experience regarding the vulnerability and resilience of such forest stands under increasing fire disturbance.

European beech (Fagus sylvatica L.), for example, represents a tree species with high economic and ecological value in Europe, and forests of beech are usually considered less fire-prone (Pezzatti et al., 2013). However, during the exceptional drought of 2003 (e.g. Beniston, 2004), beech stands in the southwestern Alps experienced numerous and atypical large forest fires. These fires may indicate a shift in fire regime driven by climate change (Valese et al., 2014).

To date, species survival strategies after fire are poorly understood, and post-fire silvicultural measures are usually limited to salvage logging followed by reforestation in very rare cases. Generally, beech is considered to be highly susceptible to fire due to its lack of fire-resistance (e.g. thick bark) and fire-adaptation (e.g. resprouting capability) traits (Peters, 1997, Packham et al., 2012). In fact, studies report that beech resprouts after fire, but the resulting shoots tend to dieback and hardly constitute a valuable new generation (van Gils et al., 2010, Conedera et al., 2010, Espelta et al., 2012, Maringer et al., 2012).

Furthermore, beech regeneration (from seeds) relies on seed dispersal by gravity and animals, and establishment is often close to the nearest seed-bearing tree (Wagner et al., 2010, van Couwenberghe et al., 2010). Consequently, natural beech regeneration becomes more limited within increasing burned area and greater distance from a seed source. Recent studies, however, suggest that beech stands exhibit surprisingly high resilience after single fire events (Ascoli et al., 2013, Maringer et al., in press). The fire-surviving strategy, in this case, is mainly based on rapid in situ seed production when mast years coincide with suitable germination conditions in the post-fire environment (e.g., improved light conditions and reduced litter cover on the soil, Ascoli et al., 2015). Thus, post-fire density and spatial distribution of mature surviving trees are critical for new cohort recruitment and rapid recovery of beech forests.

It is known that the timing of post-fire beech mortality depends on fire intensity. Beech mortality may occur immediately after very severe fires or be delayed by several years after low to moderate severe fire (Conedera et al., 2007, Ascoli et al., 2013). There is, however, a lack of knowledge regarding factors driving such delayed mortality, and especially the predictability of its timing. Such information would help forest managers in planning complex post-fire measures related to: (i) whether or not intervene with silvicultural measures, (ii) timing of the needed interventions, and (iii) the number of trees to salvage (Ascoli et al., 2013). Following the guiding principle that post-fire management decisions should be based on site- and species-specific ecological processes, we focus in this paper on the major drivers that influence post-fire beech mortality. In particular we ask:

  • (1)

    What are the mid-term temporal trends in fire-caused beech mortality?

  • (2)

    Which tree-specific traits (e.g., tree size) enhance the survivability of fire-injured beech trees?

  • (3)

    What are the main biotic and abiotic factors associated with beech mortality after fire disturbance?

Section snippets

Study area

The present study was conducted in the neighboring regions of Piedmont (Italy) and Ticino (Switzerland) located in the southwestern European Alps (Fig. 1). Both regions are characterized by a marked elevational gradient along which forest vegetation types are distributed. Beech-dominated forests occupy the intermediate elevation belt ranging from 600–1000 m a.s.l. to 1300–1700 m a.s.l. depending on the locality and aspect (Camerano et al., 2004, Ceschi, 2006). These forests are mostly in the

Forest structure

Most (61%) of the burned forest stands were classified as high-stand forests, a minority (16%) as coppices, and the remainder were intermediate in structure. In total, 3,504 mature trees (DBH >8 cm) were recorded, of which beech comprised 88% and 93% of the trees in burned and unburned forests, respectively. Other tree species rarely (<4%) grew within the pure beech stands (Appendix B).

Post-fire beech mortality

Half of the beech trees assessed in burned plots (N = 2,845) died whereas only 10% of the trees in unburned

Post-fire stand dynamics

The selected stands showed typical beech forest structural characteristics for the southwestern Alps, with overlapping transition stages from coppices to high forest stands (Nocentini, 2009, Ascoli et al., 2013). In these stands, fires of mixed severity caused changes in forest structure by triggering mortality in half of the pre-fire beech. In general, fire-induced beech mortality increased with time in the first two post-fire decades. Similar lags in mortality after fire have also been

Conclusions

In this study, we used a retrospective approach to examine post-fire dynamics and fire-related beech mortality in 36 sites in the southwestern Alps. Despite some methodological limits in our chronosequence approach, we provide important new insights on the fire ecology and post-fire mortality of European beech.

The major drivers of tree mortality in this study were related to a combination of factors: (i) the proportion of woody tissue damaged as a consequence of tree diameter in relation to

Acknowledgements

This study was partially supported by the Swiss Federal Office for the Environment (FOEN). Fieldwork assistance was carried out with the support of Franco Fibbioli, Simone Giavi, Marianne Steffen, Lisa Berghäuser, Jordi Murgadas from the Swiss Federal Institute for Forest, Snow and Landscape Research, and Sven Hofmann from the University of Karlsruhe (Germany). Thanks go to Curtis Gautschi who took care of revising the English version. Finally, we acknowledge the helpful comments of two

References (107)

  • A. Shafiei et al.

    Forest fire effects in beech dominated mountain forest of Iran

    For. Ecol. Manage.

    (2010)
  • C. Stevens-Rumann et al.

    Ten years after wildfires: How does varying tree mortality impact fire hazard and forest resiliency?

    For. Ecol. Manage.

    (2012)
  • E. Valese et al.

    Fire, humans and landscape in the European Alpine region during the Holocene

    Anthropocene

    (2014)
  • R. van Couwenberghe et al.

    Gap partitioning among temperate tree species across a regional soil gradient in windstorm-disturbed forests

    For. Ecol. Manage.

    (2010)
  • H. van Gils et al.

    From monospecific to mixed forest after fire?

    For. Ecol. Manage.

    (2010)
  • P.J. van Mantgem et al.

    Tree mortality patterns following prescribed fire for Pinus and Abies across the southwestern United States

    For. Ecol. Manage.

    (2013)
  • S. Wagner et al.

    Beech regeneration research: from ecological to silvicultural aspects

    For. Ecol. Manage.

    (2010)
  • M.N. Adel et al.

    Forest structure and woody plant species composition after a wildfire in beech forests in the north of Iran

    J. Forest. Res.

    (2013)
  • D. Bachelet et al.

    Wildfires and Global Climate Change: The Importance of Climate Change for Future Wildfire Scenarios in the Western United States

    (2007)
  • Bates, D.M., 2010. Lme4: Mixed effect modeling with R. R project. <http://lme4.r-forge.r-project.org/lMMwR/lrgprt.pdf>...
  • G. Bauer et al.

    Insulation capability of the bark trees with different fire adaption

    J. Mater. Sci.

    (2010)
  • M. Beniston

    The 2003 heat wave in Europe: a shape of things to come? An analysis based on Swiss climatological data and model simulations

    Geophys. Res. Lett.

    (2004)
  • A. Boeck et al.

    Predicting tree mortality for European beech in Southern Germany using spatially explicit competition indices

    For. Sci.

    (2014)
  • A.E. Bonyad et al.

    Evaluation of non-destructive Meyer method for determination of bark volume of beech (Fagus orientalis Lipsky) in different geographical aspects

    Caspian J. Environ. Sci.

    (2012)
  • P.M. Brando et al.

    Fire-induced tree mortality in a neotropical forest: the roles of bark traits, tree size, wood density and fire behavior

    Glob. Change Biol.

    (2012)
  • Brown, J., Reinhard, M., Kramer, K.A., 2003. Coarse woody debris: Managing benefits and fire hazard in the recovering...
  • Brownrigg, R., 2015. Draw Geographical Maps. Version 3.0.0-2. R Core Team....
  • Brunsdon, C., Chen, H., 2015. Package ‘GISTools. Version 0.7-4. R Core Team....
  • P. Camerano et al.

    Tipi forestali del Piemonte

    (2004)
  • I. Ceschi

    Il bosco nel Canton Ticino

    (2006)
  • M. Conedera et al.

    Pilze als Pioniere nach Feuer

    Wald Holz

    (2007)
  • Corpo Forestale dello Stato/Ministero delle Politiche Agricole, Alimentari e Forestali: Ufficio Territoriale per la...
  • S. Deepayan

    Lattice: Multivariate Data Visualization With R

    (2008)
  • R. Delarze et al.

    Effects of fire on forest dynamics in Southern Switzerland

    J. Veg. Sci.

    (1992)
  • D. Dujesiefken et al.

    Response of beech and oaks to wounds made at different times of the year

    Eur. J. Forest Res.

    (2005)
  • L. Dymytrova et al.

    Topographic and forest-stand variables determining epiphytic lichen diversity in the primeval beech forest in the Ukrainian Carpathians

    Biodivers. Conserv.

    (2014)
  • Eidg. Anstalt für das forstliche Versuchswesen (EAFV), 1983. Ertragstafeln Buche. EAFV (Eds.), Birmensdorf...
  • Ellenberg, H., Leuschner, C., 2010. Vegetation Mitteleuropas mit den Alpen. In ökologischer, dynamischer und...
  • J.M. Espelta et al.

    Post-fire management of Mediterranean broadleaved forests

  • ESRI. ArcGIS Desktop: Release 10. (Environmental Systems Research Institute: Redlands,...
  • G.R. Fahnestock et al.

    Heating of tree trunks in surface fires

    J. Forest. Res.

    (1964)
  • Fischer, R., Lorenz, M., Granke, O., Mues, V., Iost, S., van Dobben, H., et al., 2010. Forest condition in Europe, 2010...
  • Frehner, M., Wasser, B., Schwitter, R., 2005. Nachhaltigkeit und Erfolgskontrolle im Schutzwald. Wegleitung für...
  • E. Gerhardt

    Guida ai funghi

    (2005)
  • S.L. Gutsell et al.

    How fire scars are formed: coupling a disturbance process to its ecological effect

    Can. J. For. Res.

    (1996)
  • J.C. Harrod et al.

    Post-fire succession and 20th century reduction in fire frequency and xeric southern Appalachian sites

    J. Veg. Sci.

    (2000)
  • U. Hecht et al.

    Bark wounds caused by felling are more susceptible to discoloration and decay than wounds caused by extraction in European beech

    Ann. For. Sci.

    (2015)
  • C. Hély et al.

    Modeling tree mortality following wildfire in the Southeastern Canadian mixed-wood boreal forest

    For. Sci.

    (2003)
  • R.R. Hicks

    Ecology and Management of Central Hardwood Forests

    (1998)
  • Cited by (24)

    • Drivers of persistent post-fire recruitment in European beech forests

      2020, Science of the Total Environment
      Citation Excerpt :

      If fire regimes in beech forests shift to higher-severity or more frequent fires, immediate tree mortality particularly in immature stands may result in shifts in forest composition as a result of failed beech regeneration. The rapid die-back of beech trees after severe fires (Maringer et al., 2016a) rapidly opens the tree canopy, providing enough light to promote competing ground vegetation, which can delay beech regeneration for several decades (Koop and Hilgen, 1987). Based on our results, post-fire recruitment success is reduced in years with dry springs and summers, which might reduce the regeneration capacity post-fire under climate change.

    • Investigation of root reinforcement decay after a forest fire in a Scots pine (Pinus sylvestris) protection forest

      2017, Forest Ecology and Management
      Citation Excerpt :

      It is, thus, important to study chrono-sequences of vegetation development after different fire intensities to quantify their protective capacity. In the case of beech stands after moderate severity burns, the gradual opening of the tree canopy leads to emerging beech regeneration and to an increase in the forest-protective effect after 20 years (Maringer et al., 2016b). It is important to monitor the evolution of natural regeneration in study areas to establish the timing of the recovery of the protective effect.

    • Insights about past forest dynamics as a tool for present and future forest management in Switzerland

      2017, Forest Ecology and Management
      Citation Excerpt :

      Similarly, recent dieback of Scots pine in dry areas of the Rhone valley of the western central Alps is also related to extreme summer drought and will likely continue in the future (Bigler et al., 2006; Rebetez and Dobbertin, 2004; Rigling et al., 2013). Warming and related increases in drought frequency and severity (Rebetez, 1999) and associated fire risk (Reinhard et al., 2005; Wastl et al., 2013; Valese et al., 2014) will alter interactions among woody species (Moser et al., 2010; Maringer et al., 2016) and with pests and diseases (Battisti, 2008; Netherer and Schopf, 2010; Marini et al., 2012). In addition, newly introduced exotic species (e.g. Robinia pseudooacacia, Ailanthus altissima, Pawlonia spp.) have become invasive and highly competitive in low- to mid-elevation forest ecosystems and strongly interfere with fire regimes, silvicultural management practices (Grund et al., 2005; Maringer et al., 2012; Radtke et al., 2013; Knüsel et al., 2015), pests (Wermelinger, 2014; Roques et al., 2016) and disease (Kowalski and Holdenrieder, 2009; Pautasso et al., 2013; Sieber, 2014) as well as their possible interactions (e.g. Meyer et al., 2015).

    View all citing articles on Scopus
    View full text