Chapter 17 Importance of Primary Forests for the Conservation of Saproxylic Insects Thibault Lachat and Joerg Müller Abstract Primary forests represent the ultimate intact habitat for saproxylic insects. However, their extent has been considerably reduced over the past centuries, and those remaining are very heterogeneously distributed. Primary forests are still locally abundant in tropical and boreal zones but are rare in temperate zones. Consequently, many saproxylic insects that were adapted to typical characteristics of primary forests, such as large amounts of dead wood or overmature and senescent trees, might have become extinct regionally due to habitat loss. The remaining primary forests therefore function as refuges for those saproxylic species that cannot survive in managed forests because of their high ecological requirements. Here we identify six characteristics of primary forests important for saproxylic insects that differen- tiate these forests greatly from managed forests, namely, absence of habitat frag- mentation, continuity, natural disturbance regimes, dead-wood amount and quality, tree species composition and habitat trees. These six characteristics highlight the importance of primary forests for the conservation of saproxylic insects in all three main climatic domains (tropical, boreal and temperate). As primary forests are rare in northern temperate zones and are being dramatically lost in boreal and tropical zones, we propose that they should be strictly conserved independently of their climatic zone. Furthermore, we recommend that studies in primary forests intensify to provide reference data for integrating primary forest characteristics into managed forests to improve the conservation of saproxylic species. T. Lachat (*) Bern University of Applied Sciences BFH, School of Agricultural, Forest and Food Sciences HAFL, Zollikofen, Switzerland Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland e-mail: [email protected] J. Müller Nationalparkverwaltung Bayerischer Wald, Grafenau, Germany Feldstation Fabrikschleichach, Lehrstuhl für Tierökologie und Tropenbiologie (Zoologie III), Biozentrum Universität Würzburg, Rauhenebrach, Germany This is a U.S. government work and its text is not subject to copyright protection in the 581 United States; however, its text may be subject to foreign copyright protection 2018 M. D. Ulyshen (ed.), Saproxylic Insects, Zoological Monographs 1, https://doi.org/10.1007/978-3-319-75937-1_17 582 T. Lachat and J. Müller 17.1 Introduction As one of the last remnants of intact nature in terrestrial ecosystems, primary forests have been a focus of conservation efforts for decades. They are an irreplaceable habitat for thousands of species, including saproxylic insects (Bengtsson et al. 2000). Such forests serve as a refuge and reservoir for species that cannot survive in managed forests. Those saproxylic species that can survive in managed forests even under very unnatural conditions, e.g. in Douglas-fir plantations in Europe (Goßner and Ammer 2006) or teak plantations in tropical Africa (Lachat et al. 2007), deliver important ecosystem services, such as biomass decomposition. By contrast, specialized species cannot cope with forest degradation, especially when it impacts their livelihood as they have higher ecological requirements (Grove 2002b), namely, large amounts of dead wood, dead or old trees of large dimension, habitat continuity or natural dynamics such as wildfires or windthrows. As the anthropogenic pressure on natural forest ecosystems increases, the impor- tance of forests with negligible human influence becomes more apparent. These irreplaceable primary forests (also known as primaeval or virgin forests or even called ancient or old-growth forests if human impact cannot be excluded) worldwide have unique qualities that significantly contribute to biodiversity conservation, climate change mitigation and sustainable livelihoods (Foley et al. 2007; Luyssaert et al. 2008; Körner 2017). Yet most of the world’s forests have been influenced in the last centuries by logging, clearing or land-use change. For example, approximately half of the tropical forest that was present at the beginning of the twentieth century has already disappeared, with peak deforestation in the 1980s and 1990s (Wright 2005). In Central Europe, where the main deforestation occurred in the eighteenth century or earlier, primary forests are now scarce (Williams 2002). Depending on the definition, the status of natural primary forests can be very exclusive. The irrevocable loss of their status is reflected in their definition by the Food and Agriculture Organization of the United Nations (FAO 2016), i.e. a “nat- urally regenerated forest of native species, where there are no clearly visible indica- tions of human activities and the ecological processes are not significantly disturbed”. This definition does not completely exclude human intervention in the distant past, which cannot always be known. However, the FAO definition specifies that significant human intervention has not been known to occur or was long ago enough to have allowed the natural species composition and processes to become re-established (FAO 2016). Such recovery processes can last centuries depending on the intensity of the disturbance and on the surrounding landscape (Chazdon 2003). A key factor of primary forests is the absence of human activities that could disturb ecological processes. However, some forests that experienced human activ- ities more than 500 years ago qualify as primary forests. For example, recent archaeological research in the Amazon basin revealed pre-Columbian earthworks and settlements throughout the area (Piperno et al. 2015). Lasting legacies of these past human disturbances include earthworks, soil modification and introduction of species. However, given the spatial and temporal pattern of the data, the human 17 Importance of Primary Forests for the Conservation of Saproxylic Insects 583 impact on the Amazonian forest is not evident (Bush et al. 2015). It is therefore conceivable that large forest areas recovering from forest management and set aside as forest reserves during the past decades could be considered as primary forests in few hundreds of years, as long as the protection status is maintained. Another definition of primary forest is based on the intactness of the ecosystem as a forest landscape of conservation value. Intactness is related to ecosystem integrity and resilience to natural disturbances and to other forest ecosystem functions, such as biodiversity (Potapov et al. 2017). A seamless mosaic of forests and associated natural treeless ecosystems with a minimum area of 500 km2 that exhibits no remotely detected signs of human activity or habitat fragmentation and is large enough to maintain all native biological diversity is classified as an intact forest landscape (Potapov et al. 2017). Considering this concept, the size and the location of a primary forest also influence its status. In the following, we will first provide an overview of the state of primary forests in three main climatic domains: tropical, temperate and boreal. We will then focus on important characteristics of primary forests that might influence saproxylic insects as compared to managed forests. Finally, we will provide implications for conservation and make recommendations for the role of primary forest in the conservation of saproxylic insects. 17.2 What Remains of Primary Forests and Consequences for Conservation Globally, the history of primary forest loss mirrors the development of human settlements and population density. For example, the Roman Empire exploited forests early on in a way that left only degraded shrub vegetation cover around the Mediterranean Sea (Hughes 2011). Particularly the high demand for wood for war vessels thousands of years ago caused the loss of primary forests around the sea (Ehrlich et al. 1977). By contrast, other forest areas, e.g. in the tropics and boreal zones, were only little affected up to a few hundred years ago due to limited access and unfavourable conditions for human life, such as tropical diseases and short vegetation periods. Under the favourable conditions in Central Europe, forest deg- radation occurred in a cascade of pressure, starting with a clearance period up to 800 AD. After this, humans started to convert remaining forest fragments through silvicultural practices of coppicing, pasture establishment and the like. A shift to modern forestry starting in the late 1700s followed agricultural concepts of enhanc- ing wood production, mainly through even-aged forestry and a focus on fast- growing conifers (Bürgi and Schuler 2003; Kirby and Watkins 2015; McGrath et al. 2015). In eastern North America, most of temperate deciduous forests were cleared for agriculture during the settlement from the 1600s to the mid-1800s. Consequently, in Europe and North America, less than 1% of all temperate 584 T. Lachat and J. Müller deciduous forests remain free of deforestation or other intensive use (Reich and Frelich 2002). Boreal forests were managed later. Studies on fire regimes highlighted the predominance of climate-driven fire regimes in Fennoscandia up to 1600s, followed by an increased fire frequency due to anthropogenic influence up to 1800s (slash- and-burn cultivation and forest pasture burning) (Niklasson and Drakenberg 2001; Storaunet et al. 2013). Later, fires were suppressed due to increased value of timber resources (Rolstad et al. 2017). Similar