Past forest composition, structures and processes – How paleoecology can contribute to forest...

Biological Conservation 168 (2013) 116–127

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Biological Conservation

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Review

Past forest composition, structures and processes – How paleoecologycan contribute to forest conservation

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⇑ Corresponding author. Tel.: +46 40415196.E-mail addresses: [email protected] (M. Lindbladh), [email protected] (S. Fraver), [email protected] (J. Edvardsson), adam.felto

(A. Felton).

Matts Lindbladh a,⇑, Shawn Fraver b, Johannes Edvardsson c, Adam Felton a

a Swedish University of Agricultural Sciences – SLU, Southern Swedish Forest Research Centre, PO Box 49, 230 53 Alnarp, Swedenb School of Forest Resources, University of Maine, 5755 Nutting Hall, Orono, ME 04469, USAc Institute of Geological Sciences, Laboratory for Dendrogeomorphology, University of Berne, Baltzerstrasse 1+3, CH-3012 Berne, Switzerland

a r t i c l e i n f o

Article history:Received 28 June 2013Received in revised form 22 September2013Accepted 24 September 2013

Keywords:BiodiversityCharcoalConservationDendrochronologyForest historyFossil woodPlant macrofossilPollen analysis

a b s t r a c t

The importance of long-term historical information derived from paleoecological studies has long beenrecognized as a fundamental aspect of effective conservation. However, there remains some uncertaintyregarding the extent to which paleoecology can inform on specific issues of high conservation priority, atthe scale for which conservation policy decisions often take place. Here we review to what extent the pastoccurrence of three fundamental aspects of forest conservation can be assessed using paleoecologicaldata, with a focus on northern Europe. These aspects are (1) tree species composition, (2) old/large treesand coarse woody debris, and (3) natural disturbances. We begin by evaluating the types of relevant his-torical information available from contemporary forests, then evaluate common paleoecological tech-niques, namely dendrochronology, pollen, macrofossil, charcoal, and fossil insect and wood analyses.We conclude that whereas contemporary forests can be used to estimate historical, natural occurrencesof several of the aspects addressed here (e.g. old/large trees), paleoecological techniques are capable ofproviding much greater temporal depth, as well as robust quantitative data for tree species compositionand fire disturbance, qualitative insights regarding old/large trees and woody debris, but limited indica-tions of past windstorms and insect outbreaks. We also find that studies of fossil wood and paleoento-mology are perhaps the most underutilized sources of information. Not only can paleoentomologyprovide species specific information, but it also enables the reconstruction of former environmental con-ditions otherwise unavailable. Despite the potential, the majority of conservation-relevant paleoecolog-ical studies primarily focus on describing historical forest conditions in broad terms and for large spatialscales, addressing former climate, land-use, and landscape developments, often in the absence of a spe-cific conservation context. In contrast, relatively few studies address the most pressing conservationissues in northern Europe, often requiring data on the presence or quantities of dead wood, large treesor specific tree species, at the scale of the stand or reserve. Furthermore, even fewer examples exist ofdetailed paleoecological data being used for conservation planning, or the setting of operative restorativebaseline conditions at local scales. If ecologist and conservation biologists are going to benefit to the fullextent possible from the ever-advancing techniques developed by the paleoecological sciences, furtherintegration of these disciplines is desirable.

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Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1172. Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1173. Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

3.1. Tree species composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
3.1.1. Evidence from contemporary forests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1183.1.2. Evidence from paleoecology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1183.1.3. Summary: Potential for deriving estimates of the past . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
3.2. Old and large trees and coarse woody debris . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

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3.3. Natural disturbances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
4. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

1. Introduction

Human activities have reduced or eliminated numerous habitats,structures and processes critical to the maintenance of biodiversityin many of the world’s forests (Hunter, 1999). How abundant thesefeatures would be in the absence of human activities is a crucialquestion in conservation biology. Today’s forest reserves provideimportant reference conditions in this context (Peterken, 1996).However, forest reserves are often less than ideal at approximatingnatural conditions, as they may be compromised by their small size,isolation, biased placement in non-productive regions, altered dis-turbance regimes, and skewed representation of successional stages(Branquart et al., 2008; Nilsson and Götmark, 1992; Pickett andThompson, 1978; Pressey, 1994). Furthermore, even the largestmost famous continuous tracks of forest in Europe need to be inter-preted with caution due to their histories of human intervention,including the Białowieza forest in Poland (Niklasson et al., 2010;Samojlik and Jedrzejewska, 2004) and the remote forests of Fenno-scandia (Josefsson et al., 2009; Uotila et al., 2002). Thus, to betterunderstand the former occurrence of natural features and processes,including their historical range of variability, we must look beyondthe insights provided by contemporary forests.

Paleoecological studies allow us to assess natural conditionsby providing insights into forest composition, structure and dis-turbance regimes over extensive time periods, and coveringvarying intensities or absence of human impact. This long-termperspective is needed for improving our ecological understand-ing, not only to avoid the potentially confounding influence ofhuman impacts but also because many ecological processes vi-tal for maintaining forest biodiversity occur over extended peri-ods of time (Foster et al., 1996; Nilsson, 1997). The importanceof a long-term perspective has been recognized as a fundamen-tal aspect of effective conservation (Birks, 1996; Honnay et al.,2004; Willis et al., 2007; Willis and Bhagwat, 2010). However,what remains to be assessed is how relevant paleoecology isto informing issues of high conservation priority at the scalefor which conservation policy decisions often take place. Herewe review to what extent the past occurrence of three funda-mental aspects of forest conservation in northern Europe canbe estimated using paleoecological data. These three aspectsare:

1. Tree species composition – preservation of tree species providescontinuity for co-evolved species and the maintenance of treespecies-specific structural features. Both aspects are critical tothe conservation of forest-associated species (Felton et al.,2010; Jonsell et al., 1998; Palik and Engstrom, 1999).

2. Old/large trees and coarse woody debris – considered to be per-haps the most important substrates for the maintenance of spe-cies diversity in the temperate and boreal forests of today(Jonsell et al., 1998; Jonsson et al., 2005; Lindenmayer et al.,2012; Siitonen et al., 2000; Stokland et al., 2012).

3. Natural disturbances – windstorms, insect outbreaks and forestfires are considered to be necessary for maintaining forestheterogeneity and a diversity of disturbance-specific composi-tional and structural features vital for many threatenedforest-associated species (Everham and Brokaw, 1996; Johnsonand Miyanishi, 2001; Peterken, 1996).

For each targeted aspect we first evaluate the potential for esti-mating its natural occurrence using contemporary forests. We thenintroduce the range of paleoecological methodologies available,provide relevant examples of research studies, and assess thecapacity and limitations involved in estimating the former occur-rence of each aspect assessed. Finally, we discuss the extent towhich paleoecological techniques of relevance to forest conserva-tion are employed, and which paleoecological fields have the high-est untapped potential to make substantial future contributions toconservation.

2. Methods

We focus our review of the available scientific literature onthose paleoecological techniques used in terrestrial ecosystems,namely pollen analysis, macrofossil analysis, charcoal analysis, fos-sil beetle analysis and dendrochronology. Our review focuses onnorthern Europe and relies mainly on relevant research from thisregion. We define northern Europe as Sweden, Denmark, Norway,Finland, the Baltic States, UK and Ireland. Paleoecology has a longtradition in these countries (Iversen, 1941; von Post, 1918), andmany of the most advanced techniques in paleoecological researchare applied here, providing much needed insights as to the currentpotential of the field. Despite our focus on northern Europe, weemphasize that the issues assessed and conclusions reached areapplicable to regions of the world possessing temperate to borealforests.

It is of course impossible to promote a single time period asrepresentative of ‘‘natural’’ or ‘‘baseline’’ conditions in any re-gion (Sensu Davis, 1989). However, it is nevertheless beneficialto anchor the temporal period of our study, and to provide arelevant basis for the comparison of techniques, to a periodrelatively consistent with current climate, but comparatively de-void of anthropogenic influences. For this reason the examplesgiven are predominantly from 2000 BC and onwards, that isafter the warm and dry Holocene thermal maximum (Seppäet al., 2005). They are for the most part also limited to the per-iod occurring prior to the last 300–400 years, the period ofindustrial and agricultural revolution and an associated increasein human population and land-use intensity in northern Europe.Our focus on this time window takes us beyond that coveredby the most reliable written historical records in NorthernEurope.

We searched electronic databases and the internet using vari-ous combinations of Boolean search terms to ensure a thorough

118 M. Lindbladh et al. / Biological Conservation 168 (2013) 116–127

assessment of the available literature. The databases used wereGoogle Scholar (http://scholar.google.com.au/) and Web of Science(http://www.isiwebofknowledge.com/). We used the followingsearch term: (‘‘Forest history’’ or ‘‘vegetation history’’ or paleoecol-ogy or ‘‘fire history’’ or ‘‘macro fossil⁄’’ or macrofossil⁄ or ‘‘pollenanalysis’’ or palynology or ‘‘fossil beetle⁄’’ or ‘‘fossil insect⁄’’ or ‘‘in-sect remain⁄’’ or ‘‘dendrochronology’’ or ‘‘charcoal analysis’’or ‘‘dead wood’’) and (Sweden or Denmark or Finland or Norwayor Scandinavia or Fennoscandia or Germany or Poland or Englandor Britain or ‘‘Great Britain’’ or Ireland or Belgium or Holland orEstonia or Latvia or Lithuania or ‘‘north⁄ Europe’’) not (‘‘Late gla-cial’’ or ‘‘Early Holocene’’ or interglacial). Hence, to ensure a highprobability of capturing written material of potential relevance,we also targeted neighboring countries to Northern Europe inour searches. Search terms were run in separate or limited combi-nations depending on the requirements or limitations of the data-base used. When the previous search terms were combined with‘‘conservation’’ or ‘‘biodiversity’’ it resulted in far fewer hits(approximately 400), but as many studies could be of conservationor general relevance, even if initially not intended or interpretedfrom a conservation perspective, we excluded this constraint. Over2500 publications were appraised for the review, with the majoritydeemed not relevant for our purposes. We also obtained papersfrom colleagues and through reference lists from published studiesincluding major review articles and books on forest history andpaleoecology (e.g. Encyclopedia of Quaternary Science). Further-more, we obtained information from some government studiesand reports.

Paleoecology has been defined as the field of study ‘‘concernedwith environmental relations of once living organisms’’ (Lawrence,1971). Admittedly some methods referred to, and evaluated here(accumulated sand particles and dendrochronology on livingtrees), were not paleoecological techniques, but were neverthelessof direct relevance to the issue addressed and are therefore in-cluded. Except for sand and living trees, all techniques referredto here use the remains of living organisms found in sediment.For simplicity we refer to these remains as ‘‘fossils’’ although theyby definition are ‘‘subfossils’’.

All techniques assessed here, except dendrochronology, are sed-iment based, and hence are partially dependent on reliable datingtechniques, such as radiocarbon dating. Even though reliable dat-ing is often important in a conservation context, it is beyond thescope of this review to thoroughly evaluate this technique; instead,see Elias (2007) or Telford et al. (2004) for a detailed discussion ofthese issues.

3. Results and discussion

3.1. Tree species composition

3.1.1. Evidence from contemporary forestsTemperate forests are thought to be the biome most heavily

influenced by human activities (Hannah et al., 1995; Schmittet al., 2009). In Europe approximately 26% of the original forestarea remains as forest in this vegetation zone (Spiecker, 2003). Ofthis remaining forest area, most is significantly altered by forestmanagement, and current tree species composition is more deter-mined by management than by natural factors (Rackham, 2008;Spiecker, 2003). Even in the case of protected forest areas, multipleexogenous and endogenous factors influence tree species composi-tion; for instance via isolation, drainage, atmospheric pollution,exotic pathogens, and over-browsing (Bobbink et al., 1998; Martínet al., 2010; Rackham, 2008; Renberg et al., 2009). In contrast, bor-eal and hemi-boreal Europe harbor larger contiguous areas of for-est, and although still subjected to large-scale anthropogenic

disturbance, these forests are more likely than their temperatecounterparts to approximate natural tree species composition.However, modern forestry practices have also altered the forestsin the productive regions of these vegetation zones via the shiftto planting of coniferous monocultures, which has, to a large ex-tent, replaced natural regeneration (Östlund et al., 1997). Further-more, natural disturbance regimes have been extensively altered.For example, fires are effectively suppressed (see below), with cor-responding implications for tree species composition (den Herderet al., 2009; Uotila et al., 2002). Hence, today’s unprotected andprotected forests can only provide limited indications as to naturaltree species composition in northern Europe, with this indicationheavily distorted, especially in temperate regions.

3.1.2. Evidence from paleoecology3.1.2.1. Pollen analysis. Pollen analysis is the principal method usedfor providing quantitative estimates of the former occurrence oftree species (Seppä, 2007). It has the distinct advantage in thatthe data source (i.e. pollen) is spread in enormous quantitates intothe air, and is deposited in various sedimentary sites, such as lakes,bogs or small peatlands, making it possible to investigate mostlandscapes and forest types. Starting with von Post (1918) at thebeginning of last century, numerous pollen studies from lakesand large bogs from northern Europe have been used to demon-strate that significant changes have occurred in tree species com-position during the Holocene, and in particular during the lastseveral thousand years (see Berglund et al. (1996)). These studiesrely on the collection capacity of large basins to sample pollen fromextensive areas, and hence provide a landscape- or region-levelassessment (Broström et al., 2004; Sugita, 1994).

Pollen studies from small wetlands or bogs, so called ‘‘smallforest hollows’’, sensu Jacobson and Bradshaw (1981), provide afiner scale resolution for use in conservation. Small hollows havebeen demonstrated in theory (Broström et al., 2005; Sugita, 1994)and practice (Calcote, 1998; Parshall and Calcote, 2001) to samplethe majority of pollen from within 100–1000 m. This represents aspatial scale similar to the scales at which practical conservationoften takes place, such as reserve selection and management(Lindbladh et al., 2008), estimates of naturalness (Davies andTipping, 2004; Wallenius et al., 2005), or forest restoration(Lindbladh et al., 2007). We can gain some insights regardingthe potential of using such techniques, and their capacity to pro-vide very fine scale spatial resolution from a study which relieson pollen samples from multiple small-hollows in a 71-ha Swed-ish forest biodiversity hotspot (Hannon et al., 2010). Today thisreserve is situated in a landscape heavily dominated by produc-tion forests of Picea abies and Pinus sylvestris. The reserve containsa 5 ha core area with old trees of Fagus sylvatica, possessing thehighest associated biodiversity values, and a surrounding bufferzone of primarily younger coniferous forest. An important ques-tion for the management of the reserve was whether the corearea always has been the exception, or if the buffer zone also con-tained temperate broadleaves in the past and thereby should berestored to this species. The result of the pollen analysis showedthat the temperate broadleaved trees (Fagus and before that Quer-cus), were significantly more common in the 5-ha core area thanin the remaining reserve during the last c. 200 years, and alsomore common at least 1000 years earlier (Fig. 1). The authorsconclude that the core area alone, despite its small size, had beenable to harbor these tree species and many of their associatedsaproxylic beetles for centuries or even millennia. A study thathas had direct impact on conservation policies is also from Swe-den. There pollen studies from a large reserve identified signifi-cant amounts of pollen from Quercus and Tilia approximately1000 years ago (Karlsson, 1996; Lindbladh et al., 2008), speciesthat today are rare or absent from the area, but still extremely

http://scholar.google.com.au/

http://www.isiwebofknowledge.com/

Fig. 1. Pollen percentage values for Quercus and Fagus from three small hollow sites in the 71 ha Siggaboda reserve in Southern Sweden (Hannon et al., 2010). One site islocated in the 5 ha core area, the two other sites are located in the buffer zone. All three sites are located less than 700 m from each other.


important for conservation of associated species. Inspired bythese findings, these tree species have been actively regeneratedduring restoration of the reserve by the County Board (Bengtsson,1999).

Pollen analysis thus has a demonstrated capacity to provideinformation on past tree species composition, but several limita-tions to this methodology warrant acknowledgement. Tree spe-cies produce varying amounts of pollen, and pollen types differin their dispersal abilities. Both of these aspects create significantchallenges in the interpretation of pollen data (Davis, 2000). Re-cent advances have however been made in translating fossil pol-len records into more realistic indications of past vegetationcover. Based on a model that defines ‘‘the relevant pollen sourcearea’’; an area in which the pollen-vegetation relationship doesnot improve if the area is increased, a landscape-vegetationreconstruction algorithm is now available (Sugita, 2007a,b). It isa framework that is based on two inter-related models; one thatprovides quantitative estimates of vegetation cover in a regionusing pollen from large lakes (P100 ha), and another thatestimates vegetation composition from small sites (6100 ha) bysubtracting background pollen estimated from the regional vege-tation composition. With the development of this framework, theability to quantify local historical vegetation cover has increasedsignificantly. However, the framework is limited by its require-ments for reliable pollen productivity values from different forestand landscape types, as well as the need for reliable chronologicalcontrols. Moreover, these models are based on measurementsfrom modern surface samples and pollen productivity data andhence do not adjust for differences in the preservation of fossilpollen (Wilmshurst and McGlone, 2005). For example, a commonproblem is the underestimation of Populus, which due to poorpreservation of its pollen, in combination with the pollen grain’slack of distinctive surface ornamentation (Campbell, 1999),substantially inhibits our understanding of its historicaloccurrence.

3.1.2.2. Macrofossils. Compared to pollen analysis, plant macrofos-sils are seldom transported long distances, and thus have the po-tential to provide more reliable information on past stand-leveltree species composition. Macrofossils can also be identified witha higher taxonomic precision than can pollen grains, and can re-cord taxa that produce small amounts or fragile pollen, such as

Larix or Populus (Valsecchi et al., 2010). However, these advanta-ges are countered by the fact that macrofossils are relativelyuncommon and unevenly distributed in sediment. Thus, countscan seldom be considered as quantitative representations of theformer vegetation (Birks, 2007). Ideally macrofossils are used incombination with pollen analysis (Birks and Birks, 2000), due tothe complementarity of these two techniques. One such exampleis a pollen and macrofossil study from a small hollow in Denmark,for which the resolution of the pollen record was limited to genusor higher taxonomic levels (Hannon et al., 2000). In contrast,macrofossils from the same core could refine these results oftendown to species (Fig. 2): from around 3000 BC macrofossils fromten woody species were found, suggesting that these species co-oc-curred at that point of time (Hannon et al., 2000). These findingsreveal exceptional stand level diversity for this region, includingtree species relatively undetectable using pollen analysis alone,such as Tilia platyphyllos or Malus sylvestris, and virtually absentas tree species mixtures from contemporary forests in northernEurope.

3.1.2.3. Charcoal analysis. Charred plant remains may also beused to provide insights into past tree species composition(Carcaillet, 2007). Although macroscopic charcoal cannot beidentified with the same taxonomic precision as macrofossils,the method has the advantage of charcoal being resistant tobiological mineralization. Charred remains can therefore befound in sites with high microbial activity, such as soils, whereboth plant macrofossils and pollen are absent. Macroscopiccharcoal remains usually have a local origin, although anthropo-genic charcoal production and transportation of wood to thecharcoal production site must be considered. Another drawbackis that dating the charcoal is complicated (with dendrochronol-ogy) or expensive (Radiocarbon dating). A study on macro-char-coal in clearance cairns in southern Sweden (Lagerås andBartholin, 2003) provides an example of how the methods cannevertheless be successfully applied to address conservation is-sues. Charcoal remains were used to indicate the presence ofmixed broadleaved species from the first centuries AD, includ-ing six genera or species not typically found in pollen records(e.g., Acer). This finding strongly suggests the past occurrenceof mixed-species broadleaved forests in this area, which arecurrently lacking in this landscape.

Fig. 2. Pollen percentages and macro fossil findings from a small hollow in Suserup, Denmark. Data from (Hannon et al., 2000). Silhouettes are pollen percentages, bars aremacrofossils. The macrofossil data are numbers of specimens per 50 ml peat. b = bud, br = catkin or bud bract, c = cone, cs = cone scale, cu = cupule, f = fruit, fruitlet orfruitstone, nt = nut or nutlet, s = seed, sh = shoot, w = wood.

Fig. 3. Number of fossil saproxylic beetles from 1000 BC to AD 1600 associated withor preferring different tree species. ‘‘Preferred’’ denotes a higher degree ofdependence on a particular tree species, than those considered to be ‘‘associated’’.Beetle data are from six different studies in southern Sweden: Lemdahl (1991),Hellqvist and Lemdahl (1996), Gustavsson et al. (2009), Olsson and Lemdahl (2009,2010) and Hultberg et al. (unpublished data). The ecological data regarding the treespecies associations of different beetle species are from Dahlberg and Stokland(2004) .


3.1.2.4. Fossil beetles. Indications of past tree species compositioncan also be gleaned from remnants of species which weredependent on particular tree species of interest. Fossil beetlescan act as a proxy for tree species occurrence with greater or lesserresolution depending on the host-tree specificity of the beetle spe-cies. Saproxylic beetle species range from being monophagous(specific to a host species), to using either deciduous or coniferoustrees, to being tree species generalists. Paleoentomology has a longtradition in Britain, and a review and re-analysis of 36 paleoento-mological studies from Britain corroborate many of the conclusionsfrom pollen analysis regarding the tree species composition duringthe Holocene (Whitehouse and Smith, 2010). Beetles associatedwith shade-intolerant trees (Quercus, Pinus, Corylus and Betula)were common during the early Holocene, whereas beetles associ-ated with shade-tolerant trees (Tilia and Ulmus) became more com-mon during the mid-Holocene. In general however we found fewentomological studies from northern Europe relevant to the ques-tions in focus here, aside from a number of studies from southernSweden. When these studies are compiled (Fig. 3), a significantproportion of the beetles found within sediments from 1000 BCto AD 1600 are associated with deciduous trees, indicating a moresignificant occurrence of deciduous tree species in the past com-pared to the present.

A study from the 71 ha Siggaboda Reserve in southern Sweden(i.e. the same forests referred to in Fig. 1) provides further evidenceof the potential for using paleoentomological result in conservation(Nilsson et al., 2005 and H. Ljungberg pers. com). Today the sitesupports a large number of saproxylic beetle species, both rareand common, primarily limited to the five ha core area. A criticalconservation question is whether rare species in such small re-serves are destined for extinction (an ‘‘extinction debt’’ sensuHanski and Ovaskainen (2002)), or if they can persist within smallisolated suitable habitats for long periods of time. In a small

hollow, cores were sampled that covered the last 1000 years, with-in which 23 saproxylic fossil beetles species were found that arepresently on the Swedish red-list (Gärdenfors, 2010). These rarebeetles are primarily associated with deciduous trees and coarsewoody debris. Despite the fact that the forest has harbored themost important associated tree species (Quercus or Fagus) for


millennia, no fewer than 16 of the fossil beetles identified are cur-rently extinct from the forest and the surrounding area. Given thesmall size of the reserve, this result suggests that many of the ex-tant beetles in the reserve (and landscape) may be subject to anextinction debt, as many important structures in the reserve havebecome increasingly rare in the landscape during the 20th century,and hence these species may be more sensitive to stochasticextinction events at local scales. However, additional alterationsto forest structure may also have driven the observed shifts in bee-tle assemblages. The identification of the monophagous bark beetleXyleborus cryptographus in the sample cores provides evidence thatmedieval forests harbored large individuals of Populus tremula atthat time, an important tree species and habitat not present in thereserve today and difficult to detect with pollen analysis. The fossilfauna also includes species, such as Gnorimus nobilis, dependent onsun-exposed habitats thus raising the potential for using fossil faunato indicate not only past tree species composition, but to provide in-sights regarding processes associated with altering the light environ-ment of individual trees; such as tree species density, gap dynamics,or larger scale disturbances (see below).

3.1.3. Summary: Potential for deriving estimates of the pastThe evidence from contemporary forests can only be used to a

limited extent to estimate the natural tree species composition inthe region. Tree species composition during the time period inquestion is most commonly revealed by means of pollen analysis,as evidenced by the large number of pollen studies published.The methodology is fairly straightforward, and the skills neededfor identification of common tree taxa in a region are relativelymoderate (Table 1). Undisturbed lakes, wetlands, or bogs are tobe found in much of northern Europe, in particularly in thehemi-boreal and boreal zones. A careful choice of site makes it pos-sible to match pollen source areas to spatial scales of interest toconservation (see examples above). The possibilities for reliablequantitative reconstructions of former species occurrences haveincreased in recent years due to improved methods for relatingpollen abundance to former vegetation. Even so, complete accuracyis difficult to achieve because of different preservation rates

Table 1The potential for quantifying ‘‘natural’’ levels of three important specific structures and prousing data from contemporary forests or paleoecological methods. The estimates range frregarding the Number of published studies, Skill demand and Reliability are provided in r

Potential for deriving estimates of past or nfeatures or processes

Contemporary forests

Paleoecology

Qualitative Quan

Forest composition Species Low Very large Very

Mixedstands

Moderate Large Low

Old/large trees and CWD Large Moderate -large Low

Natural disturbances Forest fires Very low Very large, butrecent past only

Largpast

Large ModLarge Very

Windstorms Moderate Large, recent pastonly

Very

LowInsectoutbreaks

Moderate Large, recent pastonly

Low

Large Mod

between pollen types and sites, and low taxonomic precisionfor some taxa. Macrofossils, beetle fossils, or macroscopic char-coal are generally not suitable for quantitative reconstructions,but are valuable qualitative complements to pollen analysis foridentifying tree species whose pollen is rarely found in the sed-iment. Analysis of plant macrofossils and beetle fossils are timeconsuming, and the taxonomic skill needed for identification isconsiderable (Table 1). These limitations may explain why fewstudies with comprehensive plant macrofossil or paleoentomo-logical studies from the last thousands of years have been con-ducted. Importantly, these latter methods and the insights theycan provide are underutilized from a conservation point ofview.

3.2. Old and large trees and coarse woody debris

3.2.1. Evidence from contemporary forestsProtected forests often contain living and dead trees possessing

a wide diameter distribution and include a considerable proportionof old, large trees and coarse woody debris. (Nilsson et al., 2002;Siitonen et al., 2000). Large protected areas, which are subject todisturbance regimes approximating natural levels of intensityand frequency, may provide relatively accurate indications of thepast occurrence of old/large trees and woody debris. However,few protected areas are large enough to experience a completeset of all natural disturbance processes, or are non-representativeof many natural forest types (Brais et al., 2005), for instance dueto their placement on low productivity soils. Accepting these cave-ats, tree growth, tree mortality and decay rates do operate at rela-tively small spatial scales, thereby highlighting the potential to useat least some protected areas to gain valued insights regarding thenatural occurrence of old/large trees and dead wood (Table 1). Assuch, paleoecological methods may offer a means of supplement-ing and improving upon our capacity to reconstruct the past occur-rence of old and large trees, especially in those circumstances forwhich protected forest areas are not representative, or are other-wise affected by human impacts, and are thereby not reliable rep-resentations of past forest conditions (Fraver et al., 2009).

cesses critical to maintaining or restoring forest biodiversity at stand or reserve scale,om very large/many, large/many, moderate, low/few to very low/few. Our estimateselation to paleoecological methods.

atural Paleoecologicalmethods available

Number of publishedstudies

Relative skillrequirements

titative

large Pollen Many ModeratePlant macrofossils Few LargeFossil beetles Very few Very largeMacro Few LargeBeetles Few Very large

Beetles Few Very LargeLiving & dead wood Few, cover recent

past onlyLarge

Fossil wood None Large

e, but recentonly

Living & dead wood Many, but coverrecent past only

Large

erate Charcoal Moderate-many Lowlow Fossil beetles Very few Very largelow Living & dead wood Many, but cover

recent past onlyLarge

Sand accumulation Few LowLiving & dead wood Many, but cover

recent past onlyLarge

erate Fossil beetles Very few in N Europe Large

Fig. 4. Average ages and diameters of 40 subfossil trees from three different peatbogs and time periods. The oldest wood is from Viss mosse (Svensköp), theyoungest from Åbuamossen (Hästveda), and the intermediate from Hällarydsmos-sen (Stockaryd). The living trees are from three mosses in Ljungby kommun, Allsites are in southernmost Sweden.


3.2.2. Evidence from paleoecology3.2.2.1. Fossil beetles. Our capacity to estimate the past occurrenceof old/large trees and coarse woody debris using paleoecology islimited to a few techniques. Because many saproxylic beetle spe-cies have specific requirements for distinct wood sizes and/or treeages (Dahlberg and Stokland, 2004; Jonsell et al., 1998), their fossilremains can provide inferences regarding the occurrence of pasttree size/age, at least above certain minimum sizes. Though suchdata rarely allow quantification of the past abundance of thesesubstrates, they are useful in their capacity to indicate the previouspresence of these structures in a landscape. For example, severalstudies from the British Isles have documented beetle fossils of adistinctive invertebrate Urwaldtiere (ancient forest animal cf. Palm(1959)) fauna occurring in sediments from the early and mid-Holo-cene. This fauna, which disappeared 5000–3000 years ago, wascharacteristically associated with old and large trees (Bucklandand Dinnin, 1993; Whitehouse, 2006). Interestingly, even in siteswith high abundance of dead wood today, present insect faunasare dominated by beetle species associated with leaf litter ratherthan with dead wood, in marked contrast with the fossil woodlandinsect fauna from the mid-Holocene (Smith et al., 2010). This resultmay be used to argue that dead wood was an even more prominentfeature at these British sites during the mid-Holocene than can bejudged from present conditions. Studies of later time periods arerelatively rare, but from southern Sweden a number of studies ex-ist that cover the time period under focus here. Only occasionallyare saproxylic beetles found restricted to wood >40 cm diameter,but findings of beetles restricted to wood >20 cm diameter arenot uncommon. (Gustavsson et al., 2009; Hellqvist and Lemdahl,1996; Olsson and Lemdahl, 2009). Thus, for this region, fossils ofsuch species would reasonably indicate the past occurrence of logsof this size or greater.

3.2.2.2. Dendrochronology. Dendrochronological studies of living ordry dead wood also provide insights into former tree sizes andages, particularly from areas with climate conducive to slowdecomposition, for which wood can be preserved for long timeperiods. In Europe these conditions are mostly met for P. sylvestrisin the boreal zone. Under ideal conditions wood from this speciescan be preserved from the 13–14th centuries (Niklasson and Gran-ström, 2000) or even earlier (Grudd et al., 2002), though the re-mains are usually much more recent. In northern Fennoscandiawhere the human impact began relatively late, in pre-exploitationforests in the mid 19th century trees >50 cm in diameter and>200 years old were not unusual (Östlund and Linderson, 1995).Most of the studies of fossil wood address historical climate fluctu-ations, and hence tree sizes and ages are rarely reported in detail(Eckstein et al., 2011; Gunnarson et al., 2011; Lageard et al.,2000; Leuschner et al., 2002).

However, preliminary data from an on-going study of P. sylves-tris establishment and die-off phases in southern Swedish ombro-trophic bogs points to the potential application ofdendrochronology to determine tree sizes and ages from fossilwood. Hundreds of fossil Pinus trees from these sites were exam-ined, and many trees >40 cm in diameter (bark excluded) fromthe mid-Holocene were found (Edvardsson et al., 2012a,b), someof which had over 400 annual rings (Fig. 4). These sizes and agesare remarkable in comparison with contemporary Pinus trees onmost bogs in the area, suggesting both a contemporary change to-ward harsher bog-tree growth conditions as well as partial har-vests in the recent past. For example, Pinus trees growing todayat a nearby bog are on average 105 years old, only one individualis older than 200 years, and the average diameter is 16 cm. Thoughnot analyzed, fossils from other taxa, such as Alnus, Betula andQuercus were found from these same strata; these too could besubjects of similar size and age analyses. Significant tree ages were

also recently reported from Lithuania: A Fraxinus fossil from mid-Holocene had 238 rings and the oldest Quercus contained 417 rings(Vitas, 2010).

3.2.2.3. Macroscopic charcoal. Macroscopic charcoal also has poten-tial to provide insights regarding wood sizes in the past, as originaldiameters can be obtained through an estimate of the tree-ringcurvature. For example, in a study of wood charcoal samples fromMesolithic cooking pits in northern Sweden, it was shown thattrunks or branches of Pinus trees larger than 16 cm were preferablyused for fuel (Carcaillet, 2007). According to the authors, such arestrictive pattern of charcoal assemblage suggests that large fuelwood was abundant.

3.2.3. Summary: Potential for deriving estimates of the pastAs above, contemporary protected forests can be used for esti-

mating the natural abundance of old/large trees, as well as theoccurrence of coarse woody debris. Paleoentomological studiesare also quite informative in this regard (Table 1). For example,by using tree-size preferences of particular beetle species, of anumber of studies provide evidence that trees of mid-size or largedimensions were more common at several sites in the past. How-ever, to date detailed paleoentomological studies related to conser-vation are rather few in northern Europe, in particular from the lateHolocene. Dendrochronology applied to living or dry dead woodalso shows promise, as it can be used to estimate both the ageand size of trees; however, the method is limited to regions withquite low wood-decay rates and to recent time periods. In contrast,fossil wood from bogs or wetlands contains great potential thatcurrently has gone largely unexplored. This material could provideages and sizes for a large number of trees under natural conditionsand can thus be useful for both qualitative and quantitative studiesof past conditions regarding these structures relevant to forest con-servation (Table 1). Also, macroscopic charcoal can be used for esti-mations of former tree sizes and perhaps ages, although thismethod too has been underutilized.

3.3. Natural disturbances

3.3.1. Evidence from contemporary forestsForest disturbances alter tree species composition, influence

tree size distributions, alter deadwood availability, and thereby


represent an important regulatory process for the structural featuresof forests. The principle natural disturbances that shape forest eco-systems in northern Europe are wind, insect outbreak, and fire.

Wind disturbance clearly plays a major role in contemporaryforests of the region. The literature from northern Europe focuseson the role of wind in forming small-scale tree-fall gaps, e.g.Gromtsev (2002), but ample evidence exists for wind causingextensive forest damage over quite large areas in some regions.The recent windstorms in northern Europe – for example, Lothar(in the year 1999) and Gudrun (in the year 2005) – attest to theenormous areas that can be affected by such events. It may be ar-gued however that the severity of these recent storms (i.e. impactto the forest) has been elevated because of the wind-susceptibilityof even-aged plantations in the region (Valinger and Fridman,2011) and thus is only weakly indicative of past or natural distur-bance severity.

Dendrochronological evidence of past windstorms may bedrawn from growth releases seen in trees that survive storms (Fra-ver and White, 2005; Lorimer, 1985), in dated impact scars causedby windthrown trees (Storaunet and Rolstad, 2002), and in syn-chronous formation of compression wood across samples (Faustet al., 1994). However, inferences are limited to recent decadesor centuries, as the data source (the wood itself) in most circum-stances rapidly decays with time.

Like wind, insect outbreaks cause significant disturbance tocontemporary forests in northern Europe. Historical records, attimes extending back hundreds of years, clearly implicate insectoutbreaks as a major forest disturbance in this region (Gregowet al., 2008; Nilsson et al., 2004). Among the major insects respon-sible for forest disturbance are the autumnal moth (Epirrita autum-nata) and the bark beetle (Ips typographus). Historical recordsindicate periodic major bark beetle outbreaks over the last250 years (Økland and Björnstad, 2006), the most recent affectingan area of 140,000 km2 in Norway (Økland and Berryman, 2004).A compilation of outbreaks in Sweden during the period 1741–1945 also provides historical evidence for frequent occurrencesof insect damage (Lekander, 1950). Unfortunately, dendrochrono-logical methods do not lend themselves well to detecting historicalbark beetle outbreaks, because of near complete mortality in af-fected trees (i.e., no recovery period to detect). In contrast, dendro-chronological methods may be readily used to detect historicaloutbreaks of defoliating insects, such as the autumnal moth, asoutbreaks are evident as several-year periods of reduced growthin trees that ultimately survive the defoliation (Fraver et al.,2007; Swetnam and Lynch, 1993). Nevertheless, even here resultsare limited to recent decades or perhaps centuries.

Fire is also an important forest disturbance agent in the region.Compared to the detection of wind and insect outbreaks, the meth-ods of dendrochronology, in particular fire-scar dating, lendthemselves quite well to detecting past fires, simply because fire-affected conifer woods are preserved for many centuries (Verrall,1938). The use of fire scars for this purpose yields fire reconstruc-tions with high spatial and temporal precision and as such hasbeen an important research tool in the region for some time(Lehtonen and Huttunen, 1997; Niklasson and Granström, 2000;Zackrisson, 1977). Nevertheless, even fire-scarred wood seldomremains for more than 500 years, thereby limiting inferences aboutthe fire regime prior to human influence. Second, the method reliesprimarily on conifer wood, particularly Pinus, which restricts itsuse mainly to boreal and hemiboreal vegetation zones (Lehtonenand Huttunen, 1997; Lindbladh et al., 2003; Niklasson andGranström, 2000; Niklasson et al., 2010).

3.3.2. Evidence from paleoecology3.3.2.1. Windstorms. Reconstructing the history of windstorm fre-quency and severity during the time period covered in this review

presents a challenge for the methods assessed. Few if any definitivepollen or macrofossil ‘‘signals’’ exist that implicate wind. Instead,we need to rely upon alternative methods, such sand accumulationrates in costal dunes and inland peat bogs, and use these measuresas a proxy for windstorm frequency and intensity (De Jong et al.,2006). Evidence from such studies clearly shows great variabilityin storm intensity or frequency in this region since the mid-Holo-cene (Clemmensen et al., 2007, 2009; De Jong et al., 2006), withpeak periods generally associated with positive phases of the NorthAtlantic oscillation (Sjögren, 2009), as is the case at present. Peaksin sand accumulation are thought to represent both summer(Clemmensen et al., 2009) and winter storms (Sjögren, 2009), alsoconsistent with contemporary patterns. Although these studies donot provide wind speeds or the extent of past storms, they dostrongly suggest that windstorms, presumably strong enough todamage forests, have occurred in northern Europe since at leastthe mid-Holocene.

3.3.2.2. Insect outbreaks. Regarding insect outbreaks, the bestexamples from relevant paleocological studies come from NorthAmerica and are based on the varying abundance of insect headcapsules and/or feces in sediment strata that reveal the history ofparticular insect outbreaks over thousands of years (Bhiry andFilion, 1996; Lavoie et al., 2009; Simard et al., 2006; Waller, 2013).To our knowledge these methods have not been applied in northernEurope, although they clearly show promise as indicated by thestudies conducted thus far. Apart from providing important infor-mation regarding conservation issues, such studies would shed lighton the extent to which recent bark beetle (I. typographus) outbreaksin the region are outside the natural range of variability. In addition,such studies could provide insights regarding the long-term rela-tionship between insect outbreaks, climate variability, andwindstorms.

3.3.2.3. Forest fires. Charcoal particles in sediment can provide evi-dence of past fires, and in the process can be used to derive muchlonger temporal records in comparison to dendrochronology (seecompalation by Carcaillet (2007)). Numerous case studies exem-plify the broad application of charcoal analyses, which frequentlyextends the temporal reach of investigations to thousands of years.This long-term perspective reveals recurring fires, although typi-cally with marked spatial and/or temporal variability (Ohlsonet al., 2006; Pitkanen et al., 2002; Tryterud, 2003). Yet few suchstudies have linked past fire history to the presence of particularspecies or species groups of conservation concern. One exceptionis a study from a site in southern Sweden that currently supportsa very rich assemblage of red-listed saproxylic species (Lindbladhet al., 2003). The authors conclude that frequent past fires, as de-tected from sediment charcoal, kept the site sufficiently open tosupport a large number of saproxylic beetles dependent either onfire or open post-fire conditions.

It is important to note that the relationship between sedimentcharcoal abundance and fire history is rather complex (Carcaillet,2007). Based on particle transport models, Clark (1988) proposedthat micro-charcoal (<100 lm) provides information on regionalfires, whereas macro-charcoal (>200 lm), which is not likely to betransported more than 1000 m from the source, provides informa-tion on local fires. Clark’s (1988) findings have been corroboratedby a number of empirical studies (e.g. Macdonald et al., 1991; Ohlsonand Tryterud, 2000). However, a direct one-to-one temporal rela-tionship between fire and sediment charcoal peaks has been difficultto obtain. For example, a comparison between a fire-scar record anddated macro-charcoal peaks found that many, but not all, fires re-corded as scars correlated to distinct charcoal peaks (Higuera et al.,2005). In particular, low-intensity fires often do not leave clear evi-dence in the form of sediment charcoal (Niklasson et al., 2002). But


methodological tools for understanding charcoal spread and accu-mulation continue to improve (Gavin et al., 2006; Higuera et al.,2009; Lynch et al., 2004). Currently, macroscopic charcoal analysisrepresents a powerful tool for reconstructing millennial-scale firehistories, although its ability to detect the exact timing and extentof individual fires remains limited.

Several paleoecological studies highlight the relationship be-tween past fires and assemblages of pyrophilous beetles of conser-vation importance. Working in southern Sweden, Olsson andLemdahl (2009, 2010) found several pyrophilous species in sedi-ments from the last 3000 years, their presence correlating wellwith the abundance of macroscopic sediment charcoal. Workingin England, Whitehouse (2000) reported many pyrophilous insects,several now extinct, associated with burned Pinus and Betula woodfrom over 1500 years ago. These results indicate that fires had beencommon in the bogs where the study was conducted, and suggestthat the importance of fire-associated disturbance processes insuch landscapes should be given more attention.

3.3.3. Summary: Potential for deriving estimates of the pastDendrochronological methods are well suited for documenting

the history of various disturbance agents in contemporary forests.However, the methods typically do not allow inferences to bemade more than a few hundred years before present, with firescars the only possible exception. Moreover, few if any reservesin northern Europe are large enough to fully support natural dis-turbance regimes (Hunter et al., 1988), and contemporary distur-bance processes may be dominated by human impacts such thatdetails of the past disturbances are relatively unknown. Thus, char-acterizing natural disturbance regimes during the time period ad-dressed herein remains quite challenging. For example,determining the role of windstorms during this period relies onsand accumulation rates in dunes and bogs as a proxy for pastwindstorm frequency; however, this method provides poor spatialand temporal resolution, and it reveals little about the intensity(wind speed) of particular storms. Similarly, insect outbreaks cre-ate a challenge, although methods based on the varying abundanceof insect head capsules and/or feces in sediment strata (currentlynot undertaken in northern Europe to the best of our knowledge)clearly show promise in detecting the long-term history of partic-ular insect population sizes. In contrast, the methods for recon-structing historical forest fire sizes and frequencies, at least forthe last 500 years, are well developed (Table 1), which may in partexplain the emphasis on fire in studies of past disturbance in thisregion. Recent work suggests that its importance as a natural dis-turbance agent may have been over-emphasized (Kuuluvainenand Aakala, 2011; Pitkanen et al., 2003; Wallenius et al., 2002),and that it has likely overshadowed the importance of otheragents. Macro-charcoal analysis extends many thousands of yearsback in time; however, spatial and temporal resolution is ratherweak, although the methodology is constantly improving. The pos-sibility for reconstructing long-term fire histories beyond the onsetof significant human influence increases when both macro-char-coal and tree-ring data are available from the same site (Higueraet al., 2011; Lindbladh et al., 2003). The two methodologies differin accessibility, as dendrochronology methods are both training-and time-intensive, whereas charcoal analysis is less so. Paleoento-mology and pollen analyses addressing past fire do not providequantitative estimates of past fires per se, but can serve as valuablecomplementary approaches for use with other techniques.

4. Conclusions

Forest ecologists and conservation biologists often require abetter understanding of past norms and variations in forest compo-

sition, structure and disturbance regimes, which help to determinethe present ecological requirements of extant forest-associatedspecies. Contemporary forests are limited in their ability to esti-mate the natural occurrence of many of these aspects. Here wehave shown the extent to which paleoecology has the capacity tofill some of these knowledge gaps, from the spatial scale of individ-ual trees – clarifying specifics on age, size, and disturbance history– to the species composition of past forests, with a temporal reso-lution spanning years to millennia. We emphasize that robustpaleoecological data are available for quantifying past tree speciescomposition and fire disturbance, with many qualitative insightsavailable in regard to old/large trees and coarse woody debris,but less data on windstorms and insect outbreaks. However, therange of potential insights available from paleoecology, and themeans by which such insights can be provided could be improved.For example, we regard paleoentomology as perhaps the mostunderutilized source of information available to forest ecologistsand conservation biologists. In addition to providing much neededinformation on the saproxylic beetle species themselves (manyfound in the fossil record are now red-listed), paleoentomologymethods enable the reconstruction of former environmental condi-tions – rare tree species, wood of different sizes, and historical in-sect outbreak – otherwise unavailable. Similarly, the study of fossilwood and its corresponding value for gauging the sizes and ages ofpast trees remains largely unexplored, and its clear link to conser-vation science has not yet been appreciated.

Paleoecology is not, however, a panacea. As with any ap-proach, it possesses limitations that restrict our ability to recon-struct particular past ecological aspects to a desired spatial andtemporal resolution. Furthermore, past conditions may no longerbe realistic environmental benchmarks, due to the loss of spe-cies, as well as changing climatic conditions, which act as barri-ers to the recovery of past natural conditions. Nevertheless, weemphasize that despite these limitations, paleoecological meth-ods show great – and previously underutilized – potential forproviding basic historical and biological information on forest-dwelling species, thus guiding decision-making processes inconservation practice. To date, the majority of potentially conser-vation-relevant paleoecological studies have described historicalforest conditions in broad terms and for large spatial scales,addressing former climate, land-use, and landscape develop-ments, typically in the absence of specific conservation context.The studies that do link the paleoecological record to conserva-tion issues often limit this connection to coarse-scale discussionsof ‘‘naturalness’’ or ‘‘natural variability’’ (Birks, 1996; Willis andBirks, 2006), or when focusing on tree species composition(Björse and Bradshaw, 1998) or floristic diversity (Berglundet al., 2008), often do so primarily in a landscape-level context.Even fewer examples exist of detailed paleoecological data ap-plied to local-scale conservation planning or in setting operativerestoration targets at local scales (Bengtsson, 1999; Lindbladhet al., 2007). Using examples presented herein, we hope to havedemonstrated the large promise of paleoecological studies whenapplied to several of the most pressing forest conservation issuesoperating at stand and reserve scale in northern Europe.

Although forest ecologists and conservation biologists clearlyrecognize the importance of forest history, we suggest there ismuch room for improved integration of paleoecology and conser-vation science, particularly considering the rapidly-advancingtechniques in the paleoecological sciences. In the absence of betterintegration there is a risk forest ecologists and conservation biolo-gists will unnecessarily act or advise while incorrectly presumingthat certain useful knowledge is not available when it could be,and likewise, the palecological sciences could overlook the poten-tial for applying their research outcomes to the pressing environ-mental concerns of today. Thus we advocate for these respective


fields to actively embrace interdisciplinary research opportunitieswhen they arise. Our hope is that this review may provide someguidance and inspiration for future studies within the interdisci-plinary fields of paleoecology and conservation science.

Acknowledgements

We are grateful to Jörg Brunet for comments on the manuscriptand to Håkan Ljungberg for kindly sharing some paleoentomolog-ical data. ML is grateful to Bronson Bullock and Gary Blake atDepartment of Forestry and Environmental Resources, North Caro-lina State University, for hosting during a productive sabbatical.

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