European Tree Dynamics and Invasions during the Quaternary. Birks, H. J. B. and Tinner, W. In Krumm, F. and V́ıtková, L., editors, Introduced Tree Species in European Forests: Opportunities and Challenges, pages 22–43. European Forest Institute.
European Tree Dynamics and Invasions during the Quaternary [link]Paper  abstract   bibtex   
The abundance and distribution of terrestrial organisms vary in space and time over a wide range of scales from a single 25x25 m plot to whole continents and from days to millennia. Trees are no exception but the relevant temporal and spatial scales are naturally different from those for a small annual forest herb because of the long life-span and large size of trees. [Excerpt: Introduction] European trees have varied in their abundance and geographical distribution over the last 5 million years or more in response to major global climate changes (Birks and Tinner 2016). They have also undergone similarly striking changes due to the alternating glacial- interglacial cycles within the Quaternary period (last 2.6 million years). Tree dynamics have also been greatly modified in the last 5 000-6 000 years by human activities in the current Holocene epoch (plus the 'Anthropocene') in which we live. Documenting and understanding these dynamics and changes provide us with ecological 'lessons from the past' about tree dynamics (including invasions) and responses to environmental changes in the past (Birks and Tinner 2016). [\n] The problem with studying tree dynamics is that many trees are long-lived and their lifespans greatly exceed those of ecologists, foresters, and woodland historians. As we cannot directly record tree dynamics in space and time at the relevant scales, we need to reconstruct past tree dynamics indirectly using the palaeobotanical record. [\n] [...] [Lessons from past tree dynamics and invasions] We see that European forests have being changing since the Palaeogene with progressive extinction from Europe of trees of the Arcto-Tertiary geoflora in the Pliocene and early to mid-Quaternary (van der Hammen et al. 1971, Willis and McElwain 2014, Birks and Tinner 2016). The repeated glacial-interglacial cycles (Birks 1986, Lang 1994) that are so characteristic of the Quaternary (Pleistocene, Holocene) have resulted in a continuous dynamic of tree survival in refugia during glacial stages and rapid spread and population expansion and unique tree combinations in the different interglacial stages (Iversen 1958, Birks 1986). Human impact with forest clearance and agriculture are unique to the Holocene, the so-called Homo sapiens phase (Birks 1986). What emerges from the many palaeoecological studies (mainly based on pollen analysis but increasingly strengthened by macrofossil studies) is continual change at time scales of millions, thousands, and hundreds of years (Birks and Tinner 2016). Forests develop when certain plant species become abundant and dominant at specific areas under particular environmental conditions (Jackson 2006). These forests may change gradually or abruptly when the dominant trees are replaced by other trees, usually in response to extrinsic environmental change (Williams et al. 2011) or major disturbances (e.g. forest pathogens, fire, human activity) (Birks 1986, Tinner et al. 1999). Few major terrestrial forest systems in Europe have existed for more than 10 000 years and most are considerably younger, some developing only within the last few centuries (Birks 1993 Bradshaw et al. 2015). Future forest systems are thus inevitably uncertain and historically contingent (Jackson 2006). Given the richness of forest-tree responses during the Quaternary with all its climatic shifts (van der Hammen et al. 1971, Birks 1986, Bennett et al. 1991, Lang 1994), many novel future responses, outcomes, and ecological surprises are possible or even inevitable (Jackson and Williams 2004, Veloz et al. 2012, Jackson 2013, Williams et al. 2013, Reu et al. 2014). [\n] Assessing whether current forest systems are sustainable in the face of future global change can be aided by considering the range of environmental variation that these systems have experienced in the past and by reconstructing the environmental conditions under which these systems were initiated and developed (Jackson 2006). A narrow time window (e.g. 200-300 years) may underestimate the range of variation within which a forest system is sustainable, and this underestimates the risk of major disruption of the system by environmental change (Jackson 2006). Longer time periods (e.g. 1 000-2 000 years) inevitably increase the inherent range of natural variation in the Earth system (Jackson 2006). Most systems disappear, as shown by the palaeoecological record, when the time window extends to 10 000-15 000 years due to major changes in the Earth's climate system resulting from orbital forcing (Willis and McElwain 2014). Importantly the palaeoecological record can pinpoint the origination time of particular forest systems (e.g. Birks 1993, Bradshaw and Lindbladh 2005) and can, by inference in some cases, indicate the specific extrinsic or intrinsic changes that led to the development of the system and the range of environmental variation under which the system maintained itself in the past (Jackson 2006). Such information, only obtainable from the palaeoecological record, can thus help to identify critical environmental thresholds beyond which specific modern forest systems can no longer be sustained (Willis and Birks 2006, Birks 2012, Birks and Tinner 2016). [\n] The palaeoecological record for European forests provides several additional insights and important lessons from the past (Jackson 2006, Birks and Tinner 2016). First, all existing forest systems have a finite time limit to growing in the places where they occur and all have been preceded by ecosystems (not necessarily forest systems) that differ in composition, structure, plant-functional traits, and ecosystem properties (Jackson 2006). Second, similar forest ecosystems, as defined by their dominant species have developed in different places and at different times (Birks 1986, Jackson 2006). Third, similar systems had different antecedents in different places. Thus apparently similar systems may have different properties owing to different histories and to legacy effects of different antecedents (Jackson 2006). Fourth, several different systems arose at approximately the same time in different places, presumably in response to regional- or global-scale shifts in atmospheric circulation, leading to major reconfigurations of climatic variables and widespread synchronous transformation of systems (Jackson 2006, Giesecke et al. 2011, Seddon et al. 2015). This pattern is not, however, universal but rapid regime-shifts in the Earth system may be accompanied by widespread ecosystem changes in diverse regions (Jackson 2006, Williams et al. 2011). Fifth, forest ecosystems of today have no long history even in the time span of the Holocene and forest systems existed in the past that have no modern counterparts ('analogues') (Jackson and Williams 2004, Jackson 2013). Examples (Birks and Tinner 2016) include the former abundance of Corylus avellana in the early Holocene of much of north-west Europe (Huntley and Birks 1983, Birks 1986) and the importance of Abies alba in southern Europe in the mid-Holocene (Tinner 2013, di Pasquale et al. 2014). [\n] Palaeoecologists look to the past whereas global change ecologists look to the future, but both rely solely on their understanding of modern ecosystems and ecological processes as a basis for past reconstructions or future predictions. Palaeoecologists apply the concept that ” the present is the key to the past” whereas global change ecologists project this forward and use ” the present is the key to the future”. But the present is only one time-slice in the last 11 700 years since the last glacial stage (Birks and Tinner 2016). A critical question is thus are today's populations, ecosystems, and climate representative of tree and ecosystem-climate relationships under past or future climate change? Are they robust to climate conditions beyond modern states? Are species ranges in equilibrium with environmental factors such as climate (Svenning and Sandel 2013) or have their realised environmental niches been significantly altered by climate-change or millennial- long land-use activities (Jackson and Overpeck 2000)? These palaeoecological questions suggest that it is inadequate to project future ecosystem conditions solely on the basis of present-day observations (Willis and Birks 2006). A promising novel approach is to combine dynamic eco-physiological models with palaeoecological evidence to produce palaeo-validated scenarios of future vegetation dynamics under global-change conditions (Henne et al. 2015, Birks and Tinner 2016, Ruosch et al. 2016). [\n] The dynamic nature and the often non-analogue character of European forests in the time-span of the Holocene or even the last 5 000 years raises critical questions about appropriate targets ('baselines') for restoration efforts (Birks and Tinner 2016). Palaeoecological studies have revealed major human imprints on many, if not all, systems in Europe (Birks 1986, Tinner and Ammann 2005) and have shown that secular climate change has kept many targets moving at centennial to millennial time scales (Birks 1986, Jackson and Hobbs 2009, Willis and McElwain 2014). Ongoing rapid environmental changes may almost certainly ensure that many historical restoration targets will be unsustainable in the coming decades (Henne et al. 2015). Restoration efforts should aim to conserve or restore historical systems if possible, but more importantly, to design, create, and manage emerging novel ecosystems to ensure high biodiversity and a supply of ecosystem goods and services in the future (Jackson and Hobbs 2009, Birks and Tinner 2016). [\n] The palaeoecological record of European tree populations and forest history is a rich and largely untapped record of ecological and population dynamics and tree invasions over a wide range of time-scales (Birks and Tinner 2016). As Karl Flessa and Steve Jackson (2005) discuss, this record is a long-term ecological observatory where ecological responses to past climate change and the ecological legacies of societal activities can be deciphered, quantified, and used as a key to ” understanding the biotic effects of future environmental change” (Flessa and Jackson 2005). There is very much still to be learnt about past European forests and tree population dynamics and invasions using the vast amount of high quality palaeoecological data available in Europe (Huntley and Birks 1983, Birks 1986, Lang 1994, Tinner and Lotter 2001, Tinner et al. 2005, 2013, Giesecke et al. 2014, Birks and Tinner 2016). Palaeoecology and modern ecology need to work more closely together to enhance our understanding of European tree populations in the past, at present, and in the future. Much remains to be learnt from palaeoecology's 'lessons from the past'.
@incollection{birksEuropeanTreeDynamics2016,
  title = {European Tree Dynamics and Invasions during the {{Quaternary}}},
  booktitle = {Introduced Tree Species in {{European}} Forests: Opportunities and Challenges},
  author = {Birks, H. J. B. and Tinner, Willy},
  editor = {Krumm, Frank and V́ıtková, Lucie},
  date = {2016},
  pages = {22--43},
  publisher = {{European Forest Institute}},
  url = {http://mfkp.org/INRMM/article/14216874},
  abstract = {The abundance and distribution of terrestrial organisms vary in space and time over a wide range of scales from a single 25x25 m plot to whole continents and from days to millennia. Trees are no exception but the relevant temporal and spatial scales are naturally different from those for a small annual forest herb because of the long life-span and large size of trees.

[Excerpt: Introduction] European trees have varied in their abundance and geographical distribution over the last 5 million years or more in response to major global climate changes (Birks and Tinner 2016). They have also undergone similarly striking changes due to the alternating glacial- interglacial cycles within the Quaternary period (last 2.6 million years). Tree dynamics have also been greatly modified in the last 5 000-6 000 years by human activities in the current Holocene epoch (plus the 'Anthropocene') in which we live. Documenting and understanding these dynamics and changes provide us with ecological 'lessons from the past' about tree dynamics (including invasions) and responses to environmental changes in the past (Birks and Tinner 2016).

[\textbackslash n] The problem with studying tree dynamics is that many trees are long-lived and their lifespans greatly exceed those of ecologists, foresters, and woodland historians. As we cannot directly record tree dynamics in space and time at the relevant scales, we need to reconstruct past tree dynamics indirectly using the palaeobotanical record.

[\textbackslash n] [...]

[Lessons from past tree dynamics and invasions] We see that European forests have being changing since the Palaeogene with progressive extinction from Europe of trees of the Arcto-Tertiary geoflora in the Pliocene and early to mid-Quaternary (van der Hammen et al. 1971, Willis and McElwain 2014, Birks and Tinner 2016). The repeated glacial-interglacial cycles (Birks 1986, Lang 1994) that are so characteristic of the Quaternary (Pleistocene, Holocene) have resulted in a continuous dynamic of tree survival in refugia during glacial stages and rapid spread and population expansion and unique tree combinations in the different interglacial stages (Iversen 1958, Birks 1986). Human impact with forest clearance and agriculture are unique to the Holocene, the so-called Homo sapiens phase (Birks 1986). What emerges from the many palaeoecological studies (mainly based on pollen analysis but increasingly strengthened by macrofossil studies) is continual change at time scales of millions, thousands, and hundreds of years (Birks and Tinner 2016). Forests develop when certain plant species become abundant and dominant at specific areas under particular environmental conditions (Jackson 2006). These forests may change gradually or abruptly when the dominant trees are replaced by other trees, usually in response to extrinsic environmental change (Williams et al. 2011) or major disturbances (e.g. forest pathogens, fire, human activity) (Birks 1986, Tinner et al. 1999). Few major terrestrial forest systems in Europe have existed for more than 10 000 years and most are considerably younger, some developing only within the last few centuries (Birks 1993 Bradshaw et al. 2015). Future forest systems are thus inevitably uncertain and historically contingent (Jackson 2006). Given the richness of forest-tree responses during the Quaternary with all its climatic shifts (van der Hammen et al. 1971, Birks 1986, Bennett et al. 1991, Lang 1994), many novel future responses, outcomes, and ecological surprises are possible or even inevitable (Jackson and Williams 2004, Veloz et al. 2012, Jackson 2013, Williams et al. 2013, Reu et al. 2014).

[\textbackslash n] Assessing whether current forest systems are sustainable in the face of future global change can be aided by considering the range of environmental variation that these systems have experienced in the past and by reconstructing the environmental conditions under which these systems were initiated and developed (Jackson 2006). A narrow time window (e.g. 200-300 years) may underestimate the range of variation within which a forest system is sustainable, and this underestimates the risk of major disruption of the system by environmental change (Jackson 2006). Longer time periods (e.g. 1 000-2 000 years) inevitably increase the inherent range of natural variation in the Earth system (Jackson 2006). Most systems disappear, as shown by the palaeoecological record, when the time window extends to 10 000-15 000 years due to major changes in the Earth's climate system resulting from orbital forcing (Willis and McElwain 2014). Importantly the palaeoecological record can pinpoint the origination time of particular forest systems (e.g. Birks 1993, Bradshaw and Lindbladh 2005) and can, by inference in some cases, indicate the specific extrinsic or intrinsic changes that led to the development of the system and the range of environmental variation under which the system maintained itself in the past (Jackson 2006). Such information, only obtainable from the palaeoecological record, can thus help to identify critical environmental thresholds beyond which specific modern forest systems can no longer be sustained (Willis and Birks 2006, Birks 2012, Birks and Tinner 2016).

[\textbackslash n] The palaeoecological record for European forests provides several additional insights and important lessons from the past (Jackson 2006, Birks and Tinner 2016). First, all existing forest systems have a finite time limit to growing in the places where they occur and all have been preceded by ecosystems (not necessarily forest systems) that differ in composition, structure, plant-functional traits, and ecosystem properties (Jackson 2006). Second, similar forest ecosystems, as defined by their dominant species have developed in different places and at different times (Birks 1986, Jackson 2006). Third, similar systems had different antecedents in different places. Thus apparently similar systems may have different properties owing to different histories and to legacy effects of different antecedents (Jackson 2006). Fourth, several different systems arose at approximately the same time in different places, presumably in response to regional- or global-scale shifts in atmospheric circulation, leading to major reconfigurations of climatic variables and widespread synchronous transformation of systems (Jackson 2006, Giesecke et al. 2011, Seddon et al. 2015). This pattern is not, however, universal but rapid regime-shifts in the Earth system may be accompanied by widespread ecosystem changes in diverse regions (Jackson 2006, Williams et al. 2011). Fifth, forest ecosystems of today have no long history even in the time span of the Holocene and forest systems existed in the past that have no modern counterparts ('analogues') (Jackson and Williams 2004, Jackson 2013). Examples (Birks and Tinner 2016) include the former abundance of Corylus avellana in the early Holocene of much of north-west Europe (Huntley and Birks 1983, Birks 1986) and the importance of Abies alba in southern Europe in the mid-Holocene (Tinner 2013, di Pasquale et al. 2014).

[\textbackslash n] Palaeoecologists look to the past whereas global change ecologists look to the future, but both rely solely on their understanding of modern ecosystems and ecological processes as a basis for past reconstructions or future predictions. Palaeoecologists apply the concept that ” the present is the key to the past” whereas global change ecologists project this forward and use ” the present is the key to the future”. But the present is only one time-slice in the last 11 700 years since the last glacial stage (Birks and Tinner 2016). A critical question is thus are today's populations, ecosystems, and climate representative of tree and ecosystem-climate relationships under past or future climate change? Are they robust to climate conditions beyond modern states? Are species ranges in equilibrium with environmental factors such as climate (Svenning and Sandel 2013) or have their realised environmental niches been significantly altered by climate-change or millennial- long land-use activities (Jackson and Overpeck 2000)? These palaeoecological questions suggest that it is inadequate to project future ecosystem conditions solely on the basis of present-day observations (Willis and Birks 2006). A promising novel approach is to combine dynamic eco-physiological models with palaeoecological evidence to produce palaeo-validated scenarios of future vegetation dynamics under global-change conditions (Henne et al. 2015, Birks and Tinner 2016, Ruosch et al. 2016).

[\textbackslash n] The dynamic nature and the often non-analogue character of European forests in the time-span of the Holocene or even the last 5 000 years raises critical questions about appropriate targets ('baselines') for restoration efforts (Birks and Tinner 2016). Palaeoecological studies have revealed major human imprints on many, if not all, systems in Europe (Birks 1986, Tinner and Ammann 2005) and have shown that secular climate change has kept many targets moving at centennial to millennial time scales (Birks 1986, Jackson and Hobbs 2009, Willis and McElwain 2014). Ongoing rapid environmental changes may almost certainly ensure that many historical restoration targets will be unsustainable in the coming decades (Henne et al. 2015). Restoration efforts should aim to conserve or restore historical systems if possible, but more importantly, to design, create, and manage emerging novel ecosystems to ensure high biodiversity and a supply of ecosystem goods and services in the future (Jackson and Hobbs 2009, Birks and Tinner 2016).

[\textbackslash n] The palaeoecological record of European tree populations and forest history is a rich and largely untapped record of ecological and population dynamics and tree invasions over a wide range of time-scales (Birks and Tinner 2016). As Karl Flessa and Steve Jackson (2005) discuss, this record is a long-term ecological observatory where ecological responses to past climate change and the ecological legacies of societal activities can be deciphered, quantified, and used as a key to ” understanding the biotic effects of future environmental change” (Flessa and Jackson 2005). There is very much still to be learnt about past European forests and tree population dynamics and invasions using the vast amount of high quality palaeoecological data available in Europe (Huntley and Birks 1983, Birks 1986, Lang 1994, Tinner and Lotter 2001, Tinner et al. 2005, 2013, Giesecke et al. 2014, Birks and Tinner 2016). Palaeoecology and modern ecology need to work more closely together to enhance our understanding of European tree populations in the past, at present, and in the future. Much remains to be learnt from palaeoecology's 'lessons from the past'.},
  isbn = {978-952-5980-32-5},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-14216874,europe,forest-resources,invasive-species,paleoecology,quaternary}
}
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