Abstract
Our overall understanding of long-term climate dynamics is largely based on proxy data generated from archives such as ice cores, ocean sediments, tree rings, speleothems, and corals, whereas reconstructions of long-term changes in vegetation and associated climate during the Holocene are largely based on paleoecological records from peat and lake sequences, primarily pollen and plant macrofossil data. However, since no proxy can provide a complete picture of the past, it is important to integrate different types of data, and to use methods that can support the paleoecological and paleoclimatic interpretations. Here we review how tree-ring data and dendrochronological approaches can be integrated with stratigraphic records to provide complementary paleoecological and paleoclimatic information. The review includes multiproxy studies in which dendrochronological data have been either compared or integrated with stratigraphic records, mainly pollen records, with the aim to contribute to a better understanding of long-term ecosystem and climate dynamics. We mainly focus on studies from northwest Europe in which tree-ring data and at least one type of paleoecological proxy record from the same site or area has been either compared or integrated. We find that integration of dendrochronological data and paleoecological records from peat and lake sequences is a powerful but underutilized approach to reconstruct long-term ecological and climatic changes. One likely reason for its limited use is the contrasting character of the two categories of data, including their different time resolution and occurrence, making them difficult to integrate. For example, subfossil wood providing annual dendrochronological data usually only occurs sporadically in peat and lake sediments, and the presence/absence of the trees are normally expected to be recorded in the pollen data with multi-decadal or coarser resolution. Therefore, we also discuss methods to compare and integrate dendrochronological and stratigraphic records, as well as the relevant paleoecological and paleoclimatic information provided by dendrochronology, pollen, and peat stratigraphy, with the aim to facilitate new multi-proxy initiatives that will contribute to a better understanding of long-term ecosystem and climate dynamics and thereby a firmer basis for future nature conservation initiatives.
Highlights
To distinguish natural long-term climate variability and ecosystem dynamics from anthropogenic effects, reconstructions of paleoecological and paleoclimatic conditions based on both qualitative and quantitative proxy records from the time before industrialization are required (Jansen et al, 2007; Marcott et al, 2013)
We focus on available scientific literature on paleoclimatic or paleoecological studies integrating dendrochronology and stratigraphic proxy data such as pollen as a minimum, but preferably including macrofossil analysis and further analysis of the stratigraphic records (Figure 1)
The first category (“dates as data”) consist of records of sample replication, i.e., the number of overlapping trees from which a tree-ring chronology has been developed (Figures 4A,B). In this form, the dendrochronological data is used to quantify the number of dated tree-ring samples per annum, which can be used to illustrate depositional histories of subfossil trees through time (Gunnarson et al, 2003; Helama et al, 2005, 2010a, 2017a, 2020; Edvardsson et al, 2016a). Such histories can in turn be linked to past climatic and environmental changes that affected the density of tree populations, or their presence/absence, as well as deposition and preservation of trees
Summary
To distinguish natural long-term climate variability and ecosystem dynamics from anthropogenic effects, reconstructions of paleoecological and paleoclimatic conditions based on both qualitative and quantitative proxy records from the time before industrialization are required (Jansen et al, 2007; Marcott et al, 2013). Many archives consist of organic material, which under oxygenpoor (i.e., usually water saturated) or dry conditions can be preserved for thousands of years, and contain paleoecological records in the form of pollen and other microfossils In such contexts, often in water-saturated wetlands, lake sediments or deserts, wood remains referred to as subfossil trees can be found. To reach even further back in time, dendrochronological studies using subfossil trees have proved to be important, allowing precise and long-term studies of climate dynamics and environmental changes during the Holocene (Eronen et al, 2002; Leuschner et al, 2002; Helama et al, 2008; Edvardsson et al, 2016a). Records from subfossil trees are not always straightforward to develop or interpret in terms of past climate, especially since deposition, preservation and patterns of tree growth may have changed over time
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