Decomposing the mid‐Holocene Tsuga decline in eastern North America

Abstract

Abstract. The mid-Holocene decline of Tsuga canadensis (hereafter Tsuga) populations across eastern North America is widely perceived as a synchronous event, driven by pests/ pathogens, rapid climate change, or both. Pattern identification and causal attribution are hampered by low stratigraphic density of pollen-sampling and radiometric dates at most sites, and by absence of highly resolved, paired pollen and paleoclimate records from single sediment cores, where chronological order of climatic and vegetational changes can be assessed. We present an intensely sampled (contiguous 1-cm intervals) record of pollen and water table depth (inferred from testate amoebae) from a single core spanning the Tsuga decline at Irwin Smith Bog in Lower Michigan, with high-precision chronology. We also present an intensively sampled pollen record from Tower Lake in Upper Michigan. Both sites show high-magnitude fluctuations in Tsuga pollen percentages during the pre-decline maximum. The terminal decline is dated at both sites ca. 5000 cal yr BP, some 400 years later than estimates from other sites and data compilations. The terminal Tsuga decline was evidently heterochronous across its range. A transient decline ca. 5350 cal yr BP at both sites may correspond to the terminal decline at other sites in eastern North America. At Irwin Smith Bog, the terminal Tsuga decline preceded an abrupt and persistent decline in water table depths by ;200 years, suggesting the decline was not directly driven by abrupt climate change. The Tsuga decline may best be viewed as comprising at least three phases: a long-duration predecline maximum with high-magnitude and high-frequency fluctuations, followed by a terminal decline at individual sites, followed in turn by two millennia of persistently low Tsuga populations. These phases may not be causally linked, and may represent dynamics taking place at multiple temporal and spatial scales. Further progress toward understanding the phenomenon requires an expanded network of high-resolution pollen and paleoclimate chronologies.

Community ecology in a changing environment: Perspectives from the Quaternary

“…Those historical processes, although they involve both Eltonian and Grinnellian niche attributes, are effectively neutral because the ecological outcomes years, decades, or centuries later cannot be predicted from niche properties and environment alone. Recent paleoecological studies provide many examples (35,84,85).…”

“…Specific critical transitions can be targeted for intensive study, based on various criteria (e.g., knowledge of natural history of taxa, existence of independent paleoclimatic records, precision of paleoecological records, availability of multiple paleoecological sites for replication or pattern analysis, potential significance of observed patterns). The rapid increase or decline of a dominant species or the disappearance of a community, for example, is of obvious interest in conservation context and may be driven by rapid environmental change, cross-scale interactions, or both (23,84,92). Intensive, integrated study of a carefully selected array of paleoecological case studies would test fundamental theory and indicate the extent to which community turnover follows general rules.…”

Looking forward through the past: identification of 50 priority research questions in palaeoecology

“…Additional information could be obtained using process-based models to infer population dynamics [Q31, 44]. If the hemlock decline was driven by climate, then an additional question would be why this species responded more sensitively than others [Q3], or whether it was the result of cross-scale interactions between climate and the pathogen, or the interactions between multiple stressors (Booth et al 2012) [Q35, 39]. Thorough testing of the problem also requires integrating multiple palaeoecological sites [Q39].…”

Moisture and temperature changes associated with the mid-Holocene Tsuga decline in the northeastern United States

“…Evidence for regional to hemispheric climate change at ca 5.5 ka now includes reduced lake levels and other evidence of drought from Ontario to New Hampshire (Yu et al, 1997;Haas and McAndrews, 1999;Lavoie and Richard, 2000;Newby et al, 2000Newby et al, , 2009Newby et al, , 2011Shuman et al, 2001Shuman et al, , 2004Shuman et al, , 2005Shuman et al, , 2009Muller et al, 2003;Booth et al, 2012), changes in atmospheric circulation (Yu et al, 1997;Kirby et al, 2002), and shifts in sea-surface temperatures (SSTs) (deMenocal et al, 2000;Sachs, 2007). Pollen records from areas near the range limits of hemlock also indicate climate change (Calcote, 2003;Foster et al, 2006), and importantly, show that hemlock did not change independently of other taxa.…”