Developing millennial tree ring chronologies in the fire‐prone North American boreal forest

Abstract

International audienceA denser global network of millennial tree ring chronologies is needed to verify whether the warming of the last century is anomalously rapid or of large amplitude in the context of the last millennium. The North American boreal forest in particular has been poorly represented in long climatic reconstructions based on tree rings, because of short tree longevity, as well as frequent and severe wildfires. In this study, we exhaustively sampled tree remains in the littoral zone of two lakes and partially sampled seven additional lakes in the northern boreal forest of eastern Canada to verify if highly replicated millennial tree ring chronologies could be developed. In total, 989 black spruce [Picea mariana (Mill.) BSP.] tree remains were sampled, of which 529 could be crossdated, providing a master chronology spanning the AD 676–1991 time period. Radiocarbon dating of a floating chronology indicates that maximum residence time of tree remains outside of sediments is at least 1500 years. Past fires halted or reduced wood inputs at least once at all but one site and thus influenced the replication of local chronologies. However, fire effects can be minimized using appropriate site selection criteria (old-growth forest on the leeward shore, sharp deepening of the littoral zone, burial of tree remains by fine sediments), such that it would be possible to develop a network of several highly and evenly replicated multi-century local chronologies. These tree ring chronologies would have desirable properties for extracting low-frequency tree growth trends and for reconstructing forest disturbance histories

Volcano-induced regime shifts in millennial tree-ring chronologies from northeastern North America

“…The RCS method preserves long-term climate trends in tree-ring chronologies built with shortlived species, but requires high replication of trees belonging to a homogeneous population not disturbed by external factors (40). The selected sites were all characterized by an old-growth riparian forest on the side of the lake protected from dominant winds, an abrupt forest−lake transition, large stocks of subfossil trees in the littoral zone, and a well-documented low fire recurrence (23,41). This allowed the development of an exceptional network of climate-sensitive tree-ring data comprising six local chronologies in the same region (one per lake), each including from 75 to 586 subfossil trees and spanning from 1,238 to 1,440 y ( Table 1).…”

“…Most of these intervals were asynchronous among the lakes and were caused by wildfires that temporarily reduced the input of tree remains into the littoral zone (23,41). We identified the nonrobust time intervals using the Rbar statistic (mean correlation between pairs of individual series) over 31-y moving windows and discarded all intervals with negative or noncomputable Rbar values due to low replication.…”

Millennial stocks and fluxes of large woody debris in lakes of the North American taiga

“…It has been established that wildfires have major impacts on LWD stocks and recruitment rates in boreal streams and lakes (Chen, Wei & Scherer ; Arseneault, Boucher & Bouchon ; Arseneault et al . ).…”

“…; Glaz, Nozais & Arseneault ; Arseneault et al . ). However, no studies have combined dendrochronology with exhaustive LWD sampling to reconstruct the long‐term dynamics of LWD stocks in lakes.…”

Bayesian multiproxy temperature reconstruction with black spruce ring widths and stable isotopes from the northern Quebec taiga

“…In northeastern North America, developing tree-ring chronologies is highly challenging due to short tree longevity, the high frequency and severity of wildfires and the remoteness of many areas (Arseneault et al 2013). To improve the quality of reconstructions in such regions with scarce proxy data, we can both increase series replication for a single proxy by creating new chronologies, and combine proxies with an independent response to climate forcing.…”