On the 'Divergence Problem' in Northern Forests: A review of the tree-ring evidence and possible causes

Rosanne D'Arrigo, Rob Wilson, Beate Liepert, Paolo Cherubini

Research output: Contribution to journalReview articlepeer-review

674 Citations (Scopus)

Abstract

An anomalous reduction in forest growth indices and temperature sensitivity has been detected in tree-ring width and density records from many circumpolar northern latitude sites since around the middle 20th century. This phenomenon, also known as the "divergence problem", is expressed as an offset between warmer instrumental temperatures and their underestimation in reconstruction models based on tree rings. The divergence problem has potentially significant implications for large-scale patterns of forest growth, the development of paleoclimatic reconstructions based on tree-ring records from northern forests, and the global carbon cycle. Herein we review the current literature published on the divergence problem to date, and assess its possible causes and implications. The causes, however, are not well understood and are difficult to test due to the existence of a number of covarying environmental factors that may potentially impact recent tree growth. These possible causes include temperature-induced drought stress, nonlinear thresholds or time-dependent responses to recent warming, delayed snowmelt and related changes in seasonality, and differential growth/climate relationships inferred for maximum, minimum and mean temperatures. Another possible cause of the divergence described briefly herein is 'global dimming', a phenomenon that has appeared, in recent decades, to decrease the amount of solar radiation available for photosynthesis and plant growth on a large scale. It is theorized that the dimming phenomenon should have a relatively greater impact on tree growth at higher northern latitudes, consistent with what has been observed from the tree-ring record. Additional potential causes include "end effects" and other methodological issues that can emerge in standardization and chronology development, and biases in instrumental target data and its modeling. Although limited evidence suggests that the divergence may be anthropogenic in nature and restricted to the recent decades of the 20th century, more research is needed to confirm these observations. (c) 2007 Elsevier B. V. All rights reserved.

Original languageEnglish
Pages (from-to)289-305
Number of pages17
JournalGlobal and Planetary Change
Volume60
Issue number3-4
DOIs
Publication statusPublished - Feb 2008

Keywords

  • tree rings
  • dendrochronology
  • divergence
  • paleoclimate
  • reconstructions
  • SURFACE SOLAR-RADIATION
  • TEMPERATURE VARIABILITY
  • GROWTH-RESPONSES
  • UNITED-STATES
  • WHITE SPRUCE
  • GROWTH/CLIMATE RESPONSE
  • HEMISPHERE TEMPERATURES
  • SUMMER TEMPERATURES
  • LARIX-DECIDUA
  • EUROPEAN ALPS

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