Climate change and ecosystem response in the northern Columbia River basin — A paleoenvironmental perspective

Abstract

A comprehensive review of Holocene paleoenvironmental data has been prepared, providing the basis for evaluating natural variability in climate and ecosystem dynamics in the northern Columbia River basin. The paleoenvironmental record reveals four major climatic shifts and a number of less well-defined climatic changes throughout the Holocene. The major climate changes are (1) a cool or cold, late-glacial climate at the end of the last glaciation (>11 500 cal. year BP), (2) an interval of drought and maximum summer warmth during the early Holocene (ca. 10500 to 8000 cal. year BP), (3) a mid-Holocene trend towards a cooler, more moist climate (ca. 8000 to ca. 4000 cal. year BP), and (4) a relatively stable climate persisting from ca. 4000 cal. year BP until the arrival of European settlers. Air temperatures have warmed by about 1 8C over the past century. Minor climate events that are emerging as global in nature include Little Ice Age (1200-150 BP) conditions, and a late Holocene cool wet period (3500-2500 BP). These are observed in some study sites examined in this paper and may be related to large-scale cycles of 2800-2000 and 1500 years. A discussion of changing atmospheric circulation patterns, and the causes of long-term climatic change are included, together with a discussion of the implications of the paleoenvironmental record for understanding future climate, and the likely response of communities and ecosystems.

Rethinking biogeoclimatic ecosystem classification for a changing world

“…2. Biogeoclimatic ecosystem classification is based on outdated notions of climax ecosystems in equilibrium with climate and local topographic and edaphic conditionsthe "Balance of Nature" paradigm (Botkin 1992;Wu and Loucks 1995;Walker and Pellatt 2008). In addition to being out of step with mainstream thinking in ecology and earth sciences, which have rejected the equilibrium perspective (Johnson et al 1990;Pickett et al 1992), these ideas are increasingly at odds with the reality of BC's land base.…”

“…For example, conservation planning in BC, as elsewhere (Botkin 1992), has been based on unwritten assumptions that biota are optimally adapted to their current environment and forests were in pristine condition prior to industrial logging. In the practice of resource management it is rarely explicitly acknowledged that plant and animal populations have been in an ongoing state of flux since the melting of the continental ice sheets some 10 000 years ago (Walker and Pellatt 2008) and that just before that time, North America was ruled by spectacular megafauna including giant beavers, mammoths, and saber-toothed tigers (Ripple and Van Valkenburgh 2010). Within historic time alone, food webs in BC have experienced the Little Ice Age (Luckman 2000), the depredations of the fur trade (Innis 2001), invasion of moose (Spalding 1990), collapse of aboriginal hunter-gatherer societies, rerouting of streams, and incineration of forests associated with the gold rush (Heritage House 1987; Dickinson and Smith 1995), and so on.…”

“…But succession and soil formation are perpetually dynamic processes that shift or adapt to changing circumstances rather than deterministically approaching a stable equilibrium. Ecosystem classification should, therefore, evolve naturally from a static, descriptive procedure to a dynamic modeling exercise (Prentice et al 1992) that will allow users of the BEC system to project and "hindcast" (Walker and Pellatt 2008) terrestrial ecosystem development through time. The next section will outline how that evolution can take place.…”

“…This process of forest, grassland, and tundra vegetation and soils approaching the new equilibrium will take centuries to millennia (Walker and Pellatt 2008) over which time the climate will continue to change (hopefully at a slower pace) while species distributions and disturbance regimes undergo additional changes that are not directly climate-driven. As we saw in Example 1, a more realistic view is that of vegetation zones shifting and mutating under the influence of constantly moving attractors.…”

“…Bioclimatic envelope projections (Hamann and Wang 2006) should include "hindcasting" (Hebda 1995;Walker and Pellatt 2008) as well as forward simulations of the distribution of biogeoclimatic units over time for continuity and to illustrate the accelerating pace of change. • Incorporate human ecology into BEC by making a formal transition from the management of "natural" ecosystems to the management of social-ecological systems .…”