Rapid Changes and Thresholds

KEY FINDING 22. Growing understanding of rapid and unexpected changes, interactions, and thresholds, especially in relation to climate change, points to a need for policy that responds and adapts quickly to signals of environmental change in order to avert major and irreversible biodiversity losses.

This key finding is divided into three sections:

Ecosystems are dynamic complexes of plants, animals, and microorganisms, interacting with natural forces, human actions, and changing conditions. Ecosystems can adapt to certain levels of stress, however their capacity to recover from disturbance may be lowered by biodiversity loss and cumulative impacts. A point may be reached where the ecosystem undergoes a rapid, irreversible shift from one state to another. This is usually detected as a large, rapid, and persistent change in relative abundances of organisms, especially species that we notice (such as vegetation) or that we exploit (such as fish stocks).

The point at which a shift is inevitable is called a threshold or tipping point.1, 2 Thresholds preceding rapid changes are often difficult to predict, but may themselves be preceded by early-warning signals like increased variability or slower recovery from a disturbance.3 Climate change is very likely to lead to threshold-type ecosystem responses, many of them irreversible.2 Many aspects of ecosystems are not currently, or regularly, monitored and much remains unknown about how Canada’s ecosystems function. Climate change adds uncertainty and is projected to lead to responses that lie outside the ranges of historical records.2

Recognizing that rapid change occurs is important because it has implications for policy. Ecosystem responses are often unexpected, especially owing to interactions among stressors.

Early warning signals are not always detected in time, especially when ecosystem monitoring is absent or inadequate or when the measurement uncertainty is so large that change cannot be detected until a threshold has been crossed. Management policies need to be designed to minimize the social, economic, and environmental impacts of unpredictable change when it inevitably occurs. Designing “safe–fail” policies provides a measure of insurance.

Action can, however, be taken before thresholds are crossed and policy options become restricted and expensive. This involves increasing Canada’s capacity to detect and interpret the signals of ecological change and, at the same time, strengthening the science-policy interface by targeted and timely delivery of research results to policy and decision makers.

An example of rapid and unexpected change

Sockeye salmon © iStock.com/RKoopmansThe combined Smith and Rivers inlets sockeye salmon stock was historically one of the largest and most valuable salmon populations in B.C., supporting commercial fishing, canneries, and First Nations fisheries. Numbers of returning salmon declined suddenly in the early 1990s, likely due to poor marine survival during migration through the North Coast and Hecate Strait Ecozone+ and into the Gulf of Alaska.4 The specific cause and location of this mortality is unknown.

Sockeye salmon returning to smith and rivers inlets, B.C.
Thousands of fish, 1970 to 2008

Graph: sockeye salmon returning to Smith and Rivers Inlets, B.C. Click for graphic description (new window).

Source: Crawford and Irvine, 20095

Global Trends

Pressures on global ecosystems are increasing the likelihood of rapid and unexpected changes such as outbreaks of pests and diseases, catastrophic floods and landslides, desertification, fisheries collapse, and species extinctions.1


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