Rapid Changes and Thresholds
Key finding overview
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:
- Key finding overview (this page)
- Detecting change and taking action
- Lessons and examples from this report
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
The 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
Detecting change and taking action
Three complementary decision points for biodiversity conservation
1. When thresholds are crossed
(it may be too late)
Action is delayed until the evidence of change is clear. For example, species decline below minimum viable numbers; too little habitat is left to support whole groups of species; extinctions. Options for action are limited and expensive. Interventions are drastic, with low likelihood of success. Recovery, if it occurs, is slow. Socio-economic impacts are inevitable.
Some examples from this assessment
Even with moratoria on fishing and reduced harvesting, action in response to declines in marine fisheries resulting from overfishing in the Atlantic and Pacific has not always been successful. The lack of recovery of some fish stocks is likely related to alteration of food webs and other aspects of ecosystems, making it difficult to return to past conditions. Earlier interventions might have improved prospects for recovery.
Since invasive non-native species and other changes took hold in the Great Lakes, large annual investments are needed to keep this altered system producing the ecosystem services that were provided naturally in the past.
2. When ecosystem changes are detected
(it is not too late)
Earlier action, based on evidence that ecosystem change is underway, provides more options to mitigate impacts. Action is taken when cause-and-effect relations are at least partly understood and when evidence from research creates confidence that biodiversity declines are likely if no action is taken. Leads to a high probability of reversing or stabilizing impacts and reducing stressors before it is too late.
Some examples from this assessment
Fragmentation of landscapes is known to lead to the loss of habitat and species. It is difficult to measure the incremental changes in species themselves – but action to maintain large, intact landscapes will likely slow the rate of biodiversity loss.
Fire and insect disturbances have strong relationships with temperature and with forest practices. Severity and spread of certain forest insects and incidence of fire are likely to increase due to climate change. Policy options are available and have a good chance of success, including adapting fire and forestry management practices.
3. When early signals indicate there may be change
Early signals of change are a source of information to use when developing policy options, managing proactively, and ensuring appropriate monitoring and research are in place. Early signals might be detected in a few locations only or in just some animals or plants in a population. These changes may turn out to be part of natural fluctuations – or they may be signs of bigger changes to come. Early action now may prevent problems in the future, be less expensive, and consequences may be less severe.
Some examples from this assessment
Invasive non-native species, including parasites, are often detected when they are just beginning to spread. Monitoring and early intervention have prevented the spread of some potentially harmful invasive non-native species, such as the gypsy moth in western Canada.
About 20 common species of birds are showing signs of widespread decline and the causes are unclear. Adapting research and monitoring to find out why is a first step in taking action to halt or reverse these declines.
Lessons and examples from this report
Slow, incremental change may not seem important until thresholds are taken into account.
Ocean acidification, caused by uptake of carbon dioxide from the atmosphere, occurs in some Canadian marine ecosystems and is an emerging issue in others; the rate of change is slow. Research and global change models provide good evidence that acidification will continue to increase as a result of climate change. Some ocean acidity thresholds are well known because they are chemical and physiological and are relatively easy to define – when the water becomes too acidic, calcium carbonate shells and skeletons cannot form properly, affecting shellfish, corals, and other sea creatures. (See Marine Biome.)
The historical distribution of native grasslands, the most endangered of Canada’s biomes, has been greatly reduced, mainly through conversion for agriculture. There are several types of grasslands, each supporting a distinct mix of species, including many species at risk. The natural processes that maintained grasslands in the past, like fire and grazing by free-roaming bison herds, are now absent or modified. Development and recreation continue to convert and fragment the land in some areas and the spread of invasive non-native species and changes in grazing practices continue to alter the composition and structure of the vegetation. Each type of grassland will have its own threshold beyond which it will no longer be able to support its unique mix of species. (See Grasslands Biome.)
Stressors may interact in unexpected ways to produce surprises.
Nutrient loading to the Great Lakes was a problem that led to collaborative action between the United States and Canada, starting in the 1970s, to reduce nutrient inputs and clean up the lakes. These measures were successful – water quality improved, harmful algal blooms and oxygen depletion problems decreased, and diversity of native algal species increased. However, as lakeshore areas continued to be modified, human populations surrounding the lakes continued increasing and invasive non-native species have become more prevalent, altering many of the lakes’ characteristics. Although regulation continues to limit nutrient inputs, some combination of the changes that are taking place in the lakes has resulted in reappearance of harmful algal blooms in some near-shore areas. (See Nutrient Loading.)
Change in one ecosystem component brings with it a suite of widespread consequences.
Summer sea-ice extent is shrinking, a rapid change that is now well established. The decline of multi-year ice may have reached or crossed a threshold. Ecological consequences are emerging, especially in Hudson Bay, where the ice-free season has increased the most. Examples include a reduction in Arctic cod, a fish that is associated with ice; an increase in capelin, a fish more tolerant of warmer water; reduced body condition of polar bears; and range expansion of a new top predator, the killer whale, into the bay. (See Marine Biome and Ice Across Biomes.)
Large predators, including wolves, have declined or have been extirpated from much of their original ranges in the more populated areas of Canada. Smaller predators, like western coyotes and raccoons, have in turn expanded their ranges and increased in numbers. These more adaptable predators eat a wide range of food items, altering abundance of other species. In the Mixedwood Plains, with fewer predators, white-tailed deer have become more abundant, leading to major changes in forest vegetation. (See Food Webs.)
Damage to ecosystems may speed up because of interactions of stressors.
Coastal erosion in the Atlantic Maritime Ecozone+ is increasing, threatening wetlands, beach, and dune ecosystems. Development and hardening of the foreshore have made coastal ecosystems more susceptible to erosion. Rise in sea level, reduced sea ice, and more tropical storms in the Atlantic, all related to climate change, accelerate the rate of erosion. (See Coastal Biome.)
Thresholds are influenced by both environmental sensitivity and the severity of the threat.
Some lands and waters, due to their underlying geology, have greater capacity to buffer acid deposition than others, so the threshold beyond which ecosystem damage occurs varies from place to place, even with the same levels of acid deposition. Once the threshold is crossed, high levels of impacts occur rapidly. For example, certain salmon rivers in Nova Scotia have been particularly affected because of their lack of capacity to buffer acid. (See Acid Deposition.)
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