Course:CONS200/2023WT2/Impacts of Climate Change on Old Growth Forests Across North America

Old growth Forests Vancouver

Understanding Old Growth Forests

Old-growth forests are ecosystems with mature trees that have reached an advanced age and exhibit distinct ecological characteristics. Old-growth forests are climax forests in their later phases of development, with massive, old trees and a complex stand structure primarily unaffected by human activity. The definition of an old-growth forest varies by country. Still, most definitions agree that old-growth forests provide essential ecosystem services and social, cultural, economic, and spiritual value that younger forests do not . The Food and Agriculture Organization (FAO) of the United Nations defines old-growth forests, which it calls primary forests, as “naturally regenerated forest[s] of native tree species, where there are no visible indications of human activities and the ecological processes are not significantly disturbed.” Old-growth forests have an important role in biodiversity conservation and environmental health. Preserving old-growth forests is critical for biodiversity, carbon sequestration, and ecosystem resilience. However, human activities such as logging and land conversion have damaged many old-growth forests worldwide. Conservation initiatives strive to maintain and sustainably manage these ecosystems so that they can continue to operate.

Exploring the Ecological Functions and Services

Old-growth forests are ecologically valuable ecosystems that support a diverse range of biological processes and services. Old-growth forests have an important role in climate regulation and mitigation. These forests operate as carbon sinks, absorbing and storing significant amounts of CO2 from the atmosphere. By sequestering carbon, old-growth forests assist to minimize greenhouse gas emissions and moderate global warming. Old-growth woods have a vital function in water control and purification. The intricate root systems of old-growth trees help to stabilize soil and prevent erosion, thus protecting water quality in streams and rivers . Furthermore, the dense canopy of old-growth forests regulates water flow, lowering the risk of floods during heavy rain events. Old-growth forests offer a consistent supply of clean water for both humans and wildlife by preserving healthy watersheds. Old-growth forests also have an essential ecological role in biodiversity protection. These woods support diverse plant and animal species, many uncommon or endangered. ancient-growth woods frequently have a mix of ancient and young trees, resulting in a broad range of microhabitats supporting a diversity of animals. By protecting old-growth forests, we can safeguard biodiversity and contribute to the health and resilience of ecosystems. Old-growth forests are crucial ecosystems that support diverse biological processes and services. They play a role in climate regulation and mitigation by acting as carbon sinks and reducing greenhouse gas emissions. They also play a role in water control and purification, stabilizing soil and preventing erosion. They also protect biodiversity, supporting various plant and animal species, including rare or endangered species. Protecting old-growth forests contributes to ecosystem health and resilience.

Historical Coverage and the Impact of Climate Change

The historical coverage of old-growth forests in North America, particularly before European colonization, was significantly more extensive than today. In the pre-industrial era, vast expanses of old-growth forests covered much of the continent, with estimates suggesting that before European settlement, old-growth forests in the United States covered approximately 1 billion acres (about 4 million square kilometers) . This coverage constituted various forest types, ranging from the coastal rainforests of the Pacific Northwest to the hardwood forests of the Appalachian region and the mixed forests of the Northeast and Great Lakes regions. However, since the arrival of Europeans, particularly with the onset of industrial-scale logging in the 19th and 20th centuries, the extent of old-growth forests in North America has dramatically decreased. By the early 21st century, less than 10% of the original old-growth forests remained in the United States, with similar reductions observed in Canada (Birch et al., 2005) . The loss has been especially pronounced for certain forest types, such as the coastal rainforests and the longleaf pine forests of the Southeast . As the historical extent of North America's old-growth forests has dramatically declined from pre-colonial times to today, climate change poses a new and escalating threat to these remaining ecosystems. Rising temperatures, altered precipitation patterns, and increased frequency of extreme weather events further stress these already vulnerable forests. The consequences of these changes are significant: from 1990 to 2019, the amount of carbon sequestered by U.S. forest land fell by 22 percent—from 816 to 638 million tons of carbon dioxide—due mainly to drought, wildfire, and disturbances by insects and disease . The impact of climate change not only exacerbates the challenges of forest conservation but also influences the ecological balance, biodiversity, and carbon sequestration capabilities of these ancient woodlands

What are the Impacts?

The reduction in old-growth forest cover is due to several factors, including logging for timber and agricultural expansion, urban development, and, in some areas, fire suppression policies that altered natural fire regimes. While some old-growth forests are protected within national parks, wilderness areas, and other conservation lands, many areas remain vulnerable to logging, land use changes, and the impacts of climate change, which can further stress these ecosystems. Over time, the drivers of change in old-growth forest coverage include direct human impacts (deforestation, land use change) and indirect factors exacerbated by climate change (increased temperatures, altered precipitation patterns, and extreme weather events). Climate change profoundly threatens old-growth forests by affecting tree growth, health, and survival.

Exploring the Scope and Scale of Old Growth Degradation Due to Climate Change

Effects of climate change on old-growth forests in North America include a variety of ecological and climatic challenges such as increased temperature and drought stress, altered fire regimes, pest outbreaks, reduced carbon sequestration, shifts in species composition and biodiversity, and impacts on water cycles. Increased Temperature and Drought Stress: climate change leads to warmer temperatures and altered precipitation patterns, resulting in more droughts. The older, more giant trees in old-growth forests have more significant water needs and are less adaptable to sudden climate changes. Drought stress makes trees more vulnerable to diseases and pests and reduces their competitiveness against invasive species . Warmer climates favour the growth and spread of pests and diseases, such as bark beetles, causing significant tree mortality exacerbated by warmer and drier conditions. The impact of these outbreaks is stark, with "insects and disease having destroyed 1.9 million acres of mature and 134,000 acres of old growth in that time" . With the altered precipitation patterns and drier seasons, wildfires are happening more often and with greater intensity, which is a significant risk for old-growth forests. These forests have a lot of plant material that can easily catch fire. In the past, efforts to put out fires quickly have caused a buildup of this flammable material . Now, with changes in the climate, this buildup makes wildfires even more severe and destructive. It has been projected that more than 90 percent of inventoried mature and old-growth forests will be at very high exposure to wildfire-caused mortality by the end of the century . Wildfires are the biggest threat to old-growth trees, “which has consumed 2.6 million acres of mature and 689,000 acres of old-growth forest on public lands since 2000" .

Global Warming and Exclusion of Cultural Burning's Effect on Fire Regimes and Old Growth Survivorship

Forest fires and the forests of the Pacific Northwest have co-evolved over thousands of years, with fires playing a crucial role in the stand dynamics, succession, and promotion of biodiversity in forested areas . Across the West Coast of North America, native peoples additionally have played a significant role in forest fire ecology, promoting low-intensity fires to reduce ladder fuels, increase species diversity, and lower the frequency of high-intensity stand-replacing fires . The prohibition of indigenous cultural burning resulted in the loss of the positive benefits and knowledge associated with the practice, leading to the build-up of fuels and loss of understory diversity. The accumulation of fuels has increased the severity of subsequent fires, resulting in more extensive damage to forested areas and extended fire seasons. Climate change, in turn, has increased temperatures and the risk of drought across the Pacific Northwest. In union, both outcomes have increased the frequency of stand-initiating fires and present a significant threat to the longevity and health of forested ecosystems, particularly the abundance of Old-Growth forests. Since the 1980s, the frequency of moderate to severe forest fires has increased exponentially across the Western United States, correlated to earlier spring snowmelts and related higher spring temperatures drying out stand fuels . The Shift in fire regimes from stand-maintaining surface fires to stand-replacing crown fires has detrimental effects on Old-Growth forests, drastically increasing dominant species mortality and reducing structural diversity . This change accelerates the turnover rate of Old-Growth forests, Leading to the loss of Old-Growth habitat and increasing formation of newly initiated, even-aged stands .

Climate Change and Associated Species Migration Affects on Old Growth's Expected Abundance and Resilience

The spatial distribution of forested zones and associated species ranges are directly correlated to the conditions suitable for a given species/group. As temperature and precipitation regimes change in British Columbia, species distributions and ranges are expected to change as climatic conditions shift. Due to the effects of global warming, specific areas within a given species’ historical range are predicted to be unsuitable to the given species' ecological niche while simultaneously modifying previously unsuitable regions to be ideal for growth . In a given region the turnover of locally dominant species by geographically infrequent species is expected to take long periods, with global warming exceeding the natural rate of adaption to new condition . Species with ecologically narrow niches are expected to have increased mortality and possibly face extinction due to slow migration rates . This becomes especially prominent in populations located at the southern end of species distributions, facing higher rates of mortality due to slow rates of local adaptation than their northern counterparts .  The implication of predicted species migrations and associated mortality has direct influences on the abundance and total cover of Old-Growth forests across Western North America. Old-Growth populations located in the southern distribution of species ranges will likely face increased climatic stressors, shifting the conditions in which the dominant cohort species is established.

Shifting Ecological Niches and Species Relations Related to Our Changing Climate

Rising temperatures associated with climate change are shifting multiple species' natural equilibrium and threatening ecosystem diversity. One example of this effect is the relationship between Whitebark Pine and native mountain pine beetles. Whitebark Pine is a high-alpine species that provides numerous ecological services for high-alpine species. Whitebark Pine and mountain pine beetle have historically been separated by non-overlapping environmental niches due to temperature, elevation and length of seasons . However, rising temperatures have shifted this natural balance in recent years, allowing the mountain pine beetle to expand its range to high-alpine locations . In the face of increased yearly average temperatures and extended warm seasons, Bark Beetles have been able to reproduce at increased rates and shorter intervals . The shift in temperature has created severe stress on Whitebark Pine populations, lowering species productivity and decimating high montane Old-Growth stands.

Consequently, the degradation of Whitebark Pine populations indirectly threatens a multitude of species that share symbiotic relations with them, such as Clark’s Nutcracker, Grizzly Bear, and Black Bear . Shifting ecological niches due to global warming and changes in seasonality can seriously impact biodiversity, increasing the success of certain species while detrimentally affecting others. This is even more detrimental in areas of high biodiversity, such as Old-Growth forests, where species symbiosis is the keystone to the habitat’s overall productivity and diversity.

Conclusion

To summarize, old-growth forests in North America are critical ecosystems that provide a variety of biological activities and services. Maintaining and protecting these forests ensures that our world remains healthy and sustainable for future generations. We must recognize the value of old-growth forests and take action to protect and restore these vital ecosystems for humanity's benefit. North America's old-growth forests face escalating threats from climate change, with rising temperatures, altered precipitation patterns, and extreme weather events stressing these vulnerable ecosystems. From 1990 to 2019, carbon sequestered by U.S. forest land fell by 22% due to drought, wildfire, and insect disturbances. Climate change has increased temperatures and drought risk, increasing the frequency of stand-initiating fires and threatening the longevity and health of forested ecosystems, particularly old-growth forests. Climate change is causing a shift in the natural equilibrium of species, threatening ecosystem diversity. Old-growth forests are crucial for carbon sequestration and biodiversity protection. However, their destruction due to fires and resource demands increases atmospheric carbon. To prevent destruction, a response to wildfires and mass logging is needed. Collaborative management involving indigenous communities, local stakeholders, and government agencies can ensure long-term health and resilience, protecting biodiversity and sustainable ecosystem management. To protect old-growth forests from fire-related destruction, climate change reduction is crucial. Reducing greenhouse gas emissions can slow global warming, reduce drought severity, and improve resilience. Controlled burns and mechanical thinning can reduce fuel loads, promoting forest health and ecosystem resilience. Implementing early wildfire detection systems and addressing climate change can help protect these valuable ecosystems for future generations.