Colorado’s climate, like that of the rest of the planet, is undergoing significant change. Our state has experienced increasingly warmer temperatures in recent decades, as compared to longer-term averages. As a result, changes to forest environments already are occurring. What do these changes mean for Colorado forests and for communities?
Colorado’s climate is shaped by its mid-continental location, high elevations, and complex topography of the mountains, plains, and plateaus. Continental climates experience greater seasonal shifts in temperature, compared to maritime climates, and thus there is a broad range in minimum and maximum temperatures that our forests experience.
The Rocky Mountains create a rain shadow effect; moist air from the west rises over the mountains, then cools and releases precipitation on the western side. By the time the air descends on the eastern side, it has lost most of its moisture, resulting in drier conditions. Colorado’s varying elevations across the state lead to differences in air pressure and atmospheric moisture.
Coupled with solar radiation changes depending on aspect, these features can modify forest composition across relatively small spatial scales. These variations reflect how climate and topography contribute to forest composition and adaptation.
Over thousands of years, these conditions have shaped the diversity of forests in Colorado, with different microclimates supporting different types of trees and forest ecosystems.
The Earth’s climate is highly dynamic. We experience its short-term volatility, ranging from minutes to days, as weather. It also changes over much longer time scales, over years to decades. Although the global climate has experienced many such changes throughout history, in recent decades changes to the climate have been especially rapid, with increasingly observable environmental impacts.
Since 1980, the Earth’s surface has warmed by 1.4°F, with a total increase of 2.0°F since the late 19th century, primarily due to human activities (IPCC 2023). Globally, the 10 warmest years in the historical record have all occurred in the past decade (2014 to 2023).
Greenhouse gases like carbon dioxide and methane have significantly contributed to this warming. This rapid warming of the past several decades, a rate unprecedented in at least 2000 years, has led to widespread changes, including more frequent and severe heatwaves, droughts and shifts in plant and animal distributions.
Based on NOAA’s meteorological records including weather observations from hundreds of sites across the state, Colorado’s annual average temperatures warmed by 2.3°F from 1980 to 2022 (Figure 1). Only one year in the 21st century has been cooler than the 1971 to2000 average. Southwestern and South-central Colorado have experienced the largest magnitude of warming. Further and significant warming is expected in all parts of Colorado over the next several decades. By 2050, the average year is likely to be as warm as the very warmest years on record through 2022 (Bolinger et al., 2024). For more information, please refer to the Climate Change in Colorado report, published in 2024.
This significant warming trend, coupled with prolonged drought conditions, has further exacerbated disturbances in Colorado’s forests. These warmer and drier conditions create an environment where insects and disease may thrive. Mountain pine beetle and spruce beetle alone have impacted over 20% of Colorado’s forests since the turn of the century and have resulted in millions of acres with standing and down dead wood. It is important to remember that the most destructive bark beetles in Colorado are native species. Factors contributing to the rise in bark beetle activity include the availability of suitable host species, previous drought conditions that weaken trees and milder winters that reduce the mortality of bark beetle larvae. However, in the absence of suitable host species of certain sizes, populations will diminish, a trend seen over the last 15 years since the height of mountain pine beetle infestation in the late 2000’s (Figure 2).
The shift in climate has influenced wildfire behavior across the state, with varying impacts on different ecosystems. Historical practices such as extensive fire suppression, intensive grazing and land-clearing since the early 1890s, have reduced the frequency of low and moderate severity fires. This has led to a predominance of less fire-resistant and more shade-tolerant species, resulting in denser forest compositions. This increase in forest density, along with the accumulation of available fuel and ongoing drought conditions, has resulted in large increases in the annual area burned, the number of very large fires (>10,000 acres), the proportion of fire area burned at high severity and the length of fire seasons. Twenty of the state’s largest wildfires recorded have occurred since 2001, including the top three in 2020. It is also important to remember that these changes do not apply to every forest type in the state, as some forest types, such as high-elevation spruce/fir forests, have experienced a shift towards higher frequency of climatic conditions conducive to burning. In these systems, fires are generally limited by climatic conditions as fuels are ever-present, and empirical evidence for structural changes associated with fire suppression, such as seen in frequent-fire forests, is sparse.
One of the best defenses against threats associated with a changing climate is to ensure diverse, resilient forest ecosystems. This is not a “one size fits all” approach, but a concentrated effort to build both resistance and resilience into systems through various forest management techniques, while simultaneously assessing the effectiveness of these methods to improve future decision making. The CSFS aids landowners in managing forest composition, stand density and wildfire fuels while improving forest resilience.
Adapting to climate change requires planning for multiple future scenarios. Strategies to enhance forest resilience and carbon retention include:
Colorado’s year-round wildfire season threatens water quality, human health and economy. To protect Colorado’s drinking water, we use active forest management by collaborating with partnerships to promote resilient forests for the future of our watersheds.
Healthy forests lead to healthy watersheds that provide drinking water to millions. In a changing climate, our forests need to be resilient in the face of drought, wildfire, insects and diseases to ensure water remains clean and accessible to people, wildlife and the landscape.
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