Trees and the ecosystems in which they exist, such as parks and forests, can provide a range of ecological, economic, and health benefits. However, these benefits are being threatened by climate change. Today, the trees in parks and forests are faced with three key threats that impact their growth and survival: climate change, disturbances, and the amplified effects of these two combined.
Climate change is creating several shifts that impact the factors that are crucial to the growth and survival of trees and forest ecosystems: increases in temperature, changes in precipitation, and increases in carbon dioxide. In the short-term, more carbon dioxide in the atmosphere could stimulate growth rates and higher temperatures could make the growing season longer, but such benefits will only persist if enough water and nutrients are available to support these higher growth rates. As a result, the potential short-term benefits will be offset by drought stress that will result from warmer temperatures and more variable patterns of precipitation that the region will see in the future. Shifts in species composition and abundance in forests are expected to occur as many tree species gradually shift their ranges further north in response to climate changes. These shifts in species composition, in combination with increases in drought frequency and severity, can make it difficult for trees to survive in the changing climate. Other impacts exacerbated by climate change are insect outbreaks, wildfires, and invasive species that can devastate tree species in parks and forests.
Human development and land use change also present the trees in urban areas with several unique threats, including high concentrations of pollutants, including particulate matter, heavy metals, and pesticides. Trees in parks are also threatened by soil compaction from abundant foot traffic and heavy landscaping machinery. The proximity of humans from which these threats result also presents an increasingly difficult risk scenario where the parks, trees, and forests, and the humans who live near them are at risk. Cities and towns must balance the benefits that healthy park trees can provide with the potential risks that trees weakened by human activity and climate change could pose to their citizens or infrastructure.
Climate change is expected to interact with and exacerbate the problems that the trees in our parks and forests already face from disturbances, so the third and most challenging threat that forests face are the combined effects of these two groups of stressors.