Publication reviews factors influencing recent trends in forest health responses to climate change

Forests cover approximately one-third of the world’s land mass, are an important source of good and services, and influence global carbon cycles. The fate of these and other benefits is of increasing concern among scientists and policymakers, including the United Nations Intergovernmental Panel on Climate Change (IPCC).

The IPCC has projected that greenhouse gas-induced climate change will adversely impact forests in the years and decades to come and that many species will therefore be driven to extinction, some in the next few decades.

A recent paper reviews trends in United States forest health responses to climate change, and considers the historical context for recent trends, physiological tolerances of trees, and the effect of rising CO2 on tree growth rates and responses to stressors. Authors are Craig Loehle of NCASI, Craig Idso of the Center for the Study of Carbon Dioxide and Global Change, and Ben Wigley of NCASI.

Based on their review of the literature, the authors conclude that negative impacts on forests from climate change are not yet reliably detectable, which is similar to conclusions by the IPCC. With respect to the future, the authors report that they “find considerable evidence for physiological tolerance by trees for several degrees of warming, which will be further enhanced as CO2 rises. Rising CO2 will also likely enhance water use efficiency, drought tolerance, productivity, tolerance for air pollutants, and in at least some cases resistance to pests and diseases.”

The abstract for the paper follows.

“The health of United States forests is of concern for biodiversity conservation, ecosystem services, forest commercial values, and other reasons. Climate change, rising concentrations of CO2 and some pollutants could plausibly have affected forest health and growth rates over the past 150 years and may affect forests in the future. Multiple factors must be considered when assessing present and future forest health. Factors undergoing change include temperature, precipitation (including flood and drought), CO2concentration, N deposition, and air pollutants. Secondary effects include alteration of pest and pathogen dynamics by climate change. We provide a review of these factors as they relate to forest health and climate change. We find that plants can shift their optimum temperature for photosynthesis, especially in the presence of elevated CO2, which also increases plant productivity. No clear national trend to date has been reported for flood or drought or their effects on forests except for a current drought in the US Southwest. Additionally, elevated CO2 increases water use efficiency and protects plants from drought. Pollutants can reduce plant growth but concentrations of major pollutants such as ozone have declined modestly. Ozone damage in particular is lessened by rising CO2. No clear trend has been reported for pathogen or insect damage but experiments suggest that in many cases rising CO2 enhances plant resistance to both agents. There is strong evidence from the United States and globally that forest growth has been increasing over recent decades to the past 100+ years. Future prospects for forests are not clear because different models produce divergent forecasts. However, forest growth models that incorporate more realistic physiological responses to rising CO2 are more likely to show future enhanced growth. Overall, our review suggests that United States forest health has improved over recent decades and is not likely to be impaired in at least the next few decades.”



Loehle, C., C. Idso, and T.B. Wigley. 2016. Physiological and ecological factors influencing recent trends in United States forest health responses to climate change. Forest Ecology and Management 363:179–189.