finding 18.2 : changing-composition-role-of-forests

The composition of the region’s forests is expected to change as rising temperatures drive habitats for many tree species northward. The role of the region’s forests as a net absorber of carbon is at risk from disruptions to forest ecosystems, in part due to climate change.

This finding is from chapter 18 of Climate Change Impacts in the United States: The Third National Climate Assessment.

Process for developing key messages: The assessment process for the Midwest Region began with a workshop was that was held July 25, 2011, in Ann Arbor, Michigan. Ten participants discussed the scope and authors for a foundational Technical Input Report (TIR) report entitled “Midwest Technical Input Report.”2626b5ca-ec04-4e41-8405-9f582c779a7a The report, which consisted of nearly 240 pages of text organized into 13 chapters, was assembled by 23 authors representing governmental agencies, non-governmental organizations (NGOs), tribes, and other entities. The Chapter Author Team engaged in multiple technical discussions via teleconferences that permitted a careful review of the foundational TIR2626b5ca-ec04-4e41-8405-9f582c779a7a and of approximately 45 additional technical inputs provided by the public, as well as the other published literature, and professional judgment. The Chapter Author Team convened teleconferences and exchanged extensive emails to define the scope of the chapter for their expert deliberation of input materials and to generate the chapter text and figures. Each expert drafted key messages, initial text and figure drafts and traceable accounts that pertained to their individual fields of expertise. These materials were then extensively discussed by the Author Team and were approved by the Chapter Team members.

Description of evidence base: The key message and supporting text summarize extensive evidence documented in the Technical Input Report.2626b5ca-ec04-4e41-8405-9f582c779a7a Technical inputs on a wide range of topics were also received and reviewed as part of the Federal Register Notice solicitation for public input. Evidence for increased temperatures and altered growing seasons across the U.S. is discussed in Chapter 2 (Our Changing Climate, Key Messages 3 and 4) and its Traceable Accounts. “Climate Trends and Scenarios for the U.S. National Climate Assessment,”95f2ea7d-12e3-4ed5-9247-7cf139db91a9 with its references, provides specific details for the Midwest. Evidence that species have been shifting northward or ascending in altitude has been mounting for numerous species, though less so for long-lived trees. Nearly all studies to date published in the peer-reviewed literature agree that many of the boreal species of the north will eventually retreat northward. The question is when. Multiple models and paleoecological evidence show these trends have occurred in the past and are projected to continue in the future.26bd44a5-f9f3-49b5-9b96-5172e78da431 The forests of the eastern United States (including the Midwest) have been accumulating large quantities of carbon over the past century,c7ab97dd-3693-458c-8381-1625a30a086a but evidence shows this trend is slowing in recent decades. There is a large amount of forest inventory data supporting the gradual decline in carbon accumulation throughout the eastern United States,0489f172-b2e0-4b90-aa40-7ba9993bd287 as well as evidence of increasing disturbances and disturbance agents that are reducing overall net productivity in many of the forests.

New information and remaining uncertainties: A key issue (uncertainty) is the rate of change of habitats and for organisms adapting or moving as habitats move. The key questions are: How much will the habitats change (what scenarios and model predictions will be most correct)? As primary habitats move north, which species will be able to keep up with changing habitats on their own or with human intervention through assisted migration, management of migration corridors, or construction or maintenance of protected habitats within species’ current landscapes? Viable avenues to improving the information base are determining which climate models exhibit the best ability to reproduce the historical and potential future change in habitats, and determining how, how fast, and how far various species can move or adapt. An additional key source of uncertainty is whether projected disturbances to forests are chronic or episodic in nature.0c427475-7d17-4825-9728-c629435ef9ad

Assessment of confidence based on evidence: There is very high confidence in this key message, given the evidence base and remaining uncertainties.

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