Hands-on problem_biome1

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Southeast Missouri State University *

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BI-332

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Geography

Date

Feb 20, 2024

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docx

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Hands-On Problem Advance of the Tree Lines: Biome Boundaries and Climate Change (This exercise is based on Harsch M., P. Hulme, M. McGlone and R. Duncan. 2009. Are treelines advancing? A global meta-analysis of treeline response to climate warming . Ecology Letters 12: 1040–1049.) INTRODUCTION In this class on Biomes, we introduce the idea that terrestrial biomes are characterized by the growth forms of the dominant vegetation. The distribution of biomes reflects global patterns of temperature and precipitation ( see figure below ). In areas with low precipitation and low temperatures, we see a transition between the boreal forest biome and the tundra. The boundary between these two biomes is marked by the tree line: an area above which trees do not occur. Tree lines occur at high latitudes (boreal tree line) and high elevations (alpine tree line). In this exercise, we will explore the relationship between tree line locations and changes in temperature. Textbook Figure 6.2 Biomes vary with average annual temperatures and precipitation. Harsch et al 2009 looked at several hundred studies on changes in tree line. They analyzed data from 166 sites to see if general patterns associated with tree line change could be determined. The authors found that 52% of tree lines were advancing (moving toward higher latitudes or elevations), 1% of tree lines were receding, and the remaining were not changing.

Fig. 1: Map of locations included in the tree line analysis and whether they were advancing or not. (After M. A. Harsch et al. 2009. Ecol Lett 12: 1040-1049.) Two predictors emerged from this analysis of tree line advance: Tree lines that experienced strong winter warming were more likely to have advanced, and tree lines with a diffuse form ( Figure 2 ) were more likely to have advanced than those with an abrupt form ( Figure 3 ). Fig. 2: Diffuse-form tree line, California. (Courtesy of Melanie Harsch.)

Fig. 3 : Abrupt-form tree line, New Zealand. (Courtesy of Melanie Harsch.) An increase in winter temperature may lead to better survival of seedlings over the harsh winter period. Diffuse-form tree lines are less likely than abrupt tree lines to be limited by factors other than temperature, such as microclimatic conditions or water availability, so as temperatures increase, they will advance more readily. QUESTIONS Question 1 Now, let’s look at climate data from a few locations to see if temperature patterns would predict an advance in tree line. You can obtain climate data for locations in the United States from several sources, but one of the most useful for high-elevation sites is the Natural Resources Conservation Service SNOTEL site listed below. Below are mean daily temperature records for several locations for the three months of winter (December–February).

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