This graph is from Allan and Breshears (1998) and was originally published in the journal, Proceedings of the National Academy of Science. At the base of this research was the question, how does annual climatic variation influence vegetation distribution. This is an important question as climate change is expected to heavily influence how and where species are distributed. These shifts in species are expected to be greatest at ecotones (the area where one ecosystem shifts into another ecosystem) as species likely are approaching their environmental and ecological limits. These species shifts are expected to be significant in the semi-arid southwestern United States.
To answer this question Allan and Breshears used a series of photographs to assess changes in the distribution of a ponderosa pine forest and a pinon-juniper woodland between 1954 and 1963 in the Jemez Mountain in northern New Mexico. This time period is significant as the southwestern United States experienced one of its most intense droughts on record. The basic biology underlying this research is that ponderosa pine forests require cooler and more moist climates whereas pinon-juniper can tolerate both warmer and drier climates. Climate change in the southwestern United States is predicted to trends towards warmer and drier thus the hypothesis is that ponderosa pine forests should experience a reduction in total area while pinon-juniper woodlands should expand their ranges. This graph is not the typical graph with a x and y axis. Rather, using the colored-coded key, this graph shows how species redistributed along an elevation gradient between the years 1954 and 1963 – a pattern that has persisted 40 years later. The key to understanding this graph is the red area. The red areas were once ponderosa pine forests and are now pinon-juniper woodlands. For an idea of the change the persistent ponderosa pine forest (green) is an area of 365 ha., the persistent pinon-juniper woodland is 1527 ha., and the ecotone shift is an area of 486 ha where the ponderosa pine forest changed to a PJ woodland.
1.What does using historic photographic evidence tell us about future vegetation response to climate change?
2.What do these changes in forest structure mean for the dependent animal communities? Have students consider the idea that some organisms may be able to “keep up with the pace” of climate change while others may not. What does this mean for rates of extinction among forest organisms. (If you are instructing at a level where you have taught the concept of r and k selection, this would provide an opportunity to review these concepts and how they relate to the idea of environmental and climate change.)
3.Following is a link to an article from the Albuquerque Journal from 2004. Dr. Allan is profiled and some of his latest observations and science from this same ecosystem and changes that have continued to occur likely due to climate change. (http://www.abqjournal.com/news/state/243967nm10-17-04.htm
4.How are elevation and latitude gradients similar? What does Allan and Breshears’ work say about other species distributions along these gradients?
5.Is the effect of climate change equal across species?