This story highlights a current research project at the Hubbard Brook Experimental Forest. To read more about research projects at HBEF, visit Current Research page. Check back regularly to learn about new research projects.
Examining climate change at the ecosystem level:
A 50-year record from the Hubbard Brook Experimental Forest

 

Rain gauge station  
  Figure 1. Gage 1 in the Hubbard Brook Experimental Forest, NH. Temperature and precipitation data have been taken continuously at this
location since 1956.
 
  Investigators:
  Matt Vadeboncoeur
Steve Hamburg
Andrew Richardson
Amey Bailey
 
  Contact Info:
  Matt Vadeboncoeur
Center for Environmental Studies
Box 1943, Brown University
Providence, RI 02912
phone: (401) 863-3445
email: vadeboncoeur@alumni.brown.edu
 

Summary
THE PHENOMENON of global climate change is widely accepted but often difficult to observe directly at the local scale. The amount of change is still small in comparison to interannual variability, and so very high-quality, long-term records are required to discern trends with statistical confidence. Such records exist at the Hubbard Brook Experimental Forest, New Hampshire. They extend back more than 50 years, to 1956. We examined this record for climate trends, defining 22 independent climate metrics. Of these, 14 (64%) changed significantly in the direction predicted by global circulation models, while 6 changed non-significantly in the direction predicted and 2 changed in the opposite direction. Trends in temperature metrics agreed significantly with predictions most often, while analysis of precipitation and hydrologic data yielded mixed results. Temperature records from elsewhere in the region show similar trends over the same time period. These results show that climate change of the sort predicted by global circulation models has taken place at the Hubbard Brook Experimental Forest over the past 50 years.

  Graph of 50-year temperature record  
  Figure 2. The 50-year temperature record at station G1 (red) in the Hubbard Brook Experimental Forest and the regional 100-year temperature record (blue) from Mitchell and Jones (2005) are expressed as deviation from the 1991-1996 mean.  
  Graph of change in temperature distribution  
  Figure 3. Change in temperature distribution at Gage 1 in the Hubbard Brook Experimental Forest, NH. Coldest winter temperatures occurred far less frequently between 1986-2005 than between 1958-1977.  
  Graph of timing of spring melt  
  Figure 4. Timing of spring melt, calculated for Hubbard Brook W3 (green) and W7 (orange), using methodology following Hodgkins et al. (2003). This metric of spring phenology has advanced by 10 days since 1958 at south-facing W3 and by 12 days since 1966 at north-facing W7. Similar rates of change in flow rate were found for the Pemigewasset River at Plymouth (not shown).  

Temperature Trends
We examined the 50-year temperature record from the G1 station at Hubbard Brook (Figure 1), other locations within the Hubbard Brook valley with shorter records, and several locations throughout the region with longer records. Mean annual temperature (which is the average of daily high and low temperatures recorded throughout the year) has increased significantly by about 1.0ºC (1.8ºF) over the past 50 years. This trend closely matches the longer-term trend for the region (Mitchell and Jones 2005), as shown in Figure 2, as well as trends in individual records (not shown) from Mount Washington and Hanover, NH.

Winter temperatures have increased more rapidly than summer temperatures, and night temperatures have increased more rapidly than daytime temperatures, both of which are general trends found in other climate change studies (Easterling et al. 2002). As a consequence, the very coldest temperatures of the year, which occur on winter nights and may have important ecological consequences have become far less frequent, while the warmest temperatures have become marginally more frequent (Figure 3).

Trends in Seasonality
Peak spring runoff date is a robust estimate of spring snowmelt, and it is shown for Watershed 3 (south-facing) and Watershed 7 (north-facing) in figure 4. This date has advanced dramatically, by nearly two weeks during the 40+ year record of streamflow at Hubbard Brook. Hodgkins et al. (2003) found similar trends throughout New England, and Likens (2000) found the same amount of change over the past 30 years in ice-out data for nearby Mirror Lake.

Consequences of Climate Change
Soil freezing, which is more common in warm winters with little insulating snowpack, has been shown to have strong effects on soil processes at Hubbard Brook (Groffman et al. 2001). Winter temperatures, and in particular freeze-thaw cycles, can have dramatic effects on trees (Borque et al. 2005; Hawley et al. 2006) and insects (Skinner et al. 2003). Iverson and Prasad (2002) predict that the northern hardwood forest now dominant at most elevations at Hubbard Brook will slowly succumb to invasion by oak-pine forests as the climate changes over the next century, though the rate of change is unclear. Long-term climate records from the Hubbard Brook Experimental Forest, and extensive data from the Hubbard Brook Ecosystem Study, present a unique opportunity to study the effects of climate change into the future.

  Related Links  
  Intergovernmental Panel on Climate Change  
  New England Regional Climate Variability and Change Assessment  
  Union of Concerned Scientists: Global Warming in New Hampshire


 

References
Bailey, A.S., J.W. Hornbeck, J.L. Campbell, and C. Eagar. 2003. Hydrometerological database for Hubbard Brook Experimental Forest: 1955-2000. USDA Forest Service, NE Research Station General Technical Report NE-305.

Borque, C.P., R.M. Cox, D.J. Allen, P.A. Arp, and F.R. Meng. 2005. Spatial extent of winter thaw events in eastern North America: historical weather records in relation to yellow birch decline. Global Change Biology 11: 1477-1492.

Easterling, D.R., B. Horton, P.D. Jones, T.C. Peterson, T.R. Karl, D.E. Parker, M.J. Salinger, V. Rasuvayev, N. Plummer, P. Jameson, and C.K. Folland. 1997. Maximum and minimum temperature trends for the globe. Science 277: 364-367.

Groffman P.M., Driscoll C.T., Fahey T.J., Hardy J.P., Fitzhugh R.D. and G.L. Tierney. 2001. Effects of mild winter freezing on soil nitrogen and carbon dynamics in a northern hardwood forest. Biogeochemistry 56:191-213.

Hawley, G.J., P.G. Schaberg, C. Eagar, and C.H. Borer. 2006. Calcium addition at the Hubbard Brook Experimental Forest reduced winter injury to red spruce in a high-injury year. Canadian Journal of Forest Research 36: 2544-2549.

Hodgkins, G.A., R.W. Dudley, and T.G. Huntington. 2003. Changes in the timing of high river flows in New England over the 20th Century. Journal of Hydrology 278: 244–252.

Iverson, L.R., and A.M. Prasad. 2002. Potential tree species shifts with five climate change scenarios in the Eastern United States. Forest Ecology and Management 155:205-222. Data products available at:http://www.fs.fed.us/ne/delaware/atlas/

Likens, G.E. 2000. A long-term record of ice cover for Mirror Lake, New Hampshire: effects of global warming? Verh. Internat. Verein Limnol. 27: 2765-2769.

Mitchell, T.D., and P.D. Jones. 2005. An improved method of constructing a database of monthly climate observations and associated high-resolution grids. International Journal of Climatology 25: 693–712. Data products available at:http://www.cru.uea.ac.uk/~timm/data/index.html

Skinner, M., B.L. Parker, S. Gouli, and T. Ashikaga. 2003. Regional Responses of Hemlock Woolly Adelgid (Homoptera: Adelgidae) to Low Temperatures. Environmental Entomology 32: 523–528.

Date Prepared: November 2006