A lush, green swath of forest in the heart of New Hampshire’s White Mountains is not the first place you’d think of as being vital to the science of climate change. But at Hubbard Brook Experimental Forest in North Woodstock, New Hampshire, we are fortunate to have a valuable set of long-term records that give us a picture of exactly how our local climate has changed. Ongoing studies at this research station are also shedding some light on what may become of our region’s climate if the current pace of change continues.
Thanks to the foresight of the folks at the Northeast Forest Experiment Station, in 1955, the Hubbard Brook station and its alien-looking arrays of metal and plastic weather-recording instrumentation were established. These instruments have provided us with a treasure trove: over 50 years’ worth of climate measurements, from temperature to rainfall to the timing of spring snowmelt.
These measurements - of over 22 different aspects of climate recorded since 1956 - have enabled scientists to paint a picture of how the climate at Hubbard Brook - and by extension, in the rest of the Northeast - has changed in half a century. Fourteen of these measures have changed significantly, in line with global computer-generated climate-change scenarios. Of all the measurements, temperature increases most strongly match the predictions.
Temperatures at Hubbard Brook have been steadily rising over the past half-century. Mean annual temperature - an average of daily high and low temperatures throughout the year - has risen 1°C (1.8ºF). On a line graph, Hubbard Brook’s past 50 years’ worth of mean annual temperatures nearly mirrors readings over the same times pan from the few other regional recording stations.
As other regional temperature records have also shown, winters have warmed more than summers, and nights have warmed more than days. Both changes have significant ecological ramifications. Many species of plants and animals, including invasive species like the hemlock woolly adelgid, are limited by cold temperatures. As the mercury rises, the proverbial floodgates start creaking open. Low winter temperatures are important to our native species, too. Many hardy tree, shrub, and perennial species require a certain number of days below a certain temperature in order to break dormancy in the spring. And night temperatures make a difference: ask anybody who harvests maple sap in the spring. Below-freezing temperatures (in conjunction with warm days) are essential for sap runs.
Other strong indicators of change at Hubbard Brook include a shift forward in the peak spring runoff date and lower average snowpack depth overall. The date of peak spring runoff at a south-facing recording station has advanced by 10 days since 1958. On a north-facing slope, it has advanced by 12 days. Snowpack has also decreased over time, which can have significant effects on microbial life in the soil (snowpack insulates soil life - and underground plant parts - from the vicissitudes of freeze-thaw cycles). According to some scientists, less snow will cause shifts in river flow patterns that may ultimately affect the biology of fish.
Even the forest itself is predicted to change significantly. One paper’s authors say that the now-dominant northern hardwood forest will be slowly replaced with an oak-pine mix. The northern forest of today is being pressured on one flank directly by climate change, and on the other by biological invasions by competitors and predators - all of which are also facilitated by climate change.
The authors of a 2006 study used the accumulated climate data from Hubbard Brook to determine how climate change has affected the abundance and dynamics of butterflies and moths, whose larvae feast on tree leaves. They found that warmer summers generated more caterpillars in the following year, possibly by encouraging faster growth or, less directly, by affecting the defensive responses of the plants themselves, to the ultimate benefit of the caterpillars.
More caterpillars means more food for songbirds that are also influenced by a changing climate. A long-term study is currently underway at Hubbard Brook to determine how climate factors affect bird ecology, from food and habitat availability to predator pressure and, ultimately, breeding success. Changes in migratory bird arrival dates and the presence of what were formerly considered to be more southerly species, such as the tufted titmouse, have already been observed.
The measurements that have been so steadfastly collected at Hubbard Brook are now proving vital to understanding climate change and its consequences in the Northeast, for everything from the bird life that inhabits our trees to what exactly those trees are - or are going to be. Amidst all the hue and cry over models, trends, and predictions on a global scale, having precise measurements of the changes happening in our backyard will help us prepare for what’s ahead.