While many from cold northern regions might welcome a bit of climate warming, the negative consequences for others — for example, many arctic populations — clearly counterbalance the benefits. In the northeastern United States and elsewhere, one of the ironic outcomes of winter climate warming could be an increase in the frequency of soil frost in forests; long-term observations at Hubbard Brook illustrate that soil freezing has normally been the exception rather than the rule because a deep snowpack usually develops in early winter, insulating soil from severe mid-winter cold. Later and more intermittent snowpack development in a warmer winter climate is likely to result in more rather than less soil freezing. Long-term observations, field experiments and mechanistic studies at Hubbard Brook have demonstrated the consequences of soil freezing for ecosystem processes and forest health.
Long-term observations of streamwater chemistry at Hubbard Brook first suggested the co-incidence between large nitrate-nitrogen pulses and severe soil freezing events. A series of snow removal experiments have provided conclusive evidence of this connection and demonstrated the mechanisms underlying the nitrate leaching response. Soil freezing evidently damages the fine roots of northern hardwood trees, reducing the trees’ capacity for nutrient uptake in early summer. Soluble nitrogen accumulates in soil and is flushed to the streams by summer rain. The potential consequences for soil and surface water chemistry and for forest tree nutrition and health from an increased frequency of soil freezing events are yet another likely negative impact of global climate change on environmental well being.
Of course, the potential effects of winter climate change on forest ecosystem health are not confined to soil freezing and continuing studies at Hubbard Brook are exploring some of these complex effects. For example, the return to the northern forest of its dominant herbivore, the moose, following its widespread elimination in the last century has important consequences for both vegetation dynamics and the habitats of diverse animal assemblages. We are evaluating the complex interactions among winter weather and snowpack development, moose browsing activity, responses of vegetation and nitrogen cycling, and the populations of songbirds and a competing herbivore, the white-tailed deer. The long-term context provided by the 60-year record of climate and ecosystem dynamics at Hubbard is essential for demonstrating and understanding these interactions and predicting the consequences for provision of ecosystem services.