CLIMATE AND DECIDUOUS FORESTS IN MARITIME CANADA

1. CLIMATE AND DECIDUOUS FORESTS IN MARITIME CANADA Future warmer and locally drier summer climates are projected for Maritime Canada. This will cause changes of range of plant and animal species in the forests. Climate change will result in loss of habitat, decreases or extinction of native plant and animal species, and the arrival of more invasive species. The effects of climate change are likely to be compounded by other stresses, especially those caused by human use of the land. The future fate of the already highly stressed ecosystems of the remnant Acadian Forest is uncertain. Changes in ecosystems and dominant species will occur due to changes in climate. Replacement of formerly dominant species by new migrants from the southwest, and increasing significance of species present in lesser amounts today, can both be expected. Since tree species require long periods to migrate, most of the changes will involve shifts in the proportions of trees that are already present in the forests of Maritime Canada. Regional warming has resulted in the progressively earlier arrival of spring in Maritime Canada. This has lead to earlier leaf development in deciduous trees, earlier flower blooming and earlier bird nesting times. The effects are greatest in interior areas, and relatively less along the coast. Earlier spring weather can cause problems in Maritime forests. An early spring warm spell followed by frost can result in dieback of the youngest shoots and prematurely opened leaves. This is particularly a problem for yellow birch, which has suffered greatly from tree crown dieback. A decrease in the proportion of yellow birch in the forests would result in the expansion of white birch and poplar. Prior to the development of agriculture, much of Maritime Canada was covered by the Acadian deciduous forest. Broad-leaved deciduous trees, such as beech, sugar maple, and northern red oak, dominated the assemblage. Beech appears to have covered more than 50% of many inland areas of southern New Brunswick, mainland Nova Scotia, and PEI. Other southern boreal species such as yellow birch, white pine, hemlock, and white cedar were also common. Originally, white birch and jack pine were both uncommon. As a result of the changes brought by agriculture and the introduction of other tree species, the Acadian Deciduous forest has been largely replaced by a more varied assemblage of trees. The proportions of spruce, fir, pine, and maple have increased at the expense of beech and red oak. Future climate change will operate on a forest that has already undergone many changes in the last 200 years, within the lifespan of many trees. Yellow birch and cedar Mulberry (left) could expand its range as climate changes. Cedar (right) would benefit from reduced snowfall and freezing rain. Red Spruce Eastern hemlock is favoured under warm climates, but where forest fire frequency is low. In Maritime forests, suppression of forest fires has allowed hemlock to expand more rapidly than jack or red pine. Hemlock was shunned by loggers, due to its hardness and its tendency to break in shards when cut. It is a poor choice for firewood, as it tends to throw off shards explosively when burned. Consequently, hemlock has frequently expanded its geographical range and share of the forest assemblages of eastern Canada following logging. Hemlock is susceptible to damage by freezing rain and ice storms, however. Decreased summer precipitation raises the possibility of drought disturbance. Trees with deep root systems are resistant to drought, but shallow-rooting hemlock and spruce may have some difficulty. Lady-slipper orchids prefers moist, acidic peaty or conifer needle-duff soil. Lady-slippers flourish best under wetter summer conditions, beneath mature conifer forests. Summer drought and forest fires, which favour the growth of pines and maples, would gradually result in the replacement of lady-slippers with other orchid species. Transplantation of lady-slippers is extremely difficult, hampering re-population of areas. More forest fires are likely in the interior areas of the Maritimes. Increased summer heat and drought in some areas leading to increased frequency of fires would affect all forest species. Analysis of palaeo-ecological data and climate modeling suggests that an increase in forest fires can be expected in Atlantic Canada. That would favour the expansion of red pine in Nova Scotia and southern New Brunswick, and jack pine in northern New Brunswick and Cape Breton. In the Maritimes, most forest fires result from human activity. Warmer and drier summers will result in more human use of forested areas for recreation, leading to an increase in fire activity. A change in forest composition could result. Adaptation efforts for the deciduous forests involve development of management plans, protection of key habitats and species, and sustainable use. Protected areas and wildlife and forestry management policies that incorporate climate change sensitivity and risk analysis are important. The parks and protected areas of Maritime Canada help to cushion the impacts of climate change on natural ecosystems and biodiversity. Parks also allow us to see how ecosystems that are less disturbed by human activity respond. Many trees in Maritime forests live for more than 200 years. Adaptation options are more limited within the forestry industry over the short term. The best strategies promote enhancement of the capacity of the forests to cope with shifting climate conditions and affected site conditions, and preservation of genetic variability. Harvesting and reforestation should be conducted with a view towards maintaining the maximum possible degree of genetic variability. Sugar maple is well-adapted to both the present and anticipated future Maritime climates. Maples have increased in numbers over the past 200 years, as a result of cutting of other deciduous trees. Text and photographs by Norm Catto, ncatto@mun.ca