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The changing seasons Nature in the Laurentian Forest changes constantly from one season to the next. Spring is a joyous time, decked out in the bright colours of the many flowers and the soft greens of young shoots. In summer, the green of the foliage becomes more intense, and few flowers bloom in the shady underbrush. In fall, the leaves turn yellow, orange and red before dropping and carpeting the ground. In winter, a few conifers keep their dark green coats and break the monotony of the bare landscape. A matter of light The relative length of day and night (or “photoperiod”) is the main factor that regulates the changes from one season to the next. At the Biodôme, it is the natural light entering through the skylights and in particular the light from the artificial lighting system that determines the photoperiod. In fall, the days become shorter until December 21, the shortest day of the year. Then they begin to lengthen, until we reach the longest day of the year, June 21. Temperature is also important Changing temperatures also influence biological cycles from one season to the next. Cold fall nights, combined with the reduced light, provoke the phenomena that cause leaves to change colours. In the Biodôme's Laurentian Forest, the temperature also varies with the seasons, but never drops below zero — to keep the pipes from freezing and for visitors’ comfort. The leaves at the Biodôme do not turn such vibrant colours as in the actual Laurentians, perhaps because it never gets extremely cold here and because the soil acidity is different. We begin raising the temperature as of March 1, to cause spring to arrive earlier than in nature. We also increase the photoperiod by ten minutes a day throughout March. Changes in the undergrowth The plants in the undergrowth of the Laurentian Forest are subject to very changeable light and temperature conditions, depending on the season. In spring the soil begins to warm up, and the plants beneath the spreading trees take advantage of the heat and abundant light to grow, accumulate reserves, bloom and produce berries. Once summer comes, the trees blocks much of the sunlight. The plants have finished flowering. Along with their flowers and fruit, some plants also lose their foliage, leaving nothing more than a bulb or rhizomes in the soil. The reserves stored in the bulb or rhizomes allow the plant to survive and even to grow in the soil until springtime rolls around again. A bud-ful of potential! In the spring, budburst occurs once it stays mild overnight. In the Laurentians, north of Montréal, this phenomenon occurs in May. It happens earlier at the Biodôme, in late March and early April, since we begin raising the temperature sooner than in nature to bring on an early spring. Trees produce their buds during the summer, when their leaves have reached their maximum size. This is why you can already see buds on the trees when the leaves drop in the fall. In winter, the trees are dormant, and the cells of the buds can withstand the severe cold.
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