Ecology of Deciduous Forests: Living with Seasonal Shade and Winter Chill
Forests are communities where trees form a closed canopy, so only low levels of sunlight can enter when the trees are leafed out. Deciduous forests are those where trees drop their leaves each year in the autumn because when temperatures drop, the water within the leaves' cells freezes, breaking the cell walls.
These forests share the planet with desert, boreal forest, tropical forest, grassland, scrub, and tundra biomes. Often taken for granted, temperate deciduous forests are uncommon on a global scale, and should be prized and conserved.
"One of the most conspicuous and stunningly beautiful seasonal phenomena in the north temperate zone is the flowering and leafing out of the northern forest. Both the flowering and the leafing out determine the insect populations, which in turn make the summer world possible for the majority of the birds and most mammals." Heinrich, Bernd. Summer World (p. 14). HarperCollins e-books. Kindle Edition.
Adaptations and Strategies for Living in the Deciduous Forest
Vegetation is adapted to the deep shade of the summer, and the colder, but sunnier conditions of winter, as described below. The rich bounty of leaf litter that is rained onto the forest floor each autumn also plays an important role.
Large leaves in shady areas. large leaves can capture more sunlight, which is at a premium in the lower levels of the forest. Note how large the leaves are on small trees in shady sites, and how much smaller they are in the sunniest areas high in the canopy.
Multi-directional branch layers in subcanopy trees. Branches that occur in many layers and point in different directions can capture sunlight as it comes through the trees at different angles during different times of day and different times of year.
Spring flowering. In open areas, wildflowers often bloom all summer, but in forests the majority of the plants bloom in the spring before the canopy trees are fully leafed out. This allows the plants to capture much more sun energy than they will be able to when the forest floor is shady. They use this additional energy to flower and begin to form their seeds. “Spring ephemerals” are special spring bloomers that flower and set seed by early summer. Their leaves have completely disappeared by mid-summer.
Suppressed growth in the understory. “Suppressed growth” refers to trees that can live as saplings in the understory for years, even decades, all the while growing strong root systems. These small trees are “released” when a large limb or entire tree that was casting shade upon them from above dies, leaving a gap in the canopy. The trees shoot up quickly in the gap.
Straight, unbranched trunks on the canopy trees: once a gap opens above an understory tree, the tree puts all of its energy towards growing into the canopy above it, not to growing side branches in the shady understory, so trees tend to be tall and straight.
Parasitism is also an effective way to live in shady conditions: rather than photosynthesize, a few plants form connections to other plants and draw in the nutrients they need.