Cool temperatures, a short growing season, frequent forest fires, and acidic soils challenge plant life in the ecozone. In spite of this, almost 88% of the area is forested by a few highly adaptable trees, such as Black Spruce, White Spruce, Jack Pine and Balsam Fir. Black Spruce, the most common species, yields high-quality wood pulp and is a prime species for Canada's large paper industry. Further south are broadleaf trees such as Paper Birch, Trembling Aspen and Poplar, and conifers such as Balsam and White, Red and Jack Pine. In southeastern parts of the ecozone, species characteristic of more temperate climates, including Yellow Birch, Sugar Maple, Black Ash and eastern White Cedar, are common.

Throughout the Boreal Shield, these forests are mixed with innumerable bogs, marshes and other wetlands. Covering nearly 20% of the ecozone, these wetlands are among its most diverse and biologically productive ecosystems. Some larger wetlands in southern regions have been converted into commercial berry farms, which produce large volumes of cranberries and blueberries for markets around the world.

Where the scouring effects of glaciation were intense, bare rock outcrops predominate, dotted by colourful arrays of lichen and ground-hugging shrubs.

Forest fires add to the distinctive mosaic of the Boreal Shield by leaving a patchwork quilt of plant life varying in species composition and age. Although fire often destroys large tracts of forest and occasionally threatens human activities or property, it also renews the landscape by triggering new growth, purging old forests of insect pests and disease, and increasing the variety of habitats available to wildlife.