The Mixed Broadleaf-Shrub complex is characterized by the three broadleaf species that are common in southern interior British Columbia: paper birch, trembling aspen, and black cottonwood. Birch is dominant, but mixtures of two or three of these species are common. Willow and/or Sitka alder sometimes occur in the mid-storey, and thimbleberry and fireweed are common in the understorey. On sites where aspen dominates, the vegetation community is referred to as the Aspen complex, and if cottonwood is dominant, it is classified as the Cottonwood-Shrub complex.

The Mixed Broadleaf-Shrub complex is widespread in the ICH biogeoclimatic zone of southern interior B.C., and it is also common in wet-belt portions of the IDF and MS zones. Development of the Mixed Broadleaf-Shrub complex is favoured by disturbances that remove the forest canopy and increase light (e.g., harvesting or wildfire), and that expose mineral soil or mix mineral and organic materials. If a seed source is available, birch seed will readily germinate on these substrates. Sprouting of cut or burned birch stems can also contribute substantially to birch density on sites where there was a high component of vigorous birch in the original stand. Sprouts grow vigorously (50-200 cm/year) and can reach 7 m in height by age 10. Birch saplings that originate from seed grow more slowly, reaching a height of about 4 m by age 10.

The Mixed Broadleaf-Shrub complex can negatively affect conifer seedling growth and vigour by reducing light availability under and within the broadleaf canopy. In the ICH zone, juvenile birch height growth under full sun conditions exceeds that of all conifers except western larch. Broadleaf branches can also cause physical ‘whipping’ damage to young conifers. In spite of its competitive ability, however, the presence of some birch in conifer stands is favorable to ecosystem health and productivity. The benefits of birch include: retention of site productivity through annual cycling of nutrients, reduced spread of Armillaria root disease, reduced spruce weevil damage, protection against frost damage, reduced incidence of ungulate browsing, increased complexity in vertical stand structure, and possibly the transfer of nutrients to conifers via root contact.