The Willow complex can include various willow species, but upland species such as Scouler’s willow, Sitka willow, and Bebb’s willow are the most common. Although not common in southern interior British Columbia, this community may be found on moist to wet sites in the IDF, ICH, MS, and ESSF biogeoclimatic zones. In clearcuts, it is often present on wet microsites that are interspersed with drier areas where willow is sparse or absent. Although willow tolerates a wide range of nutrient conditions, it generally grows best on medium to rich sites.

Willow is very shade-intolerant and does not grow well under forest canopies. However, following logging or wildfire, willow can become abundant even where it was sparse in the original stand. Willow produces abundant seed each year and is favoured by treatments that expose mineral soil, but it can take several years for seed-origin willow to become dense enough to compete with conifer seedlings. The Willow complex develops much more quickly where harvesting or site preparation treatments have stimulated vegetative reproduction by severing existing willow stems or mixing stem and root fragments into the soil. Fire also stimulates sprouting.

In southern interior B.C., juvenile willow plants usually pose a greater competitive risk to young conifer seedlings than mature willow plants. When mature, willow does not form a dense canopy, but in its juvenile form, it produces numerous sprouts with large leaves that can reduce light availability to seedlings and inhibit soil warming. Willow grows best on wet, nutrient-rich sites, so it usually is not competing with conifers for water or nutrients. Conversely, it cycles nutrients, which improves nutrient availability and has a positive effect on long-term site productivity.

A typical example of the Willow complex showing clumpy distribution of willow and alder (14 years after broadcast burning).