Baynes Island, except for narrow gravel bars at its perimeter, is completely forested. One community of shrubs and four forest communities have been described. Shrub stands, of limited extent, are dominated by the tall shrubs Pacific willow and Pacific ninebark. Black cottonwood-red alder woods, with an understory of salmonberry and red-osier dogwood, cover much of the island. On drier sites the cottonwood stands contain bigleaf and vine maples, and hazelnut is a common understory shrub. Lastly, wet depressions support red alder trees in association with red-osier dogwood, skunk cabbage, and water-parsley. Additional trees recorded on the island are grand fir, Sitka spruce, and western

redcedar. Four species of ferns and seven of mosses have been noted.

A variety of birds, including warblers, thrushes, wrens, woodpeckers, chickadees, juncos, and kinglets has been observed in the reserve.

The reserve is an island on the Squamish River floodplain, surrounded by mountains of the Coast Range which rise to over 2000 m. Baynes Island is located where the active, high-gradient Cheakamus River enters the lower gradient Squamish (1.25 m/km) and deposits much of its coarse-grained bedload. The Squamish River is subjected to extreme variations in flow, the lowest recorded daily flow (11 m3/s) being 200 times less than the maximum daily flow (2240 m3/s). Rainfall and snowmelt events result in frequent flooding of valley bottom lands, and in erosion and deposition of material. The highest mean monthly flows are normally in June, the lowest in March. Baynes Island soils are largely poorly developed Regosols on alluvial deposits. Local climatic events include fall and winter storms funneled up Howe Sound between high mountains, strong outflow winds (“Squamish winds”) in winter, and summertime convective showers.

Reserve resides in traditional Squamish Nation territory.
The area is used by Squamish Nation for traditional salmon harvest.