Riparian types within the city include riparian scrub, riparian woodland, and riparian forest. Riparian habitats are located along drainages and streams, where the soil tends to be moist during all or part of the year. In Carlsbad, riparian communities may also be the result of agricultural runoff. All riparian habitats are considered sensitive.
Riparian scrub includes several plant communities, including mulefat scrub, southern willow scrub, and baccharis/tamarisk scrub. Riparian scrub is typically dominated by willows and cottonwood trees, by mulefat, or by broom baccharis or tamarisk, an introduced species. The understory is variable depending on canopy coverage, disturbance history and water availability, and usually includes poison oak, wild grape, western ragweed, rushes, and a variety of other water-loving plants.
Riparian woodland includes sycamore-alder riparian woodland and other riparian woodland. Sycamore-alder woodland is an open to moderately closed, winter-deciduous, broadleafed riparian woodland, dominated by well-spaced western sycamore. The community typically includes individuals of several other tree species, including willow, coast live oak, Mexican elderberry, and cottonwood. This community occurs in broad channels of intermittent streams, usually with a cobbly substrate. Sycamore-alder woodland is uncommon in Carlsbad, occurring primarily in the Sunny Creek area and along a narrow drainage south of Lake Calavera.
Riparian Forest includes southern coast live oak riparian forest. This community type is dominated by coast live oak with scattered individuals of other tree species, such as western sycamore, willow, and Mexican elderberry. The understory includes toyon, laurel sumac, California wild rose, poison oak, and currants.