Olympic Habitat Development Study
US FOREST SERVICE

 

Station 4 -
Cascara Buckthorn
(Frangula [Rhamnus] purshiana)
Family Rhamnaceae

Easily recognizable by its long, oval leaves with prominent parallel veins, this small tree rarely grows more than 9 m29 feet tall.  It tolerates shade well and grows in moist soils.  The leaf primordia (future leaf structures) of this deciduous tree are not in buds over the winter (a condition called naked buds).  Young cascaras often retain the top-most leaves as living green foliage all winter long so this small tree can often be identified from a distance in the winter.

Its very bitter bark has strong laxative qualities and was used by Native Americans and has also been harvested commercially.  Freshly collected bark is too strong for immediate use and it has to be aged for about a year before consumption.  Commercial harvest declined greatly as chemical alternatives became available; however, a renewed interest in natural remedies has resulted in greater harvest.  Bark removal needs to be done in a sustainable fashion, however, as complete removal of the bark around the stem will kill the tree..  Overharvesting and lack of interest in maintaining this tree in managed stands has sharply reduced the amount of cascaras in many areas.

The blue-black berries ripen in late summer and are a popular food for many birds and other wildlife species such as black bears who will break the branches down to facilitate stripping the branches for berries.  Band-tail pigeons historically were known to feast on the berries and some wildlife biologists have suggested the decline in numbers of these native pigeons is due in part to the decline in available cascara berries. The berries are edible by humans although regarded as not very tasty.

In modern forest landscapes cascara is found along road ditches, in canopy openings and in the understory of forest stands.  Thinning is likely to improve the growing environment for cascara.


 

Cascara occasionally grows up to 15 m tall, though more commonly a large shrub or small tree 5-10 m tall, with a trunk 20-50 cm in diameter.
Cascara have long, oval leaves with prominent parallel veins. Cascara occasionally grows up to 15 m tall, though more commonly a large shrub or small tree 5-10 m tall, with a trunk 20-50 cm in diameter. The bark is brownish to silver-grey with light splotching.
Cascara profile.