Yes, Western Yew is toxic to dogs!
Dogs accidentally consuming the Western Yew plants can show the following clinical symptoms: Vomiting, Prolonged Depression, Incoordination, Hypersalivaton, Sleepiness Or Excitation, Dilated Pupils, Low Body Temperature, Low Blood Pressure, Coma, Seizure And Death (In Rare Cases).
Western Yew consumption is also toxic to Cats and Horses.
Toxic Principles Of Western Yew: Taxine A and B, Volatile oil.
More Info About The Western Yew Plant
Scientific Name: Taxus brevifolia
Family: Taxaceae.
Also known as: English Yew, Pacific Yew, Japanese Yew, Anglo-Japanese Yew.
The answer is based on information found on The American Society for the Prevention of Cruelty to Animals (ASPCA) website.