After holding their own in the initial market upheaval that followed China's devalued currency, real estate investment trusts saw their shares succumb this week - including several that have extensive holdings in Fairfield County. Equities in Empire State Realty Trust , SL Green Realty and Urstadt Biddle Properties were trading between 5 percent and 9 percent lower than their price entering the week, with the first two among the largest office building owners in Stamford and Urstadt Biddle holding smaller commercial and retail properties throughout the region.