reserva biológica união (união biological reserve) is a relatively recent addition to the biological reserves found in brazil, being established in 1998 in the central section of the state of rio de janeiro, roughly 150 miles northwest of the city of rio, consisting of the municipalities of casimiro de abreu, macaé and the rio das ostras.

encompassing an area of close to 7,500 acres, the reserve has a colorful history dating back to the 1920s when it was founded as a 'farm union.' in subsequent years it switched hands to a british railway company in the late 1930s, which then became the property of the state railway system in the 1950s. this lasted until the middle 1990s when the land became vacant again.

over the years, eucalyptus trees were introduced into the area to combat deforestation and the wood was used first as fuel for the steam engines and later as wood for the pullman sleeper cars.