Park ranger
A park ranger, park warden, or forest ranger is a person entrusted with protecting and preserving parklands – national, state, provincial, or local parks. "Parks" may be broadly defined by some systems in this context, and include protected culturally or historically important built environments, and is not limited to the natural environment. Different countries use different names for the position. "Warden" is the favored term in Canada, Ireland, and the United Kingdom. Within the United States, the National Park Service refers to the position as a park ranger. The U.S. Forest Service refers to the position as a forest ranger. Other countries use the term "park warden" or "game warden" to describe this occupation. The profession includes a number of disciplines and specializations, and park rangers are often required to be proficient in more than one.
New York City Parks Enforcement Patrol
Begun in 1996 the NYC Parks Enforcement Patrol Mounted Auxiliary Unit is a volunteer unit within the department. This unit is made up of private citizens who volunteer their time by working with officers of the Parks Enforcement Patrol. 
Auxiliary officers patrol in full uniform and on horseback in various NYC parks, and "ensure the preservation of the natural and living resources in the city's parks, as well as the safety of those utilizing the parks, by maintaining a clearly visible presence. They monitor areas that are not accessible by vehicle; they deter, identify and report illegal or unsafe activities that require Parks Enforcement Patrol or police attention; and they advise the public on park rules and regulations."
As an IRS 501C Corporation, the Auxiliary solicits funding to purchase horses, tack and provide training for both the Volunteers and the Professional Officers. Since inception it has provided several hundred thousand dollars towards the operation of the Mounted Unit, including the Capital Construction of a new barn. Former Parks Commissioner Adrian Benepe was quoted as saying "there is some doubt that the Parks Department could afford to run a mounted unit without the Mounted Auxiliary."
Auxiliary officers do not have powers beyond a citizen and cannot make arrests. For this reason a typical patrol will include a PPEP Officer and an Auxiliary Officer. By combining the two, the manpower of the Parks Enforcement Patrol is significantly increased at no cost to the City. Should the team come upon a situation requiring enforcement, the PEP Officer can deal with it while the Auxiliary Officer covers the Officer's back and radios the situation to Parks Central and if needed will ask for additional help.