This article identifies potential land use changes and their environmental effects on nature reserves, based on case studies of the Stefan Starzyński Kabacki Forest and the Natolin Forest. The two nature reserves are located in the area of Warsaw agglomeration (i.e. Warsaw, Piaseczno and Konstancin-Jeziorna) development. Changes in land use patterns have been identified on the basis of designations of the Local Area Development Plans and of the Studies of Conditions and Directions of Spatial Development. Surface areas of the land subject to changes in land use patterns were calculated and the direction of these changes was determined. The compliance of the existing land use with planning documents’ designations (expressed in percentages) was assessed in order to identify the magnitude of area transformation. The consistency of Local Area Development Plan’s environmental provisions was scrutinized. Urban and road network development will be the key development directions in these areas, along with a serious shrinkage of farmland and green areas. Housing development is expected to increase the number of visitors to the nature reserves. In particular, this is the case of Stefan Starzyński Kabacki Forest which (unlike Natolin Forest) is open to the general public. Road network, which is to be developed also in the proximity of the reserves, is expected to be the key source of pollution. The area of the nature reserves and adjacent land is at risk of a decrease in groundwater table as a result of housing development. The key water protection factors are: (a) connection of houses to the water supply grid, which over time is expected to eliminate the local ground water uptake; and (b) connection to the sewer system, which will minimize the use of septic tanks and penetration of pollutants to the groundwater. Local development plans address these issues, albeit not quite consistently across the surveyed area. Both nature reserves undergo increasing isolation that will affect migration capabilities of animals, in particular the populations of larger mammals. Besides development of open areas, new planned roads – the South Warsaw Bypass, Rosnowskiego Street, Nowokabacka Street and Voivodship Road. 721 – are the key factors behind this process.