Conservation of natural resources Law and legislation 270 Public lands 115 Management 81 National parks and reserves 81 Environmental protection 79 Environmental policy 71 Natural resources 61 Nature conservation 55 Wildlife conservation 55 Soil conservation 52 Government policy 50 History 47 Pollution 46 Expenditures, Public 43 Human ecology 42 Water-supply 40 Land use 38 Environmental law 37 Environmental aspects 36 Forest reserves 36 Ecology 33 Biodiversity conservation 31 Ecosystem management 31 Indians of North America 31 International cooperation 31 Wilderness areas 28 Sustainable development 26 Budget 24 Land tenure 24