Conservation of natural resources Environmental policy 62 Environmental protection 49 Natural resources 33 National parks and reserves 25 Congresses 24 Ecology 24 Periodicals 22 Human ecology 17 Land use 17 Study and teaching 14 Environmental aspects 13 Nature conservation 13 History 12 Management 12 Forests and forestry 10 Government policy 10 Wilderness areas 10 Wildlife conservation 10 Citizen participation 8 Pollution 8 Conservation and restoration 7 Effect of human beings on 7 Nature 7 Planning 7 Regional planning 7 Recycling (Waste, etc.) 6 Bibliography 5 Directories 5 Economic development 5