Natural resources Management 159 Conservation of natural resources 76 Environmental policy 63 Sustainable development 56 Environmental protection 49 Environmental aspects 47 Economic conditions 42 History 42 Government policy 39 Economic aspects 35 Human ecology 25 Economic development 24 Land use 22 Power resources 22 Politics and government 21 Environmental conditions 20 Economic policy 19 Law and legislation 19 Political aspects 19 Environmental economics 17 Social change 16 Effect of human beings on 15 Nature 15 Social aspects 15 Ecology 14 Agriculture 13 International status 13 Pollution 12 Research 12