Ecology 410 Human ecology 373 Environmental aspects 229 Environmental policy 91 History 79 Nature 61 Environmental protection 58 Sustainable development 58 City planning 57 Forest ecology 55 Social aspects 55 Effect of human beings on 54 Pollution 52 Urban ecology 48 Philosophy 47 Climatic changes 40 Stream ecology 40 Aquatic ecology 38 Freshwater ecology 36 Agricultural ecology 35 Cities and towns 33 Political aspects 33 Urban ecology (Sociology) 33 Botany 32 Economic development 32 Mathematical models 32 Nature conservation 32 Environmental sciences 31 Conservation of natural resources 29 Lake ecology 28