Default properties are the properties the program uses when adding a new object. You can change the default properties of an object after you click the object’s toolbar button, but before you finish adding the object. (Any changes you make after the object has been added will only affect that object.)
Default properties are stored with the landscape, not globally. Therefore, if you want to use the default properties from one landscape when creating a new landscape, simply save the existing landscape as a new one and delete the unwanted objects.
Whenever you start a new landscape (by starting one from scratch or by selecting New from the File menu), all default properties are restored to their original settings.