One of the best things about plants and botany in general is the different varieties.
Different plants are more resilient to certain elements than others. Pick up a good
botany-book.
By the leaves. Usually the shape, color of the leaves will indicate the pear species. Geography will also be of help as some species cannot grow in very cold climes.
Pear trees are identified by their fruits.They are not identified by leaves. Their fruit looks like apple. since they grow very slowly it is difficult and time consuming to identify them.
The fruits of the pear tree will help identify it. Bradford pear tree is the shortest and its fruit grows in clusters. The Common and Callery pear trees are tallest.