What is a "native" tree species?

Why does it matter? Are these claims true about the virtues of native species?
serviceberry in a lawn setting
                                                    Serviceberry in a lawn setting

Which native species make good urban trees? Where can I find native tree species? Where can I get more information?
Buckstrup, Michelle, and Nina Bassuk.  1998.  "Native for native’s sake?"  American Nurseryman, May 15 issue.  Pp. 55-61.  Check with your local University Extension office for a list of species suitable for your region.  For other information, advice and help on this topic, call offices of your State Urban Forestry Coordinator, or visit urban forestry web sites.