The tensile strength of a material is the value at which the material fails when subjected to a tensile force. (Tensile means a force pulling the wood fibers lengthwise, as opposed to a compressive force.) There are a lot of different types and load cases for wood, so there is not one answer to this question. For example,
wood used outside will fail at a lower load than wood inside. Wood is also anisotropic, i.e. it has different strength in different directions.
Example values of tensile strength vary anywhere from 175 pounds per square inch for Utility Grade pine to 1400 PSI for Dense Select Structural grade Douglas Fir. A
good reference for material strength data for most species and grades of commercially available wood can be found in the American Institute of Timber Construction handbook.