Deleted records?

>I am trying to do a left outer join between 2 tables matrix and trees. The matrix table has 37550 rows and the trees table has 21484. I want the resultant table to have 37550. Here is the command I am using:
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>select trees.*, matrix.plot as mPlot, matrix.spc_grp as mSpc_Grp, matrix.dbh_98 as mDBH_98 from matrix left outer JOIN trees on trees.plot = matrix.plot AND trees.spc_grp = matrix.spc_grp AND trees.dbh_98 = matrix.dbh_98 AND trees.status_98 = 8 order by matrix.plot, matrix.spc_grp, matrix.dbh_98
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>I end up getting 37618 rows. Where are the extra rows coming from?
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>Any sugestion would be appreciated