my $sth1 = $db->prepare(q{
				UPDATE trees 
				SET
					department = ?
				WHERE 
					sport = ?
				AND
					round = ?
				}) 
			or die "Can't prepare first statement: ". $dbh->errstr() . "\n";
# and so with $sth2 and $sth3

# execution time
for my $i (1..13) {

# I'd suggest reworking this data structure too, but
# I'll work with what you have

# smaller sermon : initialize the variables that are
# expected to change on each step through the loop
# with my *** inside the loop ***
# that way, you get a fresh copy of the variable each time
# through without potentially having old values intrude

	my $team = $teams{"team$i"};
	my $score = $scores{"score$i'};
	$sth1->execute ($team, $sport, $i)

		or die "Execution of first update failed: ". $dbh->errstr() ."\n";
	$sth2->execute( #blah blah...
}