First, I do not think you need the "NOT IN" clauses as the "Else If" excludes those anyway.
Then a question: With "I have a field called SPECIES that could contain surveyed tree values such as E,AS,TA within each record", do you mean SPECIES can be E or AS or TA, or do you mean it can contain "E,AS,TA". In the latter case the IN statement will not work.
Finally: the test clause is by default case sensitive. Are the SPECIES values always uppercase?
First, I do not think you need the "NOT IN" clauses as the "Else If" excludes those anyway.
Then a question: With "I have a field called SPECIES that could contain surveyed tree values such as E,AS,TA within each record", do you mean SPECIES can be E or AS or TA, or do you mean it can contain "E,AS,TA". In the latter case the IN statement will not work.
Finally: the test clause is by default case sensitive. Are the SPECIES values always uppercase?
Hi...the SPECIES can contain "E,AS,TA". The values in this field will vary, so "AS" on its own is also possible, or perhaps "JP,BF,AS", etc. The SPECIES values will always be uppercase and separated by a comma if more than one species was surveyed.
I managed to figure this out using StringSearcher, Aggregator and FeatureJoiner (see images).



@aviveiro
If you use the regexps you use in the string searchers in a conditional attribute creator you would have only 1 transformer
Prevents to route the data trough 3 identical streams, and you then don't need to join the result attribute back to the features.
cleaner, more efficient and faster.
I managed to figure this out using StringSearcher, Aggregator and FeatureJoiner (see images).



Good solution.
Just be aware that the regular expression "AS|BA|TA|WB|E|BT" matches not only "E" (hardwood) but "EC" (softwood).
A quick workaround is, add leading and trailing commas to both the regex and the "Search In" value. The StringSearcher parameters dialog would look like this.
Note: If there could be spaces between a comma and the following species in the SPECIES value, remove the spaces beforehand. [Addition] Or, use this regex to find matched species even if there were spaces after/before the comma.
,\s*(AS|BA|TA|WB|E|BT)\s*,
