New Strands of Research

What is the meaning of the phrase "new strands of research" in the following sentence:

The last two decades have also seen the emergence of new strands of research on multilingualism which have incorporated critical and poststructuralist perspective from social theory and embraced new epistemologies and research methods.

Is there any synonym for this phrase or for the word strand in this context?

Solution 1:

One of the definitions of strand denotes this metaphoric application:

1.3 An element that forms part of a complex whole:

ODO

The research is the complex whole, and the strands are elements of that research.

The etymology makes the analogous word picture clear:

"individual fiber of a rope, string, etc.," late 15c., probably from a continental Germanic source akin to Old High German streno "lock, tress, strand of hair,"
Middle Dutch strene "a skein, hank of thread,"
German Strähne "a skein, strand," of unknown connection.
Perhaps to English via an Old French form.

Etymonline.com