In former times wood was a precious material in Central Tibet because it had to be imported from areas with more wood like East Tibet, Nepal or Bhutan. It was used for constructing monasteries or houses, less often for cult figures. Among these wood imports were also smaller branches unsuitable for any constructions but highly suitable for Zanpar forms.
In general sorts of wood with very fine grain were used for the Zanpars because only with these sorts of fine woods carving with the necessary delicacy were possible for any identification with the pictured motive.
Among other birch wood, wild cherry, hazel and walnut were used. Some Zanpars are red-colored which reminds of the Shorea Robusta which is used in Nepal for very fine carvings.
But the usage and patina of the surface of the Zanpar is mostly in a very bad condition which makes any serious determination of the sort of wood impossible. To ensure a reliable examination a cross section had to be made which would destroy the objects.
The Zanpars were carved by the monks themselves who also carved the sticks for the wood blocks for the Holy Scriptures. But also lay carvers were entrusted with this task.
The copying demanded very precise working which can be seen in the quality of the presented motives. Usually also letters were carved in the Zanpar sticks.
Lay carvers did not possess the education of the monks and very often they were even illiterate. This explains why some writings could not be deciphered and translated. Another possibility is that these texts were written in a dialect or some local speech variation which is hard to translate for modern experts who just know the 'pure' Tibetan language.
About the distribution of work between monks and laymen we do not know much. It can be doubted that the lay carvers were able to carve the very detailed picture alone. Probably the carvers worked under the supervision of the monks.