The Spanish UD treebank come from the universal Google dataset (version 2.0). It consists of roughly 4,000 sentences and 112,718 tokens taken from newspaper articles, blogs and consumer reviews. The conversion to the UD POS and UD dependencies have been performed automatically, using heuristic rules and fixed lists of words. The output of the conversion has not been manually corrected.
More information about the original Google dataset can be found in the following paper:
Universal Dependency Annotation for Multilingual Parsing Ryan McDonald, Joakim Nivre, Yvonne Quirmbach-Brundage, Yoav Goldberg, Dipanjan Das, Kuzman Ganchev, Keith Hall, Slav Petrov, Hao Zhang, Oscar Tackstrom, Claudia Bedini, Nuria Bertomeu Castello and Jungmee Lee Proceedings of ACL 2013