摘要
The vertex arboricity of a graph is the minimum number of colors the vertices can be labeled so that each color class induces a forest. It was well-known that for every planar graph . In this paper, we prove that if is a planar graph without 7-cycles. This extends a result in [A. Raspaud, W. Wang, On the vertex-arboricity of planar graphs, European J. Combin. 29 (2008) 1064-1075] that for each , planar graphs without -cycles have .