We proved that every planar triangle-free graph of order n has a subset of vertices that induces a forest of size at least (71n + 72)/128. This improves the earlier work of Salavatipour (2006). We also pose some questions regarding planar graphs of higher girth.
Tom Kelly;Chun‐Hung Liu, 2018, Size of the largest induced forest in subcubic graphs of girth at least four and five, Journal of Graph Theory, 89, 4, pp. 457-478, 10.1002/jgt.22361, https://doi.org/10.1002/jgt.22361.
François Dross;Mickael Montassier;Alexandre Pinlou, 2016, A lower bound on the order of the largest induced forest in planar graphs with high girth, Discrete Applied Mathematics, 214, pp. 99-107, 10.1016/j.dam.2016.06.011, https://doi.org/10.1016/j.dam.2016.06.011.