Polyhedral joins and graph complexes

Abstract: We give the homotopy type of the suspension of a polyhedral join in terms of the polyhedral smash product for the same family of pairs and show that the polyhedral join of pairs $\left(\bigvee\mathbb{S}^0,\emptyset\right)$ over a skeleton of $\Delta^n$ has the homotopy type of some wedge of spheres. We use these results to study the homotopy type of the forest filtration for some lexicographic products of graphs.