Résumé
We study the problem of realizing a given graph as an $\alpha$-complex of a set of points in the plane. We study the realizability problem for trees and $2$-trees. In the case of $2$-trees, we confine our attention to the realizability of graphs as the $\alpha$-complex minus faces of dimension two; in other words, realizability of the graph in terms of the $1$-skeleton of the $\alpha$-complex of the point set. We obtain both positive (realizability) and negative (non-realizability) results.