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Abstract

For the unrooted spanning-forest measure on any finite simple graph with arbitrary positive edge weights, we prove real stability of the full incident-edge marginal at every vertex. Thus each star is strongly Rayleigh, incident edges are nonpositively correlated, and every vertex degree has a Poisson-binomial law. The proof identifies a classical optional-component-mark forest polynomial with a stable determinant differential operator applied to a signed matching polynomial. We also prove strict pairwise negative edge correlation on every complete graph K_N, N ≥ 3, and complete bipartite graph K_(m,n), m,n ≥ 2, at every common positive fugacity. Their disjoint-edge proofs use exact Hermite and Laguerre counts, continued fractions and scalar crossing barriers, with complete exact polynomial certificates. Quantitative bipartite critical and supercritical deficit asymptotics are also established, with explicit critical-profile endpoint and supercritical matching coefficient. Empty forests and isolated vertices are included.