Regeneration of Pyrophilic Sand Pine (Pinus clausa (Chapm. ex Engelm.) Vasey ex Sarg.) in Fragmented Fire-Suppressed Scrub, South Florida, USA

Pinus clausa var. clausa (Chapm. ex Engelm.) Vasey ex Sarg., sand pine, is the dominant tree of biorich but ecologically compromised Southeast Florida scrub. Scrub habitats and P. clausa have dwindled due to habitat reduction and fragmentation, regional development, and fire suppression. The purpose of the present article was to seek correlates of P. clausa establishment under present unnatural development-impacted conditions using 428 field measurements at four sites to determine spatial positioning preferences relative to vegetation edges, then adding 120 measurements at a single site aimed at evaluating several potential predictors of P. clausa establishment. Potential establishment predictors were adjacency to other woody plants, depth to hard sand horizon, seed tree distance and direction, light-intensity, soil-core color, soil pH and soil surface firmness. Comparing frequency distributions of juvenile P. clausa locations with frequency distributions of random spots within the same perimeters, juvenile pines tended toward adjacency to other woody plants (chi2 p < 0.0001), toward shallow hard horizons (Kolmogorov–Smirnov p = 0.0006), toward soft soil surfaces (K–S p = 0.007), and toward proximity to seed trees (K–S p = 0.004). Additionally, juvenile P. clausa were often clustered under groves of Quercus geminata Small with comparatively thin canopies. Bayesian logistic regression showed adjacency to woody plants as a strong predictor of P. clausa establishment. When alongside other plants, P. clausa establishment was mostly on the north or east side of neighboring plant edges. Overall conclusions were that juvenile Pinus clausa in SE Florida scrub fragments is sensitive to positioning relative to other woody plants, and is associated with soil surface softness, soil depth to hard horizon, and light levels, except as seedlings.