UNDERSTORY LIGHT REGIME, SHRUB LAYER AND SAND PINE (PINUS-CLAUSA) REGENERATION IN 4 SCRUB STANDS

Estimates of direct and indirect light regime were derived from hemisp herical canopy photographs for four Florida sand pine (Pinus clausa) s crub stands. Shrub foliage-height density and sand pine regeneration w ere tallied in 4 m(2) cells around photo points. We found negative cor relations between shrub foliage-height density and understory light re gime in all four stands. Sand pine regeneration was spatially associat ed with higher surface light levels and reduced shrub foliage-height d ensity within only one of our four stands, a recently burned (early 19 70s) peninsular site. We found more consistent evidence of shade intol erance in our two Ocala sand pine stands. Sand pine regeneration was a bundant in high light patches within an open, recently burned site; ho wever, in an adjacent 60-yr-old, closed-canopy stand, regeneration was lacking despite a local seed source. Our two Choctawhatchee sand pine stands were characterized by higher surface light regime values than the two peninsular stands and sand pine seedling growth rates were low er than in the one peninsular stand that had regeneration. The closed- canopy stand had a sparse shrub layer; regeneration was ample in this stand, but did not covary with light regime or shrub foliage-height de nsity. The open-canopy stand was in a coastal dune setting with stunte d canopy trees exceeding 100 yr of age. Sand pine regeneration in this stand was not sufficiently abundant to test for spatial association w ith light regime or shrub layer.