Synchrony of Regeneration, Gaps, and Latitudinal Differences in Tree Species Diversity

摘要: Treefall gaps are necessary for establishment and/or growth to maturity of many forest trees. It therefore seems reasonable hypothesize that characteristics influence both persistence populations and coexistence species in forests. The purpose this essay is suggest one way gap might result differences tree diversity between tropical temperate zone Latitudinal gradients seem unlikely be a the physical or distributional different types. Gap formation rates (fraction ground area converted new per year fraction canopy trees dying year) similar variety forests (Brokaw 1985a, Denslow 1987) (Runkle 1985) zones. size varies widely within each region, but average sizes range 1982, 1985, 1987). In regions occur most years throughout year, although they may more common some months than others 1982b, Romme Martin 1982). exist ability respond conditions. That is, two with same size, shape, mechanism represent regeneration opportunities One mechanism, discussed by Poulson Platt (1989), within-gap heterogeneity light levels, especially large gaps, will greater zones, resulting potential withingap specialization levels I argue winter imposes synchronization responses reduces possible discuss relationship using "storage effect" model Chesson Warner (1981), (1985), (1986). storage effect model, as presented above papers, described follows. Species can persist community if their adults long lived reproductive success such population increases scattered good offset declines suffered frequent bad years. regenerative consequences stored long-lived individuals survive through little successful reproduction. A low-density must experience frequently enough extinction does not occur. High variance reproduction over time, environmental variability intrinsic factors, chance favorable periods encountered, at least occasionally, rare species. also assumes low densities increase greatly decline only slightly years, whereas abundant extent any given year. Tropical characterized broad interplay among seasonal variations climate. Thus arrival (before soon after formation) well survival (see Martinez-Ramos et al. 1989, Schupp 1989) have evaluated relative phenology forests, variation occurs seeds site. rhythm fruitfall seed germination has been documented (Foster Garwood 1983). Differences these properties could create predicted enhanced diversity. Being present on site before created results advantage later arrivals. Growth higher mortality lower plants establishing treefall (Denslow Uhl (1988) found 4 yr formation, advance accounted 97% all 1 m tall five artificial single-treefall 83% multiple-treefall Venezuela. Brokaw (198 5b, stems were established prior 1-3 following formation. Despite importance dispersal into production pioneer lightrequiring (Whitmore 1989), great majority rain woody understory form (Hubbell Foster 1986a, b, Scheiner 1989). Although contin-