A BSTRA CT-This compendium of fire information for selected south Florida vegetative communities will help resource managers and policymakers to better predict the consequences of their fire management decisions. Included is a brief history of fire in south Florida, along with some associated damages and benefits. Certain natural functions fulfilled by fire are outlined. Fire is rated against other specified threats to south Florida's remaining wildlands, and the impact of ongoing vegetative changes upon fire management in the near future is assessed. The effect of fire on attainment of resource management objectives and the necessity of integrating fire planning into the land management planning process are explained. Available information about fire effects is presented for each of the major vegetative types in south Florida, and fire's relationship with certain exotic species is discussed.
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Native forest species exhibit a well‐known range of ecological roles with respect to natural disturbance regimes, from pioneer phase to mature phase, and they regenerate from a range of sources, including dormant seeds, seed rain, pre‐established juveniles, and resprouts from damaged adults. In contrast, the ecological roles of invasive, non‐indigenous species in forest communities after natural disturbances are not well understood. Some previous studies of invasive species have emphasized their weedy nature and their ability to colonize anthropogenic disturbances. Tropical hardwood hammock forests in southern Florida experience frequent disturbance by hurricanes. Our studies of forest regeneration during two years following a recent severe hurricane suggest that invasive non‐indigenous forest species exhibit the same range of ecological roles as native forest species and compete with native species for particular kinds of regeneration opportunities. To study ecological roles of non‐indigenous species in regenerating forests after Hurricane Andrew, we set up four large study areas at each of three study sites that had differing amounts of hurricane‐caused canopy disturbance. There were two pairs of 30 × 60 m research plots per site, and in each pair there was one control plot and one restoration plot; restoration areas were subject to an aggressive management program, focused on reducing non‐indigenous vine cover. Within these study areas we subsampled vegetation in small study plots that were regularly spaced, and conducted vegetation censuses in April (the end of the dry season) and October (the end of the rainy season) for 2 yr, beginning in April 1993. We found that the source of regeneration for forest species was dependent upon the amount of canopy disturbance, the time since disturbance, and the autecology of the constituent species. Overall, 28% of the 90 species were non‐indigenous: 34% of the vines (N = 32) and 24% of other life‐forms (N = 58). Non‐indigenous vines seemed to have a special role; not only could they compete with native vines, but they could also negatively affect the regeneration of other natives from a diverse array of sources including pre‐established juveniles and resprouts from damaged adults. Both native and non‐indigenous vine cover in unmanipulated study areas increased following the hurricane. Non‐indigenous vine species had higher cover than native vine species, and many species formed dense “blankets.” Non‐indigenous species in general (not just vines) did not differ significantly from native species in seed mass, nor were they restricted to the pioneer type of life history. Many non‐indigenous species had invaded forests prior to hurricane disturbance and had their own banks of pre‐established juveniles; others recruited from dormant seeds, seed rain, and/or resprouts from pre‐established adults. Based on information on source of regeneration and impact on native species, we propose a classification scheme for functional roles of non‐indigenous invasive species in forests. To i...
Tritium in surface bog peats of the Red Lake wetland, northern Minnesota, exhibits about the same concentration as in atmospheric precipitation, which is still appreciably enriched by tritium from nuclear weapon testing. Past input pulses are not preserved in the peat profile, and the pattern of subsurface decline suggests that most of the modern precipitation rich in tritium is removed rapidly by evapotranspiration and by lateral runoff within the top 1.5 m of the 3.5—m thickness of little—decomposed Sphagnum peat at the crest of the raised bog. However, some bomb tritium has penetrated, presumably by molecular diffusion, down to the discontinuity between the highly permeable Sphagnum peat and the underlying well—decomposed and much less permeable fen peat. In profundal lake sediments of four Minnesota lakes the influence of highly enriched precipitation from the early 1960's has likewise been largely transitory and of major significance only in sediment depths of less than 1 m, although some penetration below the depth has occurred, presumably by molecular diffusion.
Introduction 1 Purpose and scope 3 Description of study area 3 Previous investigations 3 Acknowledgments 3 Data compilation and analysis 3 Rainfall 3 Rainfall-discharge relation 4 Well-field pumpage 4 Water-level trends 7 Background conditions 7 Wells outside the cone of depression 7 Wells within the cone of depression 8 Effects of pumping on water levels in the wetland 9 Summary 15 References cited 15 FIGURES 1. Map of study area showing data-collection sites, section A-A', and region of wetlands dewatered by pumping 2 2-3.
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