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The tree islands of the Everglades area of southern Florida, including adjacent interior and coastal areas, are classified based on species composition and environmental factors controlling tree island distribution and structure. Tree islands occur on various substrates within surrounding habitats that may be freshwater or coastal wetlands, or rockland pine forest of the Atlantic Coastal Ridge. Eight tree island groupings within seven subregions are defined by cluster analysis of data from the literature and previously unpublished studies. Additional types are recognized based on distinguishing ecological features. Most of the types are dominated by native, tropical species found in the continental United States only in southern Florida. Hurricanes, drainage, excessive burning, spread of non-native species and logging have differentially affected all types and few undisturbed tree islands exist even within federally preserved lands. Collectively, the types occur along local and regional elevation gradients, with associated vulnerability to flooding and fires. Marked differences exist in the response of tree islands to protracted flooding that are consistent with their location in the landscape. Thus bayhead swamps, which occur as part of freshwater slough tree islands and are comprised mostly of temperate swamp forest species, have been inundated up to 10 months/yr in the past several decades, while tropical hardwood hammocks on the same tree islands were inundated for 0 to 23% of the year. Hammocks within rockland pine forests seldom if ever flood, but they are subject to periodic fires. A total of 164 woody species occur naturally in the area’s forested islands, although many are rare or highly restricted in distribution. All 135 tropical species have distribution ranges centered in the West Indies where most occur in calcareous, dry sites, frequently as invaders of disturbed habitats.

Recent archaeological excavations on the heads (i.e., the most elevated and upstream parts) of several large Everglades fixed tree islands may reshape what is understood about the age and formation of these landforms, and about the role of humans in the early Everglades wetland, between 3500 and 1000 B.C. Tree islands are patches of high ground, dry enough to support trees, that rise about 1 meter above the surrounding wetland, and those islands termed “fixed” are the large teardrop-shaped islands thought to have formed over localized high points in the underlying bedrock (Figures 1a and 1b). A hard, cemented carbonate layer perched in the sediments of two tree islands in the southern Everglades was discovered by U.S. National Park Service archaeologists, and penetration of it with a concrete saw revealed that beneath the layer are unconsolidated sediments containing archaeological artifacts dating back to late-Archaic times (3000–1000 B.C.) [Schwadron, 2006].

In forests, the effects of different life forms on fire behavior may vary depending on their contributions to total fuel loads. We examined the distribution of fuel components before fire, their effects on fire behavior, and the effects of fire on subsequent fuel recovery in pine forests within the National Key Deer Refuge in the Florida Keys. We conducted a burning experiment in six blocks, within each of which we assigned 1-ha plots to three treatments: control, summer, and winter burn. Owing to logistical constraints, we burned only 11 plots, three in winter and eight in summer, over a 4-year period from 1998 to 2001. We used path analysis to model the effects of fuel type and char height, an indicator of fire intensity, on fuel consumption. Fire intensity increased with surface fuel loads, but was negatively related to the quantity of hardwood shrub fuels, probably because these fuels are associated with a moist microenvironment within hardwood patches, and therefore tend to resist fire. Winter fires were milder than summer fires, and were less effective at inhibiting shrub encroachment. A mixed seasonal approach is suggested for fire management, with burns applied opportunistically under a range of winter and summer conditions, but more frequently than that prevalent in the recent past.

A tree species replacement sequence for dry broadleaved forests (tropical hardwood hammocks) in the upper Florida Keys was inferred from species abundances in stands abandoned from agriculture or other anthropogenic acitivities at different times in the past. Stands were sampled soon after Hurricane Andrew, with live and hurricane-killed trees recorded separately; thus it was also possible to assess the immediate effect of Hurricane Andrew on stand successional status. We used weighted averaging regression to calculate successional age optima and tolerances for all species, based on the species composition of the pre-hurricane stands. Then we used weighted averaging calibration to calculate and compare inferred successional ages for stands based on (1) the species composition of the pre-hurricane stands and (2) the hurricane-killed species assemblages. Species characteristic of the earliest stages of post-agricultural stand development remains a significant component of the forest for many years, but are gradually replaced by taxa not present, even as seedlings, during the first few decades. This compositional sequence of a century or more is characterized by the replacement of deciduous by evergreen species, which is hypothesized to be driven by increasing moisture storage capacity in the young organic soils. Mortality from Hurricane Andrew was concentrated among early-successional species, thus tending to amplify the long-term trend in species composition.

Site and vegetation characteristics were examined in 113 Florida Keys locations that had been undisturbed for at least 50 years. Detrended correspondence analysis (DECORANA) indicated that Keys vegetation was arranged along two major environmental gradients: an elevational gradient within islands, and a geographic gradient associated with position along the NE-SW trending island chain. Both were complex gradients, with soil depth and type, periodicity of tidal inundation, ground water depth and salinity, climate, and geological substrate as potential contributing factors. Two-way indicator species analysis (TWINSPAN) was used to divide the samples into 14 major groups on the basis of plant species composition. Finally, the TWINSPAN classification was modified to recognize 13 Ecological Site Units which were homogeneous in important site factors as well as vegetation characteristics. Plant species diversity increased from intertidal to upland site units, while canopy height, basal area, and fine litter production increased both upslope and downslope of the supratidal units.

Surveys of the spectral photon distribution of light in the understory of eight boreal forest stands in northern Alberta were made during 1984. Two seasonal patterns of change in the red:far-red (R:FR) ratio and in the amount of photosynthetically active radiation (expressed as a percentage of full sun, %PAR) were observed. In stands dominated by broadleaf deciduous trees, the R:FR ratio and %PAR values declined rapidly in May and June during the time of leaf expansion and then increased in association with leaf senescence in September. In stands dominated by mature evergreen conifers, both the R:FR ratio and %PAR values declined continuously from an early season high to a late season low. Several young evergreen stands exhibited no seasonal change in light characteristics. During mid-July, the R:FR ratios and %PAR values were lower in older stands than in younger stands of the same successional sequence. The variability in light characteristics within mature forests was higher in mid-July than in September; the difference was attributed to the lower solar angle in September. The differences in light regime in early and late successional forests may have important implications for phytochrome-controlled development and succession in understory plant species.

The freshwater Everglades is a complex system containing thousands of tree islands embedded within a marsh-grassland matrix. The tree island-marsh mosaic is shaped and maintained by hydrologic, edaphic and biological mechanisms that interact across multiple scales. Preserving tree islands requires a more integrated understanding of how scale-dependent phenomena interact in the larger freshwater system. The hierarchical patch dynamics paradigm provides a conceptual framework for exploring multi-scale interactions within complex systems. We used a three-tiered approach to examine the spatial variability and patterning of nutrients in relation to site parameters within and between two hydrologically defined Everglades landscapes: the freshwater Marl Prairie and the Ridge and Slough. Results were scale-dependent and complexly interrelated. Total carbon and nitrogen patterning were correlated with organic matter accumulation, driven by hydrologic conditions at the system scale. Total and bioavailable phosphorus were most strongly related to woody plant patterning within landscapes, and were found to be 3 to 11 times more concentrated in tree island soils compared to surrounding marshes. Below canopy resource islands in the slough were elongated in a downstream direction, indicating soil resource directional drift. Combined multi-scale results suggest that hydrology plays a significant role in landscape patterning and also the development and maintenance of tree islands. Once developed, tree islands appear to exert influence over the spatial distribution of nutrients, which can reciprocally affect other ecological processes.

The Everglades freshwater marl prairie is a dynamic and spatially heterogeneous landscape, containing thousands of tree islands nested within a marsh matrix. Spatial processes underlie population and community dynamics across the mosaic, especially the balance between woody and graminoid components, and landscape patterns reflect interactions among multiple biotic and abiotic drivers. To better understand these complex, multi-scaled relationships we employed a three-tiered hierarchical design to investigate the effects of seed source, hydrology, and more indirectly fire on the establishment of new woody recruits in the marsh, and to assess current tree island patterning across the landscape. Our analyses were conducted at the ground level at two scales, which we term the micro- and meso-scapes, and results were related to remotely detected tree island distributions assessed in the broader landscape, that is, the macro-scape. Seed source and hydrologic effects on recruitment in the micro- and meso-scapes were analyzed via logistic regression, and spatial aggregation in the macro-scape was evaluated using a grid-based univariate O-ring function. Results varied among regions and scales but several general trends were observed. The patterning of adult populations was the strongest driver of recruitment in the micro- and meso-scape prairies, with recruits frequently aggregating around adults or tree islands. However in the macro-scape biologically associated (second order) aggregation was rare, suggesting that emergent woody patches are heavily controlled by underlying physical and environmental factors such as topography, hydrology, and fire.

The purpose of this study was to assess the clinical and pathological value of reports resulting from review of all completed surgical pathology cases submitted to the Army Histopathology Registry (AHR). All histopathological cases completed in the British Army are sent to the AHR for archiving; prior to placing cases in the archive both microscopic material and submitted reports are reviewed by staff of the AHR. A "nonagreed" report is produced for those cases in which the reviewing pathologist has a dissenting opinion or for which he thinks other comments may be helpful. All nonagreed reports produced over a 19 month period were subjected to a further pathological and clinical review. The original surgical pathology reports were compared with AHR reports and the significance of the differences in diagnosis assessed. During the study interval, 4.0% of total cases reviewed were identified as nonagreed record cases. The clinical and pathological reviews placed the nonagreed cases into significant categories in 2.1% and 1.9% of instances respectively. These findings suggest that nonselected review of completed surgical pathology cases identifies a significant proportion of cases for which dissenting opinions may have important clinical and pathological consequences.

Ross, M. S., T. L. SHARIK, and D. WM. SMITH. (Dept. Forestry, Virginia Polytechnic Inst. and State Univ., Blacksburg, VA 24061, U.S.A.). Age structure relationships of tree species in an Appalachian oak forest in southwest Virginia. Bull. Torrey Bot. Club 109: 287-298. 1982.-The complete age and diameter structures were determined for all tree species in seven Appalachian oak stands arranged along a topographic moisture gradient in southwestern Virginia. All stands but one exhibited a prominent gap in the age distribution in the 20-40 year age classes. No gap was evident in the corresponding diameter distributions. Total and juvenile age distributions were described for selected species. Age structures differed among species, and reflected the different spatial and temporal niches which they occupy. It was hypothesized that the shape of the total age distribution in individual stands is related to the disturbance sequence, and to site through its influence on the species present. Coupling of age and diameter distributions of individual populations provided insights into the functional roles of species along the moisture gradient.