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1.
Vegetation differentiation in the patterned landscape of the central Everglades: importance of local and landscape drivers 总被引:1,自引:0,他引:1
Thomas J. Givnish John C. Volin V. Dianne Owen Valeria C. Volin Jordan D. Muss Paul H. Glaser 《Global Ecology and Biogeography》2008,17(3):384-402
Aim We present a model to account for self‐assembly of the slough–ridge–tree island patterned landscape of the central Everglades in southern Florida via feedbacks among landforms, hydrology, vegetation and biogeochemistry. We test aspects of this model by analysing vegetation composition in relation to local and landscape‐level drivers. Location We quantified vegetation composition and environmental characteristics in central Water Conservation Area (WCA) 3A, southern WCA‐3A and southern WCA‐3B in southern Florida, based on their divergence in water management and flow regimes over the past 50 years. Methods In 562 quadrats, we estimated species coverages and quantified maximum, minimum and average water depth, soil depth to bedrock, normalized difference vegetation index (NDVI) and proximity to the nearest tree island. We used non‐metric multi‐dimensional scaling (NMS) to relate compositional variation to local and landscape‐level factors, and evaluated environmental differences among eight a priori vegetation types via anova . Results Water depth and hydroperiod decreased from sloughs to ridges to tree islands, but regions also differed significantly in the abundance of several community types and the hydroregimes characterizing them. NMS revealed two significant axes of compositional variation, tied to local gradients of water depth and correlated factors, and to a landscape‐scale gradient of proximity to tall tree islands. Sawgrass height and soil thickness increased toward higher ridges, and NDVI was greatest on tree islands. Main conclusions This study supports four components of our model: positive feedback of local substrate height on itself, woody plant invasion and subsequent P transport and concentration by top predators nesting on taller tree islands, compositional shifts in sites close to tree islands due to nutrient leakage, and flow‐induced feedback against total raised area. Regional divergence in the relationship of community types to current hydroregimes appears to reflect a lag of a few years after shifts in water management; a longer lag would be expected for shifts in landscape patterning. Both local and landscape‐level drivers appear to shape vegetation composition and soil thickness in the central Everglades. 相似文献
2.
Paul R. Wetzel Arnold G. van der Valk Susan Newman Carlos A. Coronado Tiffany G. Troxler-Gann Daniel L. Childers William H. Orem Fred H. Sklar 《Plant Ecology》2009,200(1):83-90
The biologically mediated transfer of nutrients from one part of a landscape to another may create nutrient gradients or subsidize
the productivity at specific locations. If limited, this focused redistribution of the nutrient may create non-random landscape
patterns that are unrelated to underlying environmental gradients. The Florida Everglades, USA, is a large freshwater wetland
that is patterned with tree islands, elevated areas that support woody vegetation. A survey of 12 tree islands found total
soil phosphorus levels 3–114 times greater on the island head than the surrounding marsh, indicating that the Florida Everglades
is not a homogeneous oligotrophic system. It was estimated that historically 67% of the phosphorus entering the central Everglades
was sequestered on tree islands, which are ~3.8% of the total land area. This internal redistribution of phosphorus onto tree
islands due to the establishment of trees may be one reason that marshes have remained oligotrophic and may explain the spatial
differentiation of the patterned Everglades landscape. 相似文献
3.
The differential accumulation or loss of carbon and nutrients during decomposition can promote differentiation of wetland
ecosystems, and contribute to landscape-scale heterogeneity. Tree islands are important ecosystems because they increase ecological
heterogeneity in the Everglades landscape and in many tropical landscapes. Only slight differences in elevation due to peat
accumulation allow the differentiation of these systems from the adjacent marsh. Hydrologic restoration of the Everglades
landscape is currently underway, and increased nutrient supply that could occur with reintroduction of freshwater flow may
alter these differentiation processes. In this study, we established a landscape-scale, ecosystem-level experiment to examine
litter decomposition responses to increased freshwater flow in nine tree islands and adjacent marsh sites in the southern
Everglades. We utilized a standard litterbag technique to quantify changes in mass loss, decay rates, and phosphorus (P),
nitrogen (N) and carbon (C) dynamics of a common litter type, cocoplum (Chrysobalanus icaco L.) leaf litter over 64 weeks. Average C. icaco leaf degradation rates in tree islands were among the lowest reported for wetland ecosystems (0.23 ± 0.03 yr−1). We found lower mass loss and decay rates but higher absolute mass C, N, and P in tree islands as compared to marsh ecosystems
after 64 weeks. With increased freshwater flow, we found generally greater mass loss and significantly higher P concentrations
in decomposing leaf litter of tree island and marsh sites. Overall, litter accumulated N and P when decomposing in tree islands,
and released P when decomposing in the marsh. However, under conditions of increased freshwater flow, tree islands accumulated
more P while the marsh accumulated P rather than mineralizing P. In tree islands, water level explained significant variation
in P concentration and N:P molar ratio in leaf tissue. Absolute P mass increased strongly with total P load in tree islands
(r
2 = 0.81). In the marsh, we found strong, positive relationships with flow rate. Simultaneous C and P accumulation in tree
island and mineralization in adjacent marsh ecosystems via leaf litter decomposition promotes landscape differentiation in
this oligotrophic Everglades wetland. However, results of this study suggest that variation in flow rates, water levels and
TP loads can shift differential P accumulation and loss leading to unidirectional processes among heterogeneous wetland ecosystems.
Under sustained high P loading that could occur with increased freshwater flow, tree islands may shift to litter mineralization,
further degrading landscape heterogeneity in this system, and signaling an altered ecosystem state. 相似文献
4.
The tree island hammock communities in the Florida Everglades provide one of many examples of self-organized wetland landscape. However, little is understood about why these elevated tree island communities have higher nutrient concentration than the surrounding freshwater marshes. Here we used stable isotopes and elemental analysis to compare dry season water limitation and soil and foliar nutrient status in upland hammock communities of 18 different tree islands located in the Shark River Slough and adjacent prairie landscapes. We observed that prairie tree islands, having a shorter hydroperiod, suffer greater water deficits during the dry season than slough tree islands by examining shifts in foliar ??13C values. We also found that prairie tree islands have lower soil total phosphorus concentration and higher foliar N/P ratio than slough tree islands. Foliar ??15N values, which often increase with greater P availability, was also found to be lower in prairie tree islands than in slough tree islands. Both the elemental N and P and foliar ??15N results indicate that the upland hammock plant communities in slough tree islands have higher amount of P available than those in prairie tree islands. Our findings are consistent with the transpiration driven nutrient harvesting chemohydrodynamic model. The water limited prairie tree islands hypothetically transpire less and harvest less P from the surrounding marshes than slough tree islands during the dry season. These findings suggest that hydroperiod is important to nutrient accumulation of tree island habitats. 相似文献
5.
We address the relative importance of nutrient availability in relation to other physical and biological factors in determining
plant community assemblages around Everglades Tree Islands (Everglades National Park, Florida, USA). We carried out a one-time
survey of elevation, soil, water level and vegetation structure and composition at 138 plots located along transects in three
tree islands in the Park’s major drainage basin. We used an RDA variance partitioning technique to assess the relative importance
of nutrient availability (soil N and P) and other factors in explaining herb and tree assemblages of tree island tail and
surrounded marshes. The upland areas of the tree islands accumulate P and show low N concentration, producing a strong island-wide
gradient in soil N:P ratio. While soil N:P ratio plays a significant role in determining herb layer and tree layer community
assemblage in tree island tails, nevertheless part of its variance is shared with hydrology. The total species variance explained
by the predictors is very low. We define a strong gradient in nutrient availability (soil N:P ratio) closely related to hydrology.
Hydrology and nutrient availability are both factors influencing community assemblages around tree islands, nevertheless both
seem to be acting together and in a complex mechanism. Future research should be focused on segregating these two factors
in order to determine whether nutrient leaching from tree islands is a factor determining community assemblages and local
landscape pattern in the Everglades, and how this process might be affected by water management. 相似文献
6.
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. 相似文献
7.
Everglades tree island restoration: testing a simple tree planting technique patterned after a natural process 下载免费PDF全文
Tree islands in the Everglades are critical landscape features, but anthropogenic modification of the Everglades during the past century has led to the degradation and loss of many of the tree islands that originally dotted the Everglades landscape. Many of the tree islands have lost elevation and the majority of their woody species such that they are now covered with emergent plants such as sawgrass (Cladium jamaicense). A simple, cost‐effective tree planting technique is needed for restoring degraded Everglades tree islands. We patterned our design after a natural Everglades process that creates floating islands, which promotes tree survival and growth in both flooded and dry conditions and may lead to the development of fixed islands. Commercial peat bags were tested as a means to provide the medium for the growth and establishment of potted tree saplings native to Everglades tree islands. Three tree species (Annona glabra, Ficus aurea, and Acer rubrum) and five treatments were evaluated. The results indicate that the preferred deployed peat‐bag configuration should provide the greatest additional elevation to minimize inundation and be planted with a single Everglades tree island species sapling, with a single commercial tree fertilizer spike inserted for nutrients. Although most plants survived and many thrived for the two‐year period of this study, determining whether the trees planted using this technique can become established will require longer‐term studies and extensive field tests. 相似文献
8.
Tree island ecosystems are important and distinct features of Florida Everglades wetlands. We described the inter-relationships
among abiotic factors describing seasonally flooded tree islands and characterized plant–soil relationships in tree islands
occurring in a relatively unimpacted area of the Everglades. We used Principal Components Analysis (PCA) to reduce our multi-factor
dataset, quantified forest structure and vegetation nutrient dynamics, and related these vegetation parameters to PCA summary
variables using linear regression analyses. We found that, of the 21 abiotic parameters used to characterize the ecosystem
structure of seasonally flooded tree islands, 13 parameters were significantly correlated with four principal components,
and they described 78% of the variance among the study islands. Most variation was described by factors related to soil oxidation
and hydrology, exemplifying the sensitivity of tree island structure to hydrologic conditions. PCA summary variables describing
tree island structure were related to variability in Chrysobalanus icaco (L.) canopy cover, Ilex cassine (L.) and Salix caroliniana (Michx.) canopy cover, Myrica cerifera (L.) plot frequency, litter turnover, % phosphorus resorption of co-dominant species, and nitrogen nutrient-use efficiency.
This study supported findings that vegetation characteristics can be sensitive indicators of variability in tree island ecosystem
structure. This study produced valuable, information which was used to recommend ecological targets (i.e. restoration performance
measures) for seasonally flooded tree islands in more impacted regions of the Everglades landscape. 相似文献
9.
Spatial heterogeneity in soils is often characterized by the presence of resource-enriched patches ranging in size from a
single shrub to wooded thickets. If the patches persist long enough, the primary constraint on production may transition from
one limiting environmental factor to another. Tree islands that are scattered throughout the Florida Everglades basin comprise
nutrient-enriched patches, or resource islands, in P-limited oligotrophic marshes. We used principal component analysis and
multiple regressions to characterize the belowground environment (soil, hydrology) of one type of tree island, hardwood hammocks,
and examined its relationship with the three structural variables (basal area, biomass, and canopy height) indicative of site
productivity. Hardwood hammocks in the southern Everglades grow on two distinct soil types. The first, consisting of shallow,
organic, relatively low-P soils, is common in the seasonally flooded Marl Prairie landscape. In contrast, hammocks on islands
embedded in long hydroperiod marsh have deeper, alkaline, mineral soils with extremely high P concentrations. However, this
edaphic variation does not translate simply into differences in forest structure and production. Relative water depth was
unrelated to all measures of forest structure and so was soil P, but the non-carbonate component of the mineral soil fraction
exhibited a strong positive relationship with canopy height. The development of P-enriched forest resource islands in the
Everglades marsh is accompanied by the buildup of a mineral soil; however, limitations on growth in mature islands appear
to differ substantively from those that dominate incipient stages in the transformation from marsh to forest. 相似文献
10.
Paolo D’Odorico Vic Engel Joel A. Carr Steven F. Oberbauer Michael S. Ross Jay P. Sah 《Ecosystems》2011,14(2):298-310
Mosaic freshwater landscapes exhibit tree-dominated patches —or tree islands—interspersed in a background of marshes and wet prairies. In the Florida Everglades, these patterned landscapes provide habitat
for a variety of plant and animal species and are hotspots of biodiversity. Even though the emergence of patchy freshwater
systems has been associated with climate histories, fluctuating hydrologic conditions, and internal feedbacks, a process-based
quantitative understanding of the underlying dynamics is still missing. Here, we develop a mechanistic framework that relates
the dynamics of vegetation, nutrients and soil accretion/loss through ecogeomorphic feedbacks and interactions with hydrologic
drivers. We show that the stable coexistence of tree islands and marshes results as an effect of their both being (meta-)
stable states of the system. However, tree islands are found to have only a limited resilience, in that changes in hydrologic
conditions or vegetation cover may cause an abrupt shift to a stable marsh state. The inherent non-linear and discontinuous
dynamics determining the stability and resilience of tree islands should be accounted for in efforts aiming at the management,
conservation and restoration of these features. 相似文献
11.
In the Florida Everglades, tree islands are conspicuous heterogeneous elements in the herbaceous wetland landscape. We characterized
the biogeochemical role of a seasonally flooded tree island during wet season inundation, specifically examining hydrologically
mediated flows of nitrogen (N) and N retention by the tree island. We estimated ecosystem N standing stocks and fluxes, soil
and litter N transformation rates, and hydrologic fluxes of N to quantify the net ecosystem N mass flux. Results showed that
hydrologic sources of N were dominated by surface water loads of nitrate (NO3) and ammonium (NH4). Nitrate immobilization by soils and surficial leaf litter was an important sink for surface water dissolved inorganic N
(DIN). We estimated that the net annual DIN retention by a seasonally flooded tree island was 20.5 ± 5.0 g m−2 during wet season inundation. Based on the estimated tree island surface water DIN loading rate, a seasonally flooded tree
island retained 76% of imported DIN. As such, seasonally flooded tree islands have the potential to retain 55% of DIN entering
the marsh landscape via upstream canal overland flow in the wet season. By increasing reactive surface area and DOC availability,
we suggest that tree islands promote convergence of elements that enhance DIN retention. Tree islands of this region are thus
important components of landscape-scale restoration efforts that seek to reduce sources of anthropogenic DIN to downstream
estuaries. 相似文献
12.
Water source utilization and foliar nutrient status differs between upland and flooded plant communities in wetland tree islands 总被引:1,自引:0,他引:1
Amartya K. Saha Leonel da Silveira O’Reilly Sternberg Michael S. Ross Fernando Miralles-Wilhelm 《Wetlands Ecology and Management》2010,18(3):343-355
Tree islands in the Everglades wetlands are centers of biodiversity and targets of restoration, yet little is known about
the pattern of water source utilization by the constituent woody plant communities: upland hammocks and flooded swamp forests.
Two potential water sources exist: (1) entrapped rainwater in the vadose zone of the organic soil (referred to as upland soil
water), that becomes enriched in phosphorus, and (2) phosphorus-poor groundwater/surface water (referred to as regional water).
Using natural stable isotope abundance as a tracer, we observed that hammock plants used upland soil water in the wet season
and shifted to regional water uptake in the dry season, while swamp forest plants used regional water throughout the year.
Consistent with the previously observed phosphorus concentrations of the two water sources, hammock plants had a greater annual
mean foliar phosphorus concentration over swamp forest plants, thereby supporting the idea that tree island hammocks are islands
of high phosphorus concentrations in the oligotrophic Everglades. Foliar nitrogen levels in swamp forest plants were higher
than those of hammock plants. Linking water sources with foliar nutrient concentrations can indicate nutrient sources and
periods of nutrient uptake, thereby linking hydrology with the nutrient regimes of different plant communities in wetland
ecosystems. Our results are consistent with the hypotheses that (1) over long periods, upland tree island communities incrementally
increase their nutrient concentration by incorporating marsh nutrients through transpiration seasonally, and (2) small differences
in micro-topography in a wetland ecosystem can lead to large differences in water and nutrient cycles. 相似文献
13.
Michael S. Ross Sherry Mitchell-Bruker Jay P. Sah Stuart Stothoff Pablo L. Ruiz David L. Reed Kris Jayachandran Charles L. Coultas 《Hydrobiologia》2006,569(1):37-59
Extensive portions of the southern Everglades are characterized by series of elongated, raised peat ridges and tree islands
oriented parallel to the predominant flow direction, separated by intervening sloughs. Tall herbs or woody species are associated
with higher elevations and shorter emergent or floating species are associated with lower elevations. The organic soils in
this “Ridge-and-Slough” landscape have been stable over millennia in many locations, but degrade over decades under altered
hydrologic conditions. We examined soil, pore water, and leaf phosphorus (P) and nitrogen (N) distributions in six Ridge and
Slough communities in Shark Slough, Everglades National Park. We found P enrichment to increase and N to decrease monotonically
along a gradient from the most persistently flooded sloughs to rarely flooded ridge environments, with the most dramatic change
associated with the transition from marsh to forest. Leaf N:P ratios indicated that the marsh communities were strongly P-limited,
while data from several forest types suggested either N-limitation or co-limitation by N and P. Ground water stage in forests
exhibited a daytime decrease and partial nighttime recovery during periods of surface exposure. The recovery phase suggested
re-supply from adjacent flooded marshes or the underlying aquifer, and a strong hydrologic connection between ridge and slough.
We therefore developed a simple steady-state model to explore a mechanism by which a phosphorus conveyor belt driven by both
evapotranspiration and the regional flow gradient can contribute to the characteristic Ridge and Slough pattern. The model
demonstrated that evapotranspiration sinks at higher elevations can draw in low concentration marsh waters, raising local
soil and water P concentrations. Focusing of flow and nutrients at the evapotranspiration zone is not strong enough to overcome
the regional gradient entirely, allowing the nutrient to spread downstream and creating an elongated concentration plume in
the direction of flow. Our analyses suggest that autogenic processes involving the effects of initially small differences
in topography, via their interactions with hydrology and nutrient availability, can produce persistent physiographic patterns
in the organic sediments of the Everglades. 相似文献
14.
Susana L. Stoffella Michael S. Ross Jay P. Sah Rene M. Price Pamela L. Sullivan Eric A. Cline Leonard J. Scinto 《应用植被学》2010,13(4):439-449
Questions: How are the early survival and growth of seedlings of Everglades tree species planted in an experimental setting on artificial tree islands affected by hydrology and substrate type? What are the implications of these responses for broader tree island restoration efforts? Location: Loxahatchee Impoundment Landscape Assessment (LILA), Boynton Beach, Florida, USA. Methods: An experiment was designed to test hydrological and substrate effects on seedling growth and survivorship. Two islands – a peat and a limestone‐core island representing two major types found in the Everglades – were constructed in four macrocosms. A mixture of eight tree species was planted on each island in March of 2006 and 2007. Survival and height growth of seedlings planted in 2006 were assessed periodically during the next two and a half years. Results: Survival and growth improved with increasing elevation on both tree island substrate types. Seedlings' survival and growth responses along a moisture gradient matched species distributions along natural hydrological gradients in the Everglades. The effect of substrate on seedling performance showed higher survival of most species on the limestone tree islands, and faster growth on their peat‐based counterparts. Conclusions: The present results could have profound implications for restoration of forests on existing landforms and artificial creation of tree islands. Knowledge of species tolerance to flooding and responses to different edaphic conditions present in wetlands is important in selecting suitable species to plant on restored tree islands 相似文献
15.
Phosphorus Biogeochemistry and the Impact of Phosphorus Enrichment: Why Is the Everglades so Unique? 总被引:10,自引:0,他引:10
The Florida Everglades is extremely oligotrophic and sensitive to small increases in phosphorus (P) concentrations. P enrichment
is one of the dominant anthropogenic impacts on the ecosystem and is therefore a main focus of restoration efforts. In this
review, we synthesize research on P biogeochemistry and the impact of P enrichment on ecosystem structure and function in
the Florida Everglades. There are clear patterns of increased P concentrations and altered structure and processes along nutrient-enrichment
gradients in the water, periphyton, soils, macrophytes, and consumers. Periphyton, an assemblage of algae, bacteria, and associated
microfauna, is abundant and has a large influence on phosphorus cycling in the Everglades. The oligotrophic Everglades is
P-starved, has lower P concentrations and higher nitrogen–phosphorus (N:P) ratios, and has oxidized to only slightly reduced
soil profiles compared to other freshwater wetland ecosystems. Possible general causes and indications of P limitation in
the Everglades and other wetlands include geology, hydrology, and dominance of oxidative microbial nutrient cycling. The Everglades
may be unique with respect to P biogeochemistry because of the multiple causes of P limitation and the resulting high degree
of limitation.
Received 23 August 2000; Accepted 23 March 2001. 相似文献
16.
M. K. Nungesser 《Wetlands Ecology and Management》2011,19(6):475-493
The Everglades of south Florida is a patterned peatland that has undergone major hydrologic modification over the last century,
including both drainage and impoundment. The Everglades ridge and slough patterns were originally characterized by regularly
spaced elevated ridges and tree islands oriented parallel to water flow through interconnected sloughs. Many areas of the
remaining Everglades have lost this patterning over time. Historical aerial photography for the years 1940, 1953, 1972, 1984,
and 2004 provides source data to measure these changes over six decades. Maps were created by digitizing the ridges, tree
islands, and sloughs in fifteen 24 km2 study plots located in the remaining Everglades, and metrics were developed to quantify the extent and types of changes in
the patterns. Pattern metrics of length/width ratios, number of ridges, and perimeter/area ratios were used to define the
details and trajectories of pattern changes in the study plots from 1940 through 2004. These metrics characterized elongation,
smoothness, and abundance of ridges and tree islands. Hierarchical agglomerative cluster analysis was used to categorize these
75 maps (15 plots by 5 years) into five categories based on a suite of metrics of pattern quality. Nonmetric multidimensional
scaling, an ordination technique, confirmed that these categories were distinct with the primary axis distinguished primarily
by the abundance of elongated ridges in each study plot. Strong patterns like those described historically were characterized
by numerous, long ridges while degraded patterns contained few large, irregularly shaped patches. Pattern degradation usually
occurred with ridges fusing into fewer, less linear patches of emergent vegetation. Patterning improved in some plots, probably
through wetter conditions facilitating expression of the underlying microtopography. Trajectories showing responses of individual
study plots over the six decades indicated that ridge and slough patterns can degrade or improve over time scales of a decade
or less. Changes in ridge and slough patterns indicate that (1) patterns can be lost quickly following severe peat dryout,
yet (2) patterns appear resilient at least over multi-decadal time periods; (3) patterns can be maintained and possibly strengthened
with deeper water depths, and (4) the sub-decadal response time of pattern changes visible in aerial imagery is highly useful
for change detection within the landscape. This analysis suggests that restoration of some aspects of these unique peatland
patterns may be possible within relatively short planning time frames. Use of aerial photography in future Everglades restoration
efforts can facilitate restoration and adaptive management by documenting sub-decadal pattern changes in response to altered
hydrology and water management. 相似文献
17.
Danielle L. Watts Matthew J. Cohen James B. Heffernan Todd Z. Osborne 《Ecosystems》2010,13(6):813-827
The ridge–slough landscape of the Everglades (Florida, USA), is characterized by elevated ridges dominated by sawgrass (Cladium jamaicense) interspersed among deeper sloughs dominated by floating, submerged and emergent macrophytes and calcareous periphyton. Interactions
among hydrologic conditions (water depth, hydroperiod), plant composition and production, and respiration are hypothesized
to create alternative peat accretion equilibria at the point scale, while spatial interactions among patches create regular
pattern at the landscape scale. Despite significant research on these interactions, few studies have examined the hypothesis
that the ridge–slough landscape consists of spatially coupled alternative stable patch states, and none has used diagnostic
indicators thereof to assess landscape resilience to hydrologic change. Dense random sampling of water depths (a proxy for
soil elevation) along a gradient of hydrologic impairment of drained to relatively natural to impounded conditions was used
to evaluate four predictions related to this hypothesis: (1) bimodal soil elevation distributions show strong fidelity to
community type; (2) positive autocorrelation at short distances with negative values at longer distances; (3) strong anisotropy
(diagnostic of flow orientation), and spatial structure (diagnostic of the strength of landscape self-organization); and (4)
loss of these features with hydrologic modification. Our results support the hypothesis that soil elevations are strongly
bimodal and anisotropic in areas with minimal hydrologic impact, and spatial autocorrelation patterns indicate the operation
of scale-dependent feedbacks. These metrics change markedly with hydrologic modification, although with differences between
drainage and impoundment. Moreover, changes in landform precede associated changes in vegetation, suggesting their utility
as diagnostic indicators of landscape degradation and recovery. 相似文献
18.
Much of the historical Everglades has been either lost or degraded as a result of human activities. Among the aquatic habitats
that comprise the Everglades landscape mosaic, open-water sloughs support critical ecological functions and appear especially
sensitive to both hydrologic and water-quality perturbations. We used a combination of remote sensing and on-the-ground sampling
to document spatial changes in the extent and vegetative composition of sloughs along a phosphorus (P) gradient in the northern
Everglades. Increasing levels of water and soil P were associated with a decline in slough coverage, loss of the abundant
native periphyton community, and a shift in dominant macrophyte species. The characteristic slough macrophyte species Eleocharis cellulosa and Nymphaea odorata exhibited different sensitivities to P enrichment, but both species declined with enrichment as slough habitats were invaded
by Typha domingensis, a species that is known to expand aggressively in response to enrichment. A limited amount of open-water habitat occurred
in highly enriched areas, but these habitats were maintained largely as a result of airboat disturbance and did not contain
characteristic slough vegetation. Many changes in slough coverage and composition occurred in areas where water and soil P
concentrations were only marginally higher than background levels. Our findings support the need for Everglades hydrologic
restoration efforts to adhere to strict water-quality standards for P to avoid further degradation of this key landscape feature.
Handling editor: L. M. Bini 相似文献
19.
In May 2004, 400 tree seedlings of seven different species found on tree islands in the Florida Everglades were planted at different elevations along five transects on eight newly constructed tree islands, four with and four without limestone cores. Seedlings suffered between 40 and 85% mortality during the first 120 days, the period with the lowest water levels. Ilex cassine L., Salix caroliniana Michx., Chrysobalanus icaco L., and Annona glabra had the highest number of surviving seedlings, whereas Magnolia virginiana L., Myrica cerifera L., and Acer rubrum L. had the fewest. During the remainder of the study, water levels were mostly higher and sometimes covered the entire islands for months at a time. After 220 days, nearly all seedlings of M. virginiana and My. cerifera had died. At the end of the study, seedlings of I. cassine and A. glabra had the highest survivorship rates. Seedling biomass of C. icaco and I. cassine was greatest at the highest elevations, whereas seedlings of A. glabra had similar biomass at all elevations. Seedling survivorship was not statistically different between islands with and without limestone cores; however, when seedlings of all species were combined, island core type was significantly different for aboveground biomass, seedling height, and canopy width. Because of the higher survivorship under both low and high water conditions, A. glabra , I. cassine , and S. caroliniana are the most suitable species for establishing tree species on restored tree islands in the Everglades. 相似文献
20.
Kim C. Diver 《Journal of Biogeography》2008,35(6):1040-1048
Aim To evaluate the role of island isolation in explaining the distribution of vascular plant species in a dense freshwater archipelago, specifically comparing conventional measures of island isolation with landscape measures of island isolation. Location Data were collected from 35 islands within Massasauga Provincial Park on the eastern shores of the Georgian Bay, Ontario, Canada. Methods Sampled islands were located using stratified random selection based on location and size variation. The number of species was recorded along stratified random transects. Island isolation variables included distance to the mainland, distance to the nearest island, largest gap in a stepping‐stone sequence, distance to the closest upwind point of land, and a landscape measure of island isolation. The landscape measure of isolation was quantified as the percentage of the land area within 100, 250, 500, 1000, 1500 and 2000 m of each island’s perimeter. The isolation variables were calculated within a geographical information system (GIS). Dependent variables in the regression analyses included species richness, the logarithm of species richness and residuals of the species–area relationship. Independent variables included island isolation variables and their logarithmic transformations. Results Isolation plays a role, albeit small, in explaining species richness in the study area. In the regression analyses, the landscape measure of isolation provided a better fit than conventional measures of island isolation. Islands with less land than water within a 250‐m buffer were more effectively isolated and had fewer species present than islands surrounded by a greater proportion of water. Main conclusions Consistent with the species–isolation relationship, fewer species were present on more isolated islands within the Massasauga study area, as elucidated using a series of island buffers in a GIS. Applying a landscape measure of isolation to similar dense, freshwater archipelagos may elucidate species–isolation patterns not evident through conventional, straight‐line distance measurements of island isolation. The low value of the regression coefficients as well as the isolation history and high density of the Massasauga islands suggests caution in extending the results, especially to dissimilar archipelagos. 相似文献