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1.
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
2.
Since 1958, L. microphyllum (Old World Climbing Fern), which originated from the Old World Tropics, has become a nuisance exotic and has rapidly spread
and is being established system-wide in extremely remote and undisturbed areas such as the Florida Everglades. Of particular
concern is that L. microphyllum is disrupting, at an alarming rate, the flora and fauna of the native ecosystem at the same time that a major 8.4 billion
dollar Everglades restoration program is trying to enhance these same attributes. This research utilized IKONOS satellite
data to map L. microphyllum within the 58,000-ha Loxahatchee National Wildlife Refuge wetland in south Florida. Results show that approximately 11.6%
of the tree/shrub vegetation within the impoundment has been infected by L. microphyllum. These data were then utilized to explore the spatial spread patterns of L. microphyllum within the Refuge. Results suggest that L. microphyllum is more likely to establish on the southeast side of a tree/shrub island and then spread to the northwest, which corresponds
to the prevailing wind direction in south Florida. Spatial pattern analysis of L. microphyllum spread indicated that it is correlated with the density and spatial distribution of tree/shrub island vegetation. It appears
that the dispersion of L. microphyllum is density dependent, which can be expressed as a logistic function and has a catastrophic threshold of 160 m of mean distance
between tree/shrub islands in the Everglades. It is predicted that 38% (or 1910 ha) of tree/shrub islands in the Refuge will
be invaded by L. microphyllum by 2012. Tree islands in the Everglades wetland could be considered similar to oceanic islands throughout the world that
are notoriously vulnerable to biological invasions. 相似文献
3.
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
4.
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
5.
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
6.
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
7.
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
8.
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
9.
The Florida Everglades freshwater landscape exhibits a distribution of islands covered by woody vegetation and bordered by marshes and wet prairies. Known as “tree islands”, these ecogeomorphic features can be found in few other low gradient, nutrient limited freshwater wetlands. In the last few decades, however, a large percentage of tree islands have either shrank or disappeared in apparent response to altered water depths and other stressors associated with human impacts on the Everglades. Because the processes determining the formation and spatial organization of tree islands remain poorly understood, it is still unclear what controls the sensitivity of these landscapes to altered conditions. We hypothesize that positive feedbacks between woody plants and soil accretion are crucial to emergence and decline of tree islands. Likewise, positive feedbacks between phosphorus (P) accumulation and trees explain the P enrichment commonly observed in tree island soils. Here, we develop a spatially-explicit model of tree island formation and evolution, which accounts for these positive feedbacks (facilitation) as well as for long range competition and fire dynamics. It is found that tree island patterns form within a range of parameter values consistent with field data. Simulated impacts of reduced water levels, increased intensity of drought, and increased frequency of dry season/soil consuming fires on these feedback mechanisms result in the decline and disappearance of tree islands on the landscape. 相似文献
10.
Hydropattern disturbance has had wide-ranging impacts on wetland communities of the Florida Everglades, especially on the habitats and the aquatic biota of the seasonally flooded marl marshes. We used the Everglades crayfish Procambarus alleni as a model to study the associations among hydrology, vegetation distribution, and population dynamics to assess the potential impacts of hydrological changes on the aquatic faunal community in Everglades National Park. To classify benthic habitats as sources or sinks for the crayfish population, we quantified vegetation community structure using GIS maps in which dominant vegetation types were weighted by local hydroperiod (length of inundation). Regression analysis showed that this habitat classification was associated with crayfish density distribution. We then used a spatially explicit, stage-structured population model to describe crayfish population fluctuations under current environmental conditions and to simulate the potential population-level responses to habitat changes that might occur following hydrological restoration. In habitat that was initially saturated with crayfish, the crayfish population size declined under current environmental conditions and then stabilized at about 13% of the initial density over a 50-year period. A 4-month increase in hydroperiod was then simulated by converting shorter-hydroperiod Muhlenbergia-dominated marsh habitat to longer-hydroperiod Cladium-dominated marshes. The model predicted a rapid 7-fold increase in crayfish density following the simulated habitat restoration. This indicated that several functional effects may result from the restoration of historical hydropatterns in marl marshes: (1) the areal extent of habitat sinks will be reduced to isolated patches, whereas the spatial distribution of aquatic source habitats will expand; (2) crayfish population size will increase and persist over time; (3) the minimum threshold needed to increase secondary aquatic productivity may be a 7-month hydroperiod over 90% of the marl marsh landscape. Restoration of historical hydropatterns could thus have cascading positive effects throughout the Everglades aquatic food web. 相似文献
11.
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
12.
Christa P. H. Mulder M. Nicole Grant-Hoffman David R. Towns Peter J. Bellingham David A. Wardle Melody S. Durrett Tadashi Fukami Karen I. Bonner 《Biological invasions》2009,11(7):1671-1688
Introduced rats (Rattus spp.) can affect island vegetation structure and ecosystem functioning, both directly and indirectly (through the reduction
of seabird populations). The extent to which structure and function of islands where rats have been eradicated will converge
on uninvaded islands remains unclear. We compared three groups of islands in New Zealand: islands never invaded by rats, islands
with rats, and islands on which rats have been controlled. Differences between island groups in soil and leaf chemistry and
leaf production were largely explained by burrow densities. Community structure of woody seedlings differed by rat history
and burrow density. Plots on islands with high seabird densities had the most non-native plant species. Since most impacts
of rats were mediated through seabird density, the removal of rats without seabird recolonization is unlikely to result in
a reversal of these processes. Even if seabirds return, a novel plant community may emerge. 相似文献
13.
Kristine J. Brooks Samantha A. Setterfield Michael M. Douglas 《Restoration Ecology》2010,18(2):188-197
Plant invasions can cause severe degradation of natural areas. The ability of an ecosystem to recover autogenically from degradation following weed control is in part determined by the type and magnitude of changes to both biotic and abiotic processes caused by the invasion and how these interact with structural and functional components of the ecosystem. Recently, a number of conceptual frameworks have been proposed to describe the dynamics of degradation and regeneration in degraded ecosystems. We assessed the utility of one of these frameworks in describing the degradation and restoration potential of Australia’s tropical savannas following exotic grass invasion. First, we identified easily measured structural characteristics of putative states. We found that a continuous cover of the exotic grasses Gamba grass (Andropogon gayanus Kunth.) and Perennial mission grass (Pennisetum polystachion (L.) Schult.) under an intact tree canopy was a common state with an understorey characterized by reduced species richness and abundance and a change in the relative contribution of functional groups. Further degradation led to a state where the canopy was severely reduced and the impacts on the understorey were more severe. In both states, the seed bank was substantially less degraded than the understorey vegetation. Guided by the framework, we combined our study with other studies to construct a conceptual model for degradation in exotic grass‐invaded savannas. 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.
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
16.
Interactions of the bacterial assemblages of a prairie stream with dissolved organic carbon from riparian vegetation 总被引:1,自引:1,他引:0
The zonation of riparian vegetation on the Konza Prairie Research Natural Area of Kansas (tallgrass prairie ecosystem) provided a situation where the influences on uptake rates of the different DOC qualities could be measured in the field. Leachates from grasses disappeared rapidly from stream water in in situ chambers at upstream sites in grassland reaches and at downstream sites in forested reaches. The reverse observation, uptake of leachates from trees, revealed that DOC disappeared rapidly from chambers placed in the forested reaches but bacteria in the grassland reaches did not utilize tree leachate as rapidly. The pattern varies seasonally. The interpretation of these observations was aided by aseptic laboratory culture on the different substrate types and by measurements in poisoned chambers to evaluate abiotic uptake. 相似文献
17.
Suspense Averti Ifo Stoffenne Binsangou Lypsia Ibocko Ngala Mady Madingou Aida Cuni‐Sanchez 《African Journal of Ecology》2019,57(1):92-103
In the Congo basin, considerable uncertainty remains about the amount and spatial variation of carbon stocks. We studied two types of seasonally flooded forests (dominated by Guibourtia demeusei and Lophira alata) and nearby terra firme forests in northern Congo. We sampled 1.25 ha per forest type and a total of 1,400 trees ≥5 cm diameter. AGB ranged from 207–343 Mg/ha, with no significant differences between forest types. Few significant differences were observed in vegetation structure or tree diversity between forest types. Species richness and stem density of small trees were lower, and dominance was higher in Guibourtia plots, which are subject to greater flooding than Lophira plots. Guibourtia was absent from smaller diameter class in Guibourtia forests; and Uapaca spp. were more abundant in terra firme than in seasonally flooded plots. We show that both types of seasonally flooded forests store important quantities of AGB and should also be considered in forest conservation programmes. We recommend more research on seasonally flooded forests, on larger geographical extent, which assesses flood depth and duration, and measures tree height in the field, as we took a conservative approach to AGB estimates, and AGB could be even greater than we report here. 相似文献
18.
The unique plant community on Middle Island, Lake Erie, Canada, has been greatly modified by double‐crested cormorants (Phalacrocorax auritus Less.) whose population has increased enormously in the last two decades. The aims of this study were to assess the impact of cormorants on island tree canopy, understorey vegetation, soil seedbank, and soil chemistry. The ultimate objective was to assess the resilience of the vegetation community for recovery should cormorant nest densities decrease significantly. Forty‐three point stations were established in a grid system covering the entire island. The herbaceous and woody vegetation was surveyed over 2 years and tree crown damage was assessed at each point station. In 2008, soil samples were collected for both chemical analysis and a seedbank inventory. Vegetation and seedbank species richness were impoverished compared to the vegetation surveyed prior to cormorant colonization. Cormorants affected not only the tree canopy where they nested but also the understorey vegetation. Exotic plant species were very common in the standing vegetation and constituted the bulk of the abundance in the seedbank. However, there was little relationship between aboveground vegetation and seedbank composition. Cormorants appeared to have little influence on seedbank richness, abundance, and composition. Notably, several species of conservation interest were found in the aboveground vegetation and in the seedbank providing a positive sign for future efforts to restore island plant communities. 相似文献
19.
Mediterranean ecosystems comprise the second biodiversity hotspot area after tropical rain forests and will be most affected by global climate change. Therefore, it is important to understand community dynamics for effective conservation in this region. We investigated the relationships between soil moisture, nitrogen forms and community structuring in Quercus ilexL., Erica arborea L. and Sarcopoterium spinosum (L.) Spach communities, representing different successional stages, distributed as Mediterranean enclaves on the Sinop Peninsula (Turkey). The soil moisture, ammonium, nitrate and nitrite content were measured seasonally. Differences in these abiotic parameters within and between communities over seasons were tested. Previously collected biotic data were then used to analyze the relationship between soil parameters and community structure. Significant differences in soil parameters within and between seasons were found within and between communities. Our results show that there are different relationships between soil moisture, nitrogen forms and community structure in Mediterranean plant communities representing different successional stages. Differentiation in vegetation structure during succession cause changes especially in the water and nitrate content of the soil, and these changes in turn affect the continuity of community structure in Mediterranean plant communities. 相似文献
20.
Sea level rise elicits short‐ and long‐term changes in coastal plant communities by altering the physical conditions that affect ecosystem processes and species distributions. While the effects of sea level rise on salt marshes and mangroves are well studied, we focus on its effects on coastal islands of freshwater forest in Florida's Big Bend region, extending a dataset initiated in 1992. In 2014–2015, we evaluated tree survival, regeneration, and understory composition in 13 previously established plots located along a tidal creek; 10 plots are on forest islands surrounded by salt marsh, and three are in continuous forest. Earlier studies found that salt stress from increased tidal flooding prevented tree regeneration in frequently flooded forest islands. Between 1992 and 2014, tidal flooding of forest islands increased by 22%–117%, corresponding with declines in tree species richness, regeneration, and survival of the dominant tree species, Sabal palmetto (cabbage palm) and Juniperus virginiana (southern red cedar). Rates of S. palmetto and J. virginiana mortality increased nonlinearly over time on the six most frequently flooded islands, while salt marsh herbs and shrubs replaced forest understory vegetation along a tidal flooding gradient. Frequencies of tidal flooding, rates of tree mortality, and understory composition in continuous forest stands remained relatively stable, but tree regeneration substantially declined. Long‐term trends identified in this study demonstrate the effect of sea level rise on spatial and temporal community reassembly trajectories that are dynamically re‐shaping the unique coastal landscape of the Big Bend. 相似文献