Ecotones

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Ecotones may also play a significant role in ecology as indicators of changes taking place on earth. Recent concerns in ecotones access their sensitivity to climate changes and many researchers support monitoring ecotones to discover several global changes. About Author / Additional Info.

Longhurst, in, 2007The ecotone, or transition zone between two ecological communities, became an established concept in terrestrial ecology but has been very little discussed in biological oceanography. Ecotones are, by definition, linear and less extensive than the communities they separate; they are associated with a gradient either in the physical environment or in an external stress, such as might be imposed if herbivore biomass differs on either side.

Ecotones may exhibit special ecological characteristics that differ from either of the separated communities, and they may be the habitat of specialized “edge-effect” species. For all these reasons, Odum notes, “we would not be surprised to find the variety and density of life greater in the ecotone.” Because the biota in convergent oceanic fronts may have access to resources supplied from each of the adjacent water masses, and because of physical aggregation there, a greater biomass may indeed build up within the frontal zone than on either side. Generally, we may expect that ecotones at sea shall be associated (i) with conjunctions, principally convergent but also divergent, between two surface water masses, (ii) with mesoscale eddies and filaments in the open ocean, but especially associated with the edges of continental shelves, and (iii) in shallower seas, associated with the effect of the semidiurnal tide. Barbour, in, 1992 I IntroductionEcotones attract biologists for a variety of reasons. Ecotones exhibit steep gradients of biotic and microenvironmental change; their locations are often dynamic; they are among the first places to show response to new environmental stresses, such as climate change, increased grazing intensity, or pollutants. The beach, as an ecotone between land and sea, possesses all these attributes. The areal and aesthetic magnitude of this meeting ground between two great biological worlds provides drama and excitement to layman and scientist alike.Beach is that strip of sandy substrate that extends from mean tide line to the top of foredune (frontal dune, littoral dune) or, in the absence of a foredune, to the farthest inland reach of storm waves.

Beach is synonymous with embryo dune, foredune, white dune, and yellow dune zones of the European literature ( Chapman, 1976; Olson and van der Maarel, 1989).The beach is a stimulating place for humans on holiday, but a stressful one for plants that must remain for a lifetime. Major environmental stresses of beaches have been well summarized most recently by Barbour et al. (1985), Rozema et al. (1985), and Hesp (1990). Their list includes salt spray, substrate mobility (sand blast, sand burial), nutrient deficiency, dry surface sand, episodic overwash (mechanical disturbance plus high salt–low oxygen concentrations in the root zone), high solar radiation (high temperatures for leaves near the sand surface), drought (low water-holding capacity of sand), high winds (carrying in salt spray and salt blast, and creating a shallow boundary layer with consequent increased eapotranspiration).

To this list, Sauer (1976) and Clark (1986) would add temporal variability—episodic, catastrophic disturbance. The beach is, in Clark's words, a stochastic environment.Typically, these stresses are thought to occupy gradients that extend inland, perpendicular to shore, each stress factor declining with increasing distance inland, from shore. I say are thought, because not all environmental factors have been quantified along continuous transects. Salt spray is one factor that has received a great deal of attention, and it shows a surprisingly steep decline inland (e.g., for California beaches, a 10-fold decline within the first 50 m of vegetated beach width and a 100-fold decline by 600 m inland; Barbour, 1978). The distribution of plant species on a beach appears to be related to stress gradients. Some taxa appear to be representative of the leading edge of vegetation; others are more abundant farther inland. Species richness also increases inland ( Doing, 1985).

In a few cases, experimentation has shown that spatial zonation is, indeed, correlated with tolerance to specific stresses (e.g., Barbour and Dejong, 1977).The objective of this chapter is to summarize the morphological traits of beach plants, especially those at the leading edge of vegetation. Excluded from discussion here are dune species characteristically found inland from the foredune. For convenience, I shall emphasize three of the four North American coastlines: Atlantic, Gulf of Mexico, and Pacific Coasts. Beaches facing the Arctic Ocean are few and narrow, and they have a rather abrupt transition to tundra ( Bliss, 1988).

I could not locate an Arctic beach study sufficiently detailed to include in my analysis below. However, their dominant taxa have a circumarctic flavor, and many extend southward along Atlantic and Pacific Coasts for some distance; thus, they are ultimately included in my review. The studies I shall use are those that include zonation data, so that species at the leading edge of vegetation can be distinguished from those characteristic of the rest of the beach and from those that typify more-stabilized dunes behind the foredune. If similarly extensive and detailed data were available for South America, I should have used them; apart from a regional study of the Chilean coast by Kohler (1970) and of the Brazilian strand by Seeliger and his students, there is little available in the international literature. One practical result of this book's publication will certainly be to elaborate and highlight existing data on South America, and to stimulate future work.We shall see that taxonomic diversity from coast to coast will resolve into a small pool of growth-form syndromes.

One can presume that each syndrome was selected through evolutionary time as being adaptative to the beach habitat, and estimate the value of a given trait by computing the percentage of the flora that share it. Of course, the basic cause-and-effect nature of those adaptations can be revealed only by laboratory experimentation and field manipulation. Wetlands often occur as ecotones (transition zones) between dryland and a water body (e.g., along the margins of lakes, ponds, reservoirs, rivers, and streams or in channels of sluggish or intermittent streams and rivers; Figure 1).

Low-lying lands in these locations may be frequently flooded during high-water periods. Many other wetlands form in areas not adjacent to a water body. These wetlands are found in isolated depressions on the land where water collects, on hill slopes where springs occur or groundwater seeps to the surface, in low areas with poorly drained soils (with seasonally high water tables), and in areas where clayey soils, impervious rock, or other restrictions near the surface create a perched water table. Wetlands may be modified for agricultural uses (cropland and pastures) or created for these and other purposes (e.g., rice paddies, cranberry bogs, and ponds constructed for storm water and wastewater treatment, aquaculture shrimp and fish, and livestock watering). Wetlands may also form in other altered landscapes such as mined lands (e.g., abandoned gravel pits). Charudutt Mishra.

Kulbhushansingh R. Suryawanshi, in, 2016 IntroductionIn the tree line ecotone habitats of Western and Central Himalaya that form the southern edge of the snow leopard’s current global distribution, a significant impact of pastoralism is seen in the pollen record as far back as 5400–5700 years before present (BP) ( Miehe et al., 2009). Farther north on the Tibet–Qinghai Plateau, the center of the snow leopard’s range, seasonal human forays are recorded as early as 30,000 years ago, and more permanent pastoral habitation about 8,200 years BP ( Brantingham et al., 2007). In the Altai Mountains that form the northernmost and easternmost parts of the snow leopard’s range, mobile groups of livestock breeders existed 5,000 years BP ( Yablonsky, 2003). Snow leopards appear in petroglyphs and in kurgan (nomad burial mounds) artifacts across the region including the westernmost parts of their range in the Tien Shan ( Davis-Kimball, 2003; Hussain, 2002; Saveljev et al., 2014). Humans and snow leopards have interacted and coexisted for a considerably long period.Instances of livestock predation by snow leopards must date back to the beginning of pastoral use of their habitats several thousand years ago.

Together with wolves ( Canis lupus) – and other sympatric carnivores to a much smaller extent – snow leopards continue to cause considerable livestock mortality; studies report annual losses ranging from 3 to 12% of local livestock holdings in some areas ( Hussain, 2000; Jackson and Wangchuk, 2004; Mishra, 1997; Namgail et al., 2007). Between these two main predators, studies attribute 20–53% of total unintended livestock mortality to snow leopards ( Li et al., 2013; Namgail et al., 2007; Suryawanshi et al., 2013). Disease, the other important cause of livestock mortality, provides a useful reference.

Depending on the level of veterinary care and livestock vaccination available, the extent of livestock losses to disease in snow leopard habitats is reported to be similar to the two predators ( Li et al., 2013), fewer (14%; Suryawanshi et al., 2013), or several times more.Annual livestock losses to snow leopards and wolves can translate to considerable economic loss for livestock-owning households, sometimes equivalent to as much as half of the regional per capita income ( Mishra, 1997). Understandably, the killing of snow leopards in response to livestock predation is believed to be one of the important causes of the species’ endangerment ( Jackson et al., 2010). Human-snow leopard conflicts are widespread and intense across large parts of Central Asia.

Cummins, M.A. Wilzbach, in, 2008 Flood pulse conceptThe flood pulse concept addresses the ecotones between rivers and their floodplains.

Unlike the lateral riparian influence on stream ecosystem processes where the impact is largely from the landscape to the stream, the flood pulse concept emphasizes the reciprocal exchange between the major river channel and its floodplain. A consequence of this distinction is that the overwhelming bulk of riverine animal biomass derives directly or indirectly from production on the floodplain and not from downstream transport of OM produced higher in the watershed. Although the importance of this aquatic/terrestrial transition zone, the floodplain ecotones, is widely acknowledged, there are few hard data to indicate whether over annual cycles, or longer periods, the primary movement of nutrients and biomass is onto or off the floodplain, or in balance. The general perception of ‘fertile floodplains’ suggests that the periodically inundated floodplains are sinks relative to the river channel. However, the high productivity of adult fish in many floodplain rivers and the concentration of reproductive activity on the floodplain supports the notion that floodplains are sources and the river is a sink, gradually exporting to the sea. At any rate, the seasonal pulsing of river discharge, the flood pulse, is the major force controlling existence, productivity, and interactions of biota in river–floodplain ecosystems.For any given storm or series of storms, the movement of material and organisms on to the floodplain follows the rising limbs of the hydrographs, and the return to the river channel follows the falling limbs. Unfortunately, application of the flood pulse concept is restricted because of the wide-scale engineering modifications that have isolated rivers from their floodplains.

Natural exceptions to the flood pulse concept are rivers flowing through deeply incised canyons. Reinhardt, in, 2008The alpine forest occurs at the interface (ecotone) between the subalpine forest community below and the alpine tundra above, and represents the highest altitude where tree species are found. This ecotone is viewed most often as a transitional, mixed community separating the subalpine forest and alpine communities.

The most common questions concerning the alpine forest involve an understanding of the impact of the specific environmental factors associated with survival at high elevation (e.g., cold temperatures, wind and blowing snow, high sunlight, dry air, and low ambient pressure (and rapid diffusion rates) that change with altitude). This treeline ecotone can vary in altitude and size (width) according to latitude and proximity to maritime influences, as well as the degree of slope and exposure to sunlight and prevailing winds at a given location.

Differences in tree size and spacing, clustering among individual trees, plus the structural distortion and disfigurement of individual trees increases with distance away from the timberline toward treeline. The altitudinal migration of this ecotone (e.g., global change effects) in the past and future is of fundamental concern, indicating potentially important changes in annual snow accumulation and water supply to the lower elevation municipalities and agricultural areas. Junk, in, 2008 I INTRODUCTIONRiparian wetlands have been defined as ‘lowland terrestrial ecotones which derive their high water tables and alluvial soils from drainage and erosion of adjacent uplands on the one side or from periodic flooding from the other’ ( McCormick, 1979). In contrast to an ‘idealized river corridor’, where vast riparian wetlands develop primarily along downstream sections, riparian wetlands associated with tropical headwater streams occur in a variety of forms, but mainly as floodplains of variable width. Like more extensive, larger ecotones associated with higher order rivers, riparian wetlands provide habitats for specific, diverse, and often endangered flora and fauna, and are thus fundamental to maintaining high biodiversity in and along streams (Naiman et al., 1998, 2005; see also Chapter 6 of this volume). Riparian wetlands are also responsible for multiple ecological functions: for instance, these serve as important hydrological buffers and key retention areas for sediments, agricultural pesticides, and fertilizers ( Brinson, 1993; Tockner and Stanford, 2002; Naiman et al., 1998, 2005).

These are sites of high primary and secondary productivity, and also act as migration corridors and/or microclimatic retreats for many taxa ( Naiman et al., 2005). Several studies have emphasized the significance of riparian wetlands for stream organic-matter budgets ( Wantzen and Junk, 2000), solute balance ( McClain et al., 1994; McClain and Elsenbeer, 2001), and the structure of benthic invertebrate assemblages ( Smock, 1994; Arscott et al., 2005). We are relatively well informed about the structure and function of large floodplains, and recent reviews by Junk and Wantzen (2004) and Tockner and Stanford (2002) indicate the present state of our knowledge and offer a detailed synopsis, which we do not wish to repeat. Comprehensive accounts of the ecology of temperate riparian zones are given by Naiman et al. (2005) and Wantzen and Junk (in press). By contrast, our understanding of riparian wetlands along headwater streams in the tropics is still in its infancy.

Accordingly, it is the ecology of these systems that we focus in this chapter. While headwater wetlands may not extend far beyond the stream channel, their importance becomes very evident from a calculation of their cumulative area within a catchment ( Table I; see also Brinson, 1993; Tockner and Stanford, 2002). As Table I shows, the extent of floodplain associated with low-order streams can match or exceed that of large rivers.

Unfortunately, these wetlands may not be considered or included in management or planning strategies. For example, 1: 250 000 scale maps employed in a landscape planning study in Mato Grosso (Brazil) omitted half of the first-order-streams in the catchment of interest, and thus no consideration was given to their associated wetlands ( Wantzen et al., 2006). EstimatedAverage lengthTotal lengthfloodplainsurface areaStream orderNumber(km)(km)width (m)(km 2)11,570,0001.62,526,350,0003.71,295,80,0008.5682,218,54,2950103.097,8200236.5,082841543.8,562981,250.2,6811012,85364,449There are several reasons for the paucity of information about riparian wetlands along low-order streams. Firstly, the investigation of these wetlands is laborious because they are integral components of a larger landscape, and are thus influenced by processes acting at a variety of scales in aquatic and terrestrial environments. Secondly, the processes acting within riparian wetlands may occur seasonally or intermittently with limited spatial extent.

Their functional performance is, therefore, often wider appreciated, despite frequently incorporating important biogeochemical and metazoan-driven turnover processes, i.e. So-called ‘hot spots’ and ‘hot moments’ ( sensu McClain et al., 2003; Wantzen and Junk, 2006). Thirdly, riparian wetlands of all types have been widely affected by sustained human impacts, such as conversion for agriculture, channelization, and flood-control structure, and these changes have already modified the structure and functional integrity of these ecotones. Fourthly, many wetlands and riparian zones in the tropics are unpleasant study sites that harbor poisonous snakes, stinging insects such as mosquitoes, and dense, thorny vegetation; when combined with their sometimes restricted spatial extent, these features help to account for the lack of attention headwater wetlands have received from researchers.The term ‘tropical’, as used throughout this book, does not refer to a single set of conditions but can be subdivided into different regional landscapes and climatic types. This caveat is important especially for the present chapter since the inundation frequency and duration of riparian wetlands depends greatly on climate, which will, for example, differ between humid equatorial regions and seasonal monsoonal latitudes with distinct wet and dry seasons.

In this chapter, we provide examples of headwater wetlands from different climatic areas including seasonal savannahs (Cerrado, Brazil), inland rainforests (Amazonia, Brazil), coastal lowland forests (peatswamp forest, Malaysia), and (sub)tropical Africa and Australia. Due to a wide range of wetland types, we first summarize the general features shared by riparian wetlands and then introduce some representative wetlands from different tropical regions. Guilty gear xx accent core plus r. We conclude with recommendations for conservation and management of these habitats, and outline some priorities for future research.

Ecotones duet

Woessner, in, 2017 8.1.4 EcotonesA second reason for studying the hyporheic zone is the importance of this ecotone in the uptake of solutes and on ecosystem metabolism (e.g., Buss et al., 2009; Boana et al., 2014) (see Chapters in Volume II, Section E). For example, rates of both nitrogen and phosphorus cycling are strongly influenced in many streams by processes occurring in the hyporheic zone (e.g., Duff and Triska, 1990; Triska et al., 1993; Valett et al., 1996, 1997; Mulholland et al., 1997; Cirmo and McDonnell, 1997; Hedin et al., 1998; Dahm et al., 1998; Dent et al., 2001; Hall et al., 2002; Thomas et al., 2003; Buss et al., 2009; Pinay et al., 2009; Boana et al., 2014). Stream metabolism also is strongly affected by hydrologic exchange between surface waters and groundwaters (e.g., Jones et al., 1995; Jones, 1995; Pusch, 1996; Fischer et al., 1996; Fuss and Smock, 1996; Naegeli and Uehlinger, 1997; Fellows et al., 2001; Crenshaw et al., 2002; Harvey et al., 2003) and the residence time of water in the hyporheic zone ( Hoehn and von Gunten, 1989; Brunke and Gonser, 1999). Fisher et al. (1998) see material spiraling between the river and hyporheic zone as a mechanism controlling nutrient retention in river systems. Metabolism rates in hyporheic zones are closely linked to dissolved organic carbon (DOC) dynamics ( Fiebig, 1995; Battin, 1999; Baker et al., 1999, 2000; Sobczak and Findlay, 2002; Clinton et al., 2002) and the availability of particulate organic matter ( Battin et al., 2003). In White Clay Creek, Pennsylvania end-member mixing analysis based on conductivity indicates that about 40% of hyporheic zone respiration comes from DOC, with the rest supported by entrained particulate organic carbon ( Battin et al., 2003).

Retention and processing of organic matter is an important process in the hyporhiec zone ( Boulton, 2007). Metabolism that depletes dissolved oxygen concentrations also impacts hyporheic zone organisms ( Malard and Hervant, 1999). Finally, the cycling of nutrients and organic matter in hyporheic zones also affects riparian vegetation along stream corridors. Harner and Stanford (2003) showed faster cottonwood growth in nutrient-rich upwelling zones, and Schade et al. (2005) tracked the movement of hyporheic zone nutrients into riparian tree species using stable isotopes. Hyporheic zones also play an important role in sequestering and releasing contaminants originating from local groundwater discharge, river sediments, or surface water (e.g., Gandy et al., 2007; Boano et al., 2014). Hyporheic zones facilitate nutrient cycling, carbon metabolism, riparian plant growth, and some contaminant processing.

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