Remnant Areas Research Articles

Ecological consequences of altered hydrological regimes in fragmented ecosystems in southern Australia: Impacts and possible management responses

Abstract Although the potential impacts of rising water tables and secondary salinization on agricultural land in southern Australia have been recognized for some time, it is only recently that the impacts on native vegetation have been considered. Despite the likely extent and severity of the problem, no comprehensive approach to assessing the impact of salinity upon native vegetation has been attempted to date. In the present paper, we discuss the causes and impacts of rising water tables and dryland salinity, assess the levels of risk in different ecosystem types and consider the possibilities for the maintenance of biodiversity and ecosystem function in vegetation at risk. We examine the salinity risk to woodland vegetation in the Western Australian (WA) wheatbelt, and consider both broad‐scale context and finer‐scale variation within individual patches of vegetation. From this information, we develop a set of conceptual models of the potential impacts of shallow saline water tables on ecosystem structure and processes in remnant vegetation in agricultural areas, particularly in the WA wheatbelt. First, we suggest that fine‐scale variability in surface topography and soil characteristics may play an important role in limiting the impacts of rising saline water tables. The outcome will depend on the interaction of the heterogeneity of the impact, species distribution in relation to small‐scale environmental heterogeneity and variation in species response to hydrological change. Second, we suggest that shallow saline water tables can be considered to cause an ‘edge effect’, which moves inwards from the edge of remnants of native vegetation. Finally, we consider how saline surface flows exacerbate the effects of shallow saline water tables and hasten vegetation decline in remnant areas. We put these models forward as hypotheses to be tested in different situations. We contrast the situation of secondary salinization in Australian vegetation with that of naturally saline systems in Australia and elsewhere, and suggest that these systems may provide important signposts toward developing management approaches for vegetation at risk. In conclusion, we consider the need to set priorities for the protection and restoration of natural vegetation at risk from altered hydrology, based on an assessment of relative threat and probability of persistence or recovery. We highlight the urgency for action that protects native vegetation from the increasing risks of rising water tables.

Remnant amount and cleanup for 3 adhesives after debracketing

The cleanup of remnant bonding adhesive from the enamel surface after debonding is an important factor for clinicians. The purposes of this study were to compare the weight, the surface area, and the cleanup times of remnant adhesive for a composite resin, Transbond (TB); a resin-modified glass ionomer, Fuji ORTHO LC bonded to enamel both conditioned (FOC) and nonconditioned (FONC); and a fluoride-releasing composite resin, Advance (ADV), bonded to nonetched enamel. In addition, 2 qualitative methods for scoring remnant adhesive were compared with the quantitative weight and area data. Forty extracted human incisors were weighed, bonded with brackets, debonded, weighed, and photographed. Area was measured from the photographs with a sonic digitizer. Mean adhesive remnant weights differed between groups (analysis of variance [ANOVA], P =.02): The remnants from ADV and FOC were equal and both significantly heavier than the remnants from FONC; the weights of the TB remnants were intermediate between the heavier ADV and FOC remnants and the lighter FONC remnants. Mean remnant areas differed between groups (ANOVA, P =.03): The remnants from ADV were significantly larger than the remnants from TB and FONC, which were equal; the areas of the FOC remnants were intermediate between the larger ADV remnants and the smaller remnants from TB and FONC. Mean cleanup times also differed between groups (ANOVA, P <.001): TB and FOC had equal times that were significantly longer than the times for ADV and FONC, which were equal. Adhesives bonded to acid-etched or conditioned enamel took about 1 and a half times longer to clean up than did those bonded to nonetched enamel. When bonded to conditioned enamel, the resin-modified glass ionomer had mean remnant adhesive weights, areas, and cleanup times statistically equivalent to TB. ADV had the fastest mean cleanup time per amount of remnant (ANOVA, P <.002). The graphs of scores for 2 qualitative methods used for scoring remnant amount did not closely resemble the graphs based on weight and area. The graph of a newly introduced qualitative method better reflected the area data. Weighing may be a useful method for quantifying remnant adhesive. (Am J Orthod Dentofacial Orthop 2002;121:291-6)

Dynamic shoot morphology in root‐climbing Araceae: Philodendron rudgeanum Schott and Ph. fragrantissimum (Hook.) G.Don

AbstractShoot organization, branching patterns and growth cycle were studied in natural populations of two herbaceous, root‐climbing lianas, Philodendron rudgeanum and Ph. fragrantissimum, occurring in remnant areas of moist tropical forest in the Brazilian States of Pernambuco and Alagoas. The shoot architecture of both species is based on a repeating pattern of primary modules, each involving the successive transformation of flagelliform shoots into stolons and then root‐climbers. Significant differences in the detailed modular construction of the two species were also observed. A comparision of the two species is made with Monstera adansonii var. klotzschiana, growing in the same habitat.

Dynamic Shoot Morphology in Monstera adansonii Schott var. klotzschiana (Schott) Madison (Araceae)

The life cycle and shoot organization of Monstera adansonii Schott var. klotzschiana (Schott) Madison, an herbaceous, root-climbing liana, were studied in populations occurring in remnant areas of moist tropical forest in the Brazilian State of Pernambuco. A field study of the shoot architecture of individual plants showed that this taxon exhibits different phases, each linked to a particular microhabitat. A terminology is proposed for the different morphological units based on the recognition of primary modules, which colonize new host trees by means of terrestrial stolons and aerial flagelliform shoots, and secondary modules, which carry out assimilation and most sexual reproduction. The architectural model which the plant most closely resembles is that of "Chamberlain". The taxonomic value of shoot architectural characters is discussed.

Estimating Clearance of Acacia-dominated Ecosystems in Central Queensland Using Land-system Mapping Data

Preferential clearance of productive Acacia-dominated ecosystems was determined using digital land-system mapping and a 1994–1995 native vegetation remnant coverage from central Queensland. The previously mapped land systems are composed of complexes of land units, covering a range of productive potentials that are not individually mapped but defined according to their proportions within the land systems. Some land units were grouped into 11 ‘Acacia ecosystems’ composed of unique combinations of geology and vegetation dominated by brigalow (Acacia harpophylla F.Muell. ex Benth.), gidgee (A. cambagei R.T.Baker) or blackwood (A. argyrodendron Domin). Calculation of the remnant area of these Acacia ecosystems, assuming equal proportions of vegetation clearance of the land unit components within the land-system complexes (equal proportion calculation), was compared with a more accurate calculation based on interpretation of aerial photography (aerial-photograph calculation) data. The aerial photograph calculation of remnant area was 44% of the equal proportion calculation for brigalow on Tertiary clay and the ratio between these calculations was greater than 100% for only one Acacia ecosystem of relatively low production potential. The proportion of the remnant Acacia ecosystems relative to less productive ecosystems on tenures assigned to production (leasehold and freehold) was consistently lower than on other tenures. The use of mapping consisting of composite ecosystems with various production potentials for area-based assessment of vegetation clearance will overestimate the remnant areas of the relatively productive types unless a procedure such as that outlined here is used to correct for preferential clearance. This study provides near-complete and accurate data on the 1994–1995 status of Acacia ecosystems in central Queensland. Relative to their original area, values ranged from 6.8% for brigalow on Tertiary clay to 37.6% for gidgee–blackwood on alluvium.

Habitat Destruction and the Extinction Debt Revisited

A very important published analysis of the problem of habitat destruction (Tilman et al. 1994 [Nature 371:65‐66]) concluded that such destruction may lead to an extinction debt, which is the irreversible, preferential loss of competitive species following a prolonged transient or delay after the habitat destruction. We analyzed this model using analytic and simulation techniques. Relating this analytic model to real‐world situations shows that it applies to scattered permanent devegetation of small patches and to across‐the‐board decreases in fecundity such as could be caused by pollution. For repeated spatially random disturbance, we develop a new model that shows an even more severe extinction‐debt effect. For larger fragments of remnant vegetation, such as forest woodlots, we argue that the assumptions of the model are violated but that an extinction debt nevertheless occurs due to gradual stochastic elimination of species that are very rare and isolated in these fragments. For habitat destruction on regional scales (reduction in ecosystem area without disturbance in remnant areas), one must, in contrast, apply species‐area relations based on the distribution of different habitat types (e.g., elevational and rainfall gradients, physiographic and edaphic variability). Such an analysis predicts rapid, not delayed, loss of all types of species, not just competitive types. We conclude that the extinction‐debt effect is real and arises in three different models, but relating the models to real‐world conservation problems must be done with care.

Städtenetze als raumordnungspolitischer Handlungsansatz: Gefährdung oder Stütze des Zentrale-Orte-Systems?

Urban networks as an approach to active spatial planning threat or support to the central place system? The article deals with the relationship between urban net works as a new instrument of spatial planning. The latter is seen as the basic structure in space, which guarantees especially in rural areas a minimum of public services and thus equivalent living conditions. Urban networks, as being in the general rule the spontaneous cooperation of neigh bouring municipalities, are to be regarded as positive. However, successful networks can interfere in the basic structure of the central place system. This is a challenge for regional planning to take up the position of a mediator to prevent the emergence of disadvantaged remnant areas. A normative definition of urban networks by regional planning is to be seen critically, because urban networks can hardly be successful without bottom-up initiatives.

Can revegetation assist in the conservation of biodiversity in agricultural areas?

It has been suggested that revegetation in agricultural areas to tackle land degradation problems can also aid in the conservation of biodiversity in these regions. Native biota is restricted to remnant areas, which are mostly small, often unconnected, and subject to a variety of impacts from the surrounding altered landscape. The current remnant network is not sufficient to ensure the long-term persistence of the biota, and requires enhancement. Revegetation provides an opportunity to protect and add to the existing remnant network. However, there are few data available with which to assess the likely impact of revegetation on conservation values, and few guidelines as to how revegetation should be designed for conservation purposes. This paper presents an initial framework for developing revegetation strategies which tie into the existing conservation network. Revegetation can either provide buffer strips around existing remnants to protect them from external impacts, corridors between them to increase connectivity, or additional habitat to increase the area of vegetation available, or can enhance degraded remnant areas. Precise design principles and specifications for these types of revegetation are lacking, and may not be appropriate since they will depend on vegetation types and the requirements of target species. In addition, revegetation will help retain biodiversity indirectly if it helps stabilize an otherwise degrading agricultural landscape. Revegetation in agricultural areas is compared with minesite rehabilitation, where the redevelopment of functioning ecosystems and faunal habitat appears to be possible. The task is harder in the agricultural situation because the scale of modification is greater, soil changes are more difficult to redress, and recolonization by native species is less likely. Increased research effort is needed on the implementation and effects of differing types of revegetation, strategies for increasing rates of adoption of revegetation and methods of integrating conservation considerations into revegetation programmes.

Effects of landscape fragmentation on ecosystem processes in the Western Australian wheatbelt

The effects of landscape fragmentation are usually considered in terms of biogeographic changes and habitat loss. I argue here that the effects of fragmentation on ecosystem processes are just as important to the long-term conservation of biota in remnant areas. In the Western Australian wheatbelt, widespread rapid clearing for agriculture has removed most of the native perennial vegetation and replaced it with an agricultural system based predominantly on annual crops and pastures. Fragmentation of the natural system has led to large changes in the water and nutrient cycles, radiation balance and wind regimes of the region. Removal of perennial vegetation has reduced evapotranspiration and altered soil water flows, such that peak runoffs have increased and water tables have risen, bringing stored salt to the surface. Salinity and waterlogging problems have resulted. The agricultural system has a very open nutrient cycle compared with the native vegetation. Changed vegetation covers have altered the radiation balance, and temperature and humidity gradients are apparent at the edges between remnants and agricultural land. Similarly, lack of perennial cover increases the wind speed near the ground and leads to increased soil erosion. These changes in the landscape impinge on the remaining fragments of native vegetation, and management of external influences is probably more important than management of internal processes within remnant areas. Remnant vegetation management has to be carried out in the context of the overall landscape.

Biological consequences of ecosystem fragmentation: A review: D. A. Saunders, R. J. Hobbs & C. R. Margules, Conservation Biology, 5(1), 1991, pp 18–32

Abstract. Abstract Research on fragmented ecosystems has focused mostly on the biogeograpbic consequences of the creation of habitat “islands” of different sizes and has provided little of practical value to managers. However, ecosystem fragmentation causes large changes in the physical environment as well as biogeograpbic changes. Fragmentation generally results in a landscape that consists of remnant areas of native vegetation surrounded by a matrix of agricultural or other developed land. As a result fluxes of radiation, momentum (La, wind), water, and nutrients across the landscape are altered significantly. These in turn can have important influences on biota within remnant areas, especially at or near the edge between the remnant and the surrounding matrix. The isolation of remnant areas by clearing also has important consequences for the biota. These consequences vary with the time since isolation distance from other remnants, and degree of connectivity with other remnants. The influences of physical and biogeographic changes are modified by the size, shape, and position in the landscape of individual remnant, with larger remnants being less adversely affected by the fragmentation process. The Dynamics of remnant areas are predominantly driven by factors arising in the surrounding landscape. Management of, and research on, fragmented ecosystems should be directed at understanding and controlling these external influences as much as at the biota of the remnants themselves. There is a strong need to develop an integrated approach to landscape management that places conservation reserves in the context of the overall landscape

Biological Consequences of Ecosystem Fragmentation: A Review

Abstract. Abstract Research on fragmented ecosystems has focused mostly on the biogeograpbic consequences of the creation of habitat “islands” of different sizes and has provided little of practical value to managers. However, ecosystem fragmentation causes large changes in the physical environment as well as biogeograpbic changes. Fragmentation generally results in a landscape that consists of remnant areas of native vegetation surrounded by a matrix of agricultural or other developed land. As a result fluxes of radiation, momentum (La, wind), water, and nutrients across the landscape are altered significantly. These in turn can have important influences on biota within remnant areas, especially at or near the edge between the remnant and the surrounding matrix. The isolation of remnant areas by clearing also has important consequences for the biota. These consequences vary with the time since isolation distance from other remnants, and degree of connectivity with other remnants. The influences of physical and biogeographic changes are modified by the size, shape, and position in the landscape of individual remnant, with larger remnants being less adversely affected by the fragmentation process. The Dynamics of remnant areas are predominantly driven by factors arising in the surrounding landscape. Management of, and research on, fragmented ecosystems should be directed at understanding and controlling these external influences as much as at the biota of the remnants themselves. There is a strong need to develop an integrated approach to landscape management that places conservation reserves in the context of the overall landscape

The landscape approach to conservation: community involvement, the only practical solution

The aim of those developing and subsequently managing land in rural areas should be to ensure that the native flora and fauna are preserved, along with the agricultural productivity of the land. Unfortunately, there are few places where this has been achieved; land degradation (as indicated by increasing soil salinization, wind and water erosion, pollution of water supplies and the loss of soil productivity due to depletion of nutrients) and species loss has usually followed development. If we are to retain nature conservation values and preserve agricultural productivity, the processes leading to soil salinization, wind erosion, water erosion and fouling of water supplies, etc. must be reversed. This will involve revegetating very large areas, i.e., whole landscapes. At present we know much about rehabilitating small areas such as mine sites and other derelict land, but we know little about restoring entire water catchments, or land systems. We need to understand how to conserve existing remnant areas to...

Neurolepis, a Sensitive Indicator of Human Activity in the High Andes

AbstractNeurolepis is an easily recognizable bamboo-grass found as the dominant vegetation in many of the wettest and most remote Andean montane grassland areas. The plant has little economic value and is usually burned to produce pasture or facilitate hunting. After burning, regrowth is extremely slow, so that areas previously occupied by Neurolepis are apparently permanently colonized by tussock pasture grasses. It seems likely, therefore, that the existing remnant areas of Neurolepis represent the areas which have not been substantially affected by man in historic, and perhaps prehistoric, times.