Landscape-level Differences Research Articles

An unprotected tributary has no detectable impact on macroinvertebrates in a Wild and Scenic River in the southeast (Chattooga)

The use of land in the Stekoa Creek watershed could impact its greater drainage basin, the Chattooga River watershed, Georgia, USA. Leaf litter packs were used to collect invertebrates in Stekoa Creek and in the Chattooga both above and below its confluence with Stekoa Creek. Macroinvertebrate community characteristics can be indicators of the health of the environment that is inhabited. Macroinvertebrates were identified and communities were analyzed to determine similarity, richness, and diversity. Land cover data were analyzed using Geographical Information System to understand land use and subsequent invertebrate community assemblages of the Stekoa and Chattooga watersheds. While no differences were found in invertebrate assemblages, there was a higher amount of urbanized land in the Stekoa watershed. These results suggest that while there are some landscape level differences between watersheds, a response in the invertebrate community was not detected.

Oyster reefs as carbon sources and sinks.

Carbon burial is increasingly valued as a service provided by threatened vegetated coastal habitats. Similarly, shellfish reefs contain significant pools of carbon and are globally endangered, yet considerable uncertainty remains regarding shellfish reefs' role as sources (+) or sinks (-) of atmospheric CO2 While CO2 release is a by-product of carbonate shell production (then burial), shellfish also facilitate atmospheric-CO2 drawdown via filtration and rapid biodeposition of carbon-fixing primary producers. We provide a framework to account for the dual burial of inorganic and organic carbon, and demonstrate that decade-old experimental reefs on intertidal sandflats were net sources of CO2 (7.1 ± 1.2 MgC ha-1 yr-1 (µ ± s.e.)) resulting from predominantly carbonate deposition, whereas shallow subtidal reefs (-1.0 ± 0.4 MgC ha-1 yr-1) and saltmarsh-fringing reefs (-1.3 ± 0.4 MgC ha-1 yr-1) were dominated by organic-carbon-rich sediments and functioned as net carbon sinks (on par with vegetated coastal habitats). These landscape-level differences reflect gradients in shellfish growth, survivorship and shell bioerosion. Notably, down-core carbon concentrations in 100- to 4000-year-old reefs mirrored experimental-reef data, suggesting our results are relevant over centennial to millennial scales, although we note that these natural reefs appeared to function as slight carbon sources (0.5 ± 0.3 MgC ha-1 yr-1). Globally, the historical mining of the top metre of shellfish reefs may have reintroduced more than 400 000 000 Mg of organic carbon into estuaries. Importantly, reef formation and destruction do not have reciprocal, counterbalancing impacts on atmospheric CO2 since excavated organic material may be remineralized while shell may experience continued preservation through reburial. Thus, protection of existing reefs could be considered as one component of climate mitigation programmes focused on the coastal zone.

Landscape-scale variation in an anthropogenic factor shapes immune gene variation within a wild population.

Understanding the spatial scale at which selection acts upon adaptive genetic variation in natural populations is fundamental to our understanding of evolutionary ecology, and has important ramifications for conservation. The environmental factors to which individuals of a population are exposed can vary at fine spatial scales, potentially generating localized patterns of adaptation. Here, we compared patterns of neutral and major histocompatibility complex (MHC) variation within an island population of Berthelot's pipit (Anthus berthelotii) to assess whether landscape-level differences in pathogen-mediated selection generate fine-scale spatial structuring in these immune genes. Specifically, we tested for spatial associations between the distribution of avian malaria, and the factors previously shown to influence that distribution, and MHC variation within resident individuals. Although we found no overall genetic structure across the population for either neutral or MHC loci, we did find localized associations between environmental factors and MHC variation. One MHC class I allele (ANBE48) was directly associated with malaria infection risk, while the presence of the ANBE48 and ANBE38 alleles within individuals correlated (positively and negatively, respectively) with distance to the nearest poultry farm, an anthropogenic factor previously shown to be an important determinant of disease distribution in the study population. Our findings highlight the importance of considering small spatial scales when studying the patterns and processes involved in evolution at adaptive loci.

Climate, streamflow, and legacy effects on growth of riparian Populus angustifolia in the arid San Luis Valley, Colorado

Knowledge of the factors affecting the vigor of desert riparian trees is important for their conservation and management. I used multiple regression to assess effects of streamflow and climate (12–14 years of data) or climate alone (up to 60 years of data) on radial growth of clonal narrowleaf cottonwood (Populus angustifolia), a foundation species in the arid, Closed Basin portion of the San Luis Valley, Colorado. I collected increment cores from trees (14–90 cm DBH) at four sites along each of Sand and Deadman creeks (total N = 85), including both perennial and ephemeral reaches. Analyses on trees <110 m from the stream channel explained 33–64% of the variation in standardized growth index (SGI) over the period having discharge measurements. Only 3 of 7 models included a streamflow variable; inclusion of prior-year conditions was common. Models for trees farther from the channel or over a deep water table explained 23–71% of SGI variability, and 4 of 5 contained a streamflow variable. Analyses using solely climate variables over longer time periods explained 17–85% of SGI variability, and 10 of 12 included a variable indexing summer precipitation. Three large, abrupt shifts in recent decades from wet to dry conditions (indexed by a seasonal Palmer Drought Severity Index) coincided with dramatically reduced radial growth. Each shift was presumably associated with branch dieback that produced a legacy effect apparent in many SGI series: uncharacteristically low SGI in the year following the shift. My results suggest trees in locations distant from the active channel rely on the regional shallow unconfined aquifer, summer rainfall, or both to meet water demands. The landscape-level differences in the water supplies sustaining these trees imply variable effects from shifts in winter-versus monsoon-related precipitation, and from climate change versus streamflow or groundwater management.

Multiple environmental drivers structure plant traits at the community level in a pyrogenic ecosystem

SummaryTrait‐based approaches offer a way to predict changes in community structure along environmental gradients using measurable properties of individuals. Promoted as being generalizable across systems, trait‐based approaches benefit from information about the environmental drivers of trait variation, how they interact and how they change with scale. However, for most diverse, natural communities, it is largely unknown whether the relationships between leaf‐level traits and interacting environmental drivers (e.g. fire, water availability) are influenced by the scale of trait aggregation.We show that landscape‐level differences in community composition in a diverse, fire‐dependent pine savanna are explained by a small subset of species groups that are strongly correlated with soil moisture and elevation, but are insensitive to the time since the last fire.We used a trait‐based approach to show that significant variation in the community‐weighted mean (CWM) of specific leaf area (SLA) and leaf dry matter content (LDMC), two traits known to drive community structure and function, was explained by a small set of factors including the time since the last fire, soil moisture, precipitation and Shannon diversity.We show that statistical inference about the environmental drivers of community traits is radically altered when using CWMs computed with landscape‐level rather than plot‐level means, even over modest spatial scales.Synthesis: Environmental drivers of community composition across the landscape differed from those explaining trait composition. CWM traits were strongly influenced by interactions between drivers. Fire, in particular, strongly mediated the effect of other environmental variables on LDMC, showing that strong environmental gradients cannot be considered independently when assessing their effects on functional traits. The importance of environmental variables such as fire was lost when using landscape‐level trait means, highlighting the importance of local trait variation. This suggests caution when using traits from distant populations to make inferences about local processes, especially across strong gradients.

Land use planning and wildfire: development policies influence future probability of housing loss.

Increasing numbers of homes are being destroyed by wildfire in the wildland-urban interface. With projections of climate change and housing growth potentially exacerbating the threat of wildfire to homes and property, effective fire-risk reduction alternatives are needed as part of a comprehensive fire management plan. Land use planning represents a shift in traditional thinking from trying to eliminate wildfires, or even increasing resilience to them, toward avoiding exposure to them through the informed placement of new residential structures. For land use planning to be effective, it needs to be based on solid understanding of where and how to locate and arrange new homes. We simulated three scenarios of future residential development and projected landscape-level wildfire risk to residential structures in a rapidly urbanizing, fire-prone region in southern California. We based all future development on an econometric subdivision model, but we varied the emphasis of subdivision decision-making based on three broad and common growth types: infill, expansion, and leapfrog. Simulation results showed that decision-making based on these growth types, when applied locally for subdivision of individual parcels, produced substantial landscape-level differences in pattern, location, and extent of development. These differences in development, in turn, affected the area and proportion of structures at risk from burning in wildfires. Scenarios with lower housing density and larger numbers of small, isolated clusters of development, i.e., resulting from leapfrog development, were generally predicted to have the highest predicted fire risk to the largest proportion of structures in the study area, and infill development was predicted to have the lowest risk. These results suggest that land use planning should be considered an important component to fire risk management and that consistently applied policies based on residential pattern may provide substantial benefits for future risk reduction.

Land use drives the physiological properties of a stream fish

Human activities within the riparian zone can alter abiotic properties of a watershed, potentially resulting in abiotic conditions that are stressful for resident fishes. The inability of fish to cope physiologically with stressful abiotic conditions can have deleterious effects on individuals, and could potentially lead to population declines or changes to community structure (biodiversity). Defining links between landscape-level processes and performance of individual stream fishes can therefore improve our ability to predict how land use changes can impact stream communities, which has relevance for management activities. This study tested the hypothesis that land use at the watershed scale influences the physiological stress response of resident fishes. For this, replicate streams in agricultural watersheds and forested watersheds were identified; sampling demonstrated that streams in agricultural watersheds were warmer and more thermally variable than streams from agricultural areas. Creek chub from each land use type were sampled for blood and muscle in the field, following exposure to thermal and oxygen stressors in the laboratory, and after prolonged holding at elevated temperatures that replicated field conditions. No differences in baseline physiological parameters were found in fish sampled directly from streams. However, when exposed to low oxygen and high temperature conditions in the laboratory, creek chub from streams within agricultural areas maintained physiological performance with a reduced stress response relative to creek chubs from streams within forested watersheds. In addition, prolonged holding at high temperature removed landscape-level differences in stress responses, resulting in improved physiological performance for all fishes after a heat challenge. Results indicate that creek chub have the ability to adjust physiological responses to improve performance in disturbed environments, and also provide a novel mechanism by which landscape-level processes can influence biodiversity.

Landscape-level differences in fire regime between block and patch-mosaicburning strategies in Mkuzi Game Reserve, South Africa

Patch-mosaic burning (PMB) is commonly advocated to create a mosaic of fire regimes that is believed to be more beneficial for maintaining biodiversity than the relatively homogeneous environment produced by block burning. This premise was examined for the 23 651 ha Mkuzi Game Reserve, in which all fires have been mapped for a period of block burning (1966–1984) and for a period of PMB (1985–1999), using a geographic information system. Patch-mosaic burning met with the expectation of creating a more heterogeneous fire regime as evidenced by a four-fold increase in average fire frequency, a greater area of reserve burnt per annum, an increase in the perimeter-to-area ratio of individual burns, and a greater proportion of fires occurring throughout the dry season as opposed to being concentrated toward the end of the dry season. In contradiction of expectation, size of individual burns did not differ between strategies, both periods were characterised by intense fires, and natural barriers to fire did not increase in importance under PMB. There was a reduced importance of arson fires and a markedly increased proportion of prescribed burns under PMB. Patch-mosaic burning has met in part its objective of creating a more heterogeneous fire regime.

The carbonate system geochemistry of shallow groundwater-surface water systems in temperate glaciated watersheds (Michigan, USA): Significance of open-system dolomite weathering

We present here a field geochemical study of controls on carbonate weathering within rapidly circulating, shallow groundwater–surface water systems in the glaciated mid-continent region. Groundwaters and surface waters in three watersheds spanning the Upper to Lower Peninsulas of Michigan consist of Ca 2+ -Mg 2+ -HCO 3 − solutions derived from the open-system dissolution of calcite and dolomite in soils developed on mixed mineralogy glacial drift. The thermodynamic stabilities of calcite and dolomite both decrease with decreasing temperature, with dolomite more strongly affected. Thus, the low mean annual temperature of these temperate weathering environments maximizes the absolute solubility of dolomite as well as its solubility relative to calcite. Many groundwaters in the study area approach equilibrium with respect to the more soluble dolomite and are moderately supersaturated with respect to calcite. Groundwaters in each watershed have distinct and relatively narrow ranges of carbon dioxide partial pressure ( P CO 2 ) values, which increase significantly from north to south (log P CO 2 of −3.0 to −2.2 atm), suggesting that there are landscape-level differences in carbon transformation rates in soil weathering zones. Increases in weathering-zone P CO 2 values produce HCO 3 − concentrations that vary by a factor of five, but the Mg 2+ /Ca 2+ and Mg 2+ /HCO 3 − ratios of all groundwaters are similar, suggesting relatively constant weathering input ratios of calcite and dolomite. Although surface waters commonly are between 2 and 10 times supersaturated with respect to calcite, the Mg 2+ /HCO 3 − ratios of surface waters are very close to initial groundwater values, suggesting that back precipitation of calcite is not a significant process in these systems. The enhanced solubility of dolomite at low temperatures coupled with the landscape-level differences in carbon cycling suggest that temperate-zone weathering reactions in glaciated terrains are significant contributors to continent-scale fluxes of both Mg 2+ and HCO 3 − .

Landscape level differences in soil carbon and nitrogen: Implications for soil carbon sequestration

The objective of this research was to understand how land cover and topography act, independently or together, as determinants of soil carbon and nitrogen storage over a complex terrain. Such information could help to direct land management for the purpose of carbon sequestration. Soils were sampled under different land covers and at different topographic positions on the mostly forested 14,000 ha Oak Ridge Reservation in Tennessee, USA. Most of the soil carbon stock, to a 40‐cm soil depth, was found to reside in the surface 20 cm of mineral soil. Surface soil carbon and nitrogen stocks were partitioned into particulate (≥53 μm) and mineral‐associated organic matter (&lt;53 μm). Generally, soils under pasture had greater nitrogen availability, greater carbon and nitrogen stocks, and lower C:N ratios than soils under transitional vegetation and forests. The effects of topography were usually secondary to those of land cover. Because of greater soil carbon stocks, and greater allocation of soil carbon to mineral‐associated organic matter (a long‐term pool), we conclude that soil carbon sequestration, but not necessarily total ecosystem carbon storage, is greater under pastures than under forests. The implications of landscape‐level variation in soil carbon and nitrogen for carbon sequestration are discussed at several different levels: (1) nitrogen limitations to soil carbon storage; (2) controls on soil carbon turnover as a result of litter chemistry and soil carbon partitioning; (3) residual effects of past land use history; and (4) statistical limitations to the quantification of soil carbon stocks.

Effects of Land Use Changes on the Landscape Composition: A Comparison Between Finnish and Russian Karelia

During the last 50 years the practising and intensity of agriculture and forestry have differed considerably between Finnish and Russian Karelia. We studied the effects of different land use practices on the landscape composition in the two countries using the road transect sampling along four study routes (99-121 km) between 1997 and 1999. Effective environmental management in Finland has resulted in more distinct agricultural land types, more even distribution of the different age classes of forests, and the higher abundance of coniferous forests. Fields (mean percentage of the landscape: Finland 28%, Russia 13%), clearcuts and sapling stands (15%, 6%), and young forests (23%, 9%) were more typical elements of the Finnish landscape, whereas settlements (9%, 13%), semi-natural grasslands (3%, 7%), and mature forests (20%, 49%) were more characteristic of the Russian landscape. Landscape-level differences between the two countries may have various effects on the diversity of fauna and flora inhabiting Finnish and Russian Karelia.

Habitat structure and plant community composition in a northern Everglades wetland landscape

The structure ofa priori-defined aquatic habitats was compared within the Arthur R. Marshall Loxahatchee National Wildlife Refuge, which comprises the northern remnant of the Everglades ecosystem. Total plant biomass, canopy height, water depth, and the relative abundance (percent cover) of plant species in adjacent sloughs (including alligator holes), wet prairies, and sawgrass stands were compared over a 30-month period. These habitats formed a mosaic of aquatic habitats of differing structure and plant community composition. Slough and alligator hole habitats were in deeper water with little or no canopy, and habitat structure was provided almost entirely by submersed bladderwort (Utricularia) and floating water lily (Nymphaea). Sawgrass stands were present in shallower water and had a well-developed canopy that was generated almost entirely byCladium. Wet prairies were intermediate in water depth and canopy stature, with emergent sedges (i.e.,Eleocharis, Rhynchospora) providing most habitat structure. Differences among adjacent habitats accounted for most of the observed variation in habitat structure and plant relative abundance, whereas differences among widely-separated areas in the Refuge (i.e., landscape-level differences) accounted for little of the observed variation. In contrast, water depth varied considerably among sampling areas, likely reflecting hydrologic gradients that occur across the Refuge landscape. Similarly, although differences among sampling months were minimal for most habitat features examined, most of the variation observed in water depth was accounted for by sampling month, as would be expected in a seasonally dynamic wetland such as the Everglades. Discriminant function analyses using plant relative abundance data, habitat structure data, or both sets of data combined correctly classified most sites with respect toa priori-defined habitat type, despite similarities in plant community composition in sloughs and wet prairies. Overall, it appears that sloughs, wet prairies, and sawgrass stands are distinct with respect to habitat structure and plant community composition and that differences among these habitats are persistent across the Refuge landscape.