ALBERT

Beschreibung: Permafrost and varying land surface properties greatly complicate modelling of the thermal response of Arctic soils to climate change. The forest-tundra transition near Nadym in west Siberia provides an excellent study area in which to examine the contrasting thermal properties of soils in a forested ecosystem without permafrost and peatlands with permafrost. We investigated the effects of forest shading, snow cover and variable organic soil horizons in three common ecosystems of the forest-tundra transition zone. Based on the year-round temperature profile data, the most informative annual parameters were: (1) the sum of positive average daily temperatures at depths of 10 and 20 cm; (2) the maximum penetration depth of temperatures above 10 °C; and (3) the number of days with temperatures below 0 °C at a depth of 20 cm. The insulative effect of snow cover in winter was at least twice that of the shading and cooling effect of vegetation in summer. In areas with shallow permafrost, the presence of a thick organic horizon, with an extremely low thermal diffusivity, creates a very steep temperature gradient that limits heat penetration to the top of the permafrost in summer. Copyright © 2015 John Wiley & Sons, Ltd.

Beschreibung: Marine invasion ecology and management have progressed significantly over the last 30 years although many knowledge gaps and challenges remain. The kelp Undaria pinnatifida , or “Wakame,” has a global non-native range and is considered one of the world's “worst” invasive species. Since its first recorded introduction in 1971, numerous studies have been conducted on its ecology, invasive characteristics, and impacts, yet a general consensus on the best approach to its management has not yet been reached. Here, we synthesize current understanding of this highly invasive species and adopt Undaria as a case study to highlight challenges in wider marine invasion ecology and management. Invasive species such as Undaria are likely to continue to spread and become conspicuous, prominent components of coastal marine communities. While in many cases, marine invasive species have detectable deleterious impacts on recipient communities, in many others their influence is often limited and location specific. Although not yet conclusive, Undaria may cause some ecological impact, but it does not appear to drive ecosystem change in most invaded regions. Targeted management actions have also had minimal success. Further research is needed before well-considered, evidence-based management decisions can be made. However, if Undaria was to become officially unmanaged in parts of its non-native range, the presence of a highly productive, habitat former with commercial value and a broad ecological niche, could have significant economic and even environmental benefit. How science and policy reacts to the continued invasion of Undaria may influence how similar marine invasive species are handled in the future. Marine invasion ecology and management have progressed significantly over the last 30 years; however, many knowledge gaps and challenges remain. The invasive kelp Undaria pinnatifida, or “Wakame,” has a global introduced range and is considered one of the world's worst invasive species. Undaria is useful case study to demonstrate that there are still limits in our capacity to understand the dynamics, impacts, and management potential of marine invaders.

Beschreibung: The role that microclimates play on soil decomposition is poorly understood. Though litter decomposition is controlled by climate and substrate quality at coarse spatial scales, at the watershed scale, microclimates mediated by forest structure and landscape position can influence decomposition rates and in turn affect nitrogen cycling. To evaluate the effects of landscape position and vegetation heterogeneity on decomposition, we employed a two-year litterbag study (2011–2013) using yellow birch leaf litter across the Weimer Run watershed, a cool, humid watershed located near Davis, West Virginia. From our results, we created a spatially explicit empirical model that we tested against both a single-pool and three-pool decomposition model, each based on climate and derived from the Long-Term Intersite Decomposition Experiment Team. Initial litter decomposition varied by elevation, with greater rates of decomposition at locations lower in the watershed. Decomposition rates differed by elevation, except during the first winter of the study. No differences in decomposition rates were seen among elevation levels when snowfall was below average for the first winter (2011–2012). During the second winter (2012–2013), elevation levels showed separation in decomposition rates, with higher elevations exhibiting lower decomposition rate. This suggests important controls on decomposition exerted by the presence or absence of snow, inter-annual climate variability, and the interaction of both with topography. Our empirical model showed greater rates of decomposition during early stages of decomposition (〈12 months), but converged with the three-pool decomposition model after 20 months. Plant available nitrogen differed by vegetation cover, largely driven by greater availability of nitrate (NO 3 − ) beneath areas of canopy closure in the forest. Controls on decomposition and nitrogen cycling within the Weimer Run watershed vary spatially by elevation and vegetation cover and are subject to complex interactions and differ from standard models of decomposition. The effect of the inter-annual variance of snow depth on litter decomposition is of note and an important consideration moving forward. Climate-based models of decomposition greatly underestimate initial rates of decomposition, potentially leading to under-accounting and compounded uncertainty.

Beschreibung: Many ecosystems around the world are rapidly deteriorating due to both local and global pressures, and perhaps none so precipitously as coral reefs. Management of coral reefs through maintenance (e.g., marine-protected areas, catchment management to improve water quality), restoration, as well as global and national governmental agreements to reduce greenhouse gas emissions (e.g., the 2015 Paris Agreement) is critical for the persistence of coral reefs. Despite these initiatives, the health and abundance of corals reefs are rapidly declining and other solutions will soon be required. We have recently discussed options for using assisted evolution (i.e., selective breeding, assisted gene flow, conditioning or epigenetic programming, and the manipulation of the coral microbiome) as a means to enhance environmental stress tolerance of corals and the success of coral reef restoration efforts. The 2014–2016 global coral bleaching event has sharpened the focus on such interventionist approaches. We highlight the necessity for consideration of alternative (e.g., hybrid) ecosystem states, discuss traits of resilient corals and coral reef ecosystems, and propose a decision tree for incorporating assisted evolution into restoration initiatives to enhance climate resilience of coral reefs. Many ecosystems around the world are rapidly deteriorating due to both local and global pressures including climate change, and perhaps none so precipitously as coral reefs. While root causes of human-driven climate change should be addressed, additional solutions are urgently required to ensure coral reefs persist into the future. In this Opinion piece, we address how breeding coral stock with enhanced environmental stress tolerance (assisted evolution) can increase reef resilience and contribute to the success of coral reef restoration efforts. We discuss traits of resilient corals and coral reef ecosystems, and provide guidelines for incorporating assisted evolution into restoration initiatives.

Beschreibung: Terrestrial ecosystem responses to temperature and precipitation have major implications for the global carbon cycle. Case studies demonstrate that complex terrain, which accounts for more than 50% of Earth's land surface, can affect ecological processes associated with land-atmosphere carbon fluxes. However, no studies have addressed the role of complex terrain in mediating ecophysiological responses of land-atmosphere carbon fluxes to climate variables. We synthesized data from AmeriFlux towers and found that for sites in complex terrain, responses of ecosystem CO 2 fluxes to temperature and precipitation are organized according to terrain slope and drainage area, variables associated with water and energy availability. Specifically, we found that for tower sites in complex terrain, mean topographic slope and drainage area surrounding the tower explained between 51% and 78% of site-to-site variation in the response of CO 2 fluxes to temperature and precipitation depending on the time scale. We found no such organization among sites in flat terrain, even though their flux responses exhibited similar ranges. These results challenge prevailing conceptual framework in terrestrial ecosystem modeling that assumes CO 2 fluxes derive from vertical soil-plant-climate interactions. We conclude that the terrain in which ecosystems are situated can also have important influences on CO 2 responses to temperature and precipitation. This work has implications for about 14% of the total land area of the conterminous US. This area is considered topographically complex and contributes to approximately 15% of gross ecosystem carbon production in the conterminous US.

Beschreibung: Satellite remote sensing data have indicated a general ‘greening’ trend in the arctic tundra biome. However, the observed changes based on remote sensing are the result of multiple environmental drivers, and the effects of individual controls such as warming, herbivory, and other disturbances on changes in vegetation biomass, community structure, and ecosystem function remain unclear. We apply ArcVeg, an arctic tundra vegetation dynamics model, to estimate potential changes in vegetation biomass and net primary production (NPP) at the plant community and functional type levels. ArcVeg is driven by soil nitrogen output from the Terrestrial Ecosystem Model, existing densities of Rangifer populations, and projected summer temperature changes by the NCAR CCSM4.0 general circulation model across the Arctic. We quantified the changes in aboveground biomass and NPP resulting from (i) observed herbivory only; (ii) projected climate change only; and (iii) coupled effects of projected climate change and herbivory. We evaluated model outputs of the absolute and relative differences in biomass and NPP by country, bioclimate subzone, and floristic province. Estimated potential biomass increases resulting from temperature increase only are approximately 5% greater than the biomass modeled due to coupled warming and herbivory. Such potential increases are greater in areas currently occupied by large or dense Rangifer herds such as the Nenets-occupied regions in Russia (27% greater vegetation increase without herbivores). In addition, herbivory modulates shifts in plant community structure caused by warming. Plant functional types such as shrubs and mosses were affected to a greater degree than other functional types by either warming or herbivory or coupled effects of the two. Potential Arctic vegetation can be 5% more than currently estimated through satellite remote sensing. Herbivory accounts for the 5% of biomass discrepancy. Such discrepancy is more profound in regions with high intensity of herbivory.

Beschreibung: In the context of ongoing climatic warming, certain landscapes could be near a tipping point where relatively small changes to their fire regimes or their postfire forest recovery dynamics could bring about extensive forest loss, with associated effects on biodiversity and carbon-cycle feedbacks to climate change. Such concerns are particularly valid in the Klamath Region of northern California and southwestern Oregon, where severe fire initially converts montane conifer forests to systems dominated by broadleaf trees and shrubs. Conifers eventually overtop the competing vegetation, but until they do, these systems could be perpetuated by a cycle of reburning. To assess the vulnerability of conifer forests to increased fire activity and altered forest recovery dynamics in a warmer, drier climate, we characterized vegetation dynamics following severe fire in nine fire years over the last three decades across the climatic aridity gradient of montane conifer forests. Postfire conifer recruitment was limited to a narrow window, with 89% of recruitment in the first 4 years, and height growth tended to decrease as the lag between the fire year and the recruitment year increased. Growth reductions at longer lags were more pronounced at drier sites, where conifers comprised a smaller portion of live woody biomass. An interaction between seed-source availability and climatic aridity drove substantial variation in the density of regenerating conifers. With increasing climatic water deficit, higher propagule pressure (i.e., smaller patch sizes for high-severity fire) was needed to support a given conifer seedling density, which implies that projected future increases in aridity could limit postfire regeneration across a growing portion of the landscape. Under a more severe prospective warming scenario, by the end of the century more than half of the area currently capable of supporting montane conifer forest could become subject to minimal conifer regeneration in even moderate-sized (10s of ha) high-severity patches. If climate change drives increases in wildfire activity while delaying postfire forest recovery, forested landscapes such as the Klamath Mountains (NW California/SW Oregon) could be at risk of extensive forest loss. To understand the vulnerability to such changes, we evaluated three decades of vegetation dynamics following high-severity fire across the regional aridity gradient. Conifers faced a highly competitive environment following severe fire. They comprised only a small portion of live woody biomass, and recruitment was limited primarily to the first four years. Seedlings that established later faced pronounced growth suppression, particularly on drier sites. With increasing climatic aridity, more abundant seed sources were needed to support conifer recruitment at densities sufficient to develop a new forest canopy. Under a more severe warming scenario, by the end of the century just over half of the landscape could be at risk of minimal conifer recruitment following severe fire, even in relatively small high-severity patches.

Beschreibung: Terrestrial ecosystem respiration (Reco) represents a large carbon source from land to atmosphere and is highly spatio-temporally heterogeneous across scales. Up-scaling of field-measured respiration data using remote sensing information is urgently needed for understanding regional and global patterns of ecosystem respiration. Using MODIS data with resolutions of one km and eight days, and flux measurements from 171 sites (total of 812 site-years) across the world from 2000 to 2014, we developed a semi-empirical, yet physiologically-based, remote sensing model, which can simulate Reco observed across most biomes with a small margin of error (R 2 = 0.55, RMSE = 1.67 gCm -2 d -1 , EF = 0.46, MBE = 0.18 gCm -2 d -1 ). The reference respiration at the annual mean nighttime Land Surface Temperature (LST) can be well represented by MODIS Enhanced Vegetation Index (EVI) and LST. A comprehensive comparison of six respiration-temperature (R-T) models shows that the more physiologically-based R-T model (extended Arrhenius model - ETA) may be most suitable for estimating the respiration rate at higher latitudes. Integrating an effect of vegetation change on Reco in different biomes effectively improves estimates of Reco in almost all of the biomes.

Beschreibung: Advances in remote sensing technology can help estimate biodiversity at large spatial extents. To assess whether we could use hyperspectral visible near-infrared (VNIR) spectra to estimate species diversity, we examined the correlations between species diversity and spectral diversity in early-successional abandoned agricultural fields in the Ridge and Valley ecoregion of north-central Virginia at the Blandy Experimental Farm. We established plant community plots and collected vegetation surveys and ground-level hyperspectral data from 350 to 1,025 nm wavelengths. We related spectral diversity (standard deviations across spectra) with species diversity (Shannon–Weiner index) and evaluated whether these correlations differed among spectral regions throughout the visible and near-infrared wavelength regions, and across different spectral transformation techniques. We found positive correlations in the visible regions using band depth data, positive correlations in the near-infrared region using first derivatives of spectra, and weak to no correlations in the red-edge region using either of the two spectral transformation techniques. To investigate the role of pigment variability in these correlations, we estimated chlorophyll, carotenoid, and anthocyanin concentrations of five dominant species in the plots using spectral vegetation indices. Although interspecific variability in pigment levels exceeded intraspecific variability, chlorophyll was more varied within species than carotenoids and anthocyanins, contributing to the lack of correlation between species diversity and spectral diversity in the red-edge region. Interspecific differences in pigment levels, however, made it possible to differentiate these species remotely, contributing to the species-spectral diversity correlations. VNIR spectra can be used to estimate species diversity, but the relationships depend on the spectral region examined and the spectral transformation technique used. As biodiversity is often correlated with ecosystem function, it is important to study biodiversity to conserve ecosystems. To assess the ability to estimate species diversity using spectral diversity, we collected vegetation survey data and ground-level hyperspectral data from community plots consisting of multiple species. There was a positive correlation in the visible region using band depth, a positive correlation in the near-infrared region using first derivatives, and weak to no correlation in the red-edge region using either spectral transformation technique; thus, species diversity can be estimated using spectral diversity, but the correlation depends on the spectral region examined and the spectral transformation technique used.