Evaluating Postfire Seeding Treatments Designed to Suppress Cheatgrass (Bromus tectorum) in a Ponderosa Pine Forest on the Colorado Plateau

The restoration of historical fuel conditions and fire regimes is one of the primary land management goals in the Shivwits Plateau region of northwestern Arizona. Fire is the primary tool used in this region to reduce fuel loads and shift landscapes back to historical conditions of a low intensity, 8- 15 year return interval, surface fire regime. However, the invasive plant cheatgrass has become the dominant understory vegetation and fuel type following initial fire treatments in many areas. There is significant concern that repeated burning at historically appropriate fire return intervals for ponderosa pine forest will benefit this invasive plant to the detriment of native species. There is additional concern that the high flammability of cheatgrass fuelbeds will lead to fire return intervals that are more frequent than occurred historically and that are prescribed in the agency fire management plans, potentially preventing recruitment of pine seedlings and leading to type conversion of native forests to alien grasslands. Federal land managers and research scientists have noted that cheatgrass does not typically cooccur with two of the dominant perennial grasses in the Shivwits plateau region, bottlebrush squirreltail (Elymus elymoides) and blue grama (Bouteloua gracilis). This suggests that these natives may be competing with and excluding the establishment of cheatgrass. If these species can be established in postfire landscapes, they may be able to pre-empt the establishment of cheatgrass and promote the restoration of native plant communities and natural fuel characteristics. This report provides results of an experimental seedings of these two perennial grasses. Seeding with or without raking had no detectable effects on any of the species or groups of species in this study as measured by: 1) the density, cover, and species diversity of standing vegetation during the first 5 post-treatment years; or 2) the density and species diversity of the soil seedbank during the first 3 post-treatment years. Blue grama had an overall low standing density and cover, and seedbank density, at the study site, whereas bottlebrush squirreltail had relatively high standing density and cover, and seedbank density, at least during some of the sampling years. Cheatgrass did not differ among treatments, including raked and unraked plots, and only increased from 1.1 seeds per 18 cubic cm of soil immediately following the fire in fall 2003 to 1.5 seeds by the fall of the third postfire year

Man and the Last Great Wilderness: Human Impact on the Deep Sea

The deep sea, the largest ecosystem on Earth and one of the least studied, harbours high biodiversity and provides a wealth of resources. Although humans have used the oceans for millennia, technological developments now allow exploitation of fisheries resources, hydrocarbons and minerals below 2000 m depth. The remoteness of the deep seafloor has promoted the disposal of residues and litter. Ocean acidification and climate change now bring a new dimension of global effects. Thus the challenges facing the deep sea are large and accelerating, providing a new imperative for the science community, industry and national and international organizations to work together to develop successful exploitation management and conservation of the deep-sea ecosystem. This paper provides scientific expert judgement and a semi-quantitative analysis of past, present and future impacts of human-related activities on global deep-sea habitats within three categories: disposal, exploitation and climate change. The analysis is the result of a Census of Marine Life – SYNDEEP workshop (September 2008). A detailed review of known impacts and their effects is provided. The analysis shows how, in recent decades, the most significant anthropogenic activities that affect the deep sea have evolved from mainly disposal (past) to exploitation (present). We predict that from now and into the future, increases in atmospheric CO2 and facets and consequences of climate change will have the most impact on deep-sea habitats and their fauna. Synergies between different anthropogenic pressures and associated effects are discussed, indicating that most synergies are related to increased atmospheric CO2 and climate change effects. We identify deep-sea ecosystems we believe are at higher risk from human impacts in the near future: benthic communities on sedimentary upper slopes, cold-water corals, canyon benthic communities and seamount pelagic and benthic communities. We finalise this review with a short discussion on protection and management methods

Quantifying the time lag between organic matter production and export in the surface ocean: Implications for estimates of export efficiency

The ocean's potential to export carbon to depth partly depends on the fraction of primary production (PP) sinking out of the euphotic zone (i.e., the e-ratio). Measurements of PP and export flux are often performed simultaneously in the field, although there is a temporal delay between those parameters. Thus, resulting e-ratio estimates often incorrectly assume an instantaneous downward export of PP to export flux. Evaluating results from four mesocosm studies, we find that peaks in organic matter sedimentation lag chlorophyll a peaks by 2 to 15 days. We discuss the implications of these time lags (TLs) for current e-ratio estimates and evaluate potential controls of TL. Our analysis reveals a strong correlation between TL and the duration of chlorophyll a buildup, indicating a dependency of TL on plankton food web dynamics. This study is one step further toward time-corrected e-ratio estimate

Evaluating Postfire Seeding Treatments Designed to Suppress Cheatgrass (\u3ci\u3eBromus tectorum\u3c/i\u3e) in a Ponderosa Pine Forest on the Colorado Plateau

The restoration of historical fuel conditions and fire regimes is one of the primary land management goals in the Shivwits Plateau region of northwestern Arizona. Fire is the primary tool used in this region to reduce fuel loads and shift landscapes back to historical conditions of a low intensity, 8- 15 year return interval, surface fire regime. However, the invasive plant cheatgrass has become the dominant understory vegetation and fuel type following initial fire treatments in many areas. There is significant concern that repeated burning at historically appropriate fire return intervals for ponderosa pine forest will benefit this invasive plant to the detriment of native species. There is additional concern that the high flammability of cheatgrass fuelbeds will lead to fire return intervals that are more frequent than occurred historically and that are prescribed in the agency fire management plans, potentially preventing recruitment of pine seedlings and leading to type conversion of native forests to alien grasslands. Federal land managers and research scientists have noted that cheatgrass does not typically cooccur with two of the dominant perennial grasses in the Shivwits plateau region, bottlebrush squirreltail (Elymus elymoides) and blue grama (Bouteloua gracilis). This suggests that these natives may be competing with and excluding the establishment of cheatgrass. If these species can be established in postfire landscapes, they may be able to pre-empt the establishment of cheatgrass and promote the restoration of native plant communities and natural fuel characteristics. This report provides results of an experimental seedings of these two perennial grasses. Seeding with or without raking had no detectable effects on any of the species or groups of species in this study as measured by: 1) the density, cover, and species diversity of standing vegetation during the first 5 post-treatment years; or 2) the density and species diversity of the soil seedbank during the first 3 post-treatment years. Blue grama had an overall low standing density and cover, and seedbank density, at the study site, whereas bottlebrush squirreltail had relatively high standing density and cover, and seedbank density, at least during some of the sampling years. Cheatgrass did not differ among treatments, including raked and unraked plots, and only increased from 1.1 seeds per 18 cubic cm of soil immediately following the fire in fall 2003 to 1.5 seeds by the fall of the third postfire year. These results suggest that blue grama may be an inappropriate species for seeding at this study site, whereas bottlebrush squirreltail may be an appropriate species. Although the natural recovery of the latter species within a few years following fire suggest that seeding may not be necessary. In addition, cheatgrass may not be a significant postfire management concern at this study site. Additional research is needed to more definitively evaluate the effects of seeding treatments, document the postfire recovery rates of cheatgrass and other species under a wider range of environmental conditions, and determine if there is a specific fire prescription that can both control cheatgrass and accomplish other fire management objectives

Oxygen flux in surface sediments (Table 1)

Over the past decade an increasing body of evidence has accumulated indicating that much, perhaps most, of the deep sea floor is an environment of substantial temporal variability (Smith and Baldwin, 1984 doi:10.1038/307624a0; Smith, 1987; Deuser and Ross, 1980 doi:10.1038/283364a0; Thiel et al., 1988). This variability is driven largely by seasonal changes of processes occurring in the surface waters (Smith, 1987; Deuser and Ross, 1980; Billett et al., 1983 doi:10.1038/302520a0). The coupling of the deep sea floor environment to the surface waters is the result of rapid vertical transport of particulate matter through the water column (Honjo, 1982 doi:10.1126/science.218.4575.883; Deuser et al., 1986 doi:10.1016/0198-0149(86)90120-2; Lampitt, 1985 doi:10.1016/0198-0149(85)90034-2), affording only limited time for degradation before arrival at the sea floor. Studies in the Pacific Ocean have indicated that temporal variations in particulate organic carbon fluxes to the sea floor are accompanied by temporal variability in sediment oxygen demand by as much as a factor of four (Smith and Baldwin, 1984; Smith, 1987). We report here time-series studies of oxygen fluxes into the sediments of the oligotrophic Atlantic near Bermuda which contrast sharply with these previous reports. At the Bermuda site, despite large seasonal variations in particulate organic carbon fluxes, in situ measured sediment oxygen consumption does not vary significantly. These results imply that large areas of the sea floor may be characterized by seasonally invariant sediment oxygen demand

Rapid Coupling of Sinking Particle Fluxes Between Surface and Deep Ocean Waters

SETTLING particles are thought to be responsible for much of the transport of mass and energy from the upper ocean to the sea floor. Photosynthetic production by phytoplankton is a major source of these particles, either as phytoplankton biomass sinks directly 1 or as it is transformed into rapidly sinking forms such as aggregates 2,3 and zooplankton faeces 4. Because a variety of processes may act on sinking matter, however, it is not known to what extent fluxes of organic matter to the deep sea are coupled to processes at the ocean surface. Some studies have provided evidence for direct coupling 2, 5-7, but transformation processes and advection exist which have the potential to modify the transmission of surface signals to the deep sea 8-11. If these mechanisms overwhelm surface production signals, seasonal and annual variations in deep-sea geochemistry and biology would be controlled largely by lateral processes associated with ocean circulation rather than by surface processes. Here we report direct measurements of seasonal variations in upper-ocean primary production concurrent with particle fluxes measured at several depths ranging from the upper to the deep ocean in the Atlantic. We find that the productivity signal can be transferred rapidly to the deep sea by settling particles, yielding close temporal coupling between the surface and deep oceans

The accumulation of mineral ballast on organic aggregates

International audienceTo address whether the incorporation of suspended minerals drives the sedimentation of particulate organic carbon in the ocean or vice versa, incubations of phytoplankton-detritus aggregates were set up in rolling tanks containing seawater and suspended clay ( illite) or calcium carbonate at concentrations ranging between 10 and 50,000 mu g L-1. The suspended minerals were efficiently scavenged by and incorporated into the organic aggregates. The volume and porosity of aggregates decreased with increasing mineral concentrations, and at suspended mineral concentrations higher than 500 mu g L-1 the initially medium-sized aggregates were fragmented into thousands of tiny, dense aggregates. Because radius and density have opposite effects on aggregate sinking rates, the relationship between aggregate particulate organic carbon (POC) to mineral ratio and sinking rate is not a straightforward one that necessarily results in higher sinking rates with increased mineral content. In these experiments the saturating capacity of organic aggregates for mineral particles appeared to be 97 to 98 weight-percent mineral (i.e., a POC to dry weight ratio of 0.02 to 0.03 mu g C mu g(-1)). This parallels the values of 0.05 mu g C mu g(-1) observed for sinking particles in the deep sea and suggests that it is the flux of POC that determines the flux of minerals to the deep and not the other way around