The Experts below are selected from a list of 20367 Experts worldwide ranked by ideXlab platform
William H Schlesinger - One of the best experts on this subject based on the ideXlab platform.
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environmental controls on nitric oxide emission from northern chihuahuan desert soils
Biogeochemistry, 2000Co-Authors: Anne E Hartley, William H SchlesingerAbstract:A survey of nitric oxide (NO) emission from Chihuahuan desert soils found mean NO fluxes <0.1 ng NO-N cm−2h−1 during the dry season. These fluxes were at thelower end of the range reported for temperate grassland and woodlandecosystems. NO fluxes from wet or watered soils were higher(0.1–35 ng NO-N cm−2 h−1).Watering of black grama grassland soils produced an initial pulse of 12ng cm−2 h−1 (12-h after 1-cm watering)with high fluxes sustained over 4 days with repeated watering. Initialpulses from Shrubland soils were lower (maximum 5 ngcm−2 h−1), and fluxes declined withrepeated watering. Repeated watering of creosotebush soils depleted thesoil NH 4 + pool, and NO emissions weredirectly related to soil NH 4 + concentrationsat the end of the experiment. In watered andNH 4 + -fertilized creosotebush soils, NO fluxeswere positively related to potential net nitrification rates.NH 4 + -fertilization boosted the initial NOpulse 15 times in the Shrubland and 5 times in black grama grasslandrelative to watered controls. These experimental results point towardgreater substrate limitation in Shrublands. In this desert basin, NOemission averaged 0.12 kg N ha−1 y−1in untreated soil and 0.76 kg N ha−1y−1 in watered soil. We multiplied these averages bythe distribution of grassland and Shrubland vegetation within a58,600-ha area of the Jornada del Muerto basin to estimate regionallosses of 0.15–0.38 kg NO-N ha−1y−1 for this area of the Chihuahuan desert.
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nutrient losses in runoff from grasslandand Shrubland habitats in southern new mexico ii field plots
Biogeochemistry, 2000Co-Authors: William H Schlesinger, T J Ward, John P AndersonAbstract:Losses of dissolved nutrients (N, P, K, Ca, Mg, Na,Cl, and SO4) in runoff were measured on grasslandand Shrubland plots in the Chihuahuan desert ofsouthern New Mexico. Runoff began at a lowerthreshold of rainfall in Shrublands than ingrasslands, and the runoff coefficient averaged 18.6%in Shrubland plots over a 7-year period. In contrast,grassland plots lost 5.0 to 6.3% of incidentprecipitation in runoff during a 5.5-year period. Nutrient losses from Shrubland plots were greater thanfrom grassland plots, with nitrogen losses averaging0.33 kg ha−1 yr−1 vs0.15 kg ha−1 yr−1, respectively, during a 3-year period. Thegreater nutrient losses in Shrublands were due tohigher runoff, rather than higher nutrientconcentrations in runoff. In spite of these nutrientlosses in runoff, all plots showed net accumulationsof most elements due to inputs from atmosphericdeposition. Therefore, loss of soil nutrients byhillslope runoff cannot, by itself, account for thedepletion of soil fertility associated withdesertification in the Chihuahuan desert.
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nutrient losses in runoff from grassland and Shrubland habitats in southern new mexico i rainfall simulation experiments
Biogeochemistry, 1999Co-Authors: William H Schlesinger, Athol D Abrahams, Anthony J Parsons, John WainwrightAbstract:Rainfall simulation experiments were performed in areas of semiarid grassland (Bouteloua eriopoda) and arid Shrubland (Larrea tridentata) in the Chihuahuan desert of New Mexico. The objective was to compare the runoff of nitrogen (N) and phosphorus (P) from these habitats to assess whether losses of soil nutrients are associated with the invasion of grasslands by shrubs. Runoff losses from grass- and shrub-dominated plots were similar, and much less than from bare plots located in the Shrubland. Weighted average concentrations of total dissolved N compounds in runoff were greatest in the grassland (1.72 mg/1) and lowest in bare plots in the Shrubland (0.55 mg/1). More than half of the N transported in runoff was carried in dissolved organic compounds. In grassland and shrub plots, the total N loss was highly correlated to the total volume of discharge. We estimate that the total annual loss of N in runoff is 0.25 kg/ha/yr in grasslands and 0.43 kg/ha/yr in Shrublands — consistent with the depletion of soil N during desertification of these habitats. Losses of P from both habitats were very small.
Javier Pereztris - One of the best experts on this subject based on the ideXlab platform.
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habitat effects on resource tracking ability do wintering blackcaps sylvia atricapilla track fruit availability
Ibis, 2006Co-Authors: Jose Luis Telleria, Javier PereztrisAbstract:If resource availability shapes population distribution, changes in resource abundance should cause parallel changes in population numbers. However, tracking ability may be disrupted by different environmental and behavioural factors that act at different spatial and temporal scales. Here we analyse the ability of wintering Blackcap Sylvia atricapilla populations to track spatio-temporal variation in fruit availability in southern Spain in two habitats (forests and Shrublands) with different population structure. Former studies had shown that forests are equally used by both adult migrant and local Blackcaps, whereas Shrublands are nearly monopolized by juvenile migrants. These differences might affect resource tracking: it should be disrupted in forests, as local birds remain over winter in their breeding territories, but not in Shrublands where similarly competitive juvenile migrants can freely track the spatial distribution of fruits. We analysed the fruit-tracking ability of Blackcap populations among sites and years in both habitat types using a habitat-matching model, which predicts spatio-temporal changes in population abundance proportional to changes in resource availability. We counted Blackcaps and fruiting shrubs (dominated by Lentiscs Pistacia lentiscus and Wild Olives Olea europaea sylvestris) during four winters in forest and Shrubland patches. The abundance of fruits was always higher in Shrublands than in forests. In Shrublands, Blackcaps seemed to move freely across fruit-rich habitat patches, tracking changes in fruiting-shrub abundance among sites and years. However, such tracking was not observed in forests. This supports the view that fruit-tracking ability may be constrained by local factors, such as the social structure of populations occurring in different habitat types, which introduces spatio-temporal variation in the way fruit availability shapes the abundance distribution of these birds in their Mediterranean wintering grounds.
Max A Moritz - One of the best experts on this subject based on the ideXlab platform.
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testing a basic assumption of Shrubland fire management how important is fuel age
Frontiers in Ecology and the Environment, 2004Co-Authors: Max A Moritz, Jon E. Keeley, E A Johnson, Andrew SchaffnerAbstract:This year's catastrophic wildfires in southern California highlight the need for effective planning and management for fire-prone landscapes. Fire frequency analysis of several hundred wildfires over a broad expanse of California Shrublands reveals that there is generally not, as is commonly assumed, a strong relationship between fuel age and fire probabilities. Instead, the hazard of burning in most locations increases only moderately with time since the last fire, and a marked age effect of fuels is observed only in limited areas. Results indicate a serious need for a re-evaluation of current fire management and policy, which is based largely on eliminating older stands of Shrubland vegetation. In many Shrubland ecosystems exposed to extreme fire weather, large and intense wildfires may need to be factored in as inevitable events.
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spatiotemporal analysis of controls on Shrubland fire regimes age dependency and fire hazard
Ecology, 2003Co-Authors: Max A MoritzAbstract:Large fires in chaparral-dominated Shrublands of southern and central California are widely attributed to decades of fire suppression. Prehistoric Shrubland landscapes are hypothesized to have exhibited fine-grained age-patch mosaics in which fire spread was limited by the age and spatial pattern of fuels. In contrast, I hypothesize that fires during extreme weather conditions have been capable of burning through all age classes of the vegetation mosaic. Using the mapped fire history (1911–1995) of Los Padres National Forest, I analyzed burning patterns for hundreds of fires using a geographic information system (GIS). To estimate the degree of age dependency exhibited by the fire regime at different spatial scales, I employed methods of fire frequency analysis (i.e., fitting a generalized Weibull function to fire interval distributions). Statistics were also calculated using a temporal breakpoint of 1950 to assess possible effects of suppression. Results indicated that Shrubland fires have frequently bur...
Troy W Ocheltree - One of the best experts on this subject based on the ideXlab platform.
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abrupt transition of mesic grassland to Shrubland evidence for thresholds alternative attractors and regime shifts
Ecology, 2014Co-Authors: Zak Ratajczak, Jesse B Nippert, Troy W OcheltreeAbstract:Ecosystems with alternative attractors are susceptible to abrupt regime shifts that are often difficult to predict and reverse. In this study, we quantify multiple system dynamics to determine whether the transition of mesic grassland to Shrubland, a widespread phenomenon, represents a linear reversible process, a nonlinear but reversible threshold process, or a transition between alternative attractors that is nonlinear and prone to hysteresis. Using a 28-yr data set with annual resolution and extensive spatial replication, we found that shrub cover is correlated with distinct thresholds of fire and C4 grass cover, resulting in temporal bimodality of shrub cover and abrupt shifts of shrub cover despite gradual changes in grass cover. These abrupt increases in shrub cover are the most rapid ever reported in grasslands, and illustrate internal thresholds that separate grasslands and Shrublands. Nonlinear transitions from low to high shrub cover were also closely associated with positive feedback mechanisms that alter fire and competition (r2 = 0.65), suggesting that grasslands and Shrublands could show hysteresis, and by definition exist as alternative attractors. Thus, the response of this ecosystem to anthropogenic activity should tend to be rapid, nonlinear, and perhaps difficult to reverse. Regime shifts in this mesic grassland were predictable: we found that grassland and Shrubland attractors were differentiated by critical thresholds of ∼50–70% grass cover, 5–10% shrub cover, and a fire return interval of ∼3 yr. These thresholds may provide adaptive potential for managing nonlinear behavior in socio-ecological systems in a changing environment.
John P Anderson - One of the best experts on this subject based on the ideXlab platform.
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directional climate change and potential reversal of desertification in arid and semiarid ecosystems
Global Change Biology, 2012Co-Authors: Osvaldo E Sala, Debra P C Peters, John P AndersonAbstract:Our objective was to determine if long-term increases in precipitation can maintain grasslands susceptible to desertification, and initiate a reversal of historic regime shifts on desertified Shrublands. Perennial grass production and species richness in a multi-year wet period were hypothesized to be greater than expected based on precipitation in a sequence of dry years. These responses were expected to differ for grasslands and Shrublands with different dominant species and topo-edaphic properties. Long-term trends in desertification were documented using vegetation maps beginning in 1858, 1915, 1928, and 1998). These trends were compared with herbaceous and woody species responses to a sequence of dry (1994–2003) and wet years (2004–2008) for two grassland (uplands, playas) and three desertified Shrubland types (honey mesquite, creosotebush, tarbush) in the Chihuahuan Desert. Analyses showed that both types of grasslands decreased in spatial extent since 1858 whereas areas dominated by mesquite or creosotebush increased. Production of upland grasslands in the wet period was greater than expected based on responses during the dry period whereas the relationships between species richness and precipitation was the same for both periods. Precipitation was not important to responses in playa grasslands in either period. For all ecosystem types, the production response in wet years primarily was an increase in herbaceous plants, and the most pronounced responses occurred on sandy sites (upland grasslands, mesquite Shrubland). Results suggest that multiple wet years are needed to initiate a sequence of grass establishment and survival processes that can maintain upland grasslands without management inputs and lead to a state change reversal in desertified Shrublands. Restoration strategies need to take advantage of opportunities provided by future climates while recognizing the importance of ecosystem type.
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nutrient losses in runoff from grasslandand Shrubland habitats in southern new mexico ii field plots
Biogeochemistry, 2000Co-Authors: William H Schlesinger, T J Ward, John P AndersonAbstract:Losses of dissolved nutrients (N, P, K, Ca, Mg, Na,Cl, and SO4) in runoff were measured on grasslandand Shrubland plots in the Chihuahuan desert ofsouthern New Mexico. Runoff began at a lowerthreshold of rainfall in Shrublands than ingrasslands, and the runoff coefficient averaged 18.6%in Shrubland plots over a 7-year period. In contrast,grassland plots lost 5.0 to 6.3% of incidentprecipitation in runoff during a 5.5-year period. Nutrient losses from Shrubland plots were greater thanfrom grassland plots, with nitrogen losses averaging0.33 kg ha−1 yr−1 vs0.15 kg ha−1 yr−1, respectively, during a 3-year period. Thegreater nutrient losses in Shrublands were due tohigher runoff, rather than higher nutrientconcentrations in runoff. In spite of these nutrientlosses in runoff, all plots showed net accumulationsof most elements due to inputs from atmosphericdeposition. Therefore, loss of soil nutrients byhillslope runoff cannot, by itself, account for thedepletion of soil fertility associated withdesertification in the Chihuahuan desert.
