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Soil characteristics and pedogenic processes are relatively unstudied on Holocene age barrier islands in the Mid-Atlantic region of the United States. The objective of this study was to assess how landform stability and hydrologic conditions (water availability) influenced pedogenesis in barrier island soils. Ten topographic transects were established on different barrier island landforms (i.e., washover fan, back-barrier flat, barrier flat, and dune field) which ranged in age from 1 to 228 years. The topographic transects spanned drainage conditions, ranging from very poorly to excessively drained. The primary evidence for pedogenesis across the chronosequence was in the accumulation of organic matter, expressed in the formation of A and O horizons. Pedogenic development was restricted by the young age and weathering resistant nature of the soil parent material. The close proximity of the water table to the soil surface was associated with greater organic matter inputs from vegetation and slower decomposition under anaerobic conditions, which together led to increased accumulation of organic carbon in lower, wetter landscape positions. Frequency and duration of saturation also impacted subsoil development, producing subtle, but noticeable color differences between oxidized and reduced horizons. [ABSTRACT FROM AUTHOR]

Questions As changing wildfire regimes modify North American deserts, can fires of greater severity and frequency negatively impact the recovery of native bryophyte communities, which are not adapted to such disturbances? Does post-fire recovery result from the survival of existing surface plants, dormant propagules in sub-surface soil banks (dispersal in time) or aerial immigration into burned sites (dispersal in space)? Do wildfires negatively affect the survival of propagules in bryophyte soil banks? Location Continental arid shrublands, Mojave Desert, southwestern US. Methods We characterized bryophyte communities along a post-fire chronosequence spanning three decades across sites where fires had different severities, ages and potential fuels. Three community profiles (surface, soil and aerial) were surveyed with a combination of on-site surveys and emergence germination techniques. We tested for differences in beta diversity, species composition and richness with PERMDISP, PERMANOVA and linear mixed models, respectively. Results Burn severity was associated with differences in beta diversity, species composition and richness, while burn age was associated only with different composition and richness. No effect of potential fuel availability was found. More variation in composition was explained by significant differences among profiles than by other fire attributes. Species richness (but not beta diversity) was higher in soil profiles than in aerial spore rain or existing surface communities. Soils from the oldest and least severe burns had a greater number of species than soils from recent and more severe burns. Conclusions Bryophyte soil banks are common elements of desert soils that facilitate post-disturbance recovery of communities, but soil banks are themselves threatened by the intensifying frequency and severity of wildfires in North American deserts. Recovery of desert bryophyte communities seems to begin (but not necessarily conclude) within 30 yr after wildfires. In the near future, communities may become perturbed from historical patterns as contemporary fire regimes undergo extensive changes. [ABSTRACT FROM AUTHOR]

Abstract: Shrub willow biomass crops (SWBC) have been developed and promoted for widespread deployment in northeastern and mid-western US as well as in Europe. There are concerns that the production system could reduce the soil organic carbon (SOC) over time due to soil disturbances and repeated three-year harvest cycles. This study assesses changes in SOC beneath shrub willow (Salix x dasyclados [SV1]) biomass crops utilizing a 0, 5, 12, 14, and 19-year old SWBC fields. The sites' management history was similar, suggesting uniform SOC contents prior to plantation establishment. SOC contents were analyzed by total (i.e. 45 cm) and by layer (i.e. 0–15 cm, 16–30 cm, and 31–45 cm) across different ages. Mean SOC contents to 45 cm depth ranged from 175 to 188 Mg ha−1, and showed no statistically significantly differences across ages (p = 0.15) and no interaction between age and depth (p = 0.19). SOC contents differed significantly with soil depth when averaged across ages (p < 0.0001). Statistical analysis of SOC contents by layer, however, showed that SOC contents in the upper 15 cm depth were significantly different (p < 0.001). Linear contrasts of mean SOC contents for the 0–15 cm depth revealed that the 0-year old was significantly different compared with the 5, 12, 14, and 19-year old SWBC. [Copyright &y& Elsevier]

Plant species composition, dominance, richness, and diversity were measured across a 15-year chronosequence of created wetland sites in Virginia, USA. Using an age-class categorization (1-2 years, 3-5 years, 6-10 years, or 11-15 years), all classes had a predominance of herbaceous species with perennial life history strategy, and perennials contributed 68.6 % to the overall dominance measure (importance value; IV) averaged across all sites. There was no significant difference in species richness or diversity among age classes. Analysis of Similarity (ANOSIM) indicated that herbaceous species composition was similar between the youngest and oldest age classes, but not the intermediate classes. For woody shrubs and saplings, planted species were more prevalent in the youngest age classes, and volunteer species predominated in the oldest age classes. These results suggest that perennial herbaceous species are important in early plant development on created wetland sites, and may be influential in observed patterns of species composition over time. In the context of plant development in newly created wetlands, dominance shifts from planted to volunteer woody species suggest that planting early successional species, or species with reproductive strategies attuned to created wetland site management, may favor survivorship and recruitment of other species over time. [ABSTRACT FROM AUTHOR]

Abstract: The long-term changes of ecosystem carbon (C) and nitrogen (N) pools in reclaimed mine soils remains poorly understood. Thus, age chronosequence sites, ranging from <1 to 25years of reclamation, under forest and pasture land use, were identified to determine ecosystem C and N pools. Ecosystem C and N pools and selected soil properties were measured for 42 reclaimed sites across northeast Ohio. Soil organic C (SOC) was estimated by determining coal C and inorganic C, and subtracting these from the total soil C. Of the total soil C in reclaimed soil, coal C ranged from 0.2 to 15%, and inorganic C from <1 to 42%, depending on soil depth and land use. The C sequestered in the minesoil ecosystem followed a polynomial function, with the highest rate of sequestration of 6.59Mgha−1 after 14years of reclamation in the forest and 1.61Mgha−1 after 6years under pasture. After 25-year of reclamation, C sequestration was 107Mgha−1 under forest ecosystem and 21Mgha−1 under pasture. In the forest ecosystem, a major portion of ecosystem C consisted of soil C (94%) during the initial period (<1year) and biomass C (66%) during the later period (>14year). In the pasture ecosystem, soil C contributed a major portion of ecosystem C throughout the reclamation period: 95% for <1year and 89% for >25years of reclamation. However, soil N contributed a significant portion of ecosystem N in both the forest and pasture ecosystems. Ecosystem C and N pools and bulk densities were strongly related with reclamation age for both forest and pasture. The rates of ecosystem C and N sequestration peaked at about 10 to 15years of reclamation. After 10 to 15years of reclamation, the rate of sequestration decreased as reclamation age increased. [Copyright &y& Elsevier]

Abstract: During 2005–2007, we used the eddy covariance and associated hydrometric methods to construct energy and water budgets along a chronosequence of loblolly pine (Pinus taeda) plantations that included a mid-rotation stand (LP) (i.e., 13–15 years old) and a recently established stand on a clearcut site (CC) (i.e., 4–6 years old) in Eastern North Carolina. Our central objective was to quantify the differences in both energy and water balances between the two contrasting stands and understand the underlining mechanisms of environmental controls. We found that the LP site received about 20% more net radiation (R n ) due to its lower averaged albedo (α) of 0.25, compared with that at the CC (α =0.34). The mean monthly averaged Bowen ratios (β) at the LP site were 0.89±0.7, significantly (p =0.02) lower than at the CC site (1.45±1.2). Higher net radiation resulted in a 28% higher (p =0.02) latent heat flux (LE) for ecosystem evapotranspiration at the LP site, but there was no difference in sensible heat flux (H) between the two contrasting sites. The annual total evapotranspiration (ET) at the LP site and CC site was estimated as 1011–1226 and 755–855mmyear−1, respectively. The differences in ET rates between the two contrasting sites occurred mostly during the non-growing seasons and/or dry periods, and they were small during peak growing seasons or wet periods. Higher net radiation and biomass in LP were believed to be responsible to the higher ET. The monthly ET/Grass Reference ET ratios differed significantly across site and season. The annual ET/P ratio for the LP and CC were estimated as 0.70–1.13 and 0.60–0.88, respectively, indicating higher runoff production from the CC site than the LP site. This study implied that reforestation practices reduced surface albedos and thus increased available energy, but they did not necessarily increase energy for warming the atmosphere in the coastal plain region where soil water was generally not limited. This study showed the highly variable response of energy and water balances to forest management due to climatic variability. [Copyright &y& Elsevier]

Abstract: Soils on a series of debris flow deposits, ranging from <1 to 244 years old, were described and sampled in order to investigate the early stages of soil development. The parent material at the site is debris flow regolith, composed mainly of gneiss, the soil moisture regime is xeric, and the vegetation is mixed coniferous forest. Ages of the deposits were assessed using dendrochronology. Morphologic trends in the organic horizons included a thickening of the humus form over time, along with the development of Fm and Hr horizons. The humus forms underwent a progression from Mormodors (20 years old), to Hemimors (26–101 years old), and finally Lignomors (163 years old) and Resimors (184–244 years old). Changes in physical properties of the uppermost mineral horizons as a function of increasing age included a decrease in the volume of coarse fragments, a linear decrease in bulk density, and a darkening and reddening of the soil color. No significant soil development took place in the subsoil during the time span of this chronosequence. The soils described were classified as Typic Xerofluvents and Typic Xerorthents (Regosols and Leptosols). Buried A horizons were observed in many of the soils. Where the A horizons could be linked to dendrochronology to assess the age of the buried surface, we found that the properties of the buried A horizons do not serve as a good indicator of the age of the surface. This study suggests rapid development of the humus form profile (organic horizons and A horizon) following debris flow deposition and rapid degradation of these horizons when the debris flow surface is buried. [Copyright &y& Elsevier]

Establishment of short-rotation woody crop (SRWC) plantations for meeting the demand of wood and bioenergy production necessitates reclamation of agricultural lands and desert soils, such as those in the southern Columbia Plateau of Oregon, USA. The effects of plantation management on soil carbon (C) storage and nutrient concentration were evaluated, using a chronosequence of poplar (Populus spp.) stands on soils of eolian origin (Xeric Torripsamments). Stands of ages 1, 3, 4, 7, 9, and 10 years (n =3 per stand age), as well as adjacent agricultural and desert lands, were compared based on soil C, inorganic C (SIC), total nitrogen (N), and nutrient concentrations within the 0-to 50-cm soil depth. The 7-through 10-year-old stands that were in a first-rotation cycle were irrigated and fertilized. The 1-through 4-year-old stands in a second-rotation cycle received a mulch application treatment in addition to the irrigation and fertilization treatments. At age 11 years, the projected plantation C (147.5Mgha−1) accumulated almost entirely in the aboveground biomass (62.2%), forest floor (24.3%), and roots (11.7%). There were no significant increases in the mineral soil C and N pools with stand age, despite the presence of increasing trends within the surface layer. The accumulation of the mineral soil C pool (∼1.8%), from the first-(23.5±1.7MgCha−1) to the second-rotation stands (26.3±3.5MgCha−1), was partially offset by a loss of SIC due to irrigation. The SIC pool had a decreasing trend, which was related to dissolution of calcite along the soil profile, from the first-(16.7±3.4MgCha−1) to the second-rotation stands (8.4±5.0MgCha−1). Soil pH (r >0.6) and exchangeable acidity (r =−0.5) patterns were dependent upon the concentration of exchangeable Ca2+. Soil Mg2+ and K+ concentrations were correlated with soil C concentration in the surface layer (r =0.5). In coarse-textured soils, a decadal time scale was insufficient to measure significant changes in the mineral soil C pool. Carbon benefits may be gained, however, in aboveground (tree and forest floor) and belowground (roots) biomass accumulations. SRWC plantations are an effective land-use option to restore degraded lands of arid regions. [Copyright &y& Elsevier]

The extrinsic factors that regulate soil microbial stability (resistance and resilience) are little understood, even though soil microbes are important drivers of ecosystem function and their stability is likely to affect soil carbon storage and plant nutrient availability. Soils were collected across three primary plant chronosequences (two in New Zealand and one in Hawaii) that differed in climate, parent material and time spans to test the following hypotheses: i) there is a tradeoff between the resistance and resilience of key soil microbial response variables, ii) this tradeoff is related to the relationship of soil microbial resistance and resilience to soil resources, iii) resources change predictably during different primary plant chronosequences, and iv) if the first three hypotheses hold and are consistent for all three chronosequences, then soil microbial resistance and resilience should change predictably across different chronosequences. Results showed that although there was a tradeoff between resistance and resilience, the role of resources in determining this was unclear. Within each chronosequence, resources that were positively related to resistance were negatively related to resilience and vice versa, consistent with our second hypothesis. However, the direction and strength of correlations between stability and soil resources depended strongly on which soil microbial response variable was measured, and the chronosequence it was measured in. Total amounts of resources often showed consistent trends with ecosystem development for each chronosequence, but the way that resource quality changed varied between chronosequences. At least partly because of the variable nature of these relationships, the trajectory of resistance and resilience during ecosystem development varied considerably across chronosequences. Thus, although consistent trends were found within each chronosequence, the relationships between the stability of different soil microbial response variables, resources and ecosystem development depended strongly on which chronosequence was considered. [ABSTRACT FROM AUTHOR]

Climate warming is most pronounced at high latitudes, which could result in the intensification of the extensively cultivated areas in the boreal zone and could further enhance rates of forest clearing in the coming decades. Using paired forest-field sampling and a chronosequence approach, we investigated the effect of conversion of boreal forest to agriculture on carbon (C) and nitrogen (N) dynamics in interior Alaska. Chronosequences showed large soil C losses during the first two decades following deforestation, with mean C stocks in agricultural soils being 44% or 8.3 kg m−2 lower than C stocks in original forest soils. This suggests that soil C losses from land-use change in the boreal region may be greater than those in other biomes. Analyses of changes in stable C isotopes and in quality of soil organic matter showed that organic C was lost from soils by combustion of cleared forest material, decomposition of organic matter and possibly erosion. Chronosequences indicated an increase in C storage during later decades after forest clearing, with 60-year-old grassland showing net ecosystem C gain of 2.1 kg m−2 over the original forest. This increase in C stock resulted probably from a combination of large C inputs from belowground biomass and low C losses due to a small original forest soil C stock and low tillage frequency. Reductions in soil N stocks caused by land-use change were smaller than reductions in C stocks (34% or 0.31 kg m−2), resulting in lower C/N ratios in field compared with forest mineral soils, despite the occasional incorporation of high-C forest-floor material into field soils. Carbon mineralization per unit of mineralized N was considerably higher in forests than in fields, which could indicate that decomposition rates are more sensitive in forest soils than in field soils to inorganic N addition (e.g. by increased N deposition from the atmosphere). If forest conversion to agriculture becomes more widespread in the boreal region, the resulting C losses (51% or 11.2 kg m−2 at the ecosystem level in this study) will induce a positive feedback to climatic warming and additional land-use change. However, by selecting relatively C-poor soils and by implementing management practices that preserve C, losses of C from soils can be reduced. [ABSTRACT FROM AUTHOR]

We measured net atmospheric exchanges of energy and water vapor using eddy covariance along a chronosequence of Pinus elliottii plantations in north Florida: a recent clear-cut, a mid-rotation stand, and a 24-year-old, rotation-aged stand. Reflected energy averaged 0.26 of incoming solar radiation at the clear-cut and 0.18 at the closed-canopy stands. The sum of sensible (S), latent (LE) and soil heat fluxes accounted for 89 and 85% of net radiation (Rnet) at the clear-cut and mid-rotation age sites. Both S and LE were linearly related to Rnet at all sites. Seasonal differences occurred in the proportion of Rnet attributable to S and LE. S was a much smaller proportion of Rnet when the clear-cut and the mid-rotation age stands were flooded in the summer. LE was a greater proportion of Rnet during the summer/fall at all sites when LAI was greatest. Bowen ratios (S/LE) were 0.34, 0.50 and 0.59 in the summer/fall and 0.71, 0.77 and 1.00 in the winter/spring at the clear-cut, mid-rotation and rotation-aged stands, respectively. Maximum rates of evapotranspiration (ET) in the summer were 0.6 mm h−1 at all sites. Mean daily rates averaged 3.3 mm per day in the summer/fall and 2.0 mm per day in the winter/spring. Although, changes in LAI and canopy structure were large, annual ET estimates were similar and averaged 959, 951 and 1110 mm per year along the chronosequence. Results suggest that energy partitioning and annual ET in these pine forests are more sensitive to environmental fluctuations than to management activities. [Copyright &y& Elsevier]

Examines changes in cesium retention and structural charge as affected by pedogenic mineral transformations in an age sequence of Hawaiian soils. Chemical weathering of volcanic debris; Cesium chloride saturated soils and clays; Cesium selectivity on soils; Effects of sample drying.

Details the construction of a soil chronosequence, a description of how the properties of soil change with time, through the use of the thickness of pedogenic carbonate coatings. Importance of chronosequences; Lost River Valley of Idaho site; Character of the study soil; Measurement and reproducibility of coating thickness; Age constraints for chronosequences.