C. Guerrero

Soil organic matter and aggregates affected by wildfire in a Pinus halepensis forest in a Mediterranean environment

et Abstract. Three Mediterranean soils located in the north of the Province of Alicante (Spain) were studied for a year after a forest fire. The percentage of water-stable aggregates (between 0.2 and 4 mm) and organic matter content were measured. Microaggregates (< 0.2 mm) were observed using electron microscopy. The results showed the importance of type of forest fire on soil organic matter and aggregates. Soil structure was more affected by surface fire (which affects mainly brushwood and soil surface) than crown fire (which burns the tops of trees and some brushwood). Accumulation of organic matter from burnt trees and brushwood in areas affected by crown fire and alterations in organic matter content through the soil profile were observed. Surface forest fire affected soil structure more negatively than crown fire as observed using electron microscopy. Soils affected by surface fire may be more easily eroded and recovery of vegetation may be delayed because of effects on soil structure. Organic matter content through the soil profile comparing burnt and adjacent unburnt soil could be used to determine the type of fire. Additional keywords: Forest fire; calcareous soil; Spain; Mediterranean type-areas.

Reclamation of a burned forest soil with municipal waste compost : macronutrient dynamic and improved vegetation cover recovery

The reclamation of burned soils in Mediterranean environments is of paramount importance in order to increase the levels of soil protection and minimise erosion and soil loss. The changes produced in the content of total organic carbon (TOC), N (Kjeldahl) and available P, K, Ca and Mg by the addition of different doses of a municipal solid waste compost to a burned soil were evaluated during one year. The effect of organic amendment on the improvement in the vegetation cover after one year was also evaluated. The organic amendment, particularly at a high dose, increased the TOC and N-Kjeldahl content of the soil in a closely related way. The levels of available K in soil were also enhanced by the organic amendment. Although the effects on all three parameters tended to decrease with time, their values in the amended soils were higher than in the control soil, which clearly indicates the improvement in the chemical quality of the soil brought about by the organic amendment. The available P content did not seem to be influenced by organic treatment, while available Mg levels were higher than in the control during the first 4 months following organic amendment. The application of compost to the burned soil improved its fertility and favoured rapid vegetal recovery, thus minimising the risk of soil erosion.

Small-scale patterns of abundance of mosses and lichens forming biological soil crusts in two semi-arid gypsum environments

Despite important advances in the understanding of biological soil crusts and their key role in ecosystem processes in arid and semi-arid environments, little is known about those factors driving the small-scale patterns of abundance and distribution of crust-forming lichens and mosses. We used constrained ordination techniques (RDAs) to test the hypothesis that the spatial patterning of lichens and mosses is related to surface and subsurface soil variables in two semi-arid gypsum environments of Spain. Our results show that the abundance of mosses and lichens forming biological soil crusts was related to a limited set of variables (cover of bare soil and litter, soil respiration, potassium content and aggregate stability). Moreover, they provide some insights into the importance of these variables as drivers of biological soil-crust composition and abundance in semi-arid gypsum environments.

Microbial recolonization and chemical changes in a soil heated at different temperatures

Samples of a Mediterranean forest soil were exposed in a muffle furnace to seven temperatures (100–700°C) for 15 min to simulate different fire intensities. Heated soils were incubated for 100 days after re-inoculation with fresh unheated soil. Immediately after heating, the extractable organic C increased with the heating temperature, reaching a maximum at 400°C. This increase in extractable organic C and nutrients in soils heated below 400°C allowed a rapid recolonization of bacteria, increasing the basal respiration. During the 100-day incubation, the cumulative values of basal respiration and carbon mineralization rates generally followed a double exponential equation in unheated and heated samples. Heating at 200°C caused a reduction of 99.6% for fungi (measured as culturable fungal propagules), which showed lower recolonization capacity than that of bacteria. Heating also caused a decrease in the organic C content of the soils, especially for the highest temperatures. As a consequence, the microbial biomass carbon recovery was short lived in heated soils. The varied effects of heating and incubation on the inorganic and organic nitrogen changes, available nutrients and metabolic quotients are also discussed. This study demonstrates that changes in soils exposed to comparatively high temperatures (>500°C) have a particularly strong impact on microbial population.

Effects of a low severity prescribed fire on water-soluble elements in ash from a cork oak (Quercus suber) forest located in the northeast of the Iberian Peninsula

Wildfire is the major disturbance in Mediterranean forests. Prescribed fire can be an alternative to reduce the amount of fuel and hence decrease the wildfire risk. However the effects of prescribed fire must be studied, especially on ash properties, because ash is an important nutrient source for ecosystem recovery. The aim of this study is to determine the effects of a low severity prescribed fire on water-soluble elements in ash including pH, electrical conductivity (EC), calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), aluminum (Al), manganese (Mn), iron (Fe), zinc (Zn), silica (SiO(2)) and total sulphur (TS). A prescribed fire was conducted in a cork oak (Quercus suber) (Q.S) forest located in the northeast part of the Iberian Peninsula. Samples were collected from a flat plot of 40×70m mainly composed of Q.S and Quercus robur (Q.R) trees. In order to understand the effects of the prescribed fire on the soluble elements in ash, we conducted our data analysis on three data groups: all samples, only Q.S samples and only Q.R samples. All three sample groups exhibited a significant increase in pH, EC (p<0.001), water-soluble Ca, Mg, Na, SiO(2) and TS and a decrease in water-soluble Mn, Fe and Zn. Differences were identified between oak species for water-soluble K, Al and Fe. In Q.S samples we registered a significant increase in the first two elements p<0.001 and p<0.01, respectively, and a non-significant impact in the third, at p<0.05. In Q.R data we identified a non-significant impact on water-soluble K and Al and a significant decrease in water-soluble Fe (p<0.05). These differences are probably due to vegetation characteristics and burn severity. The fire induced a higher variability in the ash soluble elements, especially in Q.S samples, that at some points burned with higher severity. The increase of pH, EC, Ca, Mg, Na and K will improve soil fertility, mainly in the study area where soils are acidic. The application of this low severity prescribed fire will improve soil nutrient status without causing soil degradation and thus is considered to be a good management strategy.

Different Patterns of Aggregate Stability in Burned and Restored Soils

The merits of soil aggregate stability determination by rainfall simulator method were studied. This method is based on the supposition that in standard conditions aggregate breakdown is proportional to the kinetic energy of the rainfall applied. We compared three experiments using four different soils. Two of the experiments were in controlled conditions and the other at field conditions. In one of the laboratory experiments we applied sewage sludge to a degraded soil from a semiarid climate. In the other laboratory experiment a forest soil was heated to 200°C, 400°C and 600°C, and we studied the effect of heat and loss of organic matter in soil aggregation. In the third experiment, carried out in the field, we studied the response of two soils affected by forest fire in different intensities. Aggregate stability percentage and organic matter content of soils were determined to establish trends between these parameters. Aggregate stability in soils subjected to rainfall simulation was used as an indicator for potential degradation or restoration processes of the soils. In some burned soils positive and negative relationships were obtained between aggregate stability percentage and organic matter soil contents due to heat-aggregation processes. It showed that the aggregate stability percentage method based on disruptive energy of a rainfall simulator could not always be used as an index of degradation or restoration of soils or both.

Storage Effects on Biochemical Properties of Air-Dried Soil Samples from Southeastern Spain

Soil biochemical properties are susceptible to change under sample storage, and as a consequence, these properties have usually been determined in fresh samples, kept cold or frozen for brief periods of time. However, air-dried soil would facilitate routine soil testing procedures in soils from semi-arid Mediterranean areas, which have soil water deficit most of the year. This research aims at assessing the effects of medium-term soil storage (6–9 months) at room temperature on air-dried soil samples from two Mediterranean forest locations for the measurement of various microbiological and biochemical properties (microbial biomass carbon, basal respiration, metabolic quotient, acid phosphatase activity, urease activiy, β-glucosidase activity, and soluble carbon). Storage of air-dried soil samples for 6 months had no significant effects on the studied properties in any location. With regard to samples stored for 9 months, we only found differences at the location with higher mean rainfall in the values of basal respiration, the metabolic quotient and β-glucosidase, and urease activities. Our results show that biochemical properties from Mediterranean semi-arid soils, are medium-term stable in stored air-dried soil samples. Thus, these findings would encourage the selection of biochemical properties on a practical basis, as there is no strict requirement to determine these properties immediately after sampling, as they remain valid for several months.

Effect of solid waste compost on microbiological and physical properties of a burnt forest soil in field experiments

Abstract The restoration of soil microbial activities is a basic step in the reclamation of burnt soils. For this reason, the ability of municipal solid waste compost to accelerate the re-establishment of bacterial and fungal populations, as well as to re-establish physical properties in a burnt soil, was evaluated in a field experiment. Four treatments were performed by adding different doses of compost (0, 0.5, 1 and 2 kg compost m–2 soil) to a burnt Calcic Rodoxeralf soil, and the changes in microbial populations, salt content, aggregate stability and bulk density were evaluated for 1 year. Initially, the addition of compost had a negative effect on soil microbial populations, but 3 months after compost addition, the number of viable fungal propagules increased in all the amended soils. This positive effect lasted until the end of the experiment. From 30 days onwards, all the amended soils showed a greater total number of bacterial cell forming units than the unamended burnt soil. Organic amendment increased the percentage of 2- to 4-mm aggregates, although the effect on the stability of the 0.2- to 2-mm aggregates and on bulk density was less noticeable.

Influence of plant species on physical, chemical and biological soil properties in a Mediterranean forest soil

In semiarid ecosystems plant cover plays an important role in the improvement of physical, chemical and biochemical soil properties. With the aim of studying the influence of different plant species on soil properties, and establishing the relationships between them, 160 soil samples from under four different plant species (Pinus halepensis, Quercus coccifera, Juniperus oxycedrus and Rosmarinus officinalis) were taken in a forest area of the province of Alicante (SE Spain). The following soil properties were analyzed in all soil samples: organic carbon content, microbial biomass, soluble organic carbon, aggregate stability, basal respiration, and some eco-physiological ratios. In addition, the near infrared spectra (NIR) of all soil samples were obtained to verify the similarities or differences between soil samples under the four species. Some differences in parameters such as organic carbon content or basal respiration were found mainly between the group of P. halepensis and Q. coccifera with respect to J. oxycedrus and R. officinalis. Despite this, the high organic carbon content found under the four plant species showed an influence on the rest of soil properties. Moreover, using a discriminant analysis with factorial scores from NIR absorbance data did not result in a good classification of samples in terms of the species, reflecting some similarities between them. Our results show that the high contents observed in some parameters under the four species, and the lack of significant differences in most of them, prove the important role of shrubland in semiarid conditions, it being capable of promoting good soil conditions.

Comparison of Soil Physical, Chemical, and Biochemical Properties Among Native Forest, Maintained and Abandoned Almond Orchards in Mountainous Areas of Eastern Spain

In the mountainous areas of Eastern Spain, soils have been cultivated in terraced orchards for centuries, although in the last decades, almond orchards are being abandoned. For this study, we selected four locations in SE Spain, with a similar vegetation mosaic, constituting forest, almond tree orchards, and orchards abandoned between 10 to 15 years previous to sampling. The main objective was to investigate the effects of changes in land use from forest to agricultural and posterior land abandonment on various physical, chemical, and biochemical properties. In all locations, all properties showed the highest values in forest soils, excepting pH and some eco-physiological ratios which were lowest under this land use. Abandoned agricultural soils showed a slight recovery in some properties compared to agricultural soils, the biochemical properties being the most sensitive indicators in reflecting these changes. All these results indicate that after land abandonment, soil microorganisms are more active as a consequence of the increment in the vegetation cover, with higher inputs as litter and root exudates. Moreover, the stopping of tillage may also have favored the increments in microbial biomass and activity. Nonetheless, these values are still low compared to forest soils, reflecting that 10–15 years of abandonment is not long enough to achieve a significant recovery in soil properties under semi-arid Mediterranean conditions. The metabolic quotient (qCO2) showed no general pattern in all locations in terms of land use, suggesting that this ratio is not specific enough to be used as an indicator in ecosystem succession.