Mediterranean Holm Oak Forest Research Articles

Soil biomass-related enzyme activity indicates minimal functional changes after 16 years of persistent drought treatment in a Mediterranean holm oak forest

Long-term drought impacts soil microbial responses and enzymatic activity, affecting carbon budget and nutrient cycling in terrestrial ecosystems. We examined a Mediterranean holm oak forest subjected to 16 years of drought treatment to understand the effects on soil organic matter decomposition, nutrient cycling, and enzymatic activity. We compared potential and biomass-related (normalized to microbial biomass) soil enzyme activity with measurements taken 10 years earlier. Relationships between potential enzyme activity, soil moisture, temperature, nutrient availability, and plant/microbial activity were explored. The prolonged drought led to decreased potential activities of all enzymes, especially acid phosphatase, protease, and urease. However, biomass-related activities of protease, urease, and phosphatase were unaffected. Interestingly, biomass-related beta-glucosidase activity increased during dry seasons, indicating a functional adaptation for carbon acquisition during extreme dry conditions. The negative impact of drought on potential enzyme activity intensified over time, particularly during summer when drought intensity increased. Soil water availability, microbial biomass, and nutrient availability strongly influenced potential enzyme activity. Long-term drought and summer aridity led to increased substrate accumulation in the soil. However, no significant changes were observed in biomass-related activities of nitrogen and phosphorus-acquiring enzymes. This lack of change is likely attributed to a decrease in the absolute potential enzyme activity capacity, caused by a reduction in microbial biomass in drought-affected plots, thereby favoring substrate accumulation. Specific functional adaptations were observed, including increased carbon acquisition by soil microbes during extreme summer drought. Long-term water scarcity in water-limited ecosystems diminishes the system's capacity to acquire resources through enzyme production, impacting mineralization and nutrient dynamics. Future climate scenarios may entail reduced ecosystem-level mineralization, carbon and nitrogen shifts from plants to soil, compromising plant control over nutrients, and increasing the risk of resource loss through leaching and erosion.

Chronic drought alters extractable concentrations of mineral elements in Mediterranean forest soils

Soil mineral elements play a crucial role in ecosystem productivity and pollution dynamics. Climate models project an increase in drought severity in the Mediterranean Basin in the coming decades, which could lead to changes in the composition and concentrations of mineral elements in soils. These changes can have significant impacts on the fundamental processes of plant-soil cycles. While previous studies have predominantly focused on carbon, nitrogen, and phosphorus, there is a notable lack of research on the biogeochemical responses of other mineral elements to increasing drought. In this study, we investigated the effects of chronic drought (15 years of experimental rainfall exclusion) and seasonal drought (summer period) on the extractable soil concentrations of 17 mineral elements (arsenic (As), calcium (Ca), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), mercury (Hg), potassium (K), magnesium (Mg), manganese (Mn), molybdenum (Mo), nickel (Ni), lead (Pb), sulphur (S), strontium (Sr), vanadium (V) and zinc (Zn)) in a Mediterranean holm oak forest. We also explored the potential biotic and abiotic mechanisms underlying the changes in extractable elemental concentrations under chronic drought conditions. Our findings reveal that soil elemental concentrations varied significantly due to seasonal changes and chronic drought, with soil microclimate, biological activity, and organic matter being the main drivers of this variability. Levels of soil water content primarily explained the observed variations in soil elemental concentrations. Most of the mineral elements (13 out of 17) exhibited higher concentrations during winter-spring (wet seasons) compared to summer-autumn (dry seasons). The chronic drought treatment resulted in K limitation, increasing vegetation vulnerability to drought stress. Conversely, the accumulation of S in soils due to drought may intensify the risk of S losses from the plant-soil system. Under drought conditions, certain trace elements (particularly Mn, V, and Cd) exhibited increased extractability, posing potential risks to plant health and the exportation of these elements into continental waters. Overall, our results suggest that alterations in mineral element concentrations under future drier conditions could promote ecosystem degradation and pollution dispersion in the Mediterranean Basin. Understanding and predicting these changes are essential for effective ecosystem management and mitigating the potential negative impacts on plant health and water quality.

Windstorm disturbance sets off plant species invasion, microbiota shift, and soilborne pathogens spread in an urban Mediterranean forest

We investigated the effects of a severe windstorm on vegetation, soil chemistry, understory microclimate, and soil microbiota in a Mediterranean holm oak forest. Plant species composition remained almost unchanged in the undisturbed area, whereas highly diverse plant communities were found in the disturbed area (e.g. gap area). Specifically, 11 invasive plant species were detected in 2015, but four years after, five disappeared and another five decreased, with only Ailanthus altissima increasing. Soil in disturbed areas has higher pH, Na, P, K, Ca, Cu, and Mn, but lower total limestone, organic carbon, total nitrogen, Mg, Fe, and standing litter compared to undisturbed areas. Disturbed areas had higher light availability at the ground and large variations in soil and air temperature and air relative humidity compared to undisturbed areas. The storm disturbance increased soil bacterial and fungal species richness and diversity. Moreover, the microbial co-occurrence network in the undisturbed area was more heterogeneous and complex, while modularity and number of positive correlations were higher in the disturbed area, which suggests that the structural composition of microbial communities and their co-occurrence patterns have been altered by windstorm disturbance. In the gaps, soil microbial community composition indicated a shift toward an opportunistic microbiota dominated by fast-growing but less competitive species. In addition, we found a large increase in putative plant pathogens but a decrease in simbiotrophic and ectomycorrhizal fungi in the gaps. The present work demonstrate the multiple effects of storm damage on the above- and belowground structure and diversity of forest ecosystems.

Effects of nitrogen deposition on soil enzymatic activity and soil microbial community in a Mediterranean holm oak forest

Ongoing increases in global levels of nitrogen (N) deposition are predicted to continue, causing important shifts in the structure and function of ecosystems worldwide. Soil microbes and enzymes are key components of biogeochemical cycles and ecosystem functioning, so understanding their response to N deposition is crucial. We studied the effects of N addition on the activities of five extracellular enzymes and microbial biomass and composition in a mesic Mediterranean holm oak forest characterized by moderate soil N- and P-limitation. Addition of N increased photosynthetic potential of higher plants, activities of P- and C-, but not N- related enzymes, and biomass of total microbes, bacteria and fungi, and decreased ratios of fungi:bacteria. Overall, N deposition increased general biological activity of the mesic Mediterranean forest, enhanced ecosystem investment in P mobilization and affected soil microbial community structure.

Forest dieback switches the relationships between microfaunal bacterivore guilds and soil nutrients

The current increase of severe droughts associated with climate change is one of the main causes of the observed dieback in Mediterranean holm-oak (Quercus Ilex subs ballota) forests. Effects of forest dieback in soils are greatly variable and depend on a number of local factors, but generally include increased soil organic C due to increased litter inputs, alterations in soil nutrient contents, changes in the nitrogen cycle, and detrimental effects on soil microbial communities and their functioning. There is little evidence, however, of the effects of forest dieback on soil faunal diversity. In this study, we assessed the effects of holm-oak dieback and induced nutrient shifts on soil microfaunal communities and their relationships with soil properties and functioning. We studied 13 Holm oak forest sites affected by tree dieback in the Iberian Peninsula and assessed the relationship between soil properties, microbial functions, and nematode diversity under healthy, defoliated, and dead trees at each site. We found that nematode abundances were variable and significantly patchy across sites. Bacterivore and herbivore nematodes were the most abundant nematode trophic groups. Nematode abundance increased with increasing levels of soil C only if soil P was available, indicating that nematode abundances might be P-limited in these semi-arid systems. Bacterivore nematodes were especially affected by tree death, since tree dieback switched the relationship between bacterivore abundance and soil nutrient contents. Opportunistic bacterivores, able to exploit ephemeral bacterial resources blooming after soil organic enrichment, seemed more resilient to tree death than generalist ones, while fungivores did not clearly respond to forest dieback. We found complex and unexpected effects of tree dieback on soil microfaunal communities, which should receive further attention.

Considerations on Field Methodology for Macrofungi Studies in Fragmented Forests of Mediterranean Agricultural Landscapes

The methodology used for the determination of macrofungal diversity in Mediterranean areas differs in the time of sampling and the number of years displayed, making it difficult to compare results. Furthermore, the results could be refuted because the studies are being conducted over an insufficient number of years or without considering the variation of the meteorological conditions from one year to the next and its effects on fruiting time, which might not fit the sampling. In order to optimize field work on fungal fruiting in Mediterranean environments dominated by holm oak (Quercus ilex L.), a weekly field analysis of macrofungal diversity from February 2009 to June 2013 was carried out in a Mediterranean holm oak forest in the middle-west of the Iberian Peninsula. The results revealed that fruiting bodies appeared throughout the year and that there was a delay in autumn fruiting, overlapping with spring. All this seems to indicate that weekly collection throughout the year and for a period of two years could be sufficient to estimate the macrofungal biodiversity of this ecosystem.

Effects of Nitrogen Deposition on Soil Enzymatic Activity and Soil Microbial Community in a Mediterranean Holm Oak Forest

Effects of Nitrogen Deposition on Soil Enzymatic Activity and Soil Microbial Community in a Mediterranean Holm Oak Forest

Evolution of Human Salivary Stress Markers during an Eight-Hour Exposure to a Mediterranean Holm Oak Forest. A Pilot Study

The current study analyses the evolution of different human stress markers during an 8 h exposure to a Mediterranean Holm oak forest. We conducted a pre-post study with thirty-one subjects in which saliva samples were collected before the exposure (baseline) and after 1, 2, 4 and 8 h. Our results show: (A) a significant decrease in cortisol saliva concentrations from the second hour until the end compared to basal time; (B) a significant increase in alpha amylase activity after the first hour of exposure compared to basal time that remained elevated during the rest of the study; (C) a significant decrease in IgA from the fourth hour of exposure compared to the basal time. These findings indicate an effect of forest exposure in salivary biomarkers of stress and provide relevant data for the scientific and healthcare community encouraging further research in the field.

Simulated climate change and seasonal drought increase carbon and phosphorus demand in Mediterranean forest soils

A better understanding of soil biogeochemical responses to the increasing drought predicted in many regions for the next decades by climate models is needed. Extracellular enzyme (EE) stoichiometry provides integrative information about the soil community metabolism and resource availability that is crucial to understand soil microbial and plant strategies in response to those projected changes in soil moisture and resource availability. The aim of this study was to investigate the responses of enzyme allocation to seasonal and experimental drought conditions. We measured soil extractable organic carbon (EOC), extractable total nitrogen (ETN), extractable total phosphorus (ETP) and its organic and inorganic fractions (Po and Pi), together with soil extracellular enzyme activity (EEA) across four seasons, and tested for association between variables using pairwise resource and enzyme ratios, and vector length and angle enzyme integrated indexes in a Mediterranean holm oak forest subjected to the drought projected for coming decades (15% less soil water availability). Seasonal and experimental drought consistently increased levels of EOC and ETN, while decreases in ETP and Pi in autumn amplified the imbalance between soil extractable P with C and N, increasing the probability of P limitation throughout the year. Overall EE stoichiometry and vector angle indicated a higher relative demand for P than C and N. EE stoichiometry and vector length showed that both seasonal and experimental drought increased the relative demand for C than N or P by soil microbial communities, as supported by the observed rise in EOC and ETN. Vector angle showed that the transient seasonal drought increased the relative demand for P over N by soil microorganisms, especially in control plots, possibly due to the lower mobility of P in soil than N. The results show the important role of phosphatases in the recycling of organic P in this ecosystem. Our results indicated that prolonged drought decreased average decomposition of soil organic matter (SOM), due to the negative effect on individual enzyme activities, but accelerated SOM decomposition response to rewetting due to the accumulation of C and N in soil and the relatively higher presence of C-enzymes than those of other EE. Lower levels of P and N enzymatic activities than those of C under drought infer a reduction in nutrient release that may then negatively affect plant and microbial nutrition.

Short-Term N-Fertilization Differently Affects the Leaf and Leaf Litter Chemistry of the Dominant Species in a Mediterranean Forest under Drought Conditions

Nitrogen (N) deposition is a key driver of global change with significant effects on carbon (C) cycling, species fitness, and diversity; however, its effects on Mediterranean ecosystems are unclear. Here, we simulated N deposition in an N-fertilization experiment with 15N-labeled fertilizer in a montane evergreen Mediterranean holm oak forest, in central Catalonia, to quantify short-term impacts on leaf, leaf litter elemental composition, and resorption efficiency in three dominant species (Quercus ilex, Phillyrea latifolia, and Arbutus unedo). We found that even under drought conditions, 15N isotope analysis of leaf and leaf litter showed a rapid uptake of the added N, suggesting an N deficient ecosystem. Species responses to N fertilization varied, where A. unedo was unaffected and the responses in P. latifolia and Q. ilex were similar, albeit with contrasting magnitude. P. latifolia benefited the most from N fertilization under drought conditions of the experimental year. These differences in species response could indicate impacts on species fitness, competition, and abundance under increased N loads in Mediterranean forest ecosystems. Further research is needed to disentangle interactions between long-term N deposition and the drought predicted under future climate scenarios in Mediterranean ecosystems.

Comparing i-Tree Eco Estimates of Particulate Matter Deposition with Leaf and Canopy Measurements in an Urban Mediterranean Holm Oak Forest.

Trees and urban forests remove particulate matter (PM) from the air through the deposition of particles on the leaf surface, thus helping to improve air quality and reduce respiratory problems in urban areas. Leaf deposited PM, in turn, is either resuspended back into the atmosphere, washed off during rain events or transported to the ground with litterfall. The net amount of PM removed depends on crown and leaf characteristics, air pollution concentration, and weather conditions, such as wind speed and precipitation. Many existing deposition models, such as i-Tree Eco, calculate PM2.5 removal using a uniform deposition velocity function and resuspension rate for all tree species, which vary based on leaf area and wind speed. However, model results are seldom validated with experimental data. In this study, we compared i-Tree Eco calculations of PM2.5 deposition with fluxes determined by eddy covariance assessments (canopy scale) and particulate matter accumulated on leaves derived from measurements of vacuum/filtration technique as well as scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (leaf scale). These investigations were carried out at the Capodimonte Royal Forest in Naples. Modeled and measured fluxes showed good overall agreement, demonstrating that net deposition mostly happened in the first part of the day when atmospheric PM concentration is higher, followed by high resuspension rates in the second part of the day, corresponding with increased wind speeds. The sensitivity analysis of the model parameters showed that a better representation of PM deposition fluxes could be achieved with adjusted deposition velocities. It is also likely that the standard assumption of a complete removal of particulate matter, after precipitation events that exceed the water storage capacity of the canopy (Ps), should be reconsidered to better account for specific leaf traits. These results represent the first validation of i-Tree Eco PM removal with experimental data and are a starting point for improving the model parametrization and the estimate of particulate matter removed by urban trees.

Human absorption of monoterpenes after a 2-h forest exposure: A field experiment in a Mediterranean holm oak forest

The current body of literature points monoterpenes as one of the determinant factors of the interaction between forests and human health. The present study aims at analyzing the monoterpene absorption by humans during a 2 -hs forest exposure in a Mediterranean holm oak forest focusing on the four most abundant monoterpene compounds: alpha-pinene, beta-pinene, alpha-phellandrene and limonene. Participants’ blood samples were collected before and after exposure to forest or urban environment (control). We conducted air and blood sampling using cartridges and head space method and determined the monoterpene compounds through CGMS. We identified the four compounds in forest air during the experimental study being alpha-pinene the monoterpene with the greatest concentration. Results show no significant changes in monoterpene blood concentrations for the forest and control group. However, a negative significant relationship between absorption and baseline blood concentration of the most abundant forest air monoterpenes, alpha-pinene and beta-pinene, was found in individuals visiting the forest, i.e. higher absorption was found the lower the baseline blood concentration was. Although no significant lineal correlation could be spotted between the vital variables and the monoterpene absorption, we found significant correlations between the absorption of the monoterpene compounds. This attempt, first in a Mediterranean holm oak forest, can serve as a starting point and constitute a valuable contribution for further research in regard to experimental design and laboratory analysis.

Climate Change Effects in a Mediterranean Forest Following 21 Consecutive Years of Experimental Drought

Research Highlights: A small, long-term decrease in the water availability in a Mediterranean holm oak forest elicited strong effects on tree stem growth, mortality, and species composition, which led to changes in the ecosystem function and service provision. Background and Objectives: Many forest ecosystems are increasingly challenged by stress conditions under climate change. These new environmental constraints may drive changes in species distribution and ecosystem function. Materials and Methods: An evergreen Mediterranean holm oak (Quercus ilex L.) forest was subjected to 21 consecutive years of experimental drought (performing 30% of rainfall exclusion resulted in a 15% decrease in soil moisture). The effects of the annual climatic conditions and the experimental drought on a tree and shrub basal area increment were studied, with a focus on the two most dominant species (Q. ilex and the tall shrub Phillyrea latifolia L.). Results: Stem growth decreased and tree mortality increased under the experimental drought conditions and in hot and dry years. These effects differed between the two dominant species: the basal area of Q. ilex (the current, supradominant species) was dependent on water availability and climatic conditions, whereas P. latifolia was more tolerant to drought and experienced increased growth rates in plots where Q. ilex decay rates were high. Conclusions: Our findings reveal that small changes in water availability drive changes in species growth, composition, and distribution, as demonstrated by the continuous and ongoing replacement of the current supradominant Q. ilex by the subdominant P. latifolia, which is better adapted to tolerate hot and dry environments. The consequences of these ecological transformations for ecosystem function and service provision to human society are discussed.

Positive interactions between great longhorn beetles and forest structure

Great longhorn beetles (GLBs) may affect forest structure, because their larvae colonize trees and create networks of cavities further exploited by other species, resulting in dead or broken branches and tree mortality. At the same time, tree size, condition and location are known to affect the likelihood of tree colonization by GLBs. Here, we study the relationship between GLBs and the structure of old-growth holm oak Mediterranean forests in Sardinia, Italy. Generalized linear models were used to relate presence of GLBs with structural parameters that can be affected by or can affect these ecosystem engineers. We found a strong positive relationship between GLBs and the number of trees with cavities, while the relationships between GLBs and the number of dead wood decaying classes, amount of coarse woody debris, stand basal area, forest canopy layer complexity were positive but weak. Overall, our results suggest that larval activity of GLBs could be responsible for increased tree cavity and dead wood formation, enhancing forest structure. On the other hand, forests with larger and older trees could be more likely to be colonized by GLBs. While it is not possible with observational studies to disentangle to what extent GLBs affect forest structure or vice versa, it seems likely that reciprocal interactions may enhance the structure of holm oak forests. Therefore, parasitism from native GLBs should be seen and understood more as a key ecological process that enhances the structure of Mediterranean holm oak forest habitats.

Wood vs. Canopy Allocation of Aboveground Net Primary Productivity in a Mediterranean Forest during 21 Years of Experimental Rainfall Exclusion

A Mediterranean holm oak forest was subjected to experimental partial rainfall exclusion during 21 consecutive years to study the effects of the expected decrease in water availability for Mediterranean vegetation in the coming decades. Allocation in woody structures and total aboveground allocation were correlated with annual rainfall, whereas canopy allocation and the ratio of wood/canopy allocation were not dependent on rainfall. Fruit productivity was also correlated with annual rainfall, but only in Quercus ilex. In the studied site, there were two types of forest structure: high canopy stand clearly dominated by Quercus ilex, and low canopy stand with more abundance of a tall shrub species, Phillyrea latifolia. In the tall canopy stand, the allocation to woody structures decreased in the experimental rainfall exclusion, but not the allocation to canopy. In the low canopy stand, wood allocation in Quercus ilex was very small in both control and plots with rainfall exclusion, but wood allocation in Phillyrea latifolia was even higher than that obtained in tall canopy plots, especially in the plots receiving the experimental rainfall exclusion. These results highlight likely future changes in the structure and functioning of this ecosystem induced by the decrease in water availability. A serious drop in the capacity to mitigate climate change for this Mediterranean forest can be expected, and the ability of Phillyrea latifolia to take advantage of the limited capacity to cope with drought conditions detected in Quercus ilex makes likely a forthcoming change in species dominance, especially in the low canopy stands.

Microhabitat and ectomycorrhizal effects on the establishment, growth and survival of Quercus ilex L. seedlings under drought.

The success of tree recruitment in Mediterranean holm oak (Quercus ilex) forests is threatened by the increasing intensity, duration and frequency of drought periods. Seedling germination and growth are modulated by complex interactions between abiotic (microhabitat conditions) and biotic factors (mycorrhiza association) that may mitigate the impacts of climate change on tree recruitment. To better understand and anticipate these effects, we conducted a germination experiment in a long-term precipitation reduction (PR) field experiment where we monitored seedling establishment and survival, micro-habitat conditions and ectomycorrhizal (ECM) colonization by different mycelia exploration types during the first year of seedling growth. We hypothesized that (i) the PR treatment decreases seedling survival relative to the control with ambient conditions, (ii) microhabitat conditions of water and light availability are better predictors of seedling survival than the PR treatment, (iii) the PR treatment will favour the development of ECM exploration types with drought-resistance traits such as differentiated rhizomorphs. Contrary to our first hypothesis, seedling survival was lower in control plots with overall higher soil moisture. Micro-habitat light and soil moisture conditions were better predictors of seedling survival and growth than the plot-level PR treatment, confirming our second hypothesis. Furthermore, in line with our third hypothesis, we found that ECM with longer extramatrical mycelia were more abundant in the PR treatment plots and were positively correlated to survival, which suggests a potential role of this ECM exploration type in seedling survival and recruitment. Although summer drought was the main cause of seedling mortality, our study indicates that drier conditions in spring can increase seedling survival, presumably through a synergistic effect of drought adapted ECM species and less favourable conditions for root pathogens.

Long-term drought decreases ecosystem C and nutrient storage in a Mediterranean holm oak forest

Aridity has increased in recent decades in the Mediterranean Basin and is projected to continue to increase in the coming decades. We studied the consequences of drought on the concentrations, stoichiometries and stocks of carbon (C), nitrogen (N), phosphorus (P) and potassium (K) in leaves, foliar litter of a three dominant woody species and soil of a Mediterranean montane holm oak forest where soil-water content was experimentally reduced (15 % lower than the control plots) for 15 years. Nitrogen stocks were lower in the drought plots than in the control plots (8.81 ± 1.01 kg ha−1 in the forest canopy and 856 ± 120 kg ha−1 in the 0−15 cm soil layer), thus representing 7 and 18 % lower N stocks in the canopy and soil respectively. δ15N was consistently higher under drought conditions in all samples, indicating a general loss of N. Foliar C and K stocks were also lower but to a lesser extent than N. Decreases in biomass and C and N stocks due to drought were smallest for the most dominant tall shrub, Phillyrea latifolia, so our results suggest a lower capacity of this forest to store C and nutrients but also substantial resulting changes in forest structure with increasing drought.

Human Breathable Air in a Mediterranean Forest: Characterization of Monoterpene Concentrations under the Canopy.

Monoterpenes have been identified as potential determinants of the human health effects induced by forest exposure. The present study characterizes the total monoterpene concentrations at nose height in a Mediterranean Holm oak forest located in North-East Iberian Peninsula during the annual emission peak (summer and autumn: June to November) using a Proton Transfer Reaction–Mass Spectrometry (PTR-MS). Results show a strong variability of the total monoterpene concentrations in season and daytime. The concentration peak appears during July and August. These two months displayed two average maxima in their diel cycles: One during early morning (from 6:00 to 8:00, 0.30 ppbv for July and 0.41 ppbv for August) and another one at early afternoon (from 13:00 to 15:00, 0.27 ppbv during July and 0.32 ppbv during August). Monoterpene concentrations were strongly related with the temperature (exponentially) and solar radiation (rectangular hyperbolic relationship). The concentrations registered here are similar or higher than in previous ex situ studies showcasing the effects of forests on human health. These findings provide relevant data for the scientific and healthcare community by improving the understanding of monoterpene dynamics at nose height and suggesting further research on the effects of forests on human health, particularly in the Mediterranean region.

Temporal effects of thinning on soil organic carbon pools, basal respiration and enzyme activities in a Mediterranean Holm oak forest

Soil organic carbon pools have an important role in the maintenance of ecosystems as a source of energy for soil microorganisms. Soil biological and biochemical properties are essential for the decomposition of organic matter. These soil properties can be affected by thinning, which is considered sustainable when the soil properties are maintained or improved. We studied the effects of selective thinning and shrub clearing, performed with an ecohydrological approach, in a marginal Holm oak forest in a semiarid area on soil properties. The effects of thinning (T) were compared with an untreated area (control, C). Fine woody debris was ground into mulch onto the thinned area. Forest floor and mineral soil properties were analyzed between five months and seven years after the thinning. In the forest floor, gravimetric water content (GWCff) and water soluble organic carbon (WSOCff) were analyzed and compared between T and C. In mineral soil, GWCms, soil organic carbon (SOC), WSOCms, soil basal respiration (BR), soil microbial biomass carbon (MBC) and soil enzymes (acid phosphatase (Acid PA) and urease (URE)) were analyzed. In the early stage, the results showed slightly higher SOC and WSOCms in T likely due to fine woody debris left on the forest floor. However, seven years after the thinning the effects of the thinning on all the studied variables were negligible. All variables showed high spatial-temporal variability. Our results suggest that selective thinning and shrub clearing in the studied site do not affect negatively soil properties when woody debris is left on the forest floor.

Short term effects of Bacillus thuringiensis and diflubenzuron aerial applications on non-target arthropods in a Mediterranean Forest

Several products are widely used to control gypsy moth (Lymantria dispar) populations. The main purpose of the present study is to evaluate the aerial application effects of B. thuringiensis and diflubenzuron on non-target arthropods in a Mediterranean holm-oak forest. The density of gypsy moth population at the time of application of treatments was the same in the three forests and the defoliation levels in the three holm-oak forests were between level 0 (no apparent defoliation) and level 1 (small defoliations of new leaf). Sampling litter, soil, ground-dwelling, and epiphytic arthropods showed that the holm-oak forests treated with diflubenzuron had a better quantitative faunal outcome than the Control, whereas the highest taxonomic diversity was found in the site treated with B. thuringiensis. These results could probably be explained by a temporary competitive decrease due to the huge number of gypsy moth caterpillars on plants, as well as the enormous accumulation of their excrements in the soil during a prolonged period of time.