<Emphasis Type="Italic">Quercus suber</Emphasis> forest and <Emphasis Type="Italic">Pinus</Emphasis> plantations show different post-fire resilience in Mediterranean north-western Africa

Key message

In the African rim of the Western Mediterranean Basin, cork oak forests and pine plantations coexist. Under similar fire regimes, cork oak forest is more resilient in terms of habitat structure (canopy, understory, and complexity of vegetation strata) than pine plantation. By contrast, both woodland types show similar resilience in plant species composition. Resilience in habitat structure varies between the two woodland types because of the resprouting and seeding strategies of cork oak and pine species, respectively. These differences can be relevant for the conservation of biodiversity of forested ecosystems in a future scenario of increased fire frequency and scale in the Mediterranean basin.

Context

Wildfires have major impacts on ecosystems globally. In fire-prone regions, plant species have developed adaptive traits (resprouting and seeding) to survive and persist due to long evolutionary coexistence with fire. In the African rim of the Western Mediterranean Basin, cork oak forest and pine plantation are the most frequently burnt woodlands. Both species have different strategies to respond fire: cork oak is a resprouter while pines are mostly seeders.

Aims

We have examined the hypothesis that pine plantations are less resilient in habitat structure (canopy, understory, diversity of vegetation strata) and plant composition than cork oak woodlands.

Methods

The habitat structure and plant species composition were measured in 30 burnt and 30 unburnt 700-m transects at 12 burnt sites from north-western Africa, where the two forest types can coexist. Habitat structure and plant species composition were compared between burnt and unburnt transects from cork oak and pine plantation woodlands with generalized linear mixed models and general linear models.

Results

The results showed significant interaction effect of fire and forest type, since cork oak forest was more resilient to fire than was pine plantation in habitat structure. By contrast, both forest types were resilient to fire in the composition of the plant communities, i.e., plant composition prior to fire did not change afterwards.

Conclusion

The higher structural resilience of cork oak forest compared to pine plantation is related to the resprouting and seeding strategies, respectively, of the dominant tree species. Differences in the responses to fire need to be considered in conservation planning for the maintenance of the Mediterranean biodiversity in a future scenario of changes in fire regime.

     

Effects of crown development on leaf irradiance,leaf morphology and photosynthetic capacity in a peach tree

The three-dimensional (3-D) architecture of a peach tree (Prunus persica L. Batsch) growing in an orchard near Avignon, France, was digitized in April 1999 and again four weeks later in May 1999 to quantify increases in leaf area and crown volume as shoots developed. A 3-D model of radiation transfer was used to determine effects of changes in leaf area density and canopy volume on the spatial distribution of absorbed quantum irradiance (PAR(a)). Effects of changes in PAR(a) on leaf morphological and physiological properties were determined. Leaf mass per unit area (M(a)) and leaf nitrogen concentration per unit leaf area (N(a)) were both nonlinearly related to PAR(a), and there was a weak linear relationship between leaf nitrogen concentration per unit leaf mass (N(m)) and PAR(a). Photosynthetic capacity, defined as maximal rates of ribulose-1,5-bisphosphate carboxylase (Rubisco) carboxylation (V(cmax)) and electron transport (J(max)), was measured on leaf samples representing sunlit and shaded micro-environments at the same time that the tree crown was digitized. Both V(cmax) and J(max) were linearly related to N(a) during May, but not in April when the range of N(a) was low. Photosynthetic capacity per unit N(a) appeared to decline between April and May. Variability in leaf nitrogen partitioning between Rubisco carboxylation and electron transport was small, and the partitioning coefficients were unrelated to N(a). Spatial variability in photosynthetic capacity resulted from acclimation to varying PAR(a) as the crown developed, and acclimation was driven principally by changes in M(a) rather than the amount or partitioning of leaf nitrogen.     

Mesophyll conductance to CO2 and leaf morphological characteristics under drought stress during Quercus ilex L. resprouting

? Quercus ilex L., the dominant species in Mediterranean forests and one with a great capacity for resprouting after disturbances, is threatened by the expected increase in fire frequency and drought associated with climate change.

? The aim of this study was to determine the contribution of photosynthesis limitants, especially mesophyll conductance (g _mes) during this species’ resprouting and under summer drought.

? Resprouts showed 5.3-fold increased g _mes and 3.8-fold increased stomatal conductance (g _s) at mid-day with respect to leaves of undisturbed individuals. With increased drought, structural changes (decreased density and increased thickness) in resprouts contributed to the observed higher photosynthesis and increased g _mes. However, g _mes only partially depended on leaf structure, and was also under physiological control. Resprouts also showed lower non-stomatal limitations (around 50% higher carboxylation velocity (V _c,max) and capacity for ribulose-1,5-bisphosphate regeneration (J _max)). A significant contribution of g _mes to leaf carbon isotope discrimination values was observed.

? g _mes exhibits a dominant role in photosynthesis limitation in Q. ilex and is regulated by factors other than morphology. During resprouting after disturbances, greater capacity to withstand drought, as evidenced by higher g _mes, g _s and lower non-stomatal limitants, enables increased photosynthesis and rapid growth.

     

Identification of new, odor-active thiocarbamates in cress extracts and structure-activity studies on synthesized homologues

New, odorant nitrogen- and sulfur-containing compounds are identified in cress extracts. Cress belongs to the botanical order Brassicales and produces glucosinolates, which are important precursors of nitrogen- and sulfur-containing compounds. Those compounds often present low perception thresholds and various olfactive notes and are thus of interest to the flavor and fragrance chemistry. When the study of organonitrogen and organosulfur compounds is undertaken, Brassicale extracts are one of the matrices of choice. Cress extracts were studied by analytical (GC-MS, GC-FPD) and chemical (fractionation) means to identify new interesting odorant compounds. Two compounds that have never been reported in cress extracts, containing both nitrogen and sulfur, were discovered: N-benzyl O-ethyl thiocarbamate and N-phenethyl O-ethyl thiocarbamate. These two molecules being of organoleptic interest, their homologues were synthesized and submitted to organoleptic tests (static and GC-sniffing). Their odors evolve from garlic and onion over green, mushroom- and cress-like to fresh, spearmint-like. This paper presents the origin, chemical synthesis, and organoleptic properties of a series of O-alkyl thiocarbamates.     

Are there real endogeic species in temperate forest mites?

The determinants of mite diversity in soil and the reasons why so many species co-exist are poorly understood. There is evidence that niche differentiation (i.e. microhabitat complexity) in the litter layers of forest floors is important, however, little is known for deeper horizons since mite density and diversity in deeper soil layers have been rarely studied. In order to address this dearth of information, we collected microarthropods from both the forest floor and the mineral soil to a depth of 1 m in two deciduous forest locations. The density exceeded 8×10⁵ microarthropods m⁻² in one location, and a number of individuals were collected from deep in the soil. No species was exclusively living in mineral horizons. Measurements of porosity spectrum, pH, water content, total C and total N were made at each depth and related to mite diversity and species richness. Meso- and microporosity were strongly correlated with species distribution while macroporosity and pH were correlated to density and species richness.     

Large-scale correlates of alien plant invasion in Catalonia (NE of Spain)

Identification of the main correlates of the invasion process is a fundamental step in alien species management at the regional scale. This paper explores the main climatic, territorial, and anthropic correlates of alien plant species richness and percentage in Catalonia (NE of Spain), by means of GIS techniques. We used floristic data collected in FLORACAT per UTM 10 km × 10 km to set up the number and the percentage of alien species. The association of these variables with climate, topography, landscape, human settlement, and geographic position was explored by means of stepwise regression models applied on the axes obtained from principal component analysis. The significance of the resulting correlates was tested using the modified t test of Dutilleul to remove the effects of spatial autocorrelation. PCA reduced the 22 variables to 12 principal components (PC) that explained 90% of the cumulative variance. Regression models were highly significant and captured a high proportion of total variance (adjusted r² = 0.70 for alien species richness and r² = 0.56 for alien species percentage). Both alien species richness and percentage were mainly correlated to PC summarising variables concerning climate, habitat and landscape heterogeneity, and potential anthropogenic disturbance. However, while these PC exhibited similar weights on alien species richness, species percentage was mainly determined by climate. Implications for conservation are discussed considering a future scenario of climate warming and increasing land use change in Mediterranean areas.     

Effects of bovine leukemia virus infection on milk neutrophil function and the milk lymphocyte profile

The effects of bovine leukemia virus (BLV) on the immune response have been extensively investigated; however, its effects on mammary gland immunity are only speculative. Although BLV has a tropism for B cells, it can affect both adaptive and innate immunities because these systems share many effector mechanisms. This scenario is the basis of this investigation of the effects of BLV on mammary gland immunity, which is largely dependent upon neutrophilic functions. Thus, the present study sought to examine neutrophilic functions and the lymphocyte profile in the milk of naturally BLV-infected cows. The viability of the milk neutrophils and the percentage of milk neutrophils that produced reactive oxygen species (ROS) or phagocytosed Staphylococcus aureus were similar between BLV-infected and BLV-uninfected dairy cows. Furthermore, the expression of CD62L and CD11b by the milk neutrophils and the percentage of milk neutrophils (CH138⁺ cells) that were obtained from the udder quarters of the BLV-infected cows were not altered. Conversely, the median fluorescence intensity (MFI) representing intracellular ROS production and the phagocytosis of S. aureus, the expression of CD44 by the milk neutrophils and the percentage of apoptotic B cells were lower in the milk cells from BLV-infected dairy cows, particularly those from animals with persistent lymphocytosis (PL). The lymphocyte subsets were not different among the groups, with the exception of the percentage of CD5⁻/CD11b⁻ B cells, which was higher in the milk cells from BLV-infected cows, particularly those with PL. Thus, the present study provides novel insight into the implications of BLV infection for mammary gland immunity.     

Re-ignitions and soil importance on wildfire risk and management research proposals in a Mediterranean ecosystem

European Journal of Forest Research - This study was conducted following the fires that took place in Rocallaura (Spain) between 23/06/2016 and 19/07/2017. The aim is to analyse the importance of...     

Evaluation of sediment capping effectiveness in Hyeongsan River for in-situ management of total mercury and methylmercury contamination

Journal of Soils and Sediments - In this study, the effectiveness of in situ sediment capping was investigated as a remediation option for total mercury (THg) and methylmercury (MeHg) in the...