Nutrient, metal contents and microbiological properties of litter and soil along a tree age gradient in Mediterranean forest ecosystems.

The link among the age of aboveground tree species, litter, soil quality and status in Mediterranean forests is not entirely comprehended (especially in Mediterranean forest sites). This study evaluates whether and by what extent tree stand composition and forest structure modify nutrient depository or alter physical, chemical and microbiological properties of soil and litter in a 120 years old pine forest chronosequence. In general, the enzymatic activity related to the phosphorous, carbon and nitrogen cycles were more developed in litter than in soil surface, while the sulphur enzymatic activity was not significantly different between the two analyzed systems. The higher dehydrogenase content measured in the litter may be an index of a higher extracellular microbial activity, compared to soil. A noticeable effect of forest age and structure on the majority of analyzed elements was detected, with nutrients and metals tending to accumulate in soil rather in the litter. Moreover, the contents of P and some metals and sulphur enzymatic activity in the litter are influenced by forest age and associated forest structure. Finally, since nutrient, metals and enzyme contents in the litter increase with forest age, forest management strategies targeted to increase the stand structure may be advisable in order to achieve higher soil functionality.

Regeneration of three pine species in a Mediterranean forest: A study to test predictions from species distribution models under changing climates.

The study tested the hypothesis that future changes in the composition of tree communities, as predicted by species distribution models, could already be apparent in the current regeneration patterns of three pine species (Pinus pinaster, P. nigra and P. sylvestris)inhabiting the central-eastern mountains of Spain. We carried out both an observational study and a seed-sowing experiment to analyze, along an altitudinal and latitudinal gradient, whether recent recruitment patterns indicate an expansion of P. pinaster forests to the detriment of P. nigra ones in the low-altitude southern sites of these mountains; or whether P. sylvestris is being replaced by P. nigra in the high-altitude sites from the same area. The observational study gathered data from 561 plots of the Spanish National Forest Inventory. The seed-sowing experiment tested the effects of irrigation and stand basal area on seedling emergence and survival. Data were analyzed by means of Generalized Linear Models and Generalized Linear Mixed Models. Regeneration of the three pine species responded similarly to the explicative factors studied, but the density of tree seedlings and saplings exhibited a wide spatial heterogeneity. This result suggested that a mosaic of site- and species-specific responses to climate change might mislead model projections on the future forest occupancy of tree species. Yet, we found no indications of neither an expansion nor a contraction of the near future forest occupancy of the tree species studied.

Unravelling the importance of forest age stand and forest structure driving microbiological soil properties, enzymatic activities and soil nutrients content in Mediterranean Spanish black pine(Pinus nigra Ar. ssp. salzmannii) Forest.

This study aimed to investigate the effects that stand age and forest structure have on microbiological soil properties, enzymatic activities and nutrient content. Thirty forest compartments were randomly selected at the Palancares y Agregados managed forest area (Spain), supporting forest stands of five ages; from 100 to 80years old to compartments with trees that were 19-1years old. Forest area ranging from 80 to 120years old and without forest intervention was selected as the control. We measured different soil enzymatic activities, soil respiration and nutrient content (P, K, Na, Mg, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pb and Ca) in the top cm of 10 mineral soils in each compartment. Results showed that the lowest forest stand age and the forest structure created by management presented lower values of organic matter, soil moisture, water holding capacity and litterfall and higher values of C/N ratio in comparison with the highest forest stand age and the related forest structure, which generated differences in soil respiration and soil enzyme activities. The forest structure created by no forest management (control plot) presented the highest enzymatic activities, soil respiration, NH4(+) and NO3(-). Results did not show a clear trend in nutrient content comparing all the experimental areas. Finally, the multivariate PCA analysis clearly clustered three differentiated groups: Control plot; from 100 to 40years old and from 39 to 1year old. Our results suggest that the control plot has better soil quality and that extreme forest stand ages (100-80 and 19-1years old) and the associated forest structure generates differences in soil parameters but not in soil nutrient content.

Evaluation of fire recurrence effect on genetic diversity in maritime pine (Pinus pinaster Ait.) stands using Inter-Simple Sequence Repeat profiles.

The management of maritime pine in fire-prone habitats is a challenging task and fine-scale population genetic analyses are necessary to check if different fire recurrences affect genetic variability. The objective of this study was to assess the effect of fire recurrence on maritime pine genetic diversity using inter-simple sequence repeat markers (ISSR). Three maritime pine (Pinus pinaster Ait.) populations from Northern Portugal were chosen to characterize the genetic variability among populations. In relation to fire recurrence, Seirós population was affected by fire both in 1990 and 2005 whereas Vila Seca-2 population was affected by fire just in 2005. The Vila Seca-1 population has been never affected by fire. Our results showed the highest Nei's genetic diversity (He=0.320), Shannon information index (I=0.474) and polymorphic loci (PPL=87.79%) among samples from twice burned populations (Seirós site). Thus, fire regime plays an important role affecting genetic diversity in the short-term, although not generating maritime pine genetic erosion.