Màrcia Eugenio

Quantitative Tracheid Anatomy Reveals a Complex Environmental Control of Wood Structure in Continental Mediterranean Climate

A detailed understanding of how the climate models the hydraulic system of trees is still lacking, in spite of the need to understand tree response to the ongoing process of climatic change. A systematic correlation of tracheid anatomical features with climate has not been implemented in Mediterranean ecosystems, where climatic change is expected to be particularly intense. We measured ring width and cell number—in addition to intraring position, lumen size, and wall thickness of tracheids—in 10 Juniperus thurifera individuals from north-central Spain. We used this information to perform an exploratory analysis of how these parameters correlated with climatic variables in 1965–2004. Cell number and ring width shared a relatively similar climatic signal, whereas the anatomical variables provided differentiated and diverse signals about climatic conditions during their formation. Earlywood and latewood tracheids differed in controlling factors, with earlywood tracheid size and wall thickness being positively related to rainfall during early summer and latewood tracheid size being positively related to August temperature. Tracheid anatomical variables improved our understanding of climate effects on tree growth and wood formation under harsh environmental conditions, as those experienced in continental Mediterranean climates, where limiting factors show multiple shifts across the year.

Fire recurrence effects on the structure and composition of Mediterranean Pinus halepensis communities in Catalonia (northeast Iberian Peninsula)

Abstract: Does recurrence of fires affect the composition and structure of Mediterranean plant communities? The post-fire regeneration of communities dominated by Pinus halepensis was examined using a regional approach in Catalonia (northeast Iberian Peninsula). Twenty-eight study sites were selected. Each site consisted of two adjacent areas that differed in the number of fires that occurred during a period of two decades. One area burned only once, in 1994 (recurrence category 1, r1); the other area burned twice, once between 1975 and 1993 and again during the same 1994 fire (recurrence category 2, r2). Eight years after the 1994 fire, structural (height, cover, fuel model) and compositional (abundance of dominant species) data were collected, together with data on pine density and reproductive performance. The effects of fire recurrence, fire interval (FI), real solar radiation (RSR), and precipitation (PP) were analyzed. There was a structural simplification in twice-burned areas in comparison with once-burned ones. This simplification may result from changes in species composition and from differential growth potentials caused by effects of fire on soils. In addition, lower fuel loads occurred after two fires. Pinus halepensis populations declined and shrub abundance increased in twice-burned areas; an increase in grass abundance was not observed. Fire recurrence was the most relevant variable to explain differences in plant community characteristics. The importance of fire regime parameters in determining post-fire vegetation regeneration in Mediterranean-type ecosystems is underlined by this study.

Under pressure: how a Mediterranean high‐mountain forb coordinates growth and hydraulic xylem anatomy in response to temperature and water constraints

Summary 1. Plant growth in Mediterranean high mountains is limited by the double climatic stress of low winter temperatures and summer drought. Elevational shifts in response to climate change may be complex for species whose distribution is constrained by several climatic factors. 2. We used herb-chronology, that is, the analysis of annual rings in the secondary root xylem of perennial forbs, to evaluate life-long factors constraining secondary growth and xylem hydraulic anatomy along an elevational gradient from the upper to the lower distribution limits of the alpine forb Silene ciliata at its southernmost distribution range. 3. Generalized additive models (GAM) showed that annual ring width (RW) in S. ciliata was greatest at intermediate elevations and smallest at the upper and lower limits of its elevational range. In contrast, maximal vessel area (MVA) was greatest at lower elevations. RW responded to climatic conditions in early spring and late summer, suggesting the presence of a bimodal xylogenesis. Structural equation modelling (SEM) indicated a positive influence of MVA on RW in the same year; improved hydraulic efficiency seemed to promote higher secondary growth. 4. The observed greatest secondary growth (RW) and maximal vessel area (MVA) at intermediate and intermediate-low elevations, respectively, contrasts with previous evidence of an improvement in plant reproduction and recruitment with increasing elevation for S. ciliata. However, our results are in agreement with other indicators suggesting that best conditions occur at intermediate elevations, such as better seed quality or larger genome size. 5. This study reinforces the evidence that the response of high-mountain plants to climatic change under simultaneous temperature and drought stress is complex and that models that simply assume an increase in elevation as a response to higher temperatures may fail to predict future responses to climate change.

Effects of repeated burning on Mediterranean communities of the northeastern Iberian Peninsula

Abstract Question: In relation to a single fire, do repeated wildfires in Mediterranean type ecosystems (1) reduce plant species richness or diversity; (2) modify patterns of abundance or dominance of plant species or (3) alter plant composition? Location: Pinus halepensis dominated communities of Catalonia, northeastern Iberian Peninsula, western Mediterranean Basin. Methods: Regional, paired design with 14 study sites, each consisting of a once burnt area (1994) and a twice burnt area (1975-1993 and 1994). Ten years after the last fire, we recorded all vascular plant species present in nested plots and quantified their relative abundances on transects. We compared species richness, diversity, dominance and relative abundance and species-area correlations between paired once and twice burnt areas and assessed their floristic composition similarity. Results: No statistically significant differences were found in species richness or diversity. Slopes of species-area correlations were higher in once burnt areas. In twice burnt areas, dominance by one or two species was higher. P. halepensis showed lower relative abundance and nanophanerophytes showed higher relative abundance. No differences were found for resprouter, seeder or resprouter-seeder species. Floristic composition similarity between paired areas tended to be higher in less productive sites. Conclusions: Fire recurrence had contrasting effects on species richness at different spatial scales. Repeated burning reduced the relative abundance of the dominant tree species, which resulted in a higher relative abundance of shrubs. It also promoted the dominance of herbs, particularly Brachypodium retusum. However, it did not change the relative abundance of regenerative groups. Paired areas were more similar as they were more Mediterranean in terms of climatic conditions. Nomenclature: Bolòs et al. (1990).

Recurrent wildfires constrain long-term reproduction ability in Pinus halepensis Mill.

Increasing fire recurrence is a major problem threatening Mediterranean-type ecosystems. Moreover, this pattern is predicted to increase owing to global change. Although a reduction in the density and growth of post-fire regeneration is usually observed in recurrently burnt areas, the potential effects on reproductive ability have seldom been explored. The aim of the present study is to investigate whether structural changes induced by fire recurrence may constrain reproduction ability of Pinus halepensis forests. We conducted the current study in Catalonia (NE Spain) in 12 study sites, consisting of two adjacent areas differing in the number of fire events suffered throughout the last 16 years (one v. two fires). Twice-burnt areas showed a lower density of pines, lower pine height and a lower reproductive ability, namely (i) a 3-year delay in the onset of pine reproduction; (ii) a reduction of 52% in the number of reproductive pines; and (iii) a 36% lower mean cone crop per tree. The lower mean cone production per tree coupled with a lower density resulted in an ~80% lower canopy seed bank in twice-burnt areas. These results suggest that the occurrence of a third fire event in twice-burnt areas would severely constrain natural regeneration.

Natural post-fire dynamics and serotiny in 10-year-old Pinus halepensis Mill. stands along a geographic gradient

In 1994, six large fires occurred along a climate gradient in Eastern Spain. Ten-year-old trees were selected in the plots established for each location affected by fire. Each selected tree was measured for height and trunk diameter, the number of female strobili and cones, and grouped into four types. A geographical gradient was determined to study growth by latitude and variations in reproductive characteristics. Height and diameter values decreased southwards with the exception of the lowest-density tree location, where trunk diameters were similar to those in northern locations. Strobilus and cone production were higher in lower tree density locations owing to intraspecific competition and higher availability of water, nutrients and light. Serotiny levels were highest in southern locations, although lower percentages were found in the southern locations with low tree density. The number of reproductive trees was higher with lower tree density. The reproductive phase was reached in the lowest tree density site (also low site quality) and nearly reached in the most northern locations (high tree density as well as high site quality). Results showed a geographical gradient based on growth and reproduction dynamics, where serotiny levels are higher in southern locations. Density was shown to be a significant factor influencing overall pine stand development.

Site effect is stronger than species identity in driving demographic responses of Helianthemum (Cistaceae) shrubs in gypsum environments

PREMISE OF THE STUDY Regional climatic patterns result in the synchrony of biological processes along large spatial areas. These patterns may be critical for effective plant recruitment in (semi)arid environments. Nevertheless, recruitment patterns of plant species within their range of distribution are still poorly known. Moreover, this response may be species-dependent, particularly between coexisting congenerics, which are thought to vary in demographic responses to climatic conditions as a coexistence-promoting mechanism. In this context, we investigated whether two congeneric plant species show synchronic age structures at varying spatial scales and whether they display demographic differences. METHODS We sampled 600 Helianthemum squamatum and H. syriacum individuals at six localities in Spain. We used dendrochronological techniques to estimate age and radial growth. We compared the age structure among populations and between species and assessed the effect of site and species on different demographic parameters. Correlations between age structure and climatic factors were also determined. KEY RESULTS We detected a very low intraspecific synchrony across sites but a high interspecific coupling in age structure within localities. Secondary growth, mean age, and flowering showed large intersite differences and small interspecific differences. Summer rainfall was a good predictor of age structure. CONCLUSIONS Fine-scale climatic variability plays a major role in determining age structure of the studied species. Climatic variability is more relevant than interspecific differences. Our results illustrate the relevance of including spatial variation in summer rainfall patterns when modeling the impact of climate change on Mediterranean plant demography.

Wild botanic gardens as valuable resources for innovative environmental education programmes in Latin America

Abstract Wild botanic gardens consist of natural or semi-natural land remnants immersed in large urban areas or botanic gardens, which are managed for purposes of biodiversity preservation and public recreation. In Latin America, they tend to be affected by budget limitations; however, they serve as valuable resources that permit the development of innovative environmental education programmes. Specifically, we are considering the appropriateness of implementing critical environmental education and socio-constructivist programmes. As for practical considerations, it is important to include diverse epistemologies, and therefore, strategies or procedures characteristic of science teaching, such as problem-based learning, together with other characteristics of social activism and popular education initiatives, such as assemblies or meetings, and others characteristic of more traditional and indigenous worldviews, such as celebrations of the earth. In this way, Latin American wild botanic gardens may play a role in constructing environmentally responsible societies and the nurturing of a culture of reflective inquiry.

Aleppo pine regeneration after fire along an aridity gradient

In the Mediterranean Basin, the number of large-scale fires and, consequently, the area of regenerated forests after a fire have been increasing over the last few decades. Mediterranean pine tree stand regeneration shows differences in growth and reproductive characteristics depending on site quality. Aleppo pine (Pinus halepensis Mill.) is an important obligate seeder species occupying a large surface in this area. In order to study growth and reproductive characteristics depending on different climatic conditions, six sites with similar characteristics (edaphic, exposure, slope) burned in the summer of 1994 were selected along a climate gradient. Different precipitation values determined three different ombroclimates: dry-subhumid, dry and semi-arid. Ten years after the fires, data on growth and cone production were collected from these areas in order to study the pattern of growth and reproduction and the influence of site quality (climate) on them. Results showed significantly higher values for growth and several cone characteristics; furthermore, they were positively related to site quality. Viability and seed germination percentages were higher in sites located in dry-subhumid areas. Serotiny was highest in dry locations (southern sites), and lower percentages were found in low tree density sites. The number of reproductive trees was higher northwards and the reproductive phase was reached in younger stands with lower tree density. In conclusion, results showed a geographical gradient based upon growth and reproductive characteristics, decreasing southwards in contrast to serotiny, which increases in southern sites. Density was found to be a significant factor influencing overall pine stand development.