M. de Luis

EARLY TO RISE MAKES A PLANT HEALTHY, WEALTHY, AND WISE

Seedling emergence time is a crucial event in the life cycle of a plant, determining its fitness via different components including survival, growth, and fecundity. Precocious emergents usually survive, grow, and/or reproduce earlier in the life cycle, but for perennials it is unknown whether these benefits are maintained throughout the life of the plant. Here, we examine for the first time whether fitness benefits due to the early emergence of perennial plants are perpetuated or vanish with time. For nine years, in a Mediterranean gorse community, we followed the fate of 2118 seedlings belonging to the four dominant woody species. We estimated phenotypic selection gradients on emergence time for three fitness components (survival, growth, and fecundity), under two experimentally simulated scenarios (fire and fire + erosion), at two different times in the life of the plant (3 and 9 years). Fire and erosion represent two potential selective forces constraining the temporal window of seedling emergence in Mediterranean habitats. All the species exhibited selection for early emergence, but through different fitness components. Directional selection favoring early emergence via survival in both fire scenarios was detected in the two Cistaceae species (Helianthemum marifolium and Cistus albidus), in which precocious emergents had higher fitness values late in the life cycle (9 years). In contrast, Fabaceae species (Ononis fruticosa and Ulex parviflorus) were not selected for early emergence via survival. Early emergents of all species in both fire scenarios had higher fitness values through growth early in the life cycle; these benefits decreased slightly with time but remained statistically significant, except in H. marifolium. Finally, late fecundity was enhanced by early emergence in both fire scenarios in C. albidus and U. parviflorus but not in H. marifolium. In conclusion, benefits acquired by emerging early are perpetuated for at least nine years.

Assessing components of a competition index to predict growth in an even-aged Pinus nigra stand

The relationship between tree growth and competition may depend on some subjective choices that are commonly left to the researcher. Among these are the neighborhood radius, the number of years of growth that are integrated, and tree age. We have evaluated the importance of these factors when relating growth and competition in a forest stand with contrasted densities of the dominant tree species (Pinus nigra) and understory shrub species (Adenocarpus decorticans). Previous to this evaluation we performed a randomization test to assess the relationship between tree growth and neighbors. By using Daniels index of competition we found that the use of a fixed neighborhood radius underestimated the importance of tree competition. The coefficient of determination (r2) of the relationship between tree growth and Daniels index increased asymptotically with the number of years considered. Five years of growth gave high r2 independently of the density of trees and shrubs. The intensity of competition was weakly affected by the characteristics of the plot (tree and shrub densities), and did not change with time. In contrast, the potential growth at equal competition – as represented by constant “a” in the allometric model – changed with time suggesting a gradual decrease in potential tree growth in the plots with higher tree density, and a gradual increase in those plots with high density of shrubs. These results may reflect tree canopy closure and the senescence of Adenocarpus decorticans. A method is suggested to select optimum neighborhood radius and growing period for the calculation of competition indices. By applying this method we were able to explain as much as 79–84% of the variability in tree growth of this stand.

Variation in xylem vulnerability to embolism in European beech from geographically marginal populations

Climate change is expected to increase the frequency and intensity of droughts and heatwaves in Europe, leading to effects on forest growth and major forest dieback events due to hydraulic failure caused by xylem embolism. Inter-specific variability in embolism resistance has been studied in detail, but little is known about intra-specific variability, particularly in marginal populations. We evaluated 15 European beech populations, mostly from geographically marginal sites of the species distribution range, focusing particularly on populations from the dry southern margin. We found small, but significant differences in resistance to embolism between populations, with xylem pressures causing 50% loss of hydraulic conductivity ranging from -2.84 to -3.55 MPa. Significant phenotypic clines of increasing embolism resistance with increasing temperature and aridity were observed: the southernmost beech populations growing in a warmer drier climate and with lower habitat suitability have higher resistance to embolism than those from Northern Europe growing more favourable conditions. Previous studies have shown that there is little or no difference in embolism resistance between core populations, but our findings show that marginal populations have developed ways of protecting their xylem based on either evolution or plasticity.

Summer drought reconstruction in northeastern Spain inferred from a tree ring latewood network since 1734

Drought recurrence in the Mediterranean is regarded as a fundamental factor for socio-economic development and the resilience of natural systems in context of global change. However, knowledge of past droughts has been hampered by the absence of high-resolution proxies. We present a drought reconstruction for the northeast of the Iberian Peninsula based on a new dendrochronology network considering the Standardized Evapotranspiration Precipitation Index (SPEI). A total of 774 latewood width series from 387 trees of P. sylvestris and P. uncinata were combined in an inter-regional chronology. The new chronology, calibrated against gridded climate data, reveals a robust relationship with the SPEI representing drought conditions of July and August. We developed a summer drought reconstruction for the period 1734-2013 representative for the northeastern and central Iberian Peninsula. We identified 16 extremely dry and 17 extremely wet summers, and four decadal scale dry and wet periods, including 2003-2013 as the driest episode of the reconstruction.

Application of the cross tab analysis to the spatial analysis of climatic tendencies in the eastern sector of Spain

RESUMEN: Proponemos el analisis de las tablas cruzadas (cross-tab analysis) para estudiar el solapamiento y analizar las relaciones espaciales entre las tendencias de diferentes variables del clima. Para ilustrar el metodo se presentan dos ejemplos en los que se comparan las distribuciones espaciales de las tendencias anuales de la precipitacion, del evento diario maximo y de la variabilidad anual. Los ejemplos se desarrollan en la Comunidad Valenciana y el sector central de la Depresion del Ebro. En la Comunidad Valenciana el analisis permite descubrir una relacion doble entre las tendencias de los totales anuales y las del maximo evento diario. Por su parte, en el sector central del valle del Ebro la relacion encontrada entre las tendencias de precipitacion anual y su variabilidad sugiere que los escenarios futuros, si se mantienen las pautas descritas, estaran sometidos a una mayor imprecision y aleatoriedad. ABSTRACT: We suggest cross-tab analysis to study the spatial distribution-overlapping trend between climate elements. We present two examples of such overlapping, in which we compared the spatial distribution of annual rainfall trend with spatial distribution of trend of maximum daily event and spatial distribution of annual rainfall variability. In the first ones (Comunidad de Valencia, E of Spain) we find a complex relationship between annual rainfall trend and daily maximum rainfall trend. In the second ones (Depresion del Ebro, NE inland of Spain) the relationship between annual rainfall trend and annual rainfall variability trend suggest that futures scenarios could be more and more non-predictable.