Growth and Growth-Related Traits for a Range of Quercus Species Grown as Seedlings Under Controlled Conditions and for Adult Plants from the Field

Abstract

Forests and shrublands occupy a large area in the world (c. 31% of the total continental area) and in Spain (c. 36% of the area), in which around 30% of forests are formed by Quercus species. Therefore, the ecosystem services provided by Quercus species are critical to human well-being. Thus, it is essential to understand how Quercus species grow and how they will respond to global change. Bringing together data of comparative growth experiments with seedlings, field data and allometric equations developed for adult plants, our main objectives for this chapter are: (1) to quantify the relative growth rates (RGR) and growth components of seedlings of Quercus species and compare them to values of woody species belonging to other families; (2) to characterise biomass allocation patterns in leaves, stem and roots and RGR in Quercus adults; (3) to understand how temperature, precipitation, tree size and tree density affect the RGR of adult Quercus species; and (4) to compare the RGR of seedlings and adults, and identify which functional traits can explain the differences in RGR. Compared to woody species from other families, seedlings of Quercus species were characterized by low RGR and specific leaf area (SLA), a high proportion of biomass invested in roots (RMF, root mass fraction) and a large seed mass. One of the most important traits explaining differences in RGR among seedlings of Quercus species was the leaf area ratio (LAR, total leaf area per unit of total biomass). In Quercus species, the fraction of biomass in leaves (LMF) and roots (RMF) decreased with tree size, while the proportion of biomass in stems (SMF) increased. Thus, for a tree with 20 cm diameter at breast height, the values of LMF were only between 0.01 and 0.05 (i.e. 1–5% of total biomass invested in leaves) and SMF ranged from 0.50 to 0.80. RGR values of adult Quercus species were highly variable, due to differences in tree size, stand density and abiotic factors. Tree size and density negatively affected RGR, so bigger trees tend to grow more slowly. However, the variation in RGR explained by temperature and/or precipitation was relatively low (<7% of total variation).We observed a positive relationship between the RGR of seedlings in controlled conditions and those of adults in the field. Furthermore, median RGR values of adult plants for Quercus species were positively related to SLA and leaf nitrogen. To sum up, Quercus species differ in RGR and key leaf traits from other woody species and the RGR of adult trees depend on tree size, density, temperature and precipitation. Our results suggest that climate change synchronised with density might affect future trends on the growth of Quercus species.