Patterns and drivers of regeneration of tree species in forests of peninsular Spain

Abstract

Aim Our study aimed to identify and explore the main factors that influence tree recruitment of multiple species at a regional scale across peninsular Spain, an understanding of which is essential for predicting future forest species composition in the face of ongoing environmental change. The study focused on the dynamics of the key transition phase from saplings to adult trees. Location The forests of peninsular Spain. Methods We used the extensive network of plots sampled in two consecutive Spanish national forest inventories (> 30,000 plots) to identify the factors that determine regeneration patterns of the 10 most abundant forest species of Spain at relatively large temporal (c. 10 years) and spatial scales (across Spain): five coniferous species of Pinus (pines) and five broadleaved species of the genera Fagus and Quercus. We fitted separate generalized linear models for the pine species and the broadleaved species to assess the response of sapling abundance and ingrowth rate to the spatial variability of climate (temperature, water availability and recent warming), forest structure (tree density, understorey and overstorey canopy cover, and basal area change) and disturbances (previous forest logging, wildfires and grazing). Results Mean sapling abundance was four times higher for broadleaved species than for pines, while mean annual ingrowth was twice as high. Sapling abundance and ingrowth rate were mainly determined by stand structure, both in pines and broadleaved trees. The direct effects of disturbances and climate were comparatively smaller, and there was no detectable effect of recent warming. Main conclusions The higher values of ingrowth rate of broadleaved species can be explained by their ability to maintain a higher sapling bank due to their greater shade tolerance. This differential response of pines and broadleaved species to canopy closure suggests a probable increase in broadleaved species at the expense of pines. This transition could occur earlier in stands with faster canopy closure dynamics. Spatially explicit, mixed‐species demographic models incorporating both the ingrowth and the tree mortality components are needed for predicting the composition of future forests.

Global change and terrestrial plant community dynamics

“…Tree species colonization in recent decades was more strongly related to dispersal than climate, and conifer regeneration was negatively related to competition with expanding oaks. Broadleaf species establishment was positively related to precipitation (51), but also to succession (canopy closure) (52). Demographic responses of Iberian trees to global change are highly variable among species and across climate gradients (53).…”

Stand-level drivers of tree-species diversification in Mediterranean pine forests after abandonment of traditional practices

“…These forests were intensively managed for timber harvesting and pasture grazing until the mid-20th century (Ruiz de la Torre, 2006), but from that point onwards the intensity of human practices decreased significantly (Vicente-Serrano et al, 2004). During the past few decades, just a few individual-tree selection cuttings affecting only the most vigorous and well-shaped trees have been conducted on these forests (Trasobares and Pukkala, 2004;Aunós et al, 2009) interventions and livestock grazing) has allowed the establishment of new cohorts of the dominant pine species, causing a generalized densification of the stands (DGCN, 2005) and a progressive process of colonization by late-successional tree species, mainly Quercus species (e.g., Urbieta et al, 2011;Carnicer et al, 2014;Vayreda et al, 2013).…”

Variation of Ring Width and Wood Density in Two Unmanaged Stands of the Mediterranean Oak Quercus faginea

“…Regeneration of species, typically including slow growing and late-successional species such as deciduous oaks, suggested good performances for mixed-forests with fast-growing species such as Pinus spp. [7]. Knowledge of growth features over the tree's life-time, especially for slow growing species, as is the case for Q. faginea, will be important for better designing a forest management (e.g., stand location and density, rotation age and tree selection) that will include a high-value product-oriented approach.…”