Context Excessive recruitment in post-fire regeneration of Pinus halepensis can require pre-commercial thinning. The 1994 Moratalla fire (Spain) and the thinning applied there since 2004 provided good conditions for testing pre-commercial thinning effectiveness. Aims To analyse pre-commercial thinning effects on tree size, reproductive potential, stem biomass and annual growth in 15-year-old saplings. Methods Twenty nine circular plots (5 m radius) were established based on (1) years since thinning and (2) aspect. Non-thinned plots were included as controls. Sapling variables were measured and pine cones were counted and classified according to maturity. Three saplings per plot were felled, five sample disks were extracted from each and tree rings were analysed with Windendro® software. Results Sapling size, annual growth and stem biomass were higher in thinned plots than in control plots 2–4 years after thinning. Annual growth declined five years after thinning. Cone counts were higher 2–5 years after thinning, depending on the cone type. Aspect influenced some variables. Conclusion Thinning accelerated stand maturity but positive effects were indiscernible until 2–5 years later. Serotinous cones, which are fundamental to regeneration after fire, increased in number after 5 years. The effects of aspect were inconclusive due to interactions with years since thinning.

Natural regeneration comprises different subprocesses, each of them driven by specific climatic and stand-related factors, which determine the success of natural regeneration. The objective of this study was to investigate the seed availability of maritime pine (Pinus pinaster Aiton). To meet this objective, seed rain was monitored for four different levels of stand density at the experimental site of Cuéllar, Spain, during a 10-year period. A generalized linear mixed-effects model was fitted to test the effects of climatic variables and stand density on the annual seed production and seed rain. The climatic covariates were chosen among those that are thought to affect the key physiological phases governing these subprocesses: minimum temperature in October 2 years before dispersal (cone growing), April precipitation 1 year before dispersal (cone growing), and October–November precipitation 1 year before dispersal (cone maturation). No climate variable related to flowering or seed rain process was significant. Moreover, stand density was considered through a spatially explicit index called the seed-source index. Primary cone growth was limited by extreme cold events. Absence of precipitation limits secondary growth and hinders final cone ripening. It turns out that seed production and seed rain may be a bottleneck for natural regeneration of P. pinaster under low stand densities, especially under extreme climatic scenarios.

Seed bank dynamics constitute a pool of natural regeneration, a complex and key process for stand persistence. The present work analyzes post-dispersal predation on a Pinus pinaster Ait. (maritime pine) belowground seed bank. The study was carried out at the experimental site of Mata de Cuellar (Segovia, central Spain), where an integrated analysis of maritime pine regeneration has been underway since 2004. Seed predation was monitored every month from 2010 to 2013. A generalized linear model was fitted using “next spring seed density” as the response variable and seed rain, micro-site conditions and annual climate variability as explanatory variables. Seed rain, distance to the nearest stump, basal area and Walter’s drought index, along with percentage cover of herbaceous species, pine needle litter and shrub species, had significant positive effects. The number of neighboring trees had a significant negative effect on seed density. These results demonstrate how seed rain, summer drought and micro-site conditions are crucial to understand the effects of predation on the belowground seed bank. Though greater than null, the final seed bank might be insufficient for successful natural regeneration due to high mortality caused by difficult germination and establishment conditions.

There is growing interest in mixed-species forests but also a lack of studies that analyse them at the regeneration phases or any stage other than mature stands. Information is particularly scarce about relatively unproductive species such as Pinus pinaster and Pinus halepensis in Mediterranean ecosystems. The objective of this study was to investigate inter- and intra-specific interactions of both species at different tree densities during the first years of establishment. Five Nelder wheel plots were planted to test densities ranging from 1000 to 80 000 seedlings/ha and simulate establishment sub-processes at high densities. Further, P. pinaster and P. halepensis were mixed along the spokes, to obtain three mixture levels in which 100, 80 or 60 per cent of the seedlings were of the same species. Cox proportional-hazards models and binomial logistic regressions were fitted to analyse seedling survival. Early growth (basal diameter and height at one and four years after plantation) was analysed by fitting linear mixed-effects models. In this regard, P. halepensis showed higher survival rates and basal diameter increments but more time is needed to know how P. pinaster responds to density and mixture. Both competitive and facilitating seedling interactions were observed at higher densities, which fostered seedling survival but decreased early growth.