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International audience; Despite its importance for forest regeneration, food webs, and human economies, changes in tree fecundity with tree size and age remain largely unknown. The allometric increase with tree diameter assumed in ecological models would substantially overestimate seed contributions from large trees if fecundity eventually declines with size. Current estimates are dominated by overrepresentation of small trees in regression models. We combined global fecundity data, including a substantial representation of large trees. We compared size–fecundity relationships against traditional allometric scaling with diameter and two models based on crown architecture. All allometric models fail to describe the declining rate of increase in fecundity with diameter found for 80% of 597 species in our analysis. The strong evidence of declining fecundity, beyond what can be explained by crown architectural change, is consistent with physiological decline. A downward revision of projected fecundity of large trees can improve the next generation of forest dynamic models.

Centro de Investigación Forestal (CIFOR), Annually variable and synchronous seed production by plant populations, or masting, is a widespread reproductive strategy in long-lived plants. Masting is thought to be selectively beneficial because interannual variability and synchrony increase the fitness of plants through economies of scale that decrease the cost of reproduction per surviving offspring. Predator satiation is believed to be a key economy of scale, but whether it can drive phenotypic evolution for masting in plants has been rarely explored. We used data from seven plant species (Quercus humilis, Quercus ilex, Quercus rubra, Quercus alba, Quercus montana, Sorbus aucuparia and Pinus pinea) to determine whether predispersal seed predation selects for plant phenotypes that mast. Predation selected for interannual variability in Mediterranean oaks (Q. humilis and Q. ilex), for synchrony in Q. rubra, and for both interannual variability and reproductive synchrony in S. aucuparia and P. pinea. Predation never selected for negative temporal autocorrelation of seed production. Predation by invertebrates appears to select for only some aspects of masting, most importantly high coefficient of variation, supporting individual-level benefits of the population-level phenomenon of mast seeding. Determining the selective benefits of masting is complex because of interactions with other seed predators, which may impose contradictory selective pressures., The research was supported by (Polish) National Science Centre grant nos. 2018/28/U/NZ8/00003 (Uwertura) and 2017/24/C/NZ8/00151 (Sonatina). SM and MAS recognize support from the US National Science Foundation (DEB-9442602, DBI-9978807, DEB-0642504 and DEB-15556707), the H. Fenner Endowment of Wilkes University and landowners (G. Vanesky, W. & M. Martin, F. Balliet and Hawk Mountain Sanctuary) for long-term use of their forests. RC’s research is funded by National Project OLDPINE AGL-2017-83828-C2.1R., 8 Pág.

Browsing damage by ungulates is among the most decisive factors affecting the establishment and growth of young trees. In recent decades, ungulate populations have been expanding in the Northern Hemisphere; impairment of tree regeneration by their activity is an increasing problem. Herbivore-induced changes in tree regeneration may alter the composition and biodiversity of the future tree stand. In this study we determined where young trees can leave the seedling bank and succeed to higher forest strata in a protected natural forest that is under strong herbivore pressure. We studied rowan (Sorbus aucuparia) regeneration in a subalpine spruce forest growing in a strictly protected area of Babia Gora National Park (Western Carpathians). Rowan is one of the most palatable forest species, so browsing can significantly limit its growth. We predicted that factors, that restrict the movement of red deer (Cervus elaphus), decrease their visits in some forest patches, which will result in a higher share of rowan saplings. We also considered two other factors that can affect the distribution of rowan saplings: light availability and distance to maternal trees. In particular, we tested whether the occurrence of rowan saplings was related to: (i) slope angle, amount of logs lying on the forest floor, and distance to the hiking trails; (ii) distance to fruit-bearing trees; and (iii) canopy openness. The results confirmed our main predictions concerning the relation between the occurrence of palatable tree saplings and the availability of a forest area to ungulates. Factors related to the availability of terrain to red deer significantly influenced the distribution of rowan saplings taller than 1 m. The probability of rowan sapling occurrence increased when the amount of logs was higher and the distance to hiking trails was shorter. Slope had a significant negative impact on sapling occurrence. We found no effect of proximity of fruit-bearing rowan trees or canopy gap area. Thus, in the natural forest, the likelihood that young palatable trees will make the transition from seedlings to taller saplings seems to be determined mainly by factors related to ungulate activity. This suggests that the increase of ungulate populations and their browsing behavior will affect the species composition and spatial structure of future tree stands.