Shifting demographic conflicts across recruitment cohorts in a dynamic post‐disturbance landscape

Abstract

Seed dispersal effectiveness, which measures the number of adult plant individuals produced by seed dispersal, is the product of the number of seeds dispersed and the probability a seed produces an adult. Directed dispersal to certain habitat types may enhance some stages of recruitment but disfavor others, generating demographic conflicts in plant ontogeny. We asked whether temporal changes in habitat features may affect the distribution of seedlings recruited from dispersed acorns, and whether this could induce shifts in the life-stage conflicts experienced by successive cohorts of naturally recruited plants. As early successional habitats are characterized by rapid change, we used a burnt pine stand in southern Spain to monitor the recruitment and performance of a major tree species (Quercus ilex) across 7 yr in four types of post-fire habitats. These differed in structure and included patches of unburnt forest and three management alternatives of burnt trees: logging, partial cutting, and nonintervention. Young oaks that resprouted after the fire were mainly located near acorn sources, while new seedlings initially emerged mostly in habitats with standing snags due to habitat selection by European jays, Garrulus glandarius, for dispersal. The dead pines gradually collapsed and attracted less dispersal, so subsequent seedling cohorts mainly recruited within patches of unburnt pines. These live pines enhanced the survival of the oaks located beneath their canopy but greatly reduced their growth as compared to the other post-fire habitats, thus representing a demographic conflict that was absent elsewhere. As a consequence of the directional shift in the habitat where seedlings recruited, successive seedling cohorts experienced a gradual improvement in their likelihood of survival but a reduction in growth. The progressive intensification of this life-stage conflict hinged on the reduction of vertical structures in the habitat with standing burnt pines. Recruitment success thus involved temporal variation in the habitat where recruitment occurred, likely resulting from changes in the direction of seed dispersal, and spatial variation in habitat suitability for seedling establishment and growth. Temporal changes in habitat structure can indirectly change the environment in which recruitment occurs, and consequently seed dispersal effectiveness, by shifting the direction of seed dispersal.

An ecosystem services approach to the ecological effects of salvage logging: valuation of seed dispersal

“…, Leverkus et al. ), together with the cost evaluation of reforestation under these three scenarios (Leverkus et al. ).…”

“…), whereas the lowest‐elevation plot (described in Leverkus et al. ) was not reforested and was reserved to study natural regeneration (Data ). The cost of reforestation was calculated for each subplot by the local Forest Service (for details, see Leverkus et al.…”

“…In the study plot, there was an intense regeneration after the fire, which could be ascribed to pre‐treatment and post‐treatment scenarios (Leverkus et al. ).…”

“…, Leverkus et al. ). We evaluate the dispersal service provided by the activity of vertebrates, mostly the Eurasian Jay ( Garrulus glandarius L.), as a mechanism for the natural recovery of native oak forests after fire in three contrasting post‐fire logging scenarios.…”

Salvage logging in the world’s forests: Interactions between natural disturbance and logging need recognition

“…A good example of disturbance‐induced increases in the likelihood of logging is in protected areas where conventional logging is prohibited (Müller et al, ). Cases include the Sierra Nevada National Park in Spain after a wildfire in 2005 (Leverkus, Rey Benayas, & Castro, ), bark‐beetle affected areas in the Białowieża National Park in Poland (Schiermeier, ), and windthrows in the Monarch Butterfly Reserve in Mexico, where logging aims to reduce fire risk (Leverkus et al, ). However, disturbance also increases the likelihood of logging in production forests.…”