Stochastic and deterministic effects on interactions between canopy and recruiting species in forest communities

• Published in: Functional ecology Vol. 32; no. 9; pp. 2264 - 2274
• Main Authors: Alcántara, Julio M., Pulgar, Manuel, Trøjelsgaard, Kristian, Garrido, José L., Rey, Pedro J.
• Format: Journal Article
• Language: English
• Published: London Wiley 01.09.2018; Wiley Subscription Services, Inc
• Subjects: Canopies; canopy; community assembly; COMMUNITY ECOLOGY; Coniferous forests; Consistency; ecological networks; facilitation; Foreign languages; Forest communities; Forests; genetic distance; Herbivores; interaction phylogenetics; Language; missing and forbidden links; Phylogenetics; Phylogeny; Plant communities; plant community phylogeny; Plant species; probability; Probability theory; Recruitment; replacement networks; saplings; shrubs; Spain; Species; Statistical models; Stochastic processes; Woody plants; Spain
• ISSN: 0269-8463; 1365-2435
• DOI: 10.1111/1365-2435.13140

Interactions between established (canopy) and recruiting individuals (recruits) are pervasive in plant communities. Studies on recruitment in forests have mainly focused on negative density‐dependent conspecific interactions, while the outcomes of heterospecific canopy–recruit interactions have received much less attention and are generally assumed to be driven by stochastic processes. Herein, we explore the relative influence of stochastic (abundance) and deterministic (species identity and phylogenetic distance) effects on the frequency of canopy–recruit interactions and characterize the interactions in terms of their spatial consistency and effect on recruitment (depressing, neutral or enhancing). In 12 plots (50 × 50 m) of mixed pine–oak forests in southern Spain, we identified all saplings recruiting beneath 56 shrub and tree species, and in open areas not covered by woody plants. We used generalized linear mixed models to investigate the influence of stochastic and deterministic processes on the frequency of canopy–recruit interactions, on their spatial consistency and their effects on recruitment, and applied neutral null models to evaluate the spatial consistency in the occurrence of interactions across plots. Deterministic and stochastic interactions were equally common, emphasizing the prevalence of non‐neutral effects. Among the realized interactions, 36.8% enhanced recruitment, 49.05% were neutral, and 14.1% depressed recruitment. Many potential interactions (42.08%) were not observed in any study sites, presumably due to the scarcity of the interacting species. Moreover, the probability that two species formed a canopy–recruit interaction, the frequency of their interaction and the probability that the interaction had an enhancing effect on recruitment, all increased with the phylogenetic distance between the interacting species. However, the prevalence of these effects depended on the recruitment environment (heterospecific, conspecific or open). Recruitment‐enhancing interactions between heterospecifics were more consistently realized in different sites than neutral or depressing interactions. The establishment of canopy–recruit interactions (which species recruits beneath which others, and how often) is not simply determined by stochastic events. Indeed, due to their prevalence, we argue that deterministic canopy–recruit interactions are important drivers of plant community dynamics. A plain language summary is available for this article. Plain Language Summary Foreign Language Resumen Las interacciones entre plantas establecidas (“adulto”) y los juveniles que se reclutan bajo su copa (“reclutas”) son ubicuas en las comunidades forestales. Estudios del reclutamiento en bosques han abordado principalmente las interacciones intra‐específicas negativamente dependientes de la densidad, mientras que apenas se ha estudiado el resultado de interacciones entre distintas especies y se asume generalmente que se debe principalmente a procesos estocásticos. En este trabajo exploramos la influencia relativa de efectos estocásticos (abundancia) y deterministas (identidad de las especies y distancia filogenética) sobre la frecuencia de interacciones “adulto‐recluta.” Además, caracterizamos estas interacciones en términos de su consistencia espacial y efecto (inhibidor, neutro o favorecedor) sobre el reclutamiento. Para ello, identificamos los juveniles reclutados bajo 56 especies de árboles y arbustos (y en espacios al descubierto) en 12 parcelas de 50 × 50 m en bosques mixtos de pinos y quercíneas del SE de España. Empleamos modelos mixtos lineares generalizados (GLMM) para investigar la influencia de efectos estocásticos y deterministas sobre la frecuencia, consistencia espacial y efecto de las interacciones sobre el reclutamiento. Empleamos un modelo nulo para evaluar la consistencia espacial en la presencia de las interacciones entre parcelas. La frecuencia de interacciones adulto‐recluta dependió de efectos estocásticos y deterministas. Tanto la probabilidad de que dos especies interactuaran, como la frecuencia con que lo hicieron y la probabilidad de que su interacción favoreciera el reclutamiento, aumentaron con la distancia filogenética. Muchas de las interacciones posibles (42.08%) no se realizaron en ninguna de las parcelas, probablemente debido a la escasez de ambas especies. De las interacciones presentes, 36.8% favorecieron el reclutamiento, 49.05% fueron neutrales y 14.1% lo inhibieron. La frecuencia de estos efectos dependió del ambiente en que se produjo el reclutamiento (bajo conespecíficos, heteroespecíficos o al descubierto). Las interacciones favorecedoras del reclutamiento entre heteroespecíficos se encontraron más consistentemente en distintos sitios que las interacciones neutras o inhibidoras. El establecimiento de interacciones adulto‐recluta no depende simplemente de sucesos estocásticos. De hecho, estas interacciones tienen un fuerte componente determinista que les confiere un papel importante en la dinámica de las comunidades forestales.