The decreased competition in expanding versus mature juniper woodlands is counteracted by adverse climatic effects on growth

Abstract

World-wide deforestation is being reversed in Mediterranean continental areas, where abandonment of traditional practises favours the expansion of valuable habitats, like Juniperus thurifera woodlands. We hypothesised that pre-existing trees facilitate establishment in expanding woodlands, whereas in mature woodlands, competition leads to patch disaggregation. We compared the imprint of these processes on growth, demographic and spatial structure of expanding and mature J. thurifera woodlands. We selected plots where we geopositioned, aged and quantified the morphological characteristics of all trees. In the mature woodland, trees arranged in clumps and randomly in the expanding woodland. Competition negatively affected growth, was greater in the mature woodland and led to disaggregation of juvenile clumps. Differences in growth between the mature and the expanding woodland disappeared in climatically unfavourable years, suggesting that adverse climate constrains growth more in expanding than in mature woodlands. We suggest that change in the dispersal agents and a decrease of facilitation underlay differences in spatial patters between the expanding and the mature woodland. Observed effective recruitment in less than 30 years into the expanding woodland evidenced that propagule arrival and sapling survival do not constrain woodland expansion. Furthermore, growth of juveniles established in these new areas is favoured by reduced intraspecific competition. However, we expect growth in expanding woodlands to be negatively impacted by climate change. We conclude that under current global change scenario, conservation of J. thurifera woodlands is favoured by changes in land use, but greater frequency and severity of drier than usual episodes could hamper natural reforestation.

What causes conspecific plant aggregation? Disentangling the role of dispersal, habitat heterogeneity and plant–plant interactions

“…This is shown by the prevalence of IPC models characterizing the empirical pattern of adults in all populations. It is commonly assumed that positive spatial associations between plants at a certain scale are the result of facilitative interactions (Haase et al , Zhu et al , Gimeno et al ). However, our study shows that this is not necessarily the case and that the aggregated patterns found in S. ciliata adults are most likely derived from seed‐dispersal limitation and recruitment patterns generated in early life stages.…”

“…The determining role of plant–plant interactions in the spatial distribution of individuals within populations highlights the importance of the local neighbourhood context for plant fitness, demography and ecosystem processes (Theodose and Bowman , Jones and Comita , McIntire and Fajardo ). In this context, facilitative interactions among conspecific plants are usually considered a key driver of spatial aggregation patterns observed among plants at short scales (Haase et al , Montesinos et al , Zhu et al , Gimeno et al ). Yet, intra‐specific associations can additionally be driven by either inter‐specific biotic interactions (e.g.…”

From flower to fruit: ecological and evolutionary implications of abiotic and biotic factors affecting Juniperus thurifera L. cone development

“…However, the opposite pattern is occurring in developed countries, where urbanization and agricultural intensification are leading to the abandonment of low productivity lands and cessation of traditional management practices . As a result, secondary succession is altering large tracts of land , Gimeno et al 2012a, open areas encroachment (DeSoto et al 2010, Ewers et al 2013, the expansion of woodlands into abandoned lands (Gimeno et al 2012b), forest densification (Rey , modification of perturbation patterns (Rey and changes in forest composition . These changes are driving shifts in the abundance of different community components and ecosystem processes (Laiolo et al 2004, Sirami et al 2008, Herrando et al 2016.…”

“…Changes in forest structure and composition after abandonment modify competition levels among adult trees (Gimeno et al 2012b). On the one hand, forest densification increases competition among conspecifics , while at the same time the colonization of forests by other woody species can intensify interspecific competition (Costa et al 1997, Montesinos andFabado 2015).…”

“…Como resultado, se está produciendo la expansión de los bosques hacia antiguos campos de cultivo (Gimeno et al 2012), la densificación de las masas forestales (Rey ) o cambiando su composición específica . Por un lado, estos cambios en la estructura de los bosques llevan a una mayor competencia por los recursos, a nivel intraespecífico por la densificación ) e interespecífico por la entrada de nuevas especies (Costa et al 1997, Montesinos andFabado 2015).…”