Long-term expansion of juniper populations in managed landscapes: patterns in space and time
Article first published online: 20 AUG 2014
© 2014 The Authors. Journal of Ecology © 2014 British Ecological Society
How to Cite
García, C., Moracho, E., Díaz-Delgado, R., Jordano, P. (2014), Long-term expansion of juniper populations in managed landscapes: patterns in space and time. Journal of Ecology. doi: 10.1111/1365-2745.12297
- Article first published online: 20 AUG 2014
- Manuscript Accepted: 14 JUL 2014
- Manuscript Received: 16 JUN 2014
- Fundação para a Ciência e a Tecnologia (FCT). Grant Number: PTDC/BIA-ECS/116521/2010
- European Program COMPETE. Grant Number: FCOMP-01-0124-FEDER-019772
- ‘Genomics and Evolutionary Biology’
- North Portugal Regional Operational Programme 2007/2013. Grant Number: ON.2 – O Novo Norte
- National Strategic Reference Framework (NSRF)
- European Regional Development Fund (ERDF)
- Ministerio de Ciencia y Tecnología (MICINN). Grant Number: BES-2011 044380
- Junta de Andalucía Excellence. Grant Number: RNM-5731
- Ministry of Environment and Junta de Andalucía
- ecological correlates;
- generalized additive mixed models;
- historical forest fragmentation;
- Juniperus phoenicea subsp. turbinata;
- long-term demographic trends;
- plant population and community dynamics;
- spatial statistics
- Forest cover has increased world-wide over the last decade despite continuous forest fragmentation. However, a lack of long-term demographic data hinders our understanding of the spatial dynamics of colonization in remnant populations inhabiting recently protected areas or set-aside rural lands.
- We investigated the population expansion of the Phoenician juniper (Juniperus phoenicea subsp. turbinata), which is an endozoochorous Mediterranean tree species inhabiting landscapes that have been managed for many centuries. By combining the photointerpretation of aerial photos that have been taken over the last 50 years with in situ sampling and spatial analyses of replicated plots, we estimated the population growth over the chronosequence; identified hotspots, coldspots and outliers of regeneration; and assessed the roles of key environmental factors in driving demographic expansion patterns, including elevation, initial density and distance to remnant forests.
- Ecological factors leading to seed limitation, such as initial plant density, are expected to drive colonization patterns at the early stages. Factors mediating the competition for limiting resources, such as water availability, would prevail at later stages of expansion. We further expect that nucleated colonization patterns emerge driven by vertebrate seed dispersal.
- The photointerpretation of aerial images in combination with in situ measurements has yielded reliable density data. Overall, our results show a marked demographic expansion during the first decade followed by a period of steady and heterogeneous population growth with signs of local population decline. We found evidence of nucleated establishment patterns as expected for an endozoochorous species. Hotspots and outliers of regeneration emerged throughout the study chronosequence, whereas coldspots of regeneration only appeared at advanced colonization stages. Factors influencing dispersal limitation had contrasting effects at different colonization stages, and the initial density influenced population growth at various spatial scales.
- Synthesis. The photointerpretation of aerial images shows that the influence of dispersal limitation versus factors mediating competitive responses changes throughout colonization stages. Whereas dispersal limitation is the main factor influencing colonization at early stages, competition for local resources controls population growth at later stages. Therefore, long-term studies are required to capture the overall combined influence of key ecological factors in shaping long-term spatial demographic trends.