Long-term expansion of juniper populations in managed landscapes: patterns in space and time

1. 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. 2. 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 expan-sion patterns, including elevation, initial density and distance to remnant forests. 3. 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 nucle-ated colonization patterns emerge driven by vertebrate seed dispersal. 4. The photointerpretation of aerial images in combination with in situ measurements has yielde