Abstract
Afforestation efforts have resulted in extensive plantations of either native or non-native conifers, which in many regions has led to the spread of those conifers into surrounding natural vegetation. This process of species colonization can trigger profound changes in both community dynamics and ecosystem processes. Our study disentangled the complexity of a process of colonization in a heterogeneous landscape into a simple set of rules. We analyzed the factors that control the colonization of natural woodland ecosystems by Pinus halepensis dispersing from plantations in the Mediterranean region of Israel. We developed maximum-likelihood models to explain the densities of P. halepensis colonizing natural woodlands. Our models unravel how P. halepensis colonization is controlled by factors that determine colonization pressure by dispersing seeds and by factors that control resistance to colonization of the natural ecosystems. Our models show that the combination of different seed arrival processes from local, landscape, and regional scales determine pine establishment potential, but the relative importance of each component varied according to seed source distribution. Habitat resistance, determined by abiotic and biotic conditions, was as important as propagule input in determining the density of pine colonization. Thus, despite the fact that pine propagules disperse throughout the landscape, habitat heterogeneity within the natural ecosystems generates significant variation in the actual densities of colonized pine. Our approach provides quantitative measures of how processes at different spatial scales affect the distribution and densities of colonizing species, and a basis for projection of expected distributions. Variation in colonization rates, due to landscape-scale heterogeneity in both colonization pressure and resistance to colonization, can be expected to produce a diversity of new ecosystems. This work provides a template for understanding species colonization processes, especially in light of anthropogenic impacts, and predicting future transformation of natural ecosystems by species invasion.
Highlights
The process of species colonization is fundamental in basic ecological questions of successional, metapopulation, and community dynamics (e.g., [1,2,3]), as well as in studies of biological invasions [4], conservation [5], restoration (e.g., [6,7]) and climate change adaptation [8,9]
We present an approach to discern how processes at different spatial scales determine the patterns of species colonization in heterogeneous landscapes
Pinus halepensis colonists .50 cm tall occurred in 40% of the plots sampled
Summary
The process of species colonization is fundamental in basic ecological questions of successional, metapopulation, and community dynamics (e.g., [1,2,3]), as well as in studies of biological invasions [4], conservation [5], restoration (e.g., [6,7]) and climate change adaptation [8,9]. The factors that control plant recruitment can be structured in terms of the largescale factors that determine propagule pressure – i.e. the rate of propagule arrival (propagule number, sensu [23]) [24,25], and local factors that determine the resistance of the host community to the establishment and survival of colonists [26]. This is a useful simplification when there is limited information on all intermediate stages of the colonization process (e.g., seed dispersal, germination and establishment), or for highly variable systems (e.g., spatial heterogeneity)
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