Data from: Uncovering biodiversity deficits: experimental evidence for dispersal limitation of woody species in Mediterranean forest patches

Deforestation and habitat disturbance are major drivers of local species
extinctions within remnant forest patches. In plants, seed dispersal plays
a key role in recolonising patches following disturbance; however, habitat
fragmentation may hinder seed arrival to suitable but unoccupied patches,
resulting in dispersal limitation and prolonged biodiversity deficits. We
assessed dispersal limitation in Mediterranean forest patches by
experimentally introducing plant species from the regional pool. To do so,
we sowed 61,000 seeds from ten woody species and compared their
establishment between occupied and unoccupied patches, assessing whether
absences were driven by habitat unsuitability or dispersal limitation. We
included five dry- and five fleshy-fruited species to test whether
dispersal mechanisms influenced dispersal limitation. Additionally, we
evaluated major biotic (vertebrate granivores and herbivores) and abiotic
(soil properties and moisture) factors that could act as ecological
filters in unoccupied areas. Finally, we planted saplings of four species
to assess survival at later life stages and test the effectiveness of
planting as a restoration strategy. On average, both dry- and
fleshy-fruited species exhibited similar establishment rates in occupied
and unoccupied patches, indicating that species absences were primarily
due to dispersal limitation rather than to habitat unsuitability.
Vertebrate antagonists had similar effects across patch occupancy levels,
overall reducing establishment. Soil properties and moisture did not
differ in ways that would limit establishment in unoccupied patches.
Finally, planted saplings had similar or higher survival in unoccupied
patches, indicating habitat suitability also in later life stages. Our
experiments uncover diversity deficits of woody plants in forest patches
driven by dispersal limitation, irrespective of the species’ dispersal
mechanisms. In general, neither biotic nor abiotic filters significantly
constrained the establishment of introduced species in unoccupied patches.
Synthesis and applications: Mediterranean forest patches in highly altered
landscapes may harbour greater woody plant diversity than currently
observed, suggesting ongoing dispersal limitation. Assisted colonization
through plant introductions can effectively restore this missing plant
diversity.