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Assessing the integrated effects of landscape fragmentation on plants and plant communities: the challenge of multiprocess–multiresponse dynamics

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Summary

  1. When human activities change the landscape, several processes affecting remnant vegetation take place simultaneously: there is less suitable habitat, populations become isolated and the environmental conditions of the fragments frequently shift. Such changes affect vegetation in different ways – populations become smaller, the genetic exchanges between populations decline and species interactions are altered. The combination of processes taking place during fragmentation and their subsequent consequences generate a large variety of responses, positive and negative, among plants and plant communities.
  2. To assess the integrated effects of the processes taking place as a result of fragmentation (isolation, edge effects, fragment size and time since fragmentation) on organisms, we conducted a hierarchical meta-analysis of the studies reporting the effects of landscape fragmentation on plant species and plant communities. Our review included 259 peer-reviewed journal articles and 990 data entries.
  3. We found the frequency of reports of positive and negative responses to fragmentation were comparable but largely variable. Negative effects of fragmentation due to isolation, edge effects and fragment size were significant; but only edge effects and fragment size had significant positive effects. When looking at specific types of responses to isolation, we found negative effects on density, fecundity, colonization, succession rates and species richness, while positive effects were found on fecundity, herbivory/predation and colonization. Positive responses to edge effects were significant for density, fecundity, survival, growth and richness, and significantly negative for density, survival, colonization and richness. Effects of patch size were mostly significant for both positive and negative responses.
  4. We also assessed the effects of landscape fragmentation for different attributes of the studied system and found no differences among biomes, vegetation types, functional groups or life stages.
  5. Synthesis. Results of this integrated assessment indicate that broad generalizations about the effects of fragmentation on remnant vegetation may not be possible due the large variety of processes and responses associated with fragmentation. Results also identified key knowledge gaps, and areas of research needed to improve assessment and future management of plant species and plant communities in fragmented landscapes (e.g. lag effects, the role of the matrix and the patch quality and integrated effects along life cycles).

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