Urban biogeographical analysis of spontaneous tree growth on stone retaining walls

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Abstract

Stone retaining walls in urban Hong Kong provided vertical habitats for spontaneous colonization by a diversified humid-tropical flora with large trees. A citywide survey assessed wall and tree characteristics to understand wall-tree relationships and identify conservation candidates. Nonparametric correlations were computed between 28 wall attributes versus tree count, tree biomass, and species-vegetation factors. Most of the 245 walls, with 1275 trees, were in residential areas. Moraceae dominated the 30 tree species, predominantly genus Ficus, and especially F. microcarpa. Natives formed the overwhelming majority, largely with pioneer and ruderal traits. The positive effect of adjacent built-up land use and negative effect of wall exposure indicated sheltering from wind could facilitate tree growth. Wall height was a key determinant as taller walls furnished more surfaces free from human disturbance and conducive to seed deposition by frugivorous birds and bats. Stone width offered more horizontal microsites for seeds to lodge. Stone roughness operated at the microscale to encourage nonarboreal vegetation. Joint attributes exerted strong influence on tree growth and less so on nontree affiliates. The walls-cum-vegetation, many older than 100 years, presented a precious natural-cum-cultural heritage, deserving protection as an urban ecological asset. Copyright © 2008 by Bellwether Publishing, Ltd. All rights reserved.

Original languageEnglish
Pages (from-to)351-373
JournalPhysical Geography
Volume29
Issue number4
DOIs
Publication statusPublished - 2008

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Citation

Jim, C. Y. (2008). Urban biogeographical analysis of spontaneous tree growth on stone retaining walls. Physical Geography, 29(4), 351-373. doi: 10.2747/0272-3646.29.4.351

Keywords

  • Heritage conservation
  • Ruderal habitat
  • Spontaneous vegetation
  • Stone wall
  • Tree flora
  • Urban ecology