Urban ecological networks are defined differently in ecology, urban planning and landscape ecology, but they all have linearity and linkage in common. Early urban representations evolved from the constraints of deep ecological structure in the landscape to built elements that must work around natural linear obstacles-rivers, coastlines, dunes, cliffs, hills and valley swamps. Village commons were linked by roads. The Industrial Revolution led to accelerating urban growth, where the role of open space focussed on public health and transport. The Renaissance, Baroque and Picturesque movements accentuated networks in wooded parks, boulevards and sweeping riverine vistas. These provided a new aesthetic and sense of grandeur in the urban centres of European empires and later their colonies. Grafted onto this visual connectivity has been an awakened ecological understanding of spatial dynamics. The emergent notion of ecological corridor functionality provided support for green linear features, although initially this was based on untested theory. The idea of organisms moving along green highways seemed logical, but only recently has unequivocal empirical evidence emerged that demonstrates this functionality. Nevertheless, the main role of corridors may be to provide habitat rather than to act as connectors of nodal habitats. Most organisms can utilise stepping stones, and these may accommodate desired meta-populations while deterring pest movement. Swale drains and treatment wetlands provide riparian services and serve as biodiversity corridors. However, to most people the obvious function is visual-providing green fingers through what would otherwise be urban grey. The health benefits of these are have been demonstrated to be psychological as much as biophysical.
Abs~ract. Size and age structure were used to reconstruct the population dynamics of two forested stan~s m ~he western <;ascade Range, Oregon, US~. Tre~s with different growth rates and size-age relatiOnships occ':'rred m the same stand. The relationships between diameter and age of 939 aged t~ees o~ four specres; ~lth~ugh stat~stically significant, were often weak. Data on both age and spatial dispersion adde~ cntical mformation on stand dynamics not available from size alone.. The population Stf';'Ctures and regeneration patterns described were strongly influenced by natural disturbances and speci~s' life hi~tory characteristics. Periodic fires of variable intensity and extent ~ave produced a n;tosaic of relative_ly even-a~ed patches of different conifer species. The early estabhshment and domm~nc~ by a_ species on a Site was a determinant of subsequent forest regeneration. I~ ~seudotsug_a menz1esu dommated early, regeneration of Tsuga heterophyl/a, and often Abies amabllls, was rapid. If, however, Tsuga heterophylla established first, further regeneration of other species was absent or minimal until canopy openings formed.
Size and age structure analysis, dated past disturbances, treefall replacement patterns, and spatial pattern analysis were used to reconstruct the developmental history of two old-growth Nothofagus fusca/ N. menziesii stands, South Island, New Zealand. Diameter and height class distributions suggested that N. menziesii was replacing N. fusca, however, stand history reconstruction analysis showed that both species had regenerated intermittently after small-scale disturbances. Although large-scale disturbances such as blowdowns may occasionally generate even-aged stands, gap-phase regeneration maintains the forests in compositional equilibrium. In the absence of other competing tree species and understorey plants the two species appear to coexist by way of different life history strategies, where one species (N. menziesii) has low juvenile mortality and the other (N. fusca) has faster height growth rates and greater longevity and adult survivorship.
The temporal and spatial patterns of tree establishment and stand disturbance history are often based on the interpretation of age-class frequency distributions. In particular, the presence of even-aged groups of trees is often used as compelling evidence of past disturbance. However, even-aged groups of trees may be indistinguishable in an age distribution if several different-aged patches occur, especially if their ages overlap. For two different types of forest we used spatial autocorrelation analysis to statistically test for the presence of even-aged patches in tree age data. Ordination and cluster analysis were subsequently applied to a matrix of association measures that reflected both spatial proximity and age similarity to identify even-aged groups of trees. Although the method worked well for our forests, which contained light-demanding tree species, it is likely to be less applicable to forests dominated by shade-tolerant species, because trees may be of many different ages if they were present as suppressed individuals prior to disturbance. However, in these instances the method could be usefully applied in other types of analysis, such as the distribution of growth release dates, tree-fall or fire-scar dates, and growth rates.
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