Showing papers by "Thomas T. Veblen published in 1980"

Structure and dynamics of old-growth nothofagus forests in the valdivian andes, chile

Abstract: SUMMARY (1) Analysis of the structure of old-growth Nothofagus-dominated forests in the Valdivian Andes indicates that they are not in a steady-state condition. At midelevations the lack of saplings and of relatively small-diameter individuals clearly shows that the shade-intolerant Nothofagus spp. are not regenerating in undisturbed old-growth stands. On the other hand, the population structures and reproductive behaviour of the shade-tolerant Laurelia philippiana and Saxegothaea conspicua suggest that in the absence of massive disturbance these species would replace the Nothofagus spp. at mid-elevations. (2) The failure of succession to proceed beyond the relatively early successional phase represented by the N. dombeyi- and N. alpina-dominated forests is a consequence of a long history of periodic natural catastrophes-principally landslides and volcanic eruptions. Catastrophic mass movements in the Andes of southcentral Chile, such as those triggered by the devastating 1960 earthquake, periodically destroy or drastically alter thousands of square kilometres of old-growth forest, creating conditions favourable to the establishment of the rapidly growing Nothofagus spp. (3) Models of vegetation change which assume long-term stability of site, and postulate successional development towards a stable end-point, are not fully consistent with the regional importance of the mid-elevation Nothofagus forests of the Valdivian Andes which are maintained by catastrophes. A kinetic scheme which does not require a stable end-point for succession and which emphasizes continuous change, even in old-growth forest, is more consistent with the dynamics described for the old-growth forests of the Valdivian Andes.

Comparison of forest structure and regeneration on bench and stewart islands, new zealand

Abstract: SUMMARY: The absence of introduced browsing animals from Bench Island, located 5 km east of Stewart Island, provides the opportunity to compare forest structure and regeneration in these two areas of similar vegetation with and without browsing animals. The population structures of the main canopy tree species, rata (Metrosideros umbellata), kamahi (Weinmannia racemosa), and rimu (Dacrydium cupressinum), are similar in the areas compared. However, on Stewart Island, browsing animals, mainly white-tailed deer (Odocoileus virginianus) and the Australian brush-tailed possum (Trichosurus vulpecula), have drastically reduced the abundance of subcanopy trees and shrubs such as Pseudopanax simplex, P. crassifolius, Fucshia excorticata, Myrsine australis, Schefflera digitata, Coprosma lucida and C. foetidissima; ferns such as Phymatosorus diversifolius, Asplenium bulbiferum and herbs like Kirkophytum lyallii have likewise been reduced. The regeneration of the tree fern Dicksonia squarrosa is also severely impeded by browsing, and the generally sparse character of the understorey vegetation on Stewart Island contrasts sharply with the nearly continuous cover on Bench Island. On Stewart Island, the more open main tree canopy and greatly reduced abundance of plants in the 15-140cm tier results in greater species frequencies in the 0-15 em tier, but browsing pressure impedes their further development. Introduced browsing animals have already significantly altered the structure and floristic composition of the rata-kamahi-rimu forests on Stewart Island and their effects are likely to be more severe in the future unless animal numbers are reduced.