Soil and vegetation characteristics of some tree windthrow features in a South Westland rimu forest

Abstract

The effects of tree windthrow on soil properties and vegetation were studied in an area of rimu (Dacrydium cupressinum) forest on a dissected glacial outwash surface in Saltwater State Forest, South Westland, New Zealand. Tree windthrow and the resulting formation of surface pits and mounds caused a redirection of pedogenesis, particularly on relatively better-drained low ridges; there, the normal development of a gleyed yellow-brown earth profile was altered towards organic soils in the pits and podzolised yellow-brown earths on the windthrow mounds. In poorly drained backswamps, organic soils also formed in the pits, while gleying processes predominated in both the windthrow mound soil and the adjacent unmodified soil. The sequence of vegetation development was different on windthrow pits compared with mounds. Mounds were rapidly colonised by ground-cover plants, especially ferns and tree ferns. These were subsequently replaced by broad leaved trees, particularly kamahi (Weinmannia racemosa). Pits usually pond with water. Plant litter then fills the pits within 30 years. The pit sites are subsequently colonised by vascular plants, but the succession involved is not clear. In this high rainfall environment, pits and mounds become unrecognisable on the land surface within about 100 years. Windthrow contributes to the currently observed soil pattern in these forests.

Modeling the effects of vegetation‐erosion coupling on landscape evolution

“…Sala and Calvo (1990) attributed differences in runoff quantities between a coniferous and deciduous forest, in part, to the abundance of litter in the latter and the associated storage of moisture. Of the treethrow pits investigated by Adams and Norton (1991), most contained some water, although Putz (1983) noted that none in the studied Panamanian treefall pits were ponded, even after a storm that delivered 10 cm of water in less than three hours -a result of the soil's high conductivity.…”

Relationships between pteridophytes and topography in a lowland South Westland podocarp forest

“…Palmer (1990) suggested that variation in species cover on the small scale is unrelated to variation on the large scale, with small scale variation being due to localised stochastic events such as death of canopy trees and decay of woody debris. A similar pattern appears to be happening in South Westland forests, where Adams & Norton (1991) have suggested that "anomalous" plant distributions may be related to the presence of old tree windthrow mounds providing better drained microsites on otherwise poorly drained landforms.…”

“…Paesia scaberula, Histiopteris incisa, and Hypolepis millefolium have been recorded on mounds associated with tree windthrows (Adams & Norton 1991), but are usually absent under closed forest canopies. Windthrow mounds can also be preferential establishment sites for the tree ferns Dicksonia squarrosa and Cyathea smithii.…”

New Zealand forest dynamics: a review of past and present vegetation responses to disturbance, and development of conceptual forest models

“…Payton et al 1984), W. racemosa enters a site under a Myrtaceaous canopy following disturbances such as fire, often with Knightia excelsa as a co-dominant (Richardson et al 2014). In these successions, W. racemosa also persists in mature forest by colonising smaller gaps and root-plate mounds following tree falls, through epiphytic establishment on tree fern trunks, and via resprouting (Adams & Norton 1991;Smale et al 1997;Ogden et al 2005;Gaxiola et al 2008). In Northland and the Coromandel Peninsula Weinmannia sylvicola performs a similar ecological role to that of W. racemosa elsewhere (Leathwick & Rogers 1996), also establishing following disturbances, in canopy gaps, and through epiphytic establishment on tree fern trunks.…”

“…Beilschmiedia tarairi is dominant north of Auckland in the North Island, while Beilschmiedia tawa occurs throughout the North Island and the north of the South Island. In these forests light-demanding species, including conifers such as D. cupressinum, persist over generations by colonising areas after small disturbances, such as tree-falls (Adams & Norton 1991). Such gaps are initially colonised by tree ferns, particularly Dicksonia squarrosa, followed by light-demanding broadleaved species such as W. racemosa, under which conifers may establish (Beveridge 1973;Smale et al 1997).…”