Co-dominant Tree Species Research Articles

Light environment and tree development of young Acacia melanoxylon in mixed-species regrowth forest, Tasmania, Australia

Blackwood ( Acacia melanoxylon R. Br.) is a valuable leguminous cabinetwood species which is commonly found as a canopy or subcanopy tree in a broad range of mixed-species moist forests on tablelands and coastal escarpments in eastern Australia. This paper reports on the competitive light environment of a commercially valuable multi-species regrowth forest in NW Tasmania, in order to define some of the functional interactions and competitive dynamics of these stands. Comparative observations were made of the internal forest light environment in response to small-gap silvicultural treatments, in a young regenerative mix of three codominant tree species. Light measurements were made during periods of maximum external irradiance of the regrowth Eucalyptus obliqua/ A. melanoxylon forest canopy at age 10.5 years. This was at a time of vigourous stand development, 4.5 years following the application of three experimental silvicultural treatments whose effects were observed in comparison with an untreated canopy sample designed as a control. Minimal irradiance was observed within and beneath the dense subcanopy of the native nurse species ( Pomaderris apetala) which closely surrounds young blackwood regeneration. Unlike current plantation nurse systems, the dense foliage of the native broadleaved Pomaderris all but eliminated direct side-light and low-angle illumination of the young blackwood, from the beginning of tree establishment. The results demonstrated that retention of these densely stocked native codominants effectively suppressed both size and frequency of blackwood branches on the lower bole, through effective and persistent interception of sunlight. Vigorous young blackwood crowns later overtopped the codominant nurse species, achieving a predictable height of branch-free bole. This competitive outcome offers a valuable tool for management of blackwood crown dynamics, stem form and branch habit through manipulation of light environment in young native regrowth systems. Results demonstrate that effective self-pruning in the lower bole of blackwood is achieved through a marked reduction in direct and diffuse sunlight incident on the lower crown, notably to less than 10–15% of full sunlight intensity during conditions of maximum insolation. The results also contain insights for the improved design of mixed-species plantation nurse systems using these or functionally similar species’ combinations. Based on evidence presented here for native regrowth forest, plantation nurse systems for blackwood will need to achieve 85–90% interception of external side-light during early years of tree development if self-pruning is to emulate the results achieved in the native nurse system.

Danish deciduous forest types

In this study, the first comprehensive multivariate statistical analysis of Danish native forest vegetation, based on 1768 sample plots, is presented. Data were composed of data from literature sources and newly collected data. A series of cluster analyses resulted in 24 forest community types, grouped in beech (Fagus sylvatica), oak (Quercus robur-Q. petraea), hornbeam (Carpinus betulus), alder-ash (Alnus-Fraxinus) and lime (Tilia cordata, T. platyphyllos) types, in addition to mixed forest communities with several co-dominant tree species. The described communities are provisionally arranged syntaxonomically, when possible, according to the international phytosociological system. The distribution of ecological indicator values of pH, soil moisture and nitrogen is gradual in relation to the perceived plant communities. Many forest types, such as beech and oak dominated types, obtain indicated values for pH that span most of the indicated gradient. It is suggested that natural Danish forests probably would be composed of a multitude of canopy forming tree species. The present stands with one or a few tree species forming the canopy is the result of long anthropogenic influence and selective logging.

Phosphorus acquisition in the soil-root system of Eucalyptus pilularis Sm. seedlings. I. Characteristics of the soil system

An ancient sand-dune system located in the Myall Lakes National Park, N.S.W. (32�28'S., 152�30' E.) supports an open eucalypt forest with Eucalyptus pilularis as one of the co-dominant tree species. Profile development of the sand mass is typical of a light humic podzol. The relative pool sizes of available nutrients contained by the acidic podzol were such that phosphorus was the most limiting for the growth of E. pilularis seedlings. The bulk of seedling phosphorus was assimilated from the A, horizon of this podzol. Soil from the A, horizon was characterized by a low total level of phosphorus (= 30 �g P g-1 soil). Approximately 90% of this phosphorus was 0.1 M H2SO4 insoluble and probably organic in nature. In addition, 30% of the total phosphorus was associated with compounds containing aluminium and iron. The concentration of soluble phosphorus in the soil solution (CaCl2, extractable) was 0.36 �g P g-1 soil. Although this value is comparable to those reported for fertile soils, the amount of readily exchangeable phosphorus was found to be very low (1.43 �g P g-1 soil). Anion exchange resin studies indicated that after this pool was exhausted, release of phosphorus from slowly available sources was extremely limited (0.013 �g P g-1 soil h-1). Studies showed that transfer of phosphorus to seedling roots in A, horizon soil was predominantly a diffusive process. Moreover, the effective diffusion coefficient for phosphate (10.81 x 10-8 cm2 s-1) indicated that this process was comparatively fast.

Short-Term Changes in a Cottonwood-Ash-Willow Association on a Grazed and an Ungrazed Portion of Little Ash Creek in Central Arizona

Recovery of a cottonwood-ash-willow assochttion from overgrazing has been extremely limited over a Qyear period. Seedling reproduction and herbaceous cover has increased; however, overstory tree species composition has not changed. Tree growth was not affected by grazing. The younger, associated, codominant tree species differed in composition between the grazed and ongrazed plots.