Detrimental effects of vines on tree growth in successional environments have been frequently reported. Little is known, however, about the relative importance of below and aboveground competition from vines on tree growth. The objective of this study was to quantify and compare the growth responses of Liquidambar styraciflua saplings to below and/or aboveground competition with the exotic evergreen vine, Lonicera japonica (Japanese honeysuckle), and the native deciduous vine, Parthenocissus quinquefolia (Virginia creeper). Soil trenching and/or vine-trellising were used to control the type of vine competition experienced by trees. Comparisons among untrenched treatments tested for effects of belowground competition. Comparisons among trenched treatments tested for effects of aboveground competition. After two growing seasons, Lonicera japonica had a greater effect on the growth of L. styraciflua than did P. quinquefolia. This effect was largely due to root competition, as canopy competition only had a negative effect on tree growth when it occurred in combination with root competition. Leaf expansion was consistently and similarly affected by all treatments which involved belowground competition.
The role of Brazilian pine (Araucaria angustifolia) in the process of forest succession is a topic of increasing controversy. While some authors consider the species to be pioneer, others consider it to be a climax species in relict temperate forests. We designed a field experiment to assess the role of light availability on the regeneration of A. angustifolia. The following three forests, with contrasting patterns of the species regeneration, were selected at a National Forest in southern Brazil: a Pinus plantation, an Araucaria plantation and a native araucarian forest. We analysed the population structure of Brazilian pine, the vegetation architecture, the light regime experienced by seedlings and the height growth of seedlings and sprouts. Brazilian pine colonisation and regeneration were observed in the Pinus and Araucaria plantations, respectively. No seedlings were found in the native forest. The greatest foliage area index and canopy cover were found in the native forest and the smallest in the Pinus plantation. In spite of the architectural differences, the native forest and the Araucaria plantation had similar light conditions and they both had lower levels of irradiances than the Pinus plantation. Seedlings and sprouts of Brazilian pine were found to occupy spots in the Araucaria plantation with canopy cover greater than the average forest conditions. Considering the similarity of understorey light conditions between the Araucaria plantation and the native forest (where no regeneration was taking place), we concluded that light availability was not limiting the regeneration of the species. Tolerance to shading and other aspects of the species indicate that Brazilian pine is not strictly heliophyllous and pioneer and is able to be established in the forest understorey.
Brazilian pine (Araucaria angustifolia [Bert.]
O.Ktze.) is an indigenous conifer of the southern region of South America,
typically regarded as a sun-loving species. However, there is insufficient
information on the species’ behaviour under different irradiances to
characterise its plasticity to light. The purpose of this work was to measure
some ecophysiological responses of Brazilian pine seedlings to three
irradiance levels: 100, 45 and 10% full sunlight. Thirty seedlings were
grown under each of the irradiance treatments and, after 5 months, growth
parameters, leaf chlorophyll concentration and in vivo
nitrate reductase activity, in both leaves and roots, were analysed. There was
no increase in shoot biomass allocation in response to shading, in contrast to
results from other experiments. Only low-light seedlings showed significant
increase in specific leaf area, as well as in the ratio of height to shoot
biomass. Chlorophyll content and the ratio of chlorophyll
a to chlorophyll b did not vary
among treatments. Nitrate reductase activity was detected only in roots and
was reduced in the low-light treatment. An overall analysis of the results
points to a normal growth of Brazilian pine seedlings at both high- and
medium-light sites, at least in their initial stages of development.
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