Bioavailable Nickel and Zinc in Polluted Soil Alter the Growth of Non-pioneer Trees in the Brazilian Atlantic Forest

Background and aimsThe Brazilian Atlantic forest has been affected by the deposition of Ni and Zn, among other heavy metals adsorbed from atmospheric particles, which can be incorporated into the soil. If available in the soil, they can be absorbed by plant roots. The study aimed at testing experimentally the hypotheses: 1) Ni and Zn depositions increase their bioavailable fractions in the soil; 2) pioneer tree species demonstrate a greater potential to absorb Ni and Zn from the soil and less growth changes than non-pioneer species.MethodsThe experiment was carried out with six pioneer and non-pioneer species native to the Atlantic Forest, grown for 90 days in soil from an urban fragment of the Atlantic Forest, according to the treatments: soil with balanced fertilization (control) and soil enriched with Ni, Zn and Ni+Zn. At the end, the concentrations of Ni and Zn were determined in four soil fractions (F1: soluble; F2: linked oxides/hydroxides; F3: organic matter: F4: residual metals) and in leaves, stems/branches and roots. Mobility factors in soil, concentration ratios between treatments and respective controls, translocation index and relative growth rate in height, leaf number and total biomass were also calculated.ResultsThe results showed that Ni and Zn concentrations increased significantly in the bioavailable soil fractions (F1, F2). The absolute content of Ni and Zn in the plants directly reflected the soil level in the available forms.ConclusionsThe metal accumulation in the species occurred regardless of the successional group to which they belonged. Non-pioneer species showed greater susceptibility to the metals.

Growth and Potential of Lomatia hirsuta Forests from Stump Shoots in the Valley of El Manso/Patagonia/Argentina

Lomatia hirsuta (Lam.) Diels is a pioneer tree species that develops after wildfires, and in advanced successional stages, it is often found as a secondary species in Patagonian forests. However, in El Manso Valley, Province of Río Negro in Western Argentina, L. hirsuta forms mature pure stands, originated from stump shoots. The wood is very attractive for its colourful appearance and beautiful grain. Nevertheless, these forests are not managed for timber production, they are mostly strong thinned for grazing, and the wood is mainly used as firewood. The objective of this study was to evaluate the possibility to improve quality wood production in stands through silvicultural interventions in a sustainable way. Samples have been carried out in stands of different developmental stages. We evaluated the state and quality of the trees, and their growth has been studied by means of trunk analysis. The results indicate that there is significant potential to improve the production of quality wood in dense stands by thinning to release crop trees. Thinning should start in young stands. It also became apparent that forest management is first necessary to stabilise these nearly unattended forests.

Arbuscular mycorrhizal fungi improve the growth of pioneer tree species of tropical forests on savanna and tropical rainforest soils under nursery conditions

Background: Tropical rainforests and savannas are often spatially distributed at close distances. The combined effects of soil type and arbuscular mycorrhizal fungi (AMF) might contribute to explain the preference of tropical rainforest tree species for forest areas over those of savannas. However, few studies have examined such effects on pioneer tropical tree species. Objective: Evaluate the effects of soil type and inoculation with an AMF consortium on the growth of seedlings of pioneer tree species of tropical rainforest. Methods: A factorial 2 x 2 experiment was conducted to evaluate the role of soil type (rainforest or savanna) and native AMF consortium on growth (height and stem diameter) of four native pioneer tree seedling species under tree nursery conditions. Results and conclusions: The highest growth was detected on rainforest soils inoculated with AMF. Uninoculated plants growing on savanna soils rendered the lowest performance. AMF inoculation could be a valuable procedure in ecological restoration projects of tropical forests.

Elaeagnus umbellata (autumn olive).

E. umbellata is an important deciduous shrub which reaches up to 5 m high and 10 cm in d.b.h. It is found in thickets and sparse woods of Japan, Korea and China. E. umbellata is a shade intolerant pioneer tree and is also commonly found along riversides and seashores in Japan. This species is growing in humid areas with 1000-4000 mm of annual rainfall in Japan. In China it is reported to grow even in semi-arid areas of Nei Menggu, Gansu and Shaanxi province, where annual rainfall is around 400 mm (Niu, 1990). E. umbellata can fix nitrogen and it is tolerant to salt winds, this species is therefore used for fixation of coastal sand dunes in Japan, and is frequently planted mixed with Pinus thunbergii as a soil improving tree. E. umbellata is also planted in eroded areas of mountainous zones to re-establish and develop vegetation. In China, E. umbellata is occasionally cultivated in gardens (Zhang, 1997).

Growth and Silvicultural Potentiality of Lomatia hirsuta Forests from Stump Shoots in the Valley of El Manso/Patagonia/Argentina

Lomatia hirsuta (Lam.) Diels is a pioneer tree species that regenerates mostly after fire and is more frequently found as a secondary species in Patagonian forests dominated by Austrocedrus chilensis and Nothofagus dombeyi. However, in the El Manso Valley, Province of Río Negro in Western Argentina, L. hirsuta forms pure stands, originated from stump shoots. The wood is very attractive for its colourful appearance and beautiful grain, suitable for fine furniture. Nevertheless, these forests are not managed for timber production, they are mostly thinned for grazing, and the wood is mainly used as firewood. The objective of this study was to evaluate the possibility to improve quality wood production in stands through silvicultural interventions in a sustainable way. Samples have been carried out in dense stands of different ages and in one less dense stand with the traditional use for pastures. We evaluated the state and quality of the trees, and their growth has been studied by means of trunk analysis. The results indicate that there is a significant potential to improve the production of quality wood in dense stands through thinning oriented to crop trees. This should start in young stands, because in older stands, good form and sound trees are already considerably reduced. It also became apparent that forest management is necessary to stabilize these nearly unattended forests, which in old stands are very vulnerable to damages caused by wind and wet snow. In such stands, the extraction of trees could be combined with the planting of seed trees, with the expectation to improve the quality and vigour of the trees at maturity.

Heliocarpus donnellsmithii (majagua).

Heliocarpus donnellsmithii is a pioneer tree that can be found growing in forest edges, forest gaps, secondary forests, disturbed sites, abandoned crop and pasturelands. Mature trees can produce large amounts of seeds that are easily dispersed by wind. It is a disturbance-dependent species and its germination and seedling establishment rates are high (>60%) in open areas with high sunlight intensity. Outside its native distribution range, this species only occurs in Martinique. On this island, H. donnellsmithii is listed as a "successional activator" tree with the potential to modify the natural successional patterns.