Nutrient fluxes in litterfall of a secondary successional alluvial rain forest in Southern Brazil

During forest succession, litterfall nutrient fluxes increase significantly. The higher inputs of organic matter and nutrients through litterfall affects positively soil fertility and the species composition, which are essential components in forest restoration and management programs. In the present study, the input of nutrients to the forest soil via litterfall components was estimated for two sites of different development stages, in an early successional alluvial rain forest in Brazil. Litterfall returned to the soil, in kg/ha, ca. 93 N, 79 Ca, 24 K, 15 Mg, 6 P, 1.7 Mn, 0.94 Fe, 0.18 Zn, 0.09 Cu and 11.2 Al, in the site where trees were more abundant and had higher values of basal area. In the other area, where trees where less abundant and values of basal area were comparatively low, litterfall returned <50% of those amounts to the forest soil, except for Al. The amount of Al that returned to the soil was similar in both areas due to the high contribution of Tibouchina pulchra (82% of Al returned). Comparatively, high proportion of three dominant native tree species (Myrsine coriacea, T. pulchra and Cecropia pachystachya) explained better litter nutrient use efficiency (mainly N and P) in the site with the least advanced successional stage. Although litterfall of these species show lower nutrient concentrations than the other tree species, their nutrient fluxes were high in both sites, indicating a certain independence from soil essential nutrients. Such feature of the native species is very advantageous and should be considered in forest restoration programs. Rev. Biol. Trop. 59 (4): 1869-1882. Epub 2011 December 01.

Durante la sucesión secundaria forestal, el flujo de nutrientes en la hojarasca se incrementa significativamente. Los altos ingresos de materia orgánica y nutrientes a través de la hojarasca afecta positivamente la fertilidad del suelo y la composición de especies, las cuales son componentes esenciales para programas de restauración forestal y de manejo. En el presente estudio, el ingreso de nutrientes a través de la hojarasca y sus componentes fueron estimados para dos sitios de una selva lluviosa atlántica aluvial en sucesión temprana. La cantidad anual de elementos que ingresan al suelo desde la vegetación más desarrollada (sitios con alta área basal y abundancia de árboles) fueron (en kg/ha): 93 N, 79 Ca, 24 K, 15 Mg, 6 P, 1.7 Mn, 0.94 Fe, 0.18 Zn, 0.09 Cu y 11.2 Al. Menos de la mitad de esas cantidades fueron aportadas por la vegetación menos desarrollada, excepto para el Al. La cantidad de Al aportada a este sitio fue similar a la contribución de la vegetación más desarrollada, debido a la contribución de: Tibouchina pulchra (82% de todo el Al aportado). La eficiencia en el uso de nutrientes de la hojarasca (principalmente de N y P) de la vegetación menos desarrollada fue superior a la eficiencia de una más desarrollada, debido a la alta proporción de tres especies nativas dominantes (Myrsine coriacea, Tibouchina pulchra y Cecropia pachystachya) en la primera. Si bien la hojarasca de esas especies presenta menor concentración de nutrientes que las otras especies arbóreas, el flujo de nutrientes fue mayor (para ambos sitios), marcando una cierta independencia de los nutrientes esenciales del suelo. Las cantidades de esas especies deberían ser consideradas con mayor atención para su uso en programas de restauración forestal.

Um novo paradigma para a aprendizagem da complexidade das relações água/solo/planta/atmosfera / A new paradigm for the learning process about the complexity of the relations water/soil/plant/atmosphere

Este ensaio compartilha as dificuldades e os caminhos percorridos, dentro de uma disciplina de pósgraduação,quando utilizado um novo paradigma para o ensino-aprendizagem das diversas relaçõesnaturais existentes dentro de ecossistemas. Para tanto no decorrer deste ensaio é realizada umafundamentação teórica que visa evidenciar as carências do paradigma cartesiano na compreensão deecossistemas naturais, ao final são propostos novos caminhos para este ensino-aprendizagem, os quaissugerem uma visão e abordagem mais holística e sistêmica acerca dos ecossistemas naturais, de forma ademonstrar a complexidade das infinitas relações presentes nos mesmos. Por meio de leituras e discussõesde textos escritos por autores que alertam para a necessidade de haver uma nova maneira de se entenderos ecossistemas naturais e ainda por meio de uma visita a um ecossistema particular na Ilha do Mel, PR,os discentes realizaram trocas de percepções, aonde foi evidenciada a diferença de percepções de ummesmo ecossistema, e apesar disto todos estavam à sua maneira representando a realidade. Foi possívelentão, observar que os alunos despertaram para a importância e necessidade de haver uma novaabordagem não só de ecossistemas naturais, mas também do próprio mundo urbano no qual vivemos.

This article shares the undertaken difficulties and approaches when a new paradigm is used for the teach-learning relations existing inside natural ecosystems. For this, throughout this essay, a theoretical justification is accomplished that aims to evidence the insufficiency of the Cartesian paradigm on understanding the natural ecosystem. New approaches are pointed out for this teach-learning, which are suggested a new vision and approach, much more holistic and systemic about the natural ecosystems, by the way to demonstrate the complexity of the infinities relations between them. Through lectures anddiscussions of texts, which were written by authors that show the necessity of having a new way to understand the naturals ecosystems and with a visit to an ecosystem in Ilha do Mel, PR, Brazil, the students realized changings of perceptions, and it was evidenced the difference between perceptions about the same ecosystem although each one represented the reality. It was possible to observe that all the students realized the importance and necessity to have a new approach, not only about the naturals ecosystems, but also about our urban world.