The focus of this study was to investigate the wide use of Eucalyptus spp., an exotic plant with high allelopathic ability, in the reforestation programs of urban parks in São Paulo City, Brazil, over the last century. To understand the implications of using Eucalyptus spp. in the city’s parks, this study aimed to compare nutrient cycling and litter decomposition between a mixed composition of litter (i.e., native and exotic species) and the litter of a single species (i.e., Eucalyptus). To accomplish this, newly deciduous leaves were collected from two native and two exotic species that are commonly used in the afforestation of São Paulo as well as from Eucalyptus spp. The mixed composition of litter yielded a higher dry mass loss and return of macro- and micronutrients to the forest floor. The decomposition constant (k) values were 0.00322 and 0.00207 g g−1 day−1 for the mixed composition and Eucalyptus spp., respectively. The time required for decomposition of 50 and 95% of deciduous material was 215 and 931 days, respectively, and for the mixed litterfall 334 and 1449 days, respectively, for Eucalyptus spp. Therefore, the mixed litter exhibited greater dry mass loss and nutrient cycling in an urban forest of São Paulo City, since dry mass losses as well as speed and amount of nutrients returned to the forest floor were relatively higher compared to Eucalyptus spp. Nutrient cycling via Eucalyptus spp. litter was less efficient than mixed composition of litter, demonstrating that reforestation programs carried out in the twentieth century using only one species may have had little success. The results of this work emphasize the fact that in urban reforestation programs the City of São Paulo must consider the environmental and biogeographic characteristics of the species employed and use high levels of biodiversity, since the city lies in a megadiverse biome.

中文翻译：

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二十世纪造林计划对巴西圣保罗城市森林的生态影响：一项基于凋落物和养分循环的研究

这项研究的重点是在上个世纪的巴西圣保罗城市公园的植树造林计划中，调查具有高化感能力的外来植物桉树的广泛使用。了解使用桉树的含义。在城市公园中，这项研究旨在比较枯枝落叶（即本地和外来物种）和单一物种枯枝落叶（即桉树）的混合成分之间的养分循环和凋落物分解。为此，从圣保罗和桉树的造林中常用的两种本土和两种外来物种中采集了新的落叶树叶。枯枝落叶的混合成分造成较高的干重损失，大量和微量养分返回森林。分解常数（k）值为0.00322和0。混合成分和桉树属植物分别为00207 gg-1天-1。分解50％和95％的落叶材料所需的时间分别为215天和931天，对于混合落叶来说，桉树的分解时间分别为334天和1449天。因此，混合枯枝落叶在圣保罗的城市森林中表现出更大的干燥质量损失和养分循环，因为与桉树属植物相比，干燥质量损失以及返回林地的养分的速度和数量相对较高。通过桉树种进行养分循环。垃圾的效率比混合垃圾的效率低，这表明在20世纪仅使用一种树种进行的造林计划可能收效甚微。