Land use and social-ecological legacies of Rio de Janeiro's Atlantic urban forests: from charcoal production to novel ecosystems

Historical ecology is an important tool in deciphering human–environment interactions imprinted on landscapes throughout time. However, gaps of knowledge still remain regarding the land use legacies hidden in the current Atlantic Forest landscape; and also regarding how this information can help management of the remaining forest cover. The social-ecological systems framework was applied to understand charcoal production in the urban forests of Rio de Janeiro, from the nineteenth to mid-twentieth century, and their current social-ecological legacies. Charcoal production carried out by former enslaved populations, allowed for rapid forest regeneration. Forest thinning instead of forest felling was carried out by small groups in these urban remnant forests, sparing large native trees and facilitating natural regeneration. Currently, more than one thousand former charcoal production sites are accounted for hidden underneath the forest cover. The forest landscape of today is a result of novel forest successional trajectories that recovered structural and functional attributes of the forest ecosystem. However, this came at the cost of social invisibility and marginalization of these populations. The management practices of charcoal production dispersed in the landscape is one of Rio de Janeiro's most important, albeit hidden, land use legacies. Currently, the forested landscape is comprised of regenerated forests, both structurally and functionally sound, though with significant changes in species composition including the introduction of exotic species throughout recent centuries. These urban forests are today a complex mosaic of novel ecosystems, with rich biocultural diversity, and together with managed lands and well conserved forest tracts, provide not only livelihood and sustenance for forest dwelling families, but also important ecosystem services for the entire population of Rio de Janeiro. We believe that these concepts and frameworks can offer practical solutions for urban forest management, taking into account the biocultural diversity of Rio de Janeiro, increasing awareness of sustainability and promoting food security.

Large ecosystem-scale effects of restoration fail to mitigate impacts of land-use legacies in longleaf pine savannas

Ecological restoration is a global priority, with potential to reverse biodiversity declines and promote ecosystem functioning. Yet, successful restoration is challenged by lingering legacies of past land-use activities, which are pervasive on lands available for restoration. Although legacies can persist for centuries following cessation of human land uses such as agriculture, we currently lack understanding of how land-use legacies affect entire ecosystems, how they influence restoration outcomes, or whether restoration can mitigate legacy effects. Using a large-scale experiment, we evaluated how restoration by tree thinning and land-use legacies from prior cultivation and subsequent conversion to pine plantations affect fire-suppressed longleaf pine savannas. We evaluated 45 ecological properties across four categories: 1) abiotic attributes, 2) organism abundances, 3) species diversity, and 4) species interactions. The effects of restoration and land-use legacies were pervasive, shaping all categories of properties, with restoration effects roughly twice the magnitude of legacy effects. Restoration effects were of comparable magnitude in savannas with and without a history of intensive human land use; however, restoration did not mitigate numerous legacy effects present prior to restoration. As a result, savannas with a history of intensive human land use supported altered properties, especially related to soils, even after restoration. The signature of past human land-use activities can be remarkably persistent in the face of intensive restoration, influencing the outcome of restoration across diverse ecological properties. Understanding and mitigating land-use legacies will maximize the potential to restore degraded ecosystems.

Accumulation patterns of soil organic matter in forests as a legacy of historical charcoal burning

<p>Human land use and occupation often lead to a high heterogeneity of soil stratigraphy and properties in landscapes within small, clearly delimited areas. Legacy effects of past land use also are also abundant in recent forest areas. Although such land use legacies can occur on considerable fractions of the soil surface, they are hardly considered in soil mapping and inventories. The heterogenous spatial distribution of land use legacy soils challenges the quantification of their impacts on the landscape scale. Relict charcoal hearths (RCH) are a widespread example for the long-lasting effect of historical land use on soil landscapes in forests of many European countries and also northeastern USA. Soils on RCH clearly differ from surrounding forest soils in their stratigraphy and properties, and are most prominently characterized by a technogenic substrate layer with high contents of charcoal. The properties of RCH soils have recently been studied for several regions, but their relevance on the landscape scale has hardly been quantified.</p><p>We analyse and discuss the distribution and ecological relevance of land use legacy soils across scales for RCH in the state of Brandenburg, Germany, with a focus on soil organic matter (SOM) stocks. Our analysis is based on a large-scale mapping of RCH from digital elevation models (DEM), combined with modelled SOM stocks in RCH soils. The distribution of RCH soils in the study region shows heterogeneity at different scales. The large-scale variation is related to the concentration of charcoal production to specific forest areas and the small-scale accumulation pattern is related to the irregular distribution of single RCH within the charcoal production fields. Considerable fractions of the surface area are covered by RCH soils in the major charcoal production areas within the study region. The results also show that RCH can significantly contribute to the soil organic matter stocks of forests, even for areas where they cover only a small fraction of the soil surface. The study highlights that considering land use legacy effects can be relevant for the results of soil mapping and inventories; and that prospecting and mapping land use legacies from DEM can contribute to improving such approaches.</p>