Today, climate change is assumed by many researchers and scholars as a certainty and is presented as the biggest challenge humanity has ever faced. It is commonly accepted that anthropogenic greenhouse gas emissions are the main cause that is accelerating the process. Therefore, it is urgent to find solutions to mitigate climate change, mainly because the intense effects have already been felt, in many cases in the form of the occurrence of extremely violent weather events. Forests are undoubtedly one of the most effective and easiest ways to provide the function of carbon sinks. However, it is essential and convenient to analyze the permanence time of this carbon in forests, because this permanence time depends directly on the forest management model used. This article aims to analyze forest management models from the perspective of carbon residence time in temperate forests, dividing the models into three types, namely carbon conservation models, carbon storage models, and carbon substitution models, according to their ability to contribute to functioning as carbon sinks, thereby contributing to the mitigation of climate change.

Portugal is a country with a territorial dimension of approximately 90,000 km². However, the forest occupies a prominent position, since it represents about 35% of the total area of the country. Portuguese people always had a very close connection with the forest, which has provided the necessary resources for the development of its communities. The geological substratum of continental Portugal is very old and may therefore have witnessed the evolution of its plants, from the early beginning to the present time, as well as all sort of historical and environmental landmarks such as glacial periods or mass extinctions. Also, from the perspective of human occupation, Portuguese territory was crossed by hunter-gatherer populations who, initially, were constantly moving and looking for sustenance, but at a later stage, chose to settle. This relationship between human populations and the forest is, thus, very old and demonstrates the interdependence between the subsistence of the populations and the resources exploitation. Currently, the main national economic groups are based on forest industries, which depend directly on the exploitation of the three dominant species, Eucalyptus globulus Labill., Pinus pinaster Aiton and Quercus suber L., demonstrating the human role in the development of the forest, motivated by the satisfaction of its needs. This work reviews the historical development of the forest in mainland Portugal, from geological times to the present, including the arrival of exotic species that later acquired invasive behaviors and now occupy significant areas of the national territory.

With climate change being a certainty, which today is probably the biggest challenge humanity is facing, and also accepting that greenhouse gas emissions are the main cause accelerating climate change, there is an urgent need to find solutions that lead to the mitigation of the already intense, and in some cases, even violent, effects. Forests can most easily work as carbon sinks. However, it is convenient to analyze the residence time of this carbon in forests, as this residence time will depend on the type of forest management used. This paper aims to analyze forest management models from a perspective of carbon residence time in forests, dividing the models into three types: carbon conservation, carbon storage, and carbon substitution. Carbon conservation models are those models in which the amounts of carbon stored only replace the carbon released, mainly by the industrial use of raw materials. Carbon storage models are models that foster the growth of forest areas to ensure that the amount of carbon stored grows, and where the ratio clearly leans towards sequestration and storage. Carbon substitution models are models that move towards the substitution of fossil carbon by renewable carbon, thus contributing to the creation of a neutral flow.

Forest ecosystems are divided into three major groups: boreal, temperate, and tropical. These can be subdivided according to the particularities of each type due to its relative location (littoral, mountain, etc.), climatic conditions, or even geological substrate. Climate change affects each type of forest ecosystem differently. However, it seems to affect temperate forests in Mediterranean-type climate regions more intensely. These regions are located over several continents, with major impacts of increased temperature during summer and decreased precipitation during winter. This situation affects Mediterranean forest ecosystems by increasing the risk of fires, which arise more frequently and are more severe. In addition, the emergence of pests and the spread of invasive species are well-known problems affecting these ecosystems. All of these conditions contribute to losses of productivity and biodiversity. To avoid the destruction of forest resources, and since Mediterranean-type climate regions are considered climate change hot spots with increased vulnerability to disturbances, the implementation of adaptive forest management models could contribute to increasing the resilience of such forests, which could also contribute to mitigating climate change.

Portuguese forests have always played an essential role in the socioeconomic development of national rural areas, but also in several forest-based industrial sectors, such as the cork, pulp and paper, and wood panels industries. In addition to these dominant sectors, there are also several other uses for forest timber, such as being the major raw materials to the production of furniture or devoted to the growing biomass pellets production industry. This review article presents the evolution of the forest industrial sector throughout the recent past, and its impact on the development of the rural environment, from a socioeconomic perspective, namely concerning the jobs and value-added creation, as well as the importance of the forest in national industrial development. It shows the importance of sustainable forest management for the development of the rural environment, as an essential sector for the creation of wealth and for the establishment of populations in the interior regions of the country.

In Portugal, some species are now considered invasive by law and have proliferated in recent years. Among these, Acacia dealbata stands out. This work investigated the behavior of this species, in order to characterize and evaluate its potential as raw material for biomass pellets production, while controlling its proliferation. It was found that A. dealbata has a large capacity for raw material supply, as cutting 2 ha resulted in about 140 tons of biomass. Thus, the attribution of a market value for this material could result in a reduction in the area occupied by the invasive species, once the demand for it increases, causing a pressure over the resource. This pressure on the species must be duly followed by other control measures, such as reducing the population and mitigating its proliferation. Laboratory tests have shown that both the raw material and the finished product are similar to those obtained with other species normally used for biomass pellet production, such as Pinus pinaster and Eucalyptus globulus. Thus, it can be concluded that there is a high potential for this species in the production of biomass pellets for energy, and that this may be an important contribution to controlling the proliferation of this invasive species.