Rui Almeida

Instituto da Conservação da Natureza e das Florestas, IP
Av. da República, 16-16B, 1069-040 LISBOA
Summary
1- The intervention executed on the land allowed to establish a protection break strip along the middle of the property.
2- The fire behavior models changed significantly.
3- The building plans did fit in the areas of lesser forest fire fuels combustion risk.
4- The hazard  was calculated based on a forest patch that has changed significantly.
5- There is a water point of significant dimensions on the neighbor’s land.
6- The road network in the property allows accessibility from the main entrance until the lowest point in it.
7- There are conditions to create turnaround points and guarantee the circulation without problems.
8- It’s possible to have two car access entrances on the lateral borders of the property, which can be used as alternative exits.
9- The water network conditions of the plans, should be registered.

(From the Architecture Project Memorandum delivered in the Municipal City Hall)

[…] The definition of buildings’ implementations present in the Preliminary Information Request (Pedido de Informação Prévio – PIP) VO 38/2014, was accompanied by a topographic and forestal survey started by Filipe Catry (Forest Engineer, PhD) and Pedro Marrecas (Forest Engineer), later prepared and presented by PERTIS, Consultants Engineers, which established the bases for the recognition of existing native and exotic floral species, the areas to preserve and recover with its natural values to protect, with those areas that are most suitable for the implementation of the buildings.

The construction sites are located mainly in the areas previously cleared from eucalyptus (Ec) and eucalyptus-pine (EcPb). As indicated in the study ‘Characterization and Proposal of Forest Management’, the land was subsequently cleaned in these areas and the remaining property. This work allowed to verify even more accurately the implementation locations for the constructions, with slight changes to those initially foreseen. Although these changes didn’t alter the principle of the locations, they permitted to adapt the construction topography, respecting the species to preserve better.

From the Mafra Municipality land cover study on determining the forest fire hazard risk, most of the property located in ‘Carrasqueira de Cima’ – parish of Ericeira, County of Mafra – is comprised by the Land Cover 313 – Mixed Forests of conifers and deciduous in Corine Land Cover – a patch with around 17 hectares. To this patch, two types of combustible models of Rothermel are associated, models 5 and 9. These are the models that allow us to describe the behavior of fire in case of forest fires.

The intervention done on the vegetation covering the land, altered substantially the hazard conditions as can be confirmed in – http://sumedharama.pt/terreno/. In terms of composition, it was privileged the selection of maritime-pine in the highest areas of the land and all the eucalyptus was cleared, thus avoiding excessive densities. In the most humid lower zones, the cork-oak was selected, having been cleared all the other species competing for the same space, including pine and eucalyptus.

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The development of maritime-pine in the highest areas of the land, favoured the fire hazard reduction as it had already been identified in the PMDFCI (Plano Municipal de Defesa da Floresta Contra Incêndios – Forestal Defense Against Fires Municipal Plan) fire hazard chart itself. In this space it is now identified a patch of pine with about 2.7 hectare, with heights above 15 meters, which promotes shading that will prevent the development of thicket undergrowth. In this way, the vertical continuity of vegetation is broken. The eradication of the undergrowth cover in this area allowed to eliminate the combustion model 5 and the conversion of model 9 into model 8, where the progression of fires is characterised by low intensity, with short flames that advance slowly. Only very unfavourable weather conditions can turn this model dangerous.

The two big patches of eucalyptus with 1.2 and 0.8 hectares were eliminated, along with its undergrowth, preserving at the same time the maximum regeneration of oak possible. These patches will be preferably used for the implementation of the buildings, given the great reduction of the combustible mass, since the absence of vegetation and the establishment of a strategy to conduct the regeneration of cork-oak will promote the significant reduction of fire risk hazard. Also, these areas work now as an authentic mosaic providing discontinuity between forest patches, in other words, the previous potential for the occurrence of a big fire was considerably reduced with this intervention. Along the lowest zone of the property, it was performed an intense work for cleaning the thicket involving the water stream, preserving at the same time the adult samples of cor-oak now forming a forestal aggregate in the form of a grove. This will work as the first line of protection if a fire starts near the EN 616 road. In this area is evident the conversion of model 5 into model 8.

Besides the significant changes occurred on the soil vegetation cover of the property, in Carrasqueira de Cima, changes occurred simultaneously in the neighboring land where the forest is being converted into agriculture and a water pond of great dimension was created. This water point can be used by means of forest fire aerial combat. As obvious, the alterations occurred in this space eliminated a significant area of model 5, reducing this way the forest fire risk hazard of this zone.

The road network in the property is already a guarantee of the accessibility for fire combat means.  This network is characterised by a central road that crosses all the property and allows the connection between the highest and the lowest points of the property.

The property additionally presents two access alternatives , one by the most northern boundary and the other by the most southern boundary. The elimination of the two big patches of eucalyptus and the option to locate most of the buildings of the project in these areas, guarantees the possibility of establishing protection strip breaks in accordance with law regulations. The clearing of the undergrowth near the buildings ascertains a substantial  decrease of the forest fire risk, by reducing the combustible load to the values established in the Law Decree ‘anexo do DL n.º 124/2006, 28 June‘:

ANEXO

Critérios para a gestão de combustíveis no âmbito das redes secundárias de gestão de combustíveis

A) Critérios gerais – nas faixas de gestão de combustíveis envolventes aos edifícios, aglomerados populacionais, equipamentos e infraestruturas devem ser cumpridos cumulativamente os seguintes critérios:

1 – No estrato arbóreo, a distância entre as copas das árvores deve ser no mínimo de 4 m e a desramação deve ser de 50 /prct. da altura da árvore até que esta atinja os 8 m, altura a partir da qual a desramação deve alcançar no mínimo 4 m acima do solo.

2 – No estrato arbustivo e subarbustivo, o fitovolume total não pode exceder 2000 m3/ha, devendo simultaneamente ser cumpridas as seguintes condições:

a) Deve ser garantida a descontinuidade horizontal dos combustíveis entre a infraestrutura e o limite externo da faixa de gestão de combustíveis;

b) A altura máxima da vegetação é a constante do quadro n.º 1, variando em função da percentagem de cobertura do solo.

QUADRO N.º 1

3 – Os estratos arbóreo, arbustivo e subarbustivo remanescentes devem ser organizados espacialmente por forma a evitar a continuidade vertical dos diferentes estratos combustíveis.

4 – No caso de infraestruturas da rede viária às quais se associem alinhamentos arbóreos com especial valor patrimonial ou paisagístico, deve ser garantida a preservação do arvoredo a aplicação do disposto nos números anteriores numa faixa correspondente à projeção vertical dos limites das suas copas acrescida de uma faixa de largura não inferior a 10 m para cada um lado.

5 – No caso de faixas de gestão de combustível que abranjam arvoredo classificado de interesse público, zonas de proteção a edifícios e monumentos nacionais, manchas de arvoredo com especial valor patrimonial ou paisagístico ou manchas de arvoredo e outra vegetação protegida no âmbito da conservação da natureza e biodiversidade, tal como identificado em instrumento de gestão florestal, ou outros instrumentos de gestão territorial ou de gestão da Rede Natura 2000, pode a comissão municipal de defesa da floresta aprovar critérios específicos de gestão de combustíveis.B) Critérios suplementares para as faixas envolventes a edifícios – nas faixas de gestão de combustíveis envolventes aos edifícios para além do disposto no ponto A) deste anexo, devem ainda ser cumpridos, cumulativamente, os seguintes critérios:

1 – As copas das árvores e dos arbustos devem estar distanciadas no mínimo 5 m da edificação, evitando-se ainda a sua projeção sobre a cobertura do edifício.

2 – Excecionalmente, no caso de arvoredo de especial valor patrimonial ou paisagístico pode admitir-se uma distância inferior a 5 m, desde que seja reforçada a descontinuidade horizontal e vertical de combustíveis e garantida a ausência de acumulação de combustíveis na cobertura do edifício.

3 – Sempre que possível, deverá ser criada uma faixa pavimentada de 1 m a 2 m de largura, circundando todo o edifício.

4 – Não poderão ocorrer quaisquer acumulações de substâncias combustíveis, como lenha, madeira ou sobrantes de exploração florestal ou agrícola, bem como de outras substâncias altamente inflamáveis.

  Contém as alterações dos seguintes diplomas:
– DL n.º 17/2009, de 14/01
– Lei n.º 76/2017, de 17/08

  Consultar versões anteriores deste artigo:
–1ª versão: DL n.º 124/2006, de 28/06
–2ª versão: DL n.º 17/2009, de 14/01

Report by Eng. Rui Almeida.