Chapter 1 Introduction
What types of forests are considered in this textbook? What are protective forests? Why are protective forests necessary and what future challenges will they have to face? This chapter provides insights and definitions - acting as background information for the whole textbook.
This textbook is mainly based on knowledge about the protection against natural hazards of montane forests in temperate climates. These are typically either temperate coniferous forests and broadleaved or mixed forests. Figure 1.1 shows the distribution of dominant coniferous and broadleaved forests in northern Europe. In addition to the temperate forests, the boreal (tundra) forests are also covered. In principle, the described protective effects of forests are also transferable to boreal or even partly tropical forests.
Figure 1.1: Forest Type (FTY) 2018 provided by European Environment Agency (EEA) and Copernicus Land Monitoring Service.
1.1 Protective Forests in the European Alpine Space Region
Protective forests are considered as a defining element of the alpine landscape – offering natural protection against natural hazards. Such forests, mainly occuring between the submontane and the subalpine zone, represent an essential factor in the risk reduction of natural hazard processes over long periods of time on large potential natural hazard disposition areas. For thousands of years, mountain forests have been subject to a variety of demands and uses (forest pasture, litter use, snowfall, temporary arable farming, intensive use of wood for mining, etc.), which became particularly intense at the end of the Middle Ages. It was not until the end of the 18th century that French scientists recognized intensive use and clearing in the mountains as the cause of major floods “in the lowlands”. This knowledge was soon generalized and applied to the entire Alpine region.
Since the 19th century, European countries in Alpine regions are historically leader in managing protective forests. Those ecosystems and management techniques can be seen as part of European natural and technical heritage. This is because mountain forests are a major factor in reducing risk on people, infrastructure and resources from natural hazards including floods, debris floods, debris flows, snow avalanches and rockfalls. In Austria as well as South-Tyrol (Italy) about 30\(\%\), in Switzerland about 40\(\%\) (Duc and Brändli 2010) and in Bavaria even 60\(\%\) (Binder, Macher, and Müller 2019) of the forested area is designated to forests for which the prevention of gravity-driven natural hazards is the major control function.
1.2 Protective forests in Austria
Austria is covered by more than four million hectares of forest, which can be divided into 22 (9 principal) ecoregions with special regard to the regional climate and to the woodland communities that prevail due to these climatic conditions. Within these ecoregions seven altitudinal zones are distinguished from phytocoenological and climatical points of view.
Today, about 30\(\%\) of the forest area in Austria is assigned a protective function to avoid serious natural hazards, and according to the interim evaluation of the Austrian Forest Inventory, this share is increasing (Gschwantner et al. 2019). Main tree species are spruce [Picea abies] (52\(\%\)), larch [Larix decidua] (17\(\%\)),beech [Fagus sylvatica] (13\(\%\)), swiss stone pine [Pinus cembra] (7\(\%\)) and other coniferous respectively decidual trees (6\(\%\)).
In protective forests, indirect and direct protection can be distinguished (Motta and Haudemand 2000). Indirect protection refers to the general role of forests in reducing soil erosion or improving watershed condition and air quality (“Standortsschutzwald” according to the Austrian Forest Act (1975)). Direct protection forests specifically protect people or infrastructures like buildings or utility corridors (“Objektschutzwald” according to the Austrian Forest Act (1975)).
Figure (1.2) shows the distribution of forests in Austria, either covering a direct-, indirect or any protective function. The map, provided by the Austrian Federal Ministry of Agriculture, Forestry, Regions and Water Management, is based on spatial geodata that automatically identifies natural hazard processes such as rockfall, avalanches and near-surface landslides. The information is combined with the forest and endangered objects such as settlements, roads or other important infrastructure, shows potential forest areas with a direct protective function. In addition, potential forest areas that fulfill the criteria for site protection according to the Austrian Forest Act (1975) are shown in the category indirect protective function. These are primarily forests whose location is at risk from the erosive forces of wind, water or gravity. This category also includes areas that have a clearly positive, i.e. mitigating, effect on water processes such as debris flows or floods. Windbreaks that protect agricultural land from wind erosion, for example, are also included in this category.
Figure 1.2: Map of forests with direct-, indirect- and no protective functions in Austria. Information provided by the Austrian Federal Ministry of Agriculture, Forestry, Regions and Water Management.
In addition, §27 of the Austrian Forest Act (1975) regulates the so called closed forest or enclosure protective forest type [“Bannwald”]. As a result of the 2013 amendment to the Austrian Forest Act (1975), there are three categories of closed forests. A distinction is made between closed forests with direct protective function, welfare close forests and hazard defence close forests (Brawenz et al. 2015). Banning must be initiated ex officio or by application, and is enforced by decision of the forestry authority. The purpose of the ban is to protect against avalanches, rockfall, falling rocks, snow subsidence, landslides, flooding, wind or similar hazards, as well as defence against hazards caused by emissions. Other protective purposes include the protection of medicinal springs and wooded areas, which protect tourist resorts and urban centers from adverse effects on the requirements of hygiene and recreation. An overview of closed forests in Austria is given by figure (1.3), provided by the Austrian Federal Ministry of Agriculture, Forestry, Regions and Water Management.
Figure 1.3: Map of closed forests in Austria. Information provided by the Austrian Federal Ministry of Agriculture, Forestry, Regions and Water Management.
Further spatial information concerning forests and natural hazards in Austria is provided (in German only) by the Austrian “Waldatlas”