Climate change impacts on water resources of a forested karst catchment in Austria

The Northern Limestone Alps are characterized by shallow soils which are vulnerable to nutrient loss and erosion once the forest cover is damaged. Since many settlements in the region depend on high quality drinking water supply stemming from forested headwaters, forest functions such as water retention and filtering of pollutants have to be maintained and even restored where necessary.
During the 19th century until today temperature has risen by almost 2°C in the European Alps. In the study area, which is representative for the Northern Limestone Alps in Upper Austria, a further increase of 2-5 °C is predicted until 2100, with highest increase in summer. The expected precipitation changes (up to approx. 20% increase in winter and the same range of decrease in summer), though predictions as to the latter are still rather uncertain, might cause drier summers and wetter winters and early springs.
The forests of the Northern Limestone Alps will be affected by further climatic changes. Norway spruce is the most abundant tree species in Austria but is also the most vulnerable to additional temperature increase. Many forest sites at lower to middle altitudes will not be suitable for Norway spruce in the future. Also in the present the homogeneous spruce plantations created at natural beech forest sites can be regarded as highly vulnerable and instable. At higher altitudes however, Norway spruce might even experience growth stimulation. However, a particular risk in all spruce forests is the increase of bark beetle infestations, very probable driven by climate warming, on large spatial scales causing both damage to forest ecosystem functions and less economic return for forest owners.
Forest management affects water quality in various ways. The prevalent Norway spruce management has led to even-aged, homogeneous forests. These forests are less resilient than mixed conifer-deciduous forests and therefore face stronger and more frequent disturbances. Moreover, the usual management of Norway spruce forests is done with clear-cuts or shelterwood-cuts potentially causing a contamination of water pollution. With regard to nitrate, but most probably also regarding turbidity, expected climate change will enhance the negative effects of these management interventions to water quality. An adequate management option for optimizing water protection, which is particularly important in water protected areas, is therefore the creation of mixed forest stands which includes a wider range of naturally occurring tree species and the establishment of a continuous cover forest management system. Those two goals are part of an overall Best Practice catalogue for forest management in drinking water protected areas. Particularly in the light of expected climate change effects to forests, an adaptation towards such a management system is recommended.

The Forest Service of Upper Austria is responsible for forest management planning in the entire province and the local foresters implement management plans at the very local scale. Both parties were involved in model building, the definition of concrete forest management scenarios and checked the plausibility of the model results. Jointly prepared training courses offered forest landowners respectively managers and farmers an opportunity to discuss climate change adaptation options. Since we focused on forest-water relations, experts and local authorities in the water sector also participated in the discussions. Further outreach took place through an international workshop.

The forests of the Northern Limestone Alps will be affected by further climatic changes. Norway spruce is the most abundant tree species in Austria but is also the most vulnerable to additional temperature increase. Many forest sites at lower to middle altitudes will not be suitable for Norway spruce in the future. Also in the present the homogeneous spruce plantations created at natural beech forest sites can be regarded as highly vulnerable and instable.

At higher altitudes however, Norway spruce might even experience growth stimulation. However, a particular risk in all spruce forests is the increase of bark beetle infestations, very probable driven by climate warming, on large spatial scales causing both damage to forest ecosystem functions and less
economic return for forest owners.

Forest management affects water quality in various ways. The prevalent Norway spruce management has led to even-aged, homogeneous forests. These forests are less resilient than mixed conifer-deciduous forests and therefore face stronger and more frequent disturbances. Moreover, the usual management of Norway spruce forests is done with clear-cuts or shelterwood-cuts potentially causing a contamination of water pollution. With regard to nitrate, but most probably also regarding turbidity, expected climate change will enhance the negative effects of these management interventions to water quality. An adequate management option for optimizing water protection, which is particularly important in water protected areas, is therefore the creation of mixed forest stands which includes a wider range of naturally occurring tree species and the establishment of a continuous cover forest management system. Those two goals are part of an overall Best Practice catalogue for forest management in drinking water protected areas. Particularly in the light of expected climate change effects to forests, an adaptation towards such a management system is recommended.

A number of constraints exist as to the adaptation of forest management in water protected areas. Since in many cases even-aged Norway spruce forest plantations predominate, the transformation into mixed forests is a long-term task. Educated personnel have to be built up, the appropriate planning instruments have to be made available and a monitoring and evaluation system has to be established in order to guarantee a continuous adaptation of forest management. Secondly, different user interests exist in headwater areas which might counteract continuous cover forest management. In major parts of the forests in the State of Upper Austria tree regeneration is suppressed significantly due to browsing damages caused by elevated wild ungulate populations. Hunting management is therefore as important as forest management if adaptation to climate change has to succeed. Economic constraints are the third issue. The establishment of mixed forests and a continuous cover forest management system leads to less economic return for the forest owners. This is a constraint against adaptation, particularly if the headwaters are not owned by the community so that different interests compete against each other. Hence in many cases forest management adaptation towards an optimization of water quality needs a compensation payment to the forest owner. Though financial subsidies can improve the adaptive capacity to climatic changes of the forestry in water protected areas, it is still very important to raise the awareness among forest owners, headwater managers and the local water works in the communities.

Uncertainty as to the magnitude of climate change effects is significant. Adaptation will therefore be a dynamic process rather than a single decision. The availability and the usage of the most recent modeled climate pathways would have clear benefits. However, this is novel to most local forest managers and regional forest services. Firstly this data has to be made available in an understandable way and in a meaningful resolution. Secondly, training is necessary as to how climate scenario data can be used efficiently.

Forest Service of Upper Austria:
forest management planning in the entire province; model building; definition of concrete forest management scenarios; training courses for forest landowners, managers and farmers
Local foresters:
implementation of management plans at local scale; model building; definition of concrete forest management scenarios; training courses for forest landowners, managers and farmers
Experts and local authorities:
Participation in discussions
International workshop

Decisive factors:
Drinking water protection

Limiting factors:
Not clearly defined legislative rules for drinking water protected areas

Costs: EUR 200000,- (national, EU ETZ-SEE)
Benefits: best practice example; transferrable results; development of adaptation subsidies applicable to a wider region; awareness rising

Austrian Federal Forest Law, BGBl. Nr. 440/1975 (amendment 2007)

Maintaining forests and their multifunctional effects through a sustainable form of forest management is the key objective of the Austrian Federal Forest Law. The latter defines the functions of forests as follows: economic function (sustainable production of wood), protective function (natural hazards), recreational function, and the beneficial functions. The beneficial functions
comprise the protection of water, air and climate. These functions are marked in the Forest Development Plan ("Waldentwicklungsplan"). In the Technical Forestry Plan ("Waldfachplan") a detailed management plan can be emphasized. Concerning the forest related protection of drinking water the most important issues respectively statements are:

• to achieve the objectives of the forest spatial planning forest stands with protection and welfare function, e.g. areas of important water reservoirs, due to the Forest Development Plan (Waldentwicklungsplan) should have an appropriate spatial structure;
• planning of afforestations for the improvement of water balance, especially in areas with only rare forest stands;
• obligation to reforestation of deforested areas with appropriate local species;
• prohibition of any forest devastation (i.a. incorrect manuring, any immissions, waste disposal); in the course of extensive endangerments of forest stands due to game the responsible organ of the forest monitoring authority have to elaborate an expertise for the hunting authority as well as the head of the forest monitoring authority of the provincial government about reason, nature and scope of the endangerment and proposals for improvement;
• forest clearing of more than 1000 m² needs an approval;
• for the protection of water resources “site protective forests” (Standortsschutzwälder) can be designated by a notification of the relevant authority considering public interests versus economic disadvantages due to certain prescriptions and restrictions concerning forest management measures;
• wood harvesting and transportation should be conducted carefully considering the forest soil and vegetation;
• prohibition of clear-cuts, which damage the water balance of the forest soil and clear-cuts of more than 2 ha;
• clear-cuts of more than 0,5 ha require an official permit.

2-5 years with fast implementation for training and awareness rising issues but slow implementation for subsidies

>10 years; Legislative adaptations and subsidies

Umweltbundesamt GmbH, Spittelauer Lände 5, 1090 Vienna; Thomas Dirnböck, Johannes Kobler, Michael Mirtl