Sparsely vegetated habitats

• Innhold
• Description of sparsely vegetated habitats
• Assessed ecosystem types
• Ecosystem types on the Red List
• Impact factors
• Existing knowledge
• Expert Committee
• Acknowledgements
• References

The ecosystem types assessed under "sparsely vegetated habitats" comprise terrestrial systems without trees, where the lack of trees, in the vast majority of cases, is not due to human influence. This is a heterogenous group of ecosystem types that ranges from Exposed ridge T14 and Snowbed T7 in the mountains, to Waterfall-sprayed meadow T15 and Open alluvial sediment T18 which are found across the entire country, and Rocky shore T6 and Sand dune T21 along the coast. Many of the ecosystem types in this group are widespread, and together they cover a large area on the Norwegian mainland. There is, however, considerable variation in the amount of area covered by each ecosystem type. While ecosystem types above the climatic treeline often have large, interconnected areas of distribution, many of the other ecosystem types are found as small areas in a mosaic of other ecosystem types (e.g. waterfall-sprayed meadows and the many minor ecosystem types which fall under the major type Bare rock T1).

Description of sparsely vegetated habitats

A common characteristic of all ecosystem types assessed here is that they do not include established forest. In general, we can identify three key factors that explain the absence of trees in these ecosystem types, namely shallow soil, climatic factors (primarily temperature), or disturbance (primarily abiotic).

Shallow soil

A number of ecosystem types are associated with shallow soil. Both Bare Rock T1 and Boulder field T27 usually have a vegetation cover that consists only of moss and lichen, while Open shallow-soil ground T2 usually has a thin layer of soil suitable for a vegetation cover with vascular plants. Parts of Snowbed T7 and Exposed ridge T14, as well as Patterned ground T19, Arctic-alpine dry-grass heath T22 and Wet snowbed and snowbed spring V6 also have a shallow layer of soil. The same applies to Cave and overhang T5, where there is a transition from a limited number of species within the cave itself, to the overhang which to a greater or lesser degree has a vegetation cover consisting of moss and lichen.

Climatic factors

Climatic factors restrict the distribution of forest. The most widespread ecosystem types above the climatic treeline are Arctic-alpine heath and lee side T3, Snowbed T7 and Exposed ridge T14. A little higher above the treeline, toward the mid-alpine zone and beyond, three other ecosystem types become more important. These are Patterned ground T19, Arctic-alpine dry-grass heath T22 and Wet snowbed and snowbed spring V6. It is primarily temperature and the spatial distribution of snow that are the key factors contributing to the distribution of these ecosystem types in the mountains, as these determine the length of time snow remains on the ground before the growing season can begin. Changes in the duration of snowcover will also have more indirect impacts on ecosystem types in that irrigation of crags and rock faces will diminish earlier in the season, and streambeds will dry out for longer periods.

Disturbance

Abiotic disturbance is the most common reason that areas below the treeline lack trees. However, for the major type Bird-cliff meadow T8 the reason is biotic disturbance in the form of large additions of nitrogen from avian excrement. This is tolerated by only a handful of species, and due to the large amounts of nitrogen this ecosystem type is also a very productive. There are many forms of abiotic disturbance that are vital to ensure the ongoing existence of different ecosystem types. The movement of water is significant both along the coast and inland e.g. wave erosion on Rocky shore T6 or flooding along rivers and lakes for Open alluvial sediment T18. Water can also carry material such as the twigs and leaves in a Freshwater driftline T23 or seaweed in a Coastal driftline T24. Water can also have a more indirect impact such as when saltwater evaporation leaves salt deposits and a Hypersaline tidal marsh T11 is formed. Another example is when waterfall spray freezes in a separate zone near the waterfall and the ice prevents the establishment of woody plants as in a Waterfall-sprayed meadow T15, or similarly when water which collects in hollows in the terrain freezes and prevents trees becoming established on Kettle-hole frost heath T20. For many ecosystem types wind can also be a contributing factor to trees failing to become established and areas remaining open. In addition, wind carries sand and deposits it in Sand dunes T21. Coastal shingle beach T29 is found in exposed places along the coast and is kept open by the wind, but the type is often presumed to be in a state of slow succession as a result of land uplift. Glacier foreland T26 has also been in a state of gradual succession since the glaciers melted after the "Little Ice Age". In this ecosystem type an obvious layer of soil or vegetation cover has not yet been established since the disappearance of the ice. Landslides and avalanches are important for Bare talus slope T13, Talus-slope heath and meadow T16, Open active landslide T17 and Open historical landslide T25.

For some ecosystem types there is clearly a dominant reason that forests have not developed, while for others it can be a combination of many factors. In certain cases human activity can also contribute to delay the establishment of forest and therefore keep areas open. If the human activity in question is the key factor behind the open landscape, then the ecosystem type is classified as "semi-natural" and assessed by another group of experts. Consequently, cessation of this cultural influence will have little impact on ecosystem types under "Sparsely vegetated habitats". In certain situations it can be challenging to assess the impact of cessation of grazing for example, compared with a natural disturbance. The major type Talus-slope heath and meadow T16 is an excellent example.

This is a type for which natural disturbance is a prerequisite but which often may be influenced by, or in certain cases dependant upon grazing by livestock and cervids, especially in the edge zone, without this easily being able to be measured or confirmed (Tandstad 2018).

Assessed ecosystem types

We have only assessed occurrences of ecosystem types on the Norwegian mainland. Many of the same ecosystem types can also be found on islands in the Arctic, but these are assessed in the section on Svalbard.

All 25 major types are assessed for the Red List: 24 are classified as terrestrial systems and one is classified as a wetland system in Nature in Norway NiN. The ecosystem type that falls under wetland systems (Wet snowbed and snowbed spring V6) has many of the same impact factors as Snowbed T7 and other terrestrial ecosystem types and is therefore assessed as part of this group. Correspondingly, the major type Tidal meadow T12 is assessed with semi-natural ecosystem types such as Semi-natural tidal and salt meadow T33 which is very similar.

All 211 minor types within the 25 major types were reviewed, and assessments were carried out on the minor types that had fewer than 20 occurrences (Endangered EN as per criterion B2) or a higher threat category than the major type. Regional variation was also taken into consideration, in particular variation along the bioclimatic zone and section gradients 6SO and 6SE. Based on this review, 12 additional assessment entities were created.

The additional assessment entities are subject to a different set of impacts than those affecting the major ecosystem type, and this results in a higher threat category than that which applies to the major type as a whole. Some examples include minor types associated with snowbeds and exposed ridges, which fall under the major types Bare rock T1 and Boulder field T27, yet have threat profiles resembling that of Snowbed T7 and Exposed ridge T14, rather than Bare rock T1. Similarly minor types that are associated with waterfalls, and which fall under the major type Bare rock, will have a threat profile that corresponds to that of the ecosystem type Waterfall-sprayed meadow T15.

The minor ecosystem type Silt and clay-dominated landslide T17-4 which falls under the major type Open active landslide T17 is an important habitat for a number of species of mosses and lichen that are at risk of being outcompeted. In general, the level of knowledge regarding the major type is poor, however as silt and clay-dominated landslides often occur in areas at lower elevations, such as those which usually have human settlements, we have more knowledge about this minor type. The threat level (category) is high in these areas, as preventing landslides is desirable. This is done by implementing diverse security measures that stabilise the clay soil masses.

The minor type Epilittoral consolidated shell-bed beach T29-6 was also assessed, but there was inadequate information to determine a concrete threat profile. In this case more information should be acquired prior to the next Red List assessment.

Bare rock T1 is not threatened as a major ecosystem type, but it contains several minor types with a restricted distribution, and some types are also clearly in decline. Several minor assessment entities have been created based on geographic variation with special formations, in lowland areas in the boreonemoral zone, where there is significant land conversion pressure. This applies in particular along the coast. It is the reason that "Southern fixed dunes" has been created as a separate assessment entity, as compared to the major type Sand dune 21 it is under far greater pressure due to changes in land use. This is also the background for the creation of a separate assessment entity "Lime-rich open ground" in both the boreonemoral and southern boreal zones. In addition both "Dry lime-rich rock in continental areas" and "Extremely drought-prone lime-rich rock" have been created from the major type Bare rock T1. These ecosystem types have a relatively restricted distribution and many of the occurrences are in the process of developing a layer of soil and evolving into another ecosystem type. The last type under Bare rock T1 is a high alpine ecosystem type on irrigated rock "Irrigated rock in eastern alpine areas". This type is in danger of disappearing due to climate change, as reduced irrigation from melting snow dries out the substrate and changes the vegetation in the minor types that are included in the assessment entity.

Ecosystem types on the Red List

Of the 25 major ecosystem types covered by the theme "sparsely vegetated habitats", eight are red-listed, while a further two are classified as Data Deficient DD. This is the case for Open active landslide T17 and Kettle-hole frost heath T20. Of the other 12 assessment entities assessed at the minor type level in combination with regional variation, one is classified as Data Deficient DD, while the remaining 11 are red-listed as Near Threatened NT, or placed in a higher threat category.

None of the 19 red-listed entities are assessed as Critically Endangered CR, (although there are three assessment entities where the existing knowledge is so poor that they have been assessed as data deficient DD). However four assessment entities are red-listed as Endangered EN (no major types), eight as vulnerable VU (five of which are major types), and seven as Near Threatened NT (three of which are major types).

Of the eight red-listed major types, four are associated with alpine areas. These are Arctic-alpine heath and lee side T3, Snowbed T7, Wet snowbed and snowbed spring V6 and Exposed ridge T14. Four of the 11 other red-listed assessment entities are also associated with alpine environments. Three are associated with snowbeds or wind-exposed ridges but are classified under the major types Bare rock T1 or Boulder field T27. The various assessment entities in alpine areas are assessed slightly differently with respect to threats because the ability to migrate and become established are presumed to vary, as well as the fact that some types will probably manage better over the assessment period of 50 years even if we assume that the temperature increase will be the same for all these ecosystem types.

Sand dune T21 is assessed as Vulnerable VU as a major type, while Southern fixed dunes is presumed to be more exposed than the major type because it is widespread in areas where there is a significant demand for land. It is therefore assessed as endangered EN. Waterfall-sprayed meadow T15 is another major type that is assessed as Vulnerable VU. The key reason is a reduction in the flow of water in rivers, primarily in connection with hydropower development over the past decades. The minor types under Bare rock T1 which are associated with waterfalls are assessed in the same way as the major type Waterfall-sprayed meadow T15.

A number of the entities associated with lime-rich and species-rich areas with a thin layer of soil are situated in areas where there is a relatively strong demand for land. This has led to a significant reduction in the overall area of these ecosystem types in the boreonemoral zone, and to some extent in the southern boreal as well. This applies to entities within both Bare rock T1 and Open shallow-soil ground T2.

Impact factors

For the majority of ecosystem types above the climatic treeline it is climate change that has the most significant negative impact. The effect of climate in the alpine zone is complex. Temperature has a direct effect on the vegetation, but the duration of snow cover also plays a significant role in the way in which ecosystem types are dispersed. This in turn is determined by a combination of factors such as the amount of precipitation, the amount of precipitation which falls as snow, wind and temperature. When the temperature increases, less precipitation will fall as snow, and the snow that falls will melt faster in spring. Even if it is expected that the amount of precipitation in Norway will increase, we presume that on the whole, a warmer climate will ensure that snow does not remain on the ground as long as it has in the past. Therefore we expect that the treeline will migrate upwards during the assessment period (the next 50 years). As areas at higher elevations cover a smaller area in terms of size, a migration of the treeline will in general reduce the size of the area of the ecosystem types in the mountains. Ecosystem types that are more directly dependent on the snow and meltwater that snowdrifts contribute during the season are expected to be the most vulnerable in the face of climate change (Grytnes et al. 2014; Matteodo et al. 2016). The natural habitat conditions of these ecosystem types will disappear when the snow melts earlier in the year and when the old, previously stable snowdrifts dwindle or disappear completely. Therefore they will probably also react sooner to the changes in climate than other alpine areas. Other ecosystem types will probably react more slowly because they will manage to persist even though the climate becomes warmer, but only until the most competitive species from lower regions become established and outcompete the species in these ecosystem types (Kulonen et al. 2018).

For many of the other ecosystem types there are different types of land demand pressures that make up the predominant threat profile. For Open alluvial sediment T18, Waterfall-sprayed meadow T15 and ecosystem types related to waterfalls, the greatest threat is reduced water flow, primarily in connection with hydropower development. This contrasts with the majority of threatened ecosystem types below the treeline, where the greatest threat is the construction of other types of infrastructure.

Existing knowledge

The ecosystem types assessed in this chapter are an extremely heterogenous group, and the knowledge concerning their distribution and the threats to the different types varies enormously. In general, these are ecosystem types with low productivity and of little economic interest. This is probably one of the reasons that the existing knowledge regarding distribution and impacts is poor for many of the ecosystem types. In addition, many of these ecosystem types have a scattered distribution which makes it difficult to obtain good measures of the size of the area covered by the specific types, and in particular how the distribution of the ecosystem types has changed over time.

For the distribution of the most widespread alpine types we have used map material developed by Norut – Northern Research Institute, following the methods described in Johansen (2009). This has provided a rough estimate of the distribution of different ecosystem types at different elevations in the mountains. The estimates have then been used in the assessment of the effects of climate change. Specifically, we have used the Norwegian Climate Service Centre's climate projection based on the "RCP4.5 – medium" scenario, projected fifty years into the future (see Hanssen-Bauer et al. 2015). This has then been used to calculate the extent to which the different ecosystem types would be diminished if the treeline and the bioclimatic zones migrate upwards in order to maintain the present day relationship between climate and the respective zones. With respect to the way in which alpine vegetation will actually respond to a warmer climate, we know from many studies that species have already migrated upwards as a response to a warmer climate (Felde et al. 2012; Rumpf et al. 2018; Steinbauer et al. 2018) but with a considerable delay in the response relative to climate change (Alexander et al. 2018). Knowledge regarding the effects of these delays is however limited.

Knowledge regarding the distribution of the majority of other ecosystem types, and thereby also possible changes in the distribution, is poor. To a large degree it has therefore been necessary to assess trends in distribution areas based on what is known about where these types are widespread and how these areas have changed in the course of the past fifty years, or how it is imagined these areas will change in the future.

Expert Committee

The members of the expert committee for Sparsely vegetated habitats were John-Arvid Grytnes (chair), Marianne Evju, Torbjørn Høitomt, Per Gerhard Ihlen and Per Arild Aarrestad.

Acknowledgements

Thank you to Marianne Lindau Langhelle, Espen Ørnes and Jon Prøis Rustand (all from Asplan Viak AS) for assistance with the area analyses. Thank you to Einar Timdal (University of Oslo), Tor Tønsberg (University of Bergen) and Hege Gundersen (Norwegian Institute for Water Research) for useful information concerning specific ecosystem types, and to Olga Hilmo and Snorre Henriksen (Norwegian Biodiversity Information Centre) for comments on the text.

References

Alexander JM, Chalmandrier L, Lenoir J, Burgess TI, Essl F, Haider S, Kueffer C, McDougall K, Milbau A, Nuñez MA, Pauchard A, Rabitsch W, Rew LJ, Sanders NJ, Pellissier L (2018). Lags in the response of mountain plant communities to climate change. Global Change Biology 24: 563-579.

Felde VA, Kapfer J, Grytnes J-A (2012). Upward shift in elevational plant species ranges in Sikkilsdalen, central Norway. Ecography 35: 922-932.

Grytnes J-A, Kapfer J, Jurasinski G, Birks HH, Henriksen H, Klanderud K, Odland A, Ohlson M, Wipf S, Birks HJB (2014). Identifying the driving factors behind observed elevational range shifts on European mountains. Global Ecology and Biogeography 23: 876-884.

Hanssen-Bauer I, Førland EJ, Haddeland I, Hisdal H, Mayer S, Nesje A, Nilsen JEØ, Sandven S, Sandø AB, Sorteberg A, Ådlandsvik B (2015). Klima i Norge 2100 - Kunnskapsgrunnlag for klimatilpasning oppdatert 2015. Norsk Klimaservicesenter 2015. 203 pp. [in Norwegian.]

Johansen B (2009). Vegetasjonskart for Norge basert på Landsat TM/ETM+ data. NORUT Rapport 4/2009: 87 s. [in Norwegian.]

Kulonen A, Imboden RA, Rixen C, Maier SB, Wipf S (2018). Enough space in a warmer world? Microhabitat diversity and small-scale distribution of alpine plants on mountain summits. Diversity and Distributions 24: 252-261.

Matteodo M, Ammann K, Verrecchia EP, Vittoz P (2016). Snowbeds are more affected than other subalpine–alpine plant communities by climate change in the Swiss Alps. Ecology and Evolution 6: 6969-6982.

Rumpf SB, Hülber K, Klonner G, Moser D, Schütz M, Wessely J, Willner W, Zimmermann NE, Dullinger S (2018). Range dynamics of mountain plants decrease with elevation. Proceedings of the National Academy of Sciences 115: 1848-1853.

Steinbauer MJ, Grytnes J-A, Jurasinski G, Kulonen A, Lenoir J, Pauli H, Rixen C, Winkler M, Bardy-Durchhalter M, Barni E, Bjorkman AD, Breiner FT, Burg S, Czortek P, Dawes MA, Delimat A, Dullinger S, Erschbamer B, Felde VA, Fernández-Arberas O, Fossheim KF, Gómez-García D, Georges D, Grindrud ET, Haider S, Haugum SV, Henriksen H, Herreros MJ, Jaroszewicz B, Jaroszynska F, Kanka R, Kapfer J, Klanderud K, Kühn I, Lamprecht A, Matteodo M, di Cella UM, Normand S, Odland A, Olsen SL, Palacio S, Petey M, Piscová V, Sedlakova B, Steinbauer K, Stöckli V, Svenning J-C, Teppa G, Theurillat J-P, Vittoz P, Woodin SJ, Zimmermann NE, Wipf S (2018). Accelerated increase in plant species richness on mountain summits is linked to warming. Nature 556: 231-234.

Tandstad HR (2018). Vegetation-environment analysis of the transition between avalanche meadows and semi-natural grasslands in Nærøyfjorden, Western Norway. MSc Thesis, Natural History Museum, University of Oslo.