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Interesting Facts about Moss Mats

With excerpts from documents and articles of Prof. Dr. Jan-Peter Frahm, 2013

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CONTENTS General information on mosses 3 Greening with mosses 5 Maintenance of moss mats 7

Water 7

Fertilizer 7

Temperature 8 Properties of the moss mats 9

PM adsorption and filtration of pollutants 9 Water retention and water storage 11 Temperature reduction 11

Background information about fine dust (PM) 13 Frequently asked questions 15

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General information on mosses Mosses are the oldest green terrestrial plants. They already existed in the Devonian period 350 million years ago and at that time they looked exactly as they do today. Since then, mosses have remained nearly unchanged although the earth has been undergoing extreme changes. Why is that? Mosses have a lot of survival tricks. First, they are dehydration resistant. Flowering (vascular) plants require a permanent water and nutrient absorption through the roots to maintain their vital functions. This water absorption is driven by the transpiration suction. Transpiration only works when the evaporation through the stomata on the leaves is controlled and all other surfaces are closed (by means of cuticle, bark etc.). When water supply stops the plant withers and dies off - sometimes faster (e.g. water plants) or slower (e.g. succulents).

Polytrichum formosum Tortula papilosissima Tortula ruralis

sie sahen genauso aus wie heute Tortula princeps Rhytidium rugosum Hypnum cupressiforme

In contrast to flowering plants mosses have no roots and must absorb water and nutrients through their total surface which is therefore water permeable. This enables them to grow on trees or rocks. However, that’s also the reason why they are very sensitive to air or water pollution and are used as bio indicators. Photosynthesis is performed just as long as the mosses are moistened. When they dry out, however, nothing happens! They do not wither but enter into a “quasi-dead“ state which can last long, potentially up to one year. After moistening the mosses start assimilating within a very short time. This way, mosses absorb water “from above“: from the atmosphere by means of rain, fog, due, even water vapor (humidity >80%). Absorption “from below“ is only possible where capillary water can be sucked up. Another survival trick: mosses are very temperature resistant. They can survive -30°C and +60°C (in dry condition), i.e. they are extremely robust.

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Over millions of years mosses have learned to defend themselves against their enemies. They developed substances to protect them from being eaten by snails, bugs or caterpillars. Although they live on the forest floor in close contact with fungi and bacteria they are not attacked due to their antimicrobial substances. These substances prevent cell division in bacteria and fungi, but also the division of animal cells. That’s why mosses show an anti-tumor effect. Mosses are the second largest group of green terrestrial plants. There are approx. 15.000 species all over the world, from high mountains to tropical rain forests. They successfully colonized all kinds of substrates, soils, barks, rocks, creeks and fenlands. Moss wall in Sweden

Spontaneous moss colonization of a thatched roof

Please take details on the fundamental differences between mosses and flowering plants from the booklet ”Mit Moosen begrünen“ (J.-P. Frahm, Weissdorn-Verlag, Jena)

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Greening with mosses Whilst just a few years ago mosses were considered to be annoying weeds and people removed them from walls with high-pressure cleaners, the attitude towards them has recently changed. Moss growth is understood as a natural process, even as a visible sign of clear air. Moss gardens are rather unusual and exceptional – they contrast against the existing lawns or flower gardens. This change led to various actions. Initially, mosses on walls or in shady lawns were not removed, later then people tried to establish mosses artificially on soil and walls. Here, the greening with moss mats deserves particular mention. In Japan, it has been usual to create moss gardens for a long time. However, the local climate is much wetter than here in Germany. Just few dominant species give a peaceful contemplative impression – in contrast with the hectic biodiversity of a flower bed. Maintenance of mosses is completely different from the one of flowers. This is due to the fact that mosses do not absorb water with the required nutrients through roots from the soil but through the total leaf surface. You can allow spontaneous moss growth or plant mosses in particular on small shady areas. However, such efforts are seldom successful or quite often accompanied by setbacks. The fastest greening of large areas is done by mats with pre-cultivated mosses. This method has been applied in Japan and Taiwan for a long time. In many years of work, moss mats for fine dust reduction have been developed by the company Xero Flor International in connection with the moss expert Prof. Jan-Peter Frahm at the University Bonn. They were registered for patent in USA, Canada, and Europe; the European patent has already been granted and is valid in many European countries. XF 321 moss vegetation carrier XF 321 moss mat, pre-cultivated

Primarily, moss mats shall be understood as biological protection layers. Therefore they were developed for the installation along roadsides, median strips, also on roofs – wherever fine dust comes up. However, as regards the aesthetic aspect they cannot cope with the demands on a vegetation blanket with succulents/herbaceous plants. Particularly in dry periods, the mosses discolor to brownish or gray.

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Highway A 562, exit Bonn/Germany

Production of Xeroflor moss mats in North Germany, October 2013

In order to take in their nutrients, mosses adsorb them to the leaf surface by electrostatic effect, incorporate and metabolize them. This way, the soluble inorganic components of fine dust (>50%) are “devoured” as nutrients. In addition, the bacteria living on the moss surface subsist on the organic fine dust components.

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Some information on the maintenance of moss mats

1. Water Due to the lack of roots, mosses in nature take water through their leaf surface, mostly in form of rainwater, but they can also absorb water vapor from the air. Accordingly high osmotic values ensure that mosses remain turgescent with air humidities of >80% rH. This way, they can exist in coastal deserts without any dripping water Being installed in horizontal position, the moss mats do not require any additional watering. Mosses are poikilohydric plants, i.e. they metabolize only when they are moist. Without water, they dry up and can survive droughts over weeks. However, in this condition they do not look as attractive as before. In vertical position, no rainwater can get to the mosses – such installation requires additional irrigation. Just in humid locations or in places with regular dew formation mosses can do without additional irrigation. Humidification of the mosses should follow nature, in particular the natural rainfalls. Constant humidification weakens the mosses, whereas regular drying up will harden them. Practical experience has demonstrated that the irrigation early in the morning before sunrise is a good choice. This way, the mosses are moist when the sun rises, perform photosynthesis and dry off in the course of the day. The applied water shall be similar to rainwater, i.e. slightly acidic, with a pH of approx. 5.8. Usually the pH of tap water is higher, the water is harder. Mosses are especially sensitive to lime. They absorb lime in the water, the water evaporates, and a lime crust is formed and destroys the moss. In such cases it is imperative to use rainwater or water acidification systems.

2. Fertilizer Nature shows us that mosses can cope with extremely little nutrient supplies, and the growth rate is accordingly low. All required nutrients are included in the rainwater and, in addition, dusts are caught and used for the supply of nutriments. From this it follows that no application of fertilizer is required, it may even be harmful. In general, plant fertilizer consists of a mixture of fertilizing salts. If the concentration of the liquid fertilizer is too strong the fertilizer will dehydrate the moss and cause osmotic problems, it will die off. Dry mineral fertilizer is even worse. It is spread onto the mosses, dissolves with the next rainfall or dew and forms an extremely strong salt solution.

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3. Temperature Mosses are evergreen. Contrary to frost-sensitive evergreen flowering plants, local mosses are frost-resistant down to approx. -30°C. They can also freeze in snow or ice without suffering any damage. Nature, in fact, has foreseen that mosses are dry when it is hot. This way, they can withstand temperatures of more than 60°C. Irrigation with such outdoor temperatures would make them die off. Therefore it is imperative to turn off irrigation at approx. 25°C. Photosynthesis begins to decline at 25°C air temperature. Already at 35°C mosses have no more rate of net photosynthesis, i.e. in moist condition (only in this condition they perform photosynthesis) they consume more energy than they produce and die off. In nature, it is quite unusual that mosses are moist at 35°C.

XF 321 moss roof in Wuppertal/Germany

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The Properties of Mosses

Fine dust adsorption and filtration of pollutants Due to the special nutrient uptake, mosses are forced to absorb not only dissolved salts and dust particles from rainwater or dew but also atmospheric pollutants. Therefore they are valuable bio-indicators of the air pollution. This principle is exploited with the European monitoring of heavy metals. Since mosses (must) absorb also heavy metals in the environment, it is possible to determine their content of heavy metals and thereby define the pollution level. For the uptake of nutrients in rainwater, mosses make use of ion exchange. Positively loaded hydrogen ions (H+) are produced in the cell walls by an organic acid and provided on the leaf surfaces. . Here, these hydrogen ions are exchanged with cations (B, Mg2+, Ca2+, K+). Therefore the moss surface is positively loaded. Dust particles, however, are negatively loaded. They are attracted and retained by surfaces with positive loads. Microfiber cloths work on the same principle when they hold dust particles during dry dusting. Thus, fine dust is actively retained on the moss surfaces. In wet deposition, the fine dust is washed into the moss vegetation. Contrary to all other surfaces, it is retained and accumulated by the moss plants, i.e. it is not released back to the atmosphere (e.g. in dry condition). 1. By means of the EDX-Analysis of a leaf surface, it is possible to determine elements of

which the fine dust is composed (see diagram below). X-ray spectral analysis from the surface of a moss leaf (Dicranoweisia cirrata). Location: Bonn, Haussdorfstr. By this method, the composition as well as the probable origin of fine dust particles can be determined

2. By means of an ash analysis of mosses it is also possible to determine specific elements

originating from dust, not from the plant itself (e.g. Al, Ti, Be, Zr). 3. By combustion loss determination of mosses it is possible to determine the proportion of

inorganic compounds which are stored in the mosses. The combustion loss (by weight) of pure moss is approx. 95%, dust impregnated moss from a 30 years old thatched roof shows just 87% loss.

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4. With scanning electron microscope photos it is possible to illustrate dust particles on the mosses and to measure their sizes.

5. Scanning electron microscope photos can also show bacteria which live on mosses and

are involved in the decomposition of organic fine dust.

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Water storage and water retention A climate problem of urban areas is the fast draining of rainwater. Dense building development and sealed surfaces entail the direct discharge into the sewing system. The result: a typically dry urban climate with negative consequences such as heat and dust. Water capacity of mosses is a multiple of their dry weight. They can store 2.5 – 12 times their dry weight (peat mosses even up to 25 times). This way, a moss cover of 1.5 mm thickness attains a water capacity of 24 l/m². With the installation on top of a water storing underlay (e.g. mineral wool) the water capacity can be duplicated. The water capacity data relate to 1 – 2 years old moss mats. The annual growth of the moss cover of short growing mosses is, depending on location, approx. 5 mm and continues to increase the water capacity. Release of water vapor from moss mats over a longer period of time entails a distinctly higher ambient humidity. Higher humidity has a positive effect on health and counteracts in the breathing zone. A further positive effect is the relief of the strain on the urban sewing systems, in particular during heavy rainfalls. Similar to sedum blankets, moss mats, too, retain rainwater and release it, only after full saturation, slowly to the sewing system.

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Temperature reduction The evaporative cooling effect resulting from the release of water from the moss mat reduces the ambient temperatures. This way, the effects of the urban climate in a dry-hot mesoclimate, particularly in summer, are mitigated. Also in this regard, moss mats have a similar impact to that of vegetation blankets. Following diagram illustrates the temperature reduction of the ambient air in 1 m height above a dry (blue) and a wet (green) mat.

In addition, on sunny days the moss mat increases the ambient humidity in 1 m height above a dry (blue) and a wet (green) mat (see below, left area). This effect is less significant on cloudy days (see below, right area)).

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Background information on fine dust Fine dusts are a major current problem. With a size of <10µm (PM10 = particulate matter 10) they float in the air (airborne dusts) and are inhaled, so that also pollutants get into the body through the lungs. For fine dust control, the first Daughter Directive (99/30/EG) to the Framework Directive Air Quality (96/69/EG) introduced a tightened limit for fine dusts in July 1999. In Germany, this limit value was implemented in national law by the 22nd Federal Emission Control Act as of 11.09.2002. Since 01.01.2005 there are tightened limit values saying that

- the average annual limit value of 40 µg/m³ shall not be exceeded, and - the daily limit value of 50 µg/m³ may be exceeded on max. 35 days/year

Measurements at 375 locations in Germany with very high particulate exposure levels show where and on how many days the maximum values were exceeded (www.env-it-de/luftdaten/trsyear.fwd?comp=PM). Particulate matter does not only include abrasion of brakes, tires and couplings but also ammonium salts (up to 50%). These arise in both countryside and cities and result from the compound of ammonia and nitrogen oxides or sulphur dioxide. The thus created ammonium nitrate is a composite fertilizer which, in stronger concentrations (e.g. on roadsides of motorways) leads to salinization. In depositions of particulate matter it entails an alarming overfertilization of nature, accumulation of nitrogen in the soil and finally the disappearance of many plant species and cohabiting animals. Fine dust’s share of ammonium nitrate. At this testing station ¼ to ⅓ of fine dust consists of ammonium nitrate which the mosses take in as nutrient.

So far, all efforts to reduce the exceedances of the limit values at the measuring stations have failed (e.g. by washing). Here mosses can make an important contribution. The impact on the reduction of PM due to the ion exchange capacity of mosses is the basis of the patent “moss mat”.

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The moss mats are also a biological surface since the mosses are colonized by bacteria. These bacteria subsist on the decomposition of organic substances which get to the mosses in form of particulate matter. This way, mosses have the effect that 1. particulate matter is removed from the atmosphere and sticks to the moss surface, 2. the soluble inorganic components (50%) are absorbed and metabolized by the mosses, 3. the non-soluble inorganic rock dusts are held between the mosses, and 4. the organic components (rubber abrasion etc.) are decomposed by the bacteria living on

the mosses.

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Frequently asked questions

1. Under what climate conditions can moss mats be installed?

Since mosses take their water from rainfalls and dew, the application is possible particularly in moist areas. Rule of thumb: the levels of rainfall and evaporation should be equivalent. However, this applies to most regions in Europe. If you are not sure if the region is suitable for moss mats, just take a look at the rocks along the road sides, fallow land, trees etc. If there are mosses, they will also grow on moss mats.

2. Which moss species are selected for the moss mats? The moss vegetation consists of robust species which mostly grow at road sides. This ensures that the mosses can develop and grow well. They are resistant to road traffic emissions. The composition of the vegetation stock may change over time by the settlement of better adapted moss species or airborne moss spores.

3. Is it possible to get into trouble with invasive species by imported moss mats? The used mosses are widespread in Europe. So it cannot happen that they are imported in regions where they do not grow and spread there invasively.

4. What factors influence the extent of fine dust reduction? Before fine dusts can be absorbed they must first of all get in contact with the mosses. PM is suspended particulate matter; therefore it gets to the moss mats by wind or air turbulences. This happens in particular in street canyons with vertically installed moss mats on the sides. On a horizontal installation the absorption is lower. Another factor is the size of the moss area in relation to the accruing quantity of fine dust. Small-sized moss areas generate, of course, lower values.

5. Isn’t it very likely that weeds will grow on the moss mats? No. The moss mats are installed on a plastic sheet which flowering plants cannot penetrate with their roots. At most, seeds may germinate on the moss mats; however, they cannot survive in the thin fleece layer and die off.

6. Where can moos mats be applied? 7. Due to their light weight, moss mats are most suitable for the installation on flat und

sloping roofs. However, they cannot be equated with extensive xeroflor green roofs since they do not meet the esthetic requirements (green all year, flowering). They can be used in vertical installation along roadsides, e.g. median strips or traffic islands, and horizontally, e.g. on concrete walls or noise barriers with adequate irrigation system.

8. Life span Since the moss mats were developed only a few years ago there are still no final statements available. However, mosses grow very slowly. Meanwhile the first moss mats are 10 years old. The mosses decay at the bottom and continue growing at the end of the leaves. As shown by mosses on roofs, the moss cover can exist for 100 years. I may happen that excessive cushions fall down but they grow back.

9. When is the best season to install moss mats? The wet seasons (late autumn, winter, early spring) are most suitable because then the mosses can best acclimatize after the installation of the mats.

10. Do the mosses require care? Mosses are provided with nutrients from rain water and fine dust. They grow very slowly and don’t require any mowing, fertilizer or other actions.

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11. May moss mats be fertilized? Certainly not! In nature, mosses live from atmospheric water and atmospheric nutrients. For example, inorganic fertilizer for flowers would have a lethal effect, since the included salt would crystallize and cause osmotic problems.

12. What happens when it does not rain for several weeks? Nothing bad. Like in nature, e.g. on garden walls or rocks, mosses fall into a state of suspended animation during this period. After the subsequent precipitation or dew they are reactivated as resurrection plants. However, in dry condition they do not look very attractive, do not absorb fine dust and do not grow.

13. Do moss mats require irrigation? No. Mosses tolerate even longer dry periods. After the state of suspended animation they swell again within few minutes after a rainfall.

14. When shall the moss mats be watered? If any, they shall not be watered in case of sun because the moss plants would be burnt. Same applies to temperatures of more than 25°C. The early morning hours between 4 and 6 p.m. are advisable.

15. Which water may be used for watering? Rain water. This is the water that they get in nature.

Mosses do not tolerate ”hard“ tap water, i.e. water with a high carbon content and high pH value which comes from the tap in many places. Therefore, prior to use, please perform a water analysis or request hardness level and pH value from the local waterworks. Values of <8°sH and a pH of 4 – 6 are tolerable.

In general: Better no watering at all than watering with unsuitable water.

16. How can the moss mats be moistened? Irrigation with spray heads is not ideal and shall only be applied when rainwater is used. A flow-irrigation with sprinkler hoses is better.

17. Is de-icing salt along roadsides an issue? Yes, with regard to a few moss species. The vegetation mix of the moss mat, however, includes also some salt-tolerant moss species. Over time (already within half a year), the composition of the mosses will change and, little by little it will adapt to the site.

18. Are the moss mats frost-hardy? Yes. Mosses tolerate temperatures as low as -30°C. The reasons for this frost tolerance are the missing vacuoles in the cells of mosses. These vacuoles are water-filled cavities that would form ice needles in case of frost.

19. Are mosses able to survive high temperatures? Yes, more than 60°C, but only in dry condition. In wet condition, they die off. However, the heat damages are reversible, the mosses will regenerate after a longer period of time. They will start growing from the dead shoots.

20. Are there other PM-absorbing plants? No. Flowering plants have a waxed surface. Here the dust cannot remain, it is washed off. Some leaves have very deeply grooved surfaces (e.g. some grasses) where dust (no fine dust = PM 1-10, <10µm) can remain – but it is not adsorbed, and also this dust is washed off.