Dry Sweden

Many think it's exciting that we have erected five ponds of Putt Myra woodland garden and I often get requests via e-mail about how we did to keep the water in the ponds. Therefore, I have long planned to write a post with dammgrävartips. Actually it is very easy to build functioning ponds, but it requires some prior knowledge in hydrology to get there. Therefore, it is now a further digress (into seven parts) if the water in the forest garden, how both the topography and geography play and how we can minimize competition for water in the forest horticulture. But for a while, I promise, it becomes solid advice on pond digging!

In a posts that I wrote in August 2014 I gave tips on how we can achieve a sustainable water management in the forest garden basis that there had been some dry weeks of summer 2014. In recent years, I have learned that it is the rule rather than the exception that there is a shortage of water during the summer months. Intuitively, I had, as surely many others, believed that there are plenty of water and that we in Sweden do not have to bother about saving water, besides just when there is a drought now and then. But it turns out that there is almost always water is scarce in many parts of Sweden during the vegetation period.

The evidence for this claim is a bit tucked away SMHI:website under the heading "Evaporation". Evaporation is a concept consisting of two different phenomena. Not only is it water departure from the land- and water surfaces, from snow and wet from plant parts. This rupture is called evaporation. The second part of the evaporation is called transpiration and it is the water attrition that occurs from the plants when they absorb water from the soil to transport nutrients, when they create elasticity in their leaves and stems, when they cool the blades and when they take up carbon dioxide from the air. One would roughly say that evaporation is an unnecessary loss of water from the plants' point of view, Medan transpiration fills an important physiological Funktion. In practice, however, it is almost impossible to say whether a water molecule in the air has got there through evaporation or transpiration, so therefore added two usually up to the concept of evapotranspiration, or simply evaporating.

SMHI:s website there will be two maps, an actual årsavdunstningen and one of the potential årsavdunstningen. The map of the actual årsavdunstningen shows how much water evaporate from the ground calculated, lakes, streams, plants and so on during an average year. How much evaporation is primarily determined by

• find (the single most important factor in addition to how much water is available),
• temperatures,
• solar radiation and
• soil.

The map of the potential årsavdunstningen shows how much that could evaporate if there was unlimited amounts of water. The potential årsavdunstningen is always higher or at best equal to the actual årsavdunstningen. When there is a deficit of water, Thus, when the potential årsavdunstingen is greater than the actual plants begin to suffer. They can not as good fotosytetisera, lose elasticity in the leaves and stems and cut down on biomass production. The smaller the difference between potential and actual årsavdunsting, Thus, the smaller deficit on the water, the higher the productivity and growth in culture.

I have made myself the trouble to add SMHI:s two maps at each other (SMHI were not able to do it with their mapping software) to see the difference between the two is and the result is truly amazing. What my map shows is that only a few small (of gulmarkerade) areas suffering from little or no loss (max 100 mm) water. The rest of Sweden is more or less limited water, Thus, where water is the limiting factor for plant growth. Particularly, I was surprised that it is not only Gotland and Öland suffers from a large deficit, but also large parts of the coast of Norrland and Dalarna. Even Putt Myra forest garden is located in the area with the greatest deficit of water in Sweden. What is the difference between the northern coast and islands is that every single rivulet, stream, and finally, on the river that originates in inland Norrland passes through the red range, while Gotland and Öland has no external water addition to rely on.

This red-colored map can look very intimidating out, but there are other objections that it needs to be taken with a pinch of salt. First, based SMHI:The values ​​of the measurement data and calculations with a very coarse resolution. The reality at every single place looks completely different course, because the water is distributed unequally in the landscape. How it is distributed has largely to do with the topography, Thus the terrain physical form. The higher up on the peaks, we will, the drier tends to be, while we find the most water in the valleys and lowlands. Second, the map reflects the vegetation that exists today in Sweden. As is known, it is only a tiny part of Sweden's surface area is covered with forest gardens and evaporation from a forest garden is quite different from a coniferous forest or an open field. But how thirsty is a forest garden really? More on that in the next post!

Literature:

Grip, Harald. and Rodhe, Allan. The path of water from rainfall to stream. Uppsala: Hallgren & Fallgren, 2000.

Ore, Peteroch Berglund, Peter. Focus on Nutrients. Irrigation and nutrient utilization. Hushållningssällskapet Kristianstad, 2006. http://www.lansstyrelsen.se/skane/SiteCollectionDocuments/Sv/miljo-och-klimat/vatten-och-vattenanvandning/bevattning/Bevattning_greppa_broschyr.pdf.