In the last post, I noted that most of Sweden's water limited in terms of plant growth. Thus, it is generally neither nutrient levels or lack of heat, but primarily the lack of water that makes our woodland gardens do not look as lush as in the example of England.
In order to answer the question of how we can achieve minimal competition for water in the forest garden we can begin to look at how much water a forest garden really need for optimal growth. To my knowledge there are no studies yet of established woodland garden crops that have examined the issue, but I found an older study from Canada (with similar climate that we have in southern Sweden) which provide interesting pointers [1]. In this study, various fruit violated water needs, with or without live ground cover under trees. I assumed in my comparison to the cultivation of apples and cherries with live ground cover is what comes closest to a forest garden and then could get the water requirement in mm per day, week by week from 1 May to 14 september. In order to understand the values of the Canadian study are reasonable, we made during our research project on forest gardens a small calculation with specific climatic data from Putt Myra forest garden 2016*. The picture below shows the comparison between the two. The top line is the water demand according to the Canadian study and the lower according to our specific climate parameters 2016 here Putt Myra forest garden.
If you count up the sums required under the Canadian study 85 mm of water in May, 142 etc. in June, 172 mm in July, 133 mm in August and 48 mm in the first half of the September, while the respective figures according to our own estimates, 59 mm of water in May, 90 etc. in June, 102 mm in July, 71 mm in August and 23 mm in the first half of the September. The difference between these figures is probably because it is very calm in our woodland garden and to the Canadian study was carried out on a pretty sandy soil, while we have a loamy soil here. If you grow in southern Sweden in a windy location with a sandy soil can then orient yourself by the Canadian figures, in still positions on heavier soil in central Sweden are our numbers probably better reference.
These figures can then be compared with the rainfall figures for each month for the place where you live. Precipitation data can be found at SMHI:website. If we look at the bars, it becomes obvious that the rainfall is far from able to meet forest garden's water needs if you have conditions in southern Canada. But here in Stjärnsund's huge deficit in the months when there is most sprouting, Thus May to mid-July.
These figures hit enough little to dispel the myth that all timber gardens are lush jungles, but we must not forget that there will actually be a lot of rainfall outside the vegetation period. Here in Stjärnsund we get about 630 mm of precipitation per year, and if we are to believe the Canadian figures need a mature woodland garden around 560 mm water at a season. Overall, the year the water would then suffice, but then you have to capture virtually every drop, which of course is impossible.
For several reasons, it is still not over for timber gardening in large parts of our country. Of course, we have to accept anything less than optimal production in many places and tips on how we can relate to drier places will in a later post. But while the topography varies enormously between different locations, which means that the water is distributed unequally in the landscape and create different good conditions for timber gardening. Next post is therefore about lush valleys and arid southwest slopes and how you can influence your forest garden growth through the right choice of location.
Literature
[1] Ontario, Ministry of Agriculture and Food, R.E.C. Layne, and C.S. Tan, Irrigation scheduling for fruit crops. 1990.
*The calculation is based on climate data from 2016 we measured the on our weather station that is located in Putt Ant forest garden. The calculation was made with the extremely complicated FAO Penman-Monteith equation used to calculate the potential evaporation crops. Exactly how we did the calculation and the assumptions made, we will publish a report that will be the end of 2017.
Åter aktuellt och intressant. I praktiken har alla dessa små dalgångar (10-100 m breda) stått för bra del av försörjning på en kuperad skogsgård i småländska kustbandet genom tiderna. Vi har länge skött dessa delar såg att riset ska ner i dalgångar för att snabbt brytas ned till näring. Efter permakulturstudierna är min tanke att riset ska upp på bergsryggar för att långsammare tillföras lägre nivåer och försöka bilda näringstäcke högre upp. Vatten lär ju dock fortsätta att snabbt förse dalgången med viktigt vatten, kanske t o m till optimal nivåer. Det kan finns bättre tänk att använda allt berg i dagen som resurs, än att försöka få upp näringen dit?
Tack för att du delar dina erfarenheter, Johan! I also believe that it is more worthwhile to exploit valleys maximum, eftersom det är där som vattnet finns. Men bergsknallarna kanske kan bli produktionsytor för vindruvor och annat värmekrävande? Annars kan man nog låta dem förbli som de är, med tallar och allt.