The Sombrun Forest Garden Project

Once again, the weather has been a major preoccupation this month, and my thoughts on species future for the Sombrun Forest Garden Project have moved from the back of my mind to the front! As you will see from the monthly weather report below, most of the month has been dry and hot, and I think I have to accept now, given everything else that is happening with climate change as well, that this will become the norm. Not only have temperatures been higher than ever (40° and higher on three occasions already this year, two of which were in July), but rainfall has been minimal and we are in a severe drought. Couple this with the fact that the soil here is very porous and lacking in organic matter due to its composition with pebbles and stone (see the Site Evaluation, Articles, December 1st, 2021) and you have a recipe for struggle!

Of course, over time, the forest garden system will itself overcome these difficulties, by increasing shade and underground mycelial networks, and by improving soil humus, fertility and structure with the better water retention that that brings. But it will take a good few years and until then, I need to think seriously about providing more drought resistant species. This will mean researching genus and species which are also compatible with the aims of this Forest Garden, namely biodiversity, symbiosis, utility and resilience. I am taking this seriously enough to think in terms of putting this winter’s planting on hold, and maybe getting in touch with other forest gardeners in neighbouring Spain and Italy for their advice.

In general, the Coppice area* has shown good resilience, which I would have expected because they are all local forest species – oak, chestnut, ash, acacia, hazel and so on. And I think that, although still young trees, they are already getting help from mycelial/invertebrate networks underground. Despite this, the red alders (Alnus rubra) and hazels (Corylus avellana) have become very dry and adopted their early-leaf-drop strategy (see photos below), whereby leaves turn brown and fall, thus helping the tree to reduce its transpiration rate and so save water for the roots. Obviously there is a limit to how far this process can go and it remains to be seen whether they will survive, even though I have helped them with some water.

This red alder (top left) now has a very weak profile due to premature leaf loss, and the amount of fallen leaves can be clearly seen top right (hazel) and bottom left (Italian alder), where there are even green leaves too. This robinia (bottom right), the first tree planted here nearly four years ago, came into flower (the white specks), another stress strategy to set seed and so continue the species, because it felt threatened enough by the dry conditions.

But most surprising perhaps is the resilience of the fruit trees I have planted. They have all maintained healthy-looking leaves despite the scorching they have received. Of course, I have been watering to try to keep pace with the drought, but other factors may be enhancing their apparent well-being – the fact that most of them are planted along the swales, part of the water retention strategy for the site, and that they are principally, although not all, local or semi-wild species, and thus more resilient. I am continually adding biomass and urine to the swales, and so even without rain, they tend to retain more moisture than the surrounding ground.

The greatest cause for concern is the soft fruit – gooseberries, raspberries and blackcurrants – which don’t like the direct, burning sun and cannot find the partial shade they need because the fruit trees next to them are not developed enough yet. Maybe I should have waited before planting them there. By contrast, however, the two jostaberry bushes I put in last winter on Carré 1, the first fertile square, are coping well! The ground here must now retain sufficient moisture for their needs to be supplied on a continual basis.

You might think – ‘well, why doesn’t he put in some drip irrigation?’. My answer to that is that the whole point of the Forest Garden Project is to establish a resilient, self-supporting garden, and so anything that can’t survive by itself, apart from while it gets established, will not be included here. Quite a challenge, especially now that things have become so unpredictable, but I welcome it all the same.

Nevertheless, I have been watering this month, for the reason stated above, because it is pointless not to try and keep the trees alive until they get established. The point being that, once established, they will then either survive or not. Naturally, there are paradoxes here. At what point do I consider the trees established, and do I continue watering even though I know the soil isn’t yet retaining enough moisture through natural forest garden processes?

The Monthly Weather Record (link below) shows a rainfall total of only 25mm for July, and this fell mostly in one storm on the 3rd. Thus we have had drought conditions building for virtually the whole month. There was a temperature peak of 42.7° on the 18th and we were in official canicule (heatwave) conditions from the 9th – 26th July. A canicule is defined by each département here, but it generally requires the daytime temperature to be above 34°/35° and for it not to fall below 19° or 20° at night, and this for more than three consecutive days.

I thought the deer were taking their summer holidays, but no! They must be feeling the drought too, because they have stripped my only Szechuan pepper tree of its bark (photo below), despite it being covered in thorns. It was the only tree I hadn’t protected with the wire netting, because I didn’t think they would touch it! One of my neighbours has even had her courgette plants eaten, presumably for the moisture in the leaves.

All in all, this has been quite a year, with the severe frost in early April, which affected all the fruit tree blossom and even the walnut tree, and now the drought and heat. What walnuts, greengages and mirabelles there were are now dropping from the tree before they are ripe, and the few apples on the immature trees will remain small and hard through lack of water and will eventually fall.

The young plants in the paulownia hedge (Blog, November 1st, 2021) have suffered in these conditions, with only about half surviving so far; luckily I have enough spares to replace these in the autumn. The photo below shows the survivors, which have also no doubt been helped by the nitrogen-fixing of the nearby robinia.

You may have seen reports of forest fires in the Gironde département in south-west France during July. Altogether, over 20,000 ha of pine forest were destroyed; the fires were about 160 km north of here, and on the 15th, a pall of smoke from there, carried by the wind, hung over Sombrun and there was even a strong smell of burning. Reality check!

The dry weather meant there was not a great deal of maintenance work to do, but several other routine tasks were carried out. I decided to keep just two of the moringa seedlings (see last month’s Blog and photo below left), because they will be fairly high maintenance for the first few years, including keeping them in large pots and bringing them indoors for the winter. More paradox, because during this period they will hardly be self-sustaining! However, it is such a useful, classic tree, the epitome of the true forest garden plant, widely used for timber, human and animal food, cosmetics and medicine throughout the tropics, and I think our future conditions here might just suit it. Maybe there won’t be enough moisture for it, but we’ll see.

I also potted up some of the cider apple seedlings which had grown from marc set in the ground last autumn, allowed to stratify naturally over the winter and then germinate this spring. They are very vigorous and growing away well in their pots (below right). We know they won’t come true to type because they aren’t grafted on to a consistent rootstock, but it is an interesting experiment nevertheless. I don’t even know what variety/ies they are, just that they are local to the Pyrenees region.

Carré 2 (photo below left), having grown its lentils to maturity, was covered in cardboard and the remainder of last year’s bark mulch spread on top. Under normal conditions this Carré would be planted up with the next stage of forest garden plants over the coming winter, but this may now be put on hold (see paragraph 2 above). And for the question mark last month as to whether the pumpkin plants in Carré 1 would produce any fruit, the answer is given below (right)! The pumpkins have now grown even bigger than when this photo was taken.

As mentioned last month, there will again be no Wild Flower Census, but I continue to keep an eye out for new arrivals, and there was one in July – Bastard Stone Parsley (Sison amomum). The PlantNet app was 79% sure of the ID from my photo, and I think that is similar enough to be correct (see below). Can any of my readers confirm this?

For my dip into the wider world of media this month, there have been two ‘events’ of particular relevance to the developing climatic conditions and stress strategies mentioned above. First, there was an interesting discussion of the role of ‘functional biodiversity’ in a recent research paper, and to quote from the summary in the authors’ email introduction that I received: “Forest ecosystems are repositories of biodiversity and drive carbon capture, nutrient cycling and water dynamics, among the ecosystem services that are vital for human life. One key contributor to the health of a forest is its functional biodiversity, that is, the diversity of functional traits among trees, like differences in height or leaf size. Especially in face of changing environmental conditions, high functional diversity can boost a forest’s resilience to droughts, invasive species or increasing temperatures (my italics) … The paper identifies a core set of tree traits needed to quantify global patterns in forest biodiversity. This makes it possible to predict what a tree does, where it lives, how it interacts with its environment – and how it will respond to environmental changes.”¹ As always, biodiversity is the key, and the reference to performance prediction is very interesting in the light of the problems I am currently experiencing.

And secondly, this podcast on the ‘Wood Wide Web’, a play on words dreamed up by a smart sub-editor on a research journal in the 1990’s and subsequently universally adopted to describe the underground mycelial and invertebrate networks which provide the life support for forests. The podcast is an interview with Thomas Crowther, founder of the Crowther Lab, a forest ecology research unit in Zurich, Switzerland, and is refreshingly free of scientific jargon, such that at the end of nearly 30 minutes you come away with a much clearer idea not only of how this amazing network affects the ecology of the world’s treescapes, but also of the broader environmental picture in forests and associated systems today.

* Refer to the Site Map, Blog, December 1st, 2021.

¹ Email introduction to: Maynard D. S. et al (2022). Global relationships in tree functional traits. Nature Communications, 13(1), 3185. https://doi.org/10.1038/s41467-022-30888-2