Dehesa Days

Alfredo and an old ash (Fraxinus angustifolia) pollard

Tuesday February 22nd - Madrid, Spain

Today I’d planned to meet with Alfredo Bravo Fernandez - a professor and researcher at Madrid Polytechnic Institute.  He picked me up outside the metro station entry on the University campus.  Things seemed pretty ideal in Madrid at this point.  The sky was blue, the temperatures must’ve been approaching 60 (F) and I was eager to get yet another take on woodland management in the old world.  I was wondering exactly how we would find one another with me standing on a busy street side, but a few minutes later I heard someone shout my name from across the street - guess I don't blend in as much as I’d like to think I might.

Instantly I felt Alfredo’s warm and generous spirit - a young professional, with a dark beard and a calm and pleasant demeanor, we immediately set off for a nearby park for a short field trip.  Alfredo had told me that things were very busy for him early in the week with meetings every day and other work responsibilities, but I kind of pushed hoping he could squeeze in some time with me to give me a better insight into his area of expertise.  As a phd student, his thesis explored the role of thinning in ‘monte bajo’ (the Spanish term for coppice - literally short woodland) to help improve total stand health, reduce fire danger and encourage productivity.  Also having actively studied the Spanish dehesa system, Alfredo was to prove a wonderful ally in my journey.  

For those folks who aren’t familiar, the dehesa system is a remarkable silvopasture management system (silvopasture is the integration of tree crops and grazing livestock).  In the dehesa systems which cover more than 3,000,000 hectares (7,800,000 acres) throughout much of western and southwest Spain and Portugal (but also found in and around central Spain to a lesser degree) livestock graze on pasture with a canopy of oak trees. Typically these include the Holly/holm oak (Quercus ilex) and the cork oak (Quercus suber) though other species are also integrated into these systems. More a result of active integration of production systems than a consciously established system via planting, dehesas provide myriad benefits - shaded pasture, opportunities for fuelwood production, and a livestock diet supplemented by protein-rich acorns.  During dry times (typically summer and winter months), pastoralists could also harvest the evergreen foliage of the Holly oak and use them as supplemental fodder for their animals.  In the case of those systems featuring cork oaks, the outer bark from these mature trees could be harvested on a regular rotation in a way that didn’t injure the tree, thereby allowing them continuous living cover an a sustained, long-term yield of cork.  Up until the development of plastic and screw-on corks, the global wine industry relied on this very cork production system that had been sustained for centuries.  And to top it all off, pigs grazing on fallen acorns during the last few weeks of their lives are recognized the world around for the quality and flavor of their meat.  Know as ‘jamon iberico de bellota’ - ham from the Iberian peninsula finished on acorns, it’s not uncommon for this prized product to fetch $100/lb or more.  Needless to say, the residents of the Iberian peninsula developed an elegant strategy to cope with the challenges of their Mediterranean climate.

Alfredo and I spent some time getting to know one another on our ride out of the city and learning a bit more about our respective backgrounds.  He’d grown up in the city but had long had a relationship with the woods and a love of trees, and this continued to drive his studies well into adulthood.  He’d not heard of permaculture, and I was happy to be able to introduce it to him and share some resources that had been translated into Spanish.  I’m conversational in Spanish, and he’s about the same with his English so we each provided one another with an opportunity to practice our respective speech and build some new vocabulary.  Believe it or not, they don’t teach you how to say stump sprouts, adventitious buds or polewood in Spanish in high school.

About a half hour outside of town, we pulled off to park and as we crossed the street I could instantly see why.  The park was full of incredible ash pollards (Fraxinus angustifolia or ‘fresno’ en Espanol) - some of them easily three feet in diameter.  Probably last cut 15 years ago, Alfredo explained to me how their management has become a problem for the same reasons as we’ve seen in so many other places.  As they start to grow, mature, and fall out of rotation, the stems get to be too big for the ‘bolling’ (the trunk) to support them, and they become very vulnerable to damage due to high winds.  We examined some of these pollards and saw how poor attention to detail while cutting pollard shoots in the past have caused long-lasting damage to the bolling, inviting infection, disease and decay.  Alfredo explained that the cuts should be made slanted outwards, if not vertical, to force water to drain off and away from the bolling.  In the areas where this hadn’t been done, large holes had formed, inviting more water into the stem and leading to further decay.  Of course, ‘bad’ is all a matter of perspective - if you’re looking to create habitat for invertebrates and wood-dwelling fungi, this is an exceptional way to do it and as Helen Read shared in London, these ancient trees provide vital habitat for these organisms.  But that said over time, this will lead to the demise of these ancient creatures, and without an active replacement plan in place, the pollarded landscapes of today will not be sustained.

As we left the lowlands of the park and made our way up hill the landscape quickly began to shift from ash to oak and pine (primarily oak).  Alfredo told me that the primary pine species - Stone pine (Pinus pinea) - is one that produces cones with edible pine nuts.  It proved to be a minor constituent of these woodlands, but it was great to know that such multi-purpose species populate the site.

As we started to explore the uplands, I noticed surface water in a number of spots and asked Alfredo more about the soils and bedrock geology of the site.  Largely granitic and gneiss-derived, the soils are particularly coarse sands which are excessively drained and prone to leaching of their mineral fertility.  Fractures in the bedrock provide underground water channels, and in turn, leads to the emergence of springs and seeps throughout the landscape, providing active exit points for groundwater at the soil surface.  We stopped and looked at some of this exposed soil, and it had a texture not unlike that of small textured perlite, pebble-like in appearance.  With modest annual rainfall very unevenly distributed throughout the year, even abundant sunshine can only do so much towards making this a hospitable climate for year-round food production.  It’s likely because of these challenges that grazing has become such a staple of the local agriculture.  

As we came to examine the Holly/holm oak that basically dominated the landscape here (with scattered broom - Cytisus scoparius - a shrubby legume - and the deciduous Quercus fagina) strewn about) we observed the fact that Holly oak is somewhat unique in its ability to send up sprouts from both the stump and the root system.  This strategy means that trees tend to form colonies which provide low woody browse for livestock, the grazing of which ultimately does little damage to the tree.  One problem that it does create though is a propensity for fire.

Given the brittle nature of this landscape, fire is a common ecological process, and especially without the regular wood harvest that it likely once saw when the systems were under more active management, the high density of stump and root sprouts, under a low spreading canopy create the perfect conditions for fire to spread rapidly.  It’s because of this that Alfredo has been so actively examining the role that thinning plays in stand health and overall productivity.  From the perspective of an individual interested in acorn production, because the flowers of the oaks are located at the branch tips at the periphery of the tree’s crown, it’s far more desirable to have a low spreading canopy than one that tends towards vertical growth.  Thus, allowing these trees to develop a more open grown form at ideal spacings of anywhere from 15-30 meters encourages this stand structure as well as a more even partitioning of water and minerals.  

An as of yet unmentioned benefit of this silvopasture system is the fact that the pasture growth underneath the trees stays green far later in the season.  Shaded from the intense sun, furnished by the absorptive leaf litter the trees deposit and aided by the hydraulic lift caused by tree roots bringing groundwater to the upper layers of the soil, the difference between grass underneath the oaks and out in the open is clearly evident.  And adding one more benefit on top of this, the herbaceous growth located within the intervals between trees, often supports wildflowers and other flowerings plants which in turn support a healthy pollinator complex and an active apiary industry.

Scattered within this woodland - which is now more of a public recreation site than a grazed dehesa, tree tubes fill in the gaps between more mature individuals including Holly oak and olives - another well adapted multi-functional tree.  Alfredo told me there’s really no need to plant Holly oak, they do just fine spreading from their acorns though the olives may add another valuable yield.  We looked at the unmanaged structure within the stand, and I could see how the preponderance of deadwood and shrubby stump sprouts overtopped by standing trees could pose a considerable fire hazard during the dry season.  The stunted root sprouts also show very little productive growth and so their presence appears in this case to sap energy from the dominant stems of the stools.  Again, with a functional, in-tact system, these root sprouts would be consumed by grazing animals, converting them into food and nutrients and helping to control and manage the growth.

Alfredo told me that the primary products oaks furnished in dehesas were the supplemental fodder their acorns produced and fuelwood.  To his knowledge, a craft economy was not directly linked to these systems, and I could see why.  In this dry landscape, growth was relatively slow and the oaks take on a lower form with few straight stems.  While there would certainly be some potential to add value to this material through craftsmanship, it’s not ideally suited.  The material is well-suited to fuelwood though - dense, hot burning, and reaching a reasonable diameter over a modest productive cycle, oak fuelwood makes sense.

We started to circle back towards the car and passed by a few more groves of ash pollards.  Other more mesic (moist-adapted) woody species would also typically be found in these lowland ecologies including willow, poplar/aspen and sycamore (Acer pseudoplatanus).  Upon reaching the car, we turned back towards the University where we spent the afternoon.

Alfredo shared his doctoral dissertation with me while he took care of some office work.  The specialized spanish vocabulary proved to be a bit of a challenge for me, but I could tell that it contained some very useful information.  Entitled ‘SELVICULTURA EN MONTES BAJOS Y MEDIOS DE ENCINA (Quercus ilex L.), REBOLLO (Q. pyrenaica Willd.) Y QUEJIGO (Q. faginea Lam.): TRATAMIENTOS TRADICIONALES, SITUACIÓN ACTUAL Y PRINCIPALES ALTERNATIVA’, it translates roughly into Silviculture in coppice woods of oak (three species): Traditional treatments, the current situation and alternatives.

We spent the lunch hour in the faculty lounge where I met one of his colleagues Sonia Ruiz - a silvopasture specialist who has spent considerable time researching the dehesa systems.  She gave me some great insights into the evolution and distribution of dehesa silvopastures in Spain - namely throughout western Spain and Portugal, though present in some areas in the center of the country as well.  She recommended that I spend the next day visiting the upland pine forests in the Sierras north of the city and gave me detailed instructions as to how to arrive there.  A wonderfully kind person, Sonia seemed confident and driven in her work.  

After lunch I sat in on a team-taught master’s class on Ecosystem Restoration.  Covering a wide rage of topics during the course of the semester, the opening segment was focused on an overview of silviculture and was taught by Rafael Serrada, one of the most respected forest researchers in Spain.  I struggled a bit to understand the details but he used slides to illustrate his points so I was able to follow along  enough to get the gist.  He demonstrated how silviculture is the management of forest resources to provide for various cultural and societal needs, illustrating the myriad products that woodland species can provide.  By this time in the day, slightly overheated in a warm classroom and tired both mentally (exercising the Spanish conversation side of the brain is exhausting stuff) and physically, I slipped out during the mid-class break (it was a four hour lecture!) and headed back to my hotel for the night.

Ash (Fraxinus angustifolia) pollards in wood-pasture

Holm/holly oak stump sprout (Quercus ilex)

Pollarded plane trees (Acer pseudoplatanus) along a street in Madrid