Understanding the Terroir of Burgundy: Part 3.3.1 Fracturing variations within upper vineyards

Vineyard and plot variation confuses our understanding of Burgundy

High on the upper slopes, the farthest away from the Saône Valley Fault, the magnitude of fracturing within the same vineyard can vary significantly, even within the span of a few meters. Not only that, but there is evidence that the farther one moves from the main fault, the occurrence of fracturing patterns widens in its spacing, being further and further apart, and more irregular in its distribution. This means that if the fracturing is unequal within a vineyard, so can it to be unequal within a parcel. Following this uneven fracturing distribution, it becomes quite clear that a wine produced from different vineyard sections may produce wines of differents weights, and possibly character. We can only assume that this kind of intermittent fracturing, hidden beneath the topsoil, has unequally affected not only the wine made by these plots but the reputation of the vignerons who farm these plots as well.

Fractured limestone of Les Perrieres

The patterns of fracture propagation

Looking back at Part 1.2 about the deformation and fracturing of limestone, the stress that causes the main fault, and many of the parallel faults also weakens the entire stone structure through deformation. Micro-fractures appear throughout the stone, independently of one another, usually in clusters. As the cracks propagate, they do so often in a tree-like pattern, forking and spreading upward from the origin fracture, deeper within the stone. Depending on the brittleness of the limestone and the direction of the strain, these microcracks will form tensile fractures (extensional strain) or shear planes (compressional strain). Additional strain will be concentrated on the most fractured, weakest part of the stone, and this becomes the path of the fracture. Because these areas have been forced to bend and ultimately fail, this movement causes the strain to localize, increased by the stone’s own failure, causing even greater fracturing.  Alternately in the areas between the crack arrays, the stone will be only lightly fractured, and in some places, maybe not at all. It is this that makes plots within the same vineyard unequal, as much as the skill and style vignerons are unequal.

 

I have laid a vertical tree in a horizontal fashion to more dramatically illustrate fracturing within parcels. Fracturing actually happens from deeper in the stone and moves upwards to the surface, often widening and splintering as it goes. Fracturing does not always reach the surface, and this shows the disparity in fracturing one area vs. another. Mechanical weathering will accentuate fracturing where it does extend to the surface, breaking up the stone, while chemical weathering will reduce the stone to Co3 and primary clay, creating marly limestone.
I have laid a vertical tree in a horizontal fashion to more dramatically illustrate fracturing within parcels. Fracturing actually happens from deeper in the stone and moves upwards to the surface, often widening and splintering as it goes. Fracturing does not always reach the surface, and this shows the disparity in fracturing one area vs. another. Mechanical weathering will accentuate fracturing where it does extend to the surface, breaking up the stone, while chemical weathering will reduce the stone to Co3 and primary clay, creating marly limestone.

 

Clues to the Côte by examining another fault/escarpment

 

The Arugot Fault near Jerusalem is unique because the fractures to its dolomite slabs (limestone containing magnesium) lie above ground, not covered by sand or soil. Geologists are reasonably certain that the Arugot fault was an extensional occurrence (like the Saône Fault), not caused by slip-shear or other earthquake-related stresses. The Arugot fault, like the Saône Fault, was created an escarpment as the Dead Sea Basin pulled away, in a horst/graben relationship.  The area is prone to flash flooding, particularly through the deep canyons that bisect the escarpment (not unlike the combes of the Cote), and it was the erosion that rapid water movement causes have left the vertically fractured dolomite uncovered and available to be studied. The general geographical similarities of the Saône and Arugot are marred by the fact that the Dead Sea escarpment is twice as tall (600 meters), and many times more steep, with very steep angles of 75% to 80% that drop into the Dead Sea depression.

The fault itself is believed to extend several hundred meters into the earth. Parallel to the fault, a series many extensional fractures were formed, marching up the escarpment away from the main fault.  There is ample evidence that these fractures propagated from below, as the fractures are tree-like, branching vertically, splitting the rock into smaller and smaller divisions as they move toward the surface. They often, but not always, fracture through the top of the stone. Nearest to the Arugot fault itself, the fractures are very close together, and the farther away from the fault the wider the spacing between fractures until they discontinue hundreds of meters away from the main fault. The relevance of this increased space between fractures is that explains the variation between well-fractured sections of limestone, and poorly fractured sections, all within the space of a few meters. This variation extends to, and explains not only to the difference between two vineyards, but the difference between plots, or even within sections of the same plot.

fracture propagation from the Arugot fault near Jerusalem. The fractures are tree-like, and as you move away from the fault, the fractures are spaced wider and wider apart. source: earthquakes.ou.edu
Fracture propagation from the Arugot fault near Jerusalem. The fractures are tree-like, and as you move away from the fault, the fractures are spaced wider and wider apart. source: earthquakes.ou.edu

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Understanding the Terroir of Burgundy: Part 3.3 The Upper Slopes

Shallow topsoil over hard limestone: a site of struggle

As I touched on in the introduction of slope position in Part 3.2, there are significant variables effecting which vineyards can produce weightier wines further up the slope. However, as a general rule, the steep upper-slopes are far less capable of producing dense, weighty and fruit filled Burgundies that are routinely produced on the mid and lower slopes.

The lack of water, nutrients and root space

The scree filled Les Narvaux in Meursault. photo: googlemaps
The scree filled Les Narvaux in Meursault. photo: googlemaps

In many of these upper vineyards, the crushed, sandy, and in some places powdery, or typically firmer and more compact, the marly limestone topsoil overlies a very pure limestone, such as Comblanchien, Premeaux and Pierre de Chassagne. Here, the extent of that the stone is fractured determines the vines ability to put down a healthy volume of roots to support both growth and fruit bearing activity. Any gardener can tell you that insufficient root space, whether grown above a shallow hardpan or in a pot, will cause a plant to be root bound and less healthy.

Because these steeper vineyards can neither develop, nor hold much topsoil to its slopes. The topsoil, which can be measured in inches rather than feet, tends to be very homogeneous in its makeup; a single horizon of compact, marly limestone, with a scant clay content of roughly 10-15%. The infiltration of rainwater and the drainage are one and the same. Retention of the water is performed almost solely by this clay content, and evaporation in this confined root zone can be a significant hazard to the vine. Fortunately rain in Burgundy during the growing season is common, although rainfall from April to October, and particularly in July, the loss of water in the soil is swifter than it’s replacement from the sky (Wilson, “Terroir” p120).

Infiltration Rates of Calcareous Soils

A study by A. Ruellan, of the Ecole National Supérieure Agronomique, examined the calcareous (limestone) soils of Mediterranean and desert regions, where available water and farming can be at critical odds.  He studied two major limestone soil types. The first was a light to medium textured, loamy, calcareous soil (60 – 80% CaCO3), and the second was a powdery and dry limestone soil with no cohesion. This second soil had a calcium carbonate content that exceeded 70%, and had 5% organic matter and a low clay content. The water holding capacity of this soil was a mere 14%. The depth of this soil was over 2 meters deep, which likely does not allow weathered clay accumulate near the surface, as it does in Burgundy.

Both limestone soils had very high permeability, with an infiltrate at a rate at a lightning fast 10 to 20 meters per day (or between 416 mm per hour and 832 mm per hour).  Even if rainwater infiltrated at half that rate through Burgundy’s compact limestone soils, it would virtually disappear from the topsoil. This is the area where the majority of the vines root system exists, and part of the root system responsible for nutrient uptake is within this topsoil region.  In this case of these soils, the vines must send down roots to gain water in the aquifer. Wittendal, who I wrote of in Part 3, suggests in that the vines literally wrap their roots around the stone, and suck the water from them.  I have seen little evidence that limestone actually absorbs water due to many limestone’s high calcium content and lack of porosity. This would be particularly true on the upper slopes under consideration now. It would be up to the roots to attempt to penetrate the stone in search of the needed water.

The root zone

Root development through soil
This slide represents the root development in shallow topsoil over a lightly fractured limestone base vs a deeper soil situation with four or five separate bedding horizons, such as exists lower on the slopes of burgundy.The effect infiltration rates have depends significantly on the distribution of vine roots. In most planting situations, 60 percent of vine roots are within the first two feet of topsoil, and have been known to attain a horizontal spread of 30 feet, although the majority of the root mass remains near the trunk.

By design, vines rely on the roots established within the surface soil – which is where nutrients (ie nitrogen, phosphorus, potassium) are found – to gain the majority of their sustenance. They send down deeper roots to gain water when it is not available nearer the surface. However in Burgundy, many of the steeper slopes present planting situations where not only is the soil very shallow, but the nutrients are poor. The limestone in these vineyards often is hard and clear of impurities, and within the same vineyard may vary significantly in how fractured the stone is. Because of this, in some locations vines have difficulty establishing vigorous root penetration of the limestone base, and this can dramatically limit the vine’s root zone.

Additionally, because of the soil’s shallow depth, , and because of the soils high porosity and low levels of clay and other fine earth fractions, only a limited volume of water can be retained

Water is critical for both clay’s formation and its chemical structure, and the clay will not give up the last of what it needs for it own composition. The evaporation rate of what little water there might remain, can be critically swift.

Rainwater’s infiltration of the limestone base, and its retention of water can also be limited where significant fracturing has not occurred. Any water that cannot easily infiltrate either the soil or the limestone base, will start downward movement across the topsoil as runoff. That means any vine that has been established in shallow topsoil, or the topsoil has suffered significant losses due to erosion, will be forced to send roots down to attempt to supply water and nutrients.

Vine roots and a restricted root zone

In non-cultivated, non-clonal vines, powerful tap roots are sent down for the purpose of retrieving water when it is not available in from the surface soils. However our clonal varieties are more “highly divided” according to the “Biology of the Grapevine” by Michael G. Mullins, Alain Bouquet, Larry E. Williams, Cambridge University Press, 1992. The largest, thickest, roots develop fully in their number of separate roots, by the vine’s third year, and are called the main framework roots. Old established vines in good health may have main framework roots as thick as 100cm (40 inches) thick. This main framework root system, in normal soils, typically sinks between 30 cm (11 inches) and 35 cm (13 inches) below the surface.  In shallow soils, they may hit hard limestone before full growth, and may have to turn away, or stop growing. Anne-Marie Morey, of Domaine Pierre Morey, echoes this in talking with Master of Wine, Benjamin Lewin, of their plot in Meursault Tessons. “This is a mineral terroir: the rock is about 30 cms down and the roots tend to run along the surface.”

From the main framework, grows the permanent root system. These roots are much smaller, between 2 and 6 cm, and may either grow horizontally (called spreaders) or they may grow downward (known as sinkers).  From these permanent roots grow the fibrous or absorbing roots. These absorbing roots are continually growing and dividing, and unlike the permanent roots, are short-lived. When older sections absorbing roots die, new lateral absorbing roots to replace them.

This cutaway of the topsoil of Gevrey Bel Air shows just how limited the root zone is in this premier cru vineyard. The Comblanchien below is being 'reconditioned' in this plot. More on this in a near future article. click to enlarge.
This cutaway of the topsoil of Gevrey Bel Air shows just how limited the root zone is in this premier cru vineyard. The limestone below is being ‘reconditioned’ in this plot. click to enlarge.

Although the permanent sinker roots may dive down significant depths, the absorbing roots (which account for major portion of a vine’s root system account for the highest percentage of root mass, typically only inhabit the first 20cm to 50cm, or between 8 inch and 19 inches of a soils depth (Champagnol,  Elements de Physiologie de la Vigne et de Viticulture Générale 1984). Clearly this is an issue if the topsoil is only 30 cm (12 inches) to begin with.  If the absorbing roots are not growing sufficiently on the sinkers, the vine must rely on the exceptionally poor topsoil of the marly limestone.

South African soil scientist Dr. Philip Myburgh found (1996) that restricted root growth correlated with diminished yields. He also found that the “critical limit’ of penetration by vine root was 2 MPa through a “growing medium”. Weakness in the bedrock, and the spacing of these weaknesses, contributed to a vines viability.

The vines on these slopes, on which there is limited fracturing of the harder, non-friable limestone, have difficulty surviving. These locations often shorten the lifespan of the vines planted there, compared to other, more fertile locations in Burgundy, where vines can grow in excess of 100 years. It is these vines, with barely sufficient nutrients that make wines that don’t have the fruit weight that I wrote of before, simply because they cannot gain the water and nutrients necessary to develop those characteristics. The amount of struggle the vine endures directly determines the wine’s weight, or lack of it.

It is ironic, that when we research the issues the catchphrases of wine describe, ie, the “vines must struggle”, or that a vineyard is “well-drained”, or the vineyards are “too wet to produce quality wine”, we see the simplicities, inaccuracies, or the shortcuts that those words cover up. Yet these catchphrases are so ingrained in wine writing, that we don’t even know to question them, or realize that they require significantly more nuance, or at minimum, point of reference. Yes, the vines on the upper-slopes are particularly well-drained. They do indeed struggle, sometimes to the point of producing vines are not healthy, and cannot the quality or the weight of wine that the producer (dictated by their customers) feels worthy of the price.

Extreme vineyard management

Blagny sous la dos d'Ane's shallow red soils produce a Pinot that is too light for the market to bear at the price it must be sold. photo: googlemaps
Blagny sous la dos d’Ane’s shallow red soils produce a Pinot that is too light for the market to accept – at the price it must be sold. photo: googlemaps

In Blagny, the Sous le dos d’Ane vineyard, which lies directly above the small cru of  Aux Perrières, has seen at least one frustrated producer graft their vines from Pinot Noir to Chardonnay. The Pinot, from the red, shallow, marly limestone soils, was felt to be unsatisfactorily light in weight. Not only would a lighter-styled, and minerally Chardonnay be well received, the producer will be able to sell it much more easily – and for more money because he could then label it as MeursaultSous le dos d’Ane, a much more marketable name.

Bel Air. More photos on this excellent website, and a terrific discussion in the comment section, albeit in French. Worth running through a translator. source: http://www.verre2terre.fr/
Bel Air. More photos on this excellent website, and a terrific discussion in the comment section. source: http://www.verre2terre.fr/

Producers in the Côte de Nuits rarely have the option to switch varietals. They typically must produce Pinot Noir to label as their recognized appellation. In the premier cru of Gevrey-Chambertin “Bel Air”, and Nuits St-Georges “Aux Torey”, growers have gone to the extreme lengths and expense of ‘reconditioning’ their plots. To do this, they must rip out their vines, strip back the topsoil and breaking up the limestone below. In the adjacent photo, a field of broken Premeaux limestone and White Oolite has been tenderized, if you will. The soil is replaced and the vineyard replanted. The entire process requires a decade before useful grapes can be harvested once again from the site, costing an untold number of Euros spent, not to mention the money not realize had the old vines been allowed to limp on. The same has been done in Puligny Folatières in 2007 by Vincent Girardin, and there again in 2011 by another unknown producer. Ditto with Clos de Vergers, a 1er cru in Pommard in 2009.

 

http://www.wineterroirs.com/2009/11/landscaping.html

click here: for the previous article, Understanding the Terroir of Burgundy: Part 3.2 The lower slopes