Regenerative Agriculture: Agroforestry for improved soil health and as a foil against climate change

Agroforestry is one of the key soil health and land management practices of the Regenerative Organic Certification. The practice, as defined by the US Department of Agriculture (USDA), involves "the intentional integration of trees and shrubs into crop and animal farming." Agroforestry (a term coined in the 1970s) "seeks positive interactions between its components, aiming to achieve a more ecologically diverse and socially productive output from the land than is possible through conventional agriculture" and "is a  practical and low-cost means of implementing many forms of integrated land management." (Brittanica).

According to rainwater runoff.com,

Although the story varies greatly from one place to another, the practice of maintaining or integrating trees in the agricultural landscape has existed from ancient times around the world and has constituted the default practice in terms of land use management. It was only during the last centuries that farming and trees became disassociated as monocropping became more common, in an effort to intensify food production.

Brittanica cites written records of agroforesty dating back to Roman times while my research shows the incorporation of trees into the Chianti Classico vineyards in the 14th century with a 20th-century switch to low-trained vines and monocropping accompanying the failure of the mezzadria system.

The USDA has categorized agroforestry systems as shown below.

What is the direct application of agroforestry to viticulture? The image below illustrates an alley-cropping application in a vineyard.

Alley cropping (Source: yaleclimateconnections.org)

On the basis of a comprehensive literature review in her 2021 Master's Thesis, Katherine Favor stipulates that "Agroforestry can benefit vineyards in many ways, both in terms of the above- and below-ground services that it provides to vineyard ecosystems. Agroforestry has been shown to affect below-ground parameters in vineyards positively by increasing drought resistance, reducing erosion, building organic matter, bettering soil structure, and improving vine rooting capability" and above-ground parameters by "... reducing pest and disease pressure, preventing wind damage and erosion, increasing stomatal aperture and leaf area, protecting against heat stress, and protecting against frost."

Summarizing the findings of her research on agroforestry below-ground services, Favor states:

Existing studies reveal that the presence of trees in vineyards imparts a neutral to positive effect on parameters surrounding grapevine water status and water stress despite competition, due to trees’ ability to reduce evaporation and transpiration, modify the microclimate, and distribute water through hydraulic lift. Studies show that trees likely have a slight negative effect on grapevine nutrient status within 4 m of trees; however, trees also have been proven to significantly improve vineyard soil quality. Trees may also potentially increase vine rooting depth and density by improving soil structure and inducing root plasticity. Overall, the positive below-ground services that trees provide in vineyards, paired with the ecological and cost-saving benefits that trees impart to a viticultural ecosystem as a whole, might very well balance out these negative effects.

The above-ground services revolve around pest and disease, altering light patterns and vineyard microclimate.  In the area of pest and disease management, Favor finds:

The existing research on integrated pest management in vineyard agroforestry systems demonstrates the effectiveness of utilizing agroforestry to create heterogeneous vineyard landscape designs as a way to combat pests and diseases. Monocultural vineyard designs are associated with numerous pest management issues that leave vineyards vulnerable to losses, dependent on pesticides, and economically less-resilient. Creating diverse vineyard agroforestry systems by incorporating trees into vineyards has been shown to benefit insect pest management efforts by providing habitat for natural enemy insects and vertebrates, which results in increased abundance of natural enemies, increased parasitism rates, reduced insect pest pressure, and subsequently, reduced yield losses. Although vineyard agroforestry systems can cause increases in pest insect abundance as well, the existing literature shows that the accompanied increases of natural enemy populations result in overall increased insect pest control and reduced herbivore damage. Vineyard agroforestry systems may also control bacterial and viral infections by controlling the insect vectors that transmit these pathogens, however, great care must be taken to avoid intercropping grapevines with trees that could be hosts for harmful viral and bacterial vectors. The prevalence of fungal infections in vineyard agroforestry systems may be increased by the increased shade that trees impart, but may be reduced by trees’ windbreak effects and by the beneficial reductions 52 in vine vigor that occur as a result of below-ground competition between trees and vines. The presence of trees in vineyards also facilitates the proper timing of precision pesticide applications by slowing wind and creating conditions conducive to pesticide application at the precise moment when pest pressure is at the proper threshold.

For light patterns:

The presence of trees in vineyard agroforestry systems impacts light patterns, which, in turn, affect wine grape physiological, production, and quality parameters in both positive and negative ways. Trees reduce the quality and quantity of light that reaches understory crops, trees reflect light from their canopies onto understory crops, and tree shade reduces temperature ... In wine growing regions impacted by high temperatures and more frequent heat waves, shade from trees may benefit grapevines by reducing sunburn from UV radiation, maintaining photosynthesis rates, preventing yield losses from shriveling, maintaining adequate sugar levels, preventing acid degradation, allowing anthocyanin development, and promoting synchronized development of flavor profiles for an overall balanced and high-quality wine. In wine growing regions that are less impacted by climate change, shade may have opposite effects, and may reduce levels of SS, acids, anthocyanins, and yield. In all regions, regardless of the predicted impact of climate change, shade is speculated to have a negative impact on flavonols and long-term anthocyanin stability. 

As regards microclimate:

Trees benefit vineyards by positively affecting wind patterns and the viticultural microclimate. Although incorporating trees into vineyards can increase management complexity, can reduce yields nearest to trees, and can negatively affect certain grape quality parameters, research suggests that the many above-ground benefits of vineyard agroforestry may very well outweigh their costs. The positive above-ground services that trees provide, such as preventing wind damage and erosion, increasing stomatal aperture and leaf area, increasing photosynthetic capacity, protecting against heat, protecting against frost, and reducing water stress suggest that vineyard agroforestry systems may be a wise solution to the many problems facing modern viticulture, especially considering the extreme temperatures, weather events, pest and disease pressure, and micro- and macro-climatic shifts that are predicted to come in the following years with climate change. 

When agroforestry's above- and below-ground services are paired with its ecosystem services (water purification, pollution mitigation, carbon sequestration, biodiversity conservation, maintenance of  a beautiful landscape aesthetic) "the case can be made that agroforestry's applications in vineyards have the potential to create regenerative viticultural systems that are able to both resist and mitigate many of the issues that modern viticulture is presented with" (Favor).

I will be providing greater detail on agroforestry above -- and  below-ground services -- and their parameter impacts -- in future posts.

 

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