Pecan orchard. Photo by H.F.Schwartz, CSU, Bugwood.org
(Click on the following link to listen to an audio version of this blog … Ecology of nut trees Part 2
Pecans are the sixth-most abundant dietary nut in the world. In 2022/2023, 0.164 million metric tons of pecans were sold on the world market. Pecans are primarily grown in the southern United States but with irrigation can be grown across the dry Southwestern states all the way west to California. There are also cold-hearty varieties that can be planted as far north as Oregon and Washington State. Georgia is the leading producer of pecans in the United States (142 million pounds a year) followed by New Mexico (77 million pounds per year).
A pecan tree reaches maturity at 12 years of age and may reliably produce nuts for 200 or 300 years! They generate very stable, long-term orchard ecosystems!
Pecans require about 68% of the water needed to support almond trees, and they need almost constant irrigation to survive and be productive. A pecan tree can only survive 2 or 3 weeks in drought conditions. High levels of nitrogen fertilizer are also needed to support nut production, and pest and disease control (weevils, aphids, a variety of fungal diseases) often necessitate the application of chemical pesticides and fungicides. Squirrels are also often a serious problem in pecan orchards. They are typically dealt with via guards and barriers attached to tree trunks and also by direct hunting and disposal.
The long, stable time frame of a pecan orchard is an extremely good feature of this system of nut production. The high water demand and the pesticide and fungicide uses, though, are significant environmental drawbacks.
Macadamis orchard. Photo by CABI Digital Library.
Macadamia nuts are the seventh-most abundant dietary nuts in the world. In 2022/2023, 78 thousand metric tons of macadamia nuts were sold on the world market. Macadamia trees are native to Australia and New Zealand but are grown in many countries around the world. Macadamias are the fastest growing nut crop in the world! Currently, South Africa is the leading producer of macadamia nuts (26 % TWP) with Australia in a close second place (22% TWP). China, though has been very actively planting 2 million macadamia trees a year and is expected to produce 63% of the world’s macadamia crop by 2025. The United States (primarily in Hawaii and more recently in California), Kenya, Guatemala, Malawi and Zimbabwe also grow macadamia nuts.
Macadamia trees begin to make nuts after 5 years but do not reach maturity and full production potentials until they are 10 or 12 years old. Trees can remain extremely productive for over 100 years! The very stable, long-term macadamia orchards help to stabilize watersheds and reduce soil erosion. They also act to store considerable quantities of carbon (the average macadamia orchard is a net CO2 sink of 14.5 tons of C per year!).
Macadamia trees grow best when planted in regions that receive 50+ inches of rain a year. The trees, though, handle drought very well, but need water when going through a flowering cycle. Research has shown that they have a very precise level of control of their leaf stomata and, therefore, lose very little water through transpiration. Also, studies in South Africa have shown that minimal irrigation stimulates the trees to produce more higher quality and more abundant nuts.
The trees are subject to extensive insect and disease stresses, and are often grown using extensive pesticides and fungicides. Programs in South Africa, though, are working toward management schemes that minimize chemical intervention in the growing of these nuts.
Macadamia nuts are well on their way to becoming a truly sustainable crop!
Stone pine tree. Photo by Karova. Wikimedia Commons
Pine nuts are the eighth-most abundant dietary nut in the world. In 2022/2023, 41 thousand metric tons of pine nuts were sold on the world markets. Pine nuts are primarily harvested from wild pine forests. There are a few pine nut plantations, but their overall nut production makes up a very small percentage of the world’s pine nut crop. Historically, the harvesting of pine nuts involves gathering the ripe pine cones that have fallen from their trees. Large groups of laborers pick up the cones by hand and fill great bags of cones for processing. Some newer harvesting techniques used in China and Russia, though, actually cut cone-ladened branches from standing pine trees or even cut down the trees themselves to harvest cones still attached to their trees. These destructive harvesting methods can do great damage to the pine forest.
Most pine tree stands are not managed at all. There is no irrigation, no pesticide or herbicide use and no fertilizer applications. The only drawbacks to this system of pine nut harvesting are the possible excessive removal of a natural food source upon which a number of bird and mammal species depend, the destructive harvesting techniques employed by a small number of Chinese and Russian nut gatherers, and the extreme reliance on manual labor to gather the pine cones.
Pine nuts are harvested from a large number of pine species. In Northeast Asia the Korean pine (Pinus koraiensis) is the most frequently harvested, and in West Himalaya the chilgoza pine (P. gerardiana) generates most of the harvested nuts. In Europe, most pine nuts are gathered from stone pines (P. pinea) and in North America, most pine nuts come from the various pinyon pine species of the West and Southwest United States.
Pine nuts are very expensive because of remoteness of most of the pine forests and the costs of gathering and transporting the nuts. Overall, though, pine nuts are the most “natural” of all of the edible nuts and by far the most sustainable.
Brazil nut tree emerging from rainforest. Photo by MyFavoritePetSitter, Wikimedia Commons
Brazil nuts are ninth-most abundant dietary nut in the world. In 2022/2023, 28 thousand metric tons of Brazil nuts were sold on the world market. Brazil nuts are produced by a large, wild tree of the Amazon rainforest (Bertholletia excelsa). The Brazil nut tree can grow to heights of 160 feet and can live for 500 to even a 1000 years! It is one of the largest and longest lived trees of the rainforest! Almost all commercial Brazil nuts are harvested from wild trees. Attempts to grow Brazil nuts in plantations have not been successful.
Flowers of the Brazil nut tree are pollinated by an extensive array of wild bees. These bees are most abundant in the pristine rainforest, and, so, productive Brazil nut trees only grow in undisturbed rainforest ecosystems. Deforestation of the Amazon rainforest is having a very serious impact on Brazil nut production.
Agouti (several species of the rodent Dasyprocta) are larger, longer-legged relatives of guinea pigs that live in the Brazil nut tree rainforest. Agoutis are able to crack open the tough casing of the Brazil nuts and eat and also bury the Brazil nut seeds in food caches. Some of the cached seeds germinate and form new tree seedlings. This agouti-mediated seed burial is principal way that Brazil nut trees are regenerated in their ecosystems.
Brazil nuts in husk. Photo by L.Golgher, Wikimedia Commons
Brazil nuts are very high in selenium and if eaten to excess can cause a very serious selenosis syndrome. Symptoms of high blood selenium include bad breath, nausea, diarrhea, skin rashes and fatigue.
Brazil nuts are the epitome of a sustainable crop in their rainforest ecosystems. Their harvesting, though, is extremely labor intensive and may not conform to ethical labor standards. Also, all of the global stresses negatively impacting the rainforests of South America (deforestation, Climate Change, etc.) have negative impacts on potential Brazil nut production.
Peanut field in India. Photo by Abhay iari, Wikimedia Commons
Peanuts are by far the most abundant dietary nut in the world. In 2022/2023, 50.5 million metric tons of peanuts were sold on the world markets. This is a value that is almost 10X greater than all of the other dietary nuts combined! Peanuts are a below-ground nut crop that is only grown in extensively managed agroecosystems. Peanuts require less water than most other nuts (for example, peanuts use only 11% of the water required by almonds to produce an ounce of nuts). Peanuts have a very long growth and development period (4 to 5 months) and, so, can only be cultivated in places with long growing seasons.
Peanuts are legumes and, thus, have root nodules filled with nitrogen-fixing bacteria. This ability to biologically fix nitrogen reduces the overall requirements for fertilizer application.
Peanut plant. Photo by B.Ganguly. Wikimedia Commons
Peanuts flower above ground and after self-pollination, send the fertilized, budding ovary (a structure called a “peg”) down into the ground. The peanut then develops from this ovary. A single plant may repeatedly flower and send up to 50 pegs down into the soil. A typical peanut plant makes 35 to 50 peanuts.
The green parts of the peanut plant are typically left in the field after harvesting to form a “green manure” rich with nutrients for the growth of a subsequent crop.
Peanuts are beset by a wide array of pests and diseases and require high levels of fungicides, herbicides and pesticides to produce a viable crop. Peanuts and peanut products often contain high levels of these chemical residues. Organic varieties of peanut products sound like a very good idea!
To summarize: nuts are an important part of a healthy diet. They have both direct and an indirect effects on your health. Many nuts have serious environmental or ethical problems associated with their cultivation, harvesting or gathering. Brazil nuts, pine nuts, macadamia nuts and to a lesser degree, pecans and pistachios are good choices for edible nuts. Peanuts grown organically are also a good choice for a dietary nut. Almonds, walnuts and cashews have such serious problems that it is probably best to avoid them.