Friday, 31 March 2017

Energy from the land - Photovoltaic solar panels

This post is a part of the series An Acre of Sunshine.  

While all of the posts that I've written so far have focused on the energy that we can harvest through the plants and animals that we grow on the land, these are not the only way to make the sun's energy useful to us. There have long been ways of harvesting some of the sun's energy as heat, and it has become now become feasible, and even economical, to convert the sun's energy directly into electricity, and humanity uses a lot of electricity to make our technologically intense world go round. Photovoltaic (PV) panels are not the only way of generating electricity from the sun, but have become a very practical way to provide power at both a small and large scale. All of the most complicated work of assembly is done in a factory, and once wired into place, the panels need little to no maintenance for their lifetime of several decades. 

 Solar panel arrays at the author's home

I won't bother going into the details of the history of photovoltaics, or their chemistry for that matter, but I do think that it is important to compare and contrast PV with photosynthesis at a higher level. Plants evolved photosynthesis over a very long timescale, figuring out through trial and error how to capture some small fraction of the energy pouring down in sunlight and passing it along through a quite long series of chemical reactions until it reaches a form that can be used to grow and maintain a plant. As was discussed here, this process has an efficiency of about 2%, and that is only when conditions are just right. When it comes to photovoltaics, scientists and engineers were inspired by photosynthesis, but free to explore the possibilities afforded by any materials available, not just those organic molecules that make up plants. Metals, glass, inorganic compounds of all kind were fair game as they tried to figure out how to harness sunlight. It has also turned out to be the case that it is easier to generate electric current than it is to build up sugars, fats, or other chemical energy storage. Put together this means that the PV panels widely available today can turn about 15% of the sun's energy into electricity, and can work on any day of the year; they don't take the winter off the way that our local plants do. These panels can create a steady stream of electrical energy any time they are exposed to sunny skies, and even cloudy skies to a lesser extent.

Estimate #1. From first principles.

We only really need one estimate here, as the numbers are really quite straightforward. First is the question of how efficiently PV panels can convert solar energy into electricity. At the moment, the typical commercially available panels are roughly 15% efficient, though more expensive ones approach 20%. Some laboratories are pushing to 30% or beyond with new architectures and chemistries. For the sake of argument, we shall stay with that 15% number.

 Les Mées Solar Farm, Photo by Jean-Paul Pelissier/Reuters

The second aspect to consider is how much of the ground is actually being covered with the panels. Native ecosystems often have leaves spread over every inch of ground, whether it be a forest canopy or a field of waving grasses. While one could simply spread out solar panels flat on the ground covering every inch, this isn't an efficient use of resources. Instead panels are tilted so that they are as close as possible to perpendicular with rays of sunlight streaming down. And because one doesn't want the panels to shade each other out, it is necessary to space them out on the land. In larger installations, this spacing also makes for easy access between the rows of panels for doing any needed maintenance. Solar farms often actually cover only about 25% of the surface area where they are found. With these two figures we can do the same calculations for annual harvest that we have done for other land uses:

5,112,641 kWh/acre/year of sunlight * 15% efficiency * 25% packing factor = 191724 kWh/acre/year

For those of you keeping score, this is tremendously more energy than anything that can be harvested from plants. This is 10-15 time the energy that one could get from our most productive plant of corn, and 50 times the energy that can be harvested from cutting timber. The two arrays seen at the top of the page at my house are capable of producing about 10,000 kWh/year, roughly the same as what 3 acres of forest can do. Electricity can't be easily turned into food or furniture, but for anything that electricity can do, this makes photovoltaics a very easy winner.

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Food from the land - Annual crops

This post is a part of the series An Acre of Sunshine

Going along with the main theme of this series, the following post gives some quick estimates about the energy yields that different crops can produce, starting with a more in-depth discussion of corn.

Estimate #1 for Corn - From first principles

Cereal crops are plants that are grown for their starchy seeds, including corn, wheat, barley, oats, and others. When it comes right down to it, these are some of the most important plants for feeding the world. Corn makes a good example, and is one of the most productive crops per acre, period. The following estimates are for field corn, which is quite different than the sweet corn that you have eaten at dinner. It is much richer in oils, yields much more energy per acre, and is primarily used for animal feed, ethanol fuel production, as well as thousands of other uses in processed foods and chemical products.

In looking at photosynthesis, we found that our farm has about 36000 kWh/acre/year of basic photosynthetic energy production. Out of that amount, a plant needs to grow, metabolize, fight off predators, as well as to create that portion of the plant that is useful to us. In this case, what we actually want is the kernels of corn on each ear. Research on this subject shows that approximately 50% of a mature corn plant's energy is found in the kernels on the ears of corn, while the other 50% is in the stalk, leaves, and root system. This is actually a tremendous proportion of the energy of a corn plant that is found in the kernels. It is pretty incredible that these plants are able to funnel fully half of their energy into their seeds and that such a surprisingly small proportion is needed to grow the rest of the plant.


The other thing to account for is what proportion of the energy that a plant captures is put towards growth, and what proportion to maintain the health of the plant as it lives day to day, known as respiration. One source estimates respiration on a global scale at 20%, so as I didn't quickly find an actual figure for corn, we shall use that number. With this calculation, we get:

35788 kWh/acre/year * .5 (proportion of stored energy in seeds) * .8 (losses for respiration) = 14,315 kWh/acre/year of harvested corn kernels.

Estimate #2 for Corn - Real world yields
As I was not able to easily find Quebec data, I will instead use Ontario estimates of corn production to make an estimate. These recent data state that corn yields are typically around 150 to 170 bushels per acre per year of field corn (a bushel of corn is 56 pounds). As our farmland is of a much lower quality than the average farmed acre in Ontario, it could produce perhaps only about 2/3 of the average production. This means that one of our acres could produce:

150 bushels/acre/year * 2/3 (reduction for poor quality land) * 56 pounds/bushel * 1550 Calories/pound * (1 kWh/860 Calories) = 10093 kWh/acre/year


Other crops
In my last post, I showed a graph that included Calorie yields for many staple crops, and those are easy to convert to our usual unit of kWh. I also found plenty of sources (e.g., here and here) that listed the productivity of crops of all kinds, which often end up being much lower total energy because of how few calories many vegetables have (having high water content, high fiber, low fat). I've put a few of those estimates in the following table.




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Food from the land - Growing domesticated crops

This post is a part of the series An Acre of Sunshine.

Domesticated crop plants are quite peculiar. As was discussed in my hunting and gathering post, wild plants don't tend to produce very much human food. The selection pressures that are in place on wild plants are for their own survival and reproduction, and while they often have edible seeds, fruits or roots, how good a food they are for people was a non-factor in their survival. The adoption of agriculture changed plant selection drastically as it became people doing the hard work of ensuring the survival and reproduction of their crops, while selection pressures were refocused on making bigger, better, and more nutritious edible parts that are easier to harvest. And when you look at today's crop plants, they look downright bizarre compared to their wild counterparts. All of the parts that we like to eat and use are comically large when compared to those of their wild brethren. A typical corncob is close to a foot long and weighs over a pound, whereas for corn's wild ancestor teosinte, you could hardly call the tiny seed pods a cob (see picture below). Modern corn is amazingly good at providing food for people, but would not fare well for long without people to plant and tend to it.  And of course this sort of breeding change for size is only one of a multitude of ways in which people have changed both plants and their growing environment.

Image courtesy of http://evolution.berkeley.edu/evolibrary/news/070201_corn

While plant harvest often focuses on seeds and fruits, it can also be based on many other parts of a plant. Cabbage provides a wonderful example of how a single wild plant can be bred for many different foods, and wild cabbage is the progenitor of a dozen different vegetables today. Broccoli and cauliflower are flower clusters, kohlrabi is a part of a stem, while cabbage, brussel sprouts, kale and others are all modified leaves.  Really any part of a plant that grows in such a way as to have edible sugars, fats and proteins is viable as human food. And then there are the crops for non-food purposes like fiber or oil.

 Farming and yields

Whether organic or not, mechanized or not, genetically modified or heritage breed, the goal of farming is generally to have the highest possible yield per acre. This generally means creating a relatively simple ecosystem that provides the crop plants as close as possible to 'perfect' growing conditions. Important considerations include:
-Maintaining good nutrient levels, often with fertilization of some sort.
-Maintaining proper amounts of moisture, sometimes with irrigation.
-Reducing competition between desired plants and other plant species. While there are many ways to achieve this, the most common are some form of weeding or herbicides.
-Reducing predation on the crop plants from insects, birds and mammals.
-Reducing the detrimental effects of microorganisms, be they bacterial, viral, or fungal.

The vast majority of farming today in the western world uses a very technology heavy approach, with large tractors and implements, and heavy loads of fertilizers and pesticides. Traditional small-scale farming, and such modern reinventions of it as Permaculture, have a very difficult time competing economically with these conventional broadscale farming practices. These traditional techniques generally require large amounts of human labor, and don't benefit from the economies of scale that can be gained when farming 500 acres instead of just a few. And these modern farming techniques are only increasing their yields. See below for a graph of the yield trends for a number of major staple crops.
Graph courtesy of Math Encounters Blog

Our farm and its crops

Our own farm and those around it were first developed in the last decades of the nineteenth century by Irish immigrant farmers. The Moran family founded our farm, and the neighbors had names such as Flynn, Egan, and Brennan. They arrived with, or soon after, the wave of loggers coming up the Gatineau River. In those early days the first step was to open up the forest to create fields, which required cutting down any trees remaining after the loggers passed through, followed by digging out all of the stumps in order to make it possible to till the soil. They were probably only able to open one or two acres per year, and on our property they converted a total of 18 acres of some of the less hilly terrain on our property over to fields.

The early days of our farm mixed subsistence and market farming, growing a little bit of everything, plant and animal, to provide for the needs of the family. Any excess could then be sold on to the logging camps or down to the Ottawa area. At this time, the farmers grew a wide variety of crops, from garden vegetables to row crops like wheat. Since they were growing most or all of their own food, it was absolutely necessary to maintain variety so as to have a relatively balanced diet throughout the year.


An abandoned wheat thresher on the author's property

As with small family farms all over North America, this model began to make less and less sense as the twentieth century progressed. With mechanization and additives like pesticides and fertilizers, small-scale farms just couldn't compete. This was especially true in an area like ours, with hilly and relatively infertile soil that didn't have as high of yields and was much less conducive to industrialized farming techniques. The farms in our local area slowly consolidated so that many fewer farmers each farmed much more land, and shifted to one of the only models that remained economically viable, beef cattle farming. So while our farm isn't likely to go back to annual crops anytime soon, no discussion of land use would be complete without them.


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Wednesday, 8 March 2017

Food from the land - Raising beef cattle


This post is a part of the series An Acre of Sunshine.

Every time I pass in or out of our property I have to open and close two cattle gates as our small one lane road passes through a neighbor's pasture. If our little road saw any more traffic than it does, the road would need to be fenced out of the grassy areas beside them, but for now we often have to slow down and honk to get the cattle to shuffle off to the side of the road. You really get to know the cows when you have to shoo them out of the way on a regular basis.

In the area immediately surrounding our property most of the agriculture consists of raising beef cattle, as well as some draft horses. The soil is too rocky and the hills too steep to allow our area to be economically competitive in growing row crops, but the sloping fields grow grass just fine. The fields on our own farm have been used primarily to support cattle for about the last 50 years. Before that there was a wider variety of agriculture, but these others were mostly abandoned as cattle became the mainstay of the local farms.

For these operations, the farmers are in the grass business every bit as much as the cattle business. Grasses only grow from the spring through the fall, but since cows need to eat during the winter also, farmers must harvest enough grasses to provide for the snowy months. During the summer, technically May to November, cattle are brought to the grasses, to feed on pasture. This reduces the work of the farmer tremendously, as the cows harvest their own food. The farmer does have to fence off the paddocks, ensure water supplies, and move cattle between the fields, but this is less intensive than preparing for the winter months. To provide for the winter food needs, the farmer needs to maintain other grass fields for hay, cutting and baling the growth and setting it aside to be doled out as needed to keep the animals well-fed. The same fields can be used for both haying and pasture, but can only primarily provide for one of these in a given year.



It doesn't seem like that much would be required to grow grass, just to cut down any trees, and then let the cattle come through to eat as they would. But in actuality good pasture is a crop like any other, just that it is a perennial crop that only needs to be replanted every 20 or 30 years, rather than each spring. The usual way of establishing pastures is quite similar to planting row crops. One plows up a field to prepare the soil and kill off competing plants, and then the seeds of a variety of grasses and forbs are planted, with names like alfalfa, orchard grass, Timothy, fescue, and clover. These fields often are helped by the addition of trace nutrients as well as fertilizers. Once the fields grow in, they can be maintained for many years. The degradation of pastures and hayfields can be from nutrient depletion or changes in the species composition of the grasses present. When cows are allowed a lot of space, they work through and eat only the choicest morsels, leaving all of the less desirable plants standing. Over time, these undesirable plants can come to dominate the entire fields, to such an extent that the fields must be plowed and replanted.

Once the growing of the grasses is accounted for, one has to look at the business of actually raising beef cattle. Every year there is a seasonal ebb and flow that takes advantage of the natural cycles of the region. During the winter, the herds are almost completely made up of pregnant females, with just a few bulls that are only there to sire the next generation. In the spring all of the cute little calves are born, drinking only milk for their first weeks of life, transitioning over the summer months to the adult diet of grasses. As soon as the fields are showing good signs of growth, the herd is released out to pasture for the summer. The calves put on an amazing amount of growth throughout their first year of life. In the late fall, at around the same time as the pastures go dormant for the winter, the vast majority of the calves are sold off, most often to a feedlot where the calves will continue to put on weight for up to another year before becoming someone's dinner. The calves that are kept by the local farmers are generally the best females, which become the next generation of mothers. These cows, known as heifers, can be bred when they are as young as 15 months.


The cycle actually begins again during the early summer, as cows have a gestation period of about 280 days. This means that in order for a cow to have one calf each spring, it needs to be bred the prior summer, when the prior calf is only 2-3 months old. This also means that all cows should be pregnant in the fall when the calves are sold off, and very often those cows that didn't conceive are sold at the same time. It turns out that roughly 15% of cows don't get pregnant in a given year, which can be due to age, illness, or just random chance in whether the bull did his job. Cows may continue to breed for 10 years or more before age catches up with them.

Putting all of this together, one needs to grow enough pasture and cut enough hay to maintain a mother cow for the entire year to produce an 8 month old calf for sale. Those calves sold and destined to become beef will be fed mostly grain, including a lot of corn, for the rest of their lives. We won't include this feedlot part of cattle production in our calculations here, though I'll try to return to it at a later time in another post. So how much cow does an acre support?


Estimate #1. First principles
As discussed in 'Energy capture, conversion, and storage, a good first rule of thumb is to assume that each time a new level of an ecosystem consumes energy, that only 10% of that energy goes into the next level. We already made an estimate of the total amount of energy captured by photosynthesis, which in this case would be by the grasses. This energy is then used for metabolism, growth, reproduction, etc., of the plants, and only roughly 10% would of that energy would be available to the cows in the form of leaves and stems. Then the cows of course have their own metabolism and growth to deal with, meaning that only about 10% of the energy that the cows consume will end up in the form of cow flesh, which is what the farmer is most interested in.

35788 kWh/acre/year of photosynthesis * .1 for leaves and stems eaten by cows * .1 for efficiency of cows in turning food into weight gain = 358 kWh/acre/year of cow produced


Estimate #2 Going on available data for actual production
We can also look at typical agricultural yields, and see how much food a pasture typically produces, as well as the data on how efficient cows actually are in their growth and reproduction. I wasn't able to easily track down data for western Quebec, but did find what should be roughly comparable data, from the Manitoba Forage Council. This data shows that pasture produces from 2000 to 4000 pounds of forage per year, depending on plant species, fertilization, and water availability. Lets call it 3000 pounds of dry matter, as it is called, for the sake of calculation. Hay contains roughly 800 Calories per pound, so...

3000 lbs/acre/year * 800 Calories/pound * 1 kWh/860 Calories = 2790 kWh/acre/year of grasses

Further, a cow (pregnant and/or milk producing) requires roughly 30 pounds of food a day, or 10950 pounds through a year. In that same year, the calf will grow from an embryo up to roughly 500 pounds by the time of sale in late fall. The calf primarily drinks milk for the first couple of months, transitioning to the adult diet of grazing over the summer. All told, that calf will consume perhaps 1500 pounds of forage on top of the mother's intake over the summer and fall. Put together, it then takes...

10950 lbs forage (for cow) + 1500 lbs forage (for calf) * 800 Calories/lb * 1 kWh/860 Calories = 11580 kWh to maintain a cow for a year and to produce a 500 pound calf.

Finally, how much energy is harvested out of this system in a year? It is of course all of the calf, but it also ends up being the mother cow, around 15% of the time. As mentioned above, the cows generally aren't kept another year if they do not get pregnant over the summer. These cows average about 1200 pounds. When butchered, about 50% of a cow is meat, distributed over lean and fatty cuts. Some rough estimates suggest that this meat averages around 800 Calories per pound. It was difficult to find data on the embodied energy in the rest of the cow, including entrails, bones, skin, etc., so I will assume that these other parts have the same energy density as the meat. Put together, this means that...

(500 lbs (calf) + 1200 lbs (cow)*.15 (harvest rate of female cows)) * 800 Calories/pound * 1 kWh/860 Calories = 633 kWh of energy per year from raising a cow/calf pair.

The last step is to level out this amount of energy from a cow/calf pair back to a single acre:

2790 kWh/acre/year * 1 cow calf pair/ 11950 kWh * 633 kWh/ 1 cow calf pair = 148 kWh of energy in the form of cow harvested from one acre in a year.


Estimate #3 Actual production from our farm
Finally, we can make an estimate of the productivity of our farm from the actual production that we have observed over the last few years. We have 18 acres of pasture, and have used these fields both as pasture and hayfields over the last five years. In the first couple of years after the purchase of our property, we had one of the farmer neighbors put cow/calf pairs out to pasture on our farm. Since then, another local farmer has cut hay off of the same fields.

When we had cattle on our property, this was a herd of 20 cow/calf pairs which were rotated between our property and another nearby, such that the herd was on our property half of the time. This effectively makes 10 cow/calf pairs for the six month growing season. The calculations from estimate #2 can be adapted, as we know that each cow/calf pair needs 11580 kWh per year:

11580 kWh of forage /cow calf pair * 20 pairs/18 acres * 1/2 of the year * 1/2 of the time = 3217 kWh/acre of forage produced in a year.

In the years since we switched to haying, there has been quite a bit of variability in the weather, including both one very wet as well as one very dry summer. The summer of 2016 was a more average year, and in this year the property produced 50 large round bales of hay from a cut in mid-summer. In many climates farmers can get multiple cuttings of hay from a single field in a year, but with the relatively poor soils and shorter growing season, most of the local fields are cut only once. This does mean that the late summer and early fall growth aren't available for cattle unless the cattle are allowed to graze through later in the season.  Below is the calculation for the amount of energy found in those bales, with weight and Calorie estimates for the hay drawn from here and here.

50 bales/18 acres * 1000 lbs/bale * 800 Calories/pound * 1 kWh/860 Calories = 2580 kWh/acre/year of grasses

These two estimates, that our fields produce between 3217 and 2580 kWh, are very much in line with Estimate # 2 so going forward we will go with that the final figure estimated there, of 148 kWh/acre/year of cow being harvested per year from grassy fields.


Visualizing this growth
As discussed above, before getting to cattle one has to have grasses. Below is a picture of a big round haybale, weighing around 1000 pounds. Each acre of our fields can produce about 3 of these per year. Averaged out over the entire year, each acre is growing 7 pounds of grass per day, a big handful.

Round haybale with author and son for scale

In the picture below, the calf is approaching that 500 pound size, typical for when they are sold off in the fall. The mother is still over twice that weight, around 1200 pounds, and stands around 5' tall. To support that mother and calf for the year, it requires about 4 acres of hayfield and pasture.



Growing other animal species, or for other products
The above discussion was all about cow and calf cattle farming, the mostly small scale operations feeding their animals on pastured grass. I didn't address the 'finishing' process for beef cattle, where the calves live in a more constrained environment eating more grains as they put on additional weight and size. Nor did I discuss growing other animals for food, or such products as the milk or eggs that can be obtained from those animals. In terms of the amount of energy that can be converted from sunlight to the end agricultural product, growing beef cattle is one of the least efficient. The adult cows must be maintained for many years, and they usually have only a single calf per year. Further, cows are somewhat less efficient than some other types of animals at converting feed into weight gain. And just look at other examples like chickens or pigs. Each of these produces many more young in any given year, as well as those animals reaching market size much more quickly. The takeaway is that these other types of animal husbandry can produce significantly higher yields per acre. The upside of beef cattle is that they take much less effort on the part of the farmer, they can be raised on land of marginal quality, and there is high demand and therefore a good price for beef. Needless to say, I may try to make a more quantitative comparison in a future post.


Estimate for total cow production: 148 kWh/acre/year

Previous Page: Fossil Fuel Footnote
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Monday, 6 March 2017

Fossil Fuel Footnote

This post is a part of the series An Acre of Sunshine.

The process of biomass growth and harvest that I've described in other posts for other land uses is of course very similar to how fossil fuels were formed, but occurring over thousands to millions of years. Today's oil, natural gas, and coal were originally plant matter that did not immediately decay and became buried. All this organic matter was then subjected to time, heat, and pressure in the earth's crust, and slowly transformed in these conditions to become the fuels that we use today. Of course, only a tiny portion of the energy that was in the original plants actually is still accessible in fossil fuel deposits today, but this energy is exceptionally concentrated and has powered the world for over a century.

I found one calculation of the amount of plant matter needed to create fossil fuels, here. These researchers found that it took 200,000 pounds of original plant matter to create 1 gallon of today's gasoline. If we were to tuck in some of the numbers from my discussion of firewood, we get the following:

(89000 kg biomass needed per gallon of gasoline) * (2.2 pounds/kilo) * (1 cord of maple firewood/4600 lbs) * 7034 kWh/cord = 299,000 kWh of wood to make 1 gallon gasoline (37 kWh).

This energy conversion, from ancient plants to today's oil, preserves only 1 part per 10,000 of the energy found in the original plant growth. To put this into the terms of other posts in this series, this means that a year's growth for an acre of primeval forest led to the formation of about 1/100 of a gallon of gasoline, .4 kWh/acre/year. In a typical car, this would take you less than half a mile down the road.


Previous Page: Food from the land - hunting and gathering 
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Thursday, 9 February 2017

Food from the land - hunting and gathering

This post is a part of the series An Acre of Sunshine.

Natural wild ecosystems are amazingly beautiful and complex. Though northern forests may not be as diverse as many areas nearer to the tropics, there are still thousands of species found on our farm alone, plants, animals, insects, fungi, micro-organisms and more. These species all exist in a delicate balance, each with its own niche in the environment, feeding on and being consumed by others. I am not alone in my love of being out at the lakes and mountains, forests and fields, just to soak it all in. On the other hand, the energy moving through this system is not well optimized to produce food for people. In the time before the invention of agriculture, humans everywhere existed primarily by hunting and gathering, traveling over large areas and collecting what food they could find naturally occurring in the wild.

At first blush, it seems like there would be lots of food available right out in the woods. There are many different species that have historically been hunted available right in our area. Over the last few years, just on our own property, I have seen white-tailed deer, snow-shoe hares, squirrels, ground hogs, porcupines, skunks, beavers, otters, coyotes, ruffed grouse, spruce grouse, wild turkeys, ravens, Canadian geese, several species of ducks, and even a couple of black bears. While only some of these are hunted today, they were all on the menu when times were tougher than today1.

Then there is a great diversity of wild plants that one can eat in the form of leaves, grasses, tubers, berries, nuts, and more. There are also edible mushrooms growing in our woods, including such species as morels, chanterelles, chicken of the woods, and puffballs. While I haven't been that much of a forager myself, I have dabbled in wild berries, dandelions, the occasional hickory nut. I will instead defer to other sources of expertise, and my understanding is that a couple of the very best foraging books for plants in my climate in eastern Canada come from Samuel Thayer, who lives and forages around Wisconsin, The Forager's Harvest and Nature's Garden.
Pin cherries are a bit tart but still tasty

Of course lots of variety doesn't mean that there is large total availability. We don't see too many people living as hunters and gatherers today, and there are some very good reasons for it. Though there is a bewildering array of diversity just on our farm, the flora and fauna are spread rather thinly across the landscape, with animals ranging across many acres of land to find their food. For the plants, there are only a relative few concentrations of those that provide good food sources to people. Another major problem with great diversity is the harvest. With hundreds of different species to be hunted and gathered, it takes both an incredible amount of time and depth of knowledge to find it all and harvest it efficiently. There are very few peoples in the world who have continued a hunting and gathering lifestyle for any great length of time after they have been exposed to the food concentration that comes with farming. Finally, a climate like that found in eastern Canada makes food very seasonally limited, with many types of food only available during a short window each year.

So how far will an acre get us? Unlike some of the other land uses that I discuss throughout this piece, I couldn't find any precise estimates of the total availability of wild food. So, I've taken a couple of methods and done some 'back of the envelope' calculations.

Estimate #1: Density of Native Americans prior to European colonization

Now I realize that it isn't being fair to native Americans to classify their lifestyle as solely hunting and gathering, as they did a great deal to modify their environment and practiced many forms of agriculture. However, archeological and historical knowledge of our area of eastern Canada2 suggests that hunting, fishing and gathering accounted for most of the food of the local Amerindians. The history that I have read suggests that immediately before the arrival of Europeans the local natives summered in large camps along the Ottawa River and hunted their way through the hinterlands during the winter, relying mostly on small game and stores from the fall's harvest. Our property falls squarely in the middle of those historical winter hunting grounds, being forested hills near a major navigable river. This same text suggests that the population density of these peoples was only one individual per each 27 square kilometers.

We know how much food energy each person needs, and we have an estimate of the population density, so we can make an estimate of the total food energy production per acre per year for native peoples:

(2.32 kWh/person/day) * (365 days/year) *(1 person/27 square kilometers) * (1 square kilometer / 247 acres) = .12 kWh/acre/year

This estimate suggests that each acre produced on average much less one day's worth of food each year. Most years a given acre of forest probably didn't provide any food, while others would give up a few handfuls of mushrooms, some berries, or in a lucky year, some wild game.

This sort of estimate doesn't account for seasonality or technology. There was much more food available in the summer and fall with all of the ripening plants and young of the year animals, but pre-European peoples did not have the same abilities to harvest, preserve and store food that we do today, nor did they have modern weapons that would allow them to harvest all of the available game. To account for that, and the amount of time that would really be needed to harvest all of the hundreds of edible species throughout the year, let us say that the actual population was only able to fully take advantage of 1/100th of the total potentially available food. This brings us to an estimate of:

.12 kwh/acre/year * (100 units food available/1 unit fully utilized) = 12 kWh/acre/year

Estimate #2: Ecological estimates of the carrying capacity for wild edible species
Another way to come at this same question would be to take a look at the science of ecology, in that biologists have long been studying the populations and distributions of native flora and fauna. I will start with the wild game, and then move on to a semi-educated guess about available plants and fungi.

For almost all of the larger animal species found on our property, especially those that are hunted, there are relatively good estimates of the population densities. These are especially useful for natural resource agencies and are used to evaluate the health of populations and set hunting regulations to maintain the health of those populations. To make the estimates below, I found what sources are available for the number of animals/acre. Many of these species actually have ranges of tens of acres or more per individual, so the numbers can be quite small.

Providing a few ecological estimates:
White tailed deer -  30 deer/mi sq *(1 sq mi/640 acres) * (1 of 3 deer harvested per year) * 40 pounds meat per deer * (.7 kWh/pound) = .4375 kWh/acre/year of venison
Ruffed Grouse - 50 grouse/mi sq*(1 sq mi/640 acres) * (1 of 2 grouse harvested in fall) * .5 pounds meat per bird * (.6 kWh/pound) = .012 kWh/acre/year of grouse meat
Other calculations end up being similar, for species such as wild turkeys, small mammals, bears, etc. Being generous, wild game could add up to something like 2 kWh/acre/year of meat in our region.

Edible wild plants that I have seen locally: Berries (blueberries, raspberries, strawberries, hawthorne berries), tree fruit (wild crabapples and plums, edible tubers (e.g., cattails), nuts (acorns, butternuts), stems and leaves (dandelions, basswood leaves), young growth (fiddlehead ferns, wild leeks), mushrooms (morels, chanterelles). This is of course not a comprehensive list, nor could I find precise figures on harvest rates of wild plants and edible fungi, but I did come across many admonitions to avoid overexploitation of these species, as it can cause their decline. For the sake of argument, one could imagine that it may be possible to harvest 40 pounds of plants and mushrooms per acre in unmanaged forest, field, and marsh, which would yield:
(40 pounds/acre/year) * (500 Calories/pound on average) * (1 kWh/860 Calories) = 23 kWh/acre/year

This total estimate of 25 kWh/acre/year is roughly in line with the first calculation above.

Estimate #3. Percentage of total available photosynthetic energy

From here we have an estimate of 35790 kWh/acre/year worth of energy harvest by plants on our property. This energy is the original source for all of the wild edible species available, whether they be plants, animals or even fungi. From the estimates above, this means that something on the order of one part per thousand of the total energy captured by plants in the forest reaches a form that could reasonably become food for someone who is hunting and gathering. If it truly were one part per thousand, then we would have:

35790 kWh/acre/year * .1% efficiency at creating human food = 36 kWh/acre/year

As all of these estimates are so small as compared to other land uses, we will go ahead and use this last and largest estimate going forward.

How far would hunting and gathering get me and my family?

36 kWh hours worth of tubers, berries, leaves, seeds, meat, and fungi. This really is not very much on the scale of human needs, as this is only 15 days worth of human food for each acre of land. At 150 acres, our farm property could then support the food needs of 6 people, if those people had the skills and time to harvest, process, and store all of the naturally available foods available on the property.

(36 kWh/acre/year of food produced) * (150 acres) / (849 kWh/person/year of food) = 6.4 people supported.

Even with the proper skills and knowledge, the harvest and processing of all of this food would be close to a full-time job, leaving very little time to, say, hold down a job to support those needs other than food. This would be bare subsistence and there would be no excess to sell or trade. On top of all that, even though I consider myself fairly knowledgeable in such things, I don't have anywhere near the expertise necessary to find and process all this variety of food. I think that the best takeaway from this analysis is to show that in today's world, hunting and gathering belongs in the place where it sits, as a pastime for those who enjoy being out in nature and like to eat in a more adventurous way.
Wild plums in early August

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1 I have a copy of a classic cookbook called the Joy of Cooking that I inherited from my grandmother. This edition is from 1950. The most fascinating section to me in this book is on wild game, with instructions for skinning, cleaning and cooking a wide variety of species that I have never heard spoken of as dinner possibilities, including raccoon, porcupine, and beaver.
2 Gaffield, Chad et. al. History of the Outaouais. Laval University Press, 1997.

Wednesday, 25 January 2017

Logging, cutting down trees for wood products

This post is a part of the series An Acre of Sunshine.

Logging was by far the single biggest economic driver during the settling of the region of our property, as it was in many parts of North America. Ottawa, the nearest large city and capital of Canada, began as a logging town. Ottawa is situated at the Chaudiere waterfall on the Ottawa River so as to take advantage of all of the hydropower available there, used to cut logs that were floated down the rivers. Our own property lies near the Gatineau River, which flows right into the city of Ottawa, and our area was first logged in the mid to latter part of the 1800s. Everything about our local region has been shaped by logging, down to the location of the villages up and down the Gatineau River. There is a small village every 8 to 10 miles, spaced just at the distance that a horse-drawn sleigh could move per day in the winter, with a small hotel and stable springing up at each camp that later developed into a village of its own.

While I don't have a complete history of our actual property, a look through the history of the region and the tell-tale signs left behind in our woods tell much of the story. Before the arrival of Europeans, our property was heavily forested, mostly old-growth white pine, sugar maple, basswood, white spruce and red oak. On the first pass of logging in the mid 1800s, loggers took only the large white pines. These trees make for great construction lumber and were also a favorite for ship masts, with the trees growing to four feet across and as much as 150' tall. Only the pines were cut at first, in part because these trees could be floated down the river and be brought to market; all of the maple and oak were so dense that they would sink. Starting at the end of the nineteenth century, softwoods like spruce were sent down the rivers to be made into pulp and paper. The arrival of the railway and logging trucks just after the turn of the century opened up the possibilities of cutting the denser hardwoods. Following these waves of cutting, there were many openings and clearings left behind, and these areas filled in with what is called 'secondary' forest, made up of a greater variety of species, including those that need much more sunlight, like aspens, white birch, and black cherry. Our property today is a mature secondary forest. Secondary forests similar to ours abound today throughout the northern states and eastern Canada, from Minnesota east to the ocean.

Along with these bigger logging operations, our place has been farmed since the 1870s, and every farmer throughout the region has used their woodlots to provide a steady supply of wood to build and heat their homes, barns, and workshops. Our property was commercially cut once more in 2008, harvesting some of the fast growing and sun-loving trees like aspen, as many of these trees were reaching the end of their 80 year lifespans. Our forest is now in the process of moving very slowly back towards a more old growth condition similar to what came before the waves of logging.

In eastern forests like ours, it is usually best practice to do what is called selective cutting (for more information see here, here, and here). In a regime like this, one cuts only a modest portion of the trees at any given time, while leaving the rest to grow and fill into the gaps left by those that are removed. This can preserve a relatively natural looking landscape and maintains much of the wildlife, understory, and ecological relationships of an unmanaged forest. Done properly, one cuts out those trees that are sick, weak, or poorly formed, as well as some of the 'good' trees, while leaving some healthy trees of all sizes. This allows the straightest and healthiest trees to grow with relatively little competition. Unfortunately many loggers, if left to their own means, 'high-grade' when they do selective cuts. This means that they take only the most valuable trees while leaving everything else behind, which can leave a forest without good growing stock for many decades to follow. A well managed selective cut should take approximately 1/3 of the trees at a time, and can be repeated approximately every 15 years in perpetuity. This means that one is then harvesting 15 years worth of growth and energy on each pass through the forest. One could just as easily cut less trees more often, which homesteaders and farmers often do, but for commercial logging the amount of heavy equipment used necessitates doing much bigger harvests to justify bringing in the equipment. Our own property has most likely been cut in successive 'high-grade' cuts, where loggers went through and took only the best, while leaving the rest. The forest still holds promise, but is not what it could have be, had it been taken better care of.

Clear cutting is another, and often much more villified, approach to logging. In clear cutting, loggers go through and remove every tree, or at least every tree worth harvesting. While this can be a reasonable thing to do in certain situations and areas, clearcuts require many decades before the forests can recover, and if one wants to encourage slower growing species like oak and maple, it can take even longer. In the early years after clearcutting, there is such a profusion of young trees that they end up wasting much of their energy in competing with each other, rather than turning that energy into growth. On the flipside, this is a tremendously efficient way to harvest. One can collect all the accumulated energy of decades worth of growth, and loggers don't need to be careful about working around any trees that are to be left behind.

What does an acre of forest actually include?

As we are trying to keep our understanding of energy in the human scale of one acre, it is worthwhile to talk about what that would actually mean in terms of individual trees. This amount could of course vary tremendously between a developing forest of young trees versus an old growth forest holding only a few giants; a forest could vary from just a few dozen huge trees to many thousands of seedlings in an acre. For the purposes of illustration I will go ahead and describe what an acre of our own forest looks like.

I did a tree survey of our property a couple of years back so I actually have a quite good idea of what is there. In doing tree surveys, it is not usually worthwhile to count the thousands of small saplings, so the only trees counted are those that are 4" or more in diameter at chest height. Foresters randomly sample small areas around a property, and then can extrapolate to estimate an entire site.  My sampling estimate is that on each of our acres there are a total of 318 trees bigger than 4" (as of 2012). The large majority, 257 trees, are of the smaller sizes between 4" and 8". Trees of this size are often left unharvested. Then there are the medium size trees, those 10" to 14", of which we have about 55 per acre. These are getting up to what would be a respectable size for a tree in a suburban yard, and are starting to be valuable for logging. Then finally there are the larger trees, those larger than 16" across, and our farm property has 6 of these trees per acre. It is these larger trees that are the favored target of logging in eastern forests like ours. Of all our trees, about a quarter are sugar maple, with 9 different other species each making up 5% or more of the forest, and finally another dozen species present in smaller proportions.

The numbers above make it easy to overestimate how skewed the population is towards small trees. There are almost always many more small trees than large, and while these are the growing stock of the future, many of them won't survive to reach large size. Even though 80% of the trees in our  forest are in the small sizes (8" or less), once you account for how big the average tree is, they make up only around one third of the total amount of biomass present. Each of the big trees can weigh thousands of pounds, while the smaller trees may only be one or two hundred pounds. As mentioned above, our own forest has been overharvested in the larger sizes of trees. If our forest were in peak health according to best forestry practices, it would have a much higher proportion of the biggest trees, perhaps as many as 20 per acre that were 16" or more, instead of the 6 that we currently see. With continued good management, we should return to peak condition over the next few decades; forest management requires an enormous amount of patience.

Embodied solar energy in wood.

It is easy to see that there is a lot of energy bound up in wood. An individual tree in our area can reach three or more feet across, and some reach to 100 feet or more in height. Almost everyone has sat next to a crackling campfire and felt the heat rolling off just a few small pieces of wood. Though it makes up only a small portion of the energy used in developed countries today, one needs go back only a bit more than one hundred years to reach a time when wood provided the majority of world energy needs, and wood is still a primary fuel throughout the developing world.

Wood really is an excellent energy resource. It is relatively energy dense, it grows for free, is very widely distributed, is easy to harvest and process, it stores well, and can be used on demand. The main reason that wood can't directly compete with fossil fuels is because of the sheer magnitude of fossil fuel use, but before the industrial revolution the total amount of energy being used was vastly lower than today.

Firewood is of course only a small proportion of what timber is used for today, with the lion's share of it going to lumber, paper, or other wood products. Most of the energy embodied in wood is bound up in cellulose and lignin, primary building blocks in the make-up of woody tissue. The molecular structure of these materials has very useful properties, giving cohesion, strength, compression resistance and rigidity. Most wood products take advantage of these properties, whether the final product is construction lumber, fiberboard, or paper. As long as the molecular structure is preserved, most of the energy stays locked up in the wood. In a way, all of the wood used to build your home is energy that has been frozen in time, to be released only at such a time as that wood decays or burns at some point in the future.

From an energy perspective, one of the most interesting things about forests is their ability to store energy for a relatively long time. For no other land use is it possible to store years, and even decades, worth of solar energy in the form of biomass, all in a form that is very manageable for people to process, store and use. In some ways, one can think of those long straight trunks as huge living batteries, storing up energy until such a time as that energy is needed. For the sugar maple which are the most abundant on our property today, it is not uncommon for individual trees to live 300 years or more. All of this means that one can extract tremendous amounts of energy on a single pass through a woodlot.

Energy estimate #1. From first principles.

To estimate how much energy is turned into trees in a given year, we first need to determine the steps that would reduce the total amount of energy that goes into the final product that we are interested in, wood. We have already established an estimate for the total amount of energy that plants are able to harness from sunlight at 36,000 kWh/acre/year. This is the amount of energy that our acre of forest has to grow, create leaves, produce seeds, and live the rest of its life.

The first thing that every tree needs to do is to support itself through each day, moving around water and nutrients, keeping all tissues healthy, which is known as 'maintenance respiration'. Trees, being very large and very long lived, have a lot of maintenance that they need to do to allow health and vigor for decades and even centuries. I wasn't able to get a lock on a precise number for this that would apply to our northern forest, but I did find some related information here, here, and here. I imagine that there is an expert that could give a more precise figure, but the numbers here indicate that from 50% to 80% of a tree's energy is used for maintenance, leaving the rest for growth. For the sake of argument, we will use the figure of 2/3, 67%.

The next thing to consider is where all of the growth is actually happening within each tree. A tree has to build all of its component parts, the trunk, branches, leaves, flowers, seeds, fruits, roots. Let us start with reproduction, flowers, seeds, and fruits. As will be discussed in a later section on orchards, nut and fruit orchards can be quite productive, growing up to several thousand kilowatt hours worth of nuts or fruits. These are, however, an extreme case of breeding and domestication for the purpose of maximizing fruit and nut production. Native tree stands don't produce anything like this in terms of seeds. The closest thing found in numbers around our property is red oaks, which can grow quite large crops of calorie-rich acorns. Acorns will produce something like 800 kWh of acorns per year in a pure stand of oaks (see calculation below). All other local trees produce much less total seed and fruit. Counting all of flowers, fruits, and seeds for the native trees, let us estimate that on average an acre of trees spends about 1000 kWh/acre/year to reproduce, about 10% of the energy that the tree would have left after respiration.

1000 pounds acorns/acre * 40% of acorn is edible * 1755 calories/pound * 1 kWh/860 calories = 816 kWh/acre/year of acorns

Then there are the varying parts of the tree itself. I found a couple of estimates for the relative sizes of different parts of trees, here and here. The second of these articles even gives a distribution for how much each part of a douglas fir tree weighs (not found in our area, but it should work as an approximation). This states that the breakdown is as follows; leaves 3%, small branches 8%, main trunk accounts for 62% in the wood and 10% in the bark, and finally 17% in the stump and roots. Most of the time, logging is aimed almost exclusively at harvesting the wood of the main trunk, and relatively little use is made of the rest of the tree. Occasionally small branches are chipped and bark is used for heating, but for the most part, it is that 60% of the tree that is the trunk is the desired product. For the sake of argument, let us assume that each part of the tree takes the same amount of energy to produce, meaning that it took an equal amount of energy to make the same total weight of roots, trunk, or leaves.

Putting the numbers above all together, one gets the following:

35790 kWh/acre/year productivity * (1 part growth/3 parts total respiration) * .9 (10% energy needed for seeds, flowers, fruit) * .6 (proportion of total tree that is the trunk) = 6440 kWh/acre/year of wood

Energy estimate #2. Measured sustainable wood harvests in forests like ours.

In reading about the topic and speaking with guys who sell firewood as a business, I have come across the same estimate for sustainable firewood production many times, at least for our northern forest (areas further south with longer seasons and better conditions can have higher yields). This estimate is that a well-managed woodlot can produce about half of one cord of wood per acre per year indefinitely. For those of you who don't burn wood at home, a cord is a volume measurement, equal to 128 cubic feet, often thought of as a stack of wood 4' wide, 4' tall, and 8' long. Different types of wood have very differing densities, but if this were sugar maple, which is a very commonly used firewood, this half cord would weigh around 2300 pounds. Being that folks have long been interested in how much heat (energy) they could get out of firewood, there are plenty of resources that list the amount of energy that can be wrung out of a cord of firewood. That calculation yields the following:

.5 cords harvest/acre/year * 24 million btu/cord of sugar maple * .000293 kWh/btu = 3516 kWh/acre/year.

While almost all wood could be turned into firewood or wood pulp, other lumber products can only be made with the 'best' wood, the straightest, most sound, with the fewest knots and imperfections. It turns out that the figures for lumber are also easily available, and that somewhere between 1/3 and 1/2 of harvested wood tends to be good enough quality for lumber products.

Being conservative, and given that there is a lot of guessing going on in the 'first principles' estimate above, we will go forward with this second more conservative estimate of firewood yield as our best guess for the amount of energy that can be sustainably harvested from our forest in a given year.


Energy estimate #3. How much energy is actually harvested in a selective vs. a clear cut?

I mentioned two different approaches to harvest above, and just wanted to quickly highlight the differences between them for the long term management of land. The established best practice for eastern deciduous forests would be a selective cut each 15 years or so, taking out about 1/3 of the volume of wood each time. However, after each cut, there would be healthy trees of all sizes, so that the forest is constantly in a sweet spot where it is putting on 'good' growth. This is the sort of state that would allow that 3500 kWh/acre/year, though it would actually be harvested in 15 year increments, taking out over 50,000 kWh of wood at each harvest.

Contrary to that, the clearcut takes a mature forest and removes all of it at once. The yield is great, as much as 150,000 kWh of wood. The problem is regeneration time. When the forest begins to regrow, there are far too many small trees, and they will 'waste' a lot of their energy competing with each other. What is more, if one is hoping to harvest relatively slow growing trees like maples or oaks, it will take at least 100 years for the forest to have lots of larger trees of these species. One could then clearcut again to restart the process. The quick and dirty math here shows that this would be a total yield of only 1500 kWh/acre/year, less than half the total rate of selective cutting. Unfortunately, it is difficult for people to put long term planning and interests over short term gains, and this certainly isn't a problem limited to forestry.


Visualizing wood growth

So what does this amount of wood end up looking like when gathered all in one place? As mentioned just above, that half cord is a good place to start, a pile that is 4' cube of stacked firewood pieces.
the pile in the foreground is a bit over half a cord

If you had that one year of growth all turned into lumber, one could build the frame for about a 10'x12' shed, with floor joists, stud walls, and roof trusses (siding, flooring, and roof would be extra).

this shed frame is 10'x12'

To give one more version, here is a picture of the wood that each acre of our forest produces each and every day (averaged over the year).


For a much more in-depth and technical look at this same process discussed above, see the following book chapter:
Pretzsch, H. From Primary Production to Growth and Harvestable Yield and Vice Versa: Specific Definitions and the Link Between Two Branches of Forest Science. In Forest Dynamics, Growth and Yield: From Measurement to Model, 2009.






Estimate for total wood production: 3516 kWh/acre/year


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