The meaning of the word “ecosystem” can very wildly depending on perspective. Some people might imagine the African savannah with elephants and giraffes running around. Or a lush rainforest with an amazingly biodiverse array of plants, insects and mammals. I think of those things, but I have also grown to greatly appreciate the many small ecosystems that are constantly around us, from the soil to a nearby river, pond or lake. Many of the organisms that inhabit these ecosystems are very small, or even microscopic. Despite that, they are capable of forming complex relationships and doing amazing tasks. The world would not be the way it is without them. One such small ecosystem that I have an affection for is a piece of rotting wood. I spend a lot of time in the woods, and something that is omnipresent, no matter the season, is branches and logs of various that have fallen on the forest floor in various stages of decompostion.
Woody vegetation evolved about 400 million years ago, according to Fazan et al. (1). This important adaption was essential to add stability to plants as they grew taller to outcompete other plants for precious sunlight. A side effect of this evolution was a dramatic change in the earth’s climate. Plants are among the best carbon sinks in the world, so that explosion in vegetation drew a lot of carbon out of the atmosphere. This new world order caused some problems initially for the earth’s decomposers. Wood is much more difficult for other organisms to break down than other plant material, as it not only contains cellulose, but also lignin, two very difficult polymers to break down. Lignin in particular is very difficult, as it is what is responsible for the strength of wood and bard. For a while, our decomposers were not up to the task. As explained by the US Energy Information Administration, when trees died they just stayed on the ground or sank to the bottom of a swamp, and became what is coal today (2). The reason we are not up to our necks in wood today is because of the work of some amazing decomposers. By breaking down wood, it clears the forest floors for other things to grow, and add the nutrients that were in that wood back into circulation to be used by others. This piece will discuss some of the amazing organisms that accomplish this feat.
Woody vegetation evolved about 400 million years ago, according to Fazan et al. (1). This important adaption was essential to add stability to plants as they grew taller to outcompete other plants for precious sunlight. A side effect of this evolution was a dramatic change in the earth’s climate. Plants are among the best carbon sinks in the world, so that explosion in vegetation drew a lot of carbon out of the atmosphere. This new world order caused some problems initially for the earth’s decomposers. Wood is much more difficult for other organisms to break down than other plant material, as it not only contains cellulose, but also lignin, two very difficult polymers to break down. Lignin in particular is very difficult, as it is what is responsible for the strength of wood and bard. For a while, our decomposers were not up to the task. As explained by the US Energy Information Administration, when trees died they just stayed on the ground or sank to the bottom of a swamp, and became what is coal today (2). The reason we are not up to our necks in wood today is because of the work of some amazing decomposers. By breaking down wood, it clears the forest floors for other things to grow, and add the nutrients that were in that wood back into circulation to be used by others. This piece will discuss some of the amazing organisms that accomplish this feat.
Fungi
As fun as it would be to save the stars of the show for last, the story of wood decomposition cannot be told without fungi. Fungi are the premier decomposers we have, hiding mostly unseen in the soil doing work nothing else on earth can do. While other organisms aid in the task of breaking down wood, nothing can do it as quickly and completely as fungi. Some species are considered problematic, as they can rot living trees, or can cause economic damage by destroying wood that humans need, like telephone poles or housing. Despite the issues they may cause, they are so important to the natural (and vital) degradation of wood. There are so many species of fungi that it can be tough to wrap your mind around, but as far as wood decomposition goes, they are lumped into a few different categories as pointed out by Johnston et al.(3).
White rot is the most complete form of decomposition. These fungi are capable of breaking down every component of the wood, including lignin. The texture of the wood can vary as the process proceeds, as different components will be broken down at different rates. It is called white rot because it removes the lignin that is responsible for much of wood’s brown color, and weathering will often turn it white. White rot is particularly interesting for human use, as a result of its lignin degrading properties, explained by Chaurasia et al. (4). Bio-pulping is the use of white wood rot fungi in the production of paper. Paper is a very expensive item to produce, in terms of energy and environment damage. The wood is usually chemically treated as wood chips in order to remove the lignin. But as smart as we are, millions of years of evolution is way better at this process than us. When fungi is used to treat the wood chips instead of chemicals, not only will it be more environmentally just by the lower use of chemicals, but there is also a 25-30% decrease in energy costs in the use of bio-pulping. It also reportedly creates brighter and tougher paper that is studier when folded, per research done by Kumar et al. (5).
Johnston et al. explain that another type of wood decomposing fungi is brown rot (3). It is brown because it breaks down carbohydrates, but leaves lignin. Carbohydrates are not easy to break down, as our stomachs can attest to after eating too much bread. But this fungi releases chemicals that chop up those carbs into more easily digestible form. This fungi is most responsible for the damage caused to human property. The last type of decomposer is soft rot. This type mostly breaks down carbohydrates, but can also break down lignin a bit. This leaves the wood a slightly lighter brown color, because most of the lignin remains. This gives rotting wood that characteristic soft, squishy feel that many of us are familiar with.
Hyphal growth rate is the most important factor in the rate of wood composition according to George Washington University (6). Hyphae are the underground extensions of fungi that are little threads that branch over and over in many different directions, similar to tree roots. The hyphal extensions are very important for the fungi, as they allow it to both find food and absorb those nutrients. It makes a lot of sense that this would cause faster wood decomposition. The extra hyphae increases the fungi’s contact with the wood so more of it will decompose at any one time. The rate of hyphal growth does not depend solely on the fungi though. Weather plays an important role. As you most likely know, fungi grows best in humid conditions. In dry areas wood will decompose much more slowly due too the slower fungal growth. Despite fungi’s mastery of decomposition, they do not act alone.
Bacteria
Bacteria are the most numerous and omnipresent type of organisms on the planet with Lehman estimating a population of five million trillion trillion, or five with thirty zeros behind it (7). They live everywhere, from inside our bodies, deep in the ocean, high in the atmosphere and far below the earth’s surface, so it is hardly a surprise to find them living on some rotting wood. What is remarkable about these species, however, is that they are also capable of breaking down lignin, reports Singh et al. (8). They are not as prolific as fungi, but play an important role nonetheless. Although they are much slower, the big advantage they have over fungi is their ability to thrive in harsh conditions, even conditions where oxygen is low or not even present. They even have the ability to survive the toxic chemicals people sometimes apply to wooden structures to prevent fungal growth The wood degrading bacteria use two different strategies for breaking down wood: tunneling and erosion.
Tunneling bacteria do what you would expect based on the name (science is sometimes kind in naming things). The bacteria colonize on the cell walls of the wood, attached to it by a slime they are able to produce. Then those bacteria begin to tunnel their way inside the cell. The slime helps them slide through the tunnels, and amazingly the bacteria never bump into each other’s tunnels, which suggests some kind of communication, write Singh and Nilsson (9). But why would they tunnel in rather than just start from the outside and work their way in? One hypothesis suggests that this allows them to hide from their predators, such as roundworms, that cannot fit into the tunnels. These bacteria are very important in wood degradation when fungi are not able to function properly, like trees with very high lignin content or trees that produce chemicals that are toxic too fungi.
Erosion bacteria is more commonly found in submerged wood, per research done by Pedersen et al. (10). Water can help preserve wood more a much longer period of time than on land, as the growth of many decomposers is inhibited, as proven by the survival of many old wooden objects, like a wooden well that is estimated to be 7,200 years old, reported by Wu (11). Erosion bacteria are able to live in the ocean depths or in bogs, likely covered in sediment where oxygen is low or even absent. Even though these wooden artifacts are often well preserved, they will often have a filmy, soft outer layer, and that is the result of erosion bacteria. They differ from tunneling bacteria in that they start from the outside and work their way further into the cells. Not much is known about these bacteria, as they are not well studied and have so far proven impossible to grow in culture. The last class of organisms we will discuss is one much more familiar to most of us.
Insects
Many wood boring insects are considered problematic pests, like termites, or harmful invasive species, like emerald ash borer, that cause massive ecological damage. They can cause issues, but they do play a role in natural wood degradation as well. It is believed at no insects have to ability to digest lignin, but they can degrade it so it’s easier for fungi and bacteria, or they can work in a symbiotic relationship with them according to Geib et al. (12).
Termites are most ubiquitous wood eaters. They have been the bane of many homeowners existence for many years, but they also do important work in natural areas. The National Wildlife Federation reports that termites eat wood, and much like cows when they eat grass, have bacterial and fungal communities in their guts that help break down the complicated cellulose fibers (13). There are also many families of wood boring beetles. While termites only eat dead wood, many of these species eat dead and living wood, according to Filipiak (14). These beetles spend most of their lives as larvae, that burrow their way thought the wood, eating it as they go. They only live as mature adults for as long as it takes them to be able to reproduce.
Not all insects that makes their homes eat strictly wood. The ambrosia beetle is an interesting example of this. It bores into the wood, but do so in order to get to the fungi that they exclusively feed upon. They also clean out their tunnels of wood shavings to create good growing conditions for those delicious fungi, according to research done by Stokland et al. (15). Some species eat a combination of wood and fungi. For example, the beetle species Peltis grossa is only capable of eating wood that is inhabited by a specific fungi, Fomitopsis pinicola. Stokland et al. also say the diet of the beetle will change over time, from wood that is hardly decomposed at all, to heavily decomposed wood with much of the fungal hypae mixed in (15).
There is one species that I want to give special mention, but I am cheating a bit as it is not an insect. Sea daisies, really small animals that is a relative of the sea star, are known to only live on sunken wood in the ocean at depths of about 1000 meters, per encyclopedia.com (16). These armless creatures eat the dissolved nutrients in the wood, as well as bacteria and mollusks. If they need to move to another piece of wood, they can contract their bodies and float through the water.
Since the evolution of woody vegetation, it has dominated the planet. Despite rapid human population growth and the removal of many forests, data by Ritchie shows that animals account for 0.4% of earth’s biomass, and humans 0.1% of that, while plants account for 82.4% (17). These plants are so important to the life on earth. They not only provide oxygen that sustains nearly all other life, but trap enormous amounts of carbon dioxide that would otherwise be in the atmosphere, warming it. I think most people understand and appreciate this, but maybe do not have as good an understanding of what happens on the other side, when things die. These organisms are equally important. If these trees did not decompose, not only would we be living on a mountain of dead plants, but the nutrients would be trapped and be unable to be used to help other trees grow.
In our modern world, where so much of what we regularly use is made of wood, these organisms are often viewed as pests. I hope this can help change that perspective, as these organisms are an absolutely vital part of the food web. My inspiration for this piece was my own experience looking at a beautiful rotting log. It was covered in moss and fungi of various species with all manner of insects running around on it. The array of biodiversity on such a relatively small object, in the middle of the suburbs, is super cool. I would highly recommend that anyone take the time to examine a good rotting log and see for themselves all the various fungi and insects living in it. If possible, check in on it from time to time. The transformation from hard wood that seems so strong, to a material that will crumble in your hands, is incredible. Hopefully, this piece sheds some light on some of the many organisms that make that possible.
Many wood boring insects are considered problematic pests, like termites, or harmful invasive species, like emerald ash borer, that cause massive ecological damage. They can cause issues, but they do play a role in natural wood degradation as well. It is believed at no insects have to ability to digest lignin, but they can degrade it so it’s easier for fungi and bacteria, or they can work in a symbiotic relationship with them according to Geib et al. (12).
Termites are most ubiquitous wood eaters. They have been the bane of many homeowners existence for many years, but they also do important work in natural areas. The National Wildlife Federation reports that termites eat wood, and much like cows when they eat grass, have bacterial and fungal communities in their guts that help break down the complicated cellulose fibers (13). There are also many families of wood boring beetles. While termites only eat dead wood, many of these species eat dead and living wood, according to Filipiak (14). These beetles spend most of their lives as larvae, that burrow their way thought the wood, eating it as they go. They only live as mature adults for as long as it takes them to be able to reproduce.
Not all insects that makes their homes eat strictly wood. The ambrosia beetle is an interesting example of this. It bores into the wood, but do so in order to get to the fungi that they exclusively feed upon. They also clean out their tunnels of wood shavings to create good growing conditions for those delicious fungi, according to research done by Stokland et al. (15). Some species eat a combination of wood and fungi. For example, the beetle species Peltis grossa is only capable of eating wood that is inhabited by a specific fungi, Fomitopsis pinicola. Stokland et al. also say the diet of the beetle will change over time, from wood that is hardly decomposed at all, to heavily decomposed wood with much of the fungal hypae mixed in (15).
There is one species that I want to give special mention, but I am cheating a bit as it is not an insect. Sea daisies, really small animals that is a relative of the sea star, are known to only live on sunken wood in the ocean at depths of about 1000 meters, per encyclopedia.com (16). These armless creatures eat the dissolved nutrients in the wood, as well as bacteria and mollusks. If they need to move to another piece of wood, they can contract their bodies and float through the water.
Since the evolution of woody vegetation, it has dominated the planet. Despite rapid human population growth and the removal of many forests, data by Ritchie shows that animals account for 0.4% of earth’s biomass, and humans 0.1% of that, while plants account for 82.4% (17). These plants are so important to the life on earth. They not only provide oxygen that sustains nearly all other life, but trap enormous amounts of carbon dioxide that would otherwise be in the atmosphere, warming it. I think most people understand and appreciate this, but maybe do not have as good an understanding of what happens on the other side, when things die. These organisms are equally important. If these trees did not decompose, not only would we be living on a mountain of dead plants, but the nutrients would be trapped and be unable to be used to help other trees grow.
In our modern world, where so much of what we regularly use is made of wood, these organisms are often viewed as pests. I hope this can help change that perspective, as these organisms are an absolutely vital part of the food web. My inspiration for this piece was my own experience looking at a beautiful rotting log. It was covered in moss and fungi of various species with all manner of insects running around on it. The array of biodiversity on such a relatively small object, in the middle of the suburbs, is super cool. I would highly recommend that anyone take the time to examine a good rotting log and see for themselves all the various fungi and insects living in it. If possible, check in on it from time to time. The transformation from hard wood that seems so strong, to a material that will crumble in your hands, is incredible. Hopefully, this piece sheds some light on some of the many organisms that make that possible.
References
1. Fazan L, Song Y-G, Kozlowski G. The Woody Planet: From Past Triumph to Manmade Decline. Plants [Internet]. MDPI AG; 2020 Nov 17;9(11):1593. Available from: http://dx.doi.org/10.3390/plants9111593
2. Coal Explained [Internet]. Coal explained - U.S. Energy Information Administration (EIA). 2021 [cited 2021Nov23]. Available from: https://www.eia.gov/energyexplained/coal/
3. Chaurasia, Shārdesh & Singh, Satya & Kumar, Virendra & Naithani, Sanjay & Saini, Vipin Kumar. (2015). BIOPULPING: AN ECOFRIENDLY TECHNOLOGY TO REDUCE THE DETRIMENTAL EFFECT OF CHEMICALS AND ENERGY CONSUMPTION.
4. Kumar A, Gautam A, Dutt D. Bio-pulping: An energy saving and environment-friendly approach. Physical Sciences Reviews. 2020;5(10): 20190043. https://doi.org/10.1515/psr-2019-0043
5. George Washington University. Breaking down wood decomposition by fungi [Internet]. Phys.org. [cited 2021Nov23]. Available from: https://phys.org/news/2020-05-wood-decomposition-fungi.html
6. Lehman C. Where do bacteria live? [Internet]. Sciencing. 2019 [cited 2021Nov23]. Available from: https://sciencing.com/do-bacteria-live-4603733.html
7. Singh, Adya & Kim, Yoon & Singh, Tripti. (2016). Bacterial Degradation of Wood. 10.1016/B978-0-12-802185-9.00009-7.
8. Singh A, Nilsson T. Tunnelling Bacteria: An Underestimated Threat to Wooden Structures [Internet]. Australasian Science Magazine. 2018 [cited 2021Nov23]. Available from: http://www.australasianscience.com.au/article/issue-mayjune-2018/tunnelling-bacteria-underestimated-threat-wooden-structures.html
9. Pedersen N, Łucejko J, Modugno F, Björdal C. Correlation between bacterial decay and chemical changes in waterlogged archaeological wood analysed by light microscopy and Py-GC/MS. Holzforschung. 2021;75(7): 635-645. https://doi.org/10.1515/hf-2020-0153
10. Wu K. This Czech well may be the world's oldest wooden structure [Internet]. Smithsonian.com. Smithsonian Institution; 2020 [cited 2021Nov23]. Available from: https://www.smithsonianmag.com/smart-news/czech-well-may-be-worlds-oldest-wooden-structure-180974137/
11. Geib SM, Filley TR, Hatcher PG, Hoover K, Carlson JE, Jimenez-Gasco Mdel M, et al. Lignin degradation in wood-feeding insects [Internet]. PNAS. National Academy of Sciences; 2008 [cited 2021Nov23]. Available from: https://doi.org/10.1073/pnas.0805257105
12. Termites [Internet]. National Wildlife Federation. [cited 2021Nov23]. Available from: https://www.nwf.org/Educational-Resources/Wildlife-Guide/Invertebrates/Termites
13. Filipiak M. Wood beetles are nature's recyclers – with a little help from fungi [Internet]. The Conversation. 2021 [cited 2021Nov23]. Available from: https://theconversation.com/wood-beetles-are-natures-recyclers-with-a-little-help-from-fungi-76029
14. Stokland JN, Siitonen J, Jonsson BG. Biodiversity in Dead Wood. Cambridge: Cambridge University Press; 2012. (Ecology, Biodiversity and Conservation).
15. Sea Daisies: Concentricycloidea [Internet]. Encyclopedia.com. Encyclopedia.com; [cited 2021Nov23]. Available from: https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/sea-daisies-concentricycloidea
16. Ritchie H. Humans make up just 0.01% of Earth's life – what's the rest? [Internet]. Our World in Data. 2019 [cited 2021Nov23]. Available from: https://ourworldindata.org/life-on-earth
