Natural Succession: The First Day of Your New Favorite Class, Forest 101
Fun fact: I almost skipped this blog post by accident because I forgot about this tenet and then spent about an hour writing the blog for next week instead. Whoops.
And despite what my fun fact may imply about natural secession, it is actually a really interesting topic. It starts with one of my favorite subjects in the world: forests. Forests are pretty amazing. They self-develop over hundreds of years and can last for millions more. Natural secession, as used in syntropic agriculture, is an attempt to recreate the development patterns of forests in order to create healthy conditions for crops. This is a pretty tall order: forests (and the plants inside them) are incredibly complex ecosystems, even more so because we still don’t fully understand how plants work. In order to copy forests, we first have to understand them. And with that in mind, I’d like to formally invite you to…
Forest 101
Welcome class! I’m so glad you all could make it to this bonus seminar on forest development and succession. This field has gotten heated over the past years, so prepare for The Drama. But before we get to the gossip, let’s get on the same page about development. All forests first developed over bare rock. There was no soil or no other plants, just…rock. So how did plants manage to get a foothold in bare rock? Through the use of pioneer species, plant species that are especially good at developing with little to no soil requirements. To picture this happening in real-time, we are going to mentally travel to Hawaii, where volcanic rock offers us a playing field for development. First, the wind and elements must break down the rock enough for pioneer species to get a foothold among them. Common pioneer species include lichen and mosses, which often grow on bare rock and have next to no soil requirements. In addition to lichen and moss, weedy-yet sturdy-vascular plants, such as ferns also appear, taking advantage of the open space. By the way, when I say “sturdy” here, I am referring to the fact that these plants need very little soil to survive, and I don’t mean to imply that these initial plants last a long time. They don’t. Over time, the lichen, moss, and weedy plants die off, creating a layer of biological material over the bare rock, which eventually develops into rudimentary soil. Then, slightly less sturdy (i.e. needs more soil) plant species will be able to grow there, and then these plants die off, become soil, and the next round of plants come in. This is called succession — when one species or type of plant dies off and creates a fertile environment for the next plant to grow. Over hundreds of years (our best guess is around 350–600 years, but we don’t know for sure) a full forest develops.[1][2] I cannot, however, yet explain what happens at the “end” of the successional chain. That is part of The Drama I mentioned earlier, and we have to get through one more thing before we talk about it.
Development over bare rock is a specific kind of succession called primary succession. Another kind of succession, secondary succession, is also possible, and much more likely to happen today. Secondary succession occurs after a disturbance to a forest, such as a wildfire, tornado, or human interference. I find it useful to think about the development of forests as if they were houses. In primary succession, a house is built on a craggy bluff overlooking the water from scratch. In secondary succession, a house is built on an abandoned city lot after the previous house was razed down by a mob celebrating the Philadelphia Eagles Superbowl victory. I don’t know when we jumped from Hawaii to Pennsylvania, but we’re here now. Our PA house is emblematic of secondary succession because we are not starting completely from scratch. The foundation is still there, and maybe the sewage and drainage pipe system escaped the crowd. Similarly, in secondary succession, the soil and foundations of a forest are still there, but the forest itself, trees, flowers, ferns, moss, etc., are all gone. As there is fairly limited bare rock left, this is the type of succession we see most often now. The initial disturbance of a forest could be a fire (California forest are about to undergo secondary succession in a big way), a violent tornado or wind storm, or one of the most common kinds of disturbance to our forest today: human interference. Human agricultural interference is particularly prevalent, as acres of forests were and are being cut down for farmland. Because what we are trying to do here is model succession, and my guess is that most syntropic farmers will be working on reclaimed farmland that was previously used for conventional agriculture, the majority of syntropic farms will be trying to model secondary succession.
Secondary succession pretty much works in the same way as primary succession, but instead of super hardy plants and lichen that don’t need soil, pioneer species in secondary succession, are fast-growing species able to spread and colonize an area very easily. A common example of a pioneer species are ferns, which appear in forests around the world after disturbances.[3][4] And then basically the same thing happens, except it takes less long because the soil was already there and didn’t have to be built up over generations of dead plants. Still, though, this process takes a long time (think 180–200 years) and there is a heated debate in Ecology about what happens at the “end-point” of natural succession.[5] That’s right folks, we’ve finally reached The Drama.
The Drama started about 150 years ago when a Finish botanist named Ragnar Hult came up with the idea that each forest has a climax, of a final stage of vegetation, in which it enters an equilibrium. This proved to be very controversial and was largely substituted for the idea of potential natural vegetation, or PNV, in 1965.[6] The key reason for the disagreement is that PNV presents the “end state” of a forest not as a steady-state system, where the ratios of various plants, animals, and decomposers don’t change, but as a more fluid system that naturally goes through changes over time. Basically, PNV is a hypothetical vegetation state that would occur if humans completely stopped influencing an area and allowed it to fully develop. Since then, this idea has been debated, argued, refined, developed, and I’m sure caused a few screaming matches. There are papers that argue that PNV is impossible to model on the basis that the methodology (PNV traditionally is worked without considering human impact) is unsound and therefore useless to use.[7] There are papers that argue the opposite, that PNV modeling can be used as a considerable advancement in forest reconstruction.[8] There are papers that argue PNV should not be used at all.[9] There are papers that argue to abandon PNV would be to abandon years of positive scientific development.[10] There are papers that show forests following the direction of PNV models.[11] There are papers which demonstrate that even old-growth forests never reach an “endpoint”, throwing the entire concept of PNV into disarray.[12] These heated debates (mostly found in the introduction and discussion sections of these papers, if you want to read for yourself. They get a bit academically catty, which can be quite fun) are made worse by the fact that we STILL DON’T UNDERSTAND HOW PLANTS PARTITION RESOURCES. Sorry for yelling, I just find it very exciting and baffling and curious. For more on that, see here. Basically, those who study vegetative science are still trying to accurately model and understand the shape of natural succession, and much like participants in spin-the-bottle at the first boy-girl 13th birthday party of the year, every scientist has a dream about what could happen.
So, if the world of ecological science doesn’t agree on a model or outline of restoration, how can syntropic farmers use the concept to their advantage? By simplifying it a whole lot and crossing their fingers. One of the big upsides to developing syntropic farming is that you don’t need to understand why the natural world works the way it does (although I am trying to), you just need to be able to recognize patterns and take advantage of them. In this case, it is clear that succession is successful, PNV model or otherwise, and part of this success is based on the death and biomass contribution of previous plants. Syntropic farms are designed to grow as forests grow. A farm taking 600 years to develop fully, however, is highly impractical. Instead, syntropic farms try to plant 100 years’ worth of plants at the same time. On the surface, this seems highly impractical. I can hear you muttering to yourself:
“100 years of plants at once? That’s madness! Wasn’t she just talking about limiting competition last week?”
Yes. Yes, I was. The key to this concept is that some crops develop faster than other crops. For example, corn is an emergent, fast-growing crop. Sunflowers are also an emergent species, and grow slightly less quickly, around double the time it takes for corn to grow. This means that if I were to plant corn and sunflower seeds at the same time, the corn would germinate and grow before the sunflower seed germinated. This ensures that there would be no competition between corn and sunflower, as they are both emergent, and it would ensure that there is time to harvest the corn crop before the sunflowers need to be harvested. If we take this to the extreme, as we do in syntropics, I could plant a seed from an oak tree, and in roughly 20 years, that oak tree would the primary emergent in the system. When thinking that long-term with syntropy, normally the long-term emergents are lumber trees or fruit trees that can produce fruit for a relatively long time. Essentially, as soon as one plant strata are harvested or die down, another plant in that strata rises up to take its place. With careful planning and some knowledge of how long crops take to grow and harvest, planting 100 years’ worth of plants is actually a very doable task. When planning a syntropic row, managers will often use a chart like this one to make sure that they are covering all the possible strata for the 100 years.
If a stratum is left out, a syntropic farmer will likely find that another plant, perhaps a less advantageous one, will take advantage of the space, and spring up in the middle of the row. Again, organizing a syntropic farm this way takes time and effort. It can also lead to problems. For example, if I am a corn farmer, I need to be able to harvest corn year after year. This system set up so that corn can only be harvested once, before another emergent takes its place. The solution to this problem lies in the fifth and last tenet, active management. We will talk about that two weeks from now, (I’m reserving Friday the 13th for a scary syntropic story) but in the meantime, if you are taking a walk through the woods, look around! And think about what came before.
With the excellent quote from Jeff Goldblum in Jurassic Park “Life….uh, finds a way”,
Ajah
[1]Bonnell, Tyler R., Rafael Reyna-Hurtado, and Colin A. Chapman. “Post-Logging Recovery Time is Longer than Expected in an East African Tropical Forest.” Forest Ecology and Management 261, no. 4 (2011): 855–864. doi:https://doi.org/10.1016/j.foreco.2010.12.016. http://www.sciencedirect.com/science/article/pii/S037811271000719X.
[2] Liebsch, Dieter, Marcia C. M. Marques, and Renato Goldenberg. “How Long does the Atlantic Rain Forest Take to Recover After a Disturbance? Changes in Species Composition and Ecological Features during Secondary Succession.” Biological Conservation 141, no. 6 (2008): 1717–1725. doi:https://doi.org/10.1016/j.biocon.2008.04.013. http://www.sciencedirect.com/science/article/pii/S0006320708001456.
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[3] Brock, James M. R., George L. W. Perry, William G. Lee, Luitgard Schwendenmann, and Bruce R. Burns. “Pioneer Tree Ferns Influence Community Assembly in Northern New Zealand Forests.” New Zealand Journal of Ecology 42, no. 1 (2018): 18–30. https://www.jstor.org/stable/26538092.
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[4] Dalling, J. W. and S. P. Hubbell. “Seed Size, Growth Rate and Gap Microsite Conditions as Determinants of Recruitment Success for Pioneer Species.” Journal of Ecology 90, no. 3 (2002): 557–568. http://www.jstor.org/stable/3072239.
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[5] Chiarucci, Alessandro, Miguel B. Araújo, Guillaume Decocq, Carl Beierkuhnlein, and José María Fernández-Palacios. “The Concept of Potential Natural Vegetation: An Epitaph?” Journal of Vegetation Science 21, no. 6 (2010): 1172–1178. doi:10.1111/j.1654–1103.2010.01218.x. https://doi.org/10.1111/j.1654-1103.2010.01218.x.Top of FormBottom of Form
[6] Chiarucci, Alessandro, Miguel B. Araújo, Guillaume Decocq, Carl Beierkuhnlein, and José María Fernández-Palacios. “The Concept of Potential Natural Vegetation: An Epitaph?” Journal of Vegetation Science 21, no. 6 (2010): 1172–1178. doi:10.1111/j.1654–1103.2010.01218.x. https://doi.org/10.1111/j.1654-1103.2010.01218.x.Top of FormBottom of Form
[7] Chiarucci, Alessandro, Miguel B. Araújo, Guillaume Decocq, Carl Beierkuhnlein, and José María Fernández-Palacios. “The Concept of Potential Natural Vegetation: An Epitaph?” Journal of Vegetation Science 21, no. 6 (2010): 1172–1178. doi:10.1111/j.1654–1103.2010.01218.x. https://doi.org/10.1111/j.1654-1103.2010.01218.x.Top of FormBottom of Form
[8] Hickler, Thomas, Katrin Vohland, Jane Feehan, Paul A. Miller, Benjamin Smith, Luis Costa, Thomas Giesecke, et al. “Projecting the Future Distribution of European Potential Natural Vegetation Zones with a Generalized, Tree Species-Based Dynamic Vegetation Model.” Global Ecology and Biogeography 21, no. 1 (2012): 50–63. doi:10.1111/j.1466–8238.2010.00613.x. https://doi.org/10.1111/j.1466-8238.2010.00613.x.
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[9] Zerbe, Stefan. “Potential Natural Vegetation: Validity and Applicability in Landscape Planning and Nature Conservation.” Applied Vegetation Science 1, no. 2 (1998): 165–172. doi:10.2307/1478945. https://doi.org/10.2307/1478945.
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[10] Loidi, Javier and Federico Fernández-González. “Potential Natural Vegetation: Reburying Or Reboring?” Journal of Vegetation Science 23, no. 3 (2012): 596–604. doi:10.1111/j.1654–1103.2012.01387.x. https://doi.org/10.1111/j.1654-1103.2012.01387.x.
[11] Prach, Karel, Lubomír Tichý, Kamila Lencová, Martin Adámek, Tomáš Koutecký, Jiří Sádlo, Alena Bartošová, et al. “Does Succession Run Towards Potential Natural Vegetation? an Analysis Across Seres.” Journal of Vegetation Science 27, no. 3 (2016): 515–523. doi:10.1111/jvs.12383. https://doi.org/10.1111/jvs.12383.
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[12] Brzeziecki, Bogdan, Kerry Woods, Leszek Bolibok, Jacek Zajączkowski, Stanisław Drozdowski, Kamil Bielak, and Henryk Żybura. “Over 80 Years without Major Disturbance, Late-Successional Białowieża Woodlands Exhibit Complex Dynamism, with Coherent Compositional Shifts Towards True Old-Growth Conditions.” Journal of Ecology 108, no. 3 (2020): 1138–1154. doi:10.1111/1365–2745.13367. https://doi.org/10.1111/1365-2745.13367.
