Real terraforming
September 5, 2012 10:12 AM
I want to know more about the part of forestry that explains how and why forests (any kind) are composed and developed. By "composition," I mean the relative placement of the elements of a forest, like ravines and canopies.
Books, web pages, and a massive, super-detailed time lapse animation of a forest forming from nothing would all be great.
Actually, this one, by the same author, might be worth looking at as well.
posted by bondcliff at 11:13 AM on September 5, 2012
posted by bondcliff at 11:13 AM on September 5, 2012
Hi! Plant community ecologist here. I will leave discussions of the development of the underlying geology of a forest to more qualified individuals, but I will talk a bit about how a forest might get to be a forest from nothing. (And because this is my field, I will probably raise more questions than I give you answers. Apologies! It is my job.) This will be a lot of general ecological theory, with the caveat that there are going to be specific historical factors influencing any particular forest of interest (as bondcliff mentions for New England).
A lot of fundamental questions in the field of community ecology are centered around why species are where they are. If I go out into a forest, why is that particular area of the landscape a forest and not a grassland? Given that it is a forest, why is it an oak-maple forest, versus a spruce forest, versus.... and on and on. These are open questions and there are any number of ecological theories aimed at answering them. So I won't be giving you THE answer, so much as a classic answer that has been historically foundational to a lot of discussion about how plant communities form.
If you're asking about a forest forming from nothing (really nothing: no plants, no lichen, no proper soil) you are asking about a classic ecological theory called primary succession. There are a number of theoretical models of succession, but the basic idea is that, upon your blank slate, groups of plants of specific types establish one after the other, each paving the way for the group to follow. The first plants that grow are those that are excellent at tolerating really harsh environmental conditions, and they alter the habitat slightly. (Say, as these first plants die and biodegrade, they form a better soil, and so on.) This makes the area more hospitable to a few more plants that could not tolerate the original conditions. These newcomers either happily co-exist with the first plants, or maybe out-compete them. But either way, they further change the habitat. So, you might see a theoretical progression from a barren landscape, to one covered in mosses and lichen, to a few weedy grasses, to a grassland, to a lot of shrubs, and then through various kinds of forest.
(A side note: primary succession refers specifically to generation of a plant community from a total blank slate. If you watch what regrows after a forest fire, that is called secondary succession - basically a kind of succession where there are already some leftover plants/survivors to get things going.)
This is a classic model of succession, and I should point out that current work in community ecology is more nuanced than this. In this model, the forest is what is called a "climax community"; the model assumes that all plant communities are on their way to becoming a forest. So why isn't everything already forest? Well, one idea is that ecological disturbance events (say, floods or hurricanes if we're talking large-scale, or a tree falling down if we're talking small-scale) can set back the successional process. We tend to think of the early-colonizing plants as those that can tolerate disturbances well, and the plants of the climax community to be good competitors but poor at tolerating these environmental disturbances. So at a smaller scale, imagine you are hiking in our hypothetical forest, and you come across a forest stream. There are probably some trees near the bank, sure, but it's quite likely that a lot of the stream banks are more open than the rest of the forest, and have a lot of grasses or small herb species (and fewer woody species), because consistent floods from the stream keep the plants of the riverbank at that stage.
So far, this entire discussion has been centered around the discussion that succession toward a climax community is actually happening, and there are events that may or may not interrupt the process. Another school of thought is that there is no real theoretical climax community. So if I went out and clear-cut our theoretical forest, there are no guarantees that if we left it alone it would have to eventually develop into the same kind of forest it was before. It might just be pure chance that determines what types of plants grow there - basically, whose seeds happened to get to this area first? This would make the assembly of your plant community a much more random process than is predicted by successional theory, which is a relatively strict pattern.
So there isn't really one answer, but these are the kinds of processes people talk about when they talk about the assembly of plant communities. I hope this helps somewhat more than it confuses!
tl;dr: The classic ecological model for a forest developing from nothing is primary succession, but it is almost certainly quite a bit more complex than this model suggests.
posted by pemberkins at 11:23 AM on September 5, 2012
A lot of fundamental questions in the field of community ecology are centered around why species are where they are. If I go out into a forest, why is that particular area of the landscape a forest and not a grassland? Given that it is a forest, why is it an oak-maple forest, versus a spruce forest, versus.... and on and on. These are open questions and there are any number of ecological theories aimed at answering them. So I won't be giving you THE answer, so much as a classic answer that has been historically foundational to a lot of discussion about how plant communities form.
If you're asking about a forest forming from nothing (really nothing: no plants, no lichen, no proper soil) you are asking about a classic ecological theory called primary succession. There are a number of theoretical models of succession, but the basic idea is that, upon your blank slate, groups of plants of specific types establish one after the other, each paving the way for the group to follow. The first plants that grow are those that are excellent at tolerating really harsh environmental conditions, and they alter the habitat slightly. (Say, as these first plants die and biodegrade, they form a better soil, and so on.) This makes the area more hospitable to a few more plants that could not tolerate the original conditions. These newcomers either happily co-exist with the first plants, or maybe out-compete them. But either way, they further change the habitat. So, you might see a theoretical progression from a barren landscape, to one covered in mosses and lichen, to a few weedy grasses, to a grassland, to a lot of shrubs, and then through various kinds of forest.
(A side note: primary succession refers specifically to generation of a plant community from a total blank slate. If you watch what regrows after a forest fire, that is called secondary succession - basically a kind of succession where there are already some leftover plants/survivors to get things going.)
This is a classic model of succession, and I should point out that current work in community ecology is more nuanced than this. In this model, the forest is what is called a "climax community"; the model assumes that all plant communities are on their way to becoming a forest. So why isn't everything already forest? Well, one idea is that ecological disturbance events (say, floods or hurricanes if we're talking large-scale, or a tree falling down if we're talking small-scale) can set back the successional process. We tend to think of the early-colonizing plants as those that can tolerate disturbances well, and the plants of the climax community to be good competitors but poor at tolerating these environmental disturbances. So at a smaller scale, imagine you are hiking in our hypothetical forest, and you come across a forest stream. There are probably some trees near the bank, sure, but it's quite likely that a lot of the stream banks are more open than the rest of the forest, and have a lot of grasses or small herb species (and fewer woody species), because consistent floods from the stream keep the plants of the riverbank at that stage.
So far, this entire discussion has been centered around the discussion that succession toward a climax community is actually happening, and there are events that may or may not interrupt the process. Another school of thought is that there is no real theoretical climax community. So if I went out and clear-cut our theoretical forest, there are no guarantees that if we left it alone it would have to eventually develop into the same kind of forest it was before. It might just be pure chance that determines what types of plants grow there - basically, whose seeds happened to get to this area first? This would make the assembly of your plant community a much more random process than is predicted by successional theory, which is a relatively strict pattern.
So there isn't really one answer, but these are the kinds of processes people talk about when they talk about the assembly of plant communities. I hope this helps somewhat more than it confuses!
tl;dr: The classic ecological model for a forest developing from nothing is primary succession, but it is almost certainly quite a bit more complex than this model suggests.
posted by pemberkins at 11:23 AM on September 5, 2012
I can't find a reference for you at the moment but I visited Sequoia National Park this summer. There was a lot of material in the park that showed what odds are really against another Giant Sequoia being produced i.e. a narrow band of elevation that produced the right mix of temperatures, winter snow melt at higher elevations to provide lots of water, fire to open the cones to release seeds, fire to clear brush, etc. It was all very interesting if you can get ahold of something that goes into details. Its also a pretty spectacular place to visit.
posted by mmascolino at 12:07 PM on September 5, 2012
posted by mmascolino at 12:07 PM on September 5, 2012
The shape of the landscape on the timeframe of a forest growing there (say a few hundred years) has mostly to do with 1) the geology and 2) water. The geology determines the erodibility of the underlying soil and water moves stuff around. So granite in a dry area gives you lots of rock outcroppings, stable formations and clearwater streams (sierras), heavy precipitation on limestone gives you karst caves (SE Alaska, the Burren in Ireland) , glacial till or sedimentary rock gives you highly erodible, shallow, often soils that are prone to sliding (CA coastal range) etc etc... There are tons of variations (flood plain? snow load? Avalanches?) but over the medium term a lot of landscape forms are due to water moving moveable sized stuff.
posted by fshgrl at 12:08 PM on September 5, 2012
posted by fshgrl at 12:08 PM on September 5, 2012
Check out this site devoted to the restoration of oak savannas in the Midwest. Our county was restoring one when I took the Master Gardener course and learning about it was kind of neat. If interested in local forests and landscapes, the county forestry department might be helpful (or county extension office, as we were recruited to be volunteers as part of our donate time back program).
I'm not sure what you mean by placement of ravines, but it reminded me of the Kettle Moraine Forest in Wisconsin. If you ever go there, be sure to stop at the Ice Age Museum. Here's a nifty monograph written when Gerald Ford was President. Chapter Four has a more detailed explanation and some diagrams.
One of our MG teachers was an expert in trees and woody plants, and he knew a lot about say, deciduous forests and where they grew.
Not a tree, but horsetail is a neat plant to look at, as it can grow pretty tall in some locales.
If it were me, I'd pick a particular region and study that forest (bogs, fens, coniferous, etc.) and contact the DNR and the Master Gardener folks to get detailed information, because each region is pretty specific, depending on the topography and climate.
posted by Marie Mon Dieu at 12:17 PM on September 5, 2012
I'm not sure what you mean by placement of ravines, but it reminded me of the Kettle Moraine Forest in Wisconsin. If you ever go there, be sure to stop at the Ice Age Museum. Here's a nifty monograph written when Gerald Ford was President. Chapter Four has a more detailed explanation and some diagrams.
One of our MG teachers was an expert in trees and woody plants, and he knew a lot about say, deciduous forests and where they grew.
Not a tree, but horsetail is a neat plant to look at, as it can grow pretty tall in some locales.
If it were me, I'd pick a particular region and study that forest (bogs, fens, coniferous, etc.) and contact the DNR and the Master Gardener folks to get detailed information, because each region is pretty specific, depending on the topography and climate.
posted by Marie Mon Dieu at 12:17 PM on September 5, 2012
Pemberkins' answer is excelllent and covers a lot of what you are asking about. One other key factor though is that not all locations are suitable for forests to begin with. In general, trees won't grow anywhere that is too cold or too dry. Trees as a general class of organisms have a lot of adaptations for dealing with different climates, but they aren't well-adapted to the most extreme biomes.
Areas of the Earth that are too dry for trees tend to give way to to grasslands or deserts, and areas that are too cold tend to give way to tundra or montane environments. The less extreme versions of such biomes may feature occasional trees, but not forests of them. The more extreme versions may support no trees at all.
posted by Scientist at 2:23 PM on September 5, 2012
Areas of the Earth that are too dry for trees tend to give way to to grasslands or deserts, and areas that are too cold tend to give way to tundra or montane environments. The less extreme versions of such biomes may feature occasional trees, but not forests of them. The more extreme versions may support no trees at all.
posted by Scientist at 2:23 PM on September 5, 2012
Scientist makes a good point that I neglected to emphasize in my novella above - the abiotic environment matters! My favorite example of plants dealing with extreme conditions is the krummholz: basically, mountainous regions where it is so windy all the time that trees mostly can't grow, and in the sheltered nooks and crannies where they do, they develop in really deformed, crooked ways as they are shaped by the wind. Two reasons why this is awesome: (1) No, seriously, look at those trees. (2) It is super fun to say krummholz.
If I wanted to put this in the framework of successional theory, I guess I would say that different places have different expected climax communities, based on the base environmental conditions. An alternative view would be that some things we might think of as stable biomes are really just on a very, very slow successional pathway to some other climax community, to the point where it is unrealistic to expect that climax will ever be reached, because of the frequencies of disturbances and other environmental chance.
That said, I tend not to think about community assembly from a strictly successional point of view. Basically, when I think about what is shaping the composition of an ecological community, I think about:
(1) Which species are likely to arrive in a given place (dispersal traits and random chance in arrivals);
(2) Who can potentially survive in that set of environmental conditions (esp. for extreme conditions); and
(3) How the species that qualify by points 1 and 2 are going to interact in the same space (Can they coexist, or is one out-competed by the other? If they can coexist, how/why? How many species can share the same space? And so on.)
Many questions I ask as a community ecologist boil down to looking at the balance among these three factors in shaping a given community. In some environments, as Scientist pointed out, the abiotic conditions are probably most important (only so many things can survive in a place that is really really hot, so competition among the few species that can tolerate the heat isn't a big issue in comparison). In others, conditions are pretty broadly favorable and competition or straight-up chance events might have bigger roles to play, because environmental conditions are not very limiting. Successional theory is one of many ideas about the relative roles that the three points above have to play, and when each of those filters is important.
So if we're talking about your forest arising from nothing, we'll see patterns of succession as the forest develops. But as Scientist says, not all bare ground will inevitably turn into forest. And if it IS a forest, there are still some complex things going on determining exactly which species are in this forest and which species don't get to join the club.
(My dissertation work focuses on the role of discrete disturbance events in all of this, but if I start writing about that I will never ever stop. And I should be writing about it in a manuscript right now, not on Metafilter...)
posted by pemberkins at 4:54 PM on September 5, 2012
If I wanted to put this in the framework of successional theory, I guess I would say that different places have different expected climax communities, based on the base environmental conditions. An alternative view would be that some things we might think of as stable biomes are really just on a very, very slow successional pathway to some other climax community, to the point where it is unrealistic to expect that climax will ever be reached, because of the frequencies of disturbances and other environmental chance.
That said, I tend not to think about community assembly from a strictly successional point of view. Basically, when I think about what is shaping the composition of an ecological community, I think about:
(1) Which species are likely to arrive in a given place (dispersal traits and random chance in arrivals);
(2) Who can potentially survive in that set of environmental conditions (esp. for extreme conditions); and
(3) How the species that qualify by points 1 and 2 are going to interact in the same space (Can they coexist, or is one out-competed by the other? If they can coexist, how/why? How many species can share the same space? And so on.)
Many questions I ask as a community ecologist boil down to looking at the balance among these three factors in shaping a given community. In some environments, as Scientist pointed out, the abiotic conditions are probably most important (only so many things can survive in a place that is really really hot, so competition among the few species that can tolerate the heat isn't a big issue in comparison). In others, conditions are pretty broadly favorable and competition or straight-up chance events might have bigger roles to play, because environmental conditions are not very limiting. Successional theory is one of many ideas about the relative roles that the three points above have to play, and when each of those filters is important.
So if we're talking about your forest arising from nothing, we'll see patterns of succession as the forest develops. But as Scientist says, not all bare ground will inevitably turn into forest. And if it IS a forest, there are still some complex things going on determining exactly which species are in this forest and which species don't get to join the club.
(My dissertation work focuses on the role of discrete disturbance events in all of this, but if I start writing about that I will never ever stop. And I should be writing about it in a manuscript right now, not on Metafilter...)
posted by pemberkins at 4:54 PM on September 5, 2012
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As far as I can tell it's more about how forest growth is influenced by what was there before (crops, fire) but if you're interested in New England forests they are mostly a product of what was there over the past couple hundred years.
posted by bondcliff at 11:09 AM on September 5, 2012