Wikipedia:Reference desk/Archives/Science/2023 September 20

= September 20 =

Forest fires
It is difficult to burn raw wood, or freshly broken tree branches. But burning dried wood is easy.

How do forest fires start so easily as if the trees are alive, then they are not dry, but still they burn as if they are 100% dry?

And what happens to the area which had forest fires? Does it take long time for the area to look like green forest? KarenRiner (talk) 07:32, 20 September 2023 (UTC)


 * Fires usually start in the litter (fallen leaves and branches) and shrub layer which ignite much more easily; this can heat up the trees' exteriors sufficiently that that their moisture content becomes irrelevant. Many trees (such as Conifers and Eucalyptus) also have inflammable oils, etc., in their bark and leaves which will vaporise and ignite.
 * Burned forests usually regenerate eventually, because natural fires are inevitable, and plant species of all sorts have been adapted by evolution to survive them – some even require them to aid reproduction – but how long this takes varies greatly depending on the geographical locality and the tree (and other) species involved. For more details see Wildfire and Fire ecology. {The poster formerly known as 87.81.230.195} 51.198.107.25 (talk) 08:15, 20 September 2023 (UTC)


 * There's more in a forest than living trees: dead trees, dead leaves, broken off branches, undergrowth. After some weeks of hot and dry weather, that stuff can easily ignite. In the past, this was common in only some climates (in particular the Mediterranean climate), but with changing climates and mismanaged forests (planting trees that don't belong there, artificially lowering the groundwater table for agriculture), this is spreading all over the temperate zone.
 * After a forest fire, within weeks (or at the latest the next growing season) it will turn green again with low vegetation. After some years, trees will usually return. But it can take centuries before the forest looks like before the fire.
 * The forest won't always regenerate. The Earths climate is somewhat chaotic and can depend on its history. Meaning, Brazil and Kenya could have had the same climate and vegetation, but by chance don't. Burning the forests in Brazil could push the climate past a tipping point, turning Brazil permanently into a savanna, even if we brought CO2-levels back to the pre-industrial level. Turning Kenya into a tropical rainforest isn't inconceivable, but much harder to do. PiusImpavidus (talk) 08:37, 20 September 2023 (UTC)


 * For the western United States, most forest fires are started from lightning strikes, and the anatomy and species of the tree are important. You can see the results in some google images . The strike usually follows a path to ground in a strip in the outer layers, heating the water in these layers and causing a steam explosion. This drives moisture out of the wood and also shreds the wood into finer material which is easier to ignite. For some species, such as abies concolor (white fir) the heartwood is more decayed and is easily ignited by the strike. Other species have more intact heartwood which almost never ignites but the explosion of outer layers can throw the shredded material down to the fuel bed on the forest floor, sometimes resulting in a fire.
 * No fuel in a forest fire is "100% dry", all contain some moisture and live fuels usually also have dead and drier fuel present. Fire behavior analysts model fire spread basically by looking at the burning fuels as a heat source and the unburned fuels ahead of the fire as a heat sink. The fire heats fuels ahead, the moisture content a heat sink, and the fuels eventually reach a temperature to release volatile gasses which combust. As the NWGC's introduction to fuel moisture puts it: "Any living vegetation can be consumed by fire of sufficient intensity burning in associated dead fuels. When vegetation is subjected to heating, however, marked differences appear among species in the rates of output of combustible volatiles. The result is that the living foliage of some species absorbs nearly as much heat to vaporize its contained water as it yields when burned. Living foliage of other species, except in the period of rapid spring growth, may add significantly to the total fire heat output. Among these latter species particularly, the current foliage moisture content is important in determining total flammability."


 * Serenoa repens (saw palmetto), Abies lasiocarpa (subalpine fire), oaks and sagebrush of chaparral, are some of the most discussed species. But the story of the fourteen firefighters who died on Storm King Mountain demonstrates that the dangers of live green fuels is sometimes overlooked. fiveby(zero) 14:27, 20 September 2023 (UTC)


 * Whereas, "English native woods burn like wet asbestos" according to ecologist Oliver Rackham. Forest fires in the UK are generally only a problem in plantations of non-native conifers. Alansplodge (talk) 15:46, 20 September 2023 (UTC)
 * You might have had nice clean forest fires in the understory of the pinus sylvestris if your ancestors had not gotten rid of it to make way for their sheep or whatever. Now you've got nasty, smelly peatland fires. fiveby(zero) 17:17, 20 September 2023 (UTC)
 * Indeed. The quote was specific to England though, where the Scots pine was reputed to have been introduced by King James VI and I. The native Caledonian Forest in Scotland was/is a mix of pines (which do burn) and birch/alder/rowan (which do not readily) and so less susceptable to wildfire than the 20th-century monocultures of Sitka spruce and larch which cover large chunks of our uplands and heaths today. Alansplodge (talk) 11:03, 21 September 2023 (UTC)


 * In Australia the Aboriginal people developed Fire-stick farming practices that involved deliberately lighting forest fires in order to positively change the nature of an area to improve hunting, get rid of weeds, and encourage the growth of desirable plants. By burning at particular times, the forest regenerates in the way they want it to. HiLo48 (talk) 02:52, 22 September 2023 (UTC)

When did artificial insemination of mammals become widespread?
Artificial_insemination says “Artificial insemination of farm animals is common in the developed world, especially for breeding dairy cattle (75% of all inseminations). Swine are also bred using this method (up to 85% of all inseminations).”. I'd like to know about the history here. When did artificial insemination in farm mammals first become a common practice, done in large scale? I'm interested especially in North-America. The motivation for this question is that I'm thinking about Asimov's The Naked Sun, written in 1956, in which the spacers on Solaria use artificial wombs to grow humans starting from one months after conception, but they do not (yet) use artificial insemination. – b_jonas 07:48, 20 September 2023 (UTC)
 * Says here and here, first done in a dog in 1784, first done in cattle in early 1990s 1900s, current livestock methods by 1930s and 40s. Abductive  (reasoning) 10:22, 20 September 2023 (UTC)
 * Err, shouldn't that be "first done in cattle in early 1900s". See Fontes & Lamb (2020) in your first link. Martin of Sheffield (talk) 10:39, 20 September 2023 (UTC)
 * Thank you, but I'm not asking about when artificial insemination was first possible, but when it was done in large scale to many cattle (or pigs or sheep) in agriculture. – b_jonas 11:16, 20 September 2023 (UTC)
 * Follow the first link that gave, it has useful information.  For instance Parkinson & Morrell (2019) say: "The potential for AI to be used to control venereal disease was a major impetus to the development of cattle AI in the UK during the 1940s." and Schultz & Ross (2020) state: "Massive technological advances and widespread growth of the use of AI, particularly in dairy cattle, occurred in Europe and the United States beginning in the 1930s and 1940s."  I would think those two quotes answer your question. Martin of Sheffield (talk) 11:38, 20 September 2023 (UTC)
 * One of the advances was adding chicken egg yolks to the semen after collection to buffer the sperm cells against cooling shock. Abductive  (reasoning) 11:42, 20 September 2023 (UTC)
 * Thank you, the articles indeed provide more detail than what Abductive quoted. Thank you for the help so far, though I would still appreciate further references.  – b_jonas 13:27, 20 September 2023 (UTC)


 * Does The Naked Sun make it explicit that human insemination on Solaria is natural? I remember that the foetuses are removed surgically from the mothers after one month of gestation, but nothing about how conception is typically achieved. Our article states that on Solaria "face-to-face interaction, and especially sex, are considered repugnant", making artificial insemination a plausible preferred approach. I do remember the cultural distinction between seeing (meeting in the flesh) and viewing (meeting in a video contact).
 * The foetuses in the artificial wombs of Brave New World, written in 1931, grow out of embryos obtained by test-tube insemination. From the first paragraph of Chapter Ten: "Under the microscopes, their long tails furiously lashing, spermatozoa were burrowing head first into eggs; and, fertilized, the eggs were expanding, dividing, or if bokanovskified, budding and breaking up into whole populations of separate embryos." Surely, Asimov was aware of this. --Lambiam 10:29, 20 September 2023 (UTC)
 * Lambiam: Yes. The novel makes it clear that spouses ought to physically, in order that they get used to it, because this is necessary for their making children.  The spouses normally live in separate houses on separate large estates far from each other.  In most other cases, spacers only meet through very high quality holographic projection videophone calls.  There are exceptions other than for spouses, eg. doctors may sometimes need to meet their patients in person for procedures that their robots cannot yet handle; and they have some tolerance for children meeting in person.
 * The Solarians hope that in the far future, they can eventually avoid most or all of these personal encounters as their technology improves, and this includes conception. They indeed find the sexual encounters shameful, which is why they are hoping for such improvements, but as of the time they believe it's necessary.
 * That the spouses meet each other is kind of necessary for the murder mystery plot of the novel: Rikaine Delmarre was murdered by bludgeoning when he was visiting his wife Gladia Delmarre in her house.
 * – b_jonas 11:16, 20 September 2023 (UTC)
 * Correction to the above. Spouses share an estate and a big twin-house building.  The building is still big enough that they both have their own halves and don't have to share rooms or meet unnecessarily.  – b_jonas 21:47, 21 September 2023 (UTC)