Would the absence of an axial tilt preclude the use of seasonal crops in agriculture?

Question

I'm worldbuilding an earth-like planet with no axial tilt, in order to maximize extreme climates (like deserts). However, there will still be pockets of fertile land, which will be populated by humans, with a technological level similar to that of the ancient civilizations of the fertile crescent, like the babylonians.

One of the side effects of not having an axial tilt is the minimization of seasons. So it got me thinking, on how this would interphere with an agricultural society, namely with seeding and harvest seasons...

Would it be feasible to cultivate seasonal plants in such an environment, like wheat or grapewhine? Or would it be better to use plants that are not seasonal, like barley or rice (if my research doesn't fail me they have seasons, but may be perennial)?

I would like my civilization to have wheat and wine, would it be possible?

Answer 1

Many (if not all) plants in our Earth adapted to season cycle, it's not the other way around. This means that, unless you are thinking of "straightening" our world axis, somehow, the plants in that world would have adapted to the no-seasons situation.

It is unclear (to me) what You exactly need:

• If you need wheat and grape then there's nothing to do, they would be adapted and thus have a growth cycle not synchronized with seasons (that do not exist).
  • wheat would be harvested a few months after seeding
  • grape will be flowering and maturing all year around (possibly the same plant will have flowers and grapes at the same time.
• if, OTOH, you want to have some seasonal effect on climate in a tiltless world (defeating reason for axial straightening) easiest is a very large moon (better yet: have the planet to be a satellite of a gas giant; i.e.: the "moon" is bigger than the planet) having a very slow revolution; tidal effect and "phases" would produce enough variation to allow plants to "lock" into the cycle.

Addendum:

As OP stated his interest in a no-season agriculture a few clarifications are in order:

In our Earth (the only ecosystem we can study, to date) there are several different kind of plants (please note I'm not mother-tongue English, so I don't know the correct tecnical terms, correct me as needed); main categories are:

• Perennial: these plants live several years and, generally follow a yearly cycle, but some have longer periods (e.g.: many fruit tree will produce more fruits on alternating years). These plants, with no season cycle, would adapt following one of several possible patterns:
  • Random flowering: flowers will appear randomly all year around and each blossom will follow its course to ripe fruit;these plants will likely have flowers and fruits at all degrees of maturation at the same time (oranges and lemons, while season-locked, can have fruits and flowers at the same time).
  • Synchronized flowering: the whole plant will decide to flower and it will do it in a synchronized way, following normal maturation; note several nearby plants can decide to "lock" together and follow the same cycle with few days distance, while same plants a few kilometers away can have weeks differences (citation needed).
  • Locked flowering: lock on certain external event; some desert plants will start flowering as soon as they get some rain, independently of season. If some plant originated in very arid region proves useful you can "force" start of cycle irrigating.
• Annual: these plants die each year after producing seeds; in general these will start a timed cycle whenever seeded; seeds may wait for "favorable conditions" to sprout, this may include enough humidity (rain/irrigation) or other, more exotic, triggers, like a passing swarm of insects useful for for pollination.

Answer 2

Grapevines

(Although grapewine as a riff on wine grapes is darn clever!)

Ivy, grape, are (or can be) vines. (In the UK vines means grapevines, in the US vines often refer to other plant species)

Our hearts are great examples of periodic biology. No seasons necessary. I suspect that plants evolving on a minimal season world would either be turtles, with a constant growth rate, or hares (rabbits) which grow rapidly, exhausting near-by resources and then either die off or "hibernate" to allow those resources to recover. I imagine both would occur.

On such a world, there would be almost no annual signals (assuming a sufficiently circular orbit, but whether an eccentricity of 0.01 or 0.005 would be enough to cue plant growth or reproduction? Who knows.) One scenario is like locusts or cicada, with enormous surges in numbers triggered by who knows what. Or like lemmings, which for reasons not immediately apparent suddenly gather in huge numbers and migrate to their deaths.

I picture a "wave" of some kudzu like vine feeding on and choking other plants (and animals), reproducing then dying only for the wave to reform a few miles away. One thing I'm pretty sure of, is that on such a planet the weather will be both more constant and yet have sudden "black swan" events.

As for plants, they might have triggers (and some very complex interactions between species or locations can be imagined) or they might not. Whatever maximizes their reproductive fitness in that particular location.

Answer 3

You could choose to have an elliptical orbit, and this would create a seasonal effect. It would however be pretty similar in result to having an Axial Tilt. I would look to produce a climatic variance through a different agency. There's a couple of methods I can think of

1. Multiple Moons, that have extremely slow orbits and create tidal surges that are extreme.
2. Ocean Currents that bring heat and then switch to bringing cold. Of course - explaining ocean currents that change their pattern regularly is a bit problematic. You could possibly do this by having a high iron content in the water - and having the magnetic field switch regularly. Like an annual metronome.
3. A gravitational lens that waxes and wanes - causing localised areas of massively concentrated sunlight. The basis for the gravitational lens could be some super dense minerals in mountain ranges - this would give only very specific locales this variegated weather pattern. Come to think of it - if you had a couple of these over the poles - and they switched on for three months of the year - they could melt a massive amount of ice/snow - and cause a regular seasonal movement of water. This could cause clouds and some potentially ginormous weather patterns that could create the seasons you are after.
4. Magic. Potentially through individuals that are talented in a certain way - which gives all sorts of options for conflict by controlling those individuals. Or even by those individuals controlling the people.
5. Magic. Potentially through creation of a supreme structure (Think Pyramids) that requires a massive society wide effort to put in place at massive capital cost. (Labour, Resource etc). This structure creates energy imbalances which cause your seasonal weather patterns you are after. Of course this type of construct is rife with plot opportunity - from creation of the structure through to control and maintenance and loss of knowledge of the workings.
6. Science - a technological approach where seasons are created - perhaps by space mirrors? https://www.livescience.com/22202-space-mirrors-global-warming.html Of course - developing this technology would only be desirable by your population if they knew of the benefits of seasons - that would mean they would have to at least have known of other planets - or possibly migrated here from earth.

Some of the choices I've outlined depend on the plotline you are trying to develop...

Best of luck finding a decent solution!

Answer 4

Yes you could have agriculture, but it would be limited to what grows in the tropics now.

Most temperate plants have a dormancy period and a chilling requirement. This is true for both seeds and buds.

E.g. most conifer seeds require 30-90 days stored moist at temperataures between 2 and 5 C. Peaches require somewhere around 140 days of below 40 F temps before they will break bud in spring. Some varities of peaches can't be grown in Georgia. Winters aren't cool enough long enough. Spruce trees require 300 to 1500 hours of temperatures below 5 C to break bud the next spring.

Chilling requirements are natures way to not get sucked in by an early spring, or a February thaw.

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There's a class of plants called winter annuals. Stinkweed is the main example I know. It will grow anytime the temp is above freezing, and can go through it's entire life cycle in 3 weeks. In unfavorable conditions is gets 3 inches high and produces a dozen seeds. In good conditions it grows 2 feet high and produces thousands. The seeds have variable thickness coatings so t hey don't all sprout at the same time. Some stay inthe soil for years.