Solar insolation/flux's effect on biome diversity/richness on an alien world

Question

The Questions

I'm trying to answer three main questions:

1. Does a three-axis biome chart make sense for my world?
2. How productive/life-rich should a biome be given a specific level of solar flux (holding temperature and precipitation steady)
3. Can we quantify or qualify that level of productivity/life-richness in the biome? (This could be comparative: "as productive as Earth's equatorial rainforest, as productive as the African Savannah, etc.)

The Overview

As part of my world-building I've developed an alien world. It's mostly earth-like (oceans, continents, similar atmosphere, roughly earth-like average temperature) but varies in a few big ways. Something I'm struggling with is determining how "life rich" each of its biomes should be, and how to delineate those biomes.

By "life rich" I mean something like the quantity of life you'd see within the biome. The productivity. The energy throughput. For example, on Earth a tropical rain forest is a very "rich" biome, while the tundra is not. A temperate forest in summer is a moderately rich biome, while in winter it is not.

You may be familiar with biome graphs like this one:

Terrestrial Biomes

They are work well for Earth given only two variables: precipitation and temperature. This is a generalization of course, since many factors determine the exact biome, including elevation and seasonal distribution of precipitation. However it's a good rule of thumb...for Earth.

As useful as charts like this one are for world-builders, they run into big hiccups when dealing with my alien world. The principal problem I see here is that—unlike Earth–my world exhibits variable combinations that don't exist on Earth.

I think biome charts like the one work on Earth because temperature correlates closely with latitude, and therefore with average solar insolation (i.e. energy from the sun). My world however doesn't work this way. On my world the following variables can be considered semi-independent:

• Temperature
• Average Solar Insolation (Flux)
• Precipitation

Unlike on Earth, you can have a biome that is both warm and wet (like a tropical forest) BUT it has average levels of solar flux similar to Norway. You also have biomes that are hot, wet (like tropical forests) but get 2x the average solar flux of a spot on Earth's equator.

There are also two other big variables on my world that will play a roll:

• Received Sunlight Wavelength: Amount of visible vs infrared varies based on longitude and time of year (thanks binary star!)
• Ratio of daylight/night-time over one full day-length: Varies by longitude (think orbital resonance, like mercury)

My idea is instead to create a three-axis chart as my base based on temperature, solar insolation, and precipitation. I'll then factor in the last two variables later on to go into more detail.

Does that sound like a viable approach?

Key to this is figuring out how "productive" and "life rich" a biome should be given its average amount of flux. My biomes vary widely, with average flux varying by BOTH longitude AND latitude (Earth's only varies by latitude). An example is the equator of my world. The flux at 0N and 0E is about 770w/m2 in the winter and 890w/m2 in the summer. At 0N and 180E it's about 220w/m2 in the winter and 335w/m2 in the summer.

Note: Average solar flux for Earth at Equinox is:

• 0N: 430w/m2

• 40N: 330w/m2

• 60N: 215w/m2.

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Supplemental Info

On my world you have locations with variables combinations like this:

• Equatorial Spot #1:

  • Warm (Summer), Cool (Winter)
  • Moist to Dry (seasonal)
  • Low Average Sunlight Flux (280 w/m2 per hour)
  • Summers: More flux (and bigger % from visible wavelengths)
  • Winter: Less flux (and bigger % from infrared wavelengths)
  • Long nights, short days

• Equatorial Spot #2:

  • Very Hot (year-round)
  • Very Wet
  • Very High Average Sunlight Flux (800w/m2 per hour)
  • Summers & Winters: Low seasonal flux variation by %
  • Long days, short nights

• Mid-Latitude Spot #3:

  • Hot (Summer), Cool (Winter)
  • Dry
  • High Average Sunlight Flux (400 w/m2 per hour)
  • Seasonal Flux Change: Moderate (in-between #1 and #2)
  • Equally split day/night length

Note: A full seasonal cycle (spring, summer, autumn, winter) is nearly an Earth-decade long.

Answer 1

On earth, solar irradiance strongly correlates with temperature because we get most of our energy from the sun. In order to separate these and have it make sense, you have to have significant energy input from some other source that is not the sun and is also not evenly distributed over the surface. The simplest, I think, would be geothermal. Something about the structure of the crust makes lava be much closer to the surface in some areas than in others, heating the whole area from the ground up. The difference from earth would be that the areas are both larger (making for proper big biomes) and more stable (making for fewer volcanoes).

The biggest effect of solar irradiance would be in giving energy for photosynthesis. The more sun, the more raw plant growth you are able to have. Since this plant energy directly or indirectly feeds most of the food chain, this is the simplest way of having a more vibrant ecosystem.

The most interesting cases would be where temperature and sunlight levels differs.

First, areas that have high temperature but little sunlight. This would result in a mix between a tundra and grasslands, I think. Vegetation is mostly lichens, moss, and smaller shrubs, that can make do with little light. Animals are sparse, mostly small and mobile without needing insulating fur.

Second, cold but much sunlight. Since temperature would be the limiting factor in plant growth, we would see something like thick bushlands with waxy leaves, or evergreen forests. Similar to our cold-weather plants, but faster-growing and less wooden and more green. Animals would have to be bigger and tougher, both to help against the cold and to eat much of the plants. With big but plentiful herbivores, predators would be similarly big and strong.

Answer 2

On Earth we come up with biome names to differentiate places that experience major differences. At the same temperature you could have a desert, a jungle, or a prairie depending or precipitation and local organisms; so in your world, you'd just have more named biomes such as a sunjungle, jungle, and darkjungle but a desert may just be considered a desert since the amount of light won't change the biome much kind of like how we call a tundra a tundra regardless of precipitation. In short, a 3d map of biomes may help you with figuring out where you need to name new biomes, but how the beings on this world will think about it is that a biome is just a place that is different than other places with XYZ properties; so, a full 3-d chart is kind of unnecessary.

The thing to remember is that any biome graph you look at of Earth like the one you attached only takes 2 factors of these biomes and compares them. But these biomes have tons of comparable factors: precipitation, latitude, temperature, biodiversity, biomass, soil richness, humidity, average wind-speeds, tiger to elephant ratios, etc, etc, etc... The whole point of a biome graph is to isolate variables for comparison, not to map out everything that makes a biome a biome.