# Calories production in plants per year

I am trying to estimate how much calories is available in form of plants to mammal herbivores per square meter per year in optimal conditions. By optimal conditions I mean that the climate is temperate, with enough water and sun for most of the year. By other words: how much food does the photosynthesis produce?

• Should this be on Biology instead? I don't see much relation to worldbuilding, per se. – Frostfyre Aug 3 '15 at 17:14
• I felt the question is quite general for biology (where one would have to be very specific about what kind of animal, what kind of biome, etc.) What I want is some rule of thumb, to be able to extrapolate to different planets. But if you want to move the question to biology, it is OK for me. – Irigi Aug 3 '15 at 17:18

It depends on the plants and the animals.

This website gives an estimate of calories per acre of a few different types of plants/crops. In terms of calories per square meter it works out to be:

Crop     Million calories (sic)  Calories per
per acre                square meter
----------------------------------------------------------
Wheat      6.4                   1581
Corn       12.3                  3039
Potatoes   17.8                  4398
Soybeans   2.1                   519


Note: The lower case 'c' calories is equivalent to 1/1000th of a typical nutritional Calorie (upper case 'c'). Thanks food industry! However, I suspect the author meant to use "Calories", not "calories", in this table. I used that assumption in the extra column.

Straight grassland or pasture is a bit more difficult to find values for, but this site gives a value of 8 kilocalories (Calories) per square meter.

Crop     Million Calories        Calories per
per acre                square meter
----------------------------------------------------------
Grass    0.0032                  8


This makes it clear why farming is such a good idea.

Different types of animals are better at digesting more of the plants. So the actual nutritional Calories an animal can get from these plants changes depending on that efficiency.