Penetrability of soil is geo-physical quantity used for example in agriculture. Some recent studies showed us, that this quantity is pretty useful in ecology as well. These studies measured soil parameters compared to quantity (and other parameters) of bird and solitary-bees burrows. Penetrability is measured by penetrometer. This quantity shows us how intesive preasure we need to make for penetrating (in our case) 6 mm into the soil on exact surface. Basically, we use an iron stick which is 6,3 mm in diameter. If the penetrability is too low, we can use reduction to 25,4 mm (in diameter, 16x bigger surface) which allowes us to measure really low penetrability levels.
And how penetrability influences animals and plants? Simply - it says how hard it is for animals to dig their burrows, whether burrows will not be destroyed with the first heavier rain, or how hard it is for plant roots to grow through the soil.
We would like to use penetrability and few more geo-physical quantities and link them with specific species. If we succeed we will be able to say, just judging by these soil parameters, which ecosystem could form in the area we are working in.
In the picture you can see our penetrometer, the reduction used for low penetrability levels and a sample of soil.