Current as of 2020-09-06 18:31:13 +0000
Our farm is located inside an open forest called “dehesa” in Spanish. It is a human-made sylvopasture system that exists in many parts of the world. For example, in Germany the same thing is called Hutewald. It is one form of Agroforestry.
In our opinion a combination of environmental factors and ranching traditions (eg. set stocking) have destroyed a lot of vegetation and the forest that once must have been rich and fertile is now struggling to survive.
We want to change that by using different management practices and do a lot of new planting as part of our ongoing forage production.
What follows is a description of how we understand our forest and its current situation.
From life to death and back
During fall and winter we have rainfall and nature springs back to life. During spring we have vigorous growth and our forest looks like this:
At the beginning of June - from one day to the next - the summer heat starts and our forest quickly looks dry and almost dead:
High temperatures is one issue we are facing. As we are in the mountains our temperatures are a bit lower than those around the city of Cordoba. The difference is about 5C which means that during winter we have a few hours of night frost and some plants may die because of that.
However, the bigger issue is the lack of rainfall:
Graphs created by World Weather & Climate Information.
Tree coverage, heat, and moisture
Probably because set stocking has been used for a long time the only trees left are the big oak trees (encinas) that provide the acorns that are important as fall and winter feed for the Iberian pig. Any young plants, be it a tree, a shrub, a flower, are eaten by the grazing animals. The result during summer looks like this:
The existing grass has finished its reproductive cycle and went dormant because of the heat. There is not a lot of shade and there is no moisture near the surface. When we excavate during summer we find moisture at about 70cm in a good area but it’s probably much deeper in most. We do have several wells that are some 8-9m deep and never dry out. So there is water around and likely the nearby water reservoir helps with that. However, that water is not good for anything, if the roots can’t reach it.
In comparison this is how an old Hutewald (the German term for dehesa) looks like when grazing is very limited:
The canopy is much denser and lot of moisture is kept due to increased biomass. Because of the denser canopy the temperature within the forest is much lower. And because of both factors more plants can grow. However, a denser canopy also means less sunlight which in turn may starve some plant species. How that forest looks on the ground - in a section that can be grazed - can be seen on Wikipedia.
The above picture shows the Reinhardswald near Kassel, Germany. Here are temperature and rainfall charts:
Our rainfall for comparison:
It is not that the German forest receives vastly more rain. The difference is mainly in the distribution of rainfall over the year. The summer drought common for our area does not happen in Germany and therefore the soil never dries out even if left with little cover.
In our climate the lack of cover leads to total loss of surface moisture and therefore there is no regrowth of anything except it is a heat resistant plant with a large root system.
Temperature is usually measured in the shade. Trees that form the upper layer of a forest do not grow in the shade but in direct sunlight. The temperature their leafs must sustain is much higher than what shows up in a weather report. If the trees are removed or cannot grow, the plants that require some protection cannot live.
Cold and warm season grasses
In grasslands with no or very few trees there are many different grass species. Usually there are a few species for the cold season and another group of grasses for the warm season. They all have different life cycles and grow at different times. When one species has gone to seed another might still be in the vegetative state. That means there is good forage throughout the whole year.
As it is a grassland there is no need for trees to provide shade. The grasses are happy in direct sunlight.
In our case we only have (in 2020) cold season grasses but we do see areas with more and more Cynodon dactylon emerging and that is a warm season grass which likes the heat and can grow with little moisture (it’s a C4 plant as well).
Probably because of set stocking not only have the animals grazed away all the young trees and shrubs. They also grazed away the warm season grass because they went back to the same plant again and again which couldn’t grow fast enough due to lack of rainfall during summer.
We practice rotational grazing and the Cynodon dactylon is growing but slow. With proper management we can protect it from grazing for long enough to grow leafs and roots so that it can reach the moisture deeper down in the soil.
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