Actualizado: 13 de ago de 2020
Regenerating degraded pasture in the humid tropics is one of the greatest challenges to regional climate stability. At our farm I am experimenting with a technique that has been very effective in the drylands of Africa and I think can greatly speed up the regeneration of degraded pasture back into a forest ecosystem
The past few days I have started the first prune of the abandoned cow fields which have been 3 years without cattle but burned in a brush fire 2 years ago. I have started pruning the field below the chicken house, which on the upper slopes is dominated by bracharia or like grass of 1.5 meters or higher. Very few bracken fern, which is interesting. Anywhere there has been chemical agriculture in the past, bracken fern are dominant. Another observation is that where there is more sun due to slope, the grass is more likely to be dominant with weak secondary growth. But where there has been a breakthrough of small bushes or trees there is biodiversity in the shade of different species that have germinated, some from the same consortium of early secondary growth and some from a later consortium, like the Chagualo (Rapanea Guianensis). However where there is grass dominating there are very few plants that are able to grow. I wonder if the grass has to do with sheltering the ground from the powerful sunlight more than having to do with fertility. But the secondary growth does not dominate until there is sufficient shade on the ground to shade out the grass, and in that moment the grass dies as if sprayed with gliphosate and leaves the ground bare with saplings of the next consortium spread around. There is a clear consortium of which I am not sure if the grasses are simply the lower layer or the grass is from an earlier consortium. But it is clear that the grass leaving the system is a pivotal moment for the transition to more complex forest and marks a large change that will signal the time to heavily prune and plant out the first cultivated species and begin the next consortium.
Secondary species growing vibrantly where bracharia has been shaded out.
Below the established arazá trees there is an area of secondary growth where, because of the shape of the land the bushes have shaded out the bracharia. It however does not seem to have the next consortium growing in the understory that I have seen elsewhere in the system where the bracharia has been shaded out, I only saw 2 young cauchos. This might be due to a lack of seeds, because the next consortium is mostly bird dispersed and the bushes are mostly the same strata with low biodiversity which means there is no where for birds to perch.
Secondary growth below arazá, low biodiversity and uniform height. As compared to similar areas with bracharia there are very few species of the next consortium waiting in the understory.
Caucho under secondary growth
A brush fire almost 2 years ago has had a marked effect on regrowth with bracharia of 2 meters tall and sparse secondary growth, and where the fire did not burn the field the secondary growth is much further along.
An extremely important note: the ferns only dominate where there has been conventional agriculture. They are present in other places but they do not dominate as they do in the coffee systems or in places where chemical fertilizer has been heavily applied. They are clearly showing a chemical imbalance caused by what I believe to be urea. Probably something to do with calcium but I am unsure, but lime applied to places where they dominate is effective in alleviating the chemical imbalance and they return to a background level.
High biodiversity secondary growth underneath large eucalypt. There is even bare ground visible, which shows how important even a little shade is to the system. 10 meters away outside the shadow of the eucalypt the bracharia is 2 meters high. I am still unsure how this effects the fertility of the system but it shows that the bracharia is in the system to protect the ground from the sun and I believe forms an important and necessary lower strata to this consortium when needed to protect from sun and rain. I am unsure if where there is less grass but still same species of pioneer consortium the ground is more fertile or has the ability to recover more quickly.
On the lower slope the secondary growth was agreeably biodiverse with good layering developing and only some clearings dominated by bracharia. I cut everything at chest height, around 1.5m with the hope that the resulting rush of growth will finish off the gramineas, weed out weaker individuals, and create good, green biomass for mulch for planting the beginnings of the agroforest system in 6 months. There is a marked difference in growth rate and biodiversity between upper and lower slopes, indicating that the lower slopes are in fact more fertile.
It is necessary to recognize the importance of the “mother tree” in the natural regeneration of the land in our context. As most of the accumulation consortium native species are spread by birds or other animals, the trees in the emergent and high strata are very important points for seeds from the surrounding forest and can have easily 6 or 8 saplings of the next consortium growing under their canopy. The shade from the trees, and the lower branches create spaces underneath the graminea layer for the seeds that fall to germinate and eventually push through the grass to the sunlight. I have found that this is the main mechanism for the transition from pioneer consortium to accumulation consortium. It stands to reason that the more of these transition trees that there exist in a system, the faster the system will transition to the accumulation consortium.
The “mother tree” mechanism of succession favors low fertility systems because in some systems there are not enough nutrients available in the system for an even change in consortium and creates islands of fertility which then through tight nutrient cycling and plants with short life cycles expands these “islands”, moves the system through to the next consortium, and creates the stratification necessary for efficient photosynthesis. As well as the most obvious result of creating conditions necessary for the germination of more advanced and complex life (shade and mulch).
Classification of Pioneer consortium, the lower layer is almost always bracharia or another perennial aggressive grass species sometimes with ferns and sometimes alone. The fern can shade out the grass but in that case there are no other species that will germinate in the shade underneath and it is delayed in breaking down so that a thick dry cap of ferns can form that stops any forward momentum of the system and also makes the system susceptible to fire.
Most of the common species of this early accumulation system I do not know the common or scientific names, and some probably do not have scientific names yet so I have labeled them arbitrarily according to their stata for the purpose of my notes.
Escoba de Bruja (Sida spp.) Ana Primavesi wrote that this plant indicated compacted soils.
Arrayan Blanco (Ardisia spp.)
Very similar to the larger woody tree that is abundant in this lot but flowers earlier and is smaller than the larger tree.
Guayaba Agria (Psidium Guajava)
This is one of the only woody trees that form part of this pioneer consortium. Albizzia Lebbek, planted by seedlings from seeds from the forest closeby, has also thrived in some cases probably as a transition species to the later accumulation consortium. These trees form a sort of “mother tree” that gives protection to seeds that germinate underneath and move succession forward. These transition trees also give a place to roost for one bird species in particular that is black and almost a cross between a raven and a parrot. But it plays an integral part in the ecological succession of the system because they eat fruit and tree seeds in the forest and then fly up to roost and spend time in systems in early accumulation consortium.
Mano de oso (Didymopanax Morototoni)
This vine is very aggressive and is found frequently in coffee systems, but not will only appear after there is a certain amount of secondary growth, and is not found in systems dominated by gramineas.