Category Archives: Reforestation

Swales

A man built swale is a low tract of land following a contour line made to harvest rain runoff on a slope.

Here is a swale filled in by rain water run-off;

swale-variations-01

View of profile ;

swale-profile

Swales are the most convenient way to store water in presence of a slope.

When a land has been deforested no tree can prevent erosion any more. The water run-off remove in few years the top soil. The vegetation may then take decades or even centuries to settle again, constantly removed by new run-off and by the difficulty to settle roots in a hostile subsoil.

Swales, by creating a water channel help the process of water capture and infiltration in the soil. After only few years the vegetation settle again and the topsoil regenerate.

Swales are not eternal and erosion will still impact this earth-shaping architecture if no trees with deep roots are planted to take over with the erosion prevention. Various methods exist with regards to the location of the trees and the swale. Planting the tree on top of the bern of the swale allow quick root settlement since the soil is soft. However this location tends to dry rapidly so this needs to be done at start of the humid season. Planting the trees just below the swale allow to use the bern as a platform to access the swale and harvest the fruits of the trees.

A swale follows a contour line meaning that its construction needs to be done using adequate leveling tools. Two tools are mainly used;

– a “A” shape tool. In this case you need to tare it initially using a horizontal surface and mark the position of the vertical string on the horizontal bar of the “A”
– a transparent hose filled with water which is the most convenient tool if your swale is longer than 5 meters.

swale-leveling

 

In some cases you need first to remove the vegetation to access to the most probable point on the contour line. In order to avoid removing too much vegetation not being very sure where to go horizontally, the best way to assess this with your eyes alone is to locate yourself in a perpendicular position with regards to the contour line. Only in this position you may have a good guess of the horizontal plan. Trying to evaluate the horizontal position of a line looking in the same axes that the line infers mistakes.

The swale by capturing water will deeply modify the humidity and structure of the soil down the hill. A water lens or water plume is created which shape depends on the geological layer composition and the angle of the slope. Here is a description of the typical evolution of the water storage inside the ground.

swale-plume

If you need to control and reduce the level of humidity generated down the swale the best way to do so is planting trees to monitor the water plume. This is a sensitive matter if you build a swale up the hill of a house. The humidity concentration could provoke water infiltration in the soil of the house.

Swale Overflow

Swales may include an overflow channel to redirect water to another swale or into the existing overflow network.

Water overflow channel needs to be covered using a non erodible material (e.g. plastic, … see picture below). Excavating the overflow channel without a protection from erosion will have the effect of the channel being dug up by the rain when overflow happens. The erosion will deepen the overflow channel until its bottom goes at the same level than the bottom of the swale, making the swale ineffective in holding the water.

Swale Overflow

The stones (as shown in the picture) ensure that the flow of water will not pass underneath the sheet to create erosion. The water level of the swale will be defined by the lowest border of the swale, in this case the channel protected by the sheet. To increase the swale water volume capacity the channel needs to be leveled up, taking care that it remains always the lower point of the pit borders.

 Swales customization

In places with high erosion the swale will gather a lot of sand and sediments. This earth can be used either to be transferred in locations where soft soil is needed or even be used as sand for construction. A third solution is to use this earth to transform the shape of the swale in order to create a terrace. Sediments will help create a light and humid earth bed showing potential for growing crops.

The following section mainly the different types of swale you may create depending on the situation.

First of all it is important to differentiate a swale harvesting water run-off from a sandy sector or from a vegetation established situation.

The former will be filled over time by sand, silt and organic matter. As shown on the picture below.

swale-harvesting-sand-and-silt
swale-variations-02

The erosion has brought sand (seen in the middle of the photography) and silt (on the down/right side) which are being harvested and brought to another location where sandy soil will help root development.

In this context it is necessary to let the swale empty of vegetation or mulch in order to have easy access to the sand and silt and shovel the accumulated materials for different usage. In this case the swale plays an additional role which is harvesting certain textures of soil (sand and silt) which can be very useful, for example;

– to add sand in banana circles shape in a compacted soil. Or any earth-shaping requiring good drainage(e.g. Biodigestor evapo transpiration).
– to get sand, in certain cases pure enough, to use with cement.
– to get silt to mix with earth for additional fertility.
– to transform the swales into terraces by moving the sand down hill (see the photo below)

swale-terrace

A secondary swale (e.g. located down from the former) will not receive sand because the first swale make a barrier for the sand. In this case the swale can be filled in with mulch to better keep humidity and help reconstitute the top soil on the bottom of the swale or can be used as a German pit (HugelKultur in pits). In this case the vegetation settled there will need to be adapted to a swamp ecosystem with long periods of water logging depending on the rain water accumulation. (see photo below)

swale-terrace-up

The sand and silt accumulated from the upper swale can be mixed with the earth taken to make the terrace.

A swale always need to follow the contour line in order to keep the water in. However it may play as well a different  role and have an additional specificity;

– Channeling water, to a pond for example, (see photo below)
– Have a depth variation in order to monitor the quantity of water infiltrating the soil. (see photo below)

swale-sizes

 

In case of channeling it may be necessary to add gates to monitor the overflow debit to the desired location. If let open the water flow will most of the time fill the pond and not stay at swale level. The priorities between pond level and water accumulation in the swale can be managed through simple gates. Once the water reach the top of the gate the overflow starts to fill the pond. The overflow of the pond can be avoided if necessary by having a water overflow evacuation point on the swale at the same level than the maximum desired pond water level.

Location of the plants on the swale system

Trees root system allow to fix the earth shape against erosion over time. It is then important to plant perennials, big enough to fix the swale. Over time the swale will disappear and the perennials will play the erosion control function (roots, mulch, humus, cover ground). If the slope is important deep tap root trees should be preferred.

Trees can be planted down the swale so that the mount can be used as a platform to access the fruits. In this case medium fruit trees can be planted (see photo below)

swale-plantation-down

 

If planted on the mount the fruit trees may be smaller to compensate the elevation (see photo below). The mount is usually soft since the earth has been dug up from the swale. The root system will develop easily there. The only drawback is the tendency of the mount to quickly become dry.

swale-plantation-up

It is unadvised to plant trees inside the pit since the soil is usually less fertile and very compacted. The bottom of the swale suffers as well important hydrometry variations which could impact the tree. To resolve this you may create a German pit as described above (only on secondary swales).

When defining the contour line before digging the swale it may happen that you encounter a tree on the way. It is then not necessary to remove the tree. You may dig the swale down or up the tree on the specific portion where it stands. By doing so you must make sure that the bottom of the swale and the top of the berm stay at the same level. When the slope is sharp the best alternative is digging the swale up the hill to skirt the tree. In both solutions a previous analysis of the tree root structure is necessary (size, resilience, age).

Designing the Forest Succession

When conducting the process of reforestation we may consider two kinds of trees;

The support species, in charge of creating the nurturing framework of the forest ecosystem (soil fertilization through nitrogen fixation with leguminous plants, strong root penetration for soil breaking, nurturing and ventilation, rapid biomass production for mulch production and topsoil reconstitution, wind breaking and moisture capture, etc.) and

The productive species, in charge of food production for human and animals and side products generation like timber, fibers, etc.

At start 80% of planted trees, bushes and cover-ground are leguminous (support species) in order to boost the ecosystem capability to develop, and 20% of productive species are planted taking into account their capacity to adapt and resist to the first years of a non fertile and often dry environment. The support species are planted in various sizes and  over-density and will be pruned or removed over time to produce mulch and allow productive species to receive light.

How to proceed in term of design

80% of the support plants, mainly leguminous, will disappear, either naturally or pruned or removed, to create mulch and biomass.

The design needs to show on paper the species that will stay in fine in the food forest. They are mostly productive species and 20% of supportive species (for fertilization, wind break, mulch production, etc.) The location per zone of the different productive trees needs to be defined.

Then if the support species can be spread in the field surrounding densely the productive species they don’t really need to be included in the drawing since they form a nurturing placenta evenly distributed.

The distribution of support species may be compared to the construction of a grid, mixing homogeneously the different supportive species in size and shapes. Later the landscape architecture will operate negatively and remove the unnecessary plants.

It is on one part; classical landscape drawing, in the other; design by negative space in the landscape architecture. The supportive species which will remain (not been removed) are plants with particular positive interaction, health and robustness and capability to act as a permanent species, in size, shape and adaptability (pruning recovery, propagation capability, weather adaptation, …).

In Time

With regard to the time scale it is to be considered that some (most ?) productive species have poor pioneering qualities and will be able to settle only after a buffer of time, requiring the protection and the fertilization from pioneer species.

In this case either you have resources and may invest for each plant enough organic fertilizer, enough labor (modify the soil texture at the plant location if necessary), enough biomass to ensure global moisture and carbon availability, enough money to invest in infrastructure, e.g. “Groasis Waterboxx” See external resource.

or you may schedule the plantation following some strategies;

– Pioneer productive species are planted at the same time than the support species, at start of the reforestation . They will not grow quick but will resist and settle, ready to use in the future the resources provided by the support species.

– Productive species will be planted following a calendar based on their need for fertility, humidity and protection and on the resources available. The calendar is based on global fertility of the land improved over years by the support species and on the different specificity of the various location (An outdoor shower will provide with constant humidity, an existing tree will protect from the sun, a roof may concentrate rain falls or help to water zone 1 by rain water harvesting, etc…). Resource location (swales, pond, compost, chicken tractor, dry toilets, etc.) is as well key in the way to orchestrate plantation over time.

– Recent studies show that reforestation at large scale is better done by planting clusters of trees and not spread them homogeneously. The many small forests will nurture their close environment and help the settlement of trees in their peripheries, till the clusters extend and reach each others. As an habitat for seed gathering animals the tree cluster will support biodiversity in the forest propagation.

In space

A domestic variant of the cluster distribution is to stretch vegetation in strategic directions once settled. Various techniques can apply;

– If you have the capability to harvest branches and leaves (3rd / 4th year) you may over-stack the soil in between the sun course and the tree cluster, close to it, with pruned material. The material must be 1 meter high ideally and will protect the young seedlings from the sun and represent a reserve of biomass fertilizing the soil and keeping moisture. The presence of the tree cluster will provide with fertility on its periphery and wind absorption.

– On the other side, where the shadow of the tree cluster bring humidity and cool down the temperature seedlings do not need a lot of attention and no mulch is needed. The growth is the most reduced where the shade is the most intense.

Other fountains of resources (gray water treatment, swales, dry toilets, stable, ponds, etc.) can see their flow orientated in order to nurture vegetation extensions. In this case the slope play a determinant role associated with the sun course.

In all cases the prevailing wind and wind sectors need to be taken into account in the stretching directions.

Knowing the result in space and time of the stretching process for every tree cluster or resource fountain, this knowledge can be used to anticipate the design and influence the location of the resource fountain and tree clusters themselves.

New plantations are done at the start of the humid season. Exception can happen for zone 1 where watering can be done easily.

Flora

Leguminous species

Large : Acacia Mangium (see reforestation with Acacia Mangium)…

Middle size : Inga Edulis, Leucaena, Samsao do campo…

Small size and vines : Pigeon Pea, velvet Beans, Jack beans, Crotalaria…

Cover-ground (perennial) : Amendoin Foragera…

Some pioneer productive plants:

Mango, Jackfruits, Acai, Coconut trees, Dende, lemon tree…

Plants needing a fertile soil:

Banana trees, papaya, amora, goyava, caja, graviola…

Reforestation with Acacia Mangium

Tropical food forest is a context with more practical (empirical and systemic) knowledge published in Spanish and Portuguese. If you know how to use google translate open the equivalent link from our website : https://anovafloresta.wordpress.com/2016/05/17/reflorestamento-com-acacia-mangium/ and translate it !

Acacia Mangium (Acacia Australiana or Black Wattle) is a leguminous (symbiosis with nitrogen fixing bacteria) coming from Australia and frequently found in Brazil. Acacia Mangium is defined as a support species and provide with additional functions like wind break and wood for furniture or fuel.

It has amazing growing capabilities. The one on the photo below was planted end of March 2013 and the photo was taken the 4th of June 2015. It is 2 years and 2 months old and has been growing on a depleted soil lacking of organic matter and edible minerals.

Accacia-Mangium

This shows that you can reforest and regenerate your soil rapidely. 150 Mangium have been planted over 7000 m2 and form now the main forest structure of the farm.

The one of the photo is one of the biggest and you can find on the site various sizes although planted at the same time. Some key factors are the soil compression, the capability for the tree to find and start a symbiosis with the nitrogen fixing bacteria and humidity although A.Mangium can resist well to drought, especially in soils having a fair proportion of clay (e.g. 20%).

With regards to reforestation in the tropics you may have 2 strategies;

1) Immediate forest succession…

…by planting all the trees at the same time (fruit trees, timber trees, emergent trees, leguminous and natural soil improvement trees, under story, ground cover, etc…) including large leguminous like A. Mangium. This implies that your soil has already enough fertility to sustain some species which need a good soil or that you have enough money and time to add compost, water, protect your trees from the sun and mulch intensively.

2) Or conduct a 2 phases rehabilitation

The alternative to immediate forest succession is to plant high density of Acacia Mangium (one every 4 meters) and other resistant species (including smaller leguminous) in between (Pigeon Pea, Leucaena, Gliricidia, giant grass, Pine Apples, Cassava, giant bamboo, Acai, dwarf coconut trees, lemon and orange trees, Citronella, Pau Brasil, Biriba, Umbauba, Monjoleiro, Jabuticaba, Urucum, Aruera, Amenda, Mangaba, …) and should include large fruit perennials (jack fruits, Mango trees, Jamborao, Dende, coconut trees, etc.). The Acacia Mangium represent the fertility grid of your landscape and most of the other trees the pioneers of the future design of your site, accordingly to the different zones you have defined. The population of Mangium and some other leguminous (gliricidia, leucaena) can be pruned the second year and the mulch spread in area where vegetation has issues to develop. If you have limited resources in time and money and an important surface area to reforest you may focus your reforestation;

– on tree clusters spread regularly on the site. They will become green islands you may stretch in the direction opposite to the sun course and/or prevailing drying wind. These tree clusters may as well become the habitat for fruit trees propagators like bats and birds.
– down the swales where water table will raise over time
– around your gray and brown water recycling systems (banana circle, evapo-transpiration tank)

acacia-mangium-garden

After 1 year you may plant nutrients accumulators (comfrey or tropical alternatives) which will accumulate minerals and carbohydrates.

Over 2 years you may start to have compost and identify fertile and humid spot where you can start to plant demanding or more sophisticated species (Banana, Papaya, Amora, Graviola, lemon grass, sweet potatoes, BiriBiri, Cocoa, Cupuaçu, Cherimoya, Advogado, Cashew trees, Passion Fruits, Genipapo, sugar cane, Xuxu, etc…). These spots need to be mulched intensively with the pruning of Mangium and other leguminous. At this point you may plant more sophisticated leguminous like Inga Edulis smaller than Mangium with a beautiful parasol shape. These Ingas may become part of the permanent 20% leguminous species you’ll keep in your food forest. Being in the tropics trees are not impacted by winter and can handle well the pruning. Ingas can be pruned regularly and propagated easily in the future.

acacia mangium false leaves

(Picture above : the leaves of an adult acacia mangium are false leaves; a modification of the stem. The real leaves appear here on this seedling.)

At this point some cover ground protecting and improving the soil will be able to settle like Arachis Pintoi.

You may diversify the range of productive species in order to spread the periods of harvesting over time. You may add Mycorrhizae fungi where new species are located to help them get the nutrients and resources provided by the growing forest.

When reforesting an area you’ll face the destruction of leaves cutting ants which can come from long distance (neighborhood) attracted by the new vegetation you are trying to settle. Mulching is one of the best solution to create barriers making their pathway problematic. Another solution is the settlement of Arachis Pintoi which reduces the perimeter of action of these ants.

In zone 1 dedicated to your future kitchen garden you may overload the area with pigeon peas and leucaena (that you keep always small by pruning) which can be even removed each time you need to settle a garden bed. The root systems of such plants will remain non competitive for your vegetables to grow if you keep them under control.

If a Mangium is destined to be removed (accordingly to your design) it means that other productive species can be planted very close to it and will benefit for few years from the nitrogen fixing bacteria nodules of the removed.

acacia-mangium-insect-digger

To be noted; a small coleopteron (bezouro serador) 3cm long (photo above) may arm your Mangium by digging a regular ring around the trunk of the tree (photo below) causing a fragility where the tree can break. The upward part of the tree over the ring will end up dying eventually. This happened 3 times on a population of 180 A.Mangium and only on A.Mangium species.

acacia-mangium-bark-eaten-by-insect

Important; plant only at the start of the humid season. Taking care of a forest of seedling planted at start of the dry season is just not sustainable. During the humid season the seedlings, if they are from resistant species, will have time to settle and very few of them will need watering in the following dry period. Mulching is a very good option assuming you have no chicken going errand. In this case put cardboard on top of the mulch so that chicken will not be willing to scratch the soil and damage the young plant. When the cardboard is degraded over time usually the young tree can then handle chicken activity.

Once the food forest reached its climax Acacia Mangium may be kept only in designated areas (wind break and zone 4 dedicated to wood material) since they are described as producing hormones inhibiting the growth of other plants. This impact was not noticed on the field but may play a growth reduction effect on the long term over closed-by vegetation.

Subcategories of support and productive trees

Support trees

  • Trees that accelerate regeneration and soil fertilization
    leguminous (nitrogen fixing through symbioses with bacteria)
    high level of sugar producers,
    high volume of leaves producers
    soft leaves allow faster integration in the soil ecosystem
    hard leaves allow better protection of the soil over time
    small leaves provide better litter density better keeping moisture
  • Healing trees (eg Gliricidia. Not. etc.)
  • Support trees to vines,
  • Barriers against predators the weeds
  • Producers of flowers to attract pollinators
  • Producers of food and habitat for animals
    Rising biodiversity and increasing ecosystem balance
    Nitrogen recycling improvement
    A
    ttraction of pest control animals
  • Windbreaking trees increase humidity
  • Trees with deep roots for nutrient cycling and soil unzipping
  • Trees lose all their leaves at once giving light to smaller plants periodically


Productive trees and perennials

  • Fruit trees and producers of nuts
  • Wood
    habitat construction and structures in the garden
    creating hugelkulture
    fire
    fibers and panels (palm leaves)
  • Medicine and condiments