Growing Swales, as the first step in reforesting tropical slopes.
Digging swales is hard work, by hand and can lead to erosion when heavy equipment is used.
I'm looking at doing this on sloped tropical grassland. These grasslands can be quite persistent, preventing succession toward the
native forests that were cut down.
In order to slow the progression of
water, down the slope, I'm looking at creating dense hedgerows made of nitrogen producing
trees and bushes. Ipil ipil, is a bushy type of lucena that provides much of the forage and
firewood in the Philippines. Mother of cacao is a larger nitrogen producer. It is planted all over the world with cocoa trees to shade them and provide them with nitrogen. There are about 50 trees that produce nitrogen, which will be considered. Many can reach 30 ft tall in 2 years.
Other useful trees that are hungry for nitrogen, will be included. Jackfruit, mango, breadfruit, teak and neem, are top contenders. Big non-trees like bananas and papayas can fit in, along the edge of the hedgerow. Passion fruit and grapes will be tried. Strangler figs will be planted by birds. I will let them take over some of the pioneer species, but they will be kept out of valuable fruit and timber trees.
There are other things like tagaste and pigeon peas that can be planted and left alone, until you want to graze animals or harvest firewood.
The beauty of hedgerows, is that it's a part of the farm that you don't really have to dump labour into, unless there's something useful to extract.
It provides nutrients, shade, fruit, firewood, windbreak, erosion control, water retention, a home for beneficial birds, snakes and insects...
I'm not worried about becoming overrun with these trees, since they are mostly medium hardwoods, with firewood and charcoal value. A man can harvest several times his wages, in a day. It's a crop that keeps on giving, with minimal input cost.
A large number of trunks popping up, parallel to the slope, will block and slow run off, to some degree. They also lift the soil, as the
roots and trunks take up space. When branches are cut, to
feed livestock, the leftovers can be laid along the line of the trunks, with any rocks gathered from the immediate area. This will create a physical barrier, and also allow for more water absorption.
Eventually, the landscape will have a slight stepped appearance. I won't try to change the entire shape of a hillside, as is done with rice production. Instead, there can be regular lines of trees every 50 to 70 feet all the way down the hillside.
I will graze animals along the uphill side of each hedgerow, in order to keep a pathway open.
From time to time, manure rich soil from that area, could be used for hilling around banana circles or patches of sweet potatoes. Harvesting of soil, will slowly produce a flattened area on the uphill side. Not only will this slow the progression of water down the hill, it will make it easier to use the pathways, which will in turn make it easier to move animal pens and
chicken tractors.
I'm not sure how wide something like this needs to be. We might start with five feet and see how that works. That would allow for several trunks wide instead of just a single row. It might end up being 25 ft wide, as the tops spread sideways. In areas where the
land is exceptionally steep or rough, it could be much wider. Specimens grown with others immediately beside them, tend to grow much straighter without so much branches. They can produce useful house poles within 5 years.
Whenever we get a nice looking jackfruit or teak or whatever, I will let that one become dominant, and they will eventually shade out the pioneer trees.
A thicket like this is going to produce a huge amount of leaf drop. Some will fall between the trunks and become part of the water blocking and absorption. The rest will be spread over the cropland or grazing land between the hedgerows. Leaves will be blown in the wind and moved by water. But I doubt that very many could make it all the way to the bottom of a slope, with so many barriers in the way.
Leaves from legume trees can provide 500 lb of nitrogen per acre. They also bring up other things that plants need. I expect nitrogen producing trees and other plants to supply 100% of my nitrogen needs.
The limiting factor for optimal growth is usually phosphorus, along with a number of micronutrients. This will be provided in the form of rock powders that don't easily disappear in heavy rain. Leaf drop from these trees will distribute nutrients throughout the landscape.
I expect to run for several years, possibly as much as a decade with 80% of my trees being nitrogen producing pioneer species. This will help to create the right conditions to plant the more valuable long lasting species, that will eventually dominate.
There are a few long lasting and very tall legume trees, which can be dispersed throughout the new forest. Koompassia excelsa is a long-lived nitrogen producer that grows over 200 ft tall and will never be shaded out.
By the time a forest like this has been around for 10 years, there will be a huge accumulation of biomass, which will store nutrients and water, creating a suitable environment for some of the more picky rainforest species.
The government has nurseries which carry a wide variety of native species, available at minimal cost. I will consult one of their people from the beginning, when planning drainage and more permanent plantings.
Experience in other areas has shown that in as little as 10 years, a forest like this will continue on its own, without further assistance, if people just leave it alone. I don't expect to ever
sell it and I will do whatever I can within the law, to prevent it being completely logged by future owners.
It's possible that someday, any swales that are created, will become indistinguishable. By the time that happens, they won't really be needed anymore.
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