The Valley – Physical Landscape
The entire Upper Mamoní Valley watershed comprises 11,500 hectares of area, and drains towards the Southeast, with several larger tributaries, including the Rio Bonga, Rio Zahina, Rio Caracól, Rio Madroño and Rio San Jose. The northern boundary of the Upper Mamoni watershed is the Continental Divide of Panama, with the dense forests of the Guna Yala Comarca sharing much of this 20-km border. The eastern boundary is Chagres National Park in the remote Northwest corner – the source of the Rio Mamoni. Elevations vary from 120 to 1000 meters above sea level, with much of the upper reaches still forested, much of it steep mountainous wilderness with the highest points cloaked in cloud forest. Most of the deforested lands are found lower, along the main roads and rivers. The Valley’s unique geology, soils, weather, microclimates and hydrology create the setting for its thriving nature and agricultural abundance.
The Mamoní Valley is ringed by mountains on all sides, with only a narrow entrance in the southeast corner where the river has cut through the surrounding uplands and drops down into the coastal plain to join the Rio Chepo close to the city of Chepo. The Isthmus of Panama was only formed in the last 3.5-4 million years, creating the land bridge between the Americas and cutting off the tropical Atlantic Ocean from the Pacific Ocean, isolating the Caribbean Sea. This had major effects on the evolution of both terrestrial and aquatic species, and remains part of why the Mamoní Valley is of worldwide importance for the free flow of biological diversity through the Americas.
The Region’s upheaval was a mixture of volcanic events, igneous intrusion and fault-based mountain building. The rock is predominantly igneous, with a combination of both intrusive granites and some volcanic rocks. In terms of soils, these types of rock as a parent material apportion higher levels of calcium, magnesium, key microelements and trace metals essential for plant growth. The soils tend to have a higher content of clay minerals, better Cation Exchange Capacity (CEC) and are often classified as high fertility agricultural soils.
Igneous intrusions, when combined with highly aqueous environments often are prone to concentrating precious minerals in quartz-veins, importantly those of the Platinum group metals, which includes gold, platinum, palladium and rhodium. There are apparently several such veins that have been eroded over the millennia, depositing the heavier weight metals as ‘placer deposits’ – the type made famous by the California Gold Rush in the mid-19th Century. These gold resources are currently being mined artisanally throughout the rivers and streams of the Mamoní Valley — most intensely on two properties in the western portion of the valley.
Given its volcanic, igneous intrusion, and hard rock origins within a relatively short time scale of intensive use, the Mamoní Valley has relatively high quality soils. With the exception of the volcanic soils of Chiriquí and a few pockets in E. Panama, the Darién and Los Santos, Panama as a country is not famous for high levels of fertile, agriculture grade lands. Fortunately, the soils of the Mamoní Valley are higher quality lands, far better than most typical tropical forest lands in areas with high rainfalls. The lands themselves, for the most part have not been overly worked for agriculture, despite the tradition of extensive cattle grazing throughout the area. Much of the land is in various stages of forest regeneration and long fallow periods will likely be conducive to clearing of non-forested lands and replanting.
The large expanses of flatter lands along the main river course of the Mamoní and its more significant tributaries (eg. Rio Bonga), demonstrate an alluvial texture. Most have a higher organic material content and good drainage apportioned by a higher level of sands, producing a texture considered ‘Franco-Arenoso’ – the best type of soils for most crops and trees. These are also the same soils that at this point are not covered by forest, and are typically the most accessible. At the same time, these soils are still largely impacted by cattle, when and where they are put into pasture to graze, with many sites experiencing soil compaction and erosion due to overgrazing.
The best soils in the valley are all alluvial soils with near neutral soil pH (6.2-6.5). Elsewhere, especially higher up on hills, the soils become more acidic, as these soils have been more thoroughly eroded and impacted by cattle ranching. The soils in general have medium to high levels of Calcium (Ca), Magnesium (Mg), Manganese (Mn) and Iron (Fe). The soils are deficient in Phosphorus (P), Potassium (K), and Zinc (Zn), which are all easily added using rock phosphorus and commonly available blended fertilizers with macro- and microelements. The sites all have low to medium levels of organic material, and low Cation Exchange Capacity, deficiencies that can be remedied by the application of composted biochar.
Soil pH is a critical indicator of the soil’s effectiveness in providing essential elements to plants. The soil may have high levels of key nutrients, but these nutrients may be unavailable to the plants. This is also true in the case of high levels of aluminum saturation or an overabundance of iron, both of which bind with the minerals in the soil in molecular associations that prevent the desirable elements from being readily absorbed by plants. Aluminum saturation is fortunately low in all sites tested in Mamoní.
The entire Mamoní Valley is considered to have a humid tropical climate, with rainfalls totaling 2200-2500 mm/year, while the Upper Mamoní has a specific microclimate. The lower portions of the Continental Divide in the eastern portion of the Valley allow the humid air from the Caribbean to pass easily over the Divide and into the Valley. The West end of the Preserve is ringed by higher mountains with less moisture passing over the Divide, yet more chance of orographic uplift of the humid air masses with resulting rainfall. The establishment of inexpensive solar weather stations with satellite telemetry reporting could be very informative and help determine climatological differences within the Valley. Under the Holdridge Classification System the Mamoní Valley Preserve is considered Tropical Humid Wet, with some aspects of seasonality during the dryer period from late January through April, and with February and March considered to be the driest months. The rains begin in earnest in May, with heavy rain through to August. August has a slight decline in rainfall, with one or two weeks of summerlike conditions called ‘el veranito’, prior to the return of consistent rainfall through January. October and November are considered the wettest months.
The Mamoní River is one of the Panama Province’s three major rivers. The Upper Mamoní Watershed drains approximately 11,500 hectares and has three major tributaries: Rio La Bonga, Rio Zahina, and the Rio San Jose. Apart from these more major watercourses, there are over 100 other watercourses in the Valley. Given the high rainfall and ambient humidity, more than two-thirds of these streams or ‘quebradas’ are permanent, fluctuating in streamflow depending on the rainfall.
The rivers in the Mamoní Valley have a great propensity for flash flooding during more significant rain events, especially in sub-watersheds with greater deforestation. Trees help to slow the overland flow of water, thus stabilizing river flows during high-rainfall events.