Fragile Lands of Latin America Strategies for ... - PART - USAID

Agricultural Systems on the Peruvian Floodplain 7 7
aquatic fauna, and ease of transportation and communication, served
to concentrate people on these strips of land.
Floodplain Biotopes and Climate
In my study area, the floodplain varies between 15 and 25 km in
width, and is bounded by a geologically older and slightly higher terrain.
These interfluves, rising between 5 and 40 meters above the mean river
level, are locally called altura. In the Iquitos area, the altura's surface
material consists of weathered sands and clays of the late Tertiary
period. These Miocene-Pliocene sediments, referred to as the Pebas or
Iquitos beds, are in most places heavily eroded and incised by small
streams.
Bajo is the term that refers to the low-lying floodplain. Practically
all the landforms on the bajo are the result of Quaternary ponding and
sedimentation (Putzer, 1984). The floodplain is characterized by several
biotopes. The highest relief is attained on the natural levees. These
landforms are differentiated between a restinga alta and a restinga baja.
The former is rarely flooded, while the latter are subjected to short
annual inundations. Thus, nutrient-rich silts and mud are deposited
seasonally on the restinga baja, but not on the restinga alta. The yearly
sedimentation rates vary in inverse proportion with the distance from
the river. Most of the deposits occur on a belt within 300 m from the
river's edge. Flooding is not a problem on the restinga alta, but the
absence of periodic silting does not allow the continuous cropping of
annuals.
Several other biotopes occur on the floodplain. Sand bars (playa)
and mud bars (barreales) appear regularly after the water subsides.
Some of these bars, with appropriate current, accretion, and anchorage
by vegetation may evolve into semi-permanent islands that are highly
productive. The palm swamp (aguajal), back-swamp (tahuampa), lake
(cocha), and side channels (caffos) comprise the rest of the biotopes.
These are managed for non-agricultural activities, such as, collecting
of forest products, fishing, and hunting (Hiraoka, 1985a).
The Iquitos area is characterized by a high average temperature and
precipitation. The mean annual temperature is 26 degrees C. During
the period of reduced precipitation, July through September, daytime
temperatures reach 34 to 35 degrees in the shade, but most of the year
the daily high averages 30 degrees C, while the lows often dip into the
high teens. Rainfall in the area averages 2,800 mm per year. Despite
the large total, precipitation shows some seasonality. The short dry
season is not as pronounced as in the central Amazon around Manhus.
Even the driest month receives a mean of over 160 mm. But this