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

132 Gary S. Hartshorn
especially rich in native plant species. R. Foster and A. Gentry of the
Missouri Botanical Garden (pers. comm.) are discovering an impressive
number of plant species with medicinal or pharmaceutical uses. I
estimate that there are at least 1,000 native tree species in the Palcazii
Valley.
The Palcazii Valley's soils, like most soils supporting tropical forests,
are unsuited for conventional commercial farming. The red clay soils
of the extensive rolling hills in the lower valley are highly acidic (pH
3.8-4.5), with an abundance of aluminum. Furthermore, these soils are
highly leached and almost devoid of major nutrients, especially calcium,
phosphorus, and potassium. Also present in the valley are old riverine
terraces with white sandy-clay loam soils that are even less fertile than
the red clay soils. The Amueshas do not use these old terraces for
shifting cultivation, hence these poor soils generally have well-developed
primary forests (Hartshorn 1981) with an abundance of valuable trees
such as rubber (Hevea brasiliensis, Euphorbiaceae), and tornillo (Ced-
relinga catenaeformis, Mimosaceae).
Because of the high rainfall and rolling-to-steep terrain, the red clay
soils are highly erodible when cleared of their protective forests and
used for agriculture or pasture. A survey of the land-use capability in
the lower valley indicates the following distribution of maximum sus-
tainable use: 7.6% suitable for annual or seasonal crops; 13.3% for
pasture; 14.4% for perennial crops; 46.2% for production forestry; and
18.6% should be kept in undisturbed protection forests (Tosi 1981). In
this classification system, less intensive uses are permissible, such as
production forestry on lands suitable for agriculture or grazing. But the
opposite (pasture on forestry land, for example) is not sustainable, and
should be avoided. The project includes a program for mapping land-
use capability of the lower valley, as well as actual land-use, with a
view to adjusting current land-use practices to sustainable use of the
natural resources. Thus, some 44,000 ha of remaining forests in the
lower Palcazii Valley could be under permanent management for pro-
duction forestry.
Background
Numerous efforts to manage heterogeneous tropical forests have failed
due to difficulties such as: 1) the low volume of commercial woods per
unit area, there being as many as 200 tree species in one hectare; 2)
very high extraction costs associated with the practice of high-grading
only the quality timber; 3) lack of understanding about the dynamic
nature of most tropical forests; 4) a general lack of information about
the regeneration requirements and silvics of canopy tree species; 5)