[nafex] FW: The Overstory #78

Lon J. Rombough lonrom at hevanet.com
Tue Mar 6 23:30:27 EST 2001


----------
From: William Evans <williamevans at HOME.COM>
To: OGL at LSV.UKY.EDU
Subject: The Overstory #78
Date: Tue, Mar 6, 2001, 7:27 PM


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::::::::::::::::
Overstory #78--Reforestation of Degraded Lands

::::: Background :::::
::::: Technologies :::::
::::: Land Preparation :::::
::::: Species Selection :::::
::::: Natives and Exotics, Monocultures and Polycultures :::::
::::: Planting Materials :::::
::::: Tree Care and Maintenance :::::
::::: References :::::
::::: Original Source :::::
::::: Web links :::::
::::: Related Editions of The Overstory :::::
::::: Publisher Notes :::::


This edition of The Overstory joins combines topics in preparation,
species
selection, planting materials, and tree maintenance towards reforesting
degraded lands.

BACKGROUND

Degradation of tropical land is a physical, chemical, and biological
process set in motion by activities that reduce the land's inherent
productivity. This process includes accelerated erosion, leaching, soil
compaction, decreased soil fertility, diminished natural plant
regeneration, disrupted hydrological cycle, and possible salinization,
waterlogging, flooding, or increased drought risk, as well as the
establishment of undesirable weedy plants. There is a strong
relationship
between inappropriate land-use practices and land degradation. In some
places, degradation is manifest (e.g., desertification), where in others
it
is inferred (e.g., declining crop yields).

Deforestation in mountainous regions is one of the most acute and
serious
ecological problems today. Disturbance of vegetative cover on montane
areas
with thin soil and steep slopes results in land instability (e.g.,
landslides) and soil erosion. Excessive erosion not only impairs site
productivity but may also adversely affect other sites or water bodies
farther down the watershed.

Conversion of tropical moist forest into farm or grazing land commonly
results in rapid depletion of the soil's plant nutrient supply and
accelerated soil erosion. In some places the degradation process leads
to
takeover by persistent, aggressive weed species of low nutritive value.
Often the combined problems of low soil fertility and weed infestation
become so great that the land is abandoned. Such lands are subject to
frequent uncontrolled fires and are often covered by coarse grasses.
Whenever the vegetation is burned, erosion may increase and productivity
may be reduced further.

In many arid and semiarid open woodlands, overgrazing and repeated fires
have converted the vegetation to a degraded fire climax stage.
Consequently, soils become dry and little woody plant regeneration
occurs.
Fire-tolerant vegetation‹commonly unpalatable to animals‹persists
leading
to a desert-like state. Over 20.5 million ha of tropical arid lands
become
desertified every year (Wood et al 1982).

Each year, over 500,000 ha of excessively irrigated lands become saline
or
alkaline as a result of inadequate drainage or use of salty irrigation
water. Capillary action draws moisture to the soil surface where it
evaporates, leaving salts in or on the topsoil. In some cases, salts can
be
leached from upland soils and bedrock, raising the salinity of runoff
from
deforested slopes. The increased runoff harms agricultural soil in
lowland
areas by causing temporary or lasting waterlogging and salinization.

The best solution to such problems is to prevent inappropriate land-use
practices on forested lands. Where it is too late for this approach,
reforestation is an alternative. Trees planted on degraded lands will
not
give such high yields as trees planted on rich, fertile lands. However,
it
may be the only way to raise the productivity of the most degraded
lands.
Furthermore, in many countries, fertile sites are reserved for
agricultural
activities. Given the dwindling reserves of good land and the increasing
amount of degraded tropical lands, reforestation is a technology with
potential to rehabilitate soils and to provide many goods and services.
For
example, fuelwood plantations can alleviate the worsening shortage of
firewood in some areas and prevent shortages from occurring in others.

TECHNOLOGIES

This section summarizes the mechanics of reforestation and focuses on
pertinent issues and problems that may prevent reforestation success.

::::: Land Preparation :::::

Many degraded sites need some type of preplanting preparation, such as
clearing stumps and competing weedy vegetation. Under some
circumstances,
site cultivation controls weeds and improves soil aeration, soil
biochemical activity, percolation of water, pH regulation, nutrient
application, and surface evenness. The degree and type of land
preparation
depends on several factors: site and soil conditions, vegetative cover,
species to be planted, and available capital and labor.

Land preparation can be done by hand or by machine. Manual methods are
less
constrained by the rainy season, they require few skills, and the
capital
cost is relatively low. They also provide temporary employment to
laborers
and cause minimal damage to soil. A disadvantage of manual clearing,
however is the need to recruit, manage, and provide logistical support
in
remote areas for large numbers of laborers. Mechanical clearing, on the
other hand, requires high capital inputs for equipment maintenance
supplies
of fuel and spare parts, and operator training and supervision. And
heavy
machines degrade the site through topsoil disruption. Yet, in general,
mechanical clearing is cheaper than manual clearing (Evans 1982). The
choice between manual and mechanical land preparation must be made on a
case-by-case basis, determined by all these considerations.

Sometimes, artificial barriers of brushwood or other materials
constructed
in a grid or contour pattern, or grasses and trees planted in a similar
pattern, can be used to immobilize drifting sand. Plowing the soil
surface
to increase water infiltration, ripping across the slope to retain
water,
plus construction of bench terraces on steeper slopes, and funneling
moisture onto a smaller area are all conservation measures used to
maximize
planting success. Minicatchments built to concentrate water into the
rooting zones of individual trees are a particularly important technique
in
arid zones.

It may be necessary to add nutrients during land preparation. Several
techniques exist including mulching with organic matter, planting
nitrogen-fixing trees, applying green manure (especially herbaceous
legumes), and commercial fertilizers. Mulching suppresses weeds,
improves
soil moisture conditions, and augments soil organic matter, but it may
increase problems with rodents or other pests. Nitrogen-fixing trees can
improve soil with their ability to produce nitrogen fertilizer. Foliage
dropped by legumes is nitrogen-rich and will augment soil fertility as
it
decays.

Other measures may also be used, such as the addition of small amounts
of
commercial fertilizers and amendments. Nutrient levels and fluxes in
plantations should be monitored to determine the prospective benefits
and
cost effectiveness of soil amendments. One of the less obvious soil
deficiencies, occurring particularly in eroded soils in the drier
climates
is the lack of necessary micro-organisms. An ancient and effective
method
to add micro-organisms is to inoculate either nursery soils or planting
holes in the field with a few grams of topsoil from well-established
plantations or healthy forests. The method is not practical, however,
where
well-established plantations and/or healthy forests do not exist.

::::: Species Selection :::::

Tree species selection is important to plantation success. If a tree is
grown under unsuitable soil or site conditions, it will be stressed and
thus become susceptible to attacks from insects or competition from
weeds.
Several factors influence species selection, including the objectives of
reforestation, seed availability, and costs associated with
reforestation
alternatives. For many degraded sites, the species need to be those that
can add nitrogen to the soil as well as provide products wanted by local
communities.

The importance of matching tree species with site cannot be overstated.
The
problem of species selection is complicated in the tropics by intricate
climatic and soil patterns, and in areas that have been deforested by
the
highly variable degree of site degradation. Inadequate information on
planting sites is a major cause of tree planting failure (Wadsworth
1982).
Since most tree species used in reforestation are found over broad
geographic ranges, there are different land races (subdivisions of a
species with heritable characteristics resulting from adaptation to a
specific environmental condition). Tree species races are often
described
by referring to the geographic location where the race is found
naturally.
Thus, the species' suitability to a particular site varies depending on
the
races used. Increases in yield and resistances to disease can be
achieved
through selection and use of appropriate seeds. Only by planting species
and races on the sites for which they are adapted can maximum yields be
obtained.

::::: Natives and Exotics, Monocultures and Polycultures :::::

Plantations cannot substitute wholly for natural forests as reservoirs
of
germplasm or as components of the natural environment‹they are really an
agricultural crop. Plantations contribute to preservation of the natural
environment because they concentrate wood, food, and forage production
within a minimum area, thus relieving some demands on natural forests.
However, where plantations are established on land with good potential
for
annual agricultural crops, the effect actually may be to increase
pressure
on the natural forests.

Most large-scale tropical industrial timber plantations use species that
are exotic to the planted area (Gallegos et al 1982). The widespread use
of
exotics may be a result of the preponderance of information, experience,
and research on them, especially on Pinus, Eucalyptus, and Tectona. Also
important to their use is the abundance, availability, ease of storage,
and
germination of seeds of these exotic species. The use of exotic tree
species involves risks, such as susceptibility to pests and diseases.
Because of the high yields possible with exotic species, however, the
risks
will continue to be taken.

The potential of using native species in plantations has been largely
ignored. Reasons for this vary from lack of familiarity with many
tropical
tree species to lack of seed supplies. Native species are adapted to the
local environment and, thus, may be less susceptible to stress, serious
disease, and pest damage. Local people are more familiar with their
native
plants and have more uses for them.

Forest plantations in the past usually served industrial purposes and
grew
only one product, usually sawtimber, pulpwood, or fuelwood. Now, with an
increasing demand for food, fuel, and fodder, plantations are needed to
serve a wider variety of objectives. Thus, the use of multipurpose trees
and polycultural plantings (with many species of trees) is becoming
increasingly important, especially in areas with high populations.

::::: Planting Materials :::::

To reforest lands, seeds of various species must be available in great
quantities. The seed supply for species most commonly used in tropical,
industrial plantations is adequate. However, the seed supply for
multipurpose, agroforestry species is small.

The customary way of raising planting stock in the tropics is to grow
seedlings in a forest nursery either in open beds for bareroot planting
or
in containers. Good nursery practices are essential to produce a hardy
plant with a well-balanced, straight root system. Barerooted seedlings
are
susceptible to desiccation. Containerized seedlings are more costly and
bulky to handle in the field and are subject to root coiling if
closed-bottom containers are used. The latter can be avoided if the
containers have an open bottom and are suspended above the ground.

Another technique for producing planting material is vegetative
propagation‹reproduction of planting stock without the use of seed.
Vegetative propagation is widely used for tree crops such as rubber,
coconut, tea, coffee, cocoa, and oil palm. Methods include cuttings, air
layering, budding, grafting, and tissue culture. Rooted cuttings remain
the
most popular of these. Once the technique for a particular species is
developed, the production cost is modest.

Vegetative propagation has the advantage of hastening massive
reproduction
of genetically superior plants, ensuring that all are of the desired
genetic type. It has the disadvantage of increasing plantation risks due
to
lack of genetic diversity.

Seedling survival and growth rates in the nursery and at the planting
site
sometimes can be improved by using special kinds of fungi and bacteria.
For
most tropical trees, associations between tree roots and mycorrhizal
fungi
are essential for healthy growth. The fungi are active in the transport
of
nutrients and water to plant roots, and in some cases are important for
the
release of nutrient elements from mineral and organic soil particles.
Trials have shown that seedlings inoculated with fungi show improved
growth
and survival over uninoculated controls. Populations of mycorrhizae are
found naturally in soils, but these can be depressed after long-term
clearing and/or topsoil removal, making reestablishment of vegetation on
degraded lands difficult. Various methods for reinoculating damaged
soils
with mycorrhizal fungi are being developed.

Legume trees can grow well on degraded land because their roots can be a
symbiotic host for Rhizobium bacteria which produce nitrogen fertilizer,
an
essential nutrient for plant growth. The bacteria convert nitrogen gas
in
the soil into a form the plant can use. Most soils contain Rhizobium,
but
degraded soils probably contain fewer types and lesser amounts of the
bacteria. Thus, the appropriate type of Rhizobium may not be present at
the
site of a reforestation effort, or present in enough quantity to infect
the
tree roots.

Inoculants are living organisms that must be transported and stored
carefully and used correctly to retain their viability. These
requirements
can be difficult to satisfy, especially at remote tropical sites needing
reforestation.

An alternative to using seedlings in nurseries is to plant or sow the
seed
directly at the reforestation site. This method is feasible where seed
is
plentiful and where seed and seedlings mortality is low. Direct sowing
of
drought-resistant species is sometimes preferred, especially for species
that have long and fast-growing taproots that may be damaged in a
nursery
or in transfer to the field. The advantage is that no nursery is
required
and planting costs are low. On the other hand, seedling survival may be
low
because of weed competition, lack of tending, poor weather, or animal
damage.

::::: Tree Care and Maintenance :::::

Proper care and maintenance of the planted site is essential to ensure
that
trees survive to maturity. Once grown, there is the problem of
monitoring
timber harvests and of systematic replanting. The main causes of
reforestation failure, other than inappropriate technologies, are
uncontrolled grazing and fires, competition from weeds, and uncontrolled
cutting for fuel, fodder, poles, and lumber.

Direct protection through fencing or guards tends to be expensive.
Other,
less costly methods include planting unpalatable trees (e.g., Cassia
siamea) or thorny trees (e.g., Parkinsonia) as barriers around the
plantation. The use of living fences is becoming a more widespread
practice
because they provide a number of auxiliary benefits including shade,
fodder, windbreak, fuel, and wildlife habitat. Another alternative is
subsidizing farmers with livestock feed or with cash to purchase feed
during the period when trees are most susceptible to animal damage.
Grazing
beneath the tree canopy sometimes can be beneficial as a means of
weeding.
However, livestock grazing on recently reforested watersheds can be
harmful
because animals compact the topsoil, leading to poor tree growth and
increased runoff.

Weeding is an important aspect of plantation establishment and
maintenance.
Weeds compete directly with seedlings for light, soil nutrients, and
water.
Their shade can smother and eventually kill young trees. There are three
main methods of weeding‹manual, mechanical, and chemical. The manual
method
is the most common and requires little skill or capital. Mechanical
methods
may be used in large plantation projects but generally are not
considered
profitable in the Tropics. In many tropical countries, chemical weed
control techniques have been tested and found successful, but because of
safety and cost problems they seldom become the main means of weed
control.

Whatever the type and location of tree planting, the cooperation of
local
people is essential if newly planted trees are to survive. Because most
trees do not yield much benefit for several years, the options offered
must
demonstrate explicit benefits to the people. Tree planting programs are
most successful when local communities are involved and when the people
perceive clearly that success is in their self-interest.

In local communities, support can be generated through local involvement
in
project design, demonstration plantings, commercial plantings by
entrepreneurs with larger land holdings, education of community leaders,
extension and training programs working directly with farmers or
laborers,
and direct financial assistance or provision of substitutes.

Successful reforestation requires sufficient funds, strong political
will,
massive popular support, and cooperation among all involved parties.
Foresters and policymakers must remember that "forestry is not, in
essence,
about trees. It is about people. It is only about trees so far as they
serve the needs of the people" (Gribbin 1982).

::::: References :::::

Evans, J., Plantation Forestry in the Tropics (Oxford, England:
Clarendon
Press, 1982).

Gallegos, C. M., Davey, C. B., Kellison, R. L., Sanchez, P. A., and
Zobel,
B. J., "Technologies for Reforestation of Degraded Lands in the
Tropics,"
OTA commissioned paper, 1982.

Gribbin, J., "The Other Face of Development," New Scientist
96(1334):489-495, 1982.

Wadsworth, F., "Secondary Forest Management and Plantation Forestry
Technologies to Improve the Use of Converted Tropical Lands," OTA
commissioned paper, 1982.

Wood, P. J., Burley, J., and Grainger, A., "Technologies and Technology
Systems for Reforestation of Degraded Tropical Lands," OTA commissioned
paper, 1982.

::::: Original Source :::::

This article is excerpted from _Technologies to Sustain Tropical Forest
Resources_ (Washington, D.C.: U.S. Congress, Office of Technology
Assessment, OTA-F-214, March 1984). Library of Congress Catalog Card
Number
84-601018. This book is available for sale from the Superintendent of
Documents, U.S. Government Printing Office, Washington, D.C. 20402. The
full text of the chapter excerpted here can be viewed at:
<http://www.agroforester.com/articles/refordeg.html>.

::::: Web Links :::::

Tropical Restoration for the New Millennium presents a wide range of
ecosystem restoration and reforestation articles from the 4th Annual
Puerto
Rico Forestry Conference held in San Juan, May 23-28, 1999:
<http://www.forestworld.com/newscenter/abstracts/trftnm/trftnm_frame.htm>

The University of Minnesota based Restoration and Reclamation Review
presents "information on techniques used
in restoring drastically altered lands, grasslands, lakeshores, inland
wetlands, coastal waters, rivers and streams, and forests:"
<http://www.hort.agri.umn.edu/h5015/rrr.htm>

Pacific Southwest Research Station's Imperata Grassland Rehabilitation
using Agroforestry and Assisted Natural Regeneration:
<http://www.psw.fs.fed.us/Tech_Pub/Documents/other/imperata.contents.html>

Department of Crop & Soil Science at Cornell University and EMBRAPA-CPAA
presents Agroforestry Solutions for Rehabilitating Abandoned Pasture
Land
in the Brazilian Amazon:
<http://wwwscas.cit.cornell.edu/ecf3/Web/AF/Degraded.html>

::::: Related Editions of The Overstory :::::

The Overstory #61--Effects of Trees on Soils
<http://www.agroforester.com/overstory/overstory61.html>
The Overstory #59--Choosing Species for Timber Production and Multiple
Benefits <http://www.agroforester.com/overstory/overstory59.html>
The Overstory #42--Improved Fallow
<http://www.agroforester.com/overstory/overstory49.html>
The Overstory #27--Foster Ecosystems
<http://www.agroforester.com/overstory/overstory27.html>
The Overstory #22--Pioneering
<http://www.agroforester.com/overstory/overstory22.html>
The Overstory #17--Microcatchment
<http://www.agroforester.com/overstory/overstory17.html>
The Overstory #8--Mycorrhizae
<http://www.agroforester.com/overstory/overstory8.html>

::::::::::::::::::::
::::: Publisher Notes :::::

Publisher: Permanent Agriculture Resources, P.O. Box 428, Holualoa, HI
96725 USA; Tel: 808-324-4427; Fax: 808-324-4129; E-mail:
<par at agroforestry.net>; Web site: <http://www.agroforestry.net>.

Editors: Craig R. Elevitch and Kim M. Wilkinson.

Past editions of The Overstory: <http://www.overstory.com>.

This publication is Copyright 2001.  All rights reserved worldwide. For
conditions of use please send an e-mail to <par at agroforestry.net> or
write
to Permanent Agriculture Resources at the address above.

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