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close this bookSustainable Agriculture and the Environment in the Humid Tropics (BOSTID, 1993, 720 p.)
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agricultural frontier Areas where agricultural expansion is resulting in forest conversion.

agrisilviculture An agrofroestry system that uses crops and trees, including shrubs or vines.

agrisilvopastoral system An agroforestry system that combines crops, pastures (with or without animals) and trees.

agroecological zones Geographic areas in which ecologic conditions (soil, water, climate) dictate the agricultural practices that are used.

agroecology The application of ecological concepts and principles to the study, design, and management of agricultural systems. By integrating cultural and environmental factors into its examination of food production systems, agroecology seeks to evaluate the full effect of system inputs and outputs and to use this knowledge to improve these systems, taking into account the needs of both the ecosystem as a whole and the people within it.

agroecosystem A model for the functioning of an agricultural system with all its inputs and outputs.

agroforestry A land use system in which woody perennials are de liberately used on the same land management unit as annual agricultural crops or animals, either sequentially or simultaneously,
with the aim of obtaining greater outputs on a sustained basis.

agropastoral system Farming systems that combine animals and crop production.

Alfisols One of 10 soil orders. A mineral soil, usually formed under forest.

allelopathic compounds Various metabolic substances, such as terpenes, camphor, and cineole, released by plants that biochemically inhibit other plants or microorganisms.

allelopathic effects The results of the biochemical suppression of the growth of one plant species by another, thus reducing competition for resources. For example, in a field succession, the pioneer weed stage is replaced by annual grasses because the weeds produce substances that inhibit the growth of other weeds.

alley cropping An agroforestry system in which annual food crops are grown in alleys formed by hedgerows of nutrient-cycling trees or shrubs. The hedgerow plants are pruned throughout the cropping season to prevent competition for sunlight, water, and nutrients.

allovial soils Soils made of materials deposited by running water (for example, clay, silt, sand, and gravel).

annual A plant that completes its life cycle (from seed to seed production and death) within a year or single season (for example, cultivated rice).

apiculture An agroforestry system that involves the selection of trees and their management for beekeeping.

aquasilviculture An agroforestry system that integrates fisheries and trees into a production system.

arable soils Soils that are fit for plowing or tillage to produce crops.

base saturation percentage The percentage of the cation exchange capacity occupied by cations other than hydrogen or aluminum.

biochannel The paths made by roots, animals, insects, and other soil biota that act as conduits for water and air through the soil.

biocontrol (biological control) Controlling crop pests by using living organisms harmless to the plants but which destroy or reduce the number of harmful pests.

biodiversity (biological diversity) The variety and variability among living organisms and the ecological complexes in which they occur.

biogeography The study of the origin, geography, and distribution of organisms.

biomass The total weight of organic material present per unit area.

biome A major ecological community type (for example, grassland); a major biotic unit consisting of plant and animal communities having similarities in form and environmental conditions.

biosphere The largest, all-encompassing ecosystem that includes soil,water, and the atmosphere.

biosphere reserves A series of protected areas linked through a global network and established under the Man and the Biosphere Program of the United Nations Educational, Scientific, and Cultural Organization. They are intended to demonstrate the relationship between conservation and development.

biota The living organisms of a region.

biotic Of or relating to life; caused or produced by living things.

boundary planting The method of planting trees specifically to function as boundary markers, live fences, windbreaks, or firebreaks. Additional benefits include microclimate regulation and protection and the production of green manure, fodder, or fuelwood.

broadcast seeding The action of seeding by casting or scattering seed rather than transplanting seedlings.

broadleaf forests A type of closed forest where broadleaf species (dicotyledons or monocotyledons) predominate. The broadleaf trees (especially the dicotyledons) are often referred to as "hard woods."

browse Tender shoots, twigs, and leaves of trees and shrubs used by animals for food.

buffer zones Areas on the edge of protected areas that have land use controls and allow only those activities (such as research, recreation, and tourism) that are compatible with protecting the core area.

bund An embankment used to control the flow of water.

canopy The more or less continuous cover of branches and foliage formed collectively by the crowns of adjacent trees and other woody vegetation. Layers of the canopy may be distinguished
(that is, understory and overstory).

capoeira Secondary forest.

carbon fixation The conversion of atmospheric carbon dioxide into organic compounds by plants through the process of photosynthesis.

cash crop Crops produced for sale (such as cacao, rice, and wheat) as opposed to hay and other crops grown principally as feed for animals or as seed.

cassava A tropical plant grown for its fleshy edible rootstocks, which yield a nutritious starch. Also known as manioc and tapioca. cation exchange Exchange between a cation in solution and one adsorbed on a soil colloid. The negative charge of soil colloid plays a key role in the way nutrients behave in the soil; the ability of a soil to hold nutrients is directly related to the number c cation exchange sites.

cereal crops Flowering plants of the family Poaceae (formerly Gramineae that are grown to produce grain for human and animal consumption.

cerrado A savannah of the central Brazilian plateau that support dwarf woody species.

closed forest Forest in which the stand density is greater than 2(percent of the area and tree crowns approach general contact with one another.

cocoyam A widely cultivated root crop of the tropics.

compaction, soil The squeezing together of soil particles by the weigh of farm and construction equipment, vehicles, and animal and foot traffic. Compaction reduces average pore size and total air space in the soil.

continuous cropping One crop planting following soon after harvest, without seasonal fallowing.

contour cropping The use of tillage that follows the contours of a slope, rather than up and down a slope. It helps prevent erosion and runoff.

coppice A thicket, grove, or growth of small trees or a forest that has grown from shoots or root suckers rather than seed.

coppicing Cutting trees close to ground level so they will regrow from coppice shoots.

corridor system See alley cropping.

cover crop A crop grown for its value as ground cover to reduce soil erosion, retain soil moisture, provide nitrogen for subsequent crops, control pests, improve soil texture, increase organic matter, or control erosion; also known as living mulch and green manure
In the humid tropics, they can include some woody species and many legume or grass fodders.

crop residue The organic material that remains in the field following harvest.

crop rotation The successive planting of different crops in the same field over a period of years, usually to reduce the pest population or to prevent soil exhaustion.

cropping patterns The yearly sequence and spatial arrangement of crops or alternating crops and fallow within a given area. The fallow crop may be natural or planted.

crusting The formation of a surface layer on soils, ranging in thick-ness from a few millimeters to an inch, that, when dry, is much more compact, hard, and brittle than the material immediately beneath it. cultivars (cultivated variety) A variety of a plant produced through selective breeding and improved specifically for agricultural or horticultural purposes. cultivation To mechanically loosen or break up soil, uproot weeds, and aerate the soil between rows of growing crops. Soil around crops is generally cultivated one to three times per season, depending on soil type, weather, weed pressure, and herbicide use.

deforestation The conversion of forests to land uses that have a tree cover of less than 10 percent.

degradation Refers to changes within the biological, physical, and chemical processes of the forest that negatively affect the area or site and lower its productive capacity or potential (for example, soil erosion and loss of valuable or potentially valuable genetic

domestic species Plants or animals that have evolved either naturally or through artificial selection to forms more useful to people. These characteristics of domestication are frequently absent in wild types of the organism and may constitute a negative genetic load for survival in the wild state.

dooryard forest garden A garden around a dwelling with a tree overstory and animals below.

ecosystem The complex of an ecological community, together with the nonliving components of the environment, that function together as a stable system and in which exchange of material follows a circular path.

ecotourism Environmentally oriented recreational travel.

endemic Restricted or peculiar to a locality or region.

Entisols One of 10 soil orders. Soils of such recent development that they do not show a significant degree of horizon differentiation. This order includes Fluvents (well-drained young alluvial soils), Psamments (acid infertile, deep sands), and Lithosols (shallow soils of steep regions or near rock outcrops). epiphytes A plant that derives its moisture and nutrients from air and rain. It usually grows on another plant. erosion (soil) The removal or loss of rock or soil by water, wind, biotic factors, or human interference. ethnobotany The study of the folklore and history of plant use. evapotranspiration Loss of water, usually from the soil, both directly by changes into vapor or invisible minute particles and by transpiration from plants growing on the soils or in water. even-aged forest Forest that is managed to produce trees of the same age class for commercial use. ex situ In a place other than the original location. extended-fallow swidden system A food-crop production system that involves partial clearing of vegetation followed by flash burning and an extended fallow period sufficiently long (10 to 20 years) to allow for soil regeneration and weed suppression. See also fallow, shifting cultivation, swidden cultivation. extension Agricultural activities that involve dissemination of agricultural materials, technologies, and information (for example, varieties, chemical inputs, dates of farm operation, special training) to a relatively large number of farmers or associated agricultural workers or agents. extensive agriculture A method of farming using large areas and minimum inputs to raise livestock or crops. extractive reserve Forest areas for which use rights are granted by governments to residents whose livelihoods customarily depend on extracting forest products from the specified area.

fallow The period during which land is left to recover its productivity (reduced by cropping) mainly through accumulation of water, nutrients, attrition of pathogens, or a combination of all three. During this period, the land may be bare or covered by natural or planted vegetation. The term may be applied to the land itself or to the crop growing on it.

fodder Dried or cured plant material of crops, such as maize and sorghum, grown and processed for animal feed.

forage Unharvested plant material available as food for domestic animals. It may be grazed or cut for hay, in which case it is termed feed.

forest conversion The alteration of forest cover and forest conditions through human intervention, ranging from marginal modification to fundamental transformation.

forest regeneration The process of a forest regrowing, without human intervention, as a result of both natural seed dispersal from adjacent undisturbed forest and stump sprouting.

forest reserve An area of forest that is protected by laws against excessive tree cutting and burning, enabling protection of ecosystem functions, environmental services, cultural values, and biological diversity, and providing opportunities for research, education, recreation, and tourism.

fragmentation The breaking up of extensive landscape features into disjunct, isolated, or semi-isolated patches as a result of land use changes. frugivorous Fruit-eating. fuelwood Wood used as fuel for cooking, heating, or producing power; includes wood for charcoal, kilns, and ovens.

gallery forests A forest growing among a watercourse in a region otherwise devoid of trees.
germplasm The genetic material that forms the physical basis of heredity and is transmitted from one generation to the next by means of the germ cells. Also, an individual or clone representing a type, species, or culture that may be held in a repository for agronomic, historic, or other reasons.

girdling To cut the bark and cambium in a ring around a tree, which kills it by interrupting the circulation of water and nutrients.

green revolution A term coined following the success of the International Rice Research Institute with rice and Centro Internacional de Mejoramiento de Maiz y Trigo with wheat when newly developed high-yielding varieties greatly increased crop production and changes occurred in research principles, management techniques, pesticide use, and other agroeconomic and sociopolitical aspects of food crop agriculture.

greenhouse effect Warming of the earth's surface and the lower layers of atmosphere that tends to increase with greater atmospheric carbon dioxide concentration. Solar radiation is coverted
into heat in a process involving selective transmission of short wave solar radiation by the atmosphere, its absorption by the earth's surface, and reradiation as infrared that is absorbed and partly reradiated back to the surface by carbon dioxide and water vapor in the air.

greenhouse gases Gases, including water vapor, carbon dioxide, methane, nitrous oxide, chlorofluorocarbons, and ozone, that insulate the earth, letting sunlight through to the earth's surface while trap ping outgoing radiation.

gross domestic product (GDP) Identical to gross national product (GNP), but, unlike GNP, GDP includes both nonresidents who contributed to the domestic economy and payment of foreign debt.
See also gross national product.

gross national product (GNP) The total market value of the final goods and services produced during a specific period of time (usually 1 year) by the residents of a country. See also gross
domestic product.

gully erosion The erosion process whereby water accumulates in narrow channels and, over short periods, removes the soil from this narrow area to considerable depths, ranging from 1 to 90 m (3 to 300 ft).

hectare (ha) One hectare equals 2.47 acres. One square kilometer equals 100 hectares. One square mile equals 259 hectares. Thus, 1.2 billion hectares of closed tropical forest is equal to 3 billion acres or 4.6 million square miles.

hedgerow A row of shrubs or trees enclosing or separating fields.

herbaceous Vegetation that has little or no woody tissue.

home garden A cultivated and managed area, adjacent to or surrounding a house, in which mixtures of plant species are grown and livestock is kept.

humid tropics Those areas of the earth's land surface where the mean annual biotemperature in the lowlands is greater than 24°C (75°F) and where annual rainfall exceeds or equals potential evaporative return on water to the atmosphere. In general, the humid tropics correspond to tropical areas that originally supported broadleaf evergreen forests and the humid component of vegetation above timberline. As for lowlands, this definition includes all areas receiving a total annual rainfall in excess of 1,500 mm (60 in). These areas are frost free and usually have no more than 2 dry months (precipitation <100 mm [4 in] per month) per year.

hydrological systems/processes The system by which moisture reaches the ground and percolates through the soil to a particular watercourse or body of water.

hydromorphic soils A suborder of intrazonal soils, all formed under conditions of poor drainage in marshes, swamps, seepage areas, or flats.

in situ In the original location.

Inceptisols One of 10 soil orders. Young soils of sufficient age to show horizon layers. Three major types are in the humid tropics: Aquepts (poorly drained), Andepts (well drained, volcanic origin), and Tropepts (well drained, nonvolcanic origin). They are of moderate to high fertility and support dense human populations.

indigenous Native to a specified area or region; not introduced.

infiltration rate The rate at which water enters the soil, or other porous material, in a given condition.

inputs Items purchased to carry out a farm's operation. Such items include fertilizers, pesticides, seed, fuel, and animal feeds and drugs.

integrated pest management An ecologically based strategy that relies on natural mortality factors, such as natural enemies, weather, and crop management, and seeks control tactics that disrupt these factors as little as possible while enhancing their effectiveness.

intensification The fuller use of land, water, and biotic resources to enhance agronomic performance.

intensive Use of multiple cropping techniques, usually with significant nutrient inputs, to achieve high levels of crop productivity and high use of available water and sunlight throughout the year.

intercropping The growing of more than one crop species on the same plot of ground, where the respective growing periods overlap for most of the crops' life cycles. kitchen garden See home garden.

land tenure The right to exclusively occupy and use a specified area of land.

landrace An early, cultivated form of a crop species evolved from a wild population.

landscape The combination of soil type, slope, rivers, streams, ponds, and other topographical features and the extent of uniform areas that determine appropriate land use systems and their patterns. A landscape generally has no fixed size or boundary. It is used ecologically to designate an area of intensive biological interaction. It also can be synonymous with watershed, political town ship, or community.

landscape design The selection and use of agricultural and forestry options that protect and use a landscape in a manner compatible with the social and economic environment.

leaching The removal of useful chemicals or other materials in solution from the soil through water percolation.

leguminous Of or relating to, or consisting of, a large family (Leguminosae) of dicotyledonous herbs, shrubs, and trees having fruits that are legumes or foments (peas, bans, clovers), bearing nodules on the roots that contain nitrogen-fixing bacteria.

life zone Large portions of the earth's land area that have generally uniform climate and soil, and, consequently, a biota showing a high degree of uniformity in species composition and environmental adaptation; related terms are vegetational formation and biome. Holdridge defines life zones through the effects of three weighted climatic indexes: mean annual heat, precipitation, and atmospheric moisture.

littoral savannah A savannah situated near the sea. lowlands Fertile low or level ground.

manioc See cassava.

marginal land Land that is relatively infertile or unproductive for agriculture without extraordinary capital inputs (such as irrigation, fertilizers).

microclimate The immediate environmental conditions surrounding an individual organism, as in a crop canopy, for example.

milpas A small field cleared from the jungle, cropped for a few seasons, and then abandoned for a fresh clearing.

mixed cropping system Two or more crops grown without distinct row divisions.

mixed tree plantation A plantation on which a mixture of perennial and annual tree crops are cultivated and harvested.

modified forest An ecosystem that has been managed in subtle but sophisticated ways to provide the human inhabitants with sustainable livelihoods.

monocropping (monoculture) The growing of a single plant species in one area, usually the same type of crop grown year after year.

montane In the context of this report, of, being, or related to the biogeographic zone made up of relatively moist cool upland slopes below the timberline and dominated by tropical evergreen trees and plants.

mulch Any material such as straw, sawdust, leaves, plastic film, and loose soil that is spread on the surface of the soil to protect the soil and plant roots from the effects of raindrops, soil crusting, freezing, evaporation, and other stresses.

multipurpose tree A tree that has several uses (food production, shade, erosion control) and from which a number of products can be gleaned (food, fuel, lumber).

mycorrhiza The symbiotic association of the mycelium of a fungus with the roots of a seed plant.

natural forest management system Controlled and regulated harvesting of forest trees, combined with silvicultural and protective measures, to sustain and increase the commercial value of subsequent stands; relies on natural regeneration of native species.

nitrogen fixation The conversion of atmospheric nitrogen gas to ammonia, nitrates, and other nitrogen-containing compounds, by nitrogen-fixing bacteria, photosynthetic bacteria, and blue-green algae. The nitrogen-fixing bacteria include clostridium and azotobacter (which are free-living and are believed to contribute minimally to soil nitrogen) and rhizobium (which lives symbiotically in root nodules). Atmospheric nitrogen fixation can be caused by lightning.

nitrogen-fixing trees Trees that are capable of converting free nitrogen into combined forms useful especially as starting materials for fertilizers.

nongovernmental organization A private organization that may be international or indigenous, community-based, or nationally associated, and that consists of rural farmers as well as technical and financial support intermediaries who network for information dissemination and for cross-cultural exchange.

nutrient cycling The process of retaining and efficiently recycling essential nutrients and micronutrients within the ecosystem.

nutrient depletion The detrimental removal of nutritional elements from the soil.

nutrient recycling See nutrient cycling.

Off-farm resources External support systems or components that are not available on the farm including artificial fertilizers, pesticides, and irrigation sources or systems, as well as markets, labor, machinery, and funding.

on-farm resources Internal support systems or components that are available on the farm including sunlight, natural fertilizers, seeds, biological processes, irrigation sources or systems, labor, and knowledge.

organic matter Living biota present in the soil or the decaying or decayed remains of animals or plants. The living organic matter in the soil decomposes the dead organic matter. Organic matter in soil can reduce soil erosion and increase moisture and soluble nutrient retention, cation exchange, and water infiltration.

oxidation A chemical reaction that increases the oxygen content of a compound; a chemical reaction in which a compound or radical loses electrons, that is, in which the positive valence is increased.

Oxisols One of 10 soil orders. Generally deep, well-drained red or yellowish soils with excellent granular structure and little contrast between horizon layers. Due to poor chemical properties, however, these soils are low in available nutrients and acidic.

pastureland Land where grass or other plants are grown for use as food by grazing animals.
pathogen An organism (usually parasitic) capable of causing a disease in
another organism (host).

perennial A plant that lives for more than 2 years, often for a number of years; many flower annually.

perverse policies National economic and land use policies that promote the inefficient and nonsustainable conversion of forests to

other uses by measures such as tax incentives and credits, subsidized credit, timber pricing procedures, land subsidies and rents, concessions, tenure, and property rights.

pest Any form of plant or animal life or any pathogenic agent that is injurious or potentially injurious to plants, animals, or their products.

pH A quantitative expression of the degree of acidity or alkalinity of a solution.

photosynthesis The synthesis, by chlorophyll-containing plant or bacterial cells, of organic compounds (primarily carbohydrates) from carbon dioxide and a hydrogen source such as water. There is a simultaneous liberation of oxygen. The energy for the reaction is light energy in the form of photons.

physicochemical Physical and chemical in nature.

pioneer species A plant or animal capable of establishing itself in a bare or barren area and initiating an ecological cycle.

plantation A forest crop or stand established artificially either by sowing or planting. The term includes reforestation (reestablishment of a tree cover on deforested or degraded forestlands) and replacement of natural forest by a different tree crop. It does not
include artificial regeneration (the application of postharvesting techniques to accelerate the regrowth of species that had been logged).

pollarding Cutting back of a tree to the trunk to promote the growth of a dense head of foliage.
polyculture The growing of more than one crop at once in the same field.

premontane A biogeographic zone that usually lies between 500 and 1,500 m (between 1,600 and 5,000 ft) in elevation and has a mean annual biotemperature between 18° and 24°C (between 34° and 75°F); this zone is excellent for coffee and tea culture as well as for other agricultural activities.

primary forest Relatively intact forest that has been essentially unmodified by human activity for the past 60 to 80 years.

primary productivity The accumulation of plant biomass as a direct result of photosynthesis and the fixing of atmospheric carbon.

private voluntary organization In the context of this report, a nongovernment organization, funded by private citizens and/or businesses, that sponsors projects and programs to study or enhance agricultural productivity.

privatization To alter the status of a business, industry, or land from public or government ownership or control to private ownership or control.

pruning To cut off or cut back parts of a plant for better shape or more fruitful growth.
pulse The edible seed of peas, beans, lentils, and related plants having pods.

reforestation The replacement of trees in cut-over forest areas.

resettlement policies Plans and programs that involve moving large numbers of people from heavily populated areas to less densely populated areas generally for the purposes of alleviating over crowding and unemployment.

restoration The re-creation of entire communities of organisms closely modeled on communities that occur naturally. It is closely linked to reclamation.

rhizoblum A genus of bacterium that is capable of forming a symbiotic relationship with plants of the Fabaceae (Leguminosae) and is found in root nodules, where the bacteria fix nitrogen in return for carbon from the host plant. See nitrogen fixation.

rill erosion An erosion process in which numerous small channels several inches deep are formed; occurs mainly on recently cultivated soils.

root crops A plant cultivated for its underground food-storing organ.

rotation The systematic growing of different kinds of crops in recurrent succession on the same piece of land.

ruminant Characterized by the act of regurgitation and rechewing of food. A mammal belonging to the suborder Ruminantia.

runoff The portion of precipitation that is discharged from an area through stream channels. That which is lost without entering the soil is called surface runoff, and that which enters the soil before reaching a stream is called groundwater runoff or seepage flow from groundwater.

salinization The process of accumulation of salts in soil.

savannah Tropical grassland containing scattered trees and drought resistant undergrowth.
scale The relative size of an area. In this report, small scale usually refers to a farm under 1 to 2 ha in size.

secondary forest Natural forest growth after some major interference (for example, logging, serious fire, or insect attack).

sedimentation The action or process of forming or depositing sediment.

seed dispersers Natural means of sowing or distributing seeds.

sheet erosion The removal of a fairly uniform layer of soil from the land surface by runoff water.

shifting cultivation Any farming system where land is periodically cleared, cropped, and returned to fallow; synonymous with slash-and-burn or swidden agriculture.

siltation To choke, fill over, or obstruct with silt or mud.

silviculture The science and art of cultivating forest crops, based on a knowledge of forest tree characteristics.

silvapastoral system An agroforestry system that combines pastures (with or without animals) and trees.

sink Anything that can absorb and store carbon circulating in the atmosphere.

soil amendment Any substance such as lime, sulfur, gypsum, or sawdust used to alter the properties of a soil, generally to make it more productive. Fertilizers are soil amendments, but the term is used most commonly for materials other than fertilizers.

soil biota Organisms that live in the soil.

soil degradation Degeneration of the soil through erosion, nutrient depletion, and other degenerative processes.

spatial integration Interaction of land uses or agroecosystem components because of physical proximity as, for example, in strip cropping systems.

species A group of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups.

Species is the smallest of the commonly used units of classification and the easiest to recognize intuitively.

staple crop A crop that is used, enjoyed, or needed constantly by many people in a given area or country. It is provided or imported in large quantity into the area; examples are maize in
Kenya and rice in Liberia.

subsistence farming Farming or a system of farming that provides all or almost all goods required by a farm family, usually without any significant surplus for sale.

subtropics The region bordering the tropical zone.

sustainable An agricultural production system in which the farmer increases or maintains productivity at levels that are economically viable, ecologically sound, and culturally acceptable, through the efficient management of resources with minimum damage to the environment or human health.

swidden A temporary agricultural plot produced by cutting back and burning off vegetative cover.

swidden cultivation A traditional food-crop production system that involves partial clearing of vegetation (forest or bush fallow) followed by flash burning and short-term mixed intercropping; synonymous with shifting cultivation or slash-and-burn agriculture. The fallow period must be sufficiently long to allow for soil regeneration and weed suppression. This system is based solely on the restorative properties of woody species.

symbionts Two dissimilar organisms that each benefit from the presence of the other, for example, rhizobium and the members of the Fabaceae (Leguminosae).

temperate zone The area or region between the tropic of Cancer and the arctic circle or between the tropic of Capricorn and the antarctic circle.

temporal integration Interaction of land uses or agroecosystem components over time, as, for example, in crop rotations where a previous crop affects those planted after it.

terracing The agricultural practice of using a raised strip of earth, more or less level or horizontal, usually constructed on or near a contour and designed to make the land suitable for tillage and to prevent accelerated erosion.

tillage The act of preparing the soil by mechanical manipulations for crop production.

trophic level One of the hierarchical strata of a food web characterized by organisms that are the same number of steps removed from the primary producers.

tropic Either of the two small circles of the celestial sphere on each side of and parallel to the equator at a distance of 23.5 degrees, which the sun reaches at its greatest declination north or south.

tropical moist forest Lowland, premontane, and montane tropical forest formations.

Ultisols One of 10 soil orders. Soils that are similar to Oxisols but exhibit a marked increase of clay content with depth. They are usually deep, well-drained red or yellowish soils somewhat higher in weatherable minerals than Oxisols but still acidic and low in fertility.

understory Vegetation growing in the shade of taller plants.

uplands Infertile sloping or hilly lands.

usufruct The legal right of using and enjoying the fruits or profits of something belonging to another.

volunteer species A plant that has grown from self-sown seed.

watershed A region or area draining ultimately to a particular watercourse or body of water.

weed An individual plant or species that grows where humans do not wish it to grow.

wetlands Land or areas (as tidal flats and swamps) containing much soil moisture.

wild species Species of flora or fauna that have not been domesticated or manipulated by humans.

woodlot A restricted area of woodland, usually privately maintained as a source of fuel, posts, and lumber.

woody shrub Shrubs rich in xylem and associated structures.

yield The weight or volume of the economic part of a plant harvested during plant growth or at maturity.