Zhong Gongfu Mulberry Dike

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    Human Ecology, Vol. 10, No. 2, 1982

    T h e M u lb e rr y D i k e - F i s h P o n d C o m p l ex :A C h i n e s e E c o s y s t e m o f L a n d - W a t e rI n t e r a c t io n o n t h e P e a r l R i v e r D e l t aZh o n g G o n g f u '

    The Pearl River Delta offers humans a variety of land-use alternatives. Acomplex ecosystem which has been in existence in the Delta fo r centuries hasgreatly contributed to the region's agricultural productivi ty. The principalcomponents are mulberry trees, silkworms, pon d fish , and humans,interrelated in a harmonious and mutually beneficial way. The system is notonly highly efficient and soundly balanced ecologically, but provides muchhigher economic returns than do other agrarian practices in the Delta.KEY WORDS: ecosystem; human ecology;mulberry; silkworm; fish; China.

    INTRODUCTIONDespite serious family-planning efforts undertaken by the government

    of the People's Republic of China since the 1949 revolution, the popula tionof China has continued to grow, and in the early 1980s it broke the 1billion mark; there are indications that it doubled in the last threedecades. While population growth patterns for the last 30 years cannot beascertained with precision because of a lack of reliable demographicdata, the average annual rate of growth is widely believed to be about 2~

    IZhong Gongfu is Deputy Director, Guangzhou (Canton) Institute of Geography, Guangzhou,Guangdong Province, the People's Republic of China. This paper-one of the firs t toappear in the West by a Chinese ecologist-describes a form of land use which is bothenvironmentally and economicallybeneficial. Whether the system, or part of it, can usefullybe duplicated elsewhere in the developing world may deserve some further study.-Laurence J. C. Ma, Department of Geography, University of Akron, Akron, Ohio.191

    0300-7839/82/06~-0191503.00/0 9 1982 Plenum Publishing Corporation

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    192 Gon gf u

    How has China managed to feed such a large and growing popula-tion? One basic answer is that the Chinese have intensively butcarefully used the environment in order to maximize production on acontinual basis, while resulting alterations to the environment have notnecessarily been detrimental to the plants and animals in it. This paperwill present a case to demonstrate this point. Understanding this eco-system is not only intellectually stimulating, but also offers a usefullesson for other subtropical regions with similar environments andacute pressure of population growth on the land.

    The Chinese environment is extremely diverse, containing vast coldand dry deserts in the northwest, extensive farm land in the north andnortheast, and small but numerous rice paddies in the east and south.The land in the densely settled eastern and southern area has beencultivated for thousands of years without apparent deterioration of soilfertility, and the quality of the agrarian environment has remainedfairly constant over the centuries. Chinese farmers are intimately familiarwith the attributes of the complex ecological systems of which they area part. In agrarian China, the original attributes of the environment havelong been replaced by ones that have been created by humans intheir quest for more food.

    This paper analyzes the interaction of humans, land, and water in asubtropical ecosystem on the Zhu Jiang (Pearl River) Delta nearGuangzhou (Canton) in Gu angdong Province. The major ecological agentsin this environment are humans, a plant, an insect, and fish. They forma complex but harmonious and mutually beneficial ecological system.Humans have fully utilized the resources of the environment to theiradvantage while allowing other organisms to thrive. Humans, of course,exert a controlling influence on the environment and thereby determinethe nature of ecological association. The bulk of the data used in thispaper is based on field work carried out over the past 25 years.

    T H E G E O G R A P H I C A L E N V I R O N M E N TThe Pearl River Delta is a large plain formed by silt carried down

    by the Dong, Xi, and Bei rivers, and has a total area of 12,000 squarekilometers (kin2). The Delta is located south of the Tropic of Cancer andhas an annual solar radiation of 110 kcal/ cm ~ (kilocalories per squarecentimeter); the radiation balance averages about 60 kcal/c m 2. Because it ison the northern margin of the tropical monsoon zone, the area is affectedby monsoon circulation and has an annual temperature range of about16~ In the winter season the area is often affected by dry and cold

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    T h e M u l b e r r y D i k e - F i s h P o n d C o m p l e x 193

    northeasterly winds brought down by the continental high-pressure systemsof the Arctic region. When hit by such strong cold waves, the area'stemperature may go down to about I~ more usually, the minimumwinter temperature is above 2~ and there are only two to three daysof frost per year. The weather in the summer is affected by the subtropicalhigh pressure and by the low-pressure trough of the South China Sea,which result in high temperatures and abundant precipitation; the highestrecorded temperature is 37~ The rainfall during the summer half ofthe year is about 1,700 mm, which accounts for about 84% of thetotal annual rainfall. The air is humid, with a relative humidity of be-tween 76 and 85%. The number of hours of sunshine for the entire yearis between 2,000 and 2,500. Such weather conditions are favorable formulberry growing, sericulture, and fish farming. This is one of the threemajor silk-producing areas in China. Mulberry trees can grow year round,but the temperature is most favorable between 22 and 27~ The treesbegin to bud in December and continue to grow until November of thefollowing year, when they are cut down. The leaves are picked betweenMarch and November, during which time silkworms are also raised. Themost favorable temperature for raising silkworms is between 20 and 28~while that for fish culture is between 20 and 30~ In this region thenormal temperature of the fish ponds in summer is about 30~ while inwinter it is between 15 and 20~ Most fish can be harvested three orfour times per year, while a few species can be netted five or six times.There is a dense network of rivers and tributaries on the Pearl RiverDelta with an abundant volume of water, which facilitates drainage orgravity irrigation. The rivers and tributaries also form a convenientcommunication network, and almost all settlements, filatures, andmulberry dikes can be reached by wooden boat.

    The Pearl River Delta has a total population of 10 million. Thepopulation density is very high: between 500 and 800 persons per kmLThis is favorable for sericulture, sugar cane, bananas, and fish breeding,all of which are labor intensive. The people of the Delta have also had greatexperience in sericulture.

    H I S TO R I C A L B A C K G R O U N D

    The contemporary landscape of the Pearl River Delta began to takeshape in the 9th century A.D. Before then, the area was a vast expanseof low-lying land that frequently suffered from serious flooding. Thepeople gradually turned the low-lying land into fish ponds, using theexcavated mud to construct the pond dikes. The people of the Delta did

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    194 Gongfu

    not grow mulberry, raise fish, and practice sericulture in an interrelatedway, however. After the 9th century the po nd dikes were gradually plantedwith such fruit trees as lichee, longan, and banana, and an ecologicalcomplex based on fruits and fish slowly emerged. It was not until the16th century that mulberry growing and sericulture began to be linked withfish farming as the banks of the ponds were turned into mulberry dikes.

    This process began in the northern part of the Delta, in suchplaces as Jiujiang, Xiqiao, and Datong in Nanhai County, with Jiujiang asthe center. The Xi River near Jiujiang provided fish fry for the fish ponds.From Nanhai County, the interrelated production of silk and fish beganto spread gradually to the middle and southern parts of the Delta, toShunde, Pa nyu, Zhongshan, and Xinhui counties. In 1866 the first modernfilature was established in a village in Nanhai County. Inhabitants beganto give up rice growing for fish culture or sericulture, both of which weremore profitable. In areas where sericulture was highly developed, rice wasconfined to the margins of the ponds or the lowlands along the coast,and grain needs were increasingly met through imports. The greatestnumber o f fish ponds were dug and the mulberry dike-fish pond complexdeveloPed most fully in Shunde County because of its location (in thecenter of the Pearl River Delta), its extensive low-lying land, and itsexcellent water transportation. Shunde set up its first modern filature atthe end of the 19th century, with a total workforce of between 500 and600 women. Gradually Shunde assumed the leading position in the Delta'ssilk industry. In 1905-1906 the export of raw silk from Gua ngdongProvince amounted to about 40 million silver dollars, with Shunde aloneaccounting for three-fourths of this. Before 1926 the land planted inmulberry trees in the Pearl River Delta totalled about 1.2 million m u (or200,000 acres; amu is one-sixth of an acre), and Shunde alone had half ofthe total . After 1926 the silk trade suffe red a severe decline on the inter-national market and the area was reduced to the present 350,000 m u(about 58,300 acres). Nonetheless, Shunde's leading position has remainedunchallenged, and the county still has the largest number of fish pondsand mulberry dikes in the Delta region (Fig. 1), as well as the highestaverage per m u yields (1,900 k g / m u ) . This average is almost twice thatof Japan and of the Taihu Lake area in Jiangsu Province in east China,another region noted for its silk production. In both these areas theaverage is about 1,000k g / m u .

    C H A R A C T E R I S T I C S O F T H E M U L B E R R Y D I K E - F I S HP O N D C O M P L E X

    The mulberry dike-fish pond complex is a system developed by thepeople o f the region to make full use of available land and water resources.

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    T h e M u l b e r ry D i k e - F i s h P o n d C o m p l e x 195

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    I t i s an interre lated ecosystem that br ings into ful l play the productivep o t e n t ia l o f h u m a n s a n d t h e ir e n v ir o n m e n t a n d p r o m o t e s t h e d e v e lo p m e n to f d i f fe r e nt br anc he s o f agr ic u l tur e . T he r e s u l t c an be s e e n in the mode r nlands c ape , whic h i s lus h and ne at ly ar r ange d , w i th a l l ava i lab le s pac efu l ly u t i l i z e d .

    T he mulbe r r y d ike - f i s h pond c omple x has the fo l lowing c har ac te r -is t ics : mulberry leaves are fed to the s i lkworms, whose excreta are useda s f i s h f o o d , a n d t h e f e r t i l e p o n d m u d - - c o n s i s t i n g o f f i s h e x c r e t a ,

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    196 Gongfuorganic matter, and chemical eleme nts -is brought up from the bottom andused as manure for the mulberry trees. The mutual benefits of each link inthe system have been known to the farmers of the area for many years,as reflected in the folk saying that "the more luxuriant the mulberry trees,the stronger the silkworms and the fatter the fish; the richer the pond,the more fertile the dike and the more numerous the cocoons." Inthis system, the mulberry tree is the first trophic level. Photosynthesistakes place in its leaves, which are fed to the silkworms (the primaryconsumers) whose excreta and chrysalises are in turn fed to fish (thesecondary consumers). The aquatic organisms in the pond are the reductionagents that decompose fish excreta and algae, break down the organicmatter in the pond, and produce nitrogen, phosphorus, and potassium.These are then returned to the mulberry dike when pond mud is usedas fertilizer (Fig. 2).

    The relationship of mulberry trees, silkworms, and fish to dikes,ponds, and atmosphere are based on transfers of energy and exchanges ofsubstances. Such environmental factors as temperature, light, water, air,and soil determine to a large extent the changes in the morphology,productivity, and quality of the trees, worms, and fish. The complexity

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    j , En e rg y a n d nutrient flow . . . . . .~ Energy f low onlyFig. 2. Energy and nutrient flow in the mulberry dike-fish pond ecosystem.

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    T h e M u l b e r ry D i k e - F i s h Po nd C o mpl ex 197

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    J I m u I D e r r y I < - . ~ o \ \ / /( ~ I I ~I l e a v e s I O ' ~ / / ~ / I : ; ~' ' . ' % ~ _ q , \ \ ~/o" 1 L > , :

    I m u , b e r r y d i k e s I f is h , o n ~ - - - - 1 s u g a r c a n e d i k e i ] c~Fig. 3. The to tal dike-p ond system, huma n activities, and food production.

    o f th e t o t a l e n v i r o n m e n t , t h e i n t e ra c t i o n s a m o n g t h e o r g a n i s m s i n i t, a n dt h e p r o d u c t s h u m a n s d e r i v e f r o m i t a r e s h o w n i n F i g u r e 3.

    T h e m u l b e r r y t r e e s , s i l k w o r m s , a n d f i s h h a v e d i f f e r e n t e n v i r o n m e n t a lneeds . Sun l i gh t , t em pera tu re , and so i l f e r t i li t y t oge the r de t e rmin e t hen u m b e r o f t im e s t h a t m u l b e r r y l e a v e s c a n b e p i c k e d d u r in g t h e g r o w i n gseason . Mulber ry t r ees need ample sun l i gh t ; i nadequat e sun l i gh t r esu l t s i np o o r g r o w t h a n d i n le s s p ro t e i n a n d l e ss s o l u b le c a r b o n a t e i n t h e l e a v e s .T h e t e m p e r a t u r e m u s t b e a b o v e 1 0 ~ o r th e tr e e s c e a s e t o g r o w . T h e tr e e sc a n n o t s u r v i v e a d r o u g h t w h e n t h e te m p e r a t u r e is a b o v e 3 8 ~

    So i l f e r t i l i t y has a d i r ec t e f f ec t on t r ee g rowth and on t he qua l i t y o ft h e l e a v e s a n d a n i n d i r e c t e f f e c t o n t h e s i l k w o r m s a n d t h e q u a l i t y o ft h e c o c o o n s . T e m p e r a t u r e a n d h u m i d i t y a r e i m p o r t a n t f a c t o r s a f f e c t i n gt h e g r o w t h o f t h e s i l k w o r m s , w h i c h c e a s e t o g r o w w h e n t h e t e m p e r a t u r ei s be low 15~ o r above 32~ o r t hey do no t su rv ive a d rough t i f t he t empera-t u re reaches 40~ They g row bes t when t he humid i t y i s be tween 70 and 85~

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    198 Gongfu

    In the Pearl River Delta region, the temperature and humidi ty are generallytoo high for proper growth from May to September, and the peasantsuse bamboo frames to reduce heat as well as to provide the correctamount of space in which cocoons can form.

    As noted above, the fish fry come from the Xi River, whosevolume and velocity increase rapidly between April and July. Severalspecies of river carp lay eggs in the Guangxi Zhuang AutonomousRegion, and they are carried downstream to Guangdong Province,where they are hatched. The fry are caught by the peasants, classified,and artificially raised to a certain size before they are put in the ponds.(In recent years, however, artificially bred fry have gradually replacednatural fry.)The water's temperature, oxygen content, and quantity of planktonall play an important role in fish cultivation. The water temperatureshould be between 5 ~ and 35~ no fish can survive at temperaturesbelow 3~ Five milligrams of oxygen per liter is ideal; when the oxygencontent reaches 1 mg/liter, the fish come up to the surface, and when it isless than 0.2 r ag/liter they die.

    In addition to the interrelationship of mulberry growing, sericulture,and fish farming, there is also an interrelationship between the dike andthe pond. Mulberry and sugar-cane leaves, corn, peanuts, and elephantgrass (Pennisetum purpureum schun ) are staple foods for the fish.Twenty kilograms of grass can be transformed into 0.5 kg of grass carp(Ctenopharyngodon idellus) plus 0.25 kg of bighead carp (Aristichthysnobilis) or silver carp (Hypophtha michthys molitrix), and 50 kg ofsugar-cane leaves can be transformed into 0.5 kg of grass carp. Thesefish are important sources of income and protein for the peasants. Inaddition, the pond supplies the dike with the fertile mud that the peasantsheap onto the dike two or three times a year; each new layer is 5 or 6 cmthick. Pond mud decomposes on the dike and then becomes the chieffertilizer for the mulberry trees. The peasants of Shunde County estimatedthat 100,000 kg of pond mud are the equivalent of 50 kg of chemicalfertilizers, and that each heaping adds the equivalent of 15 kg of ureato the soil. The mud is better than a chemical fertilizer because it iscomposed of about 5~ organic matter, which the plants need. In addition,the mud acts as a weed killer, retards water evaporation, and maintainssoil fertility for a longer period of time. The effects of the mud on themulberry trees are particularly noticeable during the dry but still warmmonths of September and October. During heavy rains some of themud is washed back into the pond, where it is mixed with the remains ofplankton and reacquires its fertilizing qualities. In this way the dikes areconstantly supplied with a renewable source of fertilizer. Through

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    T h e M u l b e r ry D i k e - F i s h P o n d C o m p l e x 1 9 9

    photosynthesis the algae and aquatic plants in the pond give off oxygenand produce glucose, added nutrients that benefit both fish and aquaticplants.

    The proportion of dike area to fish pond depends on the supply offish food. The peasants of the Pearl River Delta have learned fromexperience that the amount of silkworm excreta and chrysalises producedby a m u of mulberry trees can meet the food requirements of fish raisedin amu of fish pond, i.e., the ratio is 1:1. According to chemical analysis,silkworm excreta contains between 2.2 and 3.5% nitrogen, between 2.0 and2.5% phosphorus, and between 1.5 and 2.0% potassium. It contains ahigher percentage of nitrogen than pig, sheep, or cattle excreta. It is knownthat 100 kg of mulberry leaves will yield 60 kg of silkworm excreta andthat 60 kg of silkworm excreta can generate 8 kg of fish. In additionto the cocoons and silk, the average m u of mulberry trees will yield1,200 kg of silkworm excreta, which can be fed to pond fish and will thusproduce 160 kg of fish. If additional food, such as grass or corn, issupplied to the fish, the ratio can be lowered to 2:3 or even 3:7. But if,as at present, more dikes are devoted to sugar cane than to mulber rytrees, then corn, peanuts, and elephant grass must be grown around thedikes or brought in from outside of the ecosystem-which is therefore notyet an entirely closed System. On the other hand, the change fromhousehold-based production to communal production has meant that suchfish foods as elephant grass, corn, and peanut (stems) are now raisedmore easily by production teams, partially replacing silkworm excreta asfish food . This has enlarged the size of the ecosystem.

    Vegetables are grown on the dikes, either in rotation or intercroppedwith the mulberry trees. Two crops of vegetables can be grown betweenNovember and February, after the trees have been cut down. Gourds inparticular are grown, and the vines are supported by frames stretched outover the pond, both increasing the available growing space and pro-viding shade for the pond. Approximately 3,000 kg of vegetables areusually harvested from a mu of dike, two-thirds of which are marketed whilethe remainder is fed to the fish. Crops grown on the pond marginsaccount for between 5 and 10 of the peasants' annua l income.

    The fish pond normally consists of several aquatic niches, eachsuitable for a different species of fish. The bighead and silver carpsinhabit the upper part of the pond, the grass carp occupies the middlezone, and the mud (C i rrh inus s i nens i s ) and black carps ( C y p r i n u s c a p i a )live in the lower zone. The grass carp is the principal species, account ing for50% of the fish population. It feeds on silkworm excreta, and its ownexcreta, in turn, feed the phytoplankton. The phytoplankton is not onlythe major food for the silver carp but is also consumed by zoopl~/nkton;

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    200 Gongfuthese then feed the bighead carp. The unconsumed silkworm excreta andplankton sink to the bottom, where they are eaten by the mud carp andthe black carp. Thus, if the grass carp are well fed the rest of the fishwill also be provided for.

    The density of the fish population should be neither too high nor toolow. In their early stages many fish can be raised in the pond, butthe density must be reduced as the fish approach maturity. Generally,different species o f fish at diff erent stages of growth are mixed to maximizethe use of pond space and to f acilitate harvesting in stages.

    E C O N O M I C S IG N I F I C A N C E O F T H E M U L B E R R YD I K E - F I S H P O N D E C O S Y S T E M

    In terms of human ecology, the mulberry dike-fish pond complex isa system in which plants, silkworms, and fish live in a mu tually dependentand beneficial ecological whole. The system maximizes the use of localresources, generates a variety of products, provides a high income for thepeasants, and creates employment opportunities in an area underpopulation pressure. While up to this point we have concentrated on theecological and systemic aspects of the complex, here we will brieflymention the economic advantages for the peasants who have developed it.

    First, the complex provides multiple sources of income. Because ofthe warm climate, mulberry leaves can be harvested in the same year inwhich the trees are planted. They are picked every 20 days or so, andeight or nine silkworm hatchings are possible each year. The peasants'income is therefore increased. Multiple fish harvests are also normal. Thefry are put into the pond at the beginning of the year, and the fish arenetted every 3 or 4 months.

    As a result of multiple sources of income and the high pricesthe peasants receive for silk and fish, their income level is much higherthan that of those peasants for whom rice or sugar cane is the chief sourceof income. Table I compares the gross income from the three differenttypes of commune economy in the Foshan region of the Pearl RiverDelta on a per mu basis. In addition to the activities identified in Table I,the peasants also cultivate bananas, peanuts, corn, and other vegetables,and raise domestic animals. The income from these is not included in thetable, but Table II, based on another commune, gives some idea of thisadditional income. These figures only serve to reinforce the higher incometo be derived from the mulberry dike-fish pond complex. The complexshould also show a greater net income, although detailed per capita incomedata are not yet available. Nevertheless, the investment for each mu of

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    T h e M u l b e r r y D i k e - F i s h P o n d C o m p l e x

    Table !. Communal Income in Foshan, Guangdong Province, 1978201

    Per m u gross incomeProduct Per r n u yield in y u a n ( $)Paddy rice 750 kgSugar cane 5 tonsMulberry dike-fish pond complexCocoons 139 kgMulberry 750 kgbranches andleavesSilkworm excreta

    Total

    140 ( ca . $100)210 (ca. $150)

    232 (ca. $165)30 (ca. $21)750 kg (converted 80 (ca. $57)to 95 kg of fish) 342 (ca. $244)

    mulbe rry trees and its related silkworm prod ucti on is abou t 35~ ofgross income, whereas that for sugar cane is about 20% and that forpaddy rice is about 40%. Using these percentages, we obtain a rough netper mu income of 223 y u a n ($159) for silk and fish, 168 y u a n ($120) forsugar cane, and 84 y u a n ($60) for rice.

    The various components of the mulberry dike-fish pond complexcan absorb a great deal of labor of different sorts. The per m u labor re-quirement is probably twice as high as that of either rice or sugar cane.The collection of mulberry leaves 8 times a year and the raising ofsilkworms requires mostly light labor, while fish farming demands suchheavy work as placing the fish fry into the pond, feeding and catching thefish, and scraping up and applying the pond mud to the dike. In a regionwith a large population, the system obviously offers more jobs than othertypes of farm ec onomy.

    Table I1. Per m u Income from Sources in Addition to Silk andFish, Qinliu Commune, Shunde CountyPer m u gross incomeProduct Per m u yield iny u a n ( $ )

    Vegetables 2,000-2,500 kg 200 (ca. $143)Banana 750 kg 150 (ca. $107)Beans 20-25 kg 16 (ca. $11)Elephant grass 500 kg 20 (ca. $14)Corn 50 kg 25 (ca. $18)Other crops 26 (ca. $14)

    Total 431 (ca. $307)

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    202 Gongfu

    F U T U R E P R O S P E C T SAs an ecosystem, the mulberry dike-fish pond complex is highly

    efficient in the use of local resources, in the generation of income,and in the absorption of labor. This does not mean, however, that itcould not be more efficient. Various diseases affecting the growth ofmulberry trees, silkworms, and fish have not been effectively control led,and the dikes would be more productive if mulberry trees were rotatedwith sugar cane every few years. This would reduce crop disease andhelp create a different system, one based on sugar cane, animals (fedwith sugar-cane leaves and other feed), and the raising of fish fed withanimal excreta. There is no reason to believe that the two systems couldnot be practiced simultaneously, but their respective roles in the generationof income (either separately or in combination) are yet to be studied.Although the per m u yield of mulber ry leaves in the Pearl River Deltais higher than that in the Taihu Lake region or in Japan, the length andquantity of the silk are inferior and the labor time is greater. The length ofthe silk filament in Japan is sometimes as much as 1,800 meters (m),while it is between 800 and 1,000 m in the Taihu region. In the Pearl RiverDelta it is only 500 m. In terms of quantity, Japan and the Taihuregion can produce 18.5 and 6 kg of silk, respectively, from 50 kgof cocoons; in the Delta, the yield is only 5 kg. In terms of laborproductivity, in 1975 Japan produced 100 kg of cocoons with 250 hoursof labor, while in China this took more than 600 hours. This suggeststhat the technology of sericulture and the breeding of silkworms inChina needs improvement. Finally, new breeds of pond fish, betterfish foods, and an increase in the oxygen content of the fish pondare all necessary to boost fish production.In 1980 the United Nations University agreed to support a 3-yearresearch project to study the ecosystem in detail for possible duplicationoutside China. It is hoped that more basic data f rom the region, includingper capita income and detailed cost-benefit analyses for each of thecomponents of the ecosystem, will be gathered and analyzed in the nearfuture.