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Most environmental and development studies, whether they are centred on nature or economics, or at the interface between nature and society, involve demography. Although there are many different points of view, there are two main, diametrically opposed lines of thought: that of the neo-Malthusians and that of the Boserupians. Malthus, a late eighteenth-century economist, claimed that population growth was governed by resources (Malthus, 1798). Once the population exceeds a given threshold, the response may be anticipative (lower birth rate) or radical (higher death rate). Whereas Malthus concentrated on agriculture and food resources, the neo-Malthusians have broadened his theory to cover the environment as a whole. They consider that excessive population levels degrade the environment and the means of agricultural production. The Limits to Growth (Meadows et al., 1972), a major work setting out the neo-Malthusian standpoint, suggests that natural resources will be exhausted within a century unless population and economic growth stops. Malthus’s theories have often been criticized, for instance on the grounds that they are based on enclosed areas and do not take account of technological change (Le Bras, 1994). Certain specialists have countered Malthus’s theories, such as Boserup (1965), who claimed that population growth was an explanatory variable and not the opposite as suggested by Malthus. Population growth is held to be the main factor in agricultural change: it leads to intensification, new tools and techniques, and changes in the land-ownership system. Boserup’s particularly innovative theory led to generalizations about the environment that ran contrary to the views held by the neo-Malthusians. However, it has in turn been criticized for the way it takes account of spatial issues (Grigg, 1979). Certain field studies have shed light on these theories. For instance, Quesnel (1994) quoted a few cases in Africa to demonstrate that neither the Malthusian nor the Boserupian theory held true. Population growth is a precondition for change, but change is also governed by other factors. Certain studies have looked at countries or continents and established correlations between environmental and demographic data. They have often concluded by

12

Does Population Growth Affect Wooded-Cover Dynamics?

BRUNO LOCATELLI, CIRAD-FORET, FRANCE,

STANISLAS BOISSAU, WAGENINGEN UNIVERSITY, THE NETHERLANDS,

AND JACQUES WEBER, CIRAD-DS, FRANCE

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B. Locatelli, S. Boissau and J. Weber

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recommending that it is important to work on a local level if such correlations are to be explained. This chapter sets out to look at the relations between population and environment, through a 1997 field study in north-eastern Madagascar (Locatelli, 2000). The specific issue will be the factors governing wooded-cover (forest and plantation) dynamics; the hypothesis being that farmers, who are also landscape builders, base their acts on the situation in which they find themselves and that there are factors that explain wooded-cover dynamics. The chapter shows that population growth is one of those factors, but that wooded cover does not evolve consistently in line with population growth. It also demonstrates that social relations within the local community and outside economic or political factors also govern wooded-cover dynamics.

THE MANANARA REGION

The town of Mananara-Nord is on the east coast of Madagascar, 290 km north of Toamasina (Figure 12.1). The humid tropical climate in Mananara is characterized by high rainfall (2,400 mm/year), the absence of a true dry season and mean temperatures of around 24 °C. Eastern Madagascar is a region of dense evergreen forests.

Figure 12.1 Map of Madagascar showing the Mananara region and the three study villages

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Population levels in the region are quite low – twenty-seven inhabitants per square kilometre, on average, in the subprefecture in 1996 – and regularly distributed. There is a degree of ethnic homogeneity (around 80 per cent Betsimisaraka). Migratory exchanges with outside areas are currently low. Farming is the main economic activity. The main commercial crops are tree crops: cloves and coffee, which were introduced into the region a century ago. Planted trees –also known as plantations – cover large areas in the hills. Farming practices are similar to gathering, since there is minimal upkeep. Products are sold to intermediaries at the market, at variable prices. The region’s isolation means that the farmers do not make as much from their products as they might, while the major intermediaries benefit from an oligopoly that enables them to set prices. The leading food crop is rice, which is also the main staple and is not generally marketed. The rice market is relatively limited, as farmers prefer to produce it rather than buy it, given the market shortages and widely fluctuating prices. Irrigated rice is grown in bottomland areas, which are often entirely given over to it. However, these are not the only areas in which this relatively intensive type of rice growing is practised. Terraces have been built on numerous slopes, and the use of terraces is increasing, despite the amount of construction work involved. There is also a very original type of irrigated rice growing in the region: kirisana or rice cultivation on slopes, irrigated by runoff, which is often a prelude to the building of terraces. The other type of rice growing practised is upland rice after clearing and burning. The rice is planted on cleared, burnt forest areas or secondary vegetation. The system is extensive, without irrigation. Yields are relatively low, except in forest areas. The system has a marked cultural component: it was the one practised by the inhabitants’ ancestors and there are many rituals surrounding the crop cycle. Overall, in the region, the two types of rice growing (irrigated and upland) produce around the same quantities of rice, but upland rice and fallow take up more space than irrigated rice. Financial exchanges in the villages are limited and paid work is rare. The economic situation in the region is largely determined by its isolation: the communication and information infrastructures are inadequate. Forestry legislation forbids forest clearing, but the Forestry Service’s limited resources make this difficult to enforce. A protected forest area was designated in 1965 and a development and conservation project has been under way since 1989.

THE METHODOLOGY

A year’s fieldwork was required to draw up a methodology on several spatial and temporal scales. Concepts and tools were chosen for each scale, taken

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from various fields, particularly geography, economics and agronomy. The field work concentrated on landscapes, which were defined as ‘an area of land visible to an observer, in which there is a combination of facts and interactions of which only the overall result is seen at any given time’ (Deffontaines, 1973). According to this approach, landscapes are a factor in, a support for and a product of farmer practices. We intend to restrict ourselves to one aspect of landscape dynamics: wooded-cover dynamics.

In the region

The first stage in the methodology was to observe landscapes throughout the region, using a top-down approach (tour of the region, observation of terroirs and examination of plots). This generated results and hypotheses concerning wooded-cover dynamics and the underlying causes. In the terroirs (defined here as ‘physiognomic areas, of a few hundred hectares at most, in which there are certain specific signs of agricultural activity’, as in Deffontaines et al., 1977), landscapes were seen as patchworks, a concept borrowed from landscape ecology. The main tools were direct observations of slopes, through photographs and sketches. Simplified repre-sentations were used to draw up a typology that reflected the existing diversity and to identify landscape indicators. On a plot scale, the observations used concepts and tools relating to farmer practices (Milleville, 1987). The practices for each type of land use and transformation practices (such as clearing or planting) were studied. Observations, measurements and surveys were done to provide answers to the following three questions:

• What does the stakeholder do and how?

• What are the effects and consequences?

• Why does the stakeholder do what he or she does?

The aim was to identify certain groups of farmers and the reasons behind changes in the wooded cover. In addition, certain measurements were used to prepare for subsequent work, for instance by establishing the indicators required for subsequent studies.

In three villages

In the second stage, three areas around three villages were chosen for an in-depth study of landscapes and their history. The information obtained on the region in the previous stage was used to choose three villages for their differences in terms of population and isolation. The first (Antsirabe) is a large village (1,500 inhabitants) in a densely populated zone near a town and communication routes. The second (Inara) is small (350 inhabitants) in a

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sparsely populated zone and very isolated. The last (Varary, 1,000 inhabitants) is somewhere in between. The larger two villages are old (they date back over 100 years), while the smallest was built fifty years ago. We lived in the villages for nine months, enabling us to get to know the villagers, their culture and their habits, and to study the history of the local population. Population-density indicators were estimated. We also studied the landscapes around the villages and traced their history, using the following method: based on the current state of the field, we asked the villagers who built the landscape to tell us which successive land-use changes occurred, and give us the dates and the reasons of changes. At the same time, we also measured areas and sketched the slopes (Figure 12.2). Similar information was collected through surveys in the villages. The principles were the same: the household’s plots were located, the dates of any changes noted – dates prior to 1950 were not recorded – and areas estimated using indirect indicators. The people questioned were chosen at random, although we did try to include all the different lineages and ages. The 113 surveys concerned 30 per cent of the population in the smaller two villages and 16 per cent in the largest. Other data were taken from aerial photos. For instance, as the forest was not covered in the surveys, its location and the areas involved were obtained from other sources. The area around the village for which our information was representative and in which the landscape had mainly been built by the inhabitants of the village was estimated. To simplify matters, we chose a circle with a radius of 2.5 km. We then traced the history of land use within the area and developed a schematic model of land occupation dynamics.

Figure 12.2 Landscape history study method

An area of 0.5 hectares, located 1.5 km northeast of the village, currently covered by clove trees

The area was covered by forest before 1973, then used for slash-and-burn upland rice during 15 years and converted to clove tree plantation in 1988

Measurements

Survey

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With households

In the third stage, we changed scales to look at households. We based our work on the assumption that if wooded-cover dynamics were linked to population growth or the current situation, it was through the decisions made by landscape builders. In the case of Mananara, we chose the household as the scale for studying the decisions made. It corresponded to a residence, production and consumption unit. Although we studied the decisions made at this level, we also needed to determine the importance of the other decision-making levels, such as the extended family, lineage or village community. The tools we chose were those generally used to study decisions, such as the analysis of a decision-maker’s situation and how he or she is represented, the decision-maker’s aims, constraints and strategy (Sebillotte and Soler, 1990). We first used micro-economic models to represent the choices made by a simplified household, using field data concerning its practices. The diversity of households was then studied by looking at their life stories or paths: how had the household, its requirements and its available labour changed? In what context? What had it done to the wooded cover? The sample was the same as for the landscape history (113 households). The main paths taken were identified and described through portraits of households.

RESULTS

Observation of today’s landscapes

Of the different terroir landscapes observed, the most marked contrasts were between three remarkable ones (Plate 12.1). The first was a ‘primary’ forest landscape, with dense vegetation, no human occupation and no agriculture (landscape A). The second was a landscape of fallow and cleared areas, with short vegetation and few people, in which the whole area was used for extensive agriculture (landscape B). The last was terraced slopes and clove trees; it was fairly wooded, highly developed (terraces) and ‘domesticated’; the agriculture practised seemed fairly intensive and there was little fallow (landscape C). Three characteristics seemed to distinguish these landscapes from one another: wooded cover, the presence of man in the landscape and agricultural intensification. Figure 12.3 is an intuitive interpretation of the wooded cover and the presence of man in the three landscapes. This intuitive interpretation prompted the following hypothesis: wooded cover decreases and then increases as man’s presence in an area grows. We decided to call it the U-curve hypothesis (Boissau et al., 1999) (Figure 12.4). However, interpreting the landscape is not enough to estimate population pressure: the position of the three landscapes along the x-axis is therefore highly subjective. On the contrary, we could suggest that it was the

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same people who built landscapes B and C and that their activities were heterogeneously distributed in spatial terms. Furthermore, there is nothing to prove that the succession of landscapes A, B and C corresponds to a temporal pattern. In other words, we cannot assume that as population increases over time, landscapes switch from a forest to a ‘cleared’ state, eventually reaching the ‘terraces and clove trees’ state. All we know is that all three states currently coexist in the region. These simple statements are the results of observing landscapes, and provide food for future work. They also prompt questions about the history of the wooded cover and landscape builders’ practices.

Figure 12.3 Intuitive interpretation of three remarkable landscapes

Figure 12.4 The U-curve

Wooded cover

Landscape A

Landscape B

Landscape C

Presence of man in the landscape

Wooded cover

Population

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The wooded cover around three villages

We estimated the current wooded cover (forest and plantations) within a 2.5 km radius of the three villages. It is shown as a function of population density within the same area (Figure 12.5). Although three points cannot form a curve, we can imagine them on a U-shaped curve. However, the total areas mask a wide range of land occupation types. Near the villages, there is a zone dominated by planted trees and irrigated rice. The zones are larger, the higher the population of the village. Outside this zone, there is another dominated by planted trees, which is larger, the nearer the village is to communication routes and the higher the population. Beyond that zone, there are others dominated by slash-and-burn agriculture, with very little wooded cover. Lastly, natural forest is found in areas with a very low population. The history of the landscapes shows that planted areas are spreading, while forests are shrinking: we can talk of ‘the domestication of trees’. At Antsirabe, given the extension of plantations, the wooded area (forest and plantations) is growing. At Inara, it is shrinking slightly, while at Varary, the pattern is variable (Figure 12.6). The graph looks like a U-shaped curve despite the differences between the villages (isolation, existence of a national park, different economic situations for a given population density). Although the data do not say whether the wooded cover around Antsirabe has decreased in the past or whether that around Inara will expand in future, we suggest that as the population grows, wooded areas shrink and then expand. At Varary, at a population density of twenty inhabitants per square kilometre, the curve changes direction.

Figure 12.5 Population density and wooded cover

Planted trees and forest within a 2.5 km radius

Inara

Population density

40%

35%

30%

25%

20%

0 20 40 60 80 100 120

Varary

Antsirabe

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The U-shaped curve reflects a change in the type of wooded cover in the landscape, from natural forests to man-made plantations and strips of forest. This conversion also reflects the new technologies used in rice growing. The reduction in forest areas is primarily caused by rice growing after burning, which is the dominant form in areas with a low population density. As the population increases, rice growing has to be intensified, and there is enough labour to set up rice paddies and terraces. The graph showing the change in the areas given over to rice growing in the three villages between 1950 and 1997 is an inverted U (with a maximum at around twenty inhabitants per square kilometre). Likewise, the ratio of upland-rice production to irrigated production in the villages decreases as population increases, falling to below one at around twenty inhabitants per square kilometre. However, population levels do not explain everything. At Inara, there are large areas of forest near the village due to the existence of a national park, while at Antsirabe, there are large planted areas, due to its proximity to a town and to intermediaries. Population trends need to be viewed in the light of political and economic history. On looking at the dates of the different changes, it is clear that more forest is burnt during political crises, and that low clove prices for several years result in reduced planting and an increase in tree felling, particularly in less isolated areas.

Household and landscape histories

A look at the histories of households shows that households without children barely change the landscape, while those with children make the most changes when the head of the household is aged around 25 or 50. The first

Figure 12.6 Population density and wooded areas

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figure corresponds to an increase in the family’s requirements, and the second to the time when the children are in turn grown up and decide to cultivate land for their own family. These observations confirm the idea that population growth drives landscape and wooded-cover dynamics. However, not all households affect the wooded cover in the same way. A study of the diversity of their histories revealed certain factors partly responsible for wooded-cover dynamics:

• Clove and coffee price fluctuations. As prices vary considerably from one year to the next and production also varies, farmers plant a larger number of trees than they can or want to harvest. This enables them to make the most of the available opportunities in years of high prices.

• The rice market. As a result of poor market functioning (unstable rice prices and frequent shortages), very little rice is traded and villagers prefer to aim for self-sufficiency. At the same time, commercial crops help to cover cash requirements. All households therefore combine growing rice with planting trees, which partly explains the large areas of planted trees.

• Isolation. The region’s isolation limits the possibilities of temporary migration and of finding work outside family farms. This increases the need to produce rice and plant other crops.

• Previous innovations. The innovations – from outside or within – introduced in the past largely determine the technical possibilities and therefore the current dynamics of the wooded cover. Farmers grow trees that were introduced at the time of colonization and use the intensive rice-cultivation techniques brought by previous migratory exchanges.

• Social relations within villages. We noticed that households living in large villages that were not isolated planted more trees than others. This is not necessarily linked to the cost of transporting products to collection zones, but more to the higher cash requirements in villages near towns. Social relations tend to lead to uniform consumption of manufactured products, whereas in small, isolated villages, inhabitants who are ostentatious consumers may well come under pressure from others.

• Migration and land distribution. Not all villagers burn forest areas; this tends to be done by migrants or young people with no land of their own.

• Land transmission. A lot of couples lend some of their land to their children when they start their own family. The loan, which can be seen as a gift (insofar as the children generally farm the land until they inherit it), encourages the children to make the most of the small area they have by planting trees or building terraces.

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• Application of forestry legislation. Forestry legislation regulates forest burning, but some farmers take the risk, particularly during political crises, when they have the impression that they are less likely to be caught. The Forestry Service does not currently have the means to stop burning, except with the support of the National Park. The fact that the park is there therefore helps to restrict burning, but this involves a huge effort in terms of surveillance.

• Use of the forest. As the forest is publicly owned, it cannot be exploited sustainably (for example by agroforestry). It can therefore only be seen as a land reserve and has to be burnt before the land is used.

• Relationships with trees and money. Although commercial-product prices are now less attractive, young people now plant many more trees than their parents did at the same age. They have a different view of trees and money. The previous generation associated trees with the obligation to plant during and after colonization. Likewise, money was seen for a long time as a sign of subservience to outside forces (Althabe, 1969).

• Links with ancestors. Locals see growing rice after burning as a way of communicating with their ancestors. This would explain why it subsists in small plots in the most densely populated zones, at the expense of other types of land occupation such as plantations.

While population growth is a driving force behind wooded-cover dynamics, other factors steer the process. These different factors, which may be external to the social group, such as the economic, legislative and political situation, or internal, such as cultural aspects, social relations or land transmission, affect wooded-cover dynamics by influencing how households act.

DISCUSSION AND CONCLUSION

Trying to understand wooded-cover dynamics means observing the range of households and relating their actions to their life history. Our approach looked first at the regional, then local and then household scale. Some of our choices had their limitations. First, basing our work on land occupation through certain landscape elements masked the degree of diversity within plantations. Moreover, the choice of households for the study of the decisions made meant that we were less able to understand the decisions made higher up. Lastly, landscapes were studied through their agricultural use alone, and certain direct relationships between man and the landscape were overlooked. Nevertheless, this type of approach should help future research into the causes of deforestation (Brown and Pearce, 1994) and more generally into environmental dynamics. The U-shaped curve hypothesis was described in the case of tree resources. Using some of our other results, we could have demonstrated such a

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hypothesis for other resources or in relation to global environment issues (for instance carbon storage). The U-shaped curve shows that population growth changes the types of rela-tions between society and nature, and that it cannot be seen simply as either a curse or a blessing. However, the shape of the curve depends on factors specific to local conditions, hence it cannot be extrapolated to other situations. We are well aware that the results of this study are specific to the area studied. In the case of Mananara, food-crop intensification and commercial crop development are the two processes at play in wooded-cover dynamics. The same processes exist in numerous agrarian systems worldwide. However, they do not necessarily involve building terraces for rice growing or planting trees, and they result in different types of water and soil management, erosion patterns, wooded-cover densities and so on. For instance, at Beforona (on the central east coast of Madagascar), ginger is the dominant commercial crop, and soil losses with this crop are around ten times greater than with freshly cleared land (Terre Tany, 1997). At Mananara or in northern Viet Nam (Rossi, 1998), the fact that there are terraces proves a commitment to more long-term water and soil management. However, intensification does not necessarily result in more sustainable resource management; quite the contrary (Mathieu, 1998). Many other studies and approaches are dealing with the U-shaped curve, for instance a computer model simulating the evolutions of slash-and-burn, intensification and plantations in a growing-population context (Boissau, 1998) (Box 12.1). The U-shaped curve hypothesis was also observed by other authors looking at the relationships between development and the environment (Stagl, 1999) or more specifically at the changes in forests associated with economic development (Rudel, 1998). As these studies concerned a wide variety of countries covering a broad range of stages of development, they are difficult to compare with our study, but they at least proved that the relationships between development and the environment are not monotonous.

Box 12.1 Computer simulation of the U-shaped curve hypothesis (Boissau, 1998)

We built a multi-agent model to test the U-shaped curve hypothesis (Ferber, 1995), using the Cormas simulation platform (Bousquet et al., 1998). In this case, the model serves as a virtual laboratory that first makes it possible to check the coherence of a hypothesis, and then to simulate different scenarios and observe changes in the system. To this end, an artificial world is created, comprising a spatial environment in grid form and independent agents governed by behavioural rules.

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The model has three types of agents:

1. The cells making up the spatial grid represent the resource. Each cell is characterized by levels of vegetation and fertility, ranging from one to five. The level of fertility gradually declines when the field is cultivated and increases when it is not cultivated (fallow). If the cell is cultivated, the level of vegetation is minimum (level 1), but it gradually increases during fallow. A cell may be cultivated in two ways: slash-and-burn, which calls for regular fallow to enable the area to regenerate, and irrigated agriculture, which enables crop planting every year. For instance, with slash-and-burn, the level of fertility drops by one point each year, while during fallow, the level of fertility increases by 0.4 and that of vegetation by 0.2 each year, reflecting regeneration of the wooded cover and of the associated fertility potential. The level of fertility is assumed to be constant in irrigated plots.

2. ‘Farmers’, who exploit the resource under given constraints depending on the technique used. The level of fertility of each of the cells and the technique used govern production. For slash-and-burn, production is twenty times the level of fertility, compared to 200 times for irrigated crops. The total production of the whole of the cells cultivated by a ‘farmer’ determines the ‘farmer’s’ level of satisfaction. If this falls below a critical threshold, the ‘farmer’ may change techniques. This shows that ‘farmers’ do not choose their techniques according to the potential production they offer, but that they prefer those that are less labour-intensive, i.e. slash-and-burn rather than irrigated cropping, provided they can cover their requirements.

3. ‘Villages’, which represent the collective unit made up of ‘farm-ers’. Each ‘village’ is characterized by a spatial area in which its constituent ‘farmers’ evolve, notably by cultivating plots.

These behavioural principles and the interactions between agents are the basis of the model, for each one-year time step. In our simulations, we assumed a 3 per cent increase in the ‘farmer’ population each year. We shall now describe a simulation made by the above model. To begin with, the only technique practised is slash-and-burn. The ‘farmers’ exploit plots whose fertility rapidly falls after a few years. The plots then have to be left to fallow, enabling the vegetation to grow back. The ‘farmers’ then have to open up new plots as near to the village as possible and with maximum fertility. After a few time steps, the population has grown considerably, forcing ‘farmers’ to cultivate

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plots increasingly far away, but as the available land is limited, at some stage they are obliged to return to plots that have not had a long enough fallow period to restore maximum fertility. Production therefore tends to fall until the village splits as some of the ‘farmers’ move to an unoccupied area. This is the extensification phase. Once migration is impossible as the whole of the area is occupied, ‘farmers’ who have not achieved their critical level of satisfaction adopt new techniques. They therefore choose those of their plots that are best suited to a new technique, depending on their distance from the village and the specific characteristics of the cells. The other plots are either abandoned or converted into plantations, which increases the amount of wooded cover. By modifying the parameters of the model and the behavioural principles, different scenarios can be simulated, leading to different types of system evolution. Figure A shows the evolution of population and wooded cover for the simulation described above.

Figure A Changes in wooded cover and population over time

In this case, the relation between population pressure and wooded cover makes a U-shaped curve, as shown in Figure B.

Figure B Relation between population density and wooded cover over time

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In the left-hand part of the U-shaped curve described above, wooded cover is inversely proportional to population, which echoes the neo-Malthusian viewpoint. The right-hand side, on the other hand, tallies more with the Boserupian viewpoint, with the appearance of technological changes (planta-tions, intensified rice growing). Although the two theories are often presented as contradictory, they can sometimes coexist (Bilsborrow, 1987). The U-shaped curve hypothesis also shows the degree of change. With a view to sustainable development, the aim is not to control population growth but to see how the shift from the left-hand side to the right-hand side of the curve can be made more easily. This shift depends on economic or legislative factors that only governments can control.

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Does population growth affect wooded-cover dynamics?

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