Assessing the evolution of land use in Brazilian Amazônia

Transcription

1 2nd LBA SC, Manaus July 7-10 Scenarios of LUCC Session Assessing the evolution of land use in Brazilian Amazônia Diógenes S. Alves, Maria Isabel S. Escada, Morris Scherer-Warren, José C. da Silveira Jr. URL: inpe.br/dalves/amazonia.html

2 Summary Human occupation in Brazilian Amazônia has been accompanied by persistent changes in Amazonian landscapes, ecosystems, and in demographic and socioeconomic conditions of new settlers. In this study, we review agricultural production and Agricultural Census data to investigate how cattle ranching and agriculture have evolved in Amazônia from 1975 to In general, pasture has been the prevailing land use, at the same time as the number of cattle heads per hectare systematically increased during the period of study. The relative area of crops has decreased in almost all states, while pastures increased their relative importance, even in some regions of family agriculture. Grain production has considerably increased where largescale mechanized agriculture was introduced. Overall, the data suggest a scenario of land use intensification in regions of more important settlement and agricultural production. The analysis suggests that more systematic research should focus on the carrying capacity of different regions and on the relationships between land use intensification, land degradation and sustainable land use.

3 DATA All analyses were based on agricultural production and Agricultural Census data, obtained from the SAMBA data base for years 1975, 1980 and 1985 (Waniez et al 1997), and from a FIBGE web site for the 1996 Agricultural Census ( sidra.ibge.gov.br). Most data were aggregated at the state level. A few analyses considered municipio-level data.

4 The evolution of pastures and crop area Data from 1975 and 1996 show that the total area occupied by crops and pastures increased by factors of 1.2 (Roraima), 1.3 (Tocantins), 1.5 (Maranhão), 1.9 (Amazonas), 2.1 (Mato Grosso), 2.3 (Pará), 4.2 (Acre), and 8 (Rondônia)(*). The area of crops increased from ha to ha, while the area of crops increased from ha to ha, respectively, in 1975 and The area of pastures exceeded crops in all states by The state of Mato Grosso accounted for 58% of the increase in crop area and 47% of the increase in pasture area. The area of crops relative to that of pastures decreased in most states from 1975 to 1996 (figure 1). In Rondônia, crops represented 90% of the area of pastures in 1975, but only 17% in 1996, when pastures covered most of the farm area in the municipios where small farms were predominant. (*)A decrease in both crop and pasture areas was obtained for the state of Amapá, a behavior that was not further explored in the present study; it is recognized, however, that a more detailed assessment of the quality and consistency of the available data is required to validate presented results.

5 The evolution of pastures and crop area (cont) The 1996 crop and pasture areas relative to 1975 crop and pasture areas are shown in figure 2. Crop area showed important relative increases in Mato Grosso, probably due to the development of large-scale grain production 1 and to the recent settlement of small farmers in Roraima 2. Results suggest that crops have been an important activity in the initial stages of family settlement when subsistence agriculture and cash crops like cacao and coffee would play a more important role, but pastures have ended the predominant land use as the agrarian systems evolve into a more consolidated frontier. Agriculture has maintained or increased its relative importance when it has developed into large-scale, mechanized grain production. 1 - By 1996, Mato Grosso had become the third largest producer of soy beans among Brazilian states 2 - During the period, Roraima presented a 14-fold increase in the area of small farms

6 Figure 1 - Crop area relative to pasture area for 1975, 1980, 1985 and Crop/Pasture (%) AC AM AP MA MT PA RO RR TO

7 Figure crop and pasture areas relative to the respective 1975 areas Crop increase Past increase AC AM AP MA MT PA RO RR TO

8 The evolution of pasture area and cattle During the period, cattle in Legal Amazônia increased 4 times, while pastures increased by a factor of 1.7 (Table 1). Region-wide, cattle density (the average number of heads per hectare) increased from 0.32 in 1975 to 0.7 in 1996, exceeding 0.5 heads per hectare in most states by Considering only the period, data show that cattle increased faster than pasture area in all states (Figure 3) (*). Ninety five percent of the 1996 cattle was in the states of Mato Grosso (40.5 %, 0.67 heads ha -1 ), Pará (17.1 %, 0.82 heads ha -1 ), Tocantins (14.7 %, 0.47 heads ha -1 ), Rondônia (11.1 %, 1.35 heads ha -1 ) and Maranhão (11 %, 0.73 heads ha -1 ). The data suggest that large farms tend to favor more extensive ranching, with fewer heads per unit of area, while small farmers tend to intensify pasture use, keeping larger number of heads per unit of area. Overall, the data suggest that pasture use has intensified, although the average number of heads per hectare is lower than those reported by farmers in field interviews in other studies by the authors. (*)A decrease in both crop and pasture areas in the period was obtained for the state of Amapá, as detected for the period also.

9 Table 1 - Number of heads of cattle and pasture for years 1975, 1980, 1985 and 1996 Cattle (10 3 heads) Pasture area (10 3 hectares) Cattle density (heads ha -1 ) STATE AC AM AP MA MT PA RO RR TO Legal Amazonia

10 Figure 3 - Cattle and pasture area increase in the period Markers, from left to right, correspond to AP, MA, TO, AM, PA, RR, MT, AC, RO Dashed line correspond to the unitary line (pasture = cattle increase) Cattle increase (%) Pasture increase (%)

11 Annual cultures by farm size in 1996 Data from the 1996 Census show that grain production in Mato Grosso and Tocantins is dominated by large areas, with 95% of all yield reported in farms larger than 200 ha and 75% in farms larger than 1000 ha, indicating that grain production in these states is dominated by large farmers. On the other hand, data suggest that smaller farms are responsible for larger fractions of agricultural output in areas where family and small-scale agriculture subsist (MA, PA, RO, RR). Figure 4 - Area of annual crops for different farm size category in 1996 (%) MA MT PA RO RR TO < 20 ha ha ha > 1000 ha

12 Legal forest reservations and land use in 1996 Data show that more than 80% of all 1996 crop and pasture areas were located in municípios where farm legal forest reservations exceeded 50% of the total farm area (Figure 5). In such municipios, the 50%-legal limits of clearing - in force until were exceeded for all frams in the aggregate and mandatory forest reservations were probably depleted in many properties. Such behavior implies that crops and pastures are concentrated in some municipios and is associated to the spatial concentration of forest clearing that is at the origin of a landscape mostly dominated by pastures (Alves 2002), where land use is intensified and large tracts of forest or older stages of secondary vegetation can be observed rarely (Alves et al, 2002accepted).

13 Figure 5 - Crop, pasture and legal forest reservations for 1996 municipios Red and blue markers represent a cumulative distribution for municipios with municipio legal forest reservation increasing from left to right. Crop and pasture(cum. %) Forest reservation left (%) Crops (%) Pasture (%)

14 Discussion Overall, results suggest that land use has followed three major pathways during the last decades of accelerated expansion of the agricultural frontier in Legal Amazônia: a decrease in the relative importance of crop area in comparison to pastures, including in areas originally settled by small-farm, family agriculture an important increase in the production of soy beans and other annual crops within the same agricultural system (mechanized rice, corn, sorgum), where large farms and national and international production networks dominate a systematic increase in pasture productivity, although the average number of heads per hectare is still low These pathways suggest that, as the frontier has expanded, the relative importance of subsistence agriculture has decreased and relatively more land has been allocated to pastures. At the same time, agriculture increased its importance where it was managed to become part of large-scale systems with national and international links. The increase in productivity may be due to several reasons. Assuming that the average productivity has been lower than the expectation of many interviewed farmers, results appear to demonstrate that, on the average, farmers have cleared more forest than they would actually use if land use would have been managed according to their own expectations. Under this scenario, part of the depletion of mandatory forest reservations could have been avoided simply by improving land management.

15 Discussion (cont.) It can be recalled that one of the key questions of the Land Use/Land Cover Change (LUCC) component of LBA was the characterization of predominant patterns of forest conversion, abandonment and land use ( Implicit to this question is the assumption that cattle ranching is the predominant land use in Amazônia, and forest-fallow systems associated with important rates of abandonment are the rule in agriculture. Present results show that the characterization of spatial differences in agriculture and cattle ranching is critical to understand how land use evolves in the Amazon. Also, intensification of land use and the decline of family agriculture may suggest that forest-fallow systems and forest regeneration may not be predominant in areas where most deforestation is concentrated. To conclude, it might be argued that recognizing the importance of land use intensification, the relatively low land productivity and the low rates of forest regeneration may be important for linking the LUCC to other LBA components. In particular, recognizing different patterns and dynamics of LUCC could be used to refine the strategy of sampling and up-scaling in relation to the other LBA components. Finally, the present analysis also suggests that more systematic research is needed about the carrying capacity of different regions and the relationships between land use intensification, land degradation and sustainable land use.

16 REFERENCES Alves, D.S Space-time dynamics of deforestation in Brazilian Amazônia. Intern. Journal of Remote Sensing, 23, 14, Alves, D.S., Escada, M.I.S., Pereira, J.L.G., de Souza, C.L. 2002accepted. Land use intensification and abandonment in Rondonia. (accepted for publication, Intern. Journal of remote Sensing) Waniez, P., Brustlein, V., O Neill M., SAMBA 2000, CD-ROM (Rio de Janeiro/Paris: IBGE/ORSTOM/CREDAL) Acknowledgements The authors would like to thank A.P. Aguiar for comments on a preliminary version of this work.