Ecological Modelling, 49 (1990) 267-275 267 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

D E F O R E S T A T I O N A N D D I V E R S I T Y O F L I F E Z O N E S I N T H E B R A Z I L I A N A M A Z O N : A M A P A N A L Y S I S

PATRICK KANGAS

Biology Department, Eastern Michigan University, Ypsilanti, MI 48197 (U.S.A.)

(Accepted 13 July (1989)

ABSTRACT

Kangas, P., 1990. Deforestation and diversity of life zones in the Brazilian Amazon: a map analysis. Ecol. Modelling, 49: 267-275.

The diversity of Holdridge Life Zone types in the Brazilian Amazon region is studied to gain perspective on the consequences of deforestation. The study is based on a life zone map of Brazil by J.A. Tosi, Jr. at a scale of 1:10000000. The Amazon area of the map was digitized with a cell size of 50 km by 50 km. The resulting data base consists of 1789 cells from 17 life zones. Tropical moist forest covers 60% of the area followed by tropical premontane wet forest transition and tropical premontane moist forest transition at about 10% each. Each of the remaining 14 life zone types covers 3% or less of the total area. Loss of forest area in life zone types due to deforestation is simulated by removing cells from the data base. Different spatial patterns of deforestation are tested to assess their impact on life zone diversity. Deforestation along the Trans-Amazon Highway generated the least impact while deforestation along a frontier advancing from the south generated the most impact, in terms of loss of life zone diversity. These results show that the relative loss rate of life zone forest types is dependent on where deforestation begins.

INTRODUCTION

Defores ta t ion is reducing the biodivers i ty of forests t h roughou t the Trop- ics. These losses occur at several hierarchical scales inc luding the genetic

level, the species level, the habi ta t level and the l andscape level. In o rder to

cont ro l these losses, conservat ionis ts need to be able to suggest al ternat ives with the least impac t on biodivers i ty to decision makers . S imula t ion model l -

ing can be a useful tool in this regard since it allows al ternat ive scenarios to

be evaluated. Unfor tuna te ly , da ta needed to cons t ruc t models is no t widely available on tropical biodivers i ty and deforestat ion. Since models are on ly as good as the da ta used to cons t ruc t and test them, the lack of available da ta

makes model l ing largely a theoret ical exercise. However , as Caswell (1988)

2 6 8 P. V,A~GAS

has recently discussed, this is not necessarily a weakness and, in fact, theory and modelling may be the only available approaches for studying certain large-scale problems such as deforestation and loss of biodiversity. In this paper the diversity of Holdridge life zones in the Brazilian Amazon is evaluated and the loss of this form of biodiversity due to deforestation is simulated.

The life zone system is a land classification based on long-term averages of temperature and precipitation (Holdridge, 1947, 1967). Each life zone is an ecological division with an unique set of plant associations. Globally there are 120 life zones in the Holdridge system and 68 are found within the Tropics, when defined as the area between the Tropics of Cancer and Capricorn. Life zones were choosen as the object of this paper because the Holdridge system is objective, universally applicable and widely accepted as a classification. As a form of biodiversity the life zone is more-or-less at the landscape level of organization. Since each life zone contains characteristic habitats and species, the loss of a life zone would carry with it the loss of other forms of biodiversity.

M E T H O D S

The basis for the analyses described in this paper was a life zone map of Brazil by Tosi (1983). The map was drawn at a scale of 1 : 10 000 000 and was based on data from a number of climate stations throughout Brazil. The Amazon portion of the map was digitized by using a grid with a cell size of 50 km by 50 km. This cell size of 2500 km 2 was choosen since it approxi- mately matched the smallest patch size that occurred on the map. The total digitized data base consisted of 1789 cells. The area of consideration included the states and territories of Acre, Amazonas, Para, Amapa, Rondonia, Roraima and Mato Grosso, which have a combined area of 4462181 km 2 (Fearnside, 1986a).

Each patch of life zone on the map was coded separately so that the final data base included the total areas of each life zone and the number and sizes of patches of each life zone. This was done to account for diversity of patches which might have different taxonomic compositions even though they are examples of the same life zone type. Each cell which contained a river was also coded separately to account for areas that may have direct river influence.

Cells were simply removed from the data base to simulate loss of natural ecosystems due to deforestation in life zones. The removal rate of cells was scaled to correspond with data from deforestation literature. Five scenarios with different spatial configurations of deforestation were simulated and compared to investigate their relative impacts on life zone diversity.

D E F O R E S T A T I O N A N D D I V E R S I T Y O F L I F E Z O N E S I N T H E B R A Z I L I A N A M A Z O N

RESULTS

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Seventeen life zones are found within the Brazilian Amazon on Tosi's (1983) map (Table 1). The relative coverage is strongly dominated by tropical moist forest at 60.2% of the total area. Two other life zones, tropical premontane moist forest transition to tropical and tropical premontane wet forest transition to tropical, cover about 10% of the total area each. The other 14 life zones cover small areas with none greater than 3.3% of the total area. Rivers were found in 407 cells or 23% of the total data base.

Another form of diversity is the patch distribution of life zones. There are 49 life zone patches within the Brazilian Amazon on Tosi's (1983) map (Table 2). Tropical premontane wet forest had the highest number of patches (eleven) but most life zones had few patches. Seven are represented by only one patch. The size distribution of patches is dominated by those with small areas. Twenty-nine patches (59%) are between 1 and 9 cells in size, 18 patches (37%) are between 10 and 99 cells, and only two patches (4%) are greater than 100 cells in size.

To simulate loss of life zone diversity due to deforestation the data base was first initialized to 1980 conditions by removing 180 cells or approxi- mately 10% of the total area. I choose 10% loss since it is an intermediate

TABLE 1

Relative abundance of life zones in the Brazilian Amazon from Tosi's (1983) map

Life Zone type Number Percent of cells of total

Tropical Tropical Tropical Tropical Tropical Tropical Tropical Tropical Tropical

moist forest (T-mf) moist forest transition to Subtropical (T-mftS) wet forest (T-wf) dry forest (T-d 0 Premontane moist forest (TP-mf) Premontane moist forest transition to Tropical (TP-mftT) Premontane wet forest (TP-wf) Premontane wet forest transition to Tropical (TP-wftT) Premontane rain forest (TP-rf)

Tropical Lower Montane rain forest (TLM-rf) Subtropical moist forest (S-mf) Subtropical moist forest transition to Tropical (S-mftT) Subtropical moist forest transition to dry forest (S-mftdf) Subtropical moist forest transition to wet forest (S-mftwf) Subtropical wet forest (S-wf) Warm Temperate moist forest (WT-mf) Warm Temperate moist forest transition to dry forest (WT-mftdf)

1077 60.2 40 2.3 36 2.0

3 0.2 16 0.9

193 10.8 34 1.9

176 9.8 11 0.6

2 0.1 58 3.3 47 2.6 13 0.7 36 2.0 20 1.1 20 1.1

7 0.4

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TABLE 2

Diversity of life zone patches in the Brazilian Amazon from Tosi's (1983) map

P. K A N G A S

Life zone type Number of patches Size range of patches

T-mf 2 6-1071 T-mftS 4 2- 23 T-wf 3 3- 21 T-df 1 3 TP-mf 3 2- 7 TP-mftT 3 23- 146 TP-wf 11 1- 9 TP-wftT 6 4- 65 TP-rf 5 1- 6 TLM-rf 1 2 S-mr 3 1- 45 S-mftT 1 47 S-mftdf 1 13 S-mftwf 2 11- 25 S-wf 1 20 WT-mf 1 20 WT-mftdf 1 7 TOTAL 49

value between the wide range of reported estimates (Myers, 1980; Carvalho, 1984). This initial loss was distributed according to the spatial pat tern shown by Carneiro (1985). Ten fife zones were affected by the initial loss. Four life zones (T-df, S-mftdf, Wt-mf, Wt-mftdf), all located along the southern boundary in Mato Grosso, were completely removed by this initial loss. Subsequent simulations used the modified data base, initialized to 1980, as a starting point.

Rates of removal of cells to simulate deforestation were also based on published values from the literature. The estimates range over an order of magnitude but at least four estimates are similar, on the order of 10000 km2/year (Myers, 1980; Hecht, 1981). The simulations extended over 3 decades with an increasing rate of cell removal. Removal rates used in the simulations were 1981-1990:20000 km2/year (8 cells per year); 1991-2000: 30000 km2/year (12 cells per year); and 2001-2010:40000 km2/year (15 cells per year). These values are speculative but they seem to represent a realistic pattern when considered over the whole Amazon region.

Five different scenarios of deforestation were simulated. Each scenario represented a theoretical spatial pattern that deforestation might take. The actual pattern is probably a combination of these theoretical examples. The object of the simulations was to compare impacts from the different, theoretical spatial patterns of cell removal rather than to construct one

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pattern that might be expected and make predictions based on that pattern. The patterns of the scenarios were as follows:

(1) Trans-Amazon Highway - cells were removed along the margin of the highway,

(2) Eastern Frontier - cells were removed as an advancing front or line starting at the eastern edge of the Amazon and moving west,

(3) Town Seed - capital cities of each of the seven states or territories plus the town of Santarem were used as seeds or starting points for deforestation which proceeded outward in a radial pattern,

(4) Southern Frontier - same as the Eastern Frontier scenario except starting along the southern edge and moving north.

(5) Random Seed - same as the Town Seed scenario except that the seeds or starting points were choosen at random. The first four scenarios are idealized, but plausible patterns of deforestation. The random seed scenario was used as a null model for comparative purposes (Strong, 1982; Harvey et al., 1983).

Results of life zone losses through 2010 are shown in Table 3 for each of the deforestation scenarios, except for the Random Seed scenario which

TABLE 3

Percent loss of life zones in four simulated deforestation scenarios

Life zone type

Deforestation scenarios

Trans-Amazon Eastern Town Southern Highway Frontier Seed Frontier

T-mf T-mftS T-wf T-df TP-mf TP-mftT TP-wf TP-wftT TP-rf TLM-rf S-mf S-mftT S-mftdf S-mftwf S-wf WT-mf WT-mftdf

30% 12% 23% 10% 23% 8% 100%

33%

31% 88% 18% 76% 25% 41% 12% 15% 38%

9% 30% 20% 3% 9%

38% 31% 100% 69% 20% 100%

58% 100% 20% 100%

Percent losses were calculated by using life zone areas remaining after initial losses to 1980.

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TABLE 4

Comparison of impacts of simulated deforestation scenarios

P. KANGAS

Deforestation scenarios

Trans- E a s t e r n T o w n Southern Random Amazon Frontier Seed Frontier Seed Highway

Number of life zones affected 5 7 10 10 9.4 (SE = 0.7)

Number of life zones completely lost 0 0 0 5 0

Number of patches affected 12 12 26 20 19.3 (SE = 1.5)

Number of patches completely lost 0 2 9 16 6.7 (SE = 1.1)

The random seed scenario is the average of ten individual simulation runs in which deforestation was initiated at locations choosen at random.

must be averaged over several simulation runs. Although each scenario had the same number of cells removed, the pattern of losses among the life zones of the data base is obviously different for each case. The impacts of the simulations are summarized in Table 4, which includes the results of the Random Seed scenario with means and standard errors. The Trans-Amazon Highway had the least impact while the Southern Frontier had the greatest impact. Both the Trans-Amazon Highway and the Eastern Frontier had less impact than the null model of the Random Seed scenario. The Town Seed scenario had greater impact on patch diversity than the null model, both in terms of number of patches affected and number of patches lost. The Southern Frontier scenario had greater complete loss of both life zones and patches than the null model.

DISCUSSION

Large scale perspectives are needed to understand the impacts of defore- station on biodiversity. This is necessary because the functional units of many forms of biodiversity are large (such as the geographic range of a species) and because deforestation is occurring over large areas. Much has been written about deforestation in Amazonia that contributes to a large- scale perspective (Denevan, 1981; Hecht, 1981; Fearnside, 1982, 1986a, b, 1987, Fearnside and Salati, 1985; Lugo and Brown, 1982; Moeller, 1984; Carneiro, 1985; Lovejoy, 1985; Odum et al., 1986; Malingreau and Tucker, 1988), but all of these references discuss loss of forest area without dis- tinguishing between types of forests. Since different forest types can vary

D E F O R E S T A T I O N A N D D I V E R S I T Y O F L I F E Z O N E S I N T H E B R A Z I L I A N A M A Z O N 273

greatly in ecological characteristics, the lack of distinction of diversity of forests is a deficiency in most of the current literature (Lugo, 1988). This paper considers diversity of Holdridge life zones as a step towards account- ing for biodiversity in forest types. Other large data sets are becoming more widely available from remote sensing technologies (Hammond, 1977; Coch- rane, 1984; Woodwell et al., 1986a, b) which will greatly improve our understanding of spatial diversity in the Amazon and elsewhere in the Tropics in the near future.

Some assessments of life zone diversity can be made based on the results of this study. Life zone diversity in the Brazilian Amazon seems to be moderate at best. There is a high amount of dominance in the evenness component of diversity with three out of 17 life zones accounting for 80% of the total coverage. Moreover, one life zone (tropical moist forest) accounts for 60% of the total coverage. The richness component of diversity is moderate with 17 life zones found in the Brazilian Amazon. This represents 59% of the total number of life zones in all of Brazil (29). However, the number of life zones in the Brazilian Amazon (17) is actually less than the total found in Costa Rica (19), a country which covers the equivalent of only 1% of the total area of the Brazilian Amazon (50699 km 2 vs. 4462181 km2). This particular discrepancy is due to mountain ranges in Costa Rica which generate more life zones compared to the Brazilian Amazon which is generally low in elevation. Patches also contribute a fair amount of diversity to the Brazilian Amazon but this is a function of the map scale. A map with more detail might have more patches. Finally, rivers contribute diversity which augments life zone diversity.

The obvious conclusion from the simulations is that the impacts of deforestation, in terms of loss of life zone diversity, depend on where deforestation begins. Areas with a large number of life zone types or patches are more susceptible to losses than areas with less local diversity. This explains the relatively small impact from the Trans-Amazon Highway deforestation scenario which took place for the most part in the large patch of tropical moist forest. Also, the Southern Frontier deforestation scenario had the greatest impact since it occurred in an area with many subtropical life zones which were found no where else on the map. The conservation implications of these simulations seem almost trivial: don't plan or encour- age developments in areas of high local life zone diversity. However, the result that the Trans-Amazon Highway had the least impact was not expected since this development option was widely questioned by conserva- tionists. Perhaps the Trans-Amazon Highway was not such a bad idea from a conservation perspective. Other, more-or-less equivalent development scenarios such as the present one of encouraging development from the south in Rondonia may have more serious impacts. Of course, many other

274 P. KANGAS

criteria, in addi t ion to life zone diversity, need to be taken in to accoun t when fo rmula t ing an env i ronmenta l assessment of d e v e l o p m e n t plans.

The defores ta t ion, s imulat ions descr ibed here are p re l imina ry and l imited. A n obvious i m p r o v e m e n t would be to add the exist ing and p l an n ed con- servat ion areas to the da ta base. These parks and reserves could al ter the results of the de fores ta t ion s imulat ions if they preserve life zone types or pa tches by no t al lowing the removal of cer ta in cells f r o m the da ta base. At present there are 13 major parks and biological reserves in the Brazi l ian A m a z o n (Tereza et al., 1982; Camara , 1983; Carvalho, 1984) cover ing 87 644 km 2, which is the equivalent of 35 cells in the da t a base. Since I d id no t kno w the precise loca t ion of these preserves, I chose no t to inc lude them in this analysis. M o r e preserves are also be ing p lanned . Other useful add i t ions to the da ta base would be overlays of phy togeog raph i c p rov inces and the 'P le i s tocene refuges ' (Prance, 1977). These could be coded in to the exist ing da ta base and would represent significant, add i t iona l i n f o r m a t i o n on fores t biodiversi ty. A final i m p r o v e m e n t that would add signif icant ly to the analyses descr ibed here would be to expand the coverage of the da t a base to include the ent i re A m a z o n basin. This is feasible since life zone m ap s exist for all the countr ies tha t occur in the watershed.

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