Books

Tropical ecosystems and the human factor
References

Tropical ecosystems and the human factor

Ariel E. Lugo and Sandra Brown

ARIEL E. LUGO is Project Leader at the Southern Station's Institute of Tropical Forestry of the United States Forest Service, Rio Piedras, Puerto Rico. SANDRA BROWN is Assistant Professor in Forest Ecology at the University of Illinois, Urbana, Illinois.

Conversion of Tropical Moist Forests, by Norman Myers, a report prepared for the Committee on Research Priorities in Tropical Biology, National Research Council of the National Academy of Sciences, Washington, D.C. 1978. 205 p.

In 1977 the National Research Council of the National Academy of Sciences of the United States appointed a Committee on Research Priorities in Tropical Biology. As part of its activity, this committee asked Dr Norman Myers to produce a document assessing the state and rate of tropical forest conversion.

Unfortunately the report suffers from lack of an analytical approach to the issue at hand. It is also at fault in not facing the conceptual problem of the place of human beings in the tropical ecosystem: are they inside or out? Are they intruders or part of the system? If intruders, then their every action therein is by definition destructive and wrong. There is no place in this view for a forest moulded by human intelligence and will to meet basic needs for food and shelter.

The notion in this report that the human being is fundamentally a nuisance is too powerful and pervasive to be ignored. But, inside or outside the tropics, human beings must come to terms with their physical environment. In the developed countries "forest destruction" (as Myers defines it) is no longer an issue, although it presumably once was and would be again under conditions of poverty and shortage of food such as pertain in tropical countries today.

The preface of this report declares that it was published so that its findings "may be taken into account in formulating scientific priorities for tropical research and also in the search for patterns of development that can be sustained for human welfare." Yet, we find that the report's implied counsel of withdrawal from the tropical forest, its disregard for regrowth and the usefulness of secondary forest and its litany of only disaster are all distinctly unhelpful in this search.

The 205-page book contains 11 chapters with about 50 percent of the pages dedicated to regional reviews or country-by-country narrative on the state of tropical moist forests. The most important contribution of this book is that it expands the data base for rates of deforestation in tropical countries from 13 countries to 18 countries, as can be seen from our Table 1. The reader will not find this table in Myers' book, as this information is scattered throughout the book.

Methods and definitions

In the first chapter Myers highlights the problems and weaknesses of previous attempts to estimate the world's forest area, i.e., those of Sommer (1976) and Persson (1974). After reading the first chapter, one is left with the impression that the present survey resolves all the problems encountered by previous surveys. Yet, as far as we can tell, Myers' survey offers no significant improvement. His methods are the same used by previous authors. In fact, as will be evident below, we find Myers' work less quantitative and less analytical than earlier surveys. The key to understanding Myers' book is the fact that he writes about "conversion" or "disturbance" of virgin tropical forests. On pages 7-8 he defines these terms, as follows: "... conversion can range from marginal modification to fundamental transformation. Modification can be construed as the result of human intervention whereby the physiognomy, structure, and dynamics of the original forest undergo change. In turn, this change can be slight, substantial, or severe. In its lightest form, e.g., highly selective timber extraction, modification can merely entail some alteration in relative densities of tree populations and in the quantity of timber stocks; it need not necessarily cause a qualitative change in the species complement. A much more significant form of modification lies with shifting cultivation and other types of forest farming that induce secondary succession in the forest. In each of these instances, the original forest ecosystem maintains some continuity, provided there is no permanent loss of potential, e.g., through soil impaction or erosion, or extinction of species. In these circumstances, it is at least theoretically possible that the primary forest can regenerate within a moderate length of time until it eventually resembles its former make-up. Transformation, by contrast, amounts to a basically different category of conversion. In order to make way for permanent agriculture, plantations, or pasturelands, the forest is entirely eliminated, being replaced by a man established ecosystem, or by inanimate structures such as highways, industrial installations, and urban settlements." (Our emphasis.)

Tropical moist forest is defined as (p.11): "evergreen or partly evergreen forests, in areas receiving not less than 100 mm of precipitation in any month for two out of three years, with mean annual temperature of 24 + °C and essentially frost-free". This broad definition obviously includes many forest types, e.g., using the Holdridge life-zone system of classification the definition theoretically covers seven tropical (dry forest to rain forest life zones) and three subtropical (moist forest to rain forest) life zones. In fact, however, this definition covers only the tropical and subtropical rain forest life zones (a small forest area) because there are few areas in wet forests and even fewer in the moist and dry forest areas which meet the requirement of not less than 100 mm in two out of three years. Myers also stresses that primary forests should be differentiated from secondary forests as the former are "more valuable in bioecological, scientific, and economic terms".

Although Myers goes to great lengths to define many of his terms, he makes little use of them in the remaining text. For example, in the discussion of forest conversion as a result of timber harvesting, no distinction is made between the many degrees of logging, 0 whether the harvesting occurs in primary or secondary forests. One wonders why the author bothered to define terms so precisely if in the rest of the work he makes no attempt to use the definitions.

Table 1. Estimate of rates of conversion of primary moist forest to other states. (See text for definition of "conversion")

Country	Time interval a	Current forest b (103 km2)	CONVERSION RATES
			Myers (1980)		Sommer (1976)
			(103 km2/yr)	(%/yr)	(103 km2/yr)	(%/yr) c
Bangladesh	?	-	-	-	0.10	0.80
Burma	?	365	1.42	0.39	-	-
Laos	?	140	3.00	2.14	3.00	5.17
Malaysia (peninsular only)	1972-79	72	2.20	2.65	-	-
Malaysia (total)	?	-	-	-	1.50	0.64
Papua-New Guinea	?	400	0.25	0.06	0.20	0.05
Philippines	1971-76	114.6	3.00	2.62	2.60	2.05
Thailand	1972-78	131.8	d 11.49	5.73	3.00	1.05
Brazil	last 20 yrs	2860	13.00	0.42	-	-
	1966-75		12.78	0.43	-	-
Costa Rica	1967-77	16	0.40	2.00	0.60	2.73
Colombia	?	-	-	-	2.50	0.50
Nicaragua	1970s-79	35	0.40	1.10	-	-
Guyana	?	186.8	0.10	0.05	-	-
Peru	1945-75	650	1.70	0.24	-	-
Venezuela	1950-75	352.3	0.69	0.20	0.50	0.29
Gabon	?	205	3.00	1.46	-	-
Ghana	last 25 yrs	19.9	1.60	2.67	0.50	2.50
Ivory Coast	1966-74	54	4.47	4.98	4.00	4.44
Liberia	recent	25	2.30	9.20	-	-
Madagascar	?	-	-	-	3.00	4.00
Nigeria	1970-79	25.5	2.79	6.20	-	-
Vietnam	-	-	-	-	100	-
Sierre Leone	1944-79	2.9	1.34	2.69	-	-
Total		5656	65.93		21.5
Mean			e 0.75		f 1.09

^a Used by Myers (1980); time interval for Sommers' estimates is unknown. - ^b Myers (1980). - ^c Red on area of closed forests given In Persson (1974). - ^d The 1972 survey included non-productive forest, whereas the 1978 survey did not. Therefore, the real conversion rata was lower than 5.73. However. Only 33% of these forests are covered by Myers, definition of tropical forest. - ^e Weighted mean based on current area of forest in country to total forest area of sample. - ^f Weighted mean based on area of closed forest In country to total forest area of sample (1.965 x 10³ km²) Persson, 1974.

Estimate of conversion

On pages 25-26 Myers estimates the rate of conversion of tropical moist forests resulting from the activities of forest farmers as follows:

He then assumes that "it is not unrealistic to suppose that forest farmers are converting at least 100000 km² (10 million ha) of primary forest to permanent cultivation each year." However, Myers concludes that a total of 20 million ha/yr are being converted when other factors such as timber harvesting, planned agriculture and cattle raising are considered.

Nowhere else in the book is this calculation reviewed, modified or questioned. As we will show, the rest of the book does not relate to this calculation. Those using this conversion rate should be aware that, apart from the casual nature of this calculation,

- the definition of conversion could mean that several trees or all trees were cut and we have no idea of the degree of conversion implied in the 20 million hectares;

- no consideration is given to the rapid regeneration of tropical forests;

- estimates assume linear rates of deforestation everywhere regardless of life zone. In Costa Rica, Tosi (1980) found that rates of reforestation followed a pattern with life zones. In general, very wet life zones, where human populations are denser, lose their forests first.

A closer look at the data base for estimating conversion rates in the tropics reveals still more problems. For example, the time interval for which the rate is being applied is not clear at all, as is pointed out in our Table 1. This in itself could invalidate any estimate. Furthermore, much of Myers' estimate is based solely on opinion and thus subject to serious error. Also, for countries like Brazil, the estimate of deforestation is based on "several officials and authorities consulted" and unpublished agency reports.

It is clear that the data base of former tropical forest assessment is poor and conflicting, but one cannot be comfortable with Myers' predictions of total devastation of tropical forests in 20 years. The analysis in our Table 1 suggests a mean conversion rate of tropical forests of less than 1 percent/yr as opposed to the often quoted 1-2 percent/yr. As more countries are added to this calculation, the percentage change is bound to change even more. The reader should be aware that Myers' data, summarized in our Table 1, are for 18 countries out of a total of 89 tropical countries. These 18 countries contain more than 32 percent of the total tropical forests and 55 percent of the tropical closed forests. Regardless of facts, Myers does not use these data in his estimate of total rate of forest conversion rate.

Table 2. Roundwood and charcoal and fuelwood production for 1977 In countries with extensive tropical moist forest (FAO, 1977)

Country	Roundwood production (103 m3)	Charcoal and fuelwood production
		(103 m3)	Roundwood production
			Percent
Bolivia	798	400	50
Brazil	152274	116139	76
Colombia	24083	21081	86
Gabon	2487	1175	47
Indonesia	141298	114653	81
Malaysia	14366	4115	29
Peru	7075	6091	86
Venezuela	8404	7768	92
Zaire	13690	11800	86
Total	364575	283222	78

Monitoring the world's tropical ecosystem

What is the environmental state of the tropical forests of the world? It is not possible to answer this question with any degree of accuracy since systematic monitoring of these ecosystems on a unified worldwide basis does not now exist. What is required, first of all, is a baseline survey- of the world's tropical forests, one which can then be kept up-to-date to provide a single, uniform standard for comparative monitoring. This monitoring should then be carried out on a regular basis by a qualified agency. Only then can such questions be truly answered as "where has tropical forest disappeared?" "Where is it endangered?" "At how fast a rate is it being replaced and by what kind of vegetation?" And, "what are the principal human activities that endanger the tropical forest?" For the past three years the FAO Forestry Department has been working on such a baseline survey. The work is scheduled to be completed in 1981. It will then be of vital importance to have continuous monitoring, an activity which, in itself, will also be a means for maintaining and improving the quality of the baseline survey. This tropical forest resources assessment project, for which FAO has had financial assistance from the United Nations Environment Programme (UNEP), covers 82 countries, that is, virtually all those containing significantly large areas of tropical forest ecosystems. The survey is being conducted through the compilation and organization of the best existing survey information from government agencies, universities and specialized institutes inside and outside of the countries concerned. For countries were information hag been found lacking, the project has acquired and interpreted the latest available satellite imagery. A preliminary part of the survey aimed at learning broadly what amount of tropical forest may be available for industrial wood was completed and issued by FAO in May 1979 (Miscellaneous Paper FO: MISC/79/1). The results of this study were described in the article "Present and future natural forest and plantation areas of the tropics" by J.P. Lanly and J. Clement, who are also the authors of the paper in Unasylva Vol. 31, No. 123 (1979). FAO's work on the baseline survey is having another important effect. In tropical countries that lacked good inventory data, or that have allowed their inventories to fall out of date, it is creating a new appreciation of the importance of this work. FAO, again with financial support from UNEP, is now assisting developing countries of the tropics in the creation and operation of national forest monitoring facilities. The work of such facilities can then be coordinated and incorporated into a global monitoring effort. Without accurate and current inventories on continuous monitoring, no government, not to say those organizations that are concerned with the global state of the common environment, can know what is the actual condition of ecosystems that are so vital to man's present and future well-being. THE EDITOR

The human factor

With the exception of the calculation already discussed, in which each family of farmers is assumed to clear one ha of forest each year, Myers makes no attempt to relate other human activities to rates of forest conversion. The discussion of four human activities presumed to be causing forest conversion is mostly anecdotal. These activities are: farming, cattle-raising, timber trade and firewood consumption.

In Chapter 4 the author uses FAO statistics to conclude that 47 percent of the world wood production is used for fuel and the rest for other uses, particularly to meet the needs of the developed world. Myers ignores the estimate that in the tropics 80 percent of all the wood that is cut is used for fuel (FAO, 1977). He argues in Chapter 6 that the use of wood for fuel occurs mostly in the arid tropics and that it is negligible in the moist tropics. In reality, in the nine tropical countries recognized by him as having the most area of tropical moist forest, 78 percent of the roundwood production is consumed for fuel (our Table 2). This mistake is important because Myers uses FAO statistics to justify an attack on the role of the developed countries in the conversion of tropical forests. The chapter points out that tropical hardwood exports to developed countries are increasing at enormous rates to the detriment of the forest. There is no denying that exports of tropical hardwoods are increasing. However, the total consumption by the largest importers (Japan, United States, and Europe) for 1973 shown in Myers' Table 3 adds up to 49 percent of a total production of 109 million m³ from all the tropical countries. This 49 percent (53.3 million m³) corresponds to 15 percent of the total roundwood production of the nine countries depicted in our Table 2.

In the analysis of the role of cattle raising, Myers presents data on beef production and exports for Central America and Brazil (his Table 5) to substantiate his position that beef demand in the United States is causing the destruction of tropical moist forests. The table, however, is never analysed in any depth. We could not find any significant relationship between the rate of forest loss reported in that table and the increase in beef production by Brazil and the eight Central American countries. For example, El Salvador is shown to increase its forest area while also increasing beef production, while Panama and Honduras show no loss of forest area but significant increases in beef production. Guatemala, on the other hand, had the largest loss in forests and pasture, but its beef production increased.

In addition to the incomplete use of FAO statistics and the lack of analytical depth, we found numerous instances of questionable ecological statements in this book. For example:

· Myers argues that forests subject to hurricanes are also converted forests, but by natural forces, and that many decades will be required for these forests to recover. Myers seems not to be aware that steady-state ecosystems develop under natural conditions in response to a variety of causes of stress that maintain them in simplified states. Hurricanes, hypersalinity, flooding, and so on are natural factors to which forests adapt.

· Myers assumes that the wood burned by the forest farmer in the process of clearing land could be used for firewood. He appears not to be mindful that this burning is essential to release the nutrients in boles to fertilize the site and thus grow the food.

The book's usefulness

In short, Myers' analysis should be used with extreme caution because he overstates the rate of conversion of tropical forests and thus contributes significantly to the confusion that scientists from non-tropical countries exhibit when writing about the tropics. Unfortunately, in testimony to the US Congress (Raven, 1980) and in many recent publications, one finds that conversion as defined by Myers is often assumed to mean complete destruction.

Raven (1976), for example, said:

"Since all the tropical forests will be destroyed during the next 25 years, it is difficult to avoid the conclusion that up to a billion people will starve to death in the tropics during the next three decades. During this period all natural communities in the tropics will be totally destroyed before we can even begin to understand them or to learn how to use them for human benefit." (Our emphasis.)

Are the tropical forests endangered ecosystems or are scientists misleading the public? The question of the endangerment of tropical forests more than ever demands serious analysis. To what degree can we utilize these magnificent ecosystems without harming them or ourselves? Myers' analysis (or lack of it) does not help us in answering this important question. We do not venture an answer at this point, but we do know that in such places as Puerto Rico, in spite of the loss of 90 percent of the original forest cover, there has not been a significant loss of species. Is this resiliency a property of islands or is it that we don't know what we lost?

We do not want to underestimate the critical condition of a tropical forest. What we do want to make clear, however, is that Myers' analysis is far too superficial to be used for the purposes intended by the committee of fourteen scientists from the US National Academy of Sciences. The overstatement of a problem such as this one can only hurt the credibility of well intentioned scientists and may even delay the efforts to conserve tropical forests.

The common exaggeration

In terms of the atmospheric carbon dioxide issue and the possible greenhouse effect on the world's climate, we think that scientists should not use the Myers book to extrapolate the role of tropical forests. Our view is that humans are intruding at faster rates into the tropical forest, but their impact on the forest areas has often been exaggerated. This, we believe, is because:

· Biologists are trying to protect species or gene pools. But changes that affect species survival do not necessarily alter carbon pools or forest areas because the forests are not being converted to bare soil but to secondary forests that grow rapidly and store significant amounts of carbon (Brown, 1980; Brown and Lugo, 1980).

· Earlier estimates of carbon accumulation in tropical forests were high by a factor of two and this led to overestimates of the amount of carbon released to the atmosphere when the forest is "deforested" (Brown and Lugo, 1980).

· Accounts of the problem of deforestation and its effects on atmospheric carbon dioxide failed to consider the rapid rates of recovery in moist tropical forests.

In summary, the definitive work on the state of the tropical forests still needs to be done; we can only hope that next time an attempt is made to assess the tropical forests of the world less time is spent on rhetoric and more is given to analysis.

References

BROWN, S. 1980, Rates of organic matter accumulation and liner production in tropical forest ecosystems. Pages 118-139 in S. Brown, A.E. Lugo and B. Liegel, eds. The role of tropical forests on the world carbon cycle. Proc. Symposium at the Institute of Tropical Forestry, Rio Piedras, Puerto Rico. US Department of Energy, Washington, D.C. (In press)

BROWN, S. & A.E. LUGO. 1980, Preliminary estimate of the storage of organic carbon in tropical forest ecosystems. Pages 65-117 in S. Brown, A.E. Lugo and B. Liegel, eds. The role of tropical forests on the world carbon cycle. Proc. Symposium at the Institute of Tropical Forestry, Rio Piedras, Puerto Rico. US Department of Energy, Washington, D.C. (In press)

FAO. 1977, Yearbook of forest products. FAO, Rome, Italy. 462 p.

MYERS, N. 1980, Conversion of tropical moist forests. National Academy of Sciences, Washington, D. C. 205 p.

PERSSON, R. 1974, World forest resources. Review of the world's forest resources in the early 1970's. Royal College of Forestry, Stockholm, Sweden. Department of Forestry Survey, Research Notes No. 17.

RAVEN, P.H. 1976, The destruction of the tropics. Frontiers, 40: 22-23.

RAVEN, P.H. 1980, Prepared statement before the Subcommittee on International Organizations, Committee on Foreign Affairs, US House of Representatives, Washington, D.C.

SOMMER, A. 1976, Attempt at an assessment of the world's tropical moist forests. Unasylva, 28: 5-25.

TOSI, J. 1980, Life zones, land use, and forest vegetation in the tropical and subtropical regions. P. 44-64 in S. Brown, A.E. Lugo & B. Liegel, eds. The role of tropical forests on the world carbon cycle. Proc. Symposium at the Institute of Tropical Forestry, Rio Piedras, Puerto Rico. US Department of Energy, Washington, D.C. (In press)