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Loss in Species Caused by Tropical Deforestation and Their Recovery through Management Author(s): Ariel E. Lugo, John A. Parrotta, Sandra Brown Source: Ambio, Vol. 22, No. 2/3, : Ecology, Economics, Policy (May, 1993), pp. 106 -109 Published by: Allen Press on behalf of Royal Swedish Academy of Sciences Stable URL: http://www.jstor.org/stable/4314054 Accessed: 15/04/2009 16:34

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http://www.jstor.org Ariel E. Lugo, John A. Parrotta and Sandra Brown Loss in Species Caused by Tropical Deforestationand Their Recovery Through Management

productivityexplains why monoculturesare necessarywhen the The loss of species as a result of deforestation and managementobjective is to maximizenet yield andprofit. In fact, degradation of tropical lands is widely discussed. most agriculturaland silviculturalprescriptions for maximizing Models based on island biogeography theory are used to yield involve the simplificationof the , by whatever evaluate the relationship between of species means necessary,including weeding or poisoning of any species and deforestation. The analysis shows that naturalresiliency thatmay compete with those favoredfor theirhigh yield and low causes the models to overestimate the rates of species respiration.In these cases, labor, fuels,and extinctions for given intensities of deforestation. There is an substitutefor ecosystem metabolism and in so doing assures a opportunity to couple natural processes with management activities to reduce species extinctions and restore species measureof ecosystem stability. richness to degraded lands. As an example we show how Taken to the extreme, these techniques have given manage- tropical monoculture can foster diverse ment a poor image in relationto currentinterests in maximizing native in areas previously deforested. The central biodiversity. The conflict between managementfor high-yield point is that well-directed human actions provide us with the and maintainingbiodiversity cannot be reconciled in high yield means to conserve biodiversity and restore it in locations systems such as clonal or hydroponic ,be- previously degraded. cause the measurestaken to increase yields are extreme and the biota is reducedto almost uniformgenetic material.As a result, managementand monoculturesare commonly viewed as irrel- evant to the solution of preserving, conserving, or restoring biodiversityin the landscape. INTRODUCTION It is unfortunatethat extreme application of management The classic monographby McArthurand Wilson (1) on island systems that result in high yields have led to a general biogeographyvisualized the numberof species on an island as a repudiationof managementactivities with regards to the con- balancebetween species gains by immigrationand losses through servation of biodiversity. We propose that managementactivi- . Using this simple concept, McArthurand Wilson ties, including the use of monoculturetree plantations,can be developed a quantitativetheory to explain the numberof species useful for restoring the species composition of damaged sites. in islands at species steady state. Today the species-area To put managementactivities in context we will discuss first relationship,upon which island biogeographytheory is based, is the relationshipbetween species extinctions and deforestation. usedto estimatethe extinction of species as a resultof deforestation of tropicalforest lands (2, 3). Little attentionis given to the other side of the equation(gains of species on a site) to arriveat a better DEFORESTATIONAND SPECIES EXTINCTIONS estimateof the actualnumber of species presentfollowing human The relationshipbetween deforestationand species extinctions, modificationof the landscape(4, 5). Our objective is to discuss using the species-area model of McArthurand Wilson (1) is both the losses and gains of species in damaged lands with shown in equation 1 where: S = the numberof species, A = the particular attention to the opportunities for augmenting the area, and C is a parameter that depends on the taxon, its numbersof species per unit areathrough management. We focus populationdensity, and biogeographicregion. on the importanceof managedforest standsas species refugiaand moreimportantly, as tools forrestoringspecies richness in degraded S = CAZ (equation 1) sites. Studies in Caribbeanisland plantationssuggest that these human-managedecosystems served as refuges for orchids The shape of the species-areacurve is determinedby Z (Fig. (6) and avifauna(7) when high deforestationrates had consumed 1), a factor that is < 0.7 (9). Most regions of the world are char- and/orfragmented available naturalhabitat. acterized by Z factors between 0.16 and 0.39. Islands tend to have Z factors of about0.35 while comparablecontinental areas have Z factorsof about0.20 (9). However, the Z factorincreases MANAGEMENTFOR SPECIES DIVERSITY as the areaunder consideration becomes smaller.For An important area of study in ecology is succession, or the islands, tree and plant species-areacurves, covering up to 1500 changes that occur in as they mature. A working kM2, had Z factors of 0.12 and 0.23 for and all plant spe- hypothesis for which there are few exception-i.e., highly cies, respectively (10). Other examples, using tree species data stressed ecosystems-is that as ecosystems mature, their net for even smallerareas, had Z factorsof 0.67 and 0.68 for dry and primaryproductivity decreases and their respiration,ecosystem wet forests and 0.47 for lower montanerainforests (1 1). metabolism,and species richnessincrease (8). In fact, ecologists The predictedmagnitude of the extinction of species in rela- suggested that the overall biotic complexity of ecosystems tion to the loss of forest area is a function of the Z factor (Fig. increases as net primaryproductivity decreases (8). The inverse 1). The model is very sensitive to Z and thus allows for a wide relation between ecosystem complexity and net primary envelope of extinctions given a similar magnitudeof deforesta-

106 AMBIO VOL. 22 NO. 2-3, MAY 1993 ...... tion. Unfortunately,an understandingof the factors that affect ...... Z Zx44x the value of Z is still incomplete (9). Nevertheless, when Z val- ...... "M ues are low (< 0.20), the model predicts that more than 50% of the areacan be deforestedbefore the slope of the extinction ...... curve increases rapidly with increasing deforestation (Fig. 1).

Conversely, at high Z values (> 0.60) the model suggests ex- ...... sxF tU tinction rates that are almost proportionalto deforestationrates...... N For the model to predict rates of species extinctions that are 2 Z: faster than the rates of forest loss, the Z factors must be much

...... higher than empiricaldata suggest possible. ig g z Limited data for bird and plant species for the island of -mo n

3: 81 PuertoRico (4, 12) suggest that the model in Figure 1 overesti- M mates extinction rates even when Z values as low as 0.15 are used. Brash (12) reportedan extinction of 11.6% of the avian 2 species of the island after a loss of 99% of the primaryforests ...... and a net deforestationof 90%. The implication is that the rate of species extinctions cannot be explained by changes in area of forests alone. Other factors come into play and the net result Vpg-i of these is that the species-area model appearsto overestimate ...... extinction rates. An obvious explanationfor the overestimationof extinctions Figure 1. Relationship between deforestation and loss of species to extinction using different slopes (Z factor) for the species-area curve by species-area curve models is the implicit assumption that shown in 1. deforestationresults in lands that are biotically sterile, which of equation course is rarely true. Moreover, human pressure on the land is variable and after abandonment, species can reinvade sites RIX-2- MEN 8 throughsuccessional mechanisms. In addition, as discussed by gN mg Williamson (9), the species-area approachhas limitations that r reduce its usefulness for detailed explanations of biotic phe- tg MgM,M nomena. For example, the curves are based on single taxa, and o. pgm mm gg it is likely that assemblages of species will exhibit different re- with MMm 'IM lationships area than do individualtaxa because the curves g are not additive. Habitatdiversity, a key factor in the explana- N tion of species richness in islands, is not accounted for in the

species-area models except for the implicit assumption that qgi, Ojg,, 1-,migjg, gp. ;-.-g larger areas have more . These considerations make it clear that the and rate biology of species extinctions caused by a.? humanactivity are differentphenomena than that implied using only species-areamodels. The discussion above suggests the need for better models for predicting species extinctions due to human activities such as deforestation.Clearly, research is needed on the mechanisms M MEMN that cause resistance to the loss of species following distur- bances. Meanwhile, we must take action to reduce species M M extinctions and where possible, restore lost biodiversity. Figure 2. Relationship between number of understory tree species in tree plantations and the age of the . Data sources and discussion in the text. The relationship for these data is y = 0.74 + TREEPLANTATIONS AS FOSTERECOSYSTEMS 0.93 x, (r2 = 0.62). FOR DIVERSEFORESTS Treeplantations usually consist of fast growing, light-demanding tree species that have valuable propertiesor other useful productsuch as , resins, or tannins. These plantationsare Data from the above sources showed that the number of often established on degradedlands where agriculturalactivity understory species in plantations increased at a constant rate for is no longerpossible due to declines in productivity.We have approximately 30 yr (Fig. 2). These data were for 44 plantations noticed in our studies of tree plantationsin PuertoRico and in a in Puerto Rico and ranging in age from 4 to 32 yr. Rainfall review of the literature mostly from India, that species-rich among sites ranged from 500 to 3800 mm yr-'. Sampling area understoriesof nativetrees develop inside plantationsand that the for the understory ranged from 30 to 250 M2 and the minimum species composition of these understorieschange over time (5, size recorded for understory species ranged from seedlings to 13-23). Underconventional plantation management, considerable large saplings. We obtained the same relation when we analyzed effortis exertedto controlor eliminateunderstory by vegetation. Our proposal to use plantations to accelerate successional processes and increase biodiversity requires a broadening of conventional management objectives. While management for high overstory wood yields will continue to be importantin or- der to recover investments in plantationforestry, management practices that facilitate natural successional processes and the development of species-rich understorieswould be a primary managementgoal.

AMBIO VOL. 22 NO. 2-3, MAY 1993 107 Khaya nyasica, Swietenia macrophylla, Terminalia ivorensis, intolerant,their regeneration is unlikely in the newly established and Grevillea robusta. native forest. The accumulationof species in plantationsleveled off after35 Similar data in Brown and Lugo (24), for secondary forests yrs in Puerto Rico. In contrast, available plantation data from undergoing natural succession, suggest that plantations accu- India suggest that the numberof species in the understoriesde- mulate species as fast as secondary forests but secondary for- creased after 35 yrs. It is unclearwhether the apparentdecline in ests begin at higher levels of species richness (Fig. 3). This was species richness beyond 35 yrs in Indian plantations is due to surprisingto us in light of the fact that most of the plantation natural factors or management activities intended to curtail data are for degraded sites while those in Brown and Lugo are naturalsuccessional processes in the plantationunderstory. Our for naturalsuccessions on abandonedagricultural sites; gener- proposal includes using the overstory plantationtrees once the ally, . On severely degraded sites, planta- understoryis fully developed so that a new and diverse forest tions appear to serve as successional catalysts, accumulating of native species can develop in the previously degradedplan- species at markedlyhigher rates than would be the case in their tation site. Under this type of management,we don't expect a absence (20, 21). Ecological characteristicsof plantationsthat reductionin tree species diversity in the older stages of the for- favor understorybiodiversity are presentedin Box 1. est. Moreover, because the planted species are usually shade There are difficulties and risks associated with the use of plantationsto rehabilitatedegraded lands. For example, research is needed on species selection to avoid failures and excessive expenses in site preparationand planting. If exotic species are used, there is a danger of the species escaping and invading natural areas. Proper species selection and adaptability trials minimize these risks. As with all managementactivities, cost is always a factor as is the need not to abandontreatments before they achieve the plannedgoal.

MANAGINGCHANGES IN BIODIVERSITY are changing the landscape and altering the ecological balance that prevailedprior to the onset of large-scale, intensive humanactivity. Species extinctions, loss, anddegradation Management practices that facilitate natural successional processes and the development of species-rich understories would be a primary of landscapesand ecosystems have understandablybeen viewed management goal. Photo: C. Folke. with alarm and have raised public consciousness of the need to

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108 AMBIO VOL. 22 NO. 2-3, MAY 1993 References and Notes 1. McArthur,R.H. and E.O. Wilson. 1967.The Theory ofIslandBiogeography. Monographs in PopulationBiology 1. PrincetonUniversity Press, Princeton,New Jersey. 203 p.22. 2. Lovejoy, T.E. 1980. A projectionof species extinctions. In: The global 2,000 Reportto the President.Barney, G.O. (ed). Council on EnvironmentalQuality, Washington, D.C., p. 328-33 1. 3. Simberloff,D. 1986. Are we on the verge of a mass extinctionin tropicalrain forests? In: Dynamics of Extinctions.Elliot, D.K. (ed.). John Wiley and Sons, N.Y., p. 165-180. 4. Lugo, A. E. 1988a. Estimatingreductions in the diversity of tropicalforest species. In: Biodiversity.Wilson, E.O. and Peters,F.M. (eds). NationalAcademy Press, Washington, DC, p. 58-70. 5. Lugo, A.E. 1988. The future of the forest ecosystem rehabilitationin the . Environment30, 16-20 and 41-45. 6. Nir, M.A. 1988. The survivors:orchids on a PuertoRican coffe finca. Am. OrchidSoc. Bull. 57, 989-995. 7. Wunderle,J.M. and R.B. Waide. 1992. Distributionof OverwinteringNearctic Migrants in the Bahamtasand Greater Antilles. Report to the World Fund. Instituteof Tropical Forestry,USDA Forest Service, Rio Piedras,P.R. 8. Margalef,R. 1963. On certain unifying principles in ecology. Am. Nat. 97, 357-374. 9. Williamson, M. 1981. Island . Oxford University Press, Oxford, England. 286 p. 10. Beard,J.S. 1949. The naturalvegetation of the Windwardand Leewardislands. Oxford Forestry MemoirsNo. 21. ClarendonPress, Oxford. 192 p. 11. Holdridge,L.R., W.C. Grenke, W.H. Hatheway,T. Liang and J.A. Tosi. 1971. Forest While we must curtail many of the senseless human activities that Environmentsin TropicalLife Zones, a Pilot Study.Pergamon Press, N.Y. 747 p. 12. Brash,A.R. 1987. The historyof avian extinction and forest conversion on PuertoRico. needlessly destroy the ecological balance of , we must also turn Biol. Conserv. 39, 97-111. our attention to positive actions that reverse the negative impacts of 13. Bhaskar,V. andDasappa. 1986. Groundflora in Eucalyptusplantations of differentages. humans. Photo: G. Nycander. In:Eucalypts in India: Past, Presentand Future.Proceedings of a Seminarheld at Kerala Forest ResearchInstitute, Peechi, India, p. 213-224. 14. Chaubey,O.P., R. Prasadand G.P. Mishra. 1988. Studies of plantationand mixed naturalforests in MadhyaPradesh. J. Trop. For. 4, 22-35. 15. Lugo, A.E. 1992. Comparisonof tropical tree plantationswith secondary forests of similar age. Ecol. Monogr. 62, 1-41. preservecritical habitats and conserve Earth' s biological heritage. 16. Lugo, A.E. 1993. Tree plantationsfor rehabilitatingdamaged forest lands in the tropics. In: EnvironmentalRehabilitation. Wali, M.K. (ed.). SPB Academic Publishing , The While we must curtailmany of the senseless humanactivities that Hague, The Netherlands.(In Press). needlessly destroy the ecological balance of Earth,we must also 17. Mathur,H.N. and P. Soni. 1983. Comparativeanalysis of undergrowthunder and sal in three different localities of Doon Valley. Indian For. 109, 882-890. turn our attention to positive actions that reverse the negative 18. Mathur, H.N., N. Jain and S.S. Sajwan. 1980. Ground cover and undergrowthin impactsof humans.With regards to biodiversity,it is clearthat the Eucalyptus,brushwood and sal forest - an ecological assessment. Van Vigyan18, 56-6 1. 19. Panden,P.K., A.P.S. Bisht and S.C. Sharma. 1988. Comparativevegetation analysis of models that we use to anticipatethe futurecondition of the biota some plantationecosystems. Indian For. 114, 379-389. (Fig. 1) provide a wide range of scenarios that 20. Parrotta,J.A. 1992. The role of plantationforests in rehabilitatingdegraded tropical depend on the ecosystems. Agriculture,Ecosystems, and the Environment41, 115-133. species-area relationship(Z value) at each location. Given the 21. Parrotta,J.A. 1993. Secondaryforest regenerationon degradedtropical lands: the role of plantationsas 'foster ecosystems'. In: Restorationof TropicalForest Ecosystems.Lieth geographicalvariability of the Z value and the limitationsof the H. and Lohmann,M (eds). Kluwer Academic Publishers,Dortrecht, The Netherlands. approach,forecasting changes in biodiversity becomes highly 22. Soni, P., H.B. Vasisthaand 0. Kumar.1989. Biological diversity in surface mined areas after reclamation.Indian For. 115, 475-482. problematic.Moreover, these models appearto overestimatethe 23. Srivastava,V.K. 1986. Diversity anddominance in two man-madeforests at DehraDun, numberof extinctionsbecause they don't take into consideration India.Indian J. For. 9, 287-292. 24. Brown, S. and A.E. Lugo. 1990. Tropical secondaryforests. J. Trop. Ecol. 6, 1-32. ecological resiliency,habitat variability, nor the abilityof humans 25. Cruz,A. 1987. Avian communityorganization in a mahoganyplantation on a neotropical to reverse trendsin losses island. CaribbeanJ. Sci. 23, 286-296. species throughmanagement. 26. Cruz, A. 1988. Avian resourceuse in a Caribbeanpine plantation.J. Wildl.Manage. 52, We suggest the use of plantationsas one possible mechanism 274-279. 27. Lugo, A.E., E. Cuevas and M.J. Sdnchez. 1990a. Nutrientsand mass in litterand top soil to restorediverse ecosystems in degradedlands. There are other of ten tropicaltree plantations.Plant and Soil 125, 263-280. actions that can be used to restore or maintain biodiversity in 28. Lugo, A.E., D. Wang and F.H. Bormann. 1990. A comparativeanalysis of biomass productionin five tropicaltree species. For. Ecol. Manage. 31, 153-166. managed landscapes (Box 2). However, our main point is that 29. Cuevas, E., S. Brown and A.E. Lugo. 1991. Above- and belowgroundorganic matter land managementoffers an opportunityfor humans to redirect storage and productionin a tropical pine plantationand a paired broadleafsecondary forest. Plant and Soil 135, 257-268. the changes in biodiversityand in some cases to reversenegative 30. Wang, D., F.H. Bormann,A.E. Lugo and R.D. Bowden. Comparisonof nutrient-use efficiency and biomass productionin five tropical tree taxa. For. Ecol. Manage. 46, trends. 1-21.

Figure 3. Relationship between number of tree and understory species and age of secondary forests. The relationship is y = 41.89 + 0.97 x (r2 = 0.26). Data were for 22 plots ranging in age from 1-31 yr in tropical wet to dry forest life zones resulting from abandonment of agriculture, mostly shifting cultivation. Only plots with areas of < 0.05 ha were selected to be more in line with the plantation data. All data are from Brown and Lugo (24).

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Ariel E. Lugo is the director of the International Institute of Tropical Forestry (IITF). John A. Parrotta is a scientist in the (IITF). Their address: International Institute of Tropical Forestry, USDA Forest Service, Call Box 25000, Rio Piedras, Puerto Rico 00928-2500. Sandra Brown is professor at the University of . Her address: Department of Forestry, I X i; University of Illinois, W-503 Turner Hall, 1102 S. Goodwin, Urbana, IL 61801, USA. All of the authors are active in tropical forestry research in , the Caribbean, and Asia.

AMBIO VOL. 22 NO. 2-3, MAY 1993 109