10 Litter Dynamics in Plantation and Agroforestry Systems of the Tropics—A Review of Observations and Methods B. Mohan Kumar CONTENTS 10.1 Introduction 182 10.2 Litterfall Rates in Tropical Plantations Parallel Site Productivity 183 10.3 Variations in Litterfall Fluxes in Tropical Plantations 184 10.3.1 Basal Area and Stand Age 184 10.3.2 Species Attributes 184 10.3.3 Species Mixtures 189 10.3.4 Site Characteristics 189 10.3.5 Temporal Variations 190 10.3.6 Perturbations 190 10.3.7 Tree Management Practices 190 10.4 Proximate Composition of Litter 191 10.5 Methodological Aspects of Litterfall Studies 191 10.5.1 Litter Trap Design 191 10.5.2 Sampling Errors 192 10.5.3 Analysis of Litterfall Data 192 10.6 Litter Decomposition 193 10.6.1 Substrate Quality 193 10.6.2 Site Quality and Exogenous Nutrient Additions 201 10.6.3 Temperature and Soil Moisture 201 10.6.4 Soil Microfaunal and Macrofaunal Activity 203 10.6.5 Lower Decay Rates of Tropical Plantations Than Native Forests 203 10.6.6 Do Perturbations Red uce Litter Decay Rates? 204 10.6.7 Nature of Decomposing Matter and Its Processing 204 10.6.8 Methodological Aspects in Litter Decomposition Studies 205 10.6.8.1 Modified Litterbag Technique of Bubb et al. (1998) 206 10.6.8.2 Tethered Leaf Tec hnique 206 10.6.9 Analysis of Litter Decay Data 207 10.7 Nutrient Release from Decomposing Litter 207 10.8 Research Needs and Conclusions 208 References 209 Batish et al./Ecological Basis of Agroforestry 43277_C010 Final Proof page 181 4.10.2007 8:26pm Compositor Name: VBalamugundan 181 Copyright 2008 by Taylor and Francis Group, LLC 10.1 INTRODUCTION Establishing forest plantations to meet the ever-increasing demand for tree products has been a long- standing tradition in the tropics (Evans, 1982), albeit it gained momentum only after the Second World W ar. According to FAO (2001), the area under tropical forest plantations has increased at an estimated annual rate of 1.9 million ha reaching about 68 million ha in the late 1990s. Of this, India alone has about 32.58 million ha. Other important tropical countries with significant area under forest plantations areas are Indonesia (9.87 million ha), Brazil (4.98 million ha), Thailand (4.92 million ha), Vietnam (1.71 million ha), Venezuela (0.86 million ha), Myanmar (0.82 million ha), Bangladesh (0.63 million ha), Cuba (0.48 million ha), and Madagascar (0.35 million ha). The humid tropics are also characterized by diverse land use systems that integrate woody perennials with other life forms, called agroforestry. Although precise area estimates of agroforestry-type land use are not available, it probably covers a substantial part of the tropics (Nair, 1993). Overall, the man-made forests and agroforests are thought to ease pressure on the tropical forests, which are ‘‘our doomed warehouses of global biodiversity’’ (Ewel, 1999). Although agroforestry is generally regarded as sustainable (see Kumar and Nair, 2004), foster- ing quick rotation plantations to resolve the chronic wood shortages faced by millions of people in the tropical regions has raised concerns about its sustainability (Nambi ar, 1996; Vance, 2000). Loss of nutrients during the harvest, especially when rotations are short, may exceed the rate of replenishment by weathering of minerals and by atmospheric inputs (Kumar et al., 1998a) implying that site quality deterioration is alm ost a cliché (Goncalves et al., 1997). Furthermore, the global warming accelerates soil organic matter (SOM) oxidation, making degradation of nutrient-poor soils faster in the tropics (Walker and Steffen, 1997; Seneviratne, 2000). Consequently, there is a major uncertainty, that is, whether the tropical tree plantations and agroforests could be grown perpetually on the same site without serious risk to their vitality and productivity. To be sustainable, a managed land use system should imitate the structure and functioning of natural ecosystems, which are the results of natural selection over long periods (Ewel, 1999). That is, the dynamics of litterfall, decomposition, and the subsequent bioelement release, which play a fundamental role in the stability of natural ecosystems (see reviews by Bray and Gorham, 1964; Singh and Gupta, 1977; Swift et al., 1979; Brown and Lugo, 1980; Vogt et al., 1986; Ewel et al., 1991; Facelli and Pickett, 1991; Caldentey et al., 2001) should be relevant to the man-made forests and agroforests too (Cuevas and Medi na, 1988; Grigal and Vance, 2000). Although plant litter is an important source of ‘‘slow-release’’ nutrients, questions relating to organic matter turnover in the managed tropical land use systems did not receive adequate attention in the past. With the advent of ‘‘organic’’ farming practices, however, resear ch on addition and decomposition of fresh agricultural wastes, green manure and litter may regain some of its past glory in the ‘‘prechemical’’ farming era (see reviews by Kumar and Goh, 2000; Palm et al., 2001). Tropical forest plantations and agroecosystems also involve diverse kinds of trees, and their impact on the nutrient cycling process is probably variable. It is, therefore, essential to have a clear understanding of the tree species’ impacts on various aspects of SOM dynamics and nutrient cycling, including the effects of litter green manure additions on soil nutrient availability. In addition, small farmers with limited access to chemical fertilizers often remove detritus from the plantation or forest floor for use in their fields or homegardens (Byard et al., 1996; Russell et al., 1997). The impacts of such litter transfer on the nutrient dynamics of the plantation and the agroecosystems have been seldom addressed. Therefore, the current state of knowledge on litter dynamics of managed land use systems in the tropical region and their potentially important role in maintaining soil fertility are summarized here. In particular, variations in litterf all production and the factors affecting litter decomposition, will be analyzed. The need to have consistency in the methodology used for characterising litterfall and decay, and aspects relating to nutrient release from litter cannot be overstated. The paucity of information on nutrient release from litter and its synchrony with nutrient uptake by the associated crops is in part due to the inconsistent experimental approaches. So, the methodological aspects of characterising litterfall and decay rates will be addressed in this chapter. Batish et al./Ecological Basis of Agroforestry 43277_C010 Final Proof page 182 4.10.2007 8:26pm Compositor Name: VBalamugundan 182 Ecological Basis of Agroforestry Copyright 2008 by Taylor and Francis Group, LLC 10.2 LITTERFALL RATES IN TROPICAL PLANTATIONS PARALLEL SITE PRODUCTIVITY Following from the inverse relationship between total detritus production and latitude of the region, which inter alia represents a productivity gradient (Bray and Gorham, 1964), litterfall is an important covari ate of aboveground biomass production. To further gauge the nature of interrela- tionships between litterfall and productivity in plantations, published data on plantati on or agro- forest productivity and litterfall were examined. Figure 10.1 shows that total litterfall increased y = 0.0325x + 2.328 R 2 = 0.83, n = 13, p < 0.0001 0 5 10 15 Total aboveground biomass (Mg ha −1 ) Litterfall (Mg ha −1 yr −1 ) y = 0.3734x + 3.2496 R 2 = 0.17, n = 13, p = 0.155 0 5 10 15 Foliar biomass (Mg ha −1 ) Litterfall (Mg ha −1 yr −1 ) (b) (c) (a) y = 0.2276x + 2.5506 R 2 = 0.61, n = 13, p = 0.00163 0 5 10 15 Above g round biomass MAI (M g ha −1 y r −1 ) Litterfall (Mg ha −1 yr −1 ) 0 0 0 10203040 51015 50 100 150 200 250 300 350 FIGURE 10.1 Relationships between mean annual litterfall and (a) total aboveground biomass yield, (b) foliar biomass, and (c) total aboveground mean annual increment of nine tree species of two age classes (8.8 and 5 years) and grown under two experimental protocols in Kerala, India. (Compiled from the biomass data presented in Kumar, B.M., S.J. George, V. Jamaludheen and T.K. Suresh, Forest. Ecol. Manag., 112, 145, 1998a and from the litterfall data given in George, S.J. and B.M. Kumar, Int. Tree Crops J., 9, 267, 1998 and Jamaludheen, V. and B.M. Kumar, Forest Ecol. Manag., 115, 1, 1999.) Batish et al./Ecological Basis of Agroforestry 43277_C010 Final Proof page 183 4.10.2007 8:26pm Compositor Name: VBalamugundan Litter Dynamics in Plantation and Agroforestry Systems of the Tropics 183 Copyright 2008 by Taylor and Francis Group, LLC linearly with total aboveground biomass yield and biomass mean annual increment (MAI). Although this is consistent with the findings of Lugo (1992) and Parrotta (1999), due to the complex interactions among environmental factors, productivity, and biomass allocation patterns, and because the same environmental factors influence both productivity and litterfall, such relationships should not be considered as simple cause-and-effect. A key question is whether there is a direct link between litterfall and the micrometeorological parameters. In this respect, Brown and Lugo (1980) obtained a significant quadratic relationship between annual litter production and the temperature to precipitation (T=P) ratio of the site, which paralleled the biomass–T=P curve. Furthermore, increasing atmospheric concentration of CO 2 (currently at 1.8 ppm per annum) due to anthropogenic emi ssions is likely to increase the litterfall rates. This is because plant biomass production and net terrestrial carbon storage may increase as atmospheric CO 2 concentrations increase (Amthor and Koch, 1996). However, little or no direct evidences are available in this respect (Kumar et al., 2005). 10.3 VARIATIONS IN LITTERFALL FLUXES IN TROPICAL PLANTATIONS Although the general pattern of higher litterfall rates in the tropical latitudes hold good on large spatial scales, such a relationship is often masked by within-zone variations. As a result, stand-level differences in annual litterfall abound (range: 1.02–14.5 Mg ha À1 yr À1 ; Table 10.1), and such variations generally reflect the underlying influence of stand age, basal area, species characteristics, and edaphic and climatic factors. 10.3.1 BASAL A REA AND STAND AGE Basal area and age structure are recognized as major determinants of litterfall (Lugo, 1992), yet there is no consensus on that. For instance, Arunachalam et al. (1998a) noticed a strong correlation (r ¼ 0.93, p < 0.05) between annual litter production and stand basal area in three regrowing forest stands on a shifting cultivation site in northeastern India. Many others (Kumar and Deepu, 1992; Parrotta, 1999; McDonald and Healy, 2000), however, thought that litterfall rates did not directly relate to stand basal area and density, especially in old-growth stands. Understandably, in young developing stands, annual litterfall rates increase as crown coverage increases (with age and stand basal area), and it plateaus out at about the same time as that of canopy closure. It then follows an asymptotic pattern similar to that of gross primary production and may decline in very old stands. It can thus be concluded that peak litterfall for a wide range of stands under steady-state conditions is independent of stand basal area and stand density. However, the rate at which this equilibrium is approached is not; and denser stands may reach this equilibrium faster than sparse stands. 10.3.2 SPECIES ATTRIBUTES Species-related variations in quantity as well as periodicity of litterfall in managed tropical land use systems are paramount. For instance, mean annual litterfall of 49 tropical species ranged from 1.02 ( Eucalyptus tereticornis) to 14.5 Mg ha À1 yr À1 (Pinus caribaea; Table 10.1). Some authors argue that evergreen versus deciduous habit and N-fixing ability of the tree species are major determinants in this respect, in addition to their biomass production potential (Bray and Gorham, 1964; Swamy and Proctor, 1994). Therefore, the question of whether evergreen trees produce more or less litter than deciduous tree species was examined using two experimental datasets (Cuevas and Lugo, 1998; Jamaludheen and Kumar, 1999) of 11 evergreen (range in litterfall: 3.9–14.3 Mg ha À1 yr À1 ; Figure 10.2) and 7 deciduous tropical tree species (range 3.4–10.8 Mg ha À1 yr À1 ). Surprisingly, the results of homoscedastic t-test comparing functional categories such as evergreen and deciduous species were not significant (t statistic ¼ 1.4703; p (T t) one-tail ¼ 0.0804), signifying that the differences among species within a functional category exceed the variations Batish et al./Ecological Basis of Agroforestry 43277_C010 Final Proof page 184 4.10.2007 8:26pm Compositor Name: VBalamugundan 184 Ecological Basis of Agroforestry Copyright 2008 by Taylor and Francis Group, LLC TABLE 10.1 Total Litterfall and Standing Crop of Litter in Tree Plantations and Agroforestry Systems in the Tropics Species or Agroforestry System Location Stand Age (years) Litterfall (Mg ha À1 yr À1 ) Source Acacia auriculiformis Ibadan, Nigeria 3 6.92 Salako and Tian (2001) Ibadan, Nigeria 7 12.11 Salako and Tian (2001) Kerala, India (woodlot) 8.8 12.7–12.9 Kunhamu et al. (1994); Jamaludheen and Kumar (1999) Palakkad, Kerala, India (silvipasture; pruned) 5 6.27 George and Kumar (1998) Acacia leptocarpa Ibadan, Nigeria 3 7.60 Salako and Tian (2001) Ibadan, Nigeria 5 10.7 Salako and Tian (2001) Acacia nilotica Karnal, India (alkaline soil) 4 2.5 Gill et al. (1987) Karnal, India (alkaline soil) 5 3.8 Gill et al. (1987) Karnal, India (alkaline soil) 6 4.9 Gill et al. (1987) Karnal, India (alkaline soil) 7 5.7 Gill et al. (1987) Ailanthus triphysa Palakkad, Kerala, India (woodlot) 8.8 4.57 Jamaludheen and Kumar (1999) Palakkad (pruned silvipasture) 5 1.92 George and Kumar (1998) Albizia stipulata– Citrus reticulata Sikkim, India — 3.7 Sharma et al. (1997) Alnus nepalensis Darjeeling, India 7 3.15 Sharma and Ambasht (1987) Darjeeling, India 17 5.20 Sharma and Ambasht (1987) Darjeeling, India 30 5.66 Sharma and Ambasht (1987) Darjeeling, India 46 5.79 Sharma and Ambasht (1987) Darjeeling, India 56 5.45 Sharma and Ambasht (1987) Amomum subulatum þ Alnus nepalensis Sikkim, India — 7.3 Sharma et al. (1997) Amomum subulatum þ Forest Sikkim, India 4.6 Sharma et al. (1997) Anthocephalus chinensis Puerto Rico 26 8.1 Cuevas and Lugo (1998) Artocarpus heterophyllus Palakkad, Kerala, India 8.8 6.23 Jamaludheen and Kumar (1999) Artocarpus hirsutus Palakkad, Kerala, India 8.8 3.92 Jamaludheen and Kumar (1999) Casuarina equisetifolia Palakkad, Kerala, India 8.8 6.44 Jamaludheen and Kumar (1999) Palakkad (silvipasture; pruned) 5 2.31 George and Kumar (1998) Puerto Rico 1.5–3.5 8.61 Parrotta (1999) Casuarina þ Eucalyptus Puerto Rico (50:50 mixture) 1.5–3.5 7.74 Parrotta (1999) Casuarina þ Leucaena Puerto Rico (50:50 mixture) 1.5–3.5 9.98 Parrotta (1999) Citrus reticulata Sikkim, India — 3.8 Sharma et al. (1997) Coffea arabica þ Erythrina poeppigiana Turrialba, Costa Rica (inclusive of pollarded shade tree litter) 13 3.70 Glover and Beer (1986) (continued ) Batish et al./Ecological Basis of Agroforestry 43277_C010 Final Proof page 185 4.10.2007 8:26pm Compositor Name: VBalamugundan Litter Dynamics in Plantation and Agroforestry Systems of the Tropics 185 Copyright 2008 by Taylor and Francis Group, LLC TABLE 10.1 (Continued) Total Litterfall and Standing Crop of Litter in Tre e Plantations and Agroforestry Systems in the Tropics Species or Agroforestry System Location Stand Age (years) Litterfall (Mg ha À1 yr À1 ) Source Coffea arabica þ Erythrina poeppigiana þ Cordia alliodora Turrialba, Costa Rica (inclusive of pollarded shade tree litter) 13 6.65 Glover and Beer (1986) Cupressus lusitanica Central highlands, Ethiopia 28 5.01 Lisanework and Michelsen (1994) Dalbergia sissoo India — 4.75 Rajvanshi and Gupta (1985) Dendrocalamus hamiltonii Meghalaya, India (jhum fallow) 10 3.50 Toky and Ramakrishnan (1982) Meghalaya, India (jhum fallow) 15 3.90 Toky and Ramakrishnan (1982) Meghalaya, India (jhum fallow) 20 5.20 Toky and Ramakrishnan (1982) Dendrocalamus strictus Pauri Garhwal, UP, India (257–360 clumps ha À1 , 49%–62% ground coverage) — 0.35–0.58 Joshi et al. (1991) East Mirzapur, UP, India (dry tropical bamboo savanna) 5 a 7.18 Tripathi and Singh (1994) East Mirzapur, UP, India (dry tropical bamboo savanna) 1 a 4.08 Tripathi and Singh (1994) Eucalyptus globulus Central highlands, Ethiopia (lignotubers) 40 5.83 Lisanework and Michelsen (1994) Eucalyptus cf. patentinervis Puerto Rico 26 11.12 Cuevas and Lugo (1998) Eucalyptus robusta Puerto Rico 1.5–3.5 5.42 Parrotta (1999) Eucalyptus saligna Puerto Rico 25 13.17 Cuevas and Lugo (1998) Hawaii, USA 4 7–9 Binkley et al. (1992) Eucalyptus saligna þ Albizia falcataria mixed stand Hawaii, USA 4 12–13 Binkley et al. (1992) Eucalyptus tereticornis Karnal, India (alkaline soil) 4 1.02 Gill et al. (1987) Karnal, India (alkaline soil) 5 1.07 Gill et al. (1987) Karnal, India (alkaline soil) 6 1.10 Gill et al. (1987) Karnal, India (alkaline soil) 7 1.13 Gill et al. (1987) Pantnagar, India (associated with aromatic grass) 4 4.6 Singh et al. (1989) Eucalyptus þ Leucaena Puerto Rico (50:50 mixture) 1.5–3.5 8.87 Parrotta (1999) Hardwickia binata Jhansi, India (silvipasture) 23 8.15 Roy et al. (1998) Hernandia sonora Puerto Rico 26 8.96 Cuevas and Lugo (1998) Hevea brasiliensis Bendel State, Nigeria 23 10.23–13.67 Onyibe and Gill (1992) Gigantochloa spp. West Java, Indonesia (bamboo talun–kebun system) Early fallow 2.0 Christanty et al. (1996) West Java, Indonesia (bamboo–talun–kebun system) Mature stand 3.5 Christanty et al. (1996) Batish et al./Ecological Basis of Agroforestry 43277_C010 Final Proof page 186 4.10.2007 8:26pm Compositor Name: VBalamugundan 186 Ecological Basis of Agroforestry Copyright 2008 by Taylor and Francis Group, LLC TABLE 10.1 (Continued ) Total Litterfall and Standing Crop of Litter in Tree Plantations and Agroforestry Systems in the Tropics Species or Agroforestry System Location Stand Age (years) Litterfall (Mg ha À1 yr À1 ) Source Hibiscus elatus Puerto Rico 26 13.7 Cuevas and Lugo (1998) Juniperus procera Central highlands, Ethiopia 40 10.87 Lisanework and Michelsen (1994) Khaya nyasica Puerto Rico 26 10.8 Lisanework and Michelsen (1994) Leucaena leucocephala Ibadan, Nigeria 3 8.78 Salako and Tian (2001) Ibadan, Nigeria 7 10.05 Salako and Tian (2001) Palakkad, Kerala, India (silvipasture; pruned) 5 2.30 George and Kumar (1998) Palakkad, Kerala, India (woodlot) 8.8 5.09 Jamaludheen and Kumar (1999) Puerto Rico 1.5–3.5 9.69 Parrotta (1999) Paraserianthes falcataria (syn. Albizia falcataria) Kerala, India 8.8 9.17 Jamaludheen and Kumar (1999) Hawaii, USA 4 18.0 Binkley et al. (1992) Phyllanthus emblica Kerala, India 8.8 5.18 Jamaludheen and Kumar (1999) Phyllostachys pubescens South China — 3.1–5.0 Maoyi et al. (1990) Pinus caribaea var. hondurensis Puerto Rico 4 2.1–7.4 Lugo (1992) Puerto Rico 18.5 12.9–14.5 Lugo (1992) Puerto Rico 26 14.33 Cuevas and Lugo (1998) Pinus elliottii var. densa Puerto Rico 26 11.35 Cuevas and Lugo (1998) Pinus merkusii Merapi, Java, Indonesia 30 9.0 Gunadi (1994) Merbau, Java, Indonesia 25 4.0 Gunadi (1994) Populus deltoides Tarai, India 1 2.0 Lodhiyal and Lodhiyal (1997) Tarai, India 2 3.5 Lodhiyal and Lodhiyal (1997) Tarai, India 3 4.5 Lodhiyal and Lodhiyal (1997) Tarai, India 4 6.7 Lodhiyal and Lodhiyal (1997) Dehra Dun, India 13 3.08 Raizada and Srivastava (1986) Pantnagar, India (associated with aromatic grass) 4 4.5 Singh et al. (1989) Pterocarpus marsupium Kerala, India 8.8 3.42 Jamaludheen and Kumar (1999) Senna siamea Ibadan, Nigeria 3 7.78 Salako and Tian (2001) Ibadan, Nigeria 7 10.37 Salako and Tian (2001) Sphaerobambos philippinensis Davao del Norte, Philippines 4 6.72–12.58 Virtucio et al. (1994) Swietenia macrophylla Puerto Rico 17 10–12.1 Lugo (1992) Puerto Rico 40 5.40 Cintrón and Lugo (1990) Puerto Rico 49 10.7–14.1 Lugo (1992) Puerto Rico 26 9.80 Cuevas and Lugo (1998) (continued ) Batish et al./Ecological Basis of Agroforestry 43277_C010 Final Proof page 187 4.10.2007 8:26pm Compositor Name: VBalamugundan Litter Dynamics in Plantation and Agroforestry Systems of the Tropics 187 Copyright 2008 by Taylor and Francis Group, LLC between categories. This probably masks any influence of the evergreen versus deciduous nature of trees on litterfall rates. N-fixing species are widely extolled for their soil improving properties, which are partly related to their ability to produce nitrogen-rich litter (MacDicken, 1994). N-fixing species such as Casu- arina equisetifolia and Acacia auriculiformis reportedly accumulate large quantities of organic matter on the forest floor (Mailly and Margolis, 1992; Kunhamu et al., 1994). Data from Jama- ludheen and Kumar (1999) further exemplify this. They showed that exotic N-fixing species such as A. auriculiformis, Paraserianthes falcataria, and C. equisetifolia accounted for the three highest litterfall rates (6.44–12.69 Mg ha À1 yr À1 , Table 10.1) among nine multipurpose tree species studied. Pterocarpus marsupium, another indigenous legume, however, showed the lowest litterfall TABLE 10.1 (Continued ) Total Litterfall and Standing Crop of Litter in Tre e Plantations and Agroforestry Systems in the Tropics Species or Agroforestry System Location Stand Age (years) Litterfall (Mg ha À1 yr À1 ) Source Terminalia ivorensis Puerto Rico 23 9.26 Cuevas and Lugo (1998) Theobroma cacao þ Cordia alliodora Turrialba, Costa Rica (shade trees pollarded) 4.5 4.19 Alpizar et al. (1986) T. cacao þ Erythrina poeppigiana Turrialba, Costa Rica (shade trees pollarded) 4.5 1.78 Alpizar et al. (1986) T. cacao þ Hevea brasiliensis Thrissur, Kerala, India (excluding overstory litter) 7 5.32 Sreekala (1997) T. cacao (no overstory) Thrissur, Kerala, India (excluding overstory litter) 7 8.23 Sreekala (1997) Triplochiton scleroxylon Nigeria Young stand 7.44 Orimoyegun (1985) Natural fallow Ibadan, Nigeria — 7.7 Salako and Tian (2001) a Time after last harvest; pruned means the trees were pruned to facilitate grass growth in the interspaces; information not available. 0 5 10 15 20 PC HE ES AA PE EP PF CE AH LE Ah KN SM TI AC PE AT PT Species Litterfall (Mg ha −1 yr −1 ) FIGURE 10.2 Annual litterfall of 18 evergreen and deciduous tropical trees. PC—Pinus caribaea var. hondurensis,HE—Hibiscus elatus,ES—Eucalytpus saligna,AA—Acacia auriculiformis,PE—Pinus elliottii var. densa,EP—Eucalyptus cf. patentinervis,PF—Paraserianthes falcataria,CE—Casuarina equisetifolia, AH—Artocarpus heterophyllus,LE—Leucaena leucocephala,Ah—Artocarpus hirsutus,KN—Khaya nyasica,SM—Swietenia macrophylla,TI—Terminalia ivorensis,AC—Anthocephalus chinensis, PE—Phyllanthus emblica,AT—Ailanthus triphysa,PT—Pterocarpus marsupium. (From Cuevas, E. and A.E. Lugo, For. Ecol. Manage., 112, 263, 1998; Jamaludheen, V. and B.M. Kumar, For. Ecol. Manage., 115, 1, 1999.) Batish et al./Ecological Basis of Agroforestry 43277_C010 Final Proof page 188 4.10.2007 8:26pm Compositor Name: VBalamugundan 188 Ecological Basis of Agroforestry Copyright 2008 by Taylor and Francis Group, LLC (3.42 Mg ha À1 yr À1 ; Table 10.1), denoting a paradox in the litter production potential of woody tropical legumes. Some authors (e.g., O’Connell and Sankaran, 1997) also asserted that exotic plantation species, regardless of N fixing or not, generally have a higher standing crop of litter. This can perhaps be rationalized by their higher biomass production potentials and lower decay rates (explained elsewhere). Data presented in Figure 10.1 clearly show that the high litter-producing trees con- comitantly showed higher biomass production potential suggesting that more than the geographic origin (i.e., indigenous vs. exotic), growth habit (deci duous vs. evergreen), and N-fixation ability, the potential for high growth rates determines litterfall rates. Although it cannot be reasoned that biomass production potential of species exerts a cause–effect relationship on litterfall, it is perhaps the best indicator of litterfall rates. Implicit in this is also the possibility of differential litter production capacities for different clonal lines or provenances because of the variations in production potential and growth habits. Although data on litterfall potentials owing to clonal variations in forest trees are not readily available, in one study dealing with three clones of rubber (Hevea brasiliensis), Onyibe and Gill (1992) found that variations among tree clones in litterfall production were not statistically signifi- cant. More experimentation is, perhaps, necessary to make firm conclusions in this respect. 10.3.3 SPECIES MIXTURES Since litterfall rates generally parallel the trend in biomass productivity, higher litter yield is probable in mixed species stands, as they are intrinsically more productive than monospecific stands (sensu. Binkley et al., 1992). However, most studies on litterfall in tropical plantations have been conducted in monospecific stands. A notable exception is that of Parrotta (1999), who in a comparative study of single- and mixed-species plantations of C. equisetifolia, Eucalyptus robusta, and Leucaena leucocephala, found that mixed-species stands had higher litterfall rates than monospecific stands, despite variations in species attributes (Table 10.1). 10.3.4 SITE CHARACTERISTICS Fixed-site characteristics such as latitude, altitude, and aspect may strongly affect the litterfall dynamics. Perhaps there are three factors influencing productivity and biomass allocation strategies, and consequently, litter production along a latitudinal or altitudinal gradient—the energy budget , the hydrological regimes, and changes in plant growth form. The tropical zone is often characterized by a constant radiation surplus and general thermic uniformity; temperatures are often closer to the optimum for plants, and hence, it is reasonable to expect higher litterfall production rates there. In addition, the higher temperatures may accelerate leaf fall rates, especially when it is not limiting plant growth. Consistent with this, Gwada et al. (2000) showed that temperature increases between 208C and 288C stepped up leaf production and abscission rates in Kandelia candel, a mangrove species. In the moist forests of Western Ghats, Bhat and Murali (2001) also found that leaf abscission is more when the temperature increases and when the day length is short, signifying a higher amount of fine litterfall under warmer temperature and shorter photoperiodic regimes. Rainfall and actual evapotranspiration determine the hydrological regime of a site. Sites with plentiful supplies of water and nutrients will allow trees to grow quickly and attain a large leaf area index, in turn producing more leaf litter. Paradoxically, reduced water availability triggers leaf fall. Thus, soil-water retention and soil fertility are important determinants of litterfall quantity and composition within the same climatic range (Facell i and Pickett, 1991). Other workers too (Swift et al., 1979; Bernhard-Reversat, 1993) have noted that the type of soil would generally determine the rate of litterfall and its subseq uent decay dynamics. A limited amount of data also indicates that adverse soil parameters such as soil acidity, salinity, sodicity, and water logging may depress primary production and litterfall rates. For example, Eusse and Aide (1999) reported that litter Batish et al./Ecological Basis of Agroforestry 43277_C010 Final Proof page 189 4.10.2007 8:26pm Compositor Name: VBalamugundan Litter Dynamics in Plantation and Agroforestry Systems of the Tropics 189 Copyright 2008 by Taylor and Francis Group, LLC production of Pterocarpus officinalis decreased along a gradient of soil salinity and was twice greater at the low-salinity site than at the high-salinity site. 10.3.5 TEMPORAL VARIATIONS Litterfall for deciduous species especially is an episodic process, with conspicuous peaks corres- ponding either to the beginn ing or near the end of the dry period. A plausible explanation is that water or temperature stresses activate the de novo synthesis of abscissic acid in the foliage (Kumar and Deepu, 1992); thus annual or seasonal drought (Cintrón and Lugo, 1990) and hot winds may produce large pulses of leaf fall. Coinci dentally, litterfall for most species follows a unimodal distribution pattern with a distinct peak either during the dry season (Raizada and Srivastava, 1986; Pascal, 1988; Joshi et al., 1991) or during the winter season (Gill et al., 1987; Cintrón and Lugo, 1990). In some cases it, however, coincided with the peak rainfall events, for example, the Puerto Rican plantations studied by Lugo (1992) and the P. officinalis stands examined by Eusse and Aide (1999). Although unimodal litterfall pattern is most common for tropical species (e.g., George and Kumar, 1998; Jamaludheen and Kumar, 1999), Gill et al. (1987) reported that litterfall in Acacia nilotica p lantations on the highly alkaline soils of north India followed a bimodal trend, with the principal peak during the winter and a minor one in early summer. Species also may respond to seasonal changes in soil salinity (Twilley et al., 1986) and day length (Cuevas and Lugo, 1998; Bhat and Murali, 2001). Overall, within-year and year-to-year variations in tropical trees mirror pronounced climatic or edaphic cues. 10.3.6 PERTURBATIONS Disturbances such as fire, wind, and hurricanes and damages due to droughts or diseases also induce large pulses of litterfall and may probably explain much of the observed seasonal and interannual variations (Bruederle and Streans, 1985; Adu-Bredu et al., 1997). High-velocity winds not only provoke premature abscission of already senescent leaves, but may also cause fall of other litter com- ponents (Caldentey et al., 2001). Windstorms are important in tree fall, but deposition of this component is highly variable in time and space (Sollins, 1982). Premature abscission of leaves by summer storm or through pathogenic infection (e.g., abnormal leaf fall in H. brasiliensis and other species) will not only change the seasonality of litterfall, but also ensures higher nutrient returns, as nutrient reabsorption from the prematurely shed foliage had not occurred. 10.3.7 TREE MANAGEMENT PRACTICES Thinning, pruning, and fertilization are important especially in managed stands of high-value crops. As regards to thinning, Caldentey et al. (2001) reported that annual litter flux decreased by 50% two years after a shelterwood cut wherein 55% of the initial basal area was removed. Stand thinning thus lowers litterfall rates but soon the stand would be back at the plateau of litterfall, if crown closure were quickly regained. Pruning the laterals at the beginning of the crop-planting season is typical of agroforestry and the pruned trees usually yield less litter (excluding pruned materials). In a study involving four tropical species grown in silvopastoral system in the humid tropical regions of Kerala with periodical pruning, George and Kumar (1998) indicated that annual addition of litter ranged from 1.92 to 6.25 Mg ha À1 , which was substantially lower than the litterfall recorded in woodlots (unpruned) at the same location (Jamaludheen and Kumar, 1999). Moreover, pruning alters the leaf fall periodicity, especially if significant quantities of foliar biomass are removed in such operations; it, nonetheless, provides a large pulse of nutrient-rich green manur e or fodder. Fertilization may enhance litterfall in tropical hardwood species, as it enhances the leaf biomass production. Experi- mental evidences are, however, variable. For instance, Tanner and Kapos (1992) reported that application of N þ P significantly increased litterfall in Venzuelan montane forests, 4 years after the Batish et al./Ecological Basis of Agroforestry 43277_C010 Final Proof page 190 4.10.2007 8:26pm Compositor Name: VBalamugundan 190 Ecological Basis of Agroforestry Copyright 2008 by Taylor and Francis Group, LLC [...]... Taylor and Francis Group, LLC Batish et al. /Ecological Basis of Agroforestry 43277_C 010 Final Proof page 196 4 .10. 2007 8:26pm Compositor Name: VBalamugundan 196 Ecological Basis of Agroforestry TABLE 10. 2 (Continued ) Monthly Litter Decay Rate Coefficients (k) and Half-Lives of Tropical and Subtropical Tree, Shrub, and Herbaceous Species in Plantations and Agroforestry Systems as Studied by the Litterbag... Taylor and Francis Group, LLC Batish et al. /Ecological Basis of Agroforestry 43277_C 010 Final Proof page 200 4 .10. 2007 8:26pm Compositor Name: VBalamugundan 200 Ecological Basis of Agroforestry TABLE 10. 2 (Continued ) Monthly Litter Decay Rate Coefficients (k) and Half-Lives of Tropical and Subtropical Tree, Shrub, and Herbaceous Species in Plantations and Agroforestry Systems as Studied by the Litterbag... high-quality materials (high N, low lignin, and low polyphenol) release a large proportion of N rapidly, in advance of the main period of Copyright 2008 by Taylor and Francis Group, LLC Batish et al. /Ecological Basis of Agroforestry 43277_C 010 Final Proof page 208 4 .10. 2007 8:26pm Compositor Name: VBalamugundan 208 Ecological Basis of Agroforestry N uptake by the actively growing plants Materials of. .. decomposition and CO2 evolution of some agroforestry fallow species in southern Nigeria Forest Ecology and Management 50 :103 –116 Copyright 2008 by Taylor and Francis Group, LLC Batish et al. /Ecological Basis of Agroforestry 43277_C 010 Final Proof page 214 4 .10. 2007 8:26pm Compositor Name: VBalamugundan 214 Ecological Basis of Agroforestry Ola-Adams, B.A and J.K Egunjobi 1992 Effects of spacing on litterfall and... (Binkley, 1992; Bernhard-Reversat, 1993; Sharma et al., 1997; Jamaludheen and Kumar, 1999) However, it cannot Copyright 2008 by Taylor and Francis Group, LLC Batish et al. /Ecological Basis of Agroforestry 43277_C 010 Final Proof page 194 4 .10. 2007 8:26pm Compositor Name: VBalamugundan 194 Ecological Basis of Agroforestry TABLE 10. 2 Monthly Litter Decay Rate Coefficients (k) and Half-Lives of Tropical and Subtropical... 2001) at a time, and up to 10 bags in certain cases (De Costa and Atapattu, 2001) The Statistical Copyright 2008 by Taylor and Francis Group, LLC Batish et al. /Ecological Basis of Agroforestry 43277_C 010 Final Proof page 206 4 .10. 2007 8:26pm Compositor Name: VBalamugundan 206 Ecological Basis of Agroforestry Law of ‘‘Inertia of large numbers’’ indicates that larger the size of the sample, more accurate... Vogt 1986 Production, turnover and nutrient dynamics of above- and belowground detritus of world forests Advances in Ecological Research 15:303–377 Copyright 2008 by Taylor and Francis Group, LLC Batish et al. /Ecological Basis of Agroforestry 43277_C 010 Final Proof page 216 4 .10. 2007 8:26pm Compositor Name: VBalamugundan 216 Ecological Basis of Agroforestry Walker, B and W Steffen 1997 The Terrestrial... Atapattu (2001) Batish et al. /Ecological Basis of Agroforestry 43277_C 010 Final Proof page 197 4 .10. 2007 8:26pm Compositor Name: VBalamugundan 197 Litter Dynamics in Plantation and Agroforestry Systems of the Tropics TABLE 10. 2 (Continued ) Monthly Litter Decay Rate Coefficients (k) and Half-Lives of Tropical and Subtropical Tree, Shrub, and Herbaceous Species in Plantations and Agroforestry Systems as Studied... LLC Batish et al. /Ecological Basis of Agroforestry 43277_C 010 Final Proof page 207 4 .10. 2007 8:26pm Compositor Name: VBalamugundan Litter Dynamics in Plantation and Agroforestry Systems of the Tropics 10. 6.9 ANALYSIS OF 207 LITTER DECAY DATA The general approach to the analysis of the decomposition data is the fitting of mathematical models to estimate constants that describe the loss of mass over time... Sankaran (1993) Batish et al. /Ecological Basis of Agroforestry 43277_C 010 Final Proof page 199 4 .10. 2007 8:26pm Compositor Name: VBalamugundan 199 Litter Dynamics in Plantation and Agroforestry Systems of the Tropics TABLE 10. 2 (Continued ) Monthly Litter Decay Rate Coefficients (k) and Half-Lives of Tropical and Subtropical Tree, Shrub, and Herbaceous Species in Plantations and Agroforestry Systems as Studied . variations Batish et al. /Ecological Basis of Agroforestry 43277_C 010 Final Proof page 184 4 .10. 2007 8:26pm Compositor Name: VBalamugundan 184 Ecological Basis of Agroforestry Copyright 2008 by. al. (1996) Batish et al. /Ecological Basis of Agroforestry 43277_C 010 Final Proof page 186 4 .10. 2007 8:26pm Compositor Name: VBalamugundan 186 Ecological Basis of Agroforestry Copyright 2008 by. Manage., 115, 1, 1999.) Batish et al. /Ecological Basis of Agroforestry 43277_C 010 Final Proof page 188 4 .10. 2007 8:26pm Compositor Name: VBalamugundan 188 Ecological Basis of Agroforestry Copyright 2008 by