Insect Ecology - An Ecosystem Approach 2nd ed - Chapter 14 pps

14 Decomposition and Pedogenesis I. Types and Patterns of Detritivory and Burrowing A. Detritivore and Burrower Functional Groups B. Measurement of Detritivory, Burrowing, and Decomposition Rates C. Spatial and Temporal Patterns in Processing of Detritus and Soil II. Effects of Detritivory and Burrowing A. Decomposition and Mineralization B. Soil Structure, Fertility, and Infiltration C. Primary Production and Vegetation Dynamics III. Summary DECOMPOSITION IS THE BREAKDOWN OF DEAD ORGANIC MATTER THAT eventually results in release of CO 2 , other organic trace gases, water, mineral nutrients, and energy. Pedogenesis (soil development) largely reflects the activities of animals that mix organic matter with mineral soil. These two processes contribute greatly to the capacity of a site to support primary production. Accu- mulated organic litter represents a major pool of energy and nutrients in many ecosystems. Carbon and other nutrients released through decomposition can be acquired by plants or microbes or returned to abiotic pools (see Chapter 11). Incorporation of decay-resistant organic matter and nutrients into soil increases fertility, aeration, and water-holding capacity. Release of CO 2 ,CH 4 , and other trace gases affects atmospheric conditions and global climate. Decomposition can be categorized into four component processes: photooxidation, abiotic catabolism resulting from exposure to solar radiation; leaching, the loss of soluble materials as a result of percolation of water through material; comminution, the fragmentation of organic litter, largely as a result of detritivory; and mineralization, the catabolism of organic molecules by microorganisms. Vossbrinck et al. (1979) found that when arthropods and microbes were excluded, detritus lost only 5% mass, due entirely to leaching or photooxidation.A variety of macroarthropods, mesoarthropods, and microarthropods are the primary detritivores in most ecosystems. The feeding and burrowing activities of many animals, including ants, termites, and other arthropods, redistribute and mix soil and organic material. Burrowing also increases soil porosity, thereby increasing aeration and water-holding capacity. The effects of arthropod detritivores and burrowers on decomposition and soil development have been the most widely studied effects of arthropods on ecosystem processes (e.g., Ausmus 1977, Coleman et al. 2004, Crossley 1977, 405 014-P088772.qxd 1/24/06 11:04 AM Page 405 Eldridge 1993, 1994, Seastedt 1984, Swift 1977, Swift et al. 1979, Whitford 2000, Wotton et al. 1998). Arthropod detritivores and burrowers are relatively accessi- ble and often can be manipulated for experimental purposes. Their key contributions to decomposition and mineralization of litter (both fine or suspended organic matter and coarse woody debris) and pedogenesis have been demonstrated in virtually all ecosystems. Indeed, some aquatic and glacial ecosystems consist of arthropod detritivores and associated microorganisms feeding entirely on allochthonous detritus (J. Edwards and Sugg 1990, Oertli 1993, J. Wallace et al. 1992). Effects of detritivorous and fossorial species on decomposition and soil mixing depend on the size of the organism, its food source, type and rate of detritivory, volume of displaced litter or soil, and type of saprophytic microorganisms inoculated into litter. Although most studies have addressed the effects of detritivores and burrowers on soil processes, some have documented effects of animal contributions to soil development and biogeochemical cycling to primary production as well. I. TYPES AND PATTERNS OF DETRITIVORY AND BURROWING A. Detritivore and Burrower Functional Groups Functional groups of detritivorous and burrowing arthropods have been distinguished on the basis of principal food source, mode of feeding, and microhabitat preferences (e.g., J. Moore et al. 1988, J. Wallace et al. 1992). For example, functional groups can be distinguished on the basis of seasonal occurrence, habitats, and substrates (e.g., terrestrial vs. aquatic, animal vs. plant, foliage vs. wood, arboreal vs. fossorial) or particular stages in the decomposition process (N.Anderson et al. 1984, Hawkins and MacMahon 1989, Schowalter and Sabin 1991, Schowalter et al. 1998, Seastedt 1984,Siepel and de Ruiter-Dijkman 1993,Tantawi et al. 1996, Tullis and Goff 1987, J. Wallace et al. 1992, Winchester 1997, Zhong and Schowalter 1989). General functional groupings for detritivores are based on their effect on decomposition processes. Coarse and fine comminuters are instrumental in the fragmentation of litter material. Major taxa in terrestrial ecosystems include millipedes, earthworms, termites, and beetles (coarse) and mites, collembolans, and various other small arthropods (fine). Many species are primarily fungivores or bacteriovores that fragment substrates while feeding on the surface microflora. Many fungivores and bacteriovores, including nematodes and protozoa, as well as arthropods, feed exclusively on microflora and affect the abundance and distribution of these decomposers (e.g., Santos et al. 1981). A number of species, including dung beetles, millipedes, and termites, are coprophages, either feeding on feces of larger species or reingesting their own feces following microbial decay and enrichment (Cambefort 1991, Coe 1977, Dangerfield 1994, Holter 1979, Kohlmann 1991, McBrayer 1975). In aquatic ecosystems scrapers (including mayflies, caddisflies, chironomid midges, and elmid beetles), which graze or scrape microflora from mineral and organic substrates, and shredders (including stoneflies, caddisflies, crane flies, 406 14. DECOMPOSITION AND PEDOGENESIS 014-P088772.qxd 1/24/06 11:04 AM Page 406 crayfish, and shrimp), which chew or gouge large pieces of decomposing material, represent coarse comminuters; gatherers (including stoneflies, mayflies, crane flies, elmid beetles, and copepods), which feed on fine particles of decomposing organic material deposited in streams,and filterers (mayflies,caddisflies, and black flies), which have specialized structures for sieving fine suspended organic material, represent fine comminuters (Cummins 1973, J. Wallace and Webster 1996, J. Wallace et al. 1992). Xylophages are a diverse group of detritivores specialized to excavate and fragment woody litter. Major taxa include scolytid, buprestid, cerambycid and lyctid beetles, siricid wasps, carpenter ants, Camponotus spp., and termites (Fig. 14.1), with different species often specialized on particular wood species, sizes, or stages of decay (see Chapter 10). Most of these species either feed on fungal- colonized wood or support mutualistic, internal, or external fungi or bacteria that I. TYPES AND PATTERNS OF DETRITIVORY AND BURROWING 407 FIG. 14.1 Melanophila sp. (Coleoptera: Buprestidae) larva in mine in phloem of recently killed Douglas-fir tree in western Oregon. The entire phloem volume of this tree has been fragmented and converted to frass packed behind mining larvae of this species, demonstrating detritivore capacity to reduce detrital biomass. Please see extended permission list pg 572. 014-P088772.qxd 1/24/06 11:04 AM Page 407 digest cellulose and enhance the nutritional quality of wood (e.g., Breznak and Brune 1994, Siepel and de Ruiter-Dijkman 1993; see Chapter 8). Carrion feeders represent another specialized group that breaks down animal carcasses. Major taxa include staphylinid, sylphid, scarabaeid, and dermestid beetles; calliphorid, muscid, and sarcophagid flies; and various ants. Different species usually specialize on particular stages of decay (see Figs. 10.3 and 10.4) and on particular animal groups (e.g., reptiles vs. mammals) (E. Watson and Carlton 2003). An important consequence of litter fragmentation by arthropods is increased surface area for microbial colonization and decomposition. Microbes also are carried, either passively through transport of microbes acquired during feeding or dispersal or actively through inoculation of mutualistic associates, to fresh sur- faces during feeding. Many detritivores redistribute large amounts of soil or detritus during foraging or feeding activities (e.g., Kohlmann 1991). However, nondetritivores also contribute to mixing of soil and organic matter. Fossorial functional groups can be distinguished on the basis of their food source and mechanism and volume of soil/detrital mixing. Subterranean nesters burrow primarily for shelter. Verte- brates (e.g., squirrels, woodrats, and coyotes) and many invertebrates, including crickets and solitary wasps, excavate tunnels of various sizes, usually depositing soil on the surface and introducing some organic detritus into nests. Gatherers, primarily social insects, actively concentrate organic substrates in colonies. Ants and termites redistribute large amounts of soil and organic matter during con- struction of extensive subterranean, surficial, or arboreal nests (J.Anderson 1988, Haines 1978). Subterranean species concentrate organic matter in nests excavated in soil, but many species bring fine soil particles to the surface and mix soil with organic matter in arboreal nests or foraging tunnels.These insects can affect a large volume of substrate (up to 10 3 m 3 ), especially as a result of restructuring and lateral movement of the colony (Hughes 1990, Moser 1963, Whitford et al. 1976). Fossorial feeders, such as gophers, moles, earthworms, mole crickets (Gryllotalpidae), and benthic invertebrates, feed on subsurface resources (plant, animal, or detrital substrates) as they burrow, constantly mixing mineral substrate and organic material in their wake. B. Measurement of Detritivory, Burrowing, and Decomposition Rates Evaluation of the effects of detritivory and burrowing on decomposition and soil mixing requires appropriate methods for measuring rates of these processes. Several methods have been used to measure rates of decomposition and soil mixing (Coleman et al. 2004). Detritivory can be measured by providing experimental substrates and measuring colonization and consumption rates. K. Johnson and Whitford (1975) measured the rate of termite feeding on an artificial carbohydrate source and natural substrates in a desert ecosystem. Edmonds and Eglitis (1989) and Zhong and Schowalter (1989) measured the rate of wood-borer colonization and exca- 408 14. DECOMPOSITION AND PEDOGENESIS 014-P088772.qxd 1/24/06 11:04 AM Page 408 vation in freshly cut tree boles. Dissection of wood samples is necessary for measurement of excavated volume for small insects. Radiography can be used to measure larger volumes (e.g., termite galleries). Detritivory often has been estimated by multiplying the per capita feeding rate for each functional group by its abundance (N.Anderson et al. 1984,Cárcamo et al. 2000, Crossley et al. 1995,Dangerfield 1994). Cárcamo et al. (2000) estimated consumption of conifer needle litter by the millipede, Harpaphe haydeniana, at about 90 mg g -1 animal biomass day -1 ,a rate that could account for processing of 36% of annual litterfall. Laboratory conditions, however, might not represent the choices of substrates available under field conditions. For example, Dangerfield (1994) noted that laboratory studies might encourage coprophagy by millipedes by restricting the variety of available substrates, thereby overrepresenting this aspect of consumption. Mankowski et al. (1998) used both forced-feeding and choice tests to measure wood consumption by termites when a variety of substrate types was available or restricted. Radioisotope movement from litter provided early data on decomposition rate (Witkamp 1971). Stable isotopes (e.g., 13 C, 14 C, and 15 N) are becoming widely used to measure fluxes of particular organic fractions (Ågren et al. 1996,Andreux et al. 1990, Horwath et al. 1996, Mayer et al. 1995, S ˇ antru ° cˇková et al. 2000, Spain and Le Feuvre 1997, Wedin et al. 1995). The most widely used techniques for measuring decomposition rates in terrestrial and aquatic ecosystems involve measurement of respiration rate, comparison of litterfall and litter standing crop, and measurement of mass loss (J. Anderson and Swift 1983, Bernhard-Reversat 1982, Seastedt 1984, Witkamp 1971, Woods and Raison 1982). These techniques tend to oversimplify representation of the decomposition process and conse- quently yield biased estimates of decay rate. Respiration from litter or soil represents the entire heterotrophic community as well as living roots. Most commonly, a chamber containing sodalime or a solu- tion of NaOH is sealed over litter for a 24-hour period, and CO 2 efflux is measured as the weight gain of sodalime or volume of acid neutralized by NaOH (N. Edwards 1982). Comparison of respiration rates between plots with litter present and plots with litter removed provides a more accurate estimate of respiration rates from decomposing litter, but separation of litter from soil is diffi- cult and often arbitrary (J. Anderson and Swift 1983, Woods and Raison 1982). More recently, gas chromatography and infrared gas analysis (IRGA) have been used to measure CO 2 efflux (Nakadai et al. 1993,Parkinson 1981, Raich et al. 1990). The ratio of litterfall mass to litter standing crop provides an estimate of the decay constant, k, when litter standing crop is constant (Olson 1963). Decay rate can be calculated if the rate of change in litter standing crop is known (Woods and Raison 1982). This technique also is limited by the difficulty of separating litter from underlying soil for mass measurement (J. Anderson and Swift 1983, Spain and Le Feuvre 1987, Woods and Raison 1982). Weight loss of fine litter has been measured using tethered litter, litterbags, and litterboxes. Tethering allows litter to take a natural position in the litterbed and does not restrict detritivore activity or alter microclimate but is subject to loss of fragmented material and difficulty in separating litter in late stages of I. TYPES AND PATTERNS OF DETRITIVORY AND BURROWING 409 014-P088772.qxd 1/24/06 11:04 AM Page 409 decay from surrounding litter and soil (N. Anderson et al. 1984, Birk 1979, Witkamp and Olson 1963, Woods and Raison 1982). Litterbags provide a convenient means for studying litter decomposition (Crossley and Hoglund 1962, C. Edwards and Heath 1963). Litterbags retain selected litter material, and mesh size can be used to selectively restrict entry by larger functional groups (e.g., C. Edwards and Heath 1963, Wise and Schaefer 1994). However, litterbags may alter litter microclimate and restrict detritivore activity, depending on litter conformation and mesh size. Moisture retention between flattened leaves apparently is independent of mesh size. Exclusion of larger detritivores by small mesh sizes has little effect, at least until litter has been preconditioned by microbial colonization (J. Anderson and Swift 1983, Macauley 1975, O’Connell and Managé 1983, Spain and Le Feuvre 1987,Woods and Raison 1982).However,exclusion of predators by small mesh sizes can significantly affect detritivore abundances and decomposition processes (M. Hunter et al. 2003). Large woody litter (e.g.,tree boles) also can be enclosed in mesh cages for experimental restriction of colonization by wood-boring insects. The potential inter- ference with decomposition by small mesh sizes has been addressed in some studies by minimizing leaf overlap (and prolonged moisture retention) in larger litterbags, using small mesh on the bottom to retain litter fragments and large mesh on the top to maximize exchange of moisture and detritivores, and measuring decomposition over several years to account for differences resulting from changing environmental conditions (J. Anderson et al. 1983, Cromack and Monk 1975,Woods and Raison 1982, 1983). Despite limitations, litterbags have been the simplest and most widely used method for measuring decomposition rates and probably provide reasonably accurate estimates (Seastedt 1984, Spain and Le Feuvre 1987, Woods and Raison 1982). More recently, litterboxes have been designed to solve problems associated with litterbags. Litterboxes can be inserted into the litter, with the open top providing unrestricted exchange of moisture and detritivores (Seastedt and Crossley 1983), or used as laboratory microcosms to study effects of decomposers (Haimi and Huhta 1990, Huhta et al. 1991). Similar constructions can be incorporated into streams for assessment of detrital decomposition (March et al. 2001). Measurement of wood decomposition presents special problems,including the long timeframe of wood decomposition; the logistical difficulties of experimental placement; and manipulation of large, heavy material. Decomposition of large woody debris represents one of the longest ecological processes, often spanning centuries (Harmon et al. 1986). This process traditionally was studied by com- paring mass of wood of estimated age to the mass expected for the estimated original volume, based on particular tree species. However, decomposition of some wood components begins only after lag times of up to several years, decomposition of standing tree boles is much slower than fallen boles, and differences in chemistry and volume between bark and wood components affect overall decay rates (Harmon et al. 1986, Schowalter et al. 1998). Abundances of detritivore functional groups can be manipulated to some extent by use of microcosms (Setälä and Huhta 1991, Setälä et al. 1996), selective biocides or other exclusion techniques (Crossley and Witkamp 1964, 410 14. DECOMPOSITION AND PEDOGENESIS 014-P088772.qxd 1/24/06 11:04 AM Page 410 C. Edwards and Heath 1963, González and Seastedt 2001, E. Ingham et al. 1986, Macauley 1975, Pringle et al. 1999, Santos and Whitford 1981, Schowalter et al. 1992, Seastedt and Crossley 1983, J. Wallace et al. 1991) or by adding or simulat- ing detritivores in new substrates (González and Seastedt 2001, Progar et al. 2000). Naphthalene and chlordane in terrestrial studies (Crossley and Witkamp 1964, Santos and Whitford 1981, Seastedt and Crossley 1983, Whitford 1986) and methoxychlor or electric fields in aquatic studies (Pringle et al. 1999, J. Wallace et al. 1991) have been used to exclude arthropods. However, E. Ingham (1985) reviewed the use of selective biocides and concluded that none had effects limited to a particular target group, limiting their utility for evaluating effects of indi- vidual functional groups. Furthermore, Seastedt (1984) noted that biocides provide a carbon and, in some cases, nitrogen source that may alter the activity or composition of microflora. Mesh sizes of litterbags (see later in this chapter) can be manipulated to exclude detritivores larger than particular sizes, but this technique often alters litter environment and may reduce fragmentation, regard- less of faunal presence (Seastedt 1984). Few experimental studies have compared effects of manipulated abundances of boring insects on wood decomposition (Edmonds and Eglitis 1989, Progar et al. 2000, Schowalter et al. 1992). Some studies have compared species or functional group abundances in wood of estimated age or decay class, but such comparison ignores the effect of initial conditions on subsequent community development and decomposition rate. Prevailing weather conditions, the physical and chemical condition of the wood at the time of plant death, and prior colonization determine the species pools and establishment of potential colonists. Penetration of the bark and transmission by wood-boring insects generally facil- itate microbial colonization of subcortical tissues (Ausmus 1977, Dowding 1984, Swift 1977). Käärik (1974) reported that wood previously colonized by mold fungi (Ascomyctina and Fungi Imperfecti) was less suitable for establishment by decay fungi (Basidiomycotina) than was uncolonized wood. Mankowski et al. (1998) reported that wood consumption by termites was affected by wood species and fungal preconditioning. Hence, experiments should be designed to evaluate effects of species or functional groups on decomposition over long time periods using wood of standard size, composition, and condition. Assessing rates of burrowing and mixing of soil and litter is even more prob- lematic. A few studies have provided limited data on the volume of soil affected through excavation of ant nests (Moser 1963, Tschinkel 1999, Whitford et al. 1976). However, the difficulty of separating litter from soil limits measurement of mixing. Tunneling through woody litter presents similar problems. Zhong and Schowalter (1989) dissected decomposing tree boles to assess volume of wood excavated or mixed among bark, wood, and fecal substrates. C. Spatial and Temporal Patterns in Processing of Detritus and Soil All, or most, dead organic matter eventually is catabolized to CO 2 , water, and energy, reversing the process by which energy and matter were fixed in primary I. TYPES AND PATTERNS OF DETRITIVORY AND BURROWING 411 014-P088772.qxd 1/24/06 11:04 AM Page 411 production. Some materials are decomposed more readily than are others; some processes release carbon primarily as methane; and some enter long-term storage as humus, peat, coal, or oil. Moisture, litter quality (especially lignin and nitrogen content), and oxygen supply are extremely important to the decomposition process (Aerts 1997, Birk 1979, Cotrufo et al. 1998, Fogel and Cromack 1977, Fonte and Schowalter 2004, González and Seastedt 2001, Meentemeyer 1978, Progar et al. 2000, Seastedt 1984, Tian et al. 1995, Whitford et al. 1981). For example, animal carrion is readily digestible by many organisms and decomposes rapidly (Payne 1965), whereas some plant materials, especially those composed largely of lignin and cellulose, can be decomposed only by relatively few species of fungi, bacteria, or protozoa and may require long time periods for complete decomposition (Harmon et al. 1986). Conifer litter tends to decompose more slowly than does angiosperm litter because of low nitrogen content and high lignin content. Low soil or litter pH inhibits decomposition. Rapid burial or saturation with water inhibits decomposition of litter because of limited oxygen availability. Submerged litter is degraded primarily by aquatic gougers and scrapers that slowly fragment and digest consumed organic matter from the surface inward (N. Anderson et al. 1984). Decomposition processes differ among ecosystem types. Physical factors may predominate in xeric ecosystems where decomposition of exposed litter reflects catabolic effects of ultraviolet light. Decomposition resulting from biological processes is favored by warm, moist conditions. Decomposition is most rapid in wet tropical ecosystems, where litter disappears quickly, and slowest in desert, tundra, and boreal ecosystems because of dry or cold conditions. González and Seastedt (2001) and Heneghan et al. (1999) compared decomposition of a common litter species between tropical and temperate ecosystems and demonstrated that decomposition was consistently higher in the tropical wet forests. Nevertheless, decomposition may continue underground, or under snow in tundra and boreal regions, if temperature and moisture are adequate (e.g., Santos et al. 1981). As noted earlier in this section, decomposition rates may be lower in aquatic ecosystems as a result of saturation and limited oxygen supply. Low decomposition rates generally result in the accumulation of large standing crops of woody and fine litter. Different groups of detritivores and decomposers dominate different ecosystems. For example, shredders and gatherers were more abundant in pools and headwater streams, characterized by substantial inputs of largely unfragmented organic matter, whereas filter-feeders were more abundant in high gradient sec- tions or higher-order streams (the Little Tennessee River), characterized by highly fragmented, suspended organic matter (Fig. 14.2). Fungi and associated fungivores (e.g., oribatid mites and Collembola) are more prevalent in forests, whereas bacteria, bacteriovores, especially prostigmatid mites and Collembola, and earthworms are more prevalent in grasslands (Seastedt 2000). Termites are the most important detritivores in arid and semi-arid ecosystems and may largely control decomposition processes in forest and grassland ecosystems (K. E. Lee and Butler 1977, Whitford 1986). J. Jones (1989, 1990) reported that termites in dry tropical ecosystems in Africa so thoroughly decompose organic matter that 412 14. DECOMPOSITION AND PEDOGENESIS 014-P088772.qxd 1/24/06 11:04 AM Page 412 little or no carbon is incorporated into the soil. Wood-boring insects occur only in ecosystems with woody litter accumulation and are vulnerable to loss of this resource in managed forests (Grove 2002). Dung feeders are important in ecosystems where vertebrate herbivores are abundant (Coe 1977, Holter 1979). The relative contributions of physical and biological factors to pedogenesis vary among ecosystems. Erosion and earth movements (e.g., soil creep and land- slides) mix soil and litter in ecosystems with steep topography or high wind or raindrop impact on surface material. Burrowing animals are common in ecosystems with loose substrates suitable for excavation. Grasslands and forests on sandy or loamy soils support the highest diversity and abundances of burrowers. Ants often excavate nests through rocky, or other, substrates, which would preclude burrowing by larger or softer-bodied animals and are the dominant burrowers in many ecosystems. Distinct temporal patterns in decomposition rates often reflect either the preconditioning requirements for further degradation or the inhibition or facilita- tion of new colonizers by established groups. For example, leaching of toxic chemicals may be necessary before many groups are able to colonize litter (Barz and Weltring 1985). M. Hulme and Shields (1970) and Käärik (1974) reported I. TYPES AND PATTERNS OF DETRITIVORY AND BURROWING 413 0 1 2 3 4 5 Total secondary production (g m –2 yr –1 ) Outcrop Riffle Pool Gatherer Filterer Shredder Scraper Predator FIG. 14.2 Annual secondary production for aquatic functional groups in bedrock outcrop, riffle, and pool habitats of upper Ball Creek, North Carolina, during July 1983–June 1984. Data from Huryn and Wallace (1987). Please see extended permission list pg 572. 014-P088772.qxd 1/24/06 11:04 AM Page 413 that wood decay is inhibited by competition for labile carbohydrates, necessary for early growth of decay fungi, by nondecay fungi. However, Blanchette and Shaw (1978) found that decay fungus growth in wood with bacteria and yeasts was twice that in wood without bacteria and yeasts, presumably because bacteria and yeasts provide fixed nitrogen, vitamins, and other nutrients while exploit- ing carbohydrates from lignocellulose degradation. Microbes usually require bark penetration, and often inoculation, by insects to colonize woody litter. Many saprophagic arthropods require some preconditioning of litter by bacteria, fungi, or other arthropods prior to feeding. Small comminuters usually feed on fragments or feces left by larger comminuters (O’Connell and Menagé 1983). Shred- ders in streams convert coarse particulate organic matter (CPOM) to fine particulate organic matter (FPOM) that can be acquired by filterers (J. Wallace and Webster 1996, J. Wallace et al. 1991). Santos and Whitford (1981) reported that a consistent succession of microarthropods was related to the percentage of organic matter lost. Decomposition often begins long before detritus reaches the soil. Consider- able detrital accumulation occurs in forest canopies (Coxson and Nadkarni 1995, Paoletti et al. 1991). Processes of decomposition and pedogenesis in these suspended sediments are poorly known, but Paoletti et al. (1991) reported that suspended soils associated with bromeliads in a Venezuelan cloud forest had higher concentrations of organic matter, nitrogen, calcium, and magnesium and higher densities (based on bulk density of soil) of macroinvertebrates and micro- invertebrates than did forest floor soils. However, rates of litter decomposition as measured in litterbags were similar in the canopy and forest floor. Oribatid mites and Collembola are the most abundant detritivores in temperate and tropical forest canopies (Paoletti et al. 1991, Schowalter and Ganio 1998, Walter and O’Dowd 1995, Winchester 1997), and many are canopy specialists that do not occur on the forest floor (Winchester et al. 1999). Decomposition is an easily modeled process. Usually, an initial period of leaching or microbial oxidation of simple organic molecules results in a short- term, rapid loss of mass, followed by a longer-term, slower decay of recalcitrant compounds. Decomposition of foliage litter has been expressed as a single- or double-component negative exponential model (Olson 1963): (14.1) where N t is mass at time t, S 0 and L 0 are masses in short- and long-term components, and respectively; and k’s are the respective decay constants.The short-term rate of decay reflects the mass of labile organic molecules, and the long-term rate of decay reflects lignin content and actual evapotranspiration (AET) rate, based on temperature and moisture conditions (Meentemeyer 1978, Seastedt 1984). Long-term decay constants for foliage litter range from -0.14 year -1 to -1.4 year -1 , depending on nutritional value for decomposers (Table 14.1) (Laskowski et al. 1995, Seastedt 1984, Schowalter et al. 1991). Decay constants for wood range from -0.004 year -1 to -0.5 year -1 (Harmon et al. 1986). Schowalter et al. (1998) monitored decomposition of freshly cut oak, Quercus spp., logs over a 5-year period and found that a 3-component exponential model was necessary to NSe Le t kt kt =+ 00 414 14. DECOMPOSITION AND PEDOGENESIS 014-P088772.qxd 1/24/06 11:04 AM Page 414 [...]... Anderson (1973) -0 .27 -0 .28 -0 .01 4 J Anderson (1973) -0 .40 -0 .45 -0 .70 -0 .73 -0 .30 -0 .28 43 38 Cromack (1973) Madge (1969) -0 .69 -0 .73 -0 .04 8 Madge (1969) -0 .22 -0 .43 -0 .21 49 Elkins and Whitford (1982) -0 .30 -0 .36 -0 .06 17 J Williams and Wiegert (1971) -0 .14 -0 .45 -0 .31 69 Vossbrinck et al (1979) -1 .15 -1 .55 -0 .22 -1 .24 -1 .34 -0 .32 -0 .09 +0.21 -0 .10 7 -1 6 31 I TYPES AND PATTERNS OF DETRITIVORY AND BURROWING... Broomsedge (Andropogon virginicus) Blue grama grass (Bouteloua gracilis) Mixed pasture grasses Surface Buried Mixed tundra grassesa With fauna Faunal component Faunal effect (%) -0 .69 -0 .82 -0 .13 16 -0 .48 -0 .50 -0 .02 4 -0 .60 -0 .92 -0 .32 35 Cromack (unpubl), Seastedt and Crossley (1980, 1983) Cromack (unpubl), Seastedt and Crossley (1980, 1983) Witkamp and Crossley (1966) -0 .41 -0 .50 -0 .09 18 J Anderson... reported that termites brought 10–27 g m-2 of fine-textured 428 14 DECOMPOSITION AND PEDOGENESIS FIG 14. 8 Termite castle in northern Australian woodland Dimensions are approximately 3 m height and 1.5 m diameter soil material (35% coarse sand; 45% medium fine sand; and 21% very fine sand, clay, and silt) to the surface and deposited 6–20 g of soil carton per gram of litter removed (see Fig 14. 3) Herrick and... vegetation dynamics C Edwards and Lofty (1978) compared seedling emergence and shoot and root growth of barley between pots of intact, sterilized soil (from fields in which seed had been either drilled into the soil or planted during ploughing) with 431 II EFFECTS OF DETRITIVORY AND BURROWING 10 3-6 1 0-2 11 3-2 5-7 6-7 4-7 1-5 m Interpavement zone Annular zone Pavement zone Annular zone FIG 14. 11 Effect of... increased with grove size and the abundance of forest tree species in Venezuelan savanna, suggesting that active nests both facilitated and were facilitated by formation of groves L Parker et al (1982) demonstrated that termite exclusion significantly reduced biomass of four annual plant species and significantly increased biomass of one annual plant species They observed an overall trend toward increased... soil-feeding termites (Brauman et al 1992) P Zimmerman et al (1982) suggested that tropical deforestation and conversion to pasture and agricultural land could increase the biomass and methane emissions of fungus-growing and soil-feeding termites, but Martius et al (1996) concluded that methane emissions from termites in deforested areas in Amazonia would not contribute significantly to global methane... al (1993), and Sanderson (1996) calculated CO2 and methane fluxes based on global distribution of termite biomass and concluded that termites contribute ca 2% of the total global flux of CO2 (3500 tg year-1) and 4–5% of the global flux of methane (£20 tg year-1) (Fig 14. 5) However, emissions of CO2 by termites are 25–50% of annual emissions from fossil fuel com- 421 422 14 DECOMPOSITION AND PEDOGENESIS... increased mass loss of litter by 13–41% N Anderson et al (1984) noted that aquatic xylophagous tipulid larvae fragmented >90% of decayed red alder, Alnus rubra, wood in a 1-year period Termites have received considerable attention because of their substantial ecological and economic importance in forest, grassland, and desert ecosystems Based on laboratory feeding rates, K E Lee and Butler (1977) estimated... methane or acetate (Brauman et al 1992, Wheeler et al 1996) Thirty of 36 temperate and tropical termite species assayed by Brauman et al (1992), Hackstein and Stumm (1994), and Wheeler et al (1996) produced methane, acetate, or both Generally, acetogenic bacteria outproduce methanogenic bacteria in wood- and grass-feeding termites, but methanogenic bacteria are much more important in fungus-growing and... (1995) manipulated abundances of millipedes and earthworms in tropical agricultural ecosystems They found that millipedes alone significantly accounted for 10–65% of total decay over a 10week period Earthworms did not affect decay significantly by themselves, but earthworms and millipedes combined significantly accounted for 11–72% of total decay Haimi and Huhta (1990) demonstrated that earthworms significantly . foliage -0 .22 -0 .43 -0 .21 49 Elkins and Whitford (1982) (Quercus harvardii) Broomsedge -0 .30 -0 .36 -0 .06 17 J. Williams and Wiegert (1971) (Andropogon virginicus) Blue grama grass -0 .14 -0 .45 -0 .31 69 Vossbrinck. gracilis) Mixed pasture grasses Surface -1 .15 -1 .24 -0 .09 7 Curry (1969) Buried -1 .55 -1 .34 +0.21 -1 6 Curry (1969) Mixed tundra grasses a -0 .22 -0 .32 -0 .10 31 Douce and Crossley (1982) a Mean values. insects and fungi. An intermedi- ate decay rate of -0 .06 year -1 for years 2–5 reflected the slower decay rate for sapwood and outer bark, and a long-term decay rate of -0 .012 year -1 was pre- dicted,

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