Download The Significance of Coarse Woody Debris for the Diversity of Soil

The Significance of Coarse Woody Debris for
the Diversity of Soil Mites
John M. Johnston and D.A. Crossley, Jr.
Abstract
general predators, and Prostigmata as specialized predators.
However, these generalizations may lead to erroneous
conclusions due to inadequate information on feeding habits
or the specialized nature of some predator-prey relationships
(Walter 1987, 1988). As concerns about the loss of
biodiversity continue (Wilson 1992), and the relationships of
biodiversity to ecosystem function become better
understood (Schultze and Mooney 1993), increased
attention to taxonomy and diversity of soil mites is needed.
A necessary concomitant is the analysis of habitat use by
soil mites, so that the importance of habitat features, such as
coarse woody debris (CWD), can be quantified.
The community of mites inhabiting forest floors is rich in species but is
poorly known both taxonomically and biologically. Understanding the
relationship of mite species diversity to ecosystem function depends upon
better knowledge of habitat and substrate use. Coarse woody debris
(CWD) is a significant habitat variable as well as a resource for mite
communities. However, little information has been developed on the use
of woody debris by mites in southern forests. As a habitat variable, CWD
is a contributor to the microenvironmental gradients that affect soil-mite
distribution and abundance. As a resource variable, the importance of
CWD resides in its support of a varied fungal population and its nutrient
reserves. Calcium, abundant in the bark of decaying boles and twigs, is
particularly important for Oribatid mites.
Only a few scattered references can be found on the use of
woody debris by mites in southern forests. This is
surprising, given the number of studies of forest floor
arthropods done in areas ranging from upland southern pine
forests to rich bottomland hardwood forests. In this paper,
we offer a preliminary interpretation of the importance of
CWD for soil mite diversity, some directions for future
studies, and some tentative considerations for management
practices.
Introduction
Soil-dwelling mites reach their greatest abundance in the
forest floors of temperate regions (Swift and others 1979).
Mites are major participants in belowground food webs.
Some species feed directly upon decomposing plant
materials; more species are fungivores. Others are predators
on other small arthropods or their eggs, nematodes, or other
small fauna. Many species appear to be omnivorous, or at
least to have the capacity to switch food sources, depending
upon availability. A large diversity of mite species is
characteristic of most soil systems. Indeed, mites are the
most species-rich group of the North American soil
arthropod fauna (Behan-Pelletier and Bissett 1992).
Almost one-half of the soil mite species are unnamed;
perhaps as few as one-third of North American species of
soil mites have been adequately described and illustrated
(Behan-Pelletier and Bissett 1992). Furthermore,
immature stages are poorly known. Food habits for many
species remain obscure, and observations on feeding
reported in the literature often prove to be unreliable (Walter
1988).
Factors Affecting Spatial Distribution
of Soil Mites
Mite species have clumped (contagious) distributions in
forest floor habitats. It is not clear what factors affect the
spatial distribution of soil mites. Even a seemingly uniform
forest floor under a pine monoculture will contain more than
50 species of oribatid mites, and perhaps as many as 100
total mite species. Since different oribatids appear to feed on
the same foods, fungi and/or decaying organic matter, the
coexistence of so many similar species seems unusual. Two
factors have been suggested to explain this coexistence of
similar species. One is seasonal separation. Research using
litterbag methods to sample soil arthropods reveals a
succession of reproductive success by oribatids during the
year. Thus, some species of mites may be geared to a
seasonal pattern of fungal species.
For ecological analyses, soil mites may be arrayed into
functional groups (Moore and others 1988) of soil food
webs. Oribatid mites are generally considered as a
fungivore-detritivore functional group, Mesostigmata as
Microhabitat differentiation is the other factor proposed to
explain soil mite community structure. The uniform
appearance of the forest floor may be deceiving to the casual
eye: distances from tree boles, presence of understory, root
Research Assistant and Research Professor of Ecology, respectively.
Institute of Ecology, University of Georgia, Athens, GA 30602-2602.
82
distributions (Fitter and others 1985), and similar habitat
variables make for a sequence of more-or-less-distinct
microhabitats. These factors, coupled with the highly
contagious spatial distributions of most oribatid mite
species, led Anderson (1977) to propose that mites exist in a
set of "unit communities" in the forest floor. Most mite
species appear to be distributed across a variety of forest
floor habitats. The presence of microhabitats probably
contributes to the abundance and persistence of mite
species.
thysanurans and scorpions, use fallen logs or stumps as
daytime refuges, but such behavior has not been recorded
for mites in southern forests.
Finally, CWD offers a somewhat distinct habitat feature on
the forest floor. Fallen logs support lichen populations and
fungal structures that are absent or not abundant in leaf
litter. Mites, which can penetrate fallen logs either through
openings made by insects or as phoretic passengers on
insects, find a unique habitat. Some mite species are
obligate members of the intra-log community.
Relationship of Soil Mite Biodiversity
Use of Coarse Woody Debris
to Coarse Woody Debris
by Soil Mites
Coarse woody debris is a major habitat variable on forest
floors (Wallwork 1976). It contributes to the
microenvironmental gradients that affect the distribution and
abundance of soil mite species. Coarse woody debris in
mature forests provides a set of microsites that offer food
and habitat resources for unit communities of soil mites.
Coarse woody debris is part of a woody continuum, starting
with fine twigs and ranging through larger twigs and
branches to boles. Fallen logs vary by species and by mode
of decay. Fallen hardwood logs that are hollow support a
rich mite fauna, as do basal tree-holes (Park and Auerbach
1954). Tree-holes contain several unique species of
mites (Camin 1953).
Decaying woody debris is a significant nutrient sink in
southern forest floors (Cromack and Monk 1975).
Accumulations of calcium in the bark of decaying wood
may be particularly significant for Diplopoda (millipedes)
and for oribatid mite species, which use calcium oxalate or
calcium carbonate as cuticular hardening agents (Norton and
Behan-Pelletier 1991). Oribatid mites accumulate calcium
compounds from a fungal diet (Cromack and others 1977).
The food base for most oribatid mites consists of fungal
hyphae, although some species appear to use leaf litter or
woody materials directly. This aspect of nutrition has been
termed the "peanut butter sandwich" problem. Do you eat
the entire sandwich just to get the peanut butter (the
microbes) in the sandwich (the decaying substrate)?
Given the importance of CWD as a habitat factor and a set
of resources, it is not surprising that a large number of mite
species use it (tables 1 and 2). Most of the oribatid mites
that occur in the forest floor will, at some time, be found in
decaying logs. Seastedt and others (1989) found that
oribatid mites in forest floors in the Cascade Mountains of
central Oregon used both decomposing wood and leaf litter,
although mite species diversity in wood was much lower
than in litter. Table 1 shows the presence of oribatid mites
in soil cores, experimentally bagged leaf litter, and woody
debris on the forested floors of hardwood watersheds at
Coweeta Hydrologic Laboratory, Macon County, North
Carolina. Despite the uneven sampling effort (5 to 6 times
more woody samples examined than other types), it would
appear that the majority of oribatid species living in the soil
use both leaf litter (judging by the litterbags) and woody
litter. A few abundant soil forms (e.g., Ceratozetes spp.,
Eremobodes sp., Oppia minus) appear to use neither recent
leaf litter nor wood. Others (Oppiella nova, other species of
Oppiidae, Suctobelbidae spp., Tectocepheus velatus,
Trhypochtonius americanus) seem to be litter feeders. Data
suggest that species such as Carabodes spp. and Eupelops
sp. use both wood and leaf litter. Among this group of 73
species only 7—Atropacarus sp., Camisia spinifer,
Nanhermannia sp., Ommatocepheus_ocellatus, Oribatula
sp., Oripoda sp., and Scheloribates pallidus—appear to use
CWD as a preferred habitat.
Effects of CWD on microclimate are important during
drought conditions. Soil fauna are notoriously moisture
dependent. Fallen logs offer protection from desiccation,
since the soil beneath logs remains moist after the forest
floor has dried. Accumulations of macrofauna and
microarthropods under logs are commonly noted during
droughts. Nocturnal macrofauna, that is, cryptozoa such as
Other mite groups found beneath bark of decaying chestnut
oak (Quercus prinus) logs (table 2) are also common soillitter forms, at least for the most part. Most of the
Prostigmata listed are predators. Eupodids are fungal
feeders in the laboratory. The Tetranychidae (red spider
mites) and Tenuipalpidae (false spider mites) feed on green
vegetation: they probably had fallen from tree foliage and
83
Table 1—Oribatid mite species in hardwood forest floor habitats at Coweeta Hydrologic Laboratory, North Carolina"
Oribatid species
Adoribella sp.
Aeroppla sp.
Allodamaeus sp.
Allogalumna sp.
Anachipteria sp.
Atopochthonius sp.
Atropacarus sp.
Austrocarabodes sp.
Be/foz sp.
Brachychthonius sp.
Caleremaeus sp.
Camisia spinifer
Carabodes spp.
Carabodoides sp.
Cepheus cephelformis
Ceratoppia bipilis
Ceratozetes spp.
Cultroribula juncta
Damaeus grossmani
Eobrachychthonius sp.
Gracilis eohypochthonius
Cylindrica epilohmannia
Epilohmannoides sp.
Eremaeus sp.
Eremobelba sp.
Eremobodes sp.
Eremulus sp.
Eupelops sp.
Euphthiracarus sp.
Ferolocella sp.
Fosseremaeus sp.
Gymnodamaeus sp.
Hemileius sp.
Heminothrus sp.
Hermaniella sp.
Hypochthoniella sp.
Soil
cores
(N = 57)
0
0
0
0
0
0
b
0
—
—
0
2
61
0
4
3
83
2
18
—
24
—
—
3
37
113
4
15
—
0
18
8
1
0
5
1
Litter
Woody
litter
bags
(N = 78) (N = 300)
0
0
0
0
0
1
—
0
4
—
0
0
12
5
2
3
1
0
13
—
0
—
—
0
0
6
0
16
—
11
0
0
0
0
0
0
Oribatid species
1
4
1
1
3
0
83
10
10
1
2
18
71
2
17
19
11
0
2
0
7
0
0
13
1
1
2
22
7
0
0
3
2
1
1
0
Rufulus hypochthonlus
Machuella sp.
Malaconothrus sp.
Metrioppia sp.
Microtritia sp.
Multioppia sp.
Elegantula nanhermannia
Neoribates sp.
Nothrus sylvestris
Ocellatus ommatocepheus
Ophidiotrichus sp.
Oppia durhamensis
Oppia minus
Oppiella nova
Oppiidae spp.
Oribatella spp.
Oribatula sp.
Oribotritia sp.
Oripoda sp.
Parachipteria sp.
Peloptulus sp.
Phthiracarus sp.
Peltifer platynothrus
Depressa pmtokalumma
Quadroppia sp.
Rhysotritia sp.
Scapheremaeus sp.
Pallidulus scheloribates
Suctobelbidae spp.
Tectocepheus velatus
Topobates
Americanus trhypochthonius
Trimalaconothrus sp.
Xenillus sp.
Xylobates sp.
Zachvatkiniella sp.
Zygoribatula sp.
Variates = number of individuals; N = number of samples examined.
"Data from Abbott 1980.
b
Species lumped into a higher taxonomic category during analysis of soil core and litterbag samples.
84
Soil
cores
(N = 57)
5
10
—
0
—
0
8
0
2
0
0
8
146
402
44
48
31
—
1
17
4
—
7
0
19
—
0
—
286
142
0
14
—
0
33
1
0
Woody
Litter
litter
bags
(N
= 300)
(N = 78)
0
0
0
0
—
0
0
0
1
0
0
4
4
77
44
74
73
1
1
1
0
—
14
0
0
—
0
—
13
127
0
111
0
0
1
0
5
3
0
1
1
1
3
48
4
5
670
2
14
0
31
5
2
147
6
41
3
2
2
9
6
0
11
17
78
3
3
1
26
2
2
3
0
0
food resource (the "peanut butter") is often fungal hyphae,
and these occur on a broad variety of decomposing
substrates. Furthermore, twig litter or other fine litter occurs
throughout the forest floor and may provide an adequate
resource for microarthropods that can use it. In laboratory
studies, Hartenstein (1962) found nine species of oribatid
mites that appeared to feed directly on wood (including
Camisia spinifer, Ceratozetes gracilis, and Nanhermannia
elegantula; see table 1).
Table 2—Mites in the suborders Prostigmata and
Mesostigmata found beneath bark of decaying chestnut oak
(Quercus prinus) logs at Coweeta Hydrologic Laboratory,
North Carolina
Prostigmata
Alycus sp.
Bdella sp.
Bimichaelia sp.
Biscirus sp.
Cunaxa sp.
Cyta sp.
Dactyloscirus sp.
Eupodes spp.
Eustigmaeus sp.
Labidostomma mamillata
Lorryia sp.
Mullederia sp.
Paralorria sp.
Pediculaster sp.
Penthalodes sp.
Protereunetes sp.
Pyemotes sp.
Scutacarus sp.
Spinibdella sp.
Tenuipalpidae
Tetranychidae
Thoribdella sp.
Eutrombicula alfreddugesi
Tydeus sp.
Zetzellla sp.
Mesostigmata
Amblyseius sp.
Ameroseius sp.
Asra aphidoides
Asca grmanni
Calholaspis berlesei
Dendrolaelaps sp.
Discourella sp.
Eviphis sp.
Holaspina sp.
Haploseius sp.
Hypoaspis sp.
Lasioseius sp.
Neoparholaspulus hurlbutti
Parasitus sp.
Podocinum sp.
Rhodacarus sp.
Uropodidae
Veigaia sp.
Zercon sp.
In contrast, certain soil mites use CWD as substrate or
habitat in specific ways. The oribatid mite Ommatocepheus
ocellatus, listed in table 1 as very abundant in chestnut oak
logs, is arboreal as well. The fallen log habitat evidently is
in some way similar to standing tree trunks. Another
arboreal species, Humerobatesj-ostrolamellatus, occurs on
tree trunks and fallen logs in southern pine forests. This
species is viewed as a bioindicator of airborne pollution in
European forests (Andre and others 1984). One genus of
trombidiid mites ("velvet mites"), Neotrombidium, lives in
cracks in the wood of standing snags or on the vertical walls
of hollow logs. Trombiculid mites, the adult stages of
"chigger" mites, use rotting hardwood logs, where they are
predaceous on other small arthropods. Hollow hardwood
logs are especially important as habitats for the adult stages
of Eutrombicula species, our common pest chiggers. In
south Georgia (Glynn County), fallen logs and tree stumps
were the major habitat for Eutrombicula splendens. In
Georgia Piedmont habitats, a notable association occurs
between lizards (Sceloporus), chigger mites (E.
alfreddugesi), and fallen pine logs. Adult mites are found
in soil at the base of the logs. Larval stages seeking a host
ascend to the top surfaces of the logs, where lizards sunning
themselves are susceptible to parasitism (Mallow and others
1984).
Data from Abbott 1980 and Crossley unpublished.
Other mites may use hollow, rotten logs. The chigger mite
Fonsecia gumeyi is a parasite of snakes (Elaphe spp., for
example). Adult Fonsecia are predators; the larvae
parasitize snakes that enter hollow logs.
taken refuge under the bark. The Mesostigmata listed are
also predators, some common in forest canopies and forest
floors (i.e., Amblyseius sp., Asra aphidoides). The chigger
mite Eutrombicula alfreddugesi, which occurred under the
bark of fallen chestnut oak logs at Coweeta (table 2), was
not found beneath the bark of fallen logs in the Georgia
Piedmont (Mallow and others 1984). But adults occurred in
soil beneath fallen pine logs, and questing larvae were found
on the surface of those logs (see below).
Mites may enter decaying CWD as phoretic forms—as
inactive passengers on boring insects. Passalid beetles or
"Bessy bugs," (Popilius disjunctus) carry several species of
mites with them. Colonies of mites then develop among the
macerated wood and feces of these semisocial insects
(Hunter and Davis 1965). Wood feeding (or wood and fungus
feeding) oribatid mites in the genus Mesoplophora are able to
clasp the setae of passalid beetles and thus accompany them
into decomposing logs (Norton 1980).
Such a broad distribution of soil mites across habitats has
been noted by others. Anderson (1977) suggested that the
phenomenon, like the clumped or disjunct spatial
distributions, may be one of scale. In particular, sampling
methods may not be suited to microarthropods whose
habitat scale is much smaller than the sampling tools. The
85
Conclusions and Recommendations
Coarse woody debris on forest floors has a significant
impact on the distribution and abundance of soil mite
species. Furthermore, some species of mites use CWD
exclusively. However, the major importance of large
branches and fallen logs in forest floor habitats appears to
be that of a refuge for mite species normally occurring in
litter or F layers. This importance likely increases in times
of drought and perhaps under other conditions of stress.
Harvesting and site preparation both have a profound effect
on the distribution of woody debris. Often, slash piles are
created that consist of a mixture of soil, humus, and woody
material. Although these piles usually do not persist for
more than a few years, they are nonetheless an overlooked
and possibly important aspect of arthropod dispersal and
survival.
Fire, both natural and implemented as a management tool,
also affects arthropod populations. Depending on the
severity of the fire, varying amounts of the litter,
fermentation, and humus layers are removed. Sites that are
burned initially to control hardwood competition may be
recolonized at a more rapid rate if woody debris serves as a
refuge. Loblolly pine stands in the Coastal Plain often
receive prescribed fuel-reduction burns every 3 to 5 years
until the final harvest. Although CWD is largely absent from
managed stands with a rotation age of 30 years, woody
debris may yet play a key role in these frequently disturbed
systems if it is introduced or purposely generated.
The arthropod fauna of CWD in southern forests has
virtually gone unstudied. Research efforts should be
directed toward investigating this fauna, with an objective of
determining whether unique species are associated with
woody debris, especially in old-growth forests. Special
attention should be directed toward older logs, hollow logs,
and basal tree holes. These are most likely to shelter unique
species of soil mites.
Management practices aimed toward protecting the
biodiversity of soil fauna should consider the placement of
logs in even-aged pine stands. The geometry and relative
distance of logs may be important considerations, since the
scale of these organisms is a significant factor. Certainly
hardwood logs that are undergoing decomposition should be
protected. Hollow logs and trees containing basal tree-holes
might be singled out for protection as well.
86
Mallow, D.; Ludwig, D.F.; Hayes, MJ.; Crossley, D.A., Jr. 1984.
Habitat selection of postlarval Eutrombicula alfreddugesi and
Eutrombicula splendens from eight microhabitats in Georgia, U.S.A.
(Trombiculidae: Acarina). Journal of the Georgia Entomological
Society. 19:543-548.
Literature Cited
Abbott, David Thomas. 1980. Woody litter decomposition at Coweeta
Hydrologic Laboratory, North Carolina. Athens, GA: University of
Georgia. 136 p. Ph.D. dissertation.
Moore, J.C.; Walter, D.E.; Hunt, H.W. 1988. Arthropod regulation of
mesobiota in below-ground detrital food webs. Annual Review of
Entomology. 33:419-439.
Anderson, J.M. 1977. The organization of soil communities. In: Lohm,
U.; Persson, T., eds. Soil organisms as components of ecosystems.
Ecol. Bull. 25, Stockholm, Swedish Natural Science Research Council:
15-23.
Norton, Roy A. 1980. Observations on phoresy by oribatid mites (Acari:
Oribatei). International Journal of Acarology. 6:121-130.
Andre, H.M.; Lebrun, Ph.; Masson, M.; Sartor, F. 1984. On the use of
Humerobates rostrolamellatus (Acari) as an air pollution bioassay
monitor. The incidence of SO2-NO2 synergism and of winter
temperature. Science of the Total Environment. 39:177-187.
Norton, Roy A.; Behan-Pelletier, Valerie M. 1991. Calcium carbonate
and calcium pxalate as cuticular hardening agents in oribatid mites
(Acari: Oribatei). Canadian Journal of Zoology. 69:1504-1511.
Behan-Pelletier, V.M.; Bissett, B. 1992. Biodiversity of nearctic soil
arthropods. Canadian Biodiversity. 2:5-14.
Park, Orlando; Auerbach, Stanley. 1954. Further study of the tree-hole
complex with emphasis on quantitative aspects of the fauna. Ecology.
35:208-222.
Camin, J. H. 1953. Metagynellidae, a new family of uropodine mites
with the description of Metagynella parvula, a new species from tree
holes. Bulletin of the Chicago Academy of Sciences. 9(18):391-409.
Schultze, Ernst-Detlef; Mooney, Harold A., eds. 1993. Biodiversity
and ecosystem function. Berlin: Springer-Verlag. 530 p.
Seastedt, T.R.; Reddy, V.M.; Cline, S.P. 1989. Microarthropods in
decaying wood from temperate coniferous forests. Pedobiologia.
33:69-77.
Cromack, K., Jr.; Monk, C.D. 1975. Litter production and
decomposition in a mixed hardwood watershed and a white pine
plantation. In: Howell, EG.; Smith, M.H., eds. Mineral cycling in
Southeastern ecosystems. Washington, DC: ERDA Symposium Series
CONF-740513: 609-624.
Swift, MJ.; Heal, O.W.; Anderson, J.M. 1979. Decomposition in
terrestrial ecosystems. Berkeley, CA: University of California Press.
372 p.
Cromack, K., Jr.; Sollins, P.; Todd, R.L. [and others]. 1977. Soil
microorganism-arthropod interactions: Fungi as major calcium and
sodium sources. In: Mattson, W.J., ed. The role of arthropods in forest
ecosystems. New York: Springer-Verlag: 78-84.
Wallwork, John A. 1976. The distribution and diversity of soil fauna.
London: Academic Press. 355 p.
Walter, D.E. 1987. Life history, trophic behavior and description of
Gamasellodes vermivorax n. sp. (Mesostigmata: Ascidae), a predator
of nematodes and arthropods in semiarid grassland soils. Canadian
Journal of Zoology. 65:1689-1695.
Fitter, A.D.; Atkinson, D.; Read, DJ.; Usher, M.B., eds. 1985.
Ecological interactions in soil. Plants, microbes and animals. Oxford:
Blackwell Science Publishers. 451 p.
Hartenstein, R. 1962. Soil Oribatei. I: Feeding specificity among forest
soil Oribatei (Acarina). Annals Entomological Society of America.
55:202-206.
Walter, D.E. 1988. Predation and mycophagy by endeostigmatid mites
(Acariformes:Prostigmata). Experimental and Applied Acarology.
4:159-166.
Hunter, P.E.; Davis, R. 1965. Mites associated with the passalus beetle,
in. Life stages and observations on the biology of Euzercon latus
(Banks) (Acarina: Euzerconidae). Acarologia. 7(l):30-42.
Wilson, Edward O. 1992. The diversity of life. Cambridge, MA:
Belknap Press. 424 p.
87
United States
Department of
Agriculture
Forest Service
Coarse Woody Debris
in Southern Forests
Southern Research
Station
General Technical
Report SE-94
Proceedings of the Workshop on Coarse
Woody Debris in Southern Forests:
Effects on Biodiversity
Athens, GA — October 18-20,1993
The use of trade or firm names in this publication is for reader information and does not imply
endorsement of any product or service by the U.S. Department of Agriculture or other organizations
represented here.
March 1996
Southern Research Station
P.O. Box 2680
Asheviile, North Carolina 28802
j
Biodiversity and Coarse Woody Debris
in Southern Forests
Proceedings of the Workshop on Coarse Woody Debris
j
in Southern Forests: Effects on Biodiversity
Athens, GA
October 18-20,1993
1
Editors:
James W. McMinn, USDA Forest Service,
Southern Research Station, Forestry Sciences Laboratory, Athens, GA,
and D.A. Crossley, Jr., University of Georgia, Athens, GA
Sponsored by:
U.S. Department of Energy, Savannah River Site,
and the USDA Forest Service, Savannah River Forest Station,
Biodiversity Program, Aiken, SC
Conducted by:
USDA Forest Service, Southern Research Station, Asheville, NC,
and University of Georgia, Institute of Ecology, Athens, GA
^^