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Ecology |
Department of Biological Sciences, Humboldt State University, Arcata, California 95521 USA
Received for publication October 12, 2001. Accepted for publication August 15, 2002.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: epiphyte biomass • Polypodiaceae • Polypodium scouleri • Sequoia sempervirens • temperate rain forest • tree structure • vascular epiphytes
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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, 1995
). Large tree crowns provide myriad epiphytic habitats, and plants are distributed along gradients of substrate character and microclimate (ter Steege and Cornelissen, 1989
; van Leerdam, Zagt, and Veneklaas, 1990
; Wolf, 1994
; Freiberg, 1996
; Sillett and Neitlich, 1996
). Large branches and crotches of the inner and lower crown often support canopy soils that are exploited by desiccation-sensitive species, including accidental epiphytes whose primary habitat is the forest floor. Small branches of the outer and upper crown are often occupied by drought-adapted species capable of withstanding frequent and severe desiccation.
The majority of studies on vascular epiphytes have focused on tropical rain forests, presumably because temperate rain forests harbor far fewer species. Most epiphyte studies in temperate rain forests have focused on lichens and bryophytes (e.g., Pike et al., 1975
; Sillett, 1995
; Clement and Shaw, 1999
). Some temperate rain forests, however, harbor abundant vascular epiphytes. Ferns, shrubs, and trees regularly occur as epiphytes in Sequoia sempervirens (D. Don.) Endl. (hereafter "redwood") forests.
The most abundant vascular epiphyte in redwood forests is the evergreen fern, Polypodium scouleri Hook. & Grev. (Sillett, 1999
). The geographic range of P. scouleri is strictly coastal, extending from Alaska to Baja California, where it grows epiphytically in foggy forests and terrestrially in salt-spray zones (Whitmore, 1993
). In forests, this species forms sprawling mats on branches and trunks with coriaceous fronds up to a meter long and succulent rhizomes embedded in canopy soils. Redwood is also a coastal species, but it occurs farther inland than P. scouleri. Some of the tallest redwood forests, which occur on sheltered alluvial terraces 30 km from the ocean, have no P. scouleri in their canopies. Indeed, vascular epiphytes are abundant only in old-growth redwood forests within 10 km of the ocean. These rain forests contain some of the largest and most structurally complex redwoods (Van Pelt, 2001
) as well as the tallest known Picea sitchensis (Bong.) Carr. trees (hereafter "Sitka spruce").
While the great height of redwoods has long been recognized, the extreme complexity of their crowns has only recently been appreciated. Canopy studies since 1996 have revealed that large redwoods have individualized crowns with multiple, reiterated trunks arising from other trunks and branches (Sillett, 1999
; Sillett and Van Pelt, 2000
, 2001
). Reiterated trunks in redwood are orthotropic stems with their own systems of plagiotropic branches (Sillett, 1999
). They are indistinguishable from free-standing trees except for their origins within the crown of a larger tree. Fusions among reiterated trunks and their branches are common. Large redwood crowns also retain considerable quantities of rotting wood in broken trunks, dead branches, and fire cavities.
This study focused on P. scouleri in redwood forest canopies. Using rope-based methods, we climbed 32 trees of two species, redwood and Sitka spruce, to quantify both epiphytic ferns and crown structure. We had three specific objectives: (1) to develop a nondestructive method to estimate masses of P. scouleri mats, (2) to estimate whole-tree masses of P. scouleri on both redwood and Sitka spruce, and (3) to assess how tree structure may affect the abundance of vascular epiphytes in redwood rain forests.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Study areas included the redwood-dominated forests along Boyes, Godwood, and Prairie Creeks in Prairie Creek Redwoods State Park and Mill Creek in Jedediah Smith Redwoods State Park. Thirty-two trees, including several of the largest known living redwoods, were selected from these forests for detailed study (Table 1). All trees are rooted below 100 m a.s.l. and stand less than 7 km from the Pacific Ocean. Along Godwood Creek, one redwood and one Sitka spruce were chosen from each of five 0.1-ha reference stands. The mean basal area of these stands is 402 m2/ha with redwood and Sitka spruce accounting for 75.9% and 20.1% of this total, respectively. Other tree species include Tsuga heterophylla (Raf.) Sarg., Chamaecyparis lawsoniana (A. Murr.) Parl., and Rhamnus purshiana DC. Understory vegetation is dominated by Polystichum munitum (Kaulf.) Presl., Vaccinium ovatum Pursh., and Oxalis oregana Nutt. The redwoods along Boyes Creek occur within a 1.0-ha reference stand. This stand has a basal area of 394 m2/ha, 93.7% of which is redwood. Other tree species in the stand include Acer macrophyllum Pursh., R. purshiana, Pseudotsuga menziesii (Mirb.) Franco, T. heterophylla, and Umbellularia californica Nutt. Like the forest along Godwood Creek, understory vegetation is dominated by P. munitum, V. ovatum, and O. oregana. The forests along Prairie and Mill Creeks are similar in floristic composition to those along Boyes and Godwood Creeks.
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) were used to access progressively higher branches and to move laterally through tree crowns.
Fern sampling
Locations and dimensions of all epiphytic P. scouleri mats on each tree were recorded. We defined mats as assemblages of ferns with no rhizomatous connections to other ferns. The height and diameter of supporting branch (if any) of each fern mat were recorded. We also noted locations of fern mats by recording whether they occurred on branches, in crotches, or on trunks. Five dimensions of each fern mat were measured: number of live fronds, surface area (i.e., 
x [mat length/2] x [mat width/2]), mean depth, maximum frond length, and maximum number of pinnae per frond. Depth was measured with a thin metal probe graduated at 1-cm intervals. Five depth measurements were usually taken across the area of the mat, but large mats required more measurements to obtain an average representative of the entire mat. We measured depths of all fern mats in trees along Godwood Creek but only the largest fern mats in trees along Boyes, Mill, and Prairie Creeks. When depth data were available, the product of mean depth and surface area was used to estimate fern mat volume.
We randomly selected 17 of the 158 P. scouleri mats occurring on five redwoods and five Sitka spruces along Godwood Creek for destructive sampling. The mats were first stratified into size classes according to the number of live fronds counted in the field. Since redwoods along Boyes, Mill, and Prairie Creeks occasionally have fern mats larger than the largest size class found in the canopy along Godwood Creek, an additional very large fern mat was randomly selected from the Boyes Creek reference stand. In the trees, fern mats were cut into pieces and stripped down to bare bark. A tarp was suspended beneath large mats to catch material that broke loose during the removal process. A total of 18 fern mats were thus removed from the canopy and transported to the laboratory.
In the laboratory, fern mats were individually dissected and separated into the following components: live fronds, dead fronds, live rhizomes, dead rhizomes, roots, humus, and debris (e.g., leaf litter, bark, twigs, cones). The high volume and interwoven character of non-green material (hereafter "gross humus") made it impractical to completely separate individual components of large fern mats. Roots were particularly difficult to separate from humus during the initial sorting. Consequently, roots that could be easily separated at this point were removed, and the remaining clumps of gross humus were marked for subsampling. Each component, including gross humus, was bagged, dried at 60°C until a stable dry mass was obtained, and weighed to the nearest 0.1 g.
One-tenth of the gross humus was wet-sieved through a 0.5-mm screen. All material passing through the screen was considered humus. This material was washed down the drain and lost during processing. The remaining material within a subsample consisted of rhizomes easily removed by hand (i.e., those few pieces that escaped notice during initial sorting) as well as roots and debris that were separated by using forceps. After sorting, components were dried at 60°C for 24 h and weighed to the nearest 0.1 g. Proportions of subsample masses attributable to humus, rhizomes, roots, and debris were then determined and used to calculate masses of these components in entire gross humus samples. Gross humus component masses were then added to the component masses obtained during initial sorting.
Tree mapping
We quantified tree crown structure by measuring dimensions of the main trunk and all reiterated trunks over 5 cm basal diameter. Trunk diameters were measured directly with a tape, and total tree height was measured by lowering a tape from topmost foliage to average ground level. Tags were attached to the main trunk at 5-m intervals for use as benchmarks in height measurements of reiterated trunks, branches, and epiphytes. The following data were recorded for each trunk: top height, height of origin, basal diameter, and diameter at 5-m intervals along the length of the trunk. For trunks arising from branches, branch basal diameter was also measured. During mapping, we also recorded the number of vascular plant species occurring as epiphytes on each tree.
Data analyses
We used regression analysis to estimate epiphytic fern masses from nondestructive measurements of fern mat dimensions. Model equations based on data collected from the eighteen destructively sampled fern mats were developed via stepwise multiple regression (SAS, 2001
). Fern mat mass was the dependent variable. Fern mat dimensions (i.e., number of live fronds, maximum frond length, maximum number of pinnae, and mat volume) were used as independent variables. The resulting equations were used to estimate masses of each fern mat described on all 32 trees surveyed in this study. Whole-tree estimates of fern mat masses were obtained by summing estimated values for all fern mats on a tree.
Mapping data were used to generate the following 11 tree structure variables for analysis: tree height, main trunk diameter at breast height (DBH), main trunk volume, volume of reiterated trunks arising from other trunks, volume of reiterated trunks arising from branches, percentage of total trunk volume in reiterations, percentage of total reiterated trunk volume on branches, total number of reiterated trunks, number of reiterated trunks >1 m basal diameter, number of branches >0.5 m basal diameter, and diameter of the tree's largest branch. We calculated trunk volumes by applying the equation for a regular conic frustum (i.e., volume = length x /3 x [lower radius2 + lower radius x upper radius + upper radius2]) to the trunk diameter data. Since there was strong multicollinearity among the tree structure variables, we used principal components analysis (PCA) to derive orthogonal linear combinations, or components, of these variables (McCune and Mefford, 1999
). Interpretation of principal components was based on correlations (r) between the original variables and the principal components themselves.
We explored potential relationships between epiphytes and tree structure by examining correlations among tree-level variables. Epiphyte variables included the number of fern mats per tree, total fern mat mass, mass of the tree's largest fern mat, and number of epiphytic vascular plant species per tree. Tree structure variables included the 11 original variables and their significant principal components.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Along Godwood Creek, redwoods supported larger P. scouleri mats than adjacent Sitka spruces (mean fern mat mass 3.6 kg vs. 0.9 kg, P < 0.0002). Over one-fifth of the mats on the redwoods exceeded 5 kg, but only one of the fern mats on the Sitka spruces was this large. Despite these differences in individual fern mat sizes, the composition of fern mats on the two tree species was nearly identical. Mat size differences were partly attributable to differences in supporting branch diameters; redwoods had thicker branches than Sitka spruces (Table 1). Redwoods also had far more complex crowns than adjacent Sitka spruces. For example, none of the Sitka spruces in this study had any reiterations (Table 1). Further analyses focused on redwood crown structure and its potential effects on epiphytic ferns.
Tree crown structure
The redwoods sampled in this study had complex crowns with reiterated trunks accounting for up to 13% of their total trunk volume (Table 1). Many of the redwoods had multiple trunks and branches over 1 m diameter. These massive crowns supported up to eight species of vascular epiphytes, including enormous quantities of P. scouleri and associated material (Table 1). Thirteen redwoods had over 100 kg of fern mats. The highest estimated fern accumulation on a single tree was 742 kg.
The largest fern mats occurred at the bases of huge branches, in crotches at the bases of large reiterations, and on broad platforms at the tops of broken trunks. Of the total fern mass on redwoods, 79.9% occurred on branches. The remainder occurred in crotches at the bases of reiterations (11.5%) or on trunks (8.5%). Fern mats differed in frond dimensions depending on crown location. For comparably sized mats, fronds were significantly (P < 0.01) larger in crotches than on branches or trunks.
There were a number of significant positive correlations among the tree structure and epiphyte variables (Table 3). Multicollinearity among the tree structure variables was eliminated by PCA, which extracted three significant components (eigenvalues = 4.76, 2.51, 1.78) accounting for 79% of the total variation in the 11 original variables (Table 4). Principal component 1 represented the overall size and complexity of a tree and its reiterated trunks. Very large, complex trees supported more and larger fern mats and had higher vascular epiphyte species richness and than smaller, simpler trees (Table 3). Neither PC2 nor PC3 were correlated with tree-level epiphyte abundance.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Clement and Shaw, 1999
). Age differences among fern mats may account for the positive correlation between fern mat mass and maximum frond dimensions. The first P. scouleri frond emerging from a fertilized gametophyte consists of a single pinna, and as the sporophyte develops into a fern mat, frond lengths and numbers of pinnae increase. Small (<0.5 kg) P. scouleri mats rarely have fronds over 30 cm long with more than 11 pinnae, while large (>5 kg) mats frequently have fronds over 70 cm long with more than 23 pinnae.
Fern mats of the same size, however, may differ in frond dimensions depending on their locations within a tree crown. Crotches are better sites for accumulation than branches or trunks, which will tend to shed material more easily from their steep sides. Fern mats in crotches receive more stemflow (Andrade and Nobel, 1997
) and store more water than fern mats on branches (Ambrose, 2003
). A favorable moisture regime may permit fern mats to develop more quickly in crotches, thus explaining why these mats have larger fronds than more desiccation-prone mats on branches and trunks.
Coriaceous leaves and succulent rhizomes confer substantial desiccation resistance on some epiphytic ferns (Hietz and Briones, 1998
). Despite these adaptations, P. scouleri cannot withstand severe droughts and is restricted to coastal environments throughout its range (Whitmore, 1993
). Even within redwood rainforest canopies, vertical microclimatic gradients appear to affect its morphology. Regardless of overall fern mat size, maximum frond dimensions become progressively smaller with increasing height. During rainless periods, the upper forest canopy is brighter, warmer, windier, and less humid than the lower canopy (Parker, 1995
). Thus, P. scouleri is subjected to more frequent and severe periods of desiccation in the upper canopy than in the lower canopy. Thick cuticles contribute to very low rates of uncontrolled water loss from vascular epiphyte leaves (Helbsing, Reiderer, and Zotz, 2000
), but a larger frond loses more water than a smaller frond due to higher leaf area. Upper canopy fern mats may therefore produce smaller fronds than lower canopy mats because rapid desiccation restricts frond growth.
The succulent rhizomes of P. scouleri store water that can be tapped by transpiring fronds, but live rhizomes represent less than 5% of fern mat mass, and their supply of stored water is limited. Roots supply the bulk of water lost during evapotranspiration. Like other vascular epiphytes, P. scouleri invests a large proportion of its fixed carbon in root production in order to efficiently extract water and nutrients from desiccation-prone canopy soils (Vance and Nadkarni, 1992
; Bohlman, Matelson, and Nadkarni, 1995
).
The ability of fern roots to extract moisture from organic matter in large mats depends upon the depth to which they penetrate humus layers. Unfortunately, this cannot be fully evaluated with our data because we were unable to distinguish living from dead roots in our samples. Material sloughing from the bottoms of thick mats was often poorly consolidated and apparently lacking viable fern roots. It remains unclear whether or not P. scouleri can extract water stored in the deepest humus layers of very large mats. Even if it is unavailable to epiphytic ferns, other organisms in the canopy utilize this stored water.
Ecological importance
Debris from tree litterfall, especially foliage, is a major component of fern mats, but most of the dead organic matter in the mats comes from P. scouleri itself, especially humus derived from its roots. Furthermore, as mats develop, they occupy progressively larger surface areas that can more effectively capture falling debris. Therefore, P. scouleri is directly responsible for much, if not most, of the retention and accumulation of dead organic matter in large tree crowns in redwood rain forests.
The water stored by arboreal dead organic matter enables terrestrial organisms to flourish high above the ground. A wide variety of vascular plants, including ferns (e.g., Athyrium filix-femina (L.) Roth, Polystichum munitum), shrubs (e.g., Gaultheria shallon Pursh., Ribes spp., Sambucus callicarpa Greene, Vaccinium spp.), and trees (e.g., Lithocarpus densiflorus (H. & A.) Rehd., Rhamnus purshiana, Picea sitchensis, Pseudotsuga menziesii, Tsuga heterophylla, Umbellularia californica) occur as epiphytes amidst P. scouleri mats (Sillett, 1999
). Terrestrial animals, including salamanders, mollusks, earthworms, and a plethora of arthropods, also frequently inhabit these mats. Many of these organisms are highly sensitive to desiccation, and it is unlikely that they could survive in redwood canopies without substantial quantities of P. scouleri and associated material.
The trees also directly exploit the water and nutrients stored in their epiphytic fern mats. We occasionally find well-developed adventitious tree roots amidst P. scouleri in both redwood and Sitka spruce. These roots are indistinguishable from their counterparts on the forest floor; both possess well-developed mycorrhizal associations. A similar phenomenon has been observed in a wide variety of other temperate and tropical rain forest canopies (Nadkarni, 1981
, 1994
). In redwoods, adventitious roots are most frequently encountered at the bases of large reiterated trunks. The extent to which these trunks rely upon water and nutrients absorbed from fern mats remains to be determined. The size and complexity of the roots systems we have observed suggest that their contributions are not trivial.
Effects of tree structure
By measuring both epiphytes and tree structure, our results permit a quantitative assessment of crown-level complexity and its potential effects on the abundance of vascular epiphytes. Very large, complex redwoods support more fern mass and have higher epiphyte species richness than smaller redwoods. This positive correlation between tree size and vascular epiphyte abundance has been observed in other forests (e.g., Hietz and Hietz-Seifert, 1995
) and is most likely a consequence of tree age. Unfortunately, the age of large redwoods is nearly impossible to determine without causing unnecessary damage to the trees. The largest redwoods in this study may be over 2000 yr old (Sawyer et al., 1999
), while the smallest are probably less than 1000 yr old. Overall size and complexity (PC1) are undoubtedly correlated with redwood age, but the correlation between tree size and age is often weak in shade-tolerant conifers (see Lyons, Nadkarni, and North, 2000
).
A number of factors other than tree size and age contribute to crown-level complexity and epiphyte accumulation in redwoods. Similar-sized trees standing side by side in the same stand can support very different quantities of P. scouleri (e.g., Demeter and Rhea), some of the largest, most complex trees support relatively small quantities of P. scouleri (e.g., Del Norte Titan), and some relatively small trees with simple crowns support relatively large quantities of P. scouleri (e.g., Rhea). The sources of such variation remain unclear, but differences in crown-level microclimates may be important. Some of the deepest accumulations of organic matter, which occur in crotches in the lower canopy where light levels are very low (Ambrose, 2003
), contain very little if any P. scouleri. Redwoods with very dense crowns may have a disproportionate amount of poorly illuminated substrates that are currently unsuitable for P. scouleri even though this species may have thrived on these sites and contributed much of the organic matter at earlier times when conditions were more favorable for fern growth.
The disturbance history of individual trees and forest stands also influences epiphytic ferns. Fires, crown failures, and adjacent treefalls can lead to sudden, often dramatic changes in tree structure, microclimate, and epiphyte abundance. Fire scars, snapped trunks, and broken branches are widespread in large redwoods, whose crowns are highly individualized and asymmetrical (Sillett, 1999
). The mass of epiphytes on any large redwood is thus a dynamic quantity affected by both the severity and timing of past disturbance events. For example, a powerful storm in March 1998 dislodged a large fern mat from one redwood (Trapdoor) when an adjacent tree fell into the side of its crown (see Taylor, 2001
). The total fern mass on this tree was instantly diminished by over 40%.
Implications of whole-tree estimates
Very few studies supply epiphyte mass estimates for whole trees. The highest previously reported estimates are 115.0 and 141.9 kg for single trees in tropical cloud forests (Nadkarni, 1984
; Hofstede, Wolf, and Benzing, 1993
). By comparison, the Sitka spruces we sampled along Godwood Creek support a mean of 177 kg of epiphytic material, including lichens, bryophytes, ferns, and associated organic matter (Ellyson and Sillett, in press). The redwoods we sampled along Godwood, Boyes, and Mill Creeks support means of 47, 178, and 261 kg of P. scouleri mats, respectively. Many other epiphytes also occur on these redwoods. Several trees (e.g., El Viejo del Norte, Floating Raft, Terex Titan) support dozens of full-size shrubs and a few stunted epiphytic trees. Organic matter also accumulates on branches and in crotches not associated with ferns. Thus, our results greatly underestimate these trees' total masses of epiphytic material. Even so, they suggest that epiphyte masses on large trees in redwood forests rival those on trees in any other forest previously studied.
Coastal forests containing trees almost as large as those included in this study no longer exist outside Redwood National and State Parks, but historical records indicate that British Columbia, Washington, and Oregon once had such forests (e.g., see data in Carder [1995]
). The few remaining old-growth redwood forests provide a rare glimpse of conditions that were probably common in the vast low elevation temperate rain forests that once extended from Alaska to California, namely giant trees supporting dozens to hundreds of kilograms of epiphytic material. Mature second-growth redwood forests are also rare, and, aside from scattered remnant trees, the few that remain do not contain large trees with complex crowns. Consequently, vascular epiphytes, including P. scouleri, are now sparse or absent in all redwood forests except old-growth forests.
New silvicultural practices in the redwood region raise the possibility of accelerating the development of old-growth characteristics in managed forests (Thornburgh et al., 1999
). Manipulations of canopy structure and microclimate are possible via thinning, green tree retention, and controlled burning, but development of forests containing redwoods with huge branches and highly reiterated crowns will require several centuries or more. The development of large P. scouleri mats is also likely to require centuries. Thus, the diversity of desiccation-sensitive species inhabiting old-growth redwood rain forest canopies may not be able to colonize managed forest canopies into the foreseeable future. Conservation of old-growth redwood rain forests is therefore critical not only for their magnificent trees but also for their rich communities of epiphytes and associated organisms thriving high above the ground.
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FOOTNOTES |
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2 Author for reprint requests (scs6{at}humboldt.edu
)
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LITERATURE CITED |
|---|
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Andrade J. L. P. S. Nobel 1997 Microhabitats and water relations of epiphytic cacti and ferns in a lowland neotropical forest. Biotropica 29: 261-270
Benzing D. H. 1990 Vascular epiphytes: general biology and related biota. Cambridge University Press, New York, New York, USA
Benzing D. H. 1995 Vascular epiphytes. In M. D. Lowman and N. M. Nadkarni [eds.], Forest canopies, 225–254. Academic Press, New York, New York, USA
Bohlman S. A. T. J. Matelson N. M. Nadkarni 1995 Moisture and temperature patterns of canopy humus and forest floor soil of a montane cloud forest, Costa Rica. Biotropica 27: 13-19[CrossRef][ISI]
Carder A. C. 1995 Forest giants of the world, past and present. Fitzhenry and Whiteside, Markham, Ontario, Canada
Clement J. P. D. C. Shaw 1999 Crown structure and the distribution of epiphyte functional group biomass in old-growth Pseudotsuga menziesii trees. Ecoscience 6: 243-254
Dawson T. E. 1998 Fog in California redwood forests: ecosystem inputs and use by plants. Oecologia 117: 476-485[CrossRef][ISI]
Ellyson W. J. T. S. C. Sillett 2003 Epiphyte communities on Sitka spruce in an old-growth redwood forest. Bryologist, in press
Freiberg M. 1996 Spatial distribution of vascular epiphytes on three emergent canopy trees in French Guiana. Biotropica 28: 345-355[CrossRef][ISI]
Helbsing S. M. Reiderer G. Zotz 2000 Cuticles of vascular epiphytes: efficient barriers for water loss after stomatal closure?. Annals of Botany 86: 765-769
Hietz P. O. Briones 1998 Correlation between water relations and within-canopy distribution of epiphytic ferns in a Mexican cloud forest. Oecologia 114: 305-316[CrossRef][ISI]
Hietz P. U. Hietz-Seifert 1995 Structure and ecology of epiphyte communities of a cloud forest in central Veracruz, Mexico. Journal of Vegetation Science 6: 719-728[CrossRef][ISI]
Hofstede R. G. M. J. H. D. Wolf D. H. Benzing 1993 Epiphytic biomass and nutrient status of a Colombian upper montane rain forest. Selbyana 14: 37-45
Ingram S. W. N. M. Nadkarni 1993 Composition and distribution of epiphytic organic matter in a neotropical cloud forest, Costa Rica. Biotropica 25: 370-383[CrossRef][ISI]
Jepson J. 2000 The tree climber's companion. Beaver Tree Publishing, Longville, Minnesota, USA
Lyons B. N. M. Nadkarni M. P. North 2000 Spatial distribution and succession of epiphytes on Tsuga heterophylla in an old-growth Douglas-fir forest. Canadian Journal of Botany 78: 957-968
McCune B. M. J. Mefford 1999 PC-ORD. Multivariate analysis of ecological data, version 4. MjM Software Design, Gleneden Beach, Oregon, USA
Nadkarni N. M. 1981 Canopy roots: convergent evolution in rainforest nutrient cycles. Science 214: 1023-1024
Nadkarni N. M. 1984 Epiphyte biomass and nutrient capital of a neotropical elfin forest. Biotropica 16: 249-256[CrossRef][ISI]
Nadkarni N. M. 1994 Factors affecting the initiation and growth of aboveground adventitious roots in a tropical cloud forest tree: an experimental approach. Oecologia 100: 94-97[CrossRef][ISI]
Parker G. G. 1995 Structure and microclimate of forest canopies. In M. D. Lowman and N. M. Nadkarni [eds.], Forest canopies, 73–106. Academic Press, New York, New York, USA
Pike L. H. W. C. Denison D. M. Tracy M. A. Sherwood F. M. Rhoades 1975 Floristic survey of epiphytic lichens and bryophytes growing on old-growth conifers in western Oregon. Bryologist 78: 389-402[CrossRef]
SAS. 2001 JMP 4.0. SAS Institute, Cary, North Carolina, USA
Sawyer J. O. S. C. Sillett W. J. Libby T. E. Dawson J. H. Popenoe D. L. Largent R. Van Pelt S. D. Veirs R. F. Noss D. A. Thornburgh P. Del Tredici 1999 Redwood trees, communities, and ecosystems: a closer look. In R. F. Noss [ed.], The redwood forest: history, ecology, and conservation of the coast redwoods, 81–118. Island Press, Covelo, California, USA
Sillett S. C. 1995 Branch epiphyte assemblages in the forest interior and on the clearcut edge of a 700-year-old Douglas-fir canopy in western Oregon. Bryologist 98: 301-312[CrossRef][ISI]
Sillett S. C. 1999 Tree crown structure and vascular epiphyte distribution in Sequoia sempervirens rain forest canopies. Selbyana 20: 76-97
Sillett S. C. P. N. Neitlich 1996 Emerging themes in epiphyte research in westside forests with special reference to the cyanolichens. Northwest Science 70, Special Issue: 54–60
Sillett S. C. R. Van Pelt 2000 A redwood tree whose crown is a forest canopy. Northwest Science 74: 34-43[ISI]
Sillett S. C. R. Van Pelt 2001 A redwood tree whose crown may be the most complex on Earth. In M. Labrecque [ed.], L'Arbre 2000, 11–18. Isabelle Quentin, Montréal, Québec, Canada
Taylor P. L. 2001 Sitting on top of the world. In Science at the extreme, 92–117. McGraw-Hill, New York, New York, USA
ter Steege H. J. H. C. Cornelissen 1989 Distribution and ecology of vascular epiphytes in lowland rain forest of Guyana. Biotropica 21: 331-339[CrossRef][ISI]
Thornburgh D. A. R. F. Noss D. P. Angelides C. M. Olson F. Euphrat H. H. Welsh Jr 1999 Managing redwoods. In R. F. Noss [ed.], The redwood forest: history, ecology, and conservation of the coast redwoods, 229–261. Island Press, Covelo, California, USA
van Leerdam A. R. J. Zagt E. J. Veneklaas 1990 The distribution of epiphyte growth-forms in the canopy of a Colombian cloud-forest. Vegetatio 87: 59-71[CrossRef][ISI]
Van Pelt R. 2001 Forest giants of the Pacific coast. University of Washington and Global Forest Press, Seattle, Washington, USA
Vance E. D. N. M. Nadkarni 1992 Root biomass distribution in a moist tropical montane forest. Plant and Soil 142: 31-39[ISI]
Whitmore S. 1993 Polypodium. In J. C. Hickman [ed.], The Jepson manual, 100–101. University of California Press, Berkeley, California, USA
Wolf J. H. D. 1994 Factors controlling the distribution of vascular and non-vascular epiphytes in the northern Andes. Vegetatio 112: 15-28
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  H. A. Enloe, R. C. Graham, and S. C. Sillett Arboreal Histosols in Old-Growth Redwood Forest Canopies, Northern California Soil Sci. Soc. Am. J., February 2, 2006; 70(2): 408 - 418. [Abstract] [Full Text] [PDF]
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