Plants in ,The Forest Canopy: Some Reilections on Current Research and Future Direction

Pltmt G.ologj 153: 39-50. 2001. 0 200 1 Kluwer Actrdemir publisher,^. Printetl iri the Net11erlur1d.s

Plants in ,the forest canopy: some reilections on current research and future direction

Margaret D. Lowman The Marie Selby Botanical Gardens, Sarasota, FL 34236, USA

Key words: Canopy access, Canopy biology, Epiphytes, Forests, Plants

Abstract Plants are one of the sessile components of the forest canopy, and consequently quantitative studies of plant components are more widely available than for some of their mobile counterparts. From a global perspective, several exciting and innovative canopy access tools have been designed over the past few decades that have facilitated the expansion our understanding of canopy plants. These include a network of canopy cranes, the development of the French luge (or sled), and the construction of walkways and platforms for access into different levels of the canopy on a permanent basis. At the recent international forest canopy conference in Sarasota, Florida (Forest Canopies 1998: Global perspective.^, November 4-8, 1998), many canopy plant studies were presented that illustrated the achievements in this field. As co-chair at this event, 1 present here some reflections based on my observations of the development of canopy research between the first and second international conferences. A selection of case studies from the conference presentations are cited in this review, including: tree crown respiration studies from the crane in Panama; epiphyte ecology from walkways in Peru; insect-plant relationships in tree crowns of the USA using platforms; experimental studies of epiphytes in cloud forests using single rope techniques; and epiphyte diversity surveys in Africa. ldeas for the future are also mentioned such as the novel concept of canopy farming of orchids in Costa Rica, the linking of canopy processes to forest floor activities, and the construction of canopy walkways to provide a sustainable forest economy instead of the conventional practice of logging. The integration of research with sustainable use of forests provides a conservation theme for future canopy studies. Such new approaches to studies of canopy plants are important. as scientists increasingly play a role in global conservation policies.

Introduction These are exciting times, and efforts to create successful access methods over the past decade are Botanv needs help from the tropics. Its big plants will beginning to pay off. Over the past one hundred year engender big thinking. history of forest exploration, plants were undoubt- (E. J. H. Corner, 1939, Cambridge University) edly the major focus - for timber, for intrepid orchid collectors and sellers, for magic potions and cures, We have come a long way in our studies of plants in and probably for the sheer adventure of seeing enor- the tropical rain forest since Professor Corner spoke mous trees and complicated vines that soared above these words over fifty years ago, but his philosophy the heads of early explorers. Accounts such as these holds true yet today. Our scientific interest in the trop- abound in the early botanical literature: ics is manifested in part by the intrigue and mystery of Overhead, at a height, perhaps of a hundred feet, the tall trees, and of their canopies. Ecological stud- is an almost unbroken canopy of foliage formed ies of tropical rain forests canopies are a fairly recent by the meeting together of these great trees and endeavour, and the progress over the past decade is their interlacing branches;. . . . It is a world in impressive. which man seems an intruder, and where he feels overwhelmed. . . " (Alfred R. Wallace, 1878. in Any review of plants in the canopy needs to begin Tropictrl Noture) (and probably end) with links to the forest floor. The Now. perhaps 125 years after this intrepid explorer canopy is not a distinct region, and it is not totally first wrote about the wonders of plants in the canopy, separate from the rest of the forest. When some of us we are just beginning to quantify the numbers of plants first discussed the notion of canopy science, we voiced and aspects of their ecology in the upper reaches of the concern about making this a distinct discipline - none forests of the world, both temperate and tropical. of us wish to separate the canopy from the forest, but In the 1970s, several pioneers began canopy re- rather to add the canopy as an integral portion of forest search in earnest (see Sutton 2001). Mitchell (1982) science. With that in mind, we need to acknowledge scaled tall trees in Indonesia and Perry (1 986) in Costa the importance of forest floor dynamics in shaping or Rica (reviewed in Moffett 1993). Soon after them, structuring any forest of the world. other pioneers such as Nalini Nadkarni and I began Seedlings and the dynamics of their survival form climbing trees using single rope techniques and pub- the future of the canopy (e.g., Connell et al. 1984). lishing information on plants in the canopy (Lowman Studies of the maintenance of species diversity have 1984: Nadkarni 1984). In the past 20 years, canopy been a major focus of many ecologists in recent years. research publications have increased tenfold (Nad- The notion of species diversity perhaps also formed karni & Lowman 1995) as the numbers of canopy the basis for initial interest in tropical rain forests researchers expand and canopy access techniques be- by many temperate-based scientists. Both Dan Janzen come more widespread as part of conventional field and Joe Connell championed theories of species equi- equipment. Sites where ongoing canopy research takes librium that sent many temperate botanis~srushing to place now range around the world (Table 1). the tropics to expand their horizons (Connell 1978: I would like to restrict this paper to the past 5 Janzen 1970). Those two ecologists deserve thanks for years, beginning with the review paper by Lowman opening up the eyes of many biologists to see tropical & Moffett (1993) where we simplistically described forests, not just temperate ones. And it was their en- the components of canopy research as follows: mobile, thusiasm for the tropical forests during the 1970s that sedentary, and processes (Table 2). Using these three led many biologists to 'look up'. categories, we linked methodology to subject matter. To become a tree in the canopy. a seedling must We could do little else. since few long terms studies overcome many hurdles, and much of their success existed in the literature that reported extensive results. can be attributed to chance. We now know a lot more Shortly after this time. the first international canopy about seedlings and how they reach the canopy; fac- conference (titled as such) was held. Since that event, tors that affect the recruitment of seedlings and the a virtual explosion of canopy research has occurred. advanced regeneration of individuals can only be de- including increased complexity of sampling and more termined from long term studies such as those set up ambitious international collaborations. by Connell in Australia (Connell & Green 1999: Con- It is hard to believe that in 1993 we only had one nell et al. 1997) and by Foster and Hubbell in Panama canopy crane and two 'Radeau des Cimes' expedi- and elsewhere (Foster & Hubbell 1990; Hubbell & tions under our scientific belts, and there had never Foster 1990). These plots are producing important been a formal international gathering of canopy scien- information about the ecology of the forest floor; sim- tists. Yet now the network of canopy scientists, their ilar long-term studies in the canopy (e.g., crane sites) collaborative research, and their findings are distrib- will produce similar information about the dynamics uted worldwide. At the start of the new millennium, of a forest beyond the forest floor. It is important to we can look forward to an age of intensive data col- recognize that long-term studies are changing our im- lection, where canopy dynamics will become better pressions of regeneration and forest dynamics, and for understood. It is, alas. an urgent race against time to canopy research, such long term research is only just study niany forest canopies before they disappear due underway. to human activities.

Methods for studying plants in canopies

Seedlings and saplings have a distinct advantage for field research: they are accessible for study on the

Table 1. Continued.

Region Name of site Location Time frame Habitat Canopy rraearch projects

Hawaik Volcanoes NP Hawaii, USA 197 1 - 1973 Ohia forest Insect dlverslty

Mesltadel Buey Loa Alamo\, NM, USA 1984 - present pinyon-juniper woodland Watrr halance. \oil rnoihture, solar radlatlon, tree ecophysiology 34"301 N 106"27' W

BOREAS Pnnce Albert NP, 1994 - present Boreal forest Carbon balance, gab exchange & energy flux, canopy architecture & Saskatchewan, Canada remote yenslng, colar radiation -54O N -99O W

Vancouver Island Vancouver Island. BC. 1990 - pre\ent Old growth fore\t Commun~tycompos~tlon, arthropod dl\er\lt) Foreata Can:~da 48'44' N 124"37' W

Central LYT South America

JASON V Project Blue Creek, Belize 1994 - present Trop~calwet rain foreat Ant ~ardens,herbivory, arboreal insects I ha 10' N 89'5' W Luqulllo Experimental Pueno Rlco - 1962 Tropical rain forest Predator-prey relationsh~p,L~rards, arthropods. hrrbi\or) Fore\[ 1 8' 19' N 65'45' W

Coffee Plantat~ons Central Valley. Co~taRlca - 1992 - present Cuffee agroeco3ystem Arthropods, agricultural transformation Finca, La Selva La Selva, Costa Rica 1974-1 983 Tropical rain foreat Natural hlstory, canopy methods, polination

Monteverde Cloud Monteverde, pun tar en:^^ 1980 - present Leeward lower montane wet Epiphyte ecology, nutrient cycllng, bird use ofep~phytea Forest Preserve Province. Costa Rica forest 10" 18' N 84"48' W

Smithsonian Tropical Barro Colorado laland, 1972 present seaconally dry Insects, photoaynthesis, epiphytea, phenology Research Institute Panama 9" 10' N 79'51' W Tropical Moist forest

Parque Natural near Panama City, Panama 1990 - present seasonally dry rain forest Photo.;)nthesis. Ptructure, herhivury, Insects Metropolitano

Operation Drake near Punta Eycoces, Danen 1979- 1980 Tropical rain forest Insect divrrsit). walkway methods, fore\[ \tructure. polination biology, Panama bath

Radeau de Cimej - French Gu~ana 1989 Tropical raln torest Tree architecture X yn~sth.plant & animal relat~on\hipc.ecology. Expedltlon 1 S04'36" N 53"3'15" W canopy-atmosphere interface

Radeau de Cimea - Paracou, French Gulana 1996 Tropical rain forest Tree architecture & growth, plant & dnimal relationships, ecology, Expedit~on11 5" 15'36" N SZ0S6'IS" W canopy-atmoaphere iuterface Tohle I. Continued.

Region Name of site Location T~mcfrome Habitat Canopy research proiects

French Guiana Nouragues, French Guiana 1986 - pre5ent Evergreen tropical forest Gowth dynamics, gaps Research Station 4'5' N 52"401 W

Smithsonian Fogging Pakitra. Peru 1988-1992 Lowland ram forest Insect d~vers~ty Studies

ACEER Nopo Rlver. Peru 1991 - present Lowland troplcal ram forest Epiphytes, herbivo~ 3' 15' S 72'54' W

Explorama Rrrrrver Amalon & Napo R~vers, 1994 present Tropical roln forest Insect diversity Iqu~to,, Peru

Yacumami Preserve Yarapa Rlver, Peru 1998 -present Lowland tropical raln forest Insect diversity, epiphytes 4'2.1' S 73"301 W

Tiputini Biodivers~ty Tiputini River, Ecuado~ 1998 -present Lowland trop~calr:un forest Bats, birds, insect diversity Station 0'40' S 76' 10' W

Choco Canopy Walkway Los Cedros, Ecuador 1997 -present Cloud forest Pollination, epiphytes 0°20' N 78'50' W Surumoni Research Orinoco River. Vcne7uela 1995 present Lowland wet rain forest Structure, epiphytes, ant gardens, birds, phenology Project - European Science Foundation

Asla & South Pacific Larnington National Park Quernaland. Auatril~a 1979 present Subtropical cool rain forest Insect diverhity, herbivory 28" 13' S 153°07' E

Domgo Nat~onolPark NSW, Australia 1979-1990 Subtropical cool rain forest Herhivory. pherrology, insects 30°20'S 153' E

Nrw England National NSW, Australia 1979-1 990 Cool temperate forest Herbivory, phenology. ~nsects Park 30°30' S 152" E

Royal National Park NSW, Australia 19791990 Warm temperate forest Herb~vory,phenology, insects 34"lO'S 151°30' E

CSIRO Athenon, Queensland, -1980 - pre~ent Wet tropical rain forest Phenology, herbivory, reproductive Australia biology

Mr. Spec. National Park -1980 - present Lower montane tropical forest Birds, insect diversity

Cradle Mountain Central Tasmania 1989 present Cool temperare rain forest Invenebrate survey\ (I2 stre\) 41'35.4' S 145"56.Y1E

Operation Drake (Bulolo Buw. Morobe Prov~nce, 1979-1980 Tropical rain forest Insect diversity, walkway methods, Forestry College) Papui Neu Gu~nea forest structure, pollination biology, bons Table I. Continued

Region Name of slte Location T~meframe Hab~tat Canopy research projects

Wau Ecology Institute Wau. Papua New Guinea -1980 -present Lower and mid-montane Herbivory, birds 7'24' S 146'44' E tropical rain forests Operation Drake Sulawesl Tengah. Indonesia 1979-1980 Tropical rain forest Insect diversity, walkway methods, forest structure, (Morowali Nature pollination biology, hats Reserve)

Go~nbackWatershed 35 kln east of Kual Lampur, 1960 -present Hill. dlpterocarp forest Phenology, vertebrates Malaysia

Aerial Walkway Bukit Lanjan. W. Malaysia 1968-1976 Troplcal rain forest Insect vectors, phenology

Canopy Blology La~nhirHills NP, Sarawak, 199 1 present Tropical rain forest Phenelogy, insect abundance, plantkanimal intemct~ons Program in Sarwak Malaysia in canopy layers (CBPS) 4'20' N I13"50' E

Falealupo Saval'i, We\tern Samoa 1996 - Tropical island rain forest Ethnobotany, plant raxonolny

Padang Padang, Indonesia -1980's present Tropical rain forest Foliage-canopy structure, height distribution of woody species 0°53' S 100°21' E

Lake Rara National Park Nepal -1990 Alpine tree limit forest Foliage-canopy structure. height distribution of woody specie5 29O33' N 8Z05' E

Yatsugatake Yatsugatake, Japan - 1980's - present Suhalp~nenl~xed torest Foliage-canopy \tructure. height distribution of woody specie5 36O5' N 136"21' E

Daisen, Japan - 1980's - present Cool temperate deciduouc Foliage-canopy structure, helght d~stributlonof woody species 35'21' N 133"33' E broad-leaved forest

Yakushima Island Yakushima Island, Japan -1980's present Warm temperate evergreen Follage-canopy structure, height distribut~onof woody specles 30°20' N 130"24' E hroad-leaved forest

Hahaji~naIsland Hahajlnla Island. Japan - 1980's - pre\ent Subtropical evergreen broad- Foliage-canopy structure. height distribution of woody species 26O 39' N 142'8' E leaved forest

Mcngla Protected Southern Yunnan Province 1989 - Dlpterocarp forest Conservation Nature Reserve PR. China

Changbaishan Natural Jilin, P.R. Ch~na 1996- Old-growth temperate spruce- Canopy processes, structure & model~ng Reterve 41'23' N 126°55' E fir foresr

Europe

R~verEsk Woodlands Midloth~an,Scotland Phytophagous insects. woodland b~odlveristy,land structure

Gisbum Forest Lancashire, England 1955-1992 Uplands mixed Tree growth, invettebrate populations. soil processes deciduouslcon~ferplantat~on XXX CLa, 0 C 0 -7 s

P -mj. 4 ". *. '.v. mmh EO'Z forest floor (Figure 1 j. Their canopy counterparts - tree foliage, vines, epiphytes - do not have such relative ease of access, but require careful design of hypotheses and safe methodology to collect data. For- tunately, such methods have been developed over the past decade that make all this possible. A range of safe techniques for canopy access (see also Barker & Pinartl 2001: Sutton 2001) in order from simple to more complex, include: Rinocsi1ar.s - the conve~itionalmode of examin- ing the canopy that has been used worldwide. Although safe, this method has limitations for observations of small or cryptic organisms. Sirlgle rope t~cliniqnes(SRT) - a relatively inex- pensive niethod of scaling tall trees but requires a slingshot, bow, or cross-bow for setup. This method has probably been the most widely used, although it is limited to reaching one vertical transect along the rope at a time. L(irlc1er:r - when affixed to a tree trunk, they of- fer access to branches in the mid (and sometimes upper) canopy. Cherr:~~picke,:~ - can be towed by a vehicle and transported to many trees in one day, although limited to dry forests (they can get bogged in moist forests) with road access. Wa1k1vay.r - the constr~~ctionof modular units of bridges and platforms can provide permanent access to many elevated parts of a forest. Argyt-ork.idir,,, tr~folicrlcttio-ti in Ausl!.al~nn rain I'orexr (phorog~.apli hy the author). Hot-air b(i11001is and irzj7atable rufts - even the tallest tree or most remote forest stand can be reached using the dirigible and canopy raft in Advances in research on canopy plants - a few combination. case studies Cor~strirctioncrcrrzes - an excellent tool for reaching all the parts of a stand of trees within several Improved canopy access has facilitated the initiation hectares. of experimental procedures in canopy field work, just Strtellites cii~daerial rc~conntrissarzce- useful for as the advent of scuba promoted experimental ma- mapping large regions of forest or surveying nipulation of fish in and around patch reefs in ma- canopy disease vectors and/or forest distributions. rine biology. Once above the forest floor, the forest Tol,vers - used in climate studies and for mapping biologist js presented with a smorgasbord of oppor- canopy topography. tunity. I have chosen several case studies presented at the recent Canopy Conference in Sarasota, Florida I~nprovedcanopy access techniques, the network of (Lowman 1999) that represent the diversity of current cranes and walkways that facilitate comparative stud- canopy research. Many other notable studies exist, but ies, and the increased communication among re- these examples are illustrative of the breath and scope searchers have greatly expanded the potential for of current projects. For a comprehensive report, refer research on canopy plants. to Lowman & Wittman (1996); this review included all studies of canopy plants that were submitted via the International Canopy Network (ICAN) Bulletin Board. A major advancement in canopy plant research includes the improved accuracy of surveys to iden- tify vascular plants in the canopy, including orchids, bromeliacls, gesneriads, vines and canopy trees, many of whose flowers remained out of reach until improved canopy access. At Marie Selby Botanical Gardens in Florida, a major collection of epiphytes has been accessioned since 1975 including over 29 000 speci- mens of Orchidaceae and 8000 of Bromeliaceae, and these were available for the conference participants. Approximately 123 new species of bromeliads have been classified since 1990 in their Bromeliad Iden- tification Center (H. Luther pers. com.). Each year, expeditions are carried out to collect plants in different equatorial regions of the world including Venezuela, Brazil, Cameroon, Peru and Ecuador. Sometimes, the more conventional techniques for collecting flowers in the canopy such as clippers (Figure 2) are not useful, but inventions such as the canopy sled enable botanists to explore and sample even the tallest emergent (Figure 3). A second advancement in canopy plant studies is the initiation of ecological experimentation of epiphytes. Using single rope techniques (e.g., Nadkarni 1984,200 I). Nadkarni and colleagi~eshave performed the first field experiments, moving epiphytes from one local climatic condition to another. To simulate global climate change, they shifted epiphytes in Costa Rica from moist montane tree crowns to lower valley situa- FI~III.<,2. Con\,enlional means oi Iial.vcjt~ngsa~nplc\ tl.0111 cnllopy bl.anches ~~tingclippers (photograph by BI-uce Holsr, seprotluced tions where it is sunnier and drier. As predicted, the with permission). result was higher mortality of epiphytes and slower growth (Nadkarni 2001). A third major advancement involves the use of con- synthetic measurements on populations of leaves with struction cranes for canopy access that have greatly known age and micro-climatic conditions, using the expanded the scope of intensive research within one canopy crane as their access tool. Because of the ex- forest plot. The Smithsonian Tropical Research Insti- tensive information they can collect for each leaf, they tute in Panama erected the first construction crane for can hypothesize about photosynthetic rates and water canopy research in 1990 under the direction of the late use efficiency for different leaf phenotypes (Kitajima Alan Smith (Moffett & Lowman 1995). This tropical & Millkey 1998). With the excellent access provided dry forest was the site of pioneering work on forest the crane arm above the canopy, researchers can reach canopy structure and whole tree physiology, especially virtually all of the foliage of an entire tree crown for phenology and photosynthesis (Kitajima et al. 1997a, the purposes of whole tree measurenients. It is also b; Mulkey et al. 1995, 1996; Zotz 1993). In particu- possible to haul fairly heavy and bulky eqi~ip~iientsuch lar, the series of studies by Mulkey and Kitajima and as gas analyzers through the canopy in the gondola associates have shown that some tropical tree leaves with relative ease. Since 1990, a series of cranes have in the canopy live up to 700 days whereas leaves of been established in different forest types around the other tree species live less than 100 days. This in- world: USA, Venezuela, Australia, Austria, a second formation is important for creating accurate models one in Panama, and one pending in Malaysia. Sim- of productivity in forest canopies, as well as for un- ilarly a network of canopy walkways is facilitating derstanding the natural history of tropical trees. In comparative studies of other canopy organisms, such addition, they have carried out comprehensive photo- as birds and their host trees (banding studies by Stokes 1989; Wint 1983; Lowman 1984), measurements that included leaves from throughout different levels in the canopy ranged from 30% annual foliage loss in Aus- tralian temperate rain forests (Lowman 1992) to 300% in Australian dry sclerophyll woodlands where bee- tle outbreaks successively defoliated up to three new flushes of leaves (Lowman & Heatwole 1992). Im- proved canopy access has led to improved sanipling designs for measuring herbivory, accounting for vertical stratification throughout the foliage of a crown, and spatial scaling from leaf to entire forest (Figure 4). With more comprehensive canopy access, ecologists can design sampling regimes that include different spatial and temporal scales, from leaf to branch to crown height to whole tree to entire stand to forest tY Pe.

Future directions

We need improved methods for quantifying the biodiversity observed in the canopy - not just streamlining the time and effort required to collect, classify and name species, but also advances in the technology for networking between herbaria, museums and data bases. Certain field studies have not yet been un- dertaken. For example, vine diversity, growth and abundance both within and among different tropical f.i,qi~~'c.i No~i-coli\~~~r~o~~;~lIIIL,;III\ (11 II;I~\?\LIII? C;IIIO[~! /~r;~ticl~c~ forests is still unknown, even though vines may be the using a hot-air dirieihle ant1 canopy ral't (photograph hy thc ;lutlior). largest component of biomass and stems in the forest (reviewed in Putz & Mooney 1991). Do vines create & Schultz 1995) and visitors to epiphytes (Lowman highways for herbivores or other canopy organisms? et al. 1996). What is the extent of vine growth and does it limit the Herbivory is an important canopy process that di- growth of host trees? Who pollinates vines? rectly affects the amount of leaf material available More integrated studies of certain canopy processes for photosynthesis. Not only is herbivory linked to are lacking, such as pollination of vines and tree the forest carbon balance, but herbivory affects other crowns, nocturnal uses of epiphytes by different or- forest dynamics such as tree growth, soil processes, ganisms, and dispersal of epiphyte seeds and establish- successional status, and nutrient cycling (Coley 1983: ment of juveniles. Increasingly, canopy researchers Coxson & Nadkarni 1995; Leigh & Smythe 1978; are seeking protocols to facilitate collaboration of re- Lowman 1992, 1995). Forest herbivory has histori- sults, which are integral to the future management of cally been measured by collecting samples of leaves forests. The increased use of cranes, balloons, and growing in the understorey and estimating missing leaf walkways that enable groups of scientists to work area (Leigh & Smythe 1978; but see Lowman 1984). in the canopy together, also promotes collaboration With the advent of improved methods of canopy on both data bases and funding. The use of com- access, estimates of herbivory in forests are more puter bulletin boards to communicate among botanists comprehensive, and include leaves that are stratified worldwide has increased our sharing of information, vertically throughout the canopy not just those close and effectively publicized different field sites. Table 1 to the forest floor. Whereas original understorey mea- lists all the canopy research sites (Nadkarni 2001) surements of herbivory usually estimated losses of submitted through a survey conducted on the ICAN 5-7% leaf surface area annually (Landsburg & Ohmart bulletin board. With the use of computer networking, A. FOREST STAND 6. SITE C. PLOT D. TREE

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Sites Plots Trees Cro wn Zone

LECtHO. l\ LICK SOME UCHT 81 mosnr swot

G. UNIT F. BRANCH E. CROWN ZONE

Delollalion I - Epiphyfly Ape of Leal Younp (6) lo Old (I) Replicate Leaf Leaves Branches - 'l EXPERIMENTAL DESIGN FOR CANOPY FOLIAGE STUDIES Figure 4. Illustration of scaling from small (leaf) to large (entire forest stand) in canopy sampling. this list can continually be updated as scientists initiate Other ways to utilize canopy plants in forest con- studies at certain sites or establish new field projects at servation include the simple but obvious concept that a global scale. climbing trees and exploring canopy life is excit- Canopy processes must be linked to other for- ing and fun. In particular, the enormous biodiversity est components instead of treating them as discrete and the wide array of interactions in the treetops are units as we have done in the past. Studies to quantify compelling subjects for lay persons to comprehend. frass fall and the herbivory pathway in conjunction Children's books, semi-popular texts, videos and films with decomposers on the forest floor will enable us on forest canopies are promoting the cause of con- to map nutrient cycling comprehensively rather than servation in a very effective fashion. At the Sarasota keep them as separate components of the forest. Once conference, keynote speaker Tom Lovejoy strongly more ecological information about canopies is quanti- advocated that all scientists pay serious attention to fied, then the sustainable management of forests may translating their scientific results into text that can be become more feasible. For example, canopy walkways disseminated to policy makers and the voting public, are being used for both research and for eco-tourism, not just a handful of experts (see also Stork 2001). and serve to promote forest conservation. Walkways The use of canopies as a tool for effective conservation exist in Peru, Australia, Florida, Western Samoa, education cannot be underestimated, if we are to retain Costa Rica, Uganda, and Belize, with other structures intact forests for the next generation. in the planning phases. Another innovative research arena involves canopy Acknowledgements farming, whereby epiphytes could be grown and ex- ported from the tropics as a sustainable harvest. The I am grateful to Andrew Davis and Martin Speight for first canopy farming project in Costa Rica was de- their invitation to participate in the excellent confer- scribed at the Second International Forest Canopy ence Tropical Forest Canopies at Oxford University, conference (Verhoeven & Beckers 1999) whereby or- December 10-17, 1999. I am also indebted to my re- chids were propagated in natural canopy conditions search assistant, Tom Roberts, for editing; to Steve for commercial purposes. Similar projects are under- Mulkey, Kaoru Kitajima, Bruce Holst, Harry Luther, way in Cameroon (Nkongmeneck et al. 1998) and John Atwood, Nalini Nadkarni, Koen Voorhoeven, elsewhere. R.A.Oldeman, Gabriel Beckers, Neville Winchester, Phil Wittman, and Bernard Nkongmeneck for the use of their important canopy projects in my review. And to all the 263 participants at the Second International Lowman, M. D. 1995. Herbivory as a process in rain fore\t canopy Forest Canopy Conference in Sarasota, Florida (No- trees. Pp. 431455. In: Lowman, M. D. & Nadharni, N. M. (eds.) vember 1999), I am grateful for your participation and Forest canopies. Academic Press, San Diego, California. Lowman, M. D. 1999 Life in the treetops. Yale University Press, dialogue, that formulated the basis for this personal New Haven, Connecticut. assessment. This review is not meant to be comprehen- Lowman, M. D. & Heatwole. H. 1992. Spatial and temporal vari- sive, but represents a collation of several main points ability in defoliation of Australian eucalypts and its consequence for the dieback syndrome. Ecology 73: 129-142. highlighted by delegates at the 1998 conference. Lowman. M. D. & Moffett, M. 1993. The ecology of tropical rain forest canopies. Trends Ecol. Evol. 8: 104-108. References Lowman, M. D. & Wittman, P. K. 1996. Forest canopies: methods, hypotheses, and future directions. Ann. Rev. Ecol. Syst. 27: 55- Barker, M. & Pinard, M. A. 2001. Fore5t canopy research: Sam- 81. pling problems, and some solutions. Plant Ecol. 153: 23-38 (this Lowman, M. D., Wittman. P. K. & Murray, D. 1996. Herbivory in a volume). bromeliad of the Peruvian rain forest canopy. J. Brom. Soc. 46: Coley, P. D. 1983. Herbivory and defensive characteristics of tree 52-55. species in a lowland tropical forest. Ecol. Monogr. 53: 209-233. Mitchell. A. W. 1982. Reaching the Rain Forest Roof. UNEP publi- Connell, J. H. 1978. 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