Langenberger 2004 Review of Research on Philippine Forest Vegetation

7/28/2019 Langenberger 2004 Review of Research on Philippine Forest Vegetation

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Key words: Philippines, forest vegetation, vascular plant diversity, lowland forest, local names

Abstract - The Philippines is one of the most important biodiversity hotspots on earth. Thispaper reviews research on forest vegetation in the Philippines conducted since 1990, identiedusing modern search technologies such as the internet and scientic online databases. Philippineforest vegetation is still poorly represented in international research compared to other tropical

rainforest areas. Only three recent species checklists or enumerations were identied for thewhole of the Philippines, one for the island of Cebu, one for Palawan, and one for Cabra Isletin Occidental Mindoro. Two of them are not freely accessible. The number of published studiesdealing with forest vegetation is also limited. Despite the ecological importance of Philippineforests and the threats they face, knowledge about them has progressed only slightly since thebeginning of the last century when the forest types were dened and described. Most recentresearch focused on trees, often using the traditional lower diameter limit of 10 cm dbh. Smallertrees and other life forms are usually neglected although they account for the bulk of speciesrichness. Additionally, most studies deal with forest vegetation at higher elevations. Lowlandforest, the most threatened habitat in the Philippines, is rarely the focus of studies, very likely

because intact lowland forests hardly exist anymore.Local plant names and the consultation of tree spotters play an important role in Philippineforest vegetation studies. This practice, although potentially very helpful, is prone to errors.Local names used by tree spotters are not necessarily identical with the standardized use in theforestry sector and the scientic literature. The situation is further complicated by the fact thatmany Philippine tree species can be grouped into timber classes whose names at the same timerepresent single species, e.g., white lauan. The uncritical "translation" of local plant names intoscientic species results in unreliable species lists which hamper progress in understandingPhilippine forest vegetation and ecology. In this context the importance of eld characters forpreliminary identications must be stressed.

A REVIEW OF RESEARCH ON PHILIPPINE FOREST

VEGETATION, PARTICULARLY WORK SINCE 1990

INTRODUCTION

The Philippines is a global biodiversityhotspot with high degrees of species richnessand endemism (Ashton 1993, Heaney &Regalado 1998, Myers et al. 2000). Thisuniqueness is largely correlated with pristinevegetation. Devastated areas are mostlyoccupied by a few ecological generalistswhich are often pantropical, like the grass

Imperata cylindrica and the fern Pteridiumaquilinum, or have been - willingly orunwillingly - introduced by man, as theornamental amaranth Celosia argentea.

Such species have insignicant conservationvalue, and can be aggressive pests that furtherweaken destabilized ecosystems.

Despite the extraordinary status of thePhilippines as a biodiversity hotspot as wellas the threats of environmental destruction,the countrys remaining forests and theirbiodiversity are poorly represented inresearch. Sohmer (2001) stated that many so-

called narrow endemics in the Philippines arelikely to go extinct without ever having beendescribed. Concerning the most conspicuouscomponents of forests, the tree species, it has

Agham Mindanaw, 2004, Volume 2, pp. 11-24. Ateneo de Davao University

Gerhard Langenberger

University of HohenheimInstitute of Plant Production and Agroecology in the Tropics and Subtropics (380b)

70593 Stuttgart, Germany

[email protected]


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12 Gerhard Langenberger

been suggested that the Philippines might bethe least known country in southeast Asia(Soerianegara & Lemmens 1994).

Additionally, forest vegetation studies

commonly cover only trees above a givenminimum diameter, often being 10 cm atbreast height (dbh). This practice masks thereal plant biodiversity of forests since smallertrees and other life forms like herbs contributemuch to the overall plant species diversity. OnMt. Mariveles at the entrance of Manila Bay,Luzon, in the Lamao River Reserve, coveringan elevational range from sea level to c. 1400m a.s.l., of the 1151 species and varietiesidentied, 686 were woody plants, of which485 species were classied as trees reachinga height of at least 5 m (Merrill 1906). Thus58% of all plant species and varieties recordedwere either herbaceous (465 species) or woodyshrubs, undershrubs, and scandent shrubs (201species). With the application of a 10 cm dbhlimit an additional portion of woody specieswhich were taller than 5 m but did not reachthe 10 cm diameter threshold would havebeen omitted, and the proportion of the plant

species richness excluded by this diameterlimit would have been at least two-thirds.Gentry and Dodson (1987) also stressed theimportance of the contribution of trees smallerthan 10 cm dbh as well as "nontrees" to overallspecies richness in tropical rain forests. Myown studies on the species composition in alowland forest area located at an elevationalrange between 55 and 530 m a.s.l. on Leyte,Philippines, which covered all vascular plantsexcept crown epiphytes, showed similarresults (Langenberger 2003). Of all plantspecies recorded in a total sampling area of0.49 ha composed of 49 non-contiguous plots,only c. 30% of the species were trees growingtaller than 5 m.

A comprehensive overview of the literaturedealing with Philippine botany and vegetationup to 1992 has been compiled by Madulid &Agoo (1992). Since this bibliography is notreadily available outside the Philippines, I

have listed those publications dealing withPhilippine vegetation and not mentionedelsewhere in this paper in Table 1.

The broad foundation of Philippineforest vegetation analysis was established inthe beginning of the 20th century. The Floraof the Lamao Forest Reserve (Merrill 1906)

and the associated Vegetation of the LamaoForest Reserve (Whitford 1906), The Floraof Mt. Halcon (Merrill 1907), The Floraof Mt. Pulog (Merrill and Merritt 1910),

Philippine dipterocarp forests (Brown &Mathews 1914), and Vegetation of Philippine

Mountains (Brown 1919) are valuable recordsof what Philippine forests used to be. "Theascent of Mount Halcon, Mindoro" (Merrill1907) describes not only the forest conditionsencountered during that first documentedascent of Mt. Halcon, but also gives a veryvivid impression of the sacrices made duringexpeditions at that time.

The most important of the earlypublications might be The Forests of the

Philippines by Whitford (1911). Whitforddefined the Philippine forest types anddescribed their characteristic tree species aswell as the typical environment where theseforest types and tree species were found.

However, at that time, the taxonomic treatmentof Philippine plant species - both for trees andnon-trees - was still in its infancy, makingcomparisons of these early descriptions withlater vegetation studies and their respectivespecies lists difcult or even impossible.

The economically dominant role ofthe dipterocarps appears to have inhibiteddetailed vegetation studies, because the greatmajority of forest species have been of minorcommercial importance. The tendency to sortthe 65 dipterocarp species (Ashton 1993) intofew timber groups, e.g., white and red lauan,apitong, and yakal (Anonymous 1977) hampersforest vegetation analysis up to the presentday. Comparisons with or reconstructionsof the former forest composition of an areaare tricky, because it can be impossible todetermine which species are really coveredby labels like "white lauan", "red lauan", and"apitong".

The objective of this paper is to presentan overview of studies on Philippine forestvegetation over the last 15 years that areaccessible on an international level. I will try


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13Research on Philippine forest vegetation

to evaluate the current status of vegetationstudies, taking into account my ownexperience and observations on the island ofLeyte (Langenberger 2000, 2003).

METHODS

The focus of this paper is on studiespublished after 1990 that deal with the ecologyand plant-biodiversity of Philippine forestvegetation. These publications were identiedusing several procedures. The literaturealready identied for my own study from1996 to 1998 (Langenberger 2003) servedas basis. Additionally, I searched scienticarticles indexed or abstracted in the databases CAB Abstracts and Current Contentsfrom 1984 to October 2003, and I conducted aninternet search with the search engine Google.As search parameters for both electronicsearches I applied the following terms aswell as combinations of the terms: Philippines,diversity, tropical rain forest, vascular plantspecies, vegetation, undergrowth. The articlesand references brought up by the search wereevaluated concerning their relevance for this

paper. Papers discussing the importance offorest vegetation for biodiversity conservation,soil preservation, and watershed managementthat did not add any new facts about thoseforests were not included in this treatment.

RESULTS

Publications since 1990 addressingPhilippine forest vegetation can be classiedinto three categories:

Articles with a taxonomic background.The revision of Philippine Medinilla byRegalado (1995) and all revisions for FloraMalesiana (van Steenis 1950-ongoing) belongto this category. Publications on new speciesor new records also belong to this category,typical examples being the description of newmoss records from Mindanao (Tan et al. 2000)or Mindoro (Tan & Mandia 2001). Althoughsuch publications contain valuable informationon the ecology of the respective species (e.g.,

life form, distribution, habitat), their mainfocus is of a documentary and classicatorykind, and not that of an ecological approach.

A second category of article reports theplant species found in a given area or island,like the checklist of flowering plants ofCebu Island by Bicknell & Bicknell (2001).

Its information is of special importance forthe evaluation of the ecological status andconservation value of the studied locality.Such a checklist enables conclusions on thevegetation types occurring in the area, if theecology and habitat preferences of species arewell known. However, this is often not thecase, and only few species or species groupsare so characteristic for a given habitat asmangroves.

The third category of publication dealswith the interactions between plants and theirenvironment, be it other plants, animals, orthe abiotic environment comprising soils,precipitation, and elevation and temperature.These can be classied as ecological studiesaiming at a better understanding of complexenvironmental correlations. Examples areProctor et al. (1998), Buot and Okitsu (1999),or Ingle (2003).

With the exclusion of taxonomic

treatments, the rst category, all accessiblestudies and references encountered duringmy searches on articles on Philippine forestvegetation are listed in Table 2. Taxonomictreatments were omitted because they arefocused on plant groups and their classicationand not on the species composition of a givenvegetation type or locality. Theses andreports that are only locally accessible werenot included.

SPECIES LISTS

Bicknell & Bicknell (2001) compiled aspecies check list for the whole of Cebu islandand listed 1467 species of spermatophytes.They did not include plants which were foundexclusively in cultivation - a discrimination andclarication desirable also for other studies. Asa checklist for the whole island, it encompassesCebus environmental heterogeneity in termsof soils, elevation, and degree of disturbance.

In contrast to many other species lists basedon herbarium specimens which might havebeen collected 100 years ago, the list by


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Table1.PublicationsonPhilippinevegetation

(excludingmangroveforests)before1990,basedonthecompilationby

MadulidandAgoo(1992),w

ithsomeadditions.

Title1

Remarks

Abrams,N.(

1961):AshortlistofMansakaflora

andtheiruses.P

hilipp.J.Sci.9

0(1):

25-36.

Thisarticlelistsplantsusedbyth

eMansakaintheDavaoregion.

Itw

ouldnowadays

beclassiedasethnobotany.The

specieslistisinformative,comparin

gtheMansaka

name,thecommonname,andth

escienticname,aswellasgiving

theuseofthe

plants.I

tcoversfrommangrovetomountainhabitats.

Allen,M.S.(

1985):TherainforestsofNortheasternLuzonandAgtaforagers.In:The

AgtaofNE

Luzon:RecentStudies.Universityo

fSanCarlos,CebuCity,pp.4

5-68.

Bernard,M.A.(

1959):TheascentofMt.Apo,1

859-1958.Philipp.Studies7(1):7-67.

Brown,W.H.andArgelles,

A.S.

(1917):The

compositionandmoisturecontent

ofthesoils

inthetypesofvegetationatdifferentelevationsonMountMaquiling.

Philipp.J.S

ci.A,1

2(5):221-234.

Aninterestingarticleaboutmoisturecontentofsoilsanditsimpact

onvegetation.

Despitemuchprogressinknowledgeonthismatterthearticleiss

tillworthwhile

reading.

Brown,W.H.,

Merrill,

E.D.andYates,

H.S.(1

917):TherevegetationofVolcano

Island,

Luz

on,

PI,sincetheeruptionofTaalV

olcanoin1911.

Philipp.

J.Sci.

C.

Botany12(4):177-248.

Acomprehensiveaccountonthe

statusoftheplantsuccessionafter

theeruptionof

1911aswellasbackgroundinformationonthevolcanoshistory.

Colina,A.a

ndJumalom,J.(

1973):ReportonthefloraofBaseyRegion,Southwestern

Samar,P

hilippines.Leyte-SamarStudies7(1):38-68.

Colina,A.

andJumalom,

J.(1974):Thegeographicaldistributionofthefloraof

Catipla,Ce

buandBasey,Samar.P

hilipp.Scientist9:33-41.

Gates,F.C.

(1914):SwampvegetationinhotspringsareasatLosBaos,Laguna,P.I.

Philipp.J.S

ci.C.9

(6):495-516.

Theonlyarticleencountereddea

lingwithswampvegetation.

Swampvegetationat

LosBaoshasbeenseriouslymodiedsince1914.T

hearticlewithits

enumerationof

speciesisthereforeanimportantdocument.

Gates,F.C.

(1914):ThepioneervegetationofTaalVolcano.P

hilipp.J.Sci.C.Botany

9(5):391-434.

GivesanaccountonthevegetationofTaalvolcanoshortlyafterthe

1911eruption.

AsstatedbyBrownet

al.

(191

7),

theobservationsseemsometim

estobeabit

supercial.


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Herbert,D.

A.(

1924):PlantlifeonMt.Makiling.

Philipp.Agric.1

3(5):183-197.

Jacobs,

M.

(1972):TheplantworldofLuzonshighestmountains.

Rijksherbarium,

Leiden.32pp.

Kellman,M

.C.

(1970):Secondaryplantsuccess

ionintropicalmontaneMindanao.

ResearchSchoolofPacicStudies.

PublicationBG/2.

AustralianNational

University.

ISBN0708103510.

ComprehensivestudyonplantsuccessionanddeterminingfactorsonM

indanao

includingspecieslists.

Mendoza,D.R.andJacobs,

M.

(1968):Apreliminaryreportofthebotanical

exploration

ofMt.PulogandTabayoc,Kabayan,BenguetandtheSierraMadreMt.

RangesatD

ingalanandBaler,Quezon.Proc.ofthe1968Nat.Sci.andTech.Week,

Part3:411-439.

Merritt,M.L

.(1908):TheForestsofMindoro.Bur.For.Bull.No.8.Manila,51pp.

Pancho,J.V

.(1967):FloraofVolcanoIsland.P

hilipp.Agric.5

0(7):587-625.

Panot,I.A.

(1983):FloristiccompositionofMt.

Pulog.Canopy6:

Payawal,P.C.andMarkgraf,V.

(1981):VegetationandmodernpollenrainofMt.

Makiling,P

hilippines.I.VegetationanalysisoftheNEslope.Kalikasan,P

hilipp.J.

Biol.10(2-3):255-267.

ClassiesforestsonMt.Makilingusingclusteranalysis.

Namessomecommon

speciesbutdoesnotgivecomplete

specieslistusedfortheanalysis.

Seidenschw

arz,F.

(1988):ForesttypesofCebuIsland.

Philipp.

Quart.

Cult.and

Soc.1

6(2):

93-105.

Sutherland,

R.K.

(1944):VegetationStudyof

thePhilippines.

AGS,

SW

Pacic

Area,Philippines.1

14pp.

Weidelt,H.J.andBanaag,V.S.(

1982):Aspects

ofManagementandSilvicultureof

PhilippineDipterocarpForests.

TZVerlagsgesellschaftmbH,

Bruchwiesenweg19,

D-6101Rossdorf1.(GTZPublicationNr.132).

302pp.I

SBN3-88085-157-3.

Althoughdealingwiththemanagem

entofdipterocarpforests,thisbookcontainsmuch

informationaboutspeciescompositionofforesttypesandhabitatpreferencesoftree

species,especiallyonMindanao.Italsocontainsachapteronmountainforests.

Whitford,H.N.(

1909):StudiesinthevegetationofthePhilippines.I

The

compositio

nandvolumeofthedipterocarpfo

restsofthePhilippines.Phil.Jour.

Sci.C,4

(6):699-747.

Dealsmainlywitheconomicaspectsofdipterocarpforestsindifferentregions

ofthePhilippines.


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Bicknell & Bicknell (2001) is the result ofintensive eld work during recent years andrepresents the current status of the islandsspecies composition. A comparable work is

the "Preliminary checklist of the floweringplants of Palawan, Philippines" by Soejartoet al. (1995). While the check list by Bicknell& Bicknell (2001) was - at least for a short time- accessible as a web page that by Soejarto etal. (1995) is not publicly available (see entryin the Literature Cited section). A third specieslist has been published by Buot et al. (1990).They studied the flowering plants of the smallCabra Islet (965 ha) which is part of LubangIsland, Occidental Mindoro. They identied68 families, 245 genera, and 308 species offlowering plants. As the authors state and ascan be seen from the species list itself, CabraIslet is a disturbed site dominated by weeds.

For completeness, the few historicalspecies enumerations are also mentionedhere. A comprehensive treatment of the florafound around Manila was given by Merrill(1912) in his Flora of Manila . It includesplant descriptions and identication keys, but

suffers from its outdated taxonomy and age,which makes its present-day applicabilityquestionable, taking into consideration thetremendous environmental changes whichhave taken place in the Manila area sincethe beginning of the 20th century. Anotherapproach for a single mountain, the Vascular

Flora of Mount Makiling and Vicinity byPancho (1983), which includes very gooddrawings, has never been completed and isrepresented by only one volume. The mostcomprehensive species list is theEnumerationof Philippine Flowering Plants by Merrill(1923-26), which is the only publicationdealing with the whole Philippines, butwhich is also in urgent need of a revised andtaxonomically updated edition.

ECOLOGICAL STUDIES

OF VEGETATION

The second group of data set treated here

covers vegetation studies dealing with plantsand their interactions with the environment.Five data sets deal with vascular plants and arenot restricted to trees or woody plants alone.

Gruezo and Badayos (1996) conducted anEnvironmental Impact Assessment for thePhilippine National Oil Corporation aroundMt. Labo, Camarines Norte Province, Luzon.

They established six circular plots of 40 mdiameter and seven rectangular plots of 50m2 within an elevational range from 410 to1500 m a.s.l. The area was affected by largescale logging operations 30 years ago. A totalof 385 species, 255 genera, and 112 familieswere identied, but the number of speciesfound cannot be referred to the overall plotsize inventoried (ca. 0.789 ha) because plantsobserved in the vicinity of the plots were alsoincluded.

Gruezo (1998) established transect lineson Pagbilao in Quezon, Luzon, and PagbilaoGrande Island covering a total area of 0.26ha. The elevational range is not given, butthe locality is a typical lowland environment.Gruezo (1998) encountered 301 vascular plantspecies. As can be seen from the species lists- which are of prime importance for everyvegetation study - the area is highly degraded.Many of the listed species are typical pioneers,

as well as naturalized exotics. A study byBelonias (2002) on Mt. Pangasugan, Leyteused plots covering 0.35 ha in total along anelevational gradient from lowland forest to themossy forest at the summit of Mt. Pangasuganat 1158 m a.s.l. to investigate the impact ofelevation on the occurrence of dicotyledons.My own study on the foothills of the samemountain (55-530 m a.s.l.) (Langenberger2000, 2003), which comprised 49 plots of100m2 each, included all vascular plantsexcept crown epiphytes. The comprehensiveapproach of these studies is reflected in thehigh species numbers encountered, e.g., the314 dicotyledons found by Belonias (2002) onMt. Pangasugan on an inventory area of 0.35ha, or my own gure of 685 vascular planttaxa on 0.49 ha in the foothills of the samemountain. At higher elevations (1600-2701 ma.s.l.) on Mt. Amuyao, in Mountain Provinceon Luzon, Gonzales-Salcedo (2001) studied

the impact of elevation on species occurrenceand richness. In her data set the high number ofspecies in the elevational zone from 1891 m to2400 m a.s.l. is remarkable (202 species versus


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64 in the zone below and 74 in that above).However, the elevational zones cover differentranges: the lowest zone (1600-1800 m a.s.l.)comprises an elevational range of 200 m, and

the highest zone (2401-2701 m a.s.l.) covers300 m, compared to 509 m elevational rangeof the species rich zone between them. Thedifference in species numbers between thatheight zone and the zones above and belowmay simply reflect the elevational extent of thezones combined with a high species turn-overwith increasing elevation.

Six data sets published since 1990 provideinformation on species richness in forestsbelow 1000 m, but all are limited to trees. Inthe 16 ha Palanan Plot in the Sierra Madre onLuzon 333 tree species of 1 cm dbh or morehave been identied (Co et al. (year not given),CTFS 2004). As part of the Polillo IslandProject, trees 30 cm dbh were inventoriedin 88 belt transects of 10 m width at sixteendifferent sites on the island of Polillo and twosmaller neighboring islands covering a totalarea of 7.42 ha (Clements 2003). Includingspecies found outside the belt transects,

273 tree species (diameter restrictions notclear) and 37 shrubs, ferns and herbs weredocumented. For the Sibulan WatershedReserve 167 tree species 30 cm dbh wererecorded for a transect area of 0.75 ha.

Proctor et al. (2000) studied the impactof geologic parent material at the foot ofMt. Bloomeld, Palawan, at c. 50 m a.s.l.,on tree species occurrence on either side ofa sharp boundary between greywacke andserpentinized peridotite. They established12 plots (20 m x 20 m) totalling 0.48 haperpendicular to the geologic boundary. Allin all they found 79 tree species 10 cm dbh(1,4 m). A total of 75 species were conned togreywacke or serpentinized peridotite, and fouroccurred in the transition zone where soil typeswere mixed. Only one tree species occurredon greywacke as well as on serpentinizedperidotite. On the same mountain but at 170m and 200 m a.s.l. Proctor et al. (1997) had

conducted a study which was focused on soilparameters and plant physiology rather than onthe vegetation. They recorded 21 tree species

2 cm dbh in three plots of 48 m2 (total),and 9 tree species 10 cm dbh in one plotof 400m2.

Proctor et al. (1998) established 0.25 ha.

plots at seven altitudes on Mt. Giting-Gitingon Sibuyan, four of them being below 1000m a.s.l. The number of tree species 10 cmdbh in those plots below 1000 m a.s.l. rangedbetween 80 and 111. Aragones (1991) studiedtwo plots of 0.42 ha at 750 m a.s.l. and 950 ma.s.l., which contained 77 and 49 species oftrees 10 cm dbh, respectively. All other datasets listed in Table 2 cover elevations above1000 m a.s.l.

Within the studies of forest vegetationlisted in Table 2, a trend can be observed inthe pattern of species richness and elevation.The data on tree species with a dbh of 10cm or more show a clear drop of speciesnumbers between c. 700 and 1000 m a.s.l..On Mt. Giting-Giting, Proctor et al. (1998)recorded 80 111 species of trees 10 cmdbh in 0.25 ha plots from 325 to 860 m a.s.l.,but for the 1240 m a.s.l. plot the number oftree species had decreased to 38. Hamann et

al. (1999) documented 92 species of trees 10 cm dbh in a 1 ha plot at 1000 m a.s.l onNegros. Aragones (1991) documented a cleardrop in species richness of trees 10 cm dbhfrom 77 to 49 species between 750 m a.s.l.to 950 m a.s.l. This reflects the commondecrease of tree species and the change intaxa composition with elevation as it has beendescribed by Whitford (1911) and - in detail- by Koch (1982).

Three other studies providing moregeneral information on Philippine vegetationshall be mentioned here. Luna et al. 1999studied a 4 ha plot of logged-over forest in theMt. Makiling Forest Reserve. Unfortunately,they listed only the 22 dominant out of the179 tree species (=5 cm dbh) recorded duringthat study. Buot Jr. (2002) characterized thevegetation types of Mount Akiki in northernLuzon, giving altitudinal ranges of foresttypes and naming prominent plant taxa, but

without providing a species list or data onspecies richness. Madulid & Agoo (1997)described the occurrence, characteristics and


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Locality

Elev.ma.s.l.

Sampledarea/ha

Numberofspp.1

Reference2

Nodiameterorlife

formr

estrictions

Mt.Pangasugan,Leyte3

55-520

0.49

685vascularplantspp.

Langenberger2003

Mt.Pangasugan,Leyte4

90-1158

0.35

314dicotyledonspp.

Belonias2002

Mt.Amuyao,Luzon

5

1600-1800

~0.754

64vascularplantspp.

Gonzales-Salcedo2001

1891-2400

~0.754


2401-2701

~0.754

74vascularplantspp.

Pagbilao&

PagbilaoGrandeIsland

6

?(lowland)

0.26


Gruezo1998

Mt.Labo,

Luzon

7

410-1500

(~0.789)


GruezoandBadayos1996

Restrictiontotreesorwoodyplants

PalananForestDynamicsPlot

80-120

16

333treespp.>1cmdbh

Coetal.(noyear),CTFS2004

Mt.Kitang

lad,Mindanao

1450

0.75

100woodyspp.30cmcbh,

37shrubs,ferns,herbs

Clements2003

Mt.Bloom

eld,Palawan

9

~50

0.48

79treespp.5cmdbh

Lunaetal.1

999

Mt.Mandalagan,Negros

1000

1

92treespp.

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Langenberger 2004 Review of Research on Philippine Forest Vegetation

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