*Corresponding author: [email protected]
Cave Resource Evaluation Using Sensitivity Scoring Index Applied to the Capisaan Cave System,
Nueva Vizcaya, Philippines
Jayson Q. Caranza1* and Margaret M. Calderon2
1College of Forestry Environment and Resources Management, Nueva Vizcaya State University, Bayombong, Nueva Vizcaya 3700 Philippines
2College of Forestry and Natural Resources, University of the Philippines Los Baños, College, Laguna 4031 Philippines
Caves are significant nonrenewable resources that provide a variety of ecosystem services with varying sensitivities to disturbance. This study assessed the sensitivity of resources found in the Capisaan Cave System (CCS) in Kasibu, Nueva Vizcaya to below and above-ground human activities or disturbances by adopting a standardized scale or index. Cave passages comprising the whole cave system were divided into subsections and were individually evaluated. Parameters included the characterization of the biological, hydrological, geological, mineralogical, paleontological, and cultural resources of the cave system. Inventory methods such as belt transect, point-transect distance sampling, opportunistic sampling, and total enumeration were employed. Results showed that animals associated with CCS both at the surface and subsurface levels had high diversity and endemicity. Hydrology inside and surrounding CCS is also very active and continuously shapes the geological structure of CCS. Among the sensitivity parameters, biota was found to be the most sensitive to disturbance followed by speleothems and hydrology resources. The computed sensitivity of resources found in CCS places it in the “slightly sensitive” classification. However, the study recommends that managers look at the individual parameter scores of each cave section instead of simply looking at the overall score of the cave system. The sensitivity classification of CCS was changed to “severely sensitive” when the zero-indexed parameters were removed from the computation, with Section 1 obtaining a classification of “critically sensitive” and, therefore, requiring more strict and intensive management interventions. This information is important in deciding where and how to manage specific sections without sacrificing future ecological and economic uses. Overall, the study successfully tested the applicability of the modified existing standardized cave sensitivity assessment index for a tropical cave, providing a comprehensive method that may serve as a convenient model for assessing other cave systems in the country.
Keywords: cave inventory, cave management, cave resources, sensitivity assessment, scoring index
INTRODUCTION
Karst formations are geomorphologic features formed by the dissolution of soluble bedrock composed mainly of carbonate rock (USDA n/d). The dissolution results in a variety of landscapes made of large, medium, or
small-scale features both on the surface and beneath (Wagner 2013). Underground karst processes may give rise to the formation of three-dimensional systems of conduits referred to as “caves” (White 2002). In the Philippines, caves are among the least studied frontiers.
Cave environments in the country are mostly hidden and contain a variety of physical and psychological obstacles, ISSN 0031 - 7683
Date Received: 19 Dec 2022
resulting in less attention to mainstream scientific inquiry.
In most cases, adventurists, caving communities, and a few speleologists, anthropologists, and biologists appreciate these areas and study how different creatures and human communities interact with this environment. However, within the last decade, tourism and economic opportunities have increased the exploitation of caves (BMB-NCC 2018). With this increasing attention, it is essential that the management requirements of caves must be recognized by the government and the community to create, actualize, and enforce sound management policies.
Different parts of caves, specifically long cave systems, have different physical formations that have varying levels of vulnerability and sensitivity to disturbance. This poses a challenge for effective cave management on how to correctly evaluate the relative sensitivity of passages (Gillieson 2011). Thus, a cave inventory method that both provides insights into the sensitivity level of a cave and can simplify the flow of cave information to stakeholders is vital for the efficient creation and execution of cave protection and management policies at the local and national levels (Harley et al. 2011). Before caves can be actively managed, stakeholders must recognize the sensitivity levels of existing cave resources (Brown and Kirk 1999; Kovarik and Kambesis 2005). The sensitivity index is described as the vulnerability of cave resources with reference to the richness of various important resources found in a particular cave that can be exposed to human degradation (Harley et al. 2011). The sensitivity of caves and cave environments to disturbance then is related to the sum and state of cave resources (van Beynen and Townsend 2005).
An orderly scoring system can provide a calculable and impartial method of prioritizing strategies for cave management with limited time and resources. Index scores direct cave managers in deciding to be reactive or preemptive in protecting and reducing further damage to caves (Harley et al. 2011). The cave sensitivity index provides a coherent scale that measures the specific sensitivity of each physical cave attribute that is used to describe the relative sensitivity of the whole cave.
The Philippine government enacted Republic Act No. 9072, or the National Caves and Cave Resources Management and Protection Act in 2001, to safeguard karst areas in the country. However, this law is limited in approach as it is intended primarily for the classification, administration, and preservation of caves and cave resources (Restificar et al. 2006). The current law does not target sections of a particular cave that are more at risk and does not further provide a systematic way of giving measures to identify the sensitivity of a cave to external disturbance. Herein, this study improves upon the methodology currently being used by the Department of
Environment and Natural Resources (DENR) in assessing caves in the Philippines by means of a standardized cave sensitivity scoring index.
MATERIALS AND METHODS
Study Area
The Capisaan Cave System (CCS) is situated in the municipality of Kasibu in the southeastern part of Nueva Vizcaya province in Region 2 (Figure 1). It is geographically situated at 16⁰19’10” N latitude and 121⁰23’43” E longitude and has an elevation of 700–900 masl. The cave has a length of approximately 4.2 km with nine known entrance and exit points. Most of the natural vegetation of the cave was mostly confined to vertical walls of the cave openings, whereas the adjacent vegetation has already been replaced by cultivated plants.
Lion, Alayan, Sang-at Salug, and Malukbo cave entrances are interconnected into a single cave system, whereas Sabrina and Heaven caves are technically separate caves with very short passage lengths. The cave passages comprising the whole cave system were divided into subsections following segmentations created by entrance and exit points (Figure 1).
Cave Sensitivity Index
The inventory of the CCS determined the level of sensitivity of the different cave resources to below and above-ground human activities or disturbances by adopting a standardized scale or index. The Cave Sensitivity Index developed by Harley et al. (2011) served as the basis for the sensitivity assessment. Modifications were made by partitioning cave passages into specific equal intervals in relation to cave passage length, marked as stations, and measuring each station’s sensitivity score.
Parameters included the characterization of the biological, hydrological, geological, mineralogical, paleontological, and cultural resources of the cave system. The different sensitivity scales that were used, along with descriptions for each parameter, are presented in Table 1.
Identification and Measurement of Cave Biota Vegetation. Plants found at all nine cave entrances were identified from 03 –06 May 2019. To account for the relative frequencies of plants, a transect line was established from the cave entrance to the end of the twilight zone of each entrance. Stations were established every 5 m. All plant species present in each station were photo-documented, counted, and identified on-site.
Cave fauna. Opportunistic sampling was done for snails and clams, fishes, and herpetofauna from the cave entrance
to the end of the twilight zone from 06–10 May 2019. Snails and clams were identified and described as to presence or absence in the different cave entrances. Direct hand capture, use of a gill net, and photo documentation were employed for fish, anurans, and reptiles. Herpetofauna
was surveyed from 07:00 to 11:00. Visual search was used with minimal active search to avoid disturbing the natural order and habitat aesthetics of the cave entrances. In combination with opportunistic sampling, the belt transect method was used for the collection and identification
Table 1. Cave sensitivity index [adopted from Harley et al. (2011)].
Variable 3 2 1 0 Source of data
Biota
• Species richness
• Diversity index
• Evenness
• Population density
Widespread individuals of single species; or multiple individuals of multiple species; or listed as endangered species;
alternatively, possible new species found
Multiple individuals of
single species A single individual
or single species No biota Primary data
Hydrology Drips, seeps, pools wide- spread; or direct aquifer connection; or intermittent stream
Drips, seeps, pools,
multiple areas Drips, seeps, pools
sparse, localized No features Primary survey and KII
Speleothems Widespread Multiple areas Localized area No features Primary survey
Mineralogy Widespread; or possible new mineral found
Multiple areas Sparse; localized No features Primary survey
Paleontology Widespread Multiple areas Sparse; localized No features Primary survey, sec- ondary data, KII Cultural/ Historical Cave listed as a protected site
by the Government (National Museum, National Historical Commission)
Multiple areas Sparse; localized No features Secondary data, KII Figure 1. Map and sectioning of Capisaan Cave System.
of arthropods in the different cave sections. The belt transect is similar to the line transect method; only this employed the use of a 5 m x 5 m quadrat or 25 m2 plot at a standard 50-m interval if the passage was more than 500 m and 15 m for shorter passages. Specimens that were not readily identified were placed in cloth bags for later examination. All collected species were released upon identification and measurement. Species diversity, evenness, and dominance indices were measured using the PAST v.3.26 software package. Relative abundance and relative frequency of species for each section were also measured and compared.
Volant vertebrates (bats and birds). Cave bats were identified through a mist-netting technique from 12–24 Mar 2019. A 6 m x 2.5 m mist net was set up in front of cave entrances from 18:00 to 21:00. Because of their interconnectivity, sections 1, 2, and 3 passages were assessed as one area (Area 1), whereas sections 4 and 5 were also joined as one (Area 2) for bat diversity assessment.
Species identification, biometric measurements such as forearm length, body length and weight, ear and nose structure, teeth structure, tail and wing membrane structure, and total counts of trapped individuals were recorded for species richness computation. Specimens that were not readily identified on-site were placed in cloth bags and examined and identified in the camp using the key to bat species by Ingle and Heaney (1992). All captured species were released after documentation.
Birds found in the vicinity of the cave were surveyed using a point-transect distance sampling method. A transect line was laid out and surveyed representatively covering all possible ranges of habitat gradient around the vicinity of each identified sub-cave system – namely, the Alayan- Lion-Malukbo and Heaven-Sabrina Caves.
Cave Hydrology
Water flows (conduits, sinking streams, and springs) were described, measured, and traced in each subsection of the cave system from 19–22 Mar 2019 and 06–07 May 2019.
The cave passages were divided into sections with a span of 10 m and were described. The parameters for cave hydrology included checking the presence and status of water entry and flow into the cave through streams, pools, drips, seeps, and possible aquifer connections.
Speleothem
A primary survey was conducted to identify, record, and pinpoint locations of speleothems from 19–22 Mar 2019 and 06 –07 May 2019. Speleothems in CCS were surveyed following the same procedure applied in surveying cave hydrology.
Mineralogy
This parameter covered the mineral formations forming crystalline structures other than calcite, e.g. aragonite, barite, gypsum, and quartz enrichments. In most cases, caves are developed in the limestone, where CaCO3 forms the speleothems. In search of these other minerals, the following cave formations were surveyed: [1] Anthodites:
speleothems of needle-like crystal clusters that radiate outward from a common base that is sometimes quill- like or feathery, indicating the presence of aragonite. [2]
Gypsum flowers and selenite: limestone caves may harbor gypsum, though rarely, forming crystal petals radiating from a central point or long transparent rods or nests of fibrous crystals for the case of selenite. [3] Noticeable mineral veins: the exposed limestone bedrock from cave walls, ceilings, and floors can harbor other mineral enrichments formed during the sedimentation process.
Looking for this sign aids in the detection of other minerals like barite and quartz. Visual indicators were used by checking the presence of these features and evaluating the amount of these minerals in each established station inside the cave. Minerals in CCS were surveyed following the same procedure applied in surveying cave hydrology.
Paleontology
This parameter covered the identification of any form of fossilized remnants of animals embedded in the walls, ceilings, and floors of the cave. A cave developed in fossiliferous limestone often contains these materials and is of prime importance since they can be used as sources of information on past organisms and ecosystems. Distinct coral remains were excluded in this parameter since most limestones have biogenic origins, derived mostly from the remains of organisms such as clams, brachiopods, bryozoa, crinoids, skeletons of marine animals, and corals. The scale (Table 1) was based on the quantity and distribution of these materials in each subsection of the cave system.
Culture
The presence of artifacts, ecofacts, and primitive artworks was covered in this parameter, which indicates the archeological value of the cave. In the Philippines, the historical value of caves can be attributed to any of the following: [1] strongly associated with important historical events or Filipino personages who have achieved an enduring contribution toward the enrichment of Filipino cultural heritage; [2] related to a significant cultural or historical experience; and [3] those that bear strong foreign influences and those with strong evidence of active political, social, economic, and cultural relations with neighboring countries (DENR-PAWB 2009). A cave listed as a protected site by the Government (National Museum, National Historical Commission) automatically gains a maximum score on the scale (Table 1).
Scoring System
All the parameter scores for the sensitivity indices were summed up for each section (Harley et al. 2011). The sum was divided by the total possible score for all applicable sensitivity parameters. In the same manner, a relative sensitivity score of CCS using only those indicators with non-zero index scores were also computed. The resulting numbers from the computations represent the relative sensitivity of the cave. Final values that are closer to one (1.00) were interpreted to have higher overall sensitivity.
The sensitivity classification scale is presented in Table 2.
RESULTS
Biota
Plants identified included arborescent monocots and ferns, herb/herbaceous plants, non-vascular and lichenous plants, shrubs, trees, and vines/creepers. Plants in cave entrances totaled 91 plant species from 72 genera and 47 families.
The family of aroids (Araceae; nine species) recorded the highest number of species, whereas the figs (Ficus sp: six species) were the most represented genus. The majority of plants encountered in the cave openings were native to the Philippines: 10 were endemic to the country, whereas only two species were introduced (Table 3).
Only Lion and Malukbo 1 and 2 Cave entrances had flowing water and Corbicula fluminea in abundance up to the twilight zone. A single sample of Allopeas sp.
was observed in the twilight zone of the Sang-at Salug Cave entrance, whereas another single sample of a giant African snail (Achatina fulica) was observed along the Lion Cave entrance.
The arthropods identified totaled 24 species from 22 families and 12 orders. The Order Araneae (spiders) have the highest number of species recorded (9), followed by Opiliones (harvestman; 3), Orthoptera (cave crickets;
2), and Decapoda (crustaceans; 2). Species richness was highest in the Alayan-Sang-at Salug route (20 species),
Table 2. Sensitivity and disturbance classifications [adopted from Harley et al. (2011)].
Score
(sum/ total possible sum) Degree of sensitivity 0.81–1.00 Critically sensitive
0.71–0.80 Severely sensitive
0.61–0.70 Considerably sensitive
0.51–0.60 Sensitive
0.40–0.50 Moderately sensitive
0.20–0.39 Slightly sensitive
0.00–0.19 Not sensitive
Table 3. Endemicity and conservation status of plants encountered in the cave openings of the Capisaan Cave System.
Family name Common/ local
name Scientific name Distribution Conservation status
(DAO 2017-11) Acanthaceae 1. Rungia philippinensis C.B.Clarke Endemic to the Philippines
Apocynaceae 2. Hoya camphorifolia Warb. Endemic to the Philippines
Araceae 3. Alocasia cf. micholitziana Sander Endemic to the Philippines Vulnerable Aspleniaceae 4. Asplenium cf. vittiforme Cav. Native to the Philippines
(throughout Malesia) Vulnerable
Begoniaceae 5. Begonia cf. oxysperma DC. Endemic to the Philippines Vulnerable
Euphorbiaceae "Balanti-bilog" 6. Omalanthus cf. macradenius Pax
& Hoffm. in Engl. Endemic to the Philippines
Gesneriaceae 7. Rhynchoglossum cf. spumosum
Elmer Endemic to the Philippines
Meliaceae "Kalantas" 8. Toona calantas Merr. & Rolfe Native to the Philippines
(throughout Malesia) Vulnerable
Moraceae "Pakiling" 9. Ficus cf. odorata (Blanco) Merr. Endemic to the Philippines Phyllanthaceae 10. Phyllanthus cf. tenuipes C.B.Rob Endemic to the Philippines
Podocarpaceae "Malakawayan" 11. .Podocarpus rumphii Blume Native to the Philippines (China, Indonesia, Malaysia,
Papua New Guinea) Vulnerable
Thelypteridaceae 12. .Pneumatopteris laevis (Mett.)
Holttum. Endemic to the Philippines
Vitaceae 13. Leea cf. acuminatissima Merr. Endemic to the Philippines
followed by the Lion-Sang-at Salug (18 species) and Sang- at Salug-Malukbo route (14 species). Sabrina and Heaven registered a few arthropod species with only four and five, respectively. This trend was affected by the length of the passage and the number of possible entry-exit points.
Cave fishes were only seen in the Lion-Sang-at Salug (Section1: Stations 4, 5, 9, and 14) route, where clear and shallow pools of water are prevalent. The fish encountered include three common carp (Cyprinus carpio), two freshwater catfish (Clarias batrachus), two mudfish (Channa striata), four orange carp (Cyprinus rubrofuscus), and one wild guppy (Poecilia reticulata).
A total of four species of reptiles all belonging to Order Squamata with three Families, and three anurans belonging to three Families were identified during the survey (Table 4). A total of 40 individual bats were captured belonging to three families (Rhinolophidae: 1; Hipposideridae: 3;
Miniopteridae: 36) and four species (Table 5). Area 1 harbored a greater number of bats because this area has more cave openings and segments that were seldom passed by visitors because of the extreme mud and low ceiling conditions of the cave.
Birds survey revealed a total of 61 species belonging to 35 families. Thirty-six (36) species of the total birds recorded are known to be endemic to the Philippines. Of this number, eight species were categorized as threatened under the International Union for Conservation of Nature (IUCN) Red List and the DENR Administrative Order (DAO) No. 2019-09 (Table 6).
Overall Biota Sensitivity
The presence of species categorized as vulnerable and endangered in all the cave sections studied automatically gave all sections a sensitivity score of 3 under this parameter.
Cave Hydrology
Section 1 had a total surveyed length of 1,200 m. All stations had a clear presence of water as a subterranean river flow through the whole passage dominated by a series of pools and shallow, channelized flows. Drips and seepage waters could be generally observed from the ceilings and walls of the cave. Some water portions were filled-in cracks or floor gaps so deep that ropes were used
Table 5. List of bats captured in the different cave entrances of CCS.
Common name Scientific name Count and location Residence
status Conservation status (IUCN 2019-2)
Arcuate horseshoe Bat Rhinolophus
arcuatus 1 (Area 1) Native Least concern
Diadem leaf-nosed Bat Hipposideros
diadema 3 (Area 1=2; Area
2=1) Native Least concern
Schreiber's bent-winged
bat Miniopterus sch-
reibersii 15 (Area 1) Native Near threatened
Little long-fingered bat Miniopterus
australis 21 (Area 1=20; Area
2=1) Native Least concern
Table 4. List of herpetofauna encountered in the different cave entrances of CCS.
Location Common name Scientific name Residence status Conservation status (IUCN 2019-2) Malukbo 3 Philippine bent-toed
gecko Cyrtodactylus philip-
pinicus Philippine native Least concern Malukbo 1 Giant Philippine frog Limnonectes cf. mac-
rocephalus Luzon endemic Near threatened Sang-at Salug Black-sided Sphenom-
orphus Parvoscincus decip-
iens Luzon endemic Least concern
Sang-at Salug Common mabuya Eutropis multifasciata Native (SE Asia) Least concern
Sang-at Salug forest frog Platymantis sp. ND ND
Lion Philippine shrub snake Oxyrhabdium modes-
tum Philippine endemic Least concern
Lion Luzon nar-
row-mouthed frog Kaloula cf. rigida Luzon endemic Least concern
to cross these portions. The result of the survey gave a total index score of 2.43 for this section (Figure 2).
Section 2 is comparable in length to Section 1 with a length of 1,150 m. This section is a continuation of the active subterranean river passage from Section 1 with contributions from other tributaries, making this section with the deepest water levels. It has an intricate maze of water channels that disappear and re-appear from the main passage, rendering some cave floors totally devoid of water flow while inundating the whole cave floor in some areas. Deep and mud-laden pools also occur in this section.
Water also runs at higher velocities in this area, especially near the Alayan entrance/ exit. It also has widespread water seepage and drips. Overall, this section gained an average hydrology index score of 1.92 (Figure 2).
Section 3 was also carved by another subterranean river that eventually connects with Sections 1 and 2. Water quality in this section was more turbid compared to the other two sections, as water is hugely affected by farming before entering the cave. It has a total survey length of 900 m. Seepage and drips were also very active in all areas.
There were no known deep pool portions in this area but there were many low ceilings that required visitors to be submerged in water in order to pass through. Overall, this section gained an average hydrology index score of 2.30 (Figure 2).
Section 4 is a soluble bed formed on a hill limestone. The dropping of the water table left this section devoid of an active water source and relied only on seepage and drip waters to provide moisture and continuous enrichment of mineral calcite. It is short with a length of approximately 90 m. The computed hydrology index in this section was 0.11 (Figure 2).
Section 5 is situated near Section 4 but on a much higher elevation. Because this section consisted of a huge single breakdown chamber, some portions of the floor have pockets of water hidden in a maze of huge rock breakdowns. A large flowstone formation at the farthest end of the chamber suggests that active water flow once oozed from this area forming a small hidden elevated ledge with a small water impoundment full of intricate speleothem formations. This section has a total surveyed length of approximately 90 m with a computed average hydrology index score of 0.67 (Figure 2).
In all cave sections studied, all parts of the cave were moist to wet, which is a clear indication of the active hydrology inside the caves. The high relative humidity inside these caves has maintained most of the cave parts to be moist even without water flow or impoundments except near the entrance, which is normal for most tropical caves.
Speleothem
The vast and widespread speleothem formations decorating Section 1 indicate that this cave has been formed thousands of years ago. The high computed speleothem index score of 2.4 supports this assumption, further indicating the very active hydrology that dissolves and deposits the different speleothems in this section.
Section 2 is a continuation of a shallow subterranean river in Section 1; this passage contained lesser but aggregated speleothem formations. This could be attributed to deeper and faster water velocities, as well as the amount of water drips and seepage that dissolve and deposit calcites.
Nonetheless, spectacular cave formations like galleries of flowstones (draperies/curtains, stone waterfalls, rimstones, flowstone sheets, baldacchino canopies),
Table 6. List of threatened species of birds observed in sampling sites.
Species name
Conservation status Sampling site
2019.1IUCN DAO
2019-09 Alayan-Lion Heaven-Sabrina
Ashy-breasted flycatcher (Muscicapa randi) VU EN ü X
Blue-breasted blue flycatcher (Cyornis herioti) NT -- X ü
Grey-throated sunbird (Anthreptes griseigularis) LC OTS ü ü
Luzon hornbill (Penelopides manillae) LC VU ü X
Ridgetop swiftlet (Collocalia isonota) NE -- ü ü
Rufous coucal (Centropus unirufus) NT OTS ü ü
Sierra Madre ground warbler (Robsonius thompsoni) LC OTS ü X
White-browed shama (Copsychus luzoniensis) LC VU ü ü
White-fronted tit (Parus semilarvatus) NT OTS X ü
[EN] endangered; [OTS] other threatened species; [NE] not evaluated; [ü] recorded [VU] vulnerable; [LC] least concern; [--] uncategorized; [X] not recorded; [NT] near threatened
Figure 2. Raw hydrology index scores per station of each section.
dripstones (stalactites, stalagmites, columns, soda straws, erratic stalactites, and helictites) spelogems (cave corrals, and pool spars), and other forms (shelfstones, botryoids, and popcorns) abound in this section, giving a computed speleothem index score of 1.82 (Figure 3).
Section 3 has the least speleothem formations compared to Sections 1 and 2. It is believed that this section developed at the same time as Sections 1 and 2, as the three sections were connected. More speleogens or bedrock features that are created by dissolution (e.g. scallops, terraces, anastomoses, and rock pendants) can be observed than speleothems. Overall, this section gained a computed speleothem score of 1.35 (Figure 3).
Due to the very short passage length of Section 4, the quantity of speleothem formation in this section cannot be compared to the first three sections. Rather, the speleothem index score derived in this section describes the expanse of speleothem relative to the passage size. This section’s computed speleothem index score had an average of 2.56 (Figure 3).
Section 5 formed in the same limestone hill where Section 4 was located and with almost equal surveyed passage length. However, Section 5 has a wider chamber and higher elevation than Section 4. This section is also decorated with large speleothem formations such as flowstone walls combined with draperies and botryoids, stalactites, splattermites, columns, and stalagmites with large diameters. Another interesting formation is the presence of cave pearls and pool spars. The immensity of formations in a single gallery indicates that this section must be older than Section 4 and receive a computed speleothem index score of 2.56 (Figure 3).
Mineralogy
Cave minerals are secondary minerals that are the products of geochemical reactions from a primary mineral in bedrock (Hill and Forti 1997; Harley et al. 2011). Enrichment deposition of other minerals forming crystalline structures other than calcite was noted during the survey. Because the karst landscape where CCS can be found is made of limestone, it is known that its major minerals calcite and aragonite are enriched in the form of speleothems inside caves. Evidence of its origin can be seen inside the cave through coral fossils embedded in the rock walls of the caves.
The results of the survey resulted in no presence of anthodites, gypsum flowers, selenite, and noticeable mineral veins; thus, a sensitivity score of 0 was given.
Paleontology
Coral limestone dominates the area as evidenced by several fossilized corals observed within the different cave sections of CCS. No other fossil aside from corals was sighted during
the assessment nor discovered previously by other people based on records or revealed from key informant interviews (KIIs) and focus group discussion (FGD). Thus, all sections were given a sensitivity score of 0.
Culture
Site visits, literature reviews, and KII revealed no significant attribution of the different cave sections of CCS to any cultural or historical materials or events, rendering all with a sensitivity score of 0.
Relative Sensitivity Scores
In general, Section 1 received a computed mean index score of 1.31 with an equivalent sensitivity score of 0.44 relatively classified as “moderately sensitive” (Table 7).
Sections 2 and 3 had recorded mean index scores of 1.12 and 1.11, respectively, both gaining an equivalent of 0.37 sensitivity scores relatively classified as “slightly sensitive.” Section 4 gained a mean index score of 0.94 corresponding to a 0.32 sensitivity score and was relatively classified as “slightly sensitive.” Section 5 gained a mean index score of 1.04 corresponding to 0.35 relative sensitivity and was also classified under the
“slightly sensitive” bracket. In aggregate, the computed sensitivity of resources (0.37) found in CCS can be broadly classified as “slightly sensitive” based on the sensitivity classification forwarded by Harley et al. (2011) described in Table 2.
The result of the relative sensitivity score computation of CCS, where zero-index scored parameters was omitted is presented in Table 8. We can see from the results that the relative sensitivity of CCS changed from “slightly sensitive” to “severely sensitive.” Strikingly noticeable is the obtained “critically sensitive” condition of Section 1. It is noteworthy that the biota, hydrology, and speleothem index scores can be found at the upper limit for Section 1, indicating severe to critical sensitivities in these parameters. Section 2 biota parameter was found to be critically sensitive and considerably sensitive in both hydrology and speleothem parameters, whereas Section 3 was found critically sensitive for biota, severely sensitive for hydrology, and only moderately sensitive for speleothem. Sections 4 and 5 registered critical sensitivities in both biota and speleothem parameters.
DISCUSSION
Plants in cave entrances were dominated by terrestrial herbs, epilithic to epiphytic plants, with rhizomatous and adventitious stems, and those with tuberous stems, mostly belonging to the family Araceae and genus Ficus. Animals associated with CCS both at the surface and subsurface
Figure 3. Raw speleothem index scores per station of each section.
Table 8. Cave sensitivity score of CCS where zero-index scored parameters were omitted.
Section Parameters
1 2 3 4 5 Average
Biota 3.0 3.0 3.0 3.0 3.0 3
Hydrology 2.43 1.92 2.30 0.11 0.67 1.49
Speleothems 2.40 1.82 1.35 2.56 2.56 2.14 Mean index
score 2.61 2.25 2.22 1.89 2.08 2.21
Equivalent Sensitivity score
0.87 0.75 0.74 0.63 0.69
CCS sensitivity score 0.74
Table 7. Final cave sensitivity score of CCS.
Section Parameters
1 2 3 4 5 Average
Biota 3.0 3.0 3.0 3.0 3.0 3
Hydrology 2.43 1.92 2.30 0.11 0.67 1.49
Speleothems 2.40 1.82 1.35 2.56 2.56 2.14
Mineralogy 0 0 0 0 0 0
Paleontology 0 0 0 0 0 0
Cultural/His-
torical 0 0 0 0 0 0
Mean index
score 1.31 1.12 1.11 0.94 1.04 1.10
Equivalent sen-
sitivity score 0.44 0.37 0.37 0.32 0.35
CCS sensitivity score 0.37
levels were seen with high diversity and endemicity. The presence of animal and plant species included in the IUCN Red List in all cave passages allowed all cave passages to gain maximum index scores for the biota parameter, thus making it an excellent candidate for critical habitat establishment. It is exciting to note the high possibility of describing new species of cave arthropod found in CCS, though the taxonomic description and comparison to existing collections to confirm new species or new site records are not covered in this study. Species encountered such as cave tarantula, blind shrimp, and cave harvestman are among the organisms worthy of identification.
Hydrology inside and surrounding CCS is also very active and continuously shapes the geological structure of CCS.
Section 1 (Lion–Sang-at–Salug route) gained the highest hydrology index score, followed by Section 3 (Malukbo- Lion Junction route) and Section 2 (Alayan–Sang-at–
Salug route). These three sections were almost similar in hydrology where subterranean water flows in these passages had signs of frequent flooding events. These observations also imply somewhat similar speleogenic origins of these three cave sections. Sections 4 (Sabrina) and 5 (Heaven) of CCS tell a different speleogenic origin with a very minimal hydrologic feature.
All cave sections studied were immensely decorated with speleothems and speleogens. With regard to areas decorated with speleothem to total passage area ratio, Sections 4 and 5 gained the highest scores since they have the shortest passage lengths with individual distances of around 100 m only. Sections 1, 2, and 3 were all long passages measuring 1 km more or less in length and could be conveniently compared in speleothem features.
Mineralogy requirements used in this study found no significant features in any of the cave sections. The same condition was found for paleontology and cultural/
historical parameters during the study. Nonetheless, these findings do not preclude finding the presence of these features in the future as more cave openings and passages can be discovered.
For the management implications of these findings, managers should not solely focus on a cave’s relative or overall sensitivity score of each section or the cave system as a whole, but rather focus on the specific/
individual parameter scores to highlight aspects of the cave environment that need protection due to its high richness or sensitivity (North et al. 2009). Such is the case of CCS, where a low overall sensitivity score is computed, which is mainly caused by taking into account all possible sensitivity parameters that a cave environment can have.
This perceived low sensitivity might mislead management actions if the individual parameters were not examined.
The purpose of the inclusion of all possible parameters in the computation of relative sensitivity is to allow comparability between different cave systems or regions (North et al. 2009). The study of Harley et al. (2011) evaluated these scoring systems with their ability to aid in cave management and argued that managing a cave is a complicated matter, that to create effective management plans, it is essential to understand first the cave system’s level of sensitivity. Their study added that sensitivity results can be combined with disturbance data, ownership, and management status to deliver a more inclusive method for determining the management requirements of caves.
In the context of CCS alone, using only observable parameters in overall sensitivity computation would be very relevant in terms of management priorities. This would quantitatively show that whatever resources are present in each designated section of the CCS have high sensitivity entailing richer cave resources. This will guide
the cave management in weighing areas requiring stricter and intensive management interventions and strategies to preserve the richness of these areas.
Another important point to be considered in the development of this index is to provide weights to capture the perception that certain indicators are more important than others, depending on the management objectives.
While this is true, the equal weight was used in this study purposedly to maintain neutrality on the bias given by different management objectives (e.g. a biologist may give more weight to biota, geologist to speleothem, or hydrologist to water) and priorities (e.g. DENR to the preservation of natural resources, or LGU to exploitation through ecotourism). Neutrality in weights also allows the comparability between different cave systems located in different regions (van Beynen and Townsend 2005). These same studies also used equal weights due to the difficulty in determining which indicators are most important.
Nonetheless, if used in the context of the individual cave system, the difficulty can be eased by doing a multi-criteria analysis using the analytical hierarchy process developed by Saaty (1990).
CONCLUSION
The study successfully tested the applicability of the existing standardized cave sensitivity assessment index to a tropical cave, specifically to the CCS. Modifications were made to the methods employed in determining sensitivity index scores in relation to cave passage length.
Building on the work of Harley et al. (2011) and van Beynen and Townsend (2005), the application of the index by partitioning cave passages into specific equal intervals and measuring its sensitivity scores allowed a more accurate evaluation and pinpointing the exact locations in the cave passage areas needing the most attention and strict protection. It provided a better visualization of the different characteristics of the cave passage, producing a clear cave sensitivity signature created by charting the obtained scores of each passage partition. The tabulation also identified locations in the cave passage where high specific resource sensitivity could be found.
The use of the cave sensitivity index, together with the modifications presented in this study, enabled the holistic and more accurate identification of the overall resource sensitivity of the CCS. From a cave management perspective, this study reinforces information needed in cave classification by providing descriptive and quantitative data in the documentation of cave resources that should be employed in other caves, giving detailed support to policy development, management, and protection of caves.
ACKNOWLEDGMENTS
Sincere gratitude is given to the whole project management staff of USAID/ Philippines Protect Wildlife Project at DAI for generously granting full financial support for the conduct of this study.
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