Journal of Science, Engineering and Technology 5:1-14 (2017) Southern State University, Sogod, ,

Carbon Storage and Nutrient Stocks Distribution of Three Adjacent Land Use Patterns in National Park, , Leyte, Philippines

Pearl Aphrodıte Bobon-Carnıce1* Suzette B. Lına2 1Natural Sciences Department State University City, Leyte, Philippines 2Department of Soil Science, College of Agriculture and Food Science Visayas State University Visca, Baybay City, Philippines

Abstract The country experienced drastic decrease of forest cover due to land use conversion, cutting of trees and doing agriculture to support food security. Secondary forests are an important component of land cover in the tropics, and when transformed or converted into another land-use, it is believed to have negative effects on some soil properties and forest ecosystem in general. A paired-area/space-for-time substitution approach was conducted to determine the changes in carbon storage: soil organic carbon (SOC) and total above ground biomass (TAGB), soil nutrient stocks and fertility status due to land use change. The study was conducted in Lake Danao National Park (LDNP), Ormoc City, Leyte, Philippines. Adjacent to the secondary forest (<1 km away), grassland and forest plantation land uses were chosen and sampled for possible changes on SOC, TAGB and nutrient stocks due to land use change. Results showed that conversion of forest to grassland and forest plantation decreased the organic carbon, exchangeable aluminum, exchangeable acidity, effective cation exchange capacity, TAGB while pH in H2O; exchangeable magnesium and potential cation exchange capacity increased when the forest was converted to grassland and forest plantation. Additionally, available P, base saturation, Ca, K, and Na increased while total N, and SOC stocks decreased when the forest was converted to grassland and forest plantation. This study indicates that conversion of forest to grassland and forest plantation greatly affected the SOC stocks, TAGB, soils nutrient stocks and fertility status. It also revealed that changes in soil properties largely depended upon the land use.

Keywords: Andisol; forest plantation; grassland; organic carbon; secondary forest; total aboveground biomass

Introduction marked effect on the interactions in detrital inputs, perturbations of the ecosystem and could have an associated change in C Terrestrial ecosystem is the major reservoir stocks and fluxes (Bolin and Sukumar, 2000; of carbon (C) in which its amount in the soil Lal, 2005). Such changes are important is greater than that in the living vegetation from the standpoint of desired soil quality, (Post et al., 2000). Anthropogenic activities sustainability, and on their influence on the such as changing the land use can have a

*Correspondence: [email protected]; ORCID: 0000-0002-3622-0449 ISSN 2545-9732 Carnıce and Lina JSET Vol.5, 2017

atmospheric CO2 concentrations and global under secondary forest transformations in warming (Lal, 2004). However, understanding LNDP and related the SOC stocks with the of the estimation of carbon as part of the global aboveground biomass. carbon cycle in general, and understanding of soil carbon dynamics is still limited. Methodology There are few reported studies on the mechanisms and factors controlling the The Study Site stability of soil organic carbon (SOC) as affected by anthropogenic activity in the The study was conducted in LDNP, Ormoc tropics (Paul et al., 2008). However, there are City, Leyte (Figure 1) where the secondary only few studies that have been conducted forest is still preserved and intact and has an yet in the Philippines particularly in Leyte adjacent grassland and forest plantation site. province concerning the quantification of A paired-area or space-for-time substitution SOC under secondary forest transformations, approach (Paul et al., 2008; Asio, 1996; despite their large SOC sequestration Veldkamp et al., 2003) was employed with potentials. Thus, results of this study will the assumption that the adjacent grassland be useful in understanding the changes in (G) and forest plantation (FP) are land uses SOC, total above ground biomass (TAGB) converted from forest or secondary forest (F). and soil nutrient stocks as influenced by All adjacent sites were selected carefully to the transformation of secondary forest into have comparable soil physical and chemical different land use systems. This is also an properties, climate, parent material – i.e. important contribution to the databank for any change in soil properties is caused by greenhouse gas inventories as United Nations the land conversion (Veldkamp et al., 2003). Framework Convention on Climate Change The secondary forest was considered as (UNFCC) and other international agencies the reference land use. Climate, slope, where policy agenda on greenhouse gas drainage, and geographical coordinates mitigation has been advocated. Moreover, (using GPS) were determined in the field or the results will also be useful in determining from secondary sources such as maps and/or the SOC sequestration potential of Andisol in existing publications. Lake Danao National Park (LDNP). LDNP is one of the forest reserves in the Philippines Field investigation, Soil Sampling where you can at the same time find areas and Laboratory Analysis that have been converted to grassland and forest plantation, making the location very A stratified random sampling scheme was suitable for this study’s methodology. An carried out in choosing the sub-sampling understanding of the results of this study can points for composite soil collection. In every bring awareness to people that conversion of one hectare area of each land use, four forest to grassland and forest plantation would plots (20m x 20m) were randomly prepared have both positive and negative effects on which served as replications. In each plot, SOC stocks and on soil nutrient status. five sub-sampling points were randomly The study hypothesized that conversion of selected with an area 25 meters apart. Using secondary forest to grassland with similar a soil auger, soil samples in each of the Andisol soils will bring a decline in SOC sub-sampling points were collected uniformly stocks and nutrient reserves while the land from the following depths: 0–20 cm, 20–40 use change to forest plantation will lead to an cm, and 40–60 cm. Collected soil samples increase of these parameters again. Thus, were brought immediately to the screen this study quantified and evaluated the SOC house of the Department of Soil Science, stocks, TAGB and nutrient stocks of soils Visayas State Univeristy, Baybay City, Leyte,

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Figure 1. (A) Map of Leyte (Redrawn from Department of Environment and Natural Resources); (B) Sketch of the sampling sites in LDNP, Ormoc City, Leyte, Philippines air-dried, pulverized and passed through a Total SOC (Mg C ha−1) = (%SOC)/(100) 2mm sieve. The following soil physical and x soil depth (m) x bulk density (Mg m−3) chemical properties were determined: bulk x 10000 m2 ha−1 density using paraffin clod method (Blake and Hartge, 1986); porosity by calculation In the F and FP, representative sampling of particle density and bulk density; particle plots (10 m x 10 m) were laid-out. All trees size distribution (soil texture) using pipette inside the plots with a diameter at breast height method (ISRIC, 1986); soil pH was analysed (dbh) of at least 10cm were identified and potentiometrically using soil and water ratio recorded. of 1:2.5 (ISRIC, 1986); delta pH using The aboveground tree biomass with KCl (pH KCl–pH H2O) (Mekaru & Uehara, dbh <10cm (Lasco and Sales, 2003) was 1972); soil organic matter (%) using modified calculated using allometric equation (Brown Walkley-Black method (Nelson and Sommers, and Lugo, 1990). Total aboveground biomass 1982); Total N (%) using the micro-Kjeldahl (trees): method; extractable P (mg kg−1) was determined according to Bray #2 method (Bray %Y = exp [-2.134 + 2.530*ln (dbh)] and Kurtz, 1945; Murphy and Riley, 1945); cation exchange capacity (CEC) using 1N Where: NH OAc adjusted to pH 7.0 method (ISRIC, 4 • Y = biomass per tree in kg; 1986) with some modifications; exchangeable 3+ + −1 acidity (Acidity (Al and H ) (cmolc kg ) • dbh = diameter at breast height in (Thomas, 1982) and exchangeable K, Ca, centimeters Mg (mg kg−1) was quantified using Atomic −1 Absorption Spectrophotometer (AAS) (Varian C storage (t ha ) = Total biomass/ha x 0.45 Spectra 220 FS) reading. SOC contents were analyzed for the specified three depths from Aboveground and root biomass from 1 each land use. SOC stock was calculated m x 1 m plot at each grassland site were using the equation. determined. All grasses found within the plot were collected. The harvested grasses were washed thoroughly with tap water and then

3 Carnıce and Lina JSET Vol.5, 2017 distilled water. After which, fresh weight was as Typic Hapludand under the soil order determined. Representative samples were Andisols (USDA, 2003) and some evidences oven-dried at 65◦C. The carbon stock of the are presented in Table 1 along with other grass biomass was calculated with following characteristics of the site. Soil profile (cambic formula: soil horizon) development in F is poor and the area has common rock outcrops. Dipterocarp tree species are dominant in the secondary WC = WO x 0.5 forest. Based on the interview of the caretaker of LDNP, the conversion of forest occurred in Where: 1970s. G is located in the same volcanic hill which is less than 700 m away from • WC = Weight of carbon in grass biomass the secondary forest (F). FP, with less than (g); 300 m distance from F, was planted with Gymnostoma phumphianum in 1971 and was • WO = Oven-dry weight of aboveground biomass; not disturbed since then. Ormoc highlands climate is Type II in the Coronas climate • 0.5 = Estimated C percentage in classification (Asio, 1996). The presence plant biomass (Sarmiento et al., 2005; of the Central Cordillera of Leyte delineates Redondo, 2007) eastern side of the range having slightly different climate from that of the western side. Calculation and Data Analysis The eastern side of Leyte is exposed to trade winds from the Pacific Ocean resulting Using paired-site approach, the effects of in the absence of a dry season with a FP and G on SOC stocks and soil nutrient very pronounced maximum rain period from stocks were evaluated. Data generated from December to March. Average temperature is F was used as the baseline values (reference) 24.50C and average annual rainfall is 3391 against changes in SOC stocks and nutrient mm. stocks in different land uses. The effects of land use on SOC stocks and nutrient Nutrient stocks stocks within each depth and each site were subjected to one-way ANOVA and multivariate Figure 2 shows strongly acidic to moderately analysis. Multiple regression analyses were acidic pH (H2O) sites which ranged from used to evaluate the relationships between 5.2-5.7. Values of pH (H2O) in the surface SOC concentration and nutrient stocks in did not vary much as the depth increases. different land uses. Respective correlation However, pH (H2O) between land uses coefficients for each land use were calculated differed in the surface horizon (0 – 20 cm) including all soil depths from all sites. in which the forest plantation showed the highest value while grassland had the lowest. Results and Discussion Nonetheless, the significant interaction effects between these differences could be due to the Environmental Setting type of vegetation. Similarly, significant difference was noted The LDNP in Ormoc City, Leyte is one of on soil pH (KCl) between land uses (P-value: the forest reserves in the Philippines and 0.0012) which values ranges from 4.2 - 4.7 a suitable site for land use study because (Figure 2). Among the three sites, FP had the secondary forest is still preserved and higher value of pH (KCl) while F soils had the adjacent to grassland and forest plantation lowest pH which means H+ ions were held areas of <1 km apart. The soil was classified tightly in the soil particles of the F soils. In

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Table 1. Site characteristics of LDNP, Ormoc City, Leyte, Philippines Soil Characteristics Secondary Forest* Grassland* Forest Plantation* Lake Danao, Ormoc Lake Danao, Ormoc Lake Danao, Ormoc Location City, Leyte City, Leyte City, Leyte Coordinates N11.07◦ E124.89◦ N11.07◦ E124.12◦ N11.07◦ E124.7◦ Elevation 702 m asl 657 m asl 672 m asl Landform Volcanic hill Volcanic hill Volcanic hill Slope Position Shoulderslope Footslope Backslope Slope Gradient Sloping Sloping Gently Sloping Parent Material Andesitic Volcanics Andesitic Volcanics Andesitic Volcanics Soil Moisture Regime Udic Udic Udic Soil Temperature Isohyperthermic Isohyperthermic Isohyperthermic Erosion No evidence No evidence No evidence Rock outcrops/ stoniness Common Few Few Drainage Well-Drained Poorly-drained Well-Drained Axonopus Gymnostoma Vegetation Dipterocarp Species compressus phumphianum *Distance between land uses is <1 km away

comparison, pH (H2O) showed higher values decreased when forest was converted into than pH (KCl) as expected since addition of grassland but seemed to have recovered salt solution releases cations. It replaces in the forest plantation. Forest conversion some of the protons from the soil particles and to grassland significantly decreased the these process forces hydrogen ions to pass organic matter content of the soil which into the solution and make their concentration may be attributed to the clearing of forest in the bulk solution closer to the value in the vegetation that has interrupted the input of field. It can also be observed that pH (KCl) organic materials from plants (Asio et al., slightly increased with depth across land use 1998). Additionally, there were significant types. differences in SOC contents among soil depth Furthermore, differences in 4pH values horizons (P-value: 0.0079). Also, the SOC were observed between land uses and was higher in the surface and decreased between soil depths. All land uses showed as the depth increased (Figure 2). This negative charge indicating that the soil could be due to the higher accumulation of colloids possess cation exchange capacity organic matter and higher root allocation on and the occurrence of net negative charge the soil surface since it is the main habitat of could be attributed to the negative charge microorganisms. Generally, total N contents of the clay minerals. On the other hand, of soil were considerably affected by land use the 4pH values were similar across all land change because of marked influence on the uses. The negative values obtained indicate changes in detrital inputs, perturbations of that soil colloids possess cation exchange the ecosystem, and on N stocks and fluxes capacity. The occurrence of net negative (Bolin and Sukumar, 2000). Figure 3 shows charge could be attributed to the negative the total N contents among land uses where charge of the clay minerals. Forest soils a significant difference was observed. Forest had the highest SOC concentration (8.31%), soils rendered the highest N (0.3-0.9%) which followed by forest plantation (5.99%) while can be interpreted as medium to high total the lowest was grassland (2.87%). Significant N while grassland soils showed the lowest differences (P-value: 3.67308x10−7) in the (0.08–0.11%) N content. The grassland site SOC concentrations were observed between was subjected to long years of cultivation (≈15 land uses. SOC concentration significantly years) before it was converted into the present

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Figure 2. Depth function of Db (bulk density), porosity, OC and pH (H2O, KCl, and 4 pH)of soils as influenced by forest transformations in LDNP, Ormoc City, Leyte. Horizontal bars represent standard errors land use while the forest plantation. Since lower depths. slash-and-burn has been a practice in the area, less organic matter was returned to the Tropical soils are generally phosphorus (P) soil which greatly affected the N content while deficient and in most cases, it is the limiting increasing possible volatilization. Additionally, nutrient in agriculture (Sanchez and Logan, significant difference was also observed 1992). All land uses had very low amounts of between soil depths such that surface soils (0 available P (<0.2 mg kg−1) compared to P-rich – 20 cm) contained higher N content than the soils (8-15 mg kg−1) (Asio et al. 2006). As an Andisol, the soil contains large amounts of

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Figure 3. Depth function of total N, available phosphorus, exchangeable Ca, exchangeable Mg, exchangeable K, and exchangeable Na of soils as influenced by forest transformations in LDNP, Ormoc City, Leyte. Horizontal bars represent standard errors amorphous clay minerals that creates a strong its high P-fixation capacity. sorption of P in the soil which is relatively Generally, grassland soils contained unavailable for plant absorption (Asio, 1996). significantly higher amount of exchangeable The same site tends to have high aluminum bases than the forest and forest plantation. (Figure 3) which can bind P via an anion Only magnesium (Mg) was significantly exchange. Its fine-textured soil also adds to different between land use (P-value: 0.0131)

7 Carnıce and Lina JSET Vol.5, 2017 and depths (P-value: 0.0033). However, all means that the soil has low resistance to levels of exchangeable bases (Ca, Mg and changes in soil chemistry caused by land use Na) are low to very low among land uses change. Significant differences in CECeff except on grassland which had moderate (P-value: 0.0069) were observed between level of K. Base saturation of F, G, and FP land uses while no significant differences were was significantly different among land uses. observed in CECpot among land uses. G had the highest base saturation (24.5%) followed by F (15.15%) and FP (11.17%). The same trend was reported in previous studies Carbon Stocks Assessment (Asio et al., 1998) wherein conversion of forest to grassland and other land uses could SOC Stocks be beneficial as it improved the availability of such nutrients. This was attributed to The F soil contained 489 t C ha−1 total the contribution of ash produced during the SOC stock which is the highest among land slash-and-burn activity. Also, base saturation uses followed by FP (308 t C ha−1) and differed significantly with soil depths. The G (172.5 t C ha−1). Significant differences base saturation across all land uses was in SOC stocks were observed between land higher at the surface (Figure 4). A similar uses which indicate that forest conversion trend was also observed with OC content to other land uses significantly decreased which could be due to high accumulation of SOC stocks. The forest has far greater organic matter in the surface as the possible canopies which provide a larger quantity of source of bases. plant litter leading to higher accumulation of Exchangeable acidity was taken as the carbon. Previous studies (Batjes, 1996; Tian amount of H+ and Al3+ in the exchange et al., 2002) reported a similar trend that complex of the soil. Significant differences land use and soil management practices can were observed on exchangeable H+ (P-value: significantly influence the soil organic carbon 0.0091), exchangeable Al3+ (P-value: 0.0037) dynamics and carbon flux of the soil. It was and exchangeable acidity (P-value: 0.0056) also reported (Gou & Gifford, 2002) that soil among F, G, and FP. The F had higher carbon stocks decline after land use change exchangeable Al3+ and higher exchangeable from native forest to plantation (-13%) and/or acidity than G and FP (Figure 4). However, native forest to crop land (-42%). Aside from exchangeable H+ was the major component of nutrient availability, soil organic carbon stocks exchangeable acidity in all soils across all land may change depending on factors such as uses and not exchangeable Al3+ which can climate, vegetation type, nutrient availability, be observed with its pH values and its SOC disturbance, and land use and management content (Figure 3). practice (Six & Jastrow, 2002; Baker, 2007). Cation exchange capacity is the capacity of The inconsistent change of SOC stocks can the soil to absorb or hold cations and be able be partly explained by the complexity of to exchange cations. It is one of the important SOC, which consists of several pools that soil chemical properties affecting soil fertility. have a wide range of chemical properties Forest soils had 18.6 – 20.4 cmolc kg−1 and turnover times and consequently respond while grassland and forest plantation had differently to land use changes (Paul et al. approximately 2.8 – 4.3 cmolc kg−1 (Figure 2008). Soil organic carbon could be sensitive 4). These data indicated that F soils possess to the impact of anthropogenic activities and higher CECeff than those in G and FP. High conversion of natural vegetation to various CEC provides a buffering effect to the changes land uses (G and FP) which can result into in pH, available nutrients, calcium levels and a rapid decline in soil organic matter (Post & soil structural changes. A low CEC value Kwon, 2000).

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Figure 4. Depth function of base saturation, exchangeable acidity, exchangeable Al, exchangeable H, CECeff and CECpot of soils as influenced by forest transformations in LDNP, Ormoc City, Leyte. Horizontal bars represent standard errors

Total Aboveground Biomass (average dbh <40cm). LDNP secondary forest TAGB is a little higher but comparable Meanwhile, the forest rendered 690 Mg to Makiling Forest Reserve (MFR) (576 Mg ha−1 of TAGB (Figure 5) and significantly ha−1) (Lasco et al., 2004). Additionally, TAGB reduced to 1.79 Mg ha−1 when the forest of secondary or old-growth forest from other was converted into grassland and increased parts of the Philippines showed a ranged of again when the grassland was replanted with 446 – 1126 Mg ha−1 (Lasco et al., 2000, trees (163 Mg ha−1). The forest has high 2002). Meanwhile, grassland contained only TAGB due to big Dipterocarp tree species

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Figure 5. Depth function of SOC stocks and total aboveground biomass of soils as influenced by forest transformations in LDNP, Ormoc City, Leyte. Horizontal bars represent standard errors

Figure 6. Biomass carbon stocks (A), relationship between SOC stocks (t C ha−1) and Biomass carbon stocks (Mg C ha−1) of forest (B), grassland (C), forest plantation (D) in LDNP, Ormoc City, Leyte

1.79 Mg ha−1 of TAGB since the area was harvested. dominated with carabao grass (Axonopus compressus) only with very low biomass. SOC Stocks vs. Biomass Carbon Furthermore, forest plantation rendered higher Stocks TAGB due to bigger trees (average dbh <35cm). The Gymnostoma rumphianum Estimation of biomass in different land uses plantation was planted 47 years ago (1971) gives us an idea of the potential amount according to locals interviewed and was never of carbon that can be sequestered from the

10 Carnıce and Lina JSET Vol.5, 2017 atmosphere. Results showed that F rendered of the major carbon sinks. It would also the highest biomass carbon stocks of 311 give knowledge to people that conversion Mg C ha−1 but significantly decreased when of forest to grassland and forest plantation converted to G with 0.89 Mg C ha−1 but slightly would have positive and negative effects on recovered when converted to FP (73.46 Mg C SOC stocks, TAGB, biomass carbon and on ha−1). Such results are comparable with the soil nutrient stocks. However, to estimate tree carbon density (237 Mg C ha−1) of MFR; SOC stocks more accurately, the number per however, its herbaceous biomass carbon land use type should be increased and the density is quite lower (0.06 Mg C ha−1) (Lasco deeper soil depths should be considered to et al. 2004). Gymnostoma rumphianum FP include C storage potential of the subsoil. high biomass carbon stocks could possibly be Further studies should be conducted to due to its age (47); most forest plantations reveal changes in SOC, TAGB, biomass in Leyte Island are dominated by Acacia carbon and nutrient stocks at different times mangium (25.61 Mg C ha−1), Gmelina arborea such as a chronosequence study method (31.59 Mg C ha−1) and A. auriculiformis (28.58 which is used to represent and study the Mg C ha−1) at the age of 4 years (Lasco & time-dependent development of a forest. This Pulhin, 2009). will provide dynamic characteristics of SOC, Relating SOC stocks and biomass carbon TAGB, biomass carbon and nutrients after land stocks is important to know if change in SOC use change, and could therefore provide basis stocks can affect the biomass carbon stocks. for theorizing to predict future changes. However, no clear relationship was observed across all land uses (Figure 6) indicating Acknowledgment that in such soil types SOC stocks does not significantly affect the biomass carbon The researchers acknowledge Dr. Victor B. stocks across all land uses. This could be Asio and Dr. Ian A. Navarrete for their key attributed to the effect of long accumulation inputs during the conduct of this research and and decomposition of biomass that fast and the Department of Science and Technology labile carbon may have been already lost, (DOST) – Accelerated Science and leaving only the recalcitrant carbon in soil Technology Human Resource Development (Montagnini, 2000; Veldkamp et al., 2003; Program (ASTHRDP), Philippines for giving Redondo & Montagnini, 2006). the first author an MS graduate scholarship and for funding the study. Conclusion References Cited The study showed distribution of SOC, TAGB, biomass carbon, and nutrient stocks across Asio,V.B.(1996). Characteristics, weathering, three adjacent land use patterns. Results formation, and degradation of soils from from this study demonstrate that substantial volcanic rocks in Leyte, Philippines. loss of SOC stocks could be observed upon Hohenheimer Bodenkundliche Hefte, conversion of secondary forest to grassland Stuttgart, Germany. Retrieved from and subsequently recovered when converted https://scholar.google.com.ph/scholar?q= into forest plantations. However, TAGB %5B9%5D.%09ASIO%2C+V.B.+1996.+C significantly decreased as F was converted haracteristics%2C+weathering%2C+forma to G and then to FP. The results of the tion%2C+and+degradation+of+soils+from study would be useful in determining the SOC +volcanic+rocks+in+Leyte%2C+Philippine sequestration potential of the Andisol soils. s%2C+vol.+33.+Hohenheimer+Bodenkun These are also important for greenhouse gas dliche+Hefte%2C+Stuttgart%2C+German inventories since soil is considered as one y++209+pp&btnG=&hl=en&as sdt=0%2C5

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