0119-B1

Performance of Two Rhizophora Species' Wildlings under Inundated and Periodically Inundated Conditions

Marco A. Galang^[1], Loretto U. Dela Cruz, Arturo SA. Castillo and Reynaldo A. Comia

Abstract

The field performance of wildlings of bakauan-babae (Rhizophora mucronata Lamarck) and bakauan-lalake (Rhizophora apiculata Blume) under inundated and periodically inundated conditions was investigated. A 2 × 2 × 2 factorial experiment was laid out in a Randomized Complete Block Design (RCBD) in the mangrove area of Real, Quezon from 19 September 2000 to 19 March 2001. Parameters measured include survival, height increment, diameter increment, shoot dry weight, lateral root dry weight, total plant weight and root-shoot ratio.

Six months after transplanting, the best survival percentage was obtained at inundated (77.77%) over periodically inundated (57.78%) conditions. Height growth was also favorable in the former compared to the latter. However, diameter increment, lateral root dry weight, shoot dry weight and root-shoot ratio were not significantly affected by either condition.

Generally, bakauan-babae performed better than bakauan-lalake. Bakauan-babae clearly expressed its dominance in shoot dry weight, lateral root dry weight, total plant weight and root-shoot ratio. Leaf trimming did not produce significant effects in the improvement of the performance of either species under either condition. Field performance rating showed that untrimmed bakauan-babae was the best planting material for both inundated and periodically inundated conditions.

Introduction

Mangroves are the typical littoral plant formations of tropical and subtropical sheltered coastlines. They have been variously described as "coastal woodland“, “tidal forest” and "mangrove forest" (FAO Forestry Paper 117, 1994). Mangrove forests rank among the most biologically productive systems in the intertidal accretive shore and constitute one of the most common coastal ecosystem types (Lauricio, 1981). Mangrove products include tannins, charcoal, fuel, building materials, pulp, and other minor uses (Chapman, 1976; Aragones et el., 1998).

The Philippines, being an archipelago situated in the tropics, is blessed with this unique coastal ecosystem. However, with population pressure and fishpond conversion through the years, a downward trend in mangrove extent was observed. In 1920, Brown and Fischer (as cited by Chapman, 1976) reported that the country has 400,000 to 500,000 hectares of mangrove swamps. In 1977, Gonzales reported based on the Bureau of Forestry Development (BFD) statistics, that the Philippines has 254,016 hectares of remaining mangrove forest, equivalent to 0.85% of the total forest area of the country that year. This is distributed throughout the archipelago with Mindanao having 116,076 hectares; Visayas, 66,982 hectares; Palawan, 41,779 hectares; and Luzon, 28,199 hectares (Gonzales, 1977; Umali, 1977). Recent figures (1995) showed that the country has 117,700 hectares left (Apostol, 1998). Analysis of these figures shows a decrease of 76.46% in mangrove area in the span of 75 years. Thus, there is a need for rehabilitation of the mangrove areas.

Two of the most economically important species of mangrove are bakauan-babae (Rhizophora mucronata Lamarck) and bakauan-lalake (Rhizophora apiculata Blume). The Rhizophoras are used as timber, fishing stakes, piles, pit props, firewood, charcoal and tannin (Chapman, 1976; Aragones et al., 1998). Decoction of the bark of bakauan-babae also serves as cure for haematuma, diarrhea, dysentery and leprosy. Light wine can also be produced from the juice of its seedlings. These species exhibits viviparity common to mangrove species which makes it a likely candidate for use of wildlings as planting stock.

Generally, this study determined the field performance of wildlings of bakauan-babae (Rhizophora mucronata Lamarck) and bakauan-lalake (Rhizophora apiculata Blume) under inundated and periodically inundated conditions. The effect of leaf trimming, which is a common practice in nursery, was also investigated.

Methodology

The experiment was conducted in a coastal area locally known as “Baluti”, a 20-minute boat ride from the town proper of Real, Quezon, Philippines. An area of approximately 600 m² was used for the experiment that lasted for six months from September 19, 2000 to March 19, 2001. The experiment was laid out following 2 × 2 × 2 factorial in a Randomized Complete Block Design (RCBD) with three replications. A total of 360 experimental units, 180 each of the two species, were used in the study. These were collected from the nearby town of Infanta, Quezon. Fifteen experimental units were allotted for each treatment combination.

The treatments used include condition [Inundated (I), Periodically inundated (P)], Species [bakauan-babae (b), bakauan-lalake (l)], and type of wildling [leaf-trimmed (t), leaf-untrimmed (u)]. Inundated condition refers to the areas below the low tide limit while periodically inundated condition refers to areas above the low tide limit but within high tide limit. Leaf trimming was done by cutting all the leaves of wildlings in half using a scissor.

The following are the treatment combinations and their descriptions:

Condition x species

Condition x type

Species x type

Condition x species x type

Parameters measured include survival, stem diameter increment, height increment, shoot dry weight, lateral root dry weight, total plant dry weight and root-shoot ratio (Figures 1 and 2). Seawater salinity was determined using the YSI Model 30 Handheld Salinity, Conductivity and Temperature System. Soil properties were assessed by taking three samples from each block for each condition. These were brought to the soil testing laboratory of the Department of Soil Science, College of Agriculture, UP Los Baños for analysis. Electrical conductivity of soil extract was also determined using the YSI Model 30 Handheld Salinity, Conductivity and Temperature System following the 1:2 soil-water extraction procedure (Jackson, 1967). Secondary climatic data such as rainfall, relative humidity and temperature were obtained from the nearby weather station in Infanta, Quezon.

Data generated were assessed through Analysis of Variance (ANOVA) for factorial in Randomized Complete Block Design (RCBD) using the Statistical Package for Social Science (SPSS) program/software. Treatment comparison was done through Least Significant Difference (LSD).

Figure 1. Diagram showing the height and diameter references for Rhizophora mucronata Lamarck (Melana, 1993).

Figure 2. Samples collected materials for biomass determination.

Results and Discussions

Biophysical Description of the Study Area

The town of Real, Quezon falls under climatic type II based on the modified Corona System of Classification. Type II climate has no dry season with a very pronounced maximum rain period from November to January (Agpaoa et al., 1976). December 2000 (1010 mm) and January 2001 (220 mm) had the greatest and least monthly rainfall, respectively. Highest relative humidity (85%) was during the months of October to December 2000 and February 2001. The highest mean temperature was during the month of September (24.8^oC). In the conduct of the experiment, two tropical storms both having typhoon signal number 3, passed by the study site. Tropical storms locally named “Reming” and “Seniang” occurred on October 27-28, 2000 and November 3-4, 2000, respectively.

Species of bungalon (Avicennia marina) and pagatpat (Sonneratia alba) dominated the study site with some occasional patches of bare area. Species of bakauan-lalake and bakauan-babae also occupied the vicinity of the study site. Both appeared as isolated trees or patches surrounded by the dominant species at the inland or coastline area.

Low tide and high tide occurrences varied depending upon the condition of the moon. Average maximum high tide (1.68 m) was observed at the beginning of the experiment and the lowest mean high tide (0.07) during the months of January and March 2001. The same trend follows for the low tide events. Average height of high and low tides show a decreasing trend from the start to the end of the experiment.

The two conditions of the study site showed very slight differences in soil properties and water salinity (Table 1). Soil pH under inundated and periodically inundated conditions were both highly acidic. This, however, was determined at air-dried condition. Coastal areas contain large quantities of iron sulfide (FeS) and elemental sulfur which when drained results to formation of sulfuric acid (Brady, N. C. and R. R. Weil, 1996), thus the resulting acidity.

Table 1. Soil properties under inundated and periodically inundated conditions.

Effect of Inundation and Leaf Trimming on Species Survival

The survival of bakauan-babae and bakauan-lalake under the two conditions showed a decreasing trend within the six months observation period (Figure 3). The planted propagules exhibited a 77.78% survival under inundated condition which was significantly higher than that observed under periodically inundated condition (57.78%) after six months of planting. The variation in survival under the two conditions may be attributed to the splash action created by high tide occurrences that washed away the planted propagules. This was evident as only the stakes which served as support remained on site during data gathering. The occurrence of typhoons during the experiment may have also increased the effect of this condition. The effect of strong wind during the typhoon damaged planted propagules at periodically inundated site as they were more exposed to this factor. Observation also showed that crab activity was higher under periodically inundated condition than in inundated condition.

Generally, the inundated condition positively influenced the survival of the two species (Figure 4). Trend shows that both species survive best under inundated condition than in periodically inundated condition. Both bakauan-babae and bakauan-lalake exhibited a survival rate of 77.77% under inundated condition compared with the 56.67% and 58.89% survival received by the two species, respectively, under periodically inundated condition. This observation may be explained by the favorable water logging condition in inundated than in periodically inundated condition. Comparison between species and trimmed and untrimmed wildlings yield no significant results.

The observed rate of survival in this particular study may already be considered high for such kind of propagules. The percentage survival could have been higher had typhoons not visited the study site. In a study done by Mauricio (1955) on wild dipterocarp seedlings transplanted in the forest, white lauan (Shorea contorta) and bagtikan (Parashorea malaanonan) showed a relatively lower percentage survival of 66.4% and 28.8%, respectively.

Figure 3. Survival trend of bakauan-babae and bakauan-lalake under inundated and periodically inundated conditions.

Figure 4. Percentage survival as affected by inundation condition.

Effect of Inundation and Trimming on Species Growth Traits

Height Increment

The inundated condition significantly affected the height increment of the planted propagules (Figure 5). Wildlings on this area recorded a mean height increment of 13.26 cm compared to the 7.11 cm increment observed in periodically inundated condition. Clearly exhibited in this was the 46.38% improvement in height growth in inundated condition. Such observed advantage in height growth may be attributed to higher organic matter content and favorable pH in inundated condition (5.36%) compared to periodically inundated condition (3.22%) although majority of the observed soil properties did not differ between the two conditions. Long period of waterlogging may have also enhanced growth of the propagules.

Figure 5. Height increment as affected by inundation condition.

Diameter increment

The treatments used did not significantly affect the diameter growth of the wildlings. However, under inundated condition, a slightly bigger diameter increment was observed compared to that under periodically inundated condition. The insignificant result observed maybe attributed to the short duration of the experiment. Kramer and Kozlowski (1960) reported that diameter growth of most plant species starts later and continue longer than height growth.

Shoot Dry Weight

The two species showed significant difference in shoot dry weight. Bakauan-babae (2.71 g) displayed a significantly higher shoot dry weight than bakauan-lalake (2.36 g). This was equivalent to 12.92% difference between the two species. The variation in the shoot dry weight of the species may be due to the natural morphological features of the species. Bakauan-babae has broader leaves than bakauan-lalake which translate to heavier weight. It, likewise, produced longer shoots than bakauan-lalake that could have contributed to heavier shoot biomass. Condition and trimming showed no favorable response on shoot dry weight.

Lateral Root Dry Weight

Bakauan-babae (1.71 g) produced significantly larger root dry weight than bakauan-lalake (1.20 g) regardless of condition and type of wildling (Figure 6a). Above ground biomass may have enhanced root development among bakauan-babae wildlings since planted propagules also produced heavier shoots. Interaction of the three treatments however, showed that the best lateral root dry weight was for untrimmed, bakauan-babae under periodically inundated condition (Figure 6b).

Total Plant Dry Weight

Total plant dry weight was greatest under periodically inundated condition (45.12g) than in inundated condition (32.89 g). Likewise, total plant weight by species showed significant difference. In general, bakauan-babae produced greater biomass than bakauan-lalake. Bakauan-babae showed a 15.23% advantage in total plant weight over bakauan-lalake. Leaf trimming significantly enhanced growth of bakauan-lalake but not of bakauan-babae (Figure 7).

Figure 6. Comparison of the lateral root dry weight by (a) species (b) inundation condition x species x type of wildling interaction.

Figure (a)

Figure (b)

Figure 7. Total plant dry weight as affected by (a) inundation condition (b) species (c) species x type of wildling interaction.

Figure (a)

Figure (b)

Figure (c)

Root-shoot Ratio

Bakauan-babae (0.61) displayed a significantly higher root-shoot ratio than bakauan-lalake (0.48). This difference transcends under the two different conditions. Periodically inundated condition greatly enhanced root-shoot ratio of bakauan-babae by 23.19% than inundated condition (Figures 8a and 8b).

Interaction of the three treatments revealed a significantly higher root-shoot ratio for untrimmed bakauan-babae under periodically inundated condition (0.82). This value was greater than that obtained in other studies done on bakauan-babae. Apostol (1998), in his greenhouse study of bakauan-babae, reported a highest root-shoot ratio of 0.5968 for medium class propagules. Furthermore, a root-shoot ratio of 0.5998 was measured for the same species that has light propagules. In this particular study, the natural condition existing within the study site may have enhanced a more balanced root-shoot ratio. Better soil, climate and the periodic waterlogged condition compared to that of greenhouse condition may have favored better growth of the planted propagules.

Figure 8. Root-shoot ratio as affected by (a) species (b) inundation condition x species interaction (c) inundation condition x species x type of wildling interaction.

Figure (a)

Figure (b)

Figure (c)

Field Performance Rating

Generally, the field performance of wildlings of bakauan-babae and bakauan-lalake was best at inundated than in periodically inundated condition. This was clearly expressed in terms of survival and height growth of the wildlings. The remaining parameters although statistically insignificant also showed favorable results for inundated than in periodically inundated condition. Based on the results of statistical analysis of all observed parameters, under both periodically inundated and inundated conditions, the best planting material was untrimmed bakauan-babae. This was followed by trimmed bakauan-babae. Bakauan-lalake did not perform favorably, getting both the lowest rating (highest score) at the two conditions regardless of whether the leaves were trimmed or untrimmed (Table 2).

Table 2. Suitability rating of the wildlings under inundated and periodically inundated conditions based on measured parameters.

Note:

S - Survival
R - Root dry weight
H - Height increment
T - Total plant weight
D - Diameter increment
R/S - Root-shoot ratio
Sh - Shoot dry weight

Rating:

Lowest total - best
Highest total - poorest

Conclusion

The results of this study are of great help in determining the potential of directly replanted wildlings of bakauan-babae and bakauan-lalake under various conditions. With the information obtained, selection of possible source of propagules, species and site at which these materials should be planted can be made. Based on the results of the study, the best planting material was bakauan-babae with untrimmed leaves, both under inundated and periodically inundated conditions.

Literature Cited

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Mauricio, F. P. 1955. Preliminary study on the behavior of wild dipterocarp seedlings when transplanted in the forest. Investigation paper (unpublished), U. P. Los Baños, Laguna.

Umali, R. M. 1977. Present status and distribution of mangrove forests/area in the Philippines. Provisional proceedings, National symposium/workshop on mangrove research and development. 28-30 July. Parañaque, Rizal. Part III (A): 1-5.