Avicennia marina and Rhizophora mucronata seedlings growth model at different spacings using guludan planting technique

Abstract

Ecological impacts due to the destruction of mangrove ecosystem are the loss of various flora and fauna, which in the long run will disrupt the balance of mangrove ecosystem as well as coastal ecosystem. Therefore, rehabilitation efforts are urgently needed to maintain the overall functions of mangrove forest. In the last several years, there is a technique called guludan, which is developed to rehabilitate mangrove forest (Kusmana et al. 2005a). In applying guludan technique, a study had been conducted using seedlings of A. marina and R. mucronata with different spacings, i.e. 0.25 x 0.25 m, 0.5 x 0.5 m, and 1 x 1 m. There has been not many studies conducted yet to develop growth models and increments for the planted seedlings using guludan technique. It is important to obtain information on the growth models and increments in regards to the success of guludan technique. This study is aimed at: 1) formulating models and increments for diameter and height growths for A. marina and R. mucronata seedlings at different spacings, 2) determining the most ideal spacing which can result to the greatest growth and increment for trunk diameter and height of A. marina and R. mucronata seedlings. Data collections were conducted from October 2008 through October 2011 (3 years) at the Mangrove Arboretum Angke Kapuk, located at the side of Sedyatmo Toll, KM 22 through KM 23, Jakarta Province (06o06’45” LS and 106o43’54” BT). This location has water depth of 2-3 m with salinity of 28-30 ppt and pH of 6.88 – 7.52 (Kusmana 2010). Variables observed were trunk diameter and height of A. marina and R. mucronata seedlings with different spacing until reaching 36 months old of age. The starting age for A. marina was 3 months old, whereas for R. mucronata was 6 months old. The trunk diameter was measured at 10 cm above land surface using caliper. The trunk height was measured starting from where the diameter measurement was taken, up to the growth using measurement tape. The observations were conducted every 4 months during the 3 years of study. The models used were non linear regression models developed with software R, using non linear regression analysis. Models used were logistic, Gompertz and Richards. Models for height growth used were power, exponential, polynomial and invers polynomial. The best model was determined using criteria as follows: 1) the model has p value < 0.05; 2) the model has the least AIC, BIC, and RMSE; 3) the model has the greatest R2 and R2adj; 4) the model has residual value which are randomly scattered and homoscedastic. After the best model was chosen, then the mathematical equations were developed to predict the Mean Annual Increment (MAI) and the Current Annual Increment (CAI). MAI is the average of diameter growth model or height growth model over time (f(y)/t). CAI is the differential of diameter growth model or height growth model (dy/dt). Based on the study, it is observed that the diameter growth and height growth of A. marina as well as diameter growth of R. mucronata followed logistic 2 equation. On the other hand, the height growth of R. mucronata followed polynomial equation. At the beginning of the study, the 0.25 x 0.25 m spacing showed the optimum diameter and height growth for A. marina and R. mucronata seedlings wihich may have been caused by exposure to light. Since the seedlings at the beginning were small, all seedlings obtained full exposure to light, especially seedling planted with wider spacing. Denser spacing reduced exposure to light and to heat, which in turn reducing condensation. At the beginning of the study, the roots of the seedlings were not yet functioned optimally. At the end of the study, the 1 x 1 m spacing gave the greatest diameter growth for A. marina and R. mucronata. The 0.25 x 0.25 m spacing gave the least diameter growth. These occurrences indicated that there were competition to obtain nutrition. More fierce competition happens at denser spacings. Height growth showed different result, i.e. the denser the spacing ,the greatest the height growth, for seedlings of A. marina and R. mucronata. These occurrences happened because competition to obtain light is more fierce at the denser spacings, therefore, the growth was focused on height growth to obtain more light. Exception happened at height growth of 2.5 years old A. marina. A. marina seedlings aged 2.5 years old planted with 0.5 x 0.5 m spacing gave greater height than those planted with 0.25 x 0.25 m spacing. This result happened because competition to obtain nutrition was more fierce at the denser spacing, which cause unoptimal photosynthesis.