Potential, Distribution Pattern and Autecology of Diospyros celebica Bakh. in the Maleali Seed Stand Area, Central Sulawesi, Indonesia

There are about 5000 species of flowering plants in Sulawesi Island, Indonesia, and 15% of them are classified as endemic species [1]. Ebony (Diospyros celebica Bakh.) is an endemic species and is known by the public as ebony or ebony. This species is included in the category of vulnerable to extinction (A1cd) on the Red List of the International Union for Conservation of Nature and Natural Resources or IUCN [2]. D. celebica Bakh is one of the genera of Diospyros, the Ebenacea family, a plant species endemic to the island of Sulawesi. The natural population can only be found in Central and West Sulawesi province. In Central Sulawesi province, natural populations of ebony are found in the districts of Poso, Parigi Moutong, Donggala, Morowali and Tojo Una-una. Ebony produces luxurious wood with high economic value and has been approved as the mascot of the province of Central Sulawesi through a Decree of the Governor of Central Sulawesi No. 660/78/1995, dated February 27^th, 1995.

This type produces wood that is classified as luxurious, because the wood core is shiny black interspersed with black-brown lines. This wood can be used for various purposes such as carving, musical instruments, household furniture, luxury furniture, and lumber [3]. Ebony is very important in the world's timber trade, because of its high selling price so logging continues to be carried out, even though in 1990 a regulation was issued prohibiting logging through Decree No.950/IV.TPHH/90 addressed to the Governor of Central Sulawesi regarding the ban on logging of ebony trees. This situation requires that the preservation of ebony must be carried out.

Efforts to develop ebony require knowledge about the nature of the species, including semi-tolerant growth traits, where initial growth requires shade and subsequent growth does not require shade; the growth of this type is very slow so it often fails [4]. Ebony tree grows very slowly, with a life cycle between 100 up to 200 years. The slow growth of this type of wood, will be an obstacle in its development, besides there is not much data on growth criteria [5]. In addition, the properties of ebony seeds are recalcitrant. Recalcitrant seeds have a high water content, for this reason, the moisture content of the seeds needs to be maintained during storage [6]. The recalcitrant ebony seeds, with increasing time in storage will experience a decrease in their germination power, so that in ebony nurseries it can be done with natural seedlings. To obtain information about ebony seedlings, it is necessary to know their population and distribution under the stands. 

Santoso [7] conducted a study on ebony seedling populations, where they found quite a large number around the mother tree, around a 5 meter radius around the mother tree found around 500-4000 ebony seedlings, but the further away from the number of mother trees the ebony seedlings are also decreasing. The results of research by Rukmi [8] also showed ebony seedlings with a density of 19,850 ha^-1 in the area of the Maleali seed stand. At that time the seed stand area had not been disturbed. The occurrence of illegal logging and theft of ebony trees in this area has caused a change in the composition of the vegetation which in turn is likely to change the ebony in the area. The results of this study are supported by Restu [9] who stated that the natural rejuvenation potential of D.celebica is quite good. However, currently, according to Suryawan and Kinho [10], the conditions for ebony in its natural habitat are very limited, both for the stand and for its regeneration. Based on this description, it is necessary to study the population of seedlings in the ebony seed source stands in Maleali, Central Sulawesi, Indonesia.

Currently, research on the potential for regeneration and trees as a source of seeds in Central Sulawesi is still lacking. Completeness of information is an essential factor in formulating a conservation plan and management strategy for living natural resources, so it is necessary to conduct research on the potential for regeneration and trees as a source of ebony seeds in standing areas, which can be used as a source of information and preparation of conservation strategies that can be pursued in future. This research is one of the solutions to overcome this problem, in which gradual exploration activities will be carried out on regeneration and trees which are the source of seeds in the seed stand area of Maleali Village, in Central Sulawesi, Indonesia.

3.1 Species significant value index

The dominance and role of a species in a community can be predicted from the species' importance value. The type with the highest species importance value indicates the dominant species in an ecosystem. Important Value The highest ten plant species in the Maleali ebony seed stand area based on their growth rate, namely trees, poles, saplings and seedlings are presented in Table 1. The types of plants found based on their growth rate were: trees (28 species), poles (46 species), saplings (46 species) and seedlings (56 species). The difference in the number of species at various growth levels is caused by the dynamics of vegetation. Each population has different characteristics from other populations [23]. Vegetation dynamics can be described by changes in plant composition both quantitatively and qualitatively. These changes are partly caused by plant reproduction or the death of a plant species. In addition, it is caused by illegal encroachment. Population characteristics include density, birth rate, mortality, population increase rate, age and sex ratio, and aggregation [24].

Table 1. The highest species importance values of ten plant species at various growth rates in the Maleali seed stand area, Parigi Moutong Regency, Central Sulawesi

The results in Table 1 show that the species that dominates at all growth stages in the ebony maleali seed stand area at all growth stages is Diospyros celebica Bakh. (eboni), although at pole level it ranks second after Cananga odorata Hook F. Ten Dominant Species those present at every growth stage apart from the ebony species were Cananga odorata Hook F., Antiaris toxicaria Lesh., Antocephalus cadamba Miq, Homalium foetidum Benth. The species that were only dominant at the tree level were Antocephalus macrophyllus Roxb., Duabanga molucana BL. While the dominant species only at the seedling level are Arenga pinnata Merr and Corypha utan Lam. The species that dominate the level of trees and poles only. The species that dominated the seedling, sapling and pole stages was Canarium littorale BL. and Pterospermum celebicum Miq. Furthermore, the species that dominate the 10 main species for the tree level is 72.43%, the pole level is 19.02%, the sapling level is 45.63% and the seedling level is only 24.24%. The results of this study are different from the results of a study by (8) in the same area, which found important species values for the tree stage on a gentle slope of 83%, 122.36% pole level, 124.31% sapling level and 93.25% seedling level. This indicates a drastic decrease in value for the current condition of the Maleali seed stand. This change occurred as a result of illegal logging of trees with large diameters for all types, so that the trees that dominated the ten main species were small pioneer species.

Species density, frequency, species diversity and importance value have been used to measure the occurrence or dominance of plant species [25, 26]. A high IVI value indicates that the density of species in an area is also high. In addition, the distribution is even and the dominance is also high. The dominance of a species at each growth level can also be caused by the ability of that species to adapt to its environment, especially with changes in a short time due to illegal logging. Logging activities and other human activities in the forest [27]. The construction of logging roads increases accessibility to logged areas, and is therefore considered a driver of forest degradation and subsequent deforestation [28]. This was confirmed by Ogwu et al. [29, 30] who reported that species abundance decreased as a result of human activity, indicating that a forest area requires continuous surveys and monitoring. The existence of illegal logging will cause an open space that provides an opportunity for seeds to germinate, so that sometimes there is a change in the type that grows. This is in accordance with the opinion of Gobal and Bhardwaj [24], that changes that occur in a plant community are often in the form of replacement of one community by another.

3.2 Rejuvenation and tree potential of Diospyros celebica Bakh. in the Maleali seed stand area

The rejuvenation potential of ebony trees in the Maleali ebony stand area of Central Sulawesi is presented in Table 2. The results in the table show that the density of ebony species/ha both at rejuvenation and tree level is low when compared to the results of Rukmi's research [8], ebony rejuvenation at the seedling level reached 19,850 seedlings ha^-1, sapling rate 952 ha^-1, pole rate 598 ha^-1 and tree level 112 ha^-1. The results of research by Rukmi [31] in the forest group of Tambarana Village, Poso Pesisir Utara District, Poso Regency showed that the seedling rate was 19,850 ha^-1, the sapling rate was 952 ha^-1, the pole level was 112 ha^-1 and the tree level (diameter 20-29 cm) 2, 08 ha^-1, diameter 30-39 cm 2.08 ha^-1, diameter 40-49cm 1.67 ha^-1 and diameter 50-59cm 1.25 ha^-1. The low number of ebony species is due to a change in species composition due to the encroachment of species with large diameters, both ebony and other species which are natural vegetation in the Maleali ebony seed stand area. In addition, no longer found a diameter measuring more than 50 cm.

Table 2. Species density of D. celebica Bakh. at various growth rate

Changes in the structure of vegetation cause more open space so as to provide opportunities for undergrowth to grow more. The development of undergrowth causes the humidity of the surface layer of the soil to become moister which can result in the ebony fruit being attacked by fungus and unable to germinate. Ebony seeds are recalcitrant, their germination power decreases quickly and they are easily attacked by the fungus Penicilopsis clafariaeformis [25]. This change in vegetation structure is also caused by many factors. Many studies have reported on regeneration in natural forests [32]. Open forests provide opportunities for light to enter, thereby affecting forest regeneration [33]. Entry of light in forests is affected by the degree of slope in the forest. Zhang et al. [34] reported that steep slopes have lower diversity compared to gentle slopes due to differences in solar radiation intensity.

Ebony can germinate well in areas where seeds and undergrowth do not grow, although not all seeds can germinate completely. Ebony seeds are a type of recalcitrant seed, meaning they do not have a dormancy period, so they cannot be stored for a long time. Once dropped on the forest floor, it will soon germinate if germination factors are available. One week after falling on the forest floor, the seeds began to germinate which was indicated by the seeds being lifted from the media and the seed coat being separated from the cotyledons. Ebony sprouts have a long hypocotyl, with large and heavy cotyledons. These cotyledons will later fall off leaving two leaves which are known as seedlings. Stages of new leaf growth after the next six months. The growth of the seedlings can be seen in Figure 2.

2.png

Figure 2. Growth phases of ebony seedlings on a forest floor lacking undergrowth

3.3 Distribution pattern of ebony species

The distribution of species within a community can provide an overview of the relationships between species and the relationships between individuals in a plant species. The distribution pattern of ebony species at each growth level is presented in Table 3.

Table 3. Distribution pattern of D. celebica Bakh. at various growth rates in the Maleali seed stand area

The table above shows that the distribution pattern of ebony (Diospyros celebica Bakh.) seedling, sapling, pole and tree levels is in the random distribution pattern category. The distribution pattern of the ebony is different from the distribution pattern of ebony in the Educational Forest of Hasanudin University, Maros Regency [22] and in the Tombolo forest area, Bantimurung Bulusaraung National Park, South Sulawesi, Indonesia [35]. The results of their research indicated that the distribution pattern of ebony at all growth stages was clustered. It was further explained that this type of ebony is a semi-shade tolerant species, has excellent natural regeneration, its saplings can grow better and reach mature trees, if they are spread far from their parent trees. However, it is different from the results of research on the seed stand area in Maleali, Central Sulawesi, which is a random distribution pattern. Random distribution patterns are relatively rare in nature, where the environment is very uniform and there is a tendency to gather [36]. The existence of a random distribution pattern in the seed stand area in Maleali can be caused by the ebony seeds which are included in the buni fruit which are highly favored by birds. Birds take ripe fruit, fly and perch on a flat branch, so that the ebony seeds are scattered randomly. Birds taking fruit and directly perching on other trees is caused by the architecture of the ebony tree which tends to nod, making it difficult for birds to eat fruit from ebony trees, especially birds with large stature such as hornbills. Seed dispersal by birds is the cause of the random distribution pattern of ebony seedlings in the Maleali seed stand area. Apart from that, the random pattern is also caused by large-scale changes in the level of trees with large diameters, so that sunlight can penetrate to the forest floor. This allows the undergrowth in the form of weeds to grow freely, thereby covering the forest floor where the ebony pods are located. Even if there are seeds that can germinate, the undergrowth that propagates and twists causes subsequent growth failure, and many even die. In this condition, the fruit that falls under the tree is not clustered.

The distribution of plants is controlled by micro-environmental factors such as light conditions, soil moisture and the nutrients of their habitat [37]. In addition, elevation gradients often limit the distribution of tree species by decreasing soil moisture and nutrient levels [38] and otherwise aid species dispersal via strong winds at high elevations [34].

3.4 Physical, chemical and biological properties of soil in Maleali Ebony Seed Stands

The results of the analysis of the physical, chemical and biological properties of the soil in the ebony seed stands showed that the parameters varied between the three study locations (Table 4). The table shows that the soil texture of the three locations is sandy loam. The results of research by Rukmi [31] in this area are on gentle slopes with a clay texture, on steep slopes with a sandy loam texture. Total N content is low, organic C is very low except for slope positions in the low category. Likewise, P at the foot of hills and slopes is in the very low category, at the peak position is in the low category, while the pH is in the slightly acidic category for the three locations.

Soil with a sandy texture certainly facilitates the movement of water and air more, even though this condition does not hold water so it is easier to experience drought. Soil permeability in the fast and medium category is influenced by the presence of a soil texture that contains a lot of sand. The high content of sand and low clay at the foot of the hill causes high bulk density and fast soil permeability. Siregar et al. [39] stated that the measurement of soil permeability is very important for several interests in agriculture such as the entry of water into the soil, the movement of water to plant roots, the flow of drainage water, and the evaporation of water on the soil surface. Fast soil permeability shows the ability of the soil to pass water quickly which can lead to low water storage capacity in the soil. Although the porosity of the soil at the foot of the hill is lowest compared to the slopes and peaks, the fast permeability of the soil indicates that the dominance of macropores is higher at the foot of the hill. 

Table 4. Physical, chemical and biological properties of the soil at the three study locations

The bulk density of the soil on the slopes is lower than that of the soil at the top and foot of the hill. This is caused by the lowest content of the sand fraction and the highest content of organic matter. According to Nuraida et al. [40] the value of soil bulk density can describe the content of soil organic matter, minerals, porosity, water holding capacity, drainage properties and the ease with which the soil can be penetrated by roots. Sarief [41] stated that clay-textured soils have a smaller soil bulk density and sand-textured soils have a large bulk density value. Based on this, it can be said that the high bulk density value of the soil at the foot of the hill is influenced by the high content of the sand fraction and very low organic matter. Fast soil permeability indicates that the capacity of the soil to store water is low and the soil is easily penetrated by roots.

The actual pH (H₂O) of the soil at the top is higher (6.05) than at the foot of the hill (5.89) and the slope (5.76). Soil pH value is an indicator of soil fertility, because it relates to the availability of nutrients in the soil. PH indicates the concentration of H+ ions present in the soil solution. Kusuma and Yanti [42] state that soil acidity (pH) describes the level of availability of macro and micro nutrients in the soil for plant growth. Soil pH that is in the neutral range can provide the availability of soil nutrients at the optimum level because most of the nutrients are easily soluble in water. Availability of optimal macro and micro nutrients in the range of pH 6-7, and still sufficiently available in the range of pH 5.5-6 or 7-7.5. Based on this, the actual pH value of the soil at the top, slope and foot of the hill is still in the pH range that can provide nutrients in the sufficient category. According to Miah [20] that lower pH in forest soils may be caused by more accumulation of organic matter, which makes the soil more acidic.

Moderate to low total N content with very low organic matter content can be a limiting factor for plant growth in Maleali seed stands. Cation exchange capacity (CEC) related to the ability of the soil to absorb and exchange cations. A high soil CEC value indicates a high ability of the soil to absorb and exchange cations. The cations resulting from the mineralization process can be adsorbed on the surface of the colloid and can be released into the soil solution if there is a concentration gradient between the soil solution and the adsorption surface (soil colloid). Conversely, if the CEC of the soil is low, the capacity of the soil to absorb and exchange cations is low. Some of the cations resulting from mineralization will be leached from the soil so that they cannot be used by plants. The results of soil analysis showed that the soil CEC was high on the peaks and slopes, whereas at the foot of the hills the soil CEC was moderate. This means that the ability of the soil to absorb and exchange cations is moderate to high. Dissolved cations can be adsorbed and exchanged on the surface of the colloid.

The results of soil analysis showed that available P (Olsen) was very high on the slopes, high at the foot of the hills and moderate at the top. According to Surya and Suyono [43] the Olsen method can be used on acidic and alkaline soils, so that primary orthophosphate ions (H₂PO₄^-) and secondary orthophosphate (HPO₄^2-) and phosphate ions (PO₄^3-) can be read. The three ionic forms, if they are in soil solution, are called available P. In other words, available P (Olsen) is the primary orthophosphate ion, secondary orthophosphate ion and phosphate ion which are in the soil solution ready to be absorbed by plants. Among the three ions, primary orthophosphate ions and secondary orthophosphate ions are more easily absorbed by plants. Umaternate et al. [44] stated that although the P test results provided by the Olsen method were high, they could not be used as a benchmark for P availability due to interference from the high soil pH and the presence of a readable form of phosphate which was still difficult for plants to absorb, namely PO₄^3-. It was also stated that the Olsen method was more effective in determining available P than the Bray method for paddy soil samples. Plants will grow well if the availability of P in the soil is sufficient [45].

Deforestation alters the soil microbial community which can certainly affect the nature of the ecosystem as a whole because microbes play an important role in determining the sustainable status of soil fertility, decomposition of organic matter, mineralization and conservation of nutrients in tropical ecosystems [46]. Deforestation causes the habitat of the organisms to be damaged so that they move elsewhere and eventually die due to insufficient resources to support their survival [44]. Forest conversion and clearing to other land uses often results in low microbial populations [47]. 

The research results of Saragih et al. [48] showed that there was a negative correlation between soil pH and total soil bacteria on observations one day before soybean harvest; an increase in soil pH, with a range of 5-5.5, will decrease the total soil bacteria. In contrast to the results of this study, an increase in soil pH increased total bacteria and total fungi. The soil pH on the slopes is 5.76, the total bacteria 2.42x10⁸ cfu and total of fungi 4.09x10⁸ cfu. At the foot of the hill, the soil pH 5.89, total bacteria 2.89x10⁸ cfu and total of fungi 4.54x10⁸ cfu. At the top of hill, the soil pH 6.05, total bacteria 3.56x10⁸ cfu and the total of fungi 5.14x10⁸ cfu. 

According to Thammanu et al. [49] that environmental factors affect the distribution and composition of plant species in the forest. Soil fertility greatly affects the distribution of plant species in ecosystems and also changes their structural pattern in the forest [2, 27, 21, 50-52]. Nutrient deficiencies can stunt the growth of mature trees [53, 54]. In addition, the slope of the slope also affects regeneration in the forest, which of course also differs in the level of soil fertility. According to Shacha et al. [27] that the slope of the slope gives a negative correlation with the regeneration process where regeneration decreases with increasing slope.