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Diversity of plant species and the presence of Invasive Alien Species (IAS) in the Sub-Montane Forest at Pakenjeng Region, Southern Part of Garut, West Java

Plant species diversity is an important ecological characteristic, especially to observe the complexity of forest ecosystems. The research is carried out to elaborate on the species composition, species diversity and the forest structure, and to identify the presence of invasive alien species (IAS) in the sub-montane forests at the Pakenjeng region, the southern part of Garut, West Java. The vegetation survey method used was a stratified sampling technique with the transects and line plots as sampling units for inventorying the trees, forest regenerations, and ground cover. These data are further analyzed to obtain information on abundance, dominance, importance value index (IVI), species diversity and evenness. Based on the species composition, the forest formation was categorized as a primary sub-montane forest with high species diversity characterized by the presence of tree species such as Altingia excelsa, Lithocarpus sundaicus, Castanopsis spp. and Podocarpus spp. showing the curve of inversed-J for horizontal structure with A, B and C canopy layers. The species of Eupatorium inulifolium, Musa zebrina, Piper aduncum and Lantana camara are categorized as IAS.


Introduction
Ecosystems in mountainous regions are strongly influenced by typical physiography, resulting in a specific form of physiognomy which is more specific than in lowland areas. The altitude and slope of the land cause the formation of microclimates condition which is different from the tropical lowlands in general, especially climate factors. Each species lives in different habitats according to its physiological and biochemical characteristics [3,4]. Besides, the diversity of plant species is an important indicator to determine the ecological characteristics of a natural forest ecosystem, especially the forms of complexity and dynamics of forest ecosystems.
One of the regions which have the luxurious mountain forests is Garut in West Java. Actually, Garut Regency consists of several mountains including Mount Papandayan, Guntur, Cikuray, 3 To whom any correspondence should be addressed (ckmangrove@gmail.com)  2 Burangrang, and several small mountains. The forest in these mountains is generally still in the form of primary forest, and the others are secondary forests that are formerly fired and encroached.
Mountain rainforest ecosystems in West Java, including Garut Regency, contain many species of conifer (needle leaf trees) genus Dacrydium, Libecedrus, Phyllocladus, and Podocarpus. There are also broadleaf trees such as Altingia, Lithocarpus, Quercus, Castanopsis, Actinodhapne, Litsea, and Eugenia spp. Various research results show that in these mountain forests there are also many types of understorey, epiphytes, and lianas.
Sub-montane primary forest in the southern region of Garut Regency including the Pakanjeng region is one of the storage for the diversity of plant species. Its current existence needs to be known earlier regarding the structure and composition of its species as well as the tendency for the emergence of the invasive alien species (IAS) for management considerations.
This study aims to determine the species composition, species diversity, and structures of submontane natural forests, and to identify the presence of invasive alien species (IAS) in those forests located at the Pakanjeng region on the southern part of Garut. This research is urgent because many parties have an interest in using the area for other purposes. The benefits of this research are to obtain up-to-date information on the species diversity, species composition, and stand structure as well as the presence of invasive species that can disrupt the development of open areas within the region. This research can also provide input for area managers in order to control invasive species earlier.

Method
The research has been conducted on sub-montane natural forest areas located in Garumukti Village, Pakanjeng District, Garut Regency, West Java, from February until April 2012. The research location has a type of wet climate with an average rainfall of 2,500-3,500 mm/year, the altitude ranges from 1000-1500 m above sea level, generally undulating hilly topography with slopes dominated by land with slope classes> 40%, and only a small portion is flat-sloping land (<15%).
The preliminary stage is carried out by analyzing the images and maps which are divided into three classes based on canopy cover characteristics interpreted using WorldView Panchromatic (WorldView-2) high-resolution satellite images as follows (figure 1): • Low canopy cover forest (HJR): forests with low canopy cover are natural forest cover conditions with a percentage of canopy cover from dominant trees less than 40%. The dominant trees are trees in the A and B strata. Forest areas tend to be located on steep cliffs, dominated by natural tree species such as pasang and huru, also found various types of rattan and herbs. Trees and other plants tend to be dense with high natural regeneration. • Medium canopy cover forest (HSD): Forests with medium canopy cover are natural forest cover conditions with the percentage of canopy cover from dominant trees ranging from 41% to 70%. It is a forest which is in the succession process towards a stable forest (climax). • High canopy cover forest (HLB): Forests with high canopy cover are forests generally having a very tight percentage of canopy cover which is greater than 70%. Forests with this criterion are generally old natural forests which are heading towards climax.  The next step is to make observations and measurements in the field. A vegetation analysis plot was made in each part of the forest by applying stratified systematic sampling techniques with sample units in the form of the transect. The stratification of vegetation is made based on the classification of forest cover conditions. In the observation areas transect of 20 m wide each with length based on field conditions was divided into subplots for analysis of tree and its regeneration (seedling, sapling, and pole) and other plant forms (understorey, epiphytes, lianas, and palms).
This study also identified types of invasive alien species (IAS) for finding out the distribution condition within the region and then described it based on the list of IAS types in Indonesia [1,2].

Species composition
The results of the overall vegetation analysis in the research area, there are 75 species of trees (from all growth stages), 69 species of plants (including herbs and shrubs), 5 types of epiphytes (orchids and ferns), and 14 species of lianas (including rattan). The description of the species composition condition in each forest canopy cover type for each habitus and tree growth stage is presented in figure 2. Based on the information on figure 2, it can be seen that forests with low canopy cover (HJR) have the highest tendency at the level of regeneration and understorey compared to HLB and HSD, while epiphytic and liana communities tend to have no difference. This condition is presumed because HJR still has quite a light canopy and open spaces, and it allows various types of regeneration and understorey to emerge. Furthermore, the species commonly found in each forest canopy cover class are presented in table 1.

Note: numbers in parentheses indicate Important Value Index (IVI)
Based on the information in table 1, the sub-montane forest ecosystem is composed of types of mountain primary forests, including genera found in all areas and at all tree growth stages, namely Lithocarpus, Altingia, Castanopsis, Schima, Dacrycarpus, and Podocarpus. Based on IVI, there is no prominence in certain species, but at the tree level, it is found that Altingia excelsa has a sufficiently large IVI compared to others because of a large diameter size.

Abundance and dominance
The abundance conditions in each class of forest canopy cover tend to be the same, the seedling stage has a very large abundance (3600-4000 ind/ha), followed by a sapling, pole, and tree stages ( figure 3). This abundance condition shows that the number of regeneration is generally very large, then decreases until lagging behind a few individuals at the tree stage. In general, the number of individuals per hectare is in abundant condition. Basal area of the tree and its regeneration tend to be the same in the three classes of forest canopy cover (table 2). The observations in the field show that dominant trees such as Altingia excelsa, Lithocarpus sundaicus, and Schima wallichii generally have large stem diameters resulting in the large basal area.
Sub-montane forest in the Pakanjeng region on high canopy forest (HLB), medium canopy forest (HSD) and low canopy forest (HJR) have not so high tree densities (ranging from 28-32 trees ha -1 ), but the basal area is relatively high ranging from 68,83-90,33 m 2 ha -1 .

Species diversity and evennes
All forest communities (HLB, HSD, and HJR) have high species diversity and evenness (figures 3 and 4).    figure 4, the forests with low canopy cover (HJR) have the highest level of species diversity, especially in seedling and sapling growth stages. Light intensity is thought to be a determining factor for this condition, namely, in HJR there are many gaps and open areas compared to HLB and HSD. The diversity of tree species and regeneration in this forest area is categorized as high (H '≥ 2.5), with 72 species in HJR and 67 species in both HLB and HSD. Tropical mountain forests have high biodiversity, this is due to the scale of the mountain, various characteristics, orographic heterogeneity, and geological as well as edaphic conditions also have an important role in the plant community [6].
The pattern of plant dominance and animal species richness tends to be determined by changes in elevation gradient (altitude) [7]. The maximum richness levels found at medium altitude (especially between 500-2,000 m asl). It is probably caused by the support of climate variables such as temperature and humidity, energy availability and productivity of ecosystems, historical and evolutionary processes, and the extent of distribution.  Figure 5 shows that in the three forest communities, trees and it is regeneration there are fairly distributed. It means that both the number of species and individuals trees and it is regeneration tend to be proportional. There are no prominence dominant tree species. The forest floors have a very diverse abundance of various species of understorey (around 46 species) which are generally in the form of herbs and shrubs. There were also many epiphytes (7 species) in the form of orchids (Orchidaceae), Asplenium, and lianas (mainly in the form of 10 species of rattan, enriched the high complexity of the plant community. Based on the composition of plant species and forest stand structure which is similar to the sub-montane forest climax typical of West Java (Faga-Lauraceous forest), the forest ecosystem in the research site categorized as a sub-montane forest climax.

Stand structure
The stand structure in all forest communities tends to have similarities both viewed horizontally based on the distribution of stem diameter and vertically based on the position of the trees in occupying the canopy stratum. The horizontal stand structure is indicated by the abundance of trees based on stem diameter classes. The results of the study show that the community horizontal structure of trees in this region tends to form the curve of inversed-J ( figure 6). This kind of horizontal stand structure is usually the case in primary/climax natural forests, generally with a tree stand population of 10 cm up, mostly concentrated in the C canopy layer. Besides that, it is indicated that the stand population tends to be normal.
The vertical structure can be seen based on the distribution of trees in the stratum of tree canopy heights, namely: A stratum (tree height reaches> 30 m); B stratum (height 20-30 m); and C stratum (height 4-20 m). The result shows that the trees dominated the C stratum, while the A stratum was only occupied by a small number of trees, especially the species of Altingia excelsa, Lithocarpus sundaicus and Castanopsis tungurrut (figure 7).

Presence of invasive alien species (IAS)
Invasive alien species (IAS) are species originating from outside which also invade natural areas, then widely affecting habitat they invade. Those species, both native and non-native species, colonizing habitat massively. The effects of alien species on native species and ecosystems are numerous and usually irreversible. The impact is sometimes massive but often subtle. Natural barriers such as oceans, mountains, rivers, and deserts which allowed the intricate co-evolution of species and the development of unique ecosystems have been breached over the past five centuries, especially during