1. Introduction
Papandayan Mountain Nature Reserve is a region that often experiences various natural disasters, such as volcanic eruptions and anthropogenic disturbances in the form of forest encroachment, opening up the environment to be more vulnerable [1]. These exposed conditions and scars of disturbance prove to be a suitable environment for the growth of invasive species [2]. Invasive species are native or non-native species that grow uncontrollably, have an effective way of seed dispersion and rapid reproduction, with their presence resulting on the disturbance of native species. [3]. In natural ecosystems, the presence of invasive species frequently results in negative impacts towards the environment, economy, and health of humans and animals [3, 4]. In Baluran National Park, East Java, Acacia nilotica has invaded almost 6,000 ha out of the 10,000 hectares of the savanna. The area has been converted into shrubs, causing a decrease in grass productivity for animal feed, and thus consequently threatening the lives of wildlife such as bull, buffalo, and deer [5]. In the United States, the impact of invasive species is expected to reach USD 167.9 billion [6]. Also, invasive species can cause health problems, for example, Ambrosia artemisiifolia, native in Central America, can cause sunburn on direct contact with humans [7].
The control of invasive species needs to be planned seriously to prevent the distribution of invasive species, especially to the natural ecosystems [8]. Several efforts in controlling invasive species have been implemented: mechanically, through felling or burning; chemical controls through the usage of natural herbicides; or, through biological controls, by bringing natural enemies. However, the results of these methods have been deemed ineffective, with staggeringly expensive costs [8]. The study of preventing the arrival of invasive foreign species is the most effective strategy compared to eradication [9]. Risk analysis is an effort to predict the chances of risk, distribution impacts, and threats to the preservation of natural resources due to the presence of invasive alien species [10]. Therefore, in this paper, conducting a review through risk assessments of invasiveness and management feasibility of invasive species is established as the basis for more effective and efficient management [10]. A risk assessment is needed to determine the risk of each invasive species, before being able to propose recommendations for appropriate invasive species management in Papandayan Nature Reserve.
2. Methods
2.1. Study Area and Sampling Time
The research was carried out in March until October 2019 in the Papandayan Mountain Nature Reserve, Garut, West Java. The research location is divided into three types of land cover, i.e. grassland (Pondok Salada and Tegal Alun), Tepi Kawah, and Cisupabeureum (Fig. 1).
2.2. Vegetation Analysis
The research was carried out in March until October 2019 in the Papandayan Mountain Nature Reserve, Garut, West Java. The research location is divided into three types of land cover, i.e. grassland (Pondok Salada and Tegal Alun), Tepi Kawah, and Cisupabeureum (Fig. 1).
Vegetation analysis was conducted to determine the invasive species, using the quadratic method. This was done by purposively sampling plots on three types of land cover, i.e. grassland, crater rim, and mixed forest. There were 18 plot of 5 x 5 m for the shrubs and 36 plots of 2 x 2 m for the herb. The composition of the invasive species in Papandayan was determined by the Index of Important Values (IV). The calculation of IV for herbs and shrubs were obtained by summing the relative density values and the frequency relative values, by using the following equation [11]:
Density (D) = OPQRST UV WKXWYWXPZJ[ WK M\S [ZQ]JS ^UMZJ ZTSZ UV M\S [ZQ]JS Relative Density (RD) = _SK[WM` UV UKS []SaWS[ WK M\S [ZQ]JS ^UMZJ XSK[WM` UV ZJJ []SaWS[ WK M\S [ZQ]JS x 100% Frequency (F) = OPQRST UV [PRG]JUM[ WK b\Wa\ Z []SaWS[ UaaPT[ ^UMZJ KPQRST UV [PRG]JUM[ WK [ZQ]JS Relative frequency (RF) = cTSdPSKa` UV Z []SaWS[ ^UMZJ VTSdPSKa` UV ZJJ []SaWS[ WK [ZQ]JS x 100%
The Important Value index (IV) of shrubs and herbs = RD + RF
2.3. The identification of Invasive Species
The specimens were identified based on Flora of Java book volume I-III [12-14]. Specimens not available in the book were identified based on local name references from Papandayan Mountain Nature Reserve officials and other
references. Invasive species were classified by checking into online databases such as Invasive Species Specialist Group (ISSG), Convention of Biological Diversity (CBD), Center for Agriculture Biosciences International (CABI), Guide Book to Invasive Species in Indonesia, dan Forest in Southeast Asia-Indonesia Program (FORIS-INDONESIA).
Figure 1 Research Site of Study (a) Tegal Alun (grassland), (b) Tepi Kawah (crater rim), (c) Pondok Saladah (grassland), (d) Cisupabeureum (mixed forest)
2.4. Risk Assessment
The research was carried out in March until October 2019 in the Papandayan Mountain Nature Reserve, Garut, West Java. The research location is divided into three types of land cover, i.e grassland (Pondok Salada and Tegal Alun), Tepi Kawah, and Cisupabeureum (Fig. 1).
A risk assessment of invasive species was analysed using The Invasive Species Risk Management System Protocol [15] modified by [10]. It was further adapted to suit the conditions of the Indonesian habitat. The risk assessment was further determined by three components, i.e. Risk Index, Feasibility Index, and Management Recommendation.
Risk index (R) was obtained after all questions from three related parameters were answered. The scores from each parameter were processed by the equation as follows [10]:
The risk index = I × Ip × DP [10]. Invasiveness (I), the total score is divided by 15 and multiplied by 10; Impact (Ip), the total score is divided by 19 and multiplied by 10; Distribution potential (DP), total score.
One of the parameters to obtain F (feasibility index) is the actual distribution (AD) of invasive species. The AD value was determined in percentage units using the following formula [16]:
Percentage of AD = \[\times 100\%\] \(\frac{\sum_{j} FiAj}{APNR} \times 100\%\)
with, Fi = Frequency of species, iAj = Area of ecosystem where species found (ha) A PNR = Area of Papandayan Mountain Nature Reserve.
F was obtained after answering all questions from three related parameters using formula as follows [10]: The feasibility index = C × IPD × P. Control Cost (C), the total score is divided by 15 multiplied by 10; Actual Distribution (AD), the total score is divided by 12 multiplied by 10; Persistence (P), the total score is divided 11 multiplied by 10. Risk Index and Feasibility index categorized as showed in Table 1 [10].
The R and F score obtained were classified into the following categories [10]: The higher the value of R showed a higher risk of invasive species, while the higher the value of F showed lower feasibility to manage invasive species. The recommended strategy of invasive species management was determined based on the matrix of score and category of R and F, as shown in Table 2 [10].
3. Results and discussion
3.1. Invasive Species in Papandayan Nature Reserve
There were six invasive species belong to three families of Asteraceae, Poaceae, and Rosaceae grow in Papandayan Nature Reserve (Table 3). The invasive species mostly grew in an open area of the grassland, but none in the vegetation at the edge of crater. The grassland area has been disturbed in the form of forest fires and has open vegetation cover so that 6 invasive alien species can be found in this area because invasive alien species are relatively easy to grow in the open and experience disturbance [3] The type of soil conditions in the edges of the dry craters was considered not suitable for invasive species to grow [10, 17]. One of the factors that prevent invasive alien species from growing and spreading is unsuitable abiotic conditions [17]. In Cisupabeureum forest area, only two invasive species, i.e. A. riparia and A. adenophora had grown because of the coverage of vegetation is difficult to make other species grow [3].
3.2. Invasive Species Risk Assessment
Based on the calculation of Risk Index, the invasive species in Papandayan was categorized as low risk (A. conyzoides) (4.18), to high risk (A. riparia (Regel) R.M.King & H.Rob.) (154.22) (Table 4). A. riparia has the highest Risk index, which means that its ability to invade a new habitat is considerably high. A. riparia, a shade-tolerant plant, can also appear on disturbed forest habitats [18, 19]. The species is also a prolific seeder and grows very fast compared to other invasive species [20-22]. Additionally, A. riparia can suppress the growth of other species due to its rapid and high-density growth, dominating ground covers among the locations [23]. In our research, A. riparia grew in a large area, and based on an estimated calculation, its potential distribution resulted in more than 50% of study area. The species was tolerant of shade. The branches of each individual A. riparia plants intertwined with each other, producing a blanket effect with 100% ground covers. This means that the seeds of other forest species may not be able to reach the soil to initiate germination [23]. Other invasive species that are not tolerant of shade require open land and high light intensity to grow such as A. adenophora can be established in open areas, forest areas, forest edges, and clearing disturbed areas [24].
The feasibility control of invasive species in Papandayan varied from the low to the high. The Feasibility Index of A.riparia was found to have the highest score (226.90), compared to other invasive species (Table 5). This indicates that the feasibility of management A. riparia in Papandayan is low, or substantially difficult to implement. This is could be related to A. riparia widespread distribution. In another study, the widespread growth species of Dioscorea centruroides had low management feasibility [16].
A. riparia was considered to spread widely in Papandayan. In our study, the species grew in three locations of sampling area, i.e Tegal Alun, Pondok Salada and Cisupabeureum. In contrast, other invasive species was usually only found in one or two sampling areas. Based on our research, the percentage distribution of A. riparia was predicted to be amounting to 50-60% of study area. Further A. riparia was found to produce an allelopathy compound i.e. phenolic O-Coumaric acid (2-hydroxycoumaric), which can inhibit the growth of other species [25, 26]. A. adenophora invaded 30-40% of land, mostly in open areas in grassland (Pondok Salada) and A. inulaefolium invaded 19% of the land. The number was only scattered in grassland areas A. conyzoides (1%), I cylindrical (9%) and R. mollucanus (24%) were found to be localized only in Pondok Salada. Control costs are not too high because the distribution is not too broad.
The traditional management of invasive species in Papandayan can be considered a solution. This is usually done through a mechanical control method, by slashing or cutting using a simple local equipment called parang. The predicted cost can amount to Rp 600,000,- per day. The costs were calculated based on the wages of labors at Rp. 100.000/day, multiplied by the number of workers, at six people.
Based on the matrix of recommendation management, Risk Index, and Feasibility Index, there are four recommendations for managing invasive species in Papandayan; managing its invasive species, managing the location of the growing place, performing limited action to the location of the growing invasive species; and lastly, monitoring (Table 6).
Table 1 Classification of risk and feasibility indices [10]
| Risk Score | Category | Feasibility Score | Category |
|---|---|---|---|
| >192 | Very high | >113 | Very low |
| 101 – 192 | High | 56 – 112 | Low |
| 39 – 100 | Hose | 31 – 55 | Medium |
| 13 – 38 | Low | 14 – 30 | High |
| < 13 | Very low | <14 | Very High |
Table 2 Matrix of Invasive Species Recommendations of Management [10]
| Feasibility Index | |||||
|---|---|---|---|---|---|
| Risk Index | Very low | Low | Medium | High | Very high |
| >113 | 56-112 | 31-55 | 14-30 | <14 | |
| Very low <14 | Limited action | Limited action | Limited action | Limited action | Monitoring |
| Low 15-38 | Limited action | Limited action | Limited action | Monitoring | Monitoring |
| Medium 39-101 | Manage location | Manage location | Manage location | Protect location | Contain spread |
| High 102-192 | Manage species | Manage species | Protect location | Contain spread | Destroy infestation |
| Very high >192 | Manage species | Protec location and manage species | Contain spread | Destroy infestation | Eradicate |
Table 3 Index Value (IV) of Invasive Species in Papandayan Nature Reserve
| Species | Family | IV (%) | ||
|---|---|---|---|---|
| Grassland | Crater side | Forest | ||
| Ageratina riparia (Regel) R.M.King & H.Rob. | Asteraceae | 56.50 | - | 58.40 |
| Ageratina adenophora (Spreng.) R.M.King & H.Rob. | Asteraceae | 51.71 | - | 43.20 |
| Rubus moluccanus L. | Rosaceae | 22.92 | - | - |
| Austroeupatorium inulaefolium (Kunth) R.M.King & | Asteraceae | 19.70 | - | - |
| H.Rob. | ||||
| Imperata cylindrica (L.) Raeusch | Poaceae | 16.70 | - | - |
| Ageratum conyzoides (L.) L. | Asteraceae | 1.33 | - | - |
Table 4 Risk Index and Category of Invasive Species in Papandayan Nature Reserve
| Species | Parameters | Risk Index | Risk | ||
|---|---|---|---|---|---|
| Category | |||||
| Invasiveness | Impact | Potential Distribution | |||
| A. riparia | 7.33 | 2.63 | 8 | 154.22 | High |
| A. adenophora | 6 | 2.63 | 4 | 63.12 | Medium |
| I. cylindrical | 5.33 | 2.63 | 1 | 14.01 | Very low |
| R. mollucanus | 5.33 | 1.05 | 2 | 11.19 | Very low |
| A. inulaefolium | 5.33 | 1.05 | 2 | 11.19 | Very low |
| A. conyzoides | 5.33 | 1.57 | 0.5 | 4.18 | Very low |
Table 5 Feasibility Index and Category of Invasive Species in Papandayan Nature Reserve
| Parameters | ||||||
|---|---|---|---|---|---|---|
| Species | Control Cost | Distribution | Persistence | Feasibility Index | Feasibility Category | |
| A. riparia | 6 | 6.66 | 4.54 | 182.21 | Very low | |
| A. adenophora | 4.67 | 5 | 5.45 | 127.25 | Very low | |
| R. mollucanus | 3.33 | 3.33 | 4.54 | 50.34 | Medium | |
| I. cylindrica | 4 | 1.67 | 4.54 | 30.32 | High | |
| A. inulaefolium | 4 | 0.83 | 4.54 | 15.07 | High | |
| A. conyzoides | 3.33 | 0.41 | 3.63 | 4.95 | Very high | |
Table 6 Recommendation of Invasive Species Management in Papandayan Nature Reserve
| Species name | Risk Category | Feasibility Category | Recommendation of Management |
|---|---|---|---|
| A. conyzoides | Very low | Very high | Monitoring |
| I. cylindrical | Very low | High | Limited action |
| R. mollucanus | Very low | High | Limited action |
| A. inulaefolium | Very low | High | Limited action |
| A. riparia | High | Very low | Manage species |
| A. adenophora | Medium | Low | Manage location |
Management recommendation to manage invasive species for A. riparia is aimed to reduce the environmental, economic, and social impacts of invasive species. This particular management approach is recommended by [10] especially for invasive species with high risk categories. The control feasibility of A. riparia is considered significantly low, due to its already-expanding distribution, thus causing considerable difficulties to control. Mapping of priority management locations can serve as a solution. This is done by modelling the distribution of species to configure the main environmental factors which affects the invasive species distribution [27, 28]. Another way is through mechanical controls, such as physically uprooting small plants and disposing them either by before the flowering of A. riparia. Cultivation, grubbing, hoeing, burning, replanting competitive pastures, or replacing A. riparia with native species can also prevent re-infestations [29]. Another management effort is to regularly monitor the cleaned areas every month [10].
Management location is recommended for A. adenophora aim to maintain environmental conditions of the conservation area [10]. This recommendation focuses more on location management, due to the lower potential distribution of A. adenophora. Mapping out the distribution of A. adenophora in Papandayan can be implemented [10, 15]. Management can also be done by slashing the seeds and flowers as they emerge, as well as clearing of colonization areas [22]. Utilization of biological control agents can be implemented by using the Procecidocares utilis flies and the Eupatorii cercospora mushrooms, considered as natural enemies to inhibit the growth of A. adenophora [30,31]. Limiting the invaded locations of A. adenopora from human access is also needed. This reduces the potential of A. adenophora being carried by human clothing and footwear to other places [23].
The recommended management of I. cylindrica, A. inulaefolium, and R. mollucanus is to perform limited actions aimed at reducing potential distribution invasive species to all research locations. This can be done by collecting the species bio-ecological data and analyze its response to management, to determine the best time for control [27]. Another method is by periodically monitoring the distribution of three species in Papandayan [10,15].
The monitoring recommendation for A. conyzoides is to detect changes in the risk of invasive species [10]. Generally, monitoring applies to species that have high management feasibility but with a low risk, therefore it does not necessarily need to be eradicated. Monitoring efforts can be implemented by making a permanent sample plot to monitor the spread of A. conyzoides [25], or by reviewing the invasiveness changes of A. conyzoides through a risk assessment within a certain period [32].
The recommendations above require continual monitoring efforts to detect threats of invasive species at the earliest possible time and evaluate any action that has been taken. These recommendations can become the foundational effort to control invasive species in Papandayan. This will further protect conservation areas in West Java. The role, support, and awareness of the threat of invasive species from various parties are needed. Therefore, dissemination, information exchange, and transfer of knowledge about invasive species are significantly important efforts in preventing the spread of invasive species in Papandayan Nature Reserve.
4. Conclusion
There are six invasive species within the area of the Papandayan moor i.e Ageratina riparia Ageratina adenophora, Austroeupatorium inulaefolium, Imperata cylindrica, Rubus mollucanus and Ageratum conyzoides. Recommendations towards the management of invasive species in Papandayan Nature Reserve depends on the character of each species. A. riparia is managed by managing the invasiveness of the species. A. adenophora is managed through the location its growing location. The management of I. cylindrica, R. mollucanus and, A inulaefolium is focused on limited actions. Finally, A. conyzoides can be managed effectively by periodical monitoring. A. riparia will need to be managed in the highest priority in Papandayan Nature Reserve, due to the highest risk of invasiveness (154.22), with low feasibility of control (182.21).