188 3.1.1 Parthenium hysterophorus across physiographic regions 189 Parthenium hysterophorus was present in 21.2% of the 4,838 locations examined (Fig. 1, Table 190 2). It was more common in the Tarai and Siwalik regions than in the Middle Mountains region 191 while the weed was present only at a few locations in High Mountains region and absent in High 192 Himal (Table 2). In some grazing lands of the valleys of Siwalik (e.g. Gaighat in the east, 193 Hetaunda and Chitwan in the centre, and Dang and Surkhet in the west), P. hysterophorus 194 covered > 80% of the grazing lands (Supplementary Fig. 1). In the Middle Mountains, P. 195 hysterophorus was more common in the central and western regions than in the east. Small 196 satellite populations (cf. Radosevich et al., 2007) – small isolated populations far from invasion Author Manuscript 197 front of the source population – were present at a number of locations in the Middle and High 198 Mountains regions (Fig. 1). 199 <>
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> 201 Parthenium hysterophorus was found in all five National Parks of Nepal (viz. Parsa, Chitwan, 202 Banke, Bardia, and Sukla Phanta) and one Wildlife Reserve Koshi Tappu in the Tarai-Siwalik 203 region (Supplementary Fig. 2). It was also present in the buffer zone areas of Langtang National 204 Park (e.g. Syabrubensi and Timbure of Rasuwa district) which lies in the High Mountains region. 205 Parthenium hysterophorus was present at and around all 17 India-Nepal border entry points in 206 the Tarai region. There are no border entry points in the Siwalik region. Out of the two border 207 entry points in the Middle Mountains region with India, P. hysterophorus was present at the 208 western border crossing (Jhulaghat of Baitadi district) but absent at the eastern crossing 209 (Pashupatinagar of Ilam District). Darchula at the western border of Nepal was the only entry 210 point from India in the High Mountains region and P. hysterophorus was already common at this 211 location. Out of the two border entry points to Tibet (both within the High Mountains regions), 212 P. hysterophorus was present at Timbure near Rasuwagadhi where the weed was observed to be 213 spreading from south to north, towards Tibet (China) (Fig. 1)
214 Abundance of the weed varied from a single plant in some locations in the eastern Middle 215 Mountains (e.g. Dhankuta, Myanglung) to 100% cover in the grazing lands in some locations of 216 Siwalik (e.g. Surkhet). Out of 362 locations with P. hysterophorus (based on the road-side 217 survey undertaken in 2013), the weed cover had become high (> 50%) in 52% of locations, 218 medium (10-50%) in 29% of locations and low (< 10%) in 19% of the locations. The locations 219 with high cover were mainly in the Tarai, Siwalik and Middle Mountains regions of the country 220 (Supplementary Fig. 3).
221 3.1.2 Parthenium hysterophorus distribution across elevation, land use and road types 222 Parthenium hysterophorus was found from < 100 m asl in the Tarai to about 2,000 m asl in the 223 High Mountains region, representing the tropical to warm temperate climatic regions of the 224 country (Fig. 2A). With the weed present in 70% of the locations examined at < 500 m asl, the 225 fraction of the ‘present’ locations declined with increasing elevation. The highest elevation at 226 which it was recordedAuthor Manuscript at the flowering stage (plant height 55 cm) was 1,935 m asl at Siddhapaila 227 of Surkhet district along the road to Dailekh district. A few individuals at the juvenile stage were 228 observed at 1987 m asl in Api Municipality of Darchula district in north-western Nepal.
This article is protected by copyright. All rights reserved 229 <>
230 Land use types had significant impact on the frequency of P. hysterophorus occurrence (Fig. 231 2B). Occurrence was highest in the land use types that had high human activity, such as those in 232 fallow-grazing (80%) and agriculture lands (42%). In agriculture land, the weed was found in 233 maize (Zea mays L.), mustard (Brassica rapa L.), sugarcane (Saccharum officinarum L), potato 234 (Solanum tuberosum L.) and paddy rice (Oryza sativa L.) cropping systems. In forest, shrubland 235 and wetlands, about 25% of the survey locations had the weed. In forested areas, it was limited 236 mainly to the forest edges and low canopy forest stands used for livestock grazing. At a few 237 locations it was noticed that it would die after the land was flooded or water-logged during the 238 rainy season.
239 There was a weak but significant relationship between type of road and the frequency of the 240 weed’s occurrence (Fig. 2C). The frequency was higher along highways and secondary roads 241 than along main roads. Along the East-West highway, and the highway which connects the 242 Kathmandu valley with southern part of Nepal (a part of the Prithvi highway), the weed was 243 present in more than one-third of the surveyed locations (data not presented). The weed was less 244 frequent along other highways running north-south, either connecting the Middle and High 245 Mountains regions with the Tarai lowlands (e.g. Mechi and Koshi highways in eastern Nepal) or 246 the Kathmandu valley with the Tibetan border (e.g. Pasang Lhamu highway). Along the roads, 247 all satellite populations of this weed found in the Middle and High Mountains regions (see 248 section 3.1.1) were in areas with a bus station. For example, along the Pasang Lhamu highway 249 (Kathmandu-Trishuli-Syabrubensi), the weed was absent for about 50 km to the north from the 250 Trishuli valley, but reappeared at Syabrubensi which is the last station on that bus route, a station 251 used by thousands of tourists visiting Langtang National Park every year. 252 253 3.1.3 Plant height of Parthenium hysterophorus across elevation gradient 254 The mean height of the tallest individual of the weed at the flowering stage during rainy season 255 was 128 ± 42 cm (n = 362) but varied from 15 to 240 cm. The maximum height did not exhibit Author Manuscript 256 any relationship with elevation when determined within the entire range of elevations (p = 0.80) 257 but segmented regression analysis revealed a slight increase up to 1,300 m asl and a sharp 258 decline above it (Fig. 3).
This article is protected by copyright. All rights reserved 259 <>
260 3.2 Distribution and Impact of Zygogramma bicolorata
261 Zygogramma bicolorata was found in only 15.4% of the 1,027 survey locations with P. 262 hysterophorus. It was found in the Tarai, Siwalik and Middle Mountains regions up to 1,350 m 263 asl (Supplementary Fig. 4). Comparison of the distribution suggests that the invasion front of the 264 weed to the north was > 50 km ahead of the beetle. At a few locations, satellite populations of 265 the beetle were also found. For example, the populations in Dipayal of Doti district were 160 km 266 road distance from the nearest other beetle populations in Tarai region and P. hysterophorus was 267 also absent between these sites. The damage by the beetle was high (> 50% leaves damaged) in 268 15%, medium (10-50% leaves damaged) in 28%, and low (< 10% leaves damaged) in 57% of the 269 locations (Supplementary Fig. 5). Both larva and adult stages were seen to feed on leaves and 270 young flowers of the weed.
271 3.3 Climatically Suitable Regions for Parthenium hysterophorus and Zygogramma 272 bicolorata
273 The CLIMEX projection showed that the Tarai, Siwalik, Middle Mountains and a small area 274 in High Mountains regions are climatically suitable for P. hysterophorus, with a 275 concentration of grids with high suitability (EI > 30) in Middle Mountains region (Fig. 4). In 276 eastern and central Nepal, only a narrow stretch of geographic area along the northern border 277 is unsuitable for it, while a relatively large geographical area is unsuitable in western Nepal. 278 Interestingly, again, a large geographic area of Middle Mountains region has high suitability 279 in western Nepal. The current distribution matches well with the CLIMEX predictions, 280 except for a few locations in the Rasuwa district near the Nepal-Tibet border, within north- 281 central Nepal (Syabrubensi at 1,450 m asl and Timbure at 1,700 m asl). A closer look into the 282 climatically suitable regions and the current distribution of P. hysterophorus revealed that 283 satellite populations established in the Middle Mountains region were in the areas of high
284 habitat suitability.Author Manuscript 285 <> 286
This article is protected by copyright. All rights reserved 287 CLIMEX predictions showed that the southern part of Nepal is climatically suitable for the 288 establishment of Z. bicolorata (Fig. 4B). It’s current distribution almost perfectly matches that of 289 the CLIMEX prediction. It also shows that there are still climatically suitable areas to the north 290 of the current northernmost distribution range. Most of the regions currently invaded by the weed 291 have been predicted to be suitable climatically for the beetle but for four invaded localities in 292 central Nepal which lie in a region that is unsuitable for it (Supplementary Fig. 6).
293 When EI values for beetle and weed were compared, 76% of the grids, mostly in the southern 294 part of the country, had higher EI values for the beetle than for the weed (Supplementary Fig. 7). 295 However, 24% of the grids, mostly in the northern part, had EI values indicating that these areas 296 are climatically more suitable to the weed than to the beetle.
297
298 4. Discussion
299 Using the most extensive spatial distribution mapping of invasive plants in Nepal, we showed 300 that P. hysterophorus has already invaded diverse physiographic and climatic regions and land 301 use types, thereby posing a significant threat to national food security, biodiversity conservation 302 and ecosystem function. The distribution data and CLIMEX modelling also revealed that the 303 available biological control agent Z. bicolorata is unlikely to prevent further spread of this weed 304 through Nepal. Finally, management priorities and research needs for informed policy have been 305 discussed.
306 4.1 Distribution Pattern of Parthenium hysterophorus
307 Parthenium hysterophorus has spread rapidly in tropical and subtropical regions of the world and 308 has become one of the most widespread and damaging invasive plant species (Adkins & Shabbir, 309 2014). In Nepal, even though the weed was first observed in 1967 (Tiwari et al., 2005), the most 310 rapid expansion of its range has occurred in the last 20 to 25 years (Shrestha et al., 2015) so that
311 currently there areAuthor Manuscript several satellite populations that are dispersed in regions considered to be 312 climatically suitable (Fig. 1 and 4A). The pattern of spread shown in Nepal can be described as 313 ‘jump spread’ (sensu Williamson, 2010) in which satellite populations appear at a distance from
This article is protected by copyright. All rights reserved 314 the main populations. These could not have been produced by natural processes alone. A similar 315 dispersal pattern has also been reported in Pakistan (Shabbir et al., 2012), Africa (McConnachie 316 et al., 2011; Wabuyele et al., 2014) and in Australia (Blackmore & Johnson, 2010). When the 317 expansion rate of satellite populations of invasive weeds is faster than that of source populations 318 (Radosevich et al., 2003), the occurrence of satellite populations in climatically suitable regions 319 (Fig. 4A) is of great concern for management. Eradication should be possible with early 320 detection of such satellite populations, but the eradication option would rapidly disappear 321 (Wittenberg & Cock, 2001). Therefore, as an immediate response to the present invasion pattern, 322 the destruction of these small satellite populations would help protect these climatically suitable 323 and, therefore, highly vulnerable regions from further invasion and subsequent environmental 324 and economic damage.
325 It appears that the road network is the major conduit for the dispersal and subsequent 326 development of satellite populations of this weed in Nepal, similar to that reported in other parts 327 of the world (Blackmore & Johnson, 2010; McConnachie et al., 2011; Wabuyele et al., 2014). 328 The single- seeded fruit is small but, unlike other members of the Asteraceae, less likely to be 329 dispersed over long distances by wind (Navie et al., 1996). It was interesting to note that 330 although the weed was absent for several km along the roadsides, it reappeared at many bus 331 stations, indicating that the dispersal of the weed was clearly linked with human movement 332 and/or vehicle transport.
333 Parthenium hysterophorus was common in urban areas, grazing lands and other agro- 334 ecosystems. This has direct economic consequences, both in the form of health hazards to people 335 and livestock, and reduced productivity of grazing lands and agro-ecosystems (Adkins & 336 Shabbir, 2014). Though the weed was frequently recorded in agro-ecosystems, the damage has 337 not been significant until now in Nepal as compared to other regions of the world, such as 338 eastern Africa (Pratt et al., 2017). However, it is highly likely that the damage will be significant 339 in near future this weed is starting to invade diverse cropping systems rapidly (Shrestha et al., 340 2015) and the geographic extent of its suitable habitat is likely to increase under future climate Author Manuscript 341 change scenarios (Shrestha et al., 2018). Furthermore, similar to the report from Africa 342 (McConnachie et al., 2011; Wabuyele et al., 2014), it’s widespread occurrence in fertile zones 343 with agriculture potential (e.g. the Tarai, valleys of Siwalik and Middle Mountains regions) may
This article is protected by copyright. All rights reserved 344 have serious consequences to food security. Besides human dominated ecosystems, there are 345 several reports of the occurrence of P. hysterophorus in natural ecosystems including protected 346 areas (Adkins & Shabbir, 2014; Wabuyele et al., 2014). The blocking effect of native vegetation 347 present in the protected area, against invasive species (Foxcroft et al., 2011), may be less 348 effective in situations where the highway passes along park borders (as with Parsa and Sukla 349 Panta National Parks) or through them (as in Bardia and Banke National Parks). Furthermore, 350 promotion of tourism in protected areas such as Chitwan National Park has substantially 351 increased the frequency of vehicle and elephant safaris into these protected areas. This has 352 resulted in rapid spread from the buffer zone to the core areas of the National Park (BB Shrestha, 353 personal observation).
354 Although the maximum height of P. hysterophorus declined sharply above 1,300 m asl, the 355 upper limit of the current distribution in Nepal may not represent the upper limit of the potential 356 habitat because the individuals examined at the highest elevation (1,935 m asl) were still > 50 cm 357 tall, healthy, and in a reproductive phase. The weed was located up to 2,600 m asl in Bhutan 358 (Tshering & Adkins, 2012), 2,300 m asl in Tanzania (Wabuyele et al., 2014) and 2,627 m asl in 359 Ethiopia (McConnachie et al., 2011). Therefore, even under the current climate, spread of this 360 weed to higher elevations in Nepal is highly plausible. Under a typical climate change scenario 361 for Nepal, the suitable weed habitat in Nepal will shift northward and most likely upward in 362 elevation (Shrestha et al., 2015; Shrestha et al. 2018).
363 4.2 Distribution and Impact of Zygogramma bicolorata
364 Zygogramma bicolorata, which was first noticed in Nepal in 2009 (Shrestha et al., 2010), is 365 already widespread from east to west throughout the Tarai and Siwalik regions, and some parts 366 of the Middle Mountains region. Since there has been no record of introduction and mass rearing 367 in Nepal (Shrestha et al., 2015), the reported distribution must be attributed to its natural 368 dispersal from India and its subsequent spread within Nepal. A similar dispersal from India, 369 where it was first released in 1984 (Jayanth & Ganga Visalakshy, 1994), to Pakistan has been 370 also reported (JavaidAuthor Manuscript & Shabbir, 2006). Natural dispersal of Z. bicolorata to a large area could be 371 possible (Jayanth & Ganga Visalakshy 1994), but the distribution pattern in Nepal cannot be 372 explained by natural dispersal alone. It appears that natural dispersal has been complemented by
This article is protected by copyright. All rights reserved 373 the agency of vehicle transportation. Occurrence of isolated satellite populations of the beetle in 374 areas such as the Dipayal valley (Doti district) in western Nepal would not have been possible 375 unless it had ‘hitch-hiked’ by vehicle from the Tarai region. The distribution pattern, in 376 comparison to that of P. hysterophorus showed a considerable geographic gap between their 377 fronts of spread. It implies that the beetle will not naturally reach the invasion front of the weed 378 anytime soon, which will continue to spread further in absence of the beetle. Though Z. 379 bicolorata was found to be widespread, the level of damage that it inflicted on the weed was low 380 at most of the locations, probably due to small population size (Jayanth & Ganga Visalakshy, 381 1994; Sushilkumar, 2009). It could be expected that the beetle population will build up over time 382 and its damage to the weed will increase in the future.
383 4.3 Climate Suitability and Model Fit 384 The geographic distribution of P. hysterophorus and Z. bicolorata in Nepal were in general 385 within the regions predicted to be suitable climatically by CLIMEX modelling. Even though the 386 model was developed without using distribution data from Nepal for both organisms, the model 387 output fitted well with their current distribution in Nepal. Therefore, our results support the 388 previous findings that CLIMEX can be a useful tool both for invasive species and for their 389 biological control agents (Dhileepan & Senaratne, 2009; McConnachie et al., 2011). A few 390 outlying weed populations near the northern border of Nepal can readily be attributed to the 391 effect of microhabitats (McConnachie et al., 2011).
392 The CLIMEX projection (Fig. 4) shows that the northward movement of Z. bicolorata, 393 particularly in eastern and western Nepal, following the path of P. hysterophorus spread, will not 394 be limited by climatic factors. There is, therefore, a strong expectation that mass beetle rearing 395 and release into those locations which are climatically suitable, and where the weed has already 396 arrived, would be a suitable management tool. Use of biological control agents, including Z. 397 bicolorata, has been effective in suppressing P. hysterophorus and bringing ecological and 398 economic benefits in Australia and India (Dhileepan, 2007; Sushilkumar, 2009). Comparisons of 399 CLIMEX projections also reveal that some regions in the northern part of the country have Author Manuscript 400 relatively lower habitat suitability for the beetle than the weed. To a minor extent, regions 401 unsuitable for the beetle have been already invaded the weed. Preventing spread of P.
This article is protected by copyright. All rights reserved 402 hysterophorus to these regions that are climatically unsuitable for Z. bicolorata should be, 403 therefore, one of the major management strategies applied to this weed.
404 There are several modelling tools to predict suitable geographic areas for the establishment and 405 spread of invasive species and CLIMEX is one of them. The CLIMEX tool is a process-based 406 model that is mainly based on tolerances of an organism to recorded climate (Sutherst & 407 Maywald, 1985), but the current and potential distribution of a species also depends upon biotic 408 and abiotic factors other than just climate. Biotic factors such as hosts, predators, natural 409 enemies, competitors etc. are important for the establishment and spread of a species. Similarly, 410 abiotic factors other than climate such as microhabitat (e.g. irrigation, deep valley in mountain 411 range) and physical features (e.g. sea, mountain) also limit the distribution of an organism. The 412 use of other environmental variables such as land-cover, in addition to climate, has been found to 413 be important in predicting potential invasion (Meentemeyer et al., 2008). Further, the CLIMEX 414 model uses average meteorological data of the world based on a 0.5o grid scale, which may not 415 capture variation at an appropriate scale for the predicted climate of areas where an organism is 416 present. 417 418 5. Conclusion 419 Although biological invasions have been recognized as emerging threats to the environment and 420 economy of Nepal, management response to these problems has been inadequate and sporadic. 421 This has led to uncontrolled and rapid spread of globally significant noxious invasive weeds such 422 as P. hysterophorus into diverse land use systems and physiographic and climatic regions 423 through the agency of human constructed dispersal corridors such as roads. Further spread to 424 agroecosystems, protected areas, and mountain regions is highly likely, with serious 425 consequences to food security, biodiversity conservation, and mountain ecosystem services, 426 respectively. Currently, the available biological control agent is unlikely to prevent further 427 spread of this weed. Therefore, immediate management responses are needed, which are in line 428 with activities targeted in Nepal’s national biodiversity strategy and action plan (2014-2020), to 429 manage invasive Author Manuscript alien species. Eradication of satellite populations of P. hysterophorus through 430 physical and chemical measures should help prevent further spread (Dhileepan, 2009) and this 431 should be the first priority for management. Roadside vegetation and bus station precincts need
This article is protected by copyright. All rights reserved 432 to be monitored regularly, particularly along the roads leading to areas predicted to be 433 climatically suitable for this weed, to prevent further spread. In areas where P. hysterophorus is 434 already widespread, an integrated approach combining biological control with competitive native 435 or multipurpose species needs to be implemented to reduce the impact on invaded ecosystems 436 (Adkins & Shabbir, 2014). For informed policy decisions and management to take place, future 437 research should focus, but not be limited to, ecological and economic impact studies of this weed 438 invasion in Nepal, and on better understanding of the foraging behaviour, population dynamics 439 and potentiality for host-range expansion of the beetle Z. bicolorata. In addition, repeating 440 distribution mapping activities after further interval of time will help in gaining a better 441 understanding of the dispersal pattern and spread rate of both weed and beetle, and to follow the 442 outcomes of management.
443 Acknowledgements
444 The funding for roadside survey (2013) came from the International Foundation for Science 445 (IFS), Sweden (Grants no. C/5306-1). KP was supported by Targeted Investment for Research 446 with Impact program of Colorado State University, USA (Sub-award no. G-9650-35). Survey in 447 Kailash Sacred Landscape Nepal was supported by International Center for Integrated Mountain 448 Development, Kathmandu, and Tarai Arc Landscape and Chitwan Annapurna Landscape by 449 National Trust for Nature Conservation, Kathmandu and Nepal Academy of Science and 450 Technology (Climate Change Research Grants Program of the Mainstreaming Climate Change 451 Risk Management in Development project). We are thankful to Srijana Joshi, Neha Bisth, Mohan 452 Pandey, Krishna Sharma, Yadu Paudel, Kalyan Shrestha, Sibaraj Ghimire, Sajita Dhakal, 453 Samikshya Banjade, Sangita Thapa, Sonia Pujara, Gajendra Chataut and Kusmum Shrees for 454 their supports during field data collection. We are also thankful to Hari Sharma for help in 455 statistical analysis; Kumar Mainali for useful comments on the first draft of the manuscript; and 456 Mike Foale for improving English language of the final manuscript. 457 References Author Manuscript 458 ADKINS SW & SHABBIR A (2014) Biology, ecology and management of the invasive 459 parthenium weed (Parthenium hysterophorus L.). Pest Management Science 70,
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581 Author Manuscript 582 Table
This article is protected by copyright. All rights reserved 583 Table 1 CLIMEX parameter values of the variables used in this present study for modelling the 584 potential distribution of Parthenium hysterophorus and leaf feeding beetle Zygogramma 585 bicolorata (Shrestha et al. 2015).
Index Parameter Parthenium Zygogramma Units hysterophorus bicolorata
Temperature DV0 = limiting low temperature 5 12 ºC DV1 = lower optimum temperature 25 18 ºC DV2 = upper optimum temperature 30 32 ºC DV3 = limiting high temperature 42 39 ºC
Moisture SM0 = limiting low soil moisture 0.08 0.1 SM1 = lower optimum soil moisture 0.2 0.2 SM2 = upper optimum soil moisture 0.6 1.0 SM3 = limiting high soil moisture 1.6 2.0
Cold stress TTCS = temperature threshold 4 6 ºC
-1 THCS = stress accumulation rate 0.001 0.001 week DTCS = degree-day threshold 12 7 day ºC -1 DHCS = degree-day stress rate 0.0001 0.001 week
Heat stress TTHS = temperature threshold 42 40 ºC THHS = stress accumulation rate 0.001 0.005 week-1
Dry stress SMDS = wet stress threshold 0.07 0.05 week-1 HDS = stress accumulation rate 0.001 0.05
Wet stress SMWS = wet stress threshold 2.3 2.0 week-1 HWS = stress accumulation rate 0.002 0.005 - Hot-dry stress TTHD = hot-dry temperature 36 week-1 threshold 0.2 MTHD = hot-dry moisture threshold 0.001
PHDAuthor Manuscript = stress accumulation rate
Annual heat PDD = degree-day threshold 2000 - day ºC sum 586
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589 590 Table 2 Occurrence of Parthenium hysterophorus in different physiographic regions of Nepal. Physiographic Number of locations regions Presence Absence (Percentage of total)
Tarai 446 (30.6) 1,011
Siwalik 343 (28.2) 875
Middle Mountains 221 (15.0) 1,251
High Mountains 17 (3.0) 558
High Himal 0 (0) 116
Total 1,027 (21.2) 3,811
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602 603 Figure legends 604 Fig. 1 The distribution of Parthenium hysterophorus in different physiographic regions and 605 ecological zones of Nepal. Locations with satellite populations of P. hysterophorus 606 and major border points have been named. ‘KTM’ stands for the capital city 607 Kathmandu.
608 Fig. 2 Number of locations examined in the 2013 roadside survey where Parthenium 609 hysterophorus was either present (dark bar) or absent (light bar) across land use types 610 (A), elevation gradient (B) and road types (C).
611 Fig. 3 Variation of height of the tallest individuals of Parthenium hysterophorus with locality 612 elevation. Fitted lines are based on segmented linear regression with cut-off point at
613 1300 m asl. For <1300 m asl, F1, 320 = 4.8, p = 0.03; for >1300 m asl, F1, 38 = 25, p 614 <0.0001.
615 Fig. 4 Climatically suitable regions predicted from CLIMEX modelling based on Eco- 616 climatic Index (EI) for Parthenium hysterophorus (A) and Zygogramma bicolorata 617 (B) growth and their current distributions in Nepal. For P. hysterophorus, the EI value 618 1-15 represents marginally, 15-30 moderately and >30 optimally suitable areas. For Z. 619 bicolorata, the EI value 1-30 represents marginally, 31-45 moderately and >45 620 optimally suitable areas. Unshaded northern part has EI value 0 indicating unsuitable 621 region.
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628 Figures
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633 Fig. 2
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637 638 Fig. 4
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