Journal of Threatened Taxa | www.threatenedtaxa.org | 26 September 2019 | 11(12): 14562–14568

 

 

Shola tree regeneration is lower under Lantana camara L. thickets in the upper Nilgiris plateau, India

 

Muneer Ul Islam Najar ¹, Jean-Philippe Puyravaud ² & Priya Davidar ³

 

^1,3 Pondicherry University, Bharat Ratna Dr. B.R. Ambedkar Administrative Building, R.V. Nagar, Kalapet, Puducherry 605014, India.

² The Sigur Nature Trust, Chadapatti, Masinagudi PO, Nilgiris, Tamil Nadu 643223, India.

¹ mislam.esst@gmail.com (corresponding author), ² jp.puyravaud@gmail.com, ³ pdavidar@gmail.com

 

 

 

Abstract: Lantana camara is a dominant invasive shrub in many protected areas of India including the Nilgiri Biosphere Reserve (NBR).  We conducted a study to assess the regeneration potential of endemic native (shola) trees under different levels of Lantana infestation in the upper plateau of NBR.  A total of 61 plots in a total area of 0.73ha were sampled, out of which 0.57ha was in Lantana dominated sites and 0.16ha in undisturbed shola forests.  The plots were classified as per the level of Lantana infestation (intensive, moderate, and low infestation). We found that regeneration of shola trees, including endemics decreased with increasing intensity of Lantana invasion.  No regeneration occurred in the intensively infested plots whereas regeneration was high in undisturbed shola forests.

 

Keywords: India, invasive alien species, Lantana infestation, Nilgiris, shola forest, regeneration.

 

 

 

 

 

 

Introduction

 

Invasion by alien species is one of the major threats to the local and global biological diversity (D’Antonio & Kark 2002), and is regarded as one among the five top ecosystem disrupters (Millennium Ecosystem Assessment 2005). Besides affecting the native flora and fauna, a single invasive plant can alter biodiversity (Powell et al. 2011), hydrology (Le Maitre 2004), soil properties (Ehrenfeld 2010), disturbance regimes (Mack & D’Antonio 1998), fire frequency (Brooks et al. 2004), as well as above and below ground trophic interactions (Levine et al. 2003).  There is a close link between invasion by exotics and extinction of native species because deforestation, decline of native species, and spread of invasive species occur simultaneously (Gurevitch & Padilla 2004).  Plant extinctions, however, are least noticeable as they happen over a larger time scale (Gilbert & Levine 2013).

Lantana camara L. (hereafter referred to as Lantana) is one of the most successful invasive alien plants with its origin in Neotropical region.  This plant has successfully established itself in more than 60 countries (Day et al. 2003).  It was first introduced into India at the National Botanical Garden of Calcutta in the early 19^th Century by the British as an ornamental plant (Iyengar 1933; Anonymous 1942).  Since then Lantana has spread extensively throughout the country up to altitudes of 2,000m (Sharma et al. 1988).  It occurs in a wide variety of habitat types ranging from tropical evergreen forests, tropical moist- and dry deciduous forests, tropical scrub forests to subtropical moist and dry deciduous forests (Hiremath & Sundaram 2013).  It is prevalent in the Himalaya and Western Ghats (WG) biodiversity hotspots (Shaanker et al. 2010) where it affects native plant diversity (Cruz et al. 1986).  Presently, Lantana is a dominant shrub in many important protected areas of the Nilgiri Biosphere Reserve which includes Mudumalai National Park, Bandipur National Park, and Wayanad Wildlife Sanctuary (Hiremath & Sundaram 2013).  In these ecosystems, Lantana negatively impacts biota (Sharma & Raghubanshi 2007; Prasad 2010) by reducing grass cover which is important for the survival of herbivores like elephants (Kumar et al. 2012; Prasad 2012).  In Mudumalai, it is reported that the presence of excessive amounts of Lantana has led to a decrease in the feeding rates and changes in the behavior of elephants (Wilson et al. 2014).  Lantana invasion increases the fuel load making an area prone to fire and the fire in turn, paves the way for more invasion (Hiremath & Sundaram 2005).

 

The upper plateau of the Nilgiri Mountains (≥ 1,800m), part of the Western Ghats biodiversity hotspot, supports the unique tropical montane evergreen forests locally called ‘sholas’, interspersed with grasslands.  Sholas support many endemic plants including Cinnamomum wightii, Daphniphyllum neilgherrense, Lasianthus venulosus, Litsea wightiana, Magnolia nilagirica, Mahonia leschenaultii, Neolitsea cassia, Psychotria nilgiriensis, Symplocos foliosa, and Syzygium tamilnadensis (Mohandass & Davidar 2009).  These forests are highly threatened due to extensive deforestation and other anthropogenic pressures (Rawat 2008; Rao 2012).  There has been a considerable loss of shola forests since 1850 A.D. due to conversion to monoculture plantations (Rawat et al. 2003).

Lantana invasion could potentially alter the successional processes operating in shola forests (Mohandass & Davidar 2010), that could affect the recruitment of slow growing native trees and lianas, leading to decreased diversity and biomass.  The invasion is so extreme in some parts of the Nilgiris that it has rendered some agricultural lands barren (Muneer Ul Islam Najar pers. obs. 15 February 2017) making it very difficult for poor farmers to afford the costs of removal and subsequent management of the fields.

In this study we selected 61 plots with differing densities of Lantana including four control plots in shola forests in different sites above 1,800m in the Nilgiris South Division of the Nilgiri Biosphere Reserve (NBR).  We assessed Lantana densities, and densities of regenerating shola trees including endemic species under Lantana cover and in shola forests.  Our objective was to assess regeneration of shola trees under different levels of Lantana infestation, and to see which shola species survive under Lantana, because these species could be more useful for shola restoration under Lantana cover.  We tested the null hypothesis that shola tree densities would not be associated with differing Lantana densities.

 

 

Material and Methods

 

Study area

This study was conducted in the reserved forests of Nilgiris South Division (11.20–11.49⁰N & 76.55– 76.68⁰E; Fig. 1) of the Nilgiri Biosphere Reserve (NBR), India.  Located in the Nilgiris District of Tamil Nadu, the Nilgiris South Division includes mostly the upper plateau of the biosphere reserve at about 2,200m and some areas extend to lower elevations of about 900m.  The forest department of Tamil Nadu has divided it into seven forest ranges.  Two ranges namely, Kundah and Naduvattam, have been extensively invaded by Lantana.

The Nilgiris upper plateau receives rainfall annually from both the southwest and northeast monsoons. Temperature ranges from a mean maximum of 24⁰C in April to a mean minimum of 5⁰C in December.  Frost occurs between November and March and mainly in the valleys rather than on the higher hill slopes (Caner et al. 2007).

Nilgiris is home to many endemic plant and animal species.  Some of these plant genera having maximum endemic taxa are Actinodaphne, Cinnamomum, Glochidion, Litsea, Memecylon, Symplocos, and Syzygium (Rao 2012).  The Nilgiris has viable populations of the Endangered and endemic Nilgiri Tahr Nilgiritragus hylocrius, the Asian Elephant Elephas maximus, and the Lion-tailed Macaque Macaca silenus.

 

Methods

This study was conducted between April 2016 and May 2017 in the study sites at altitudes ranging 913–2,033 m. All the ranges of Nilgiris South Division were covered except Naduvattam.

A total of 61 plots were studied: 57 plots each of size 10×10 m in the Lantana dominated sites, the total area sampled being 0.57ha, and  four control plots each of size 20×20 m in undisturbed shola patches of total area 0.16ha (Table 1; Image 1).  The number of trees (tree density, ≥10cm GBH) and the number of Lantana stems (Lantana density) inside the plots was recorded.  The number of endemic trees was noted separately.  The plots were assigned to different classes as per intensity of Lantana invasion: plots with >400 Lantana stems were assigned to the ‘Intensive’ infestation class, those with 200–400 stems to the ‘moderately’ infested class, and those with <200 stems to the ‘low’ infestation class.

The data were checked for normal distribution by Shapiro-Wilk test and the Spearman’s rank correlation coefficient was used to test for association between Lantana and tree densities.  The analysis was carried out using R (R Core Team 2019).

 

 

Results

 

The distribution of Lantana densities differed significantly from normality (Shapiro-Wilk test=0.95, p=0.03). Similarly the distribution of tree densities (Shapiro-Wilk test=0.5, p<0.0001), and endemic tree densities (Shapiro-Wilk test=0.33, p<0.0001) also deviated from normality.

As the density values were not normally distributed, the median was used as a measure of density.  The Lantana density in 57 plots ranged from a minimum of zero stems to a maximum of 908 stems per plot with a median of 330.  Tree density ranged from zero to 117 with a median of six trees per plot.  There were zero to 33 endemic trees with a median of zero trees per plot (Table 1).  In contrast, the four control plots were composed of shola trees belonging to the following genera: Cinnamomum, Daphniphyllum, Ilex, Lasianthus, Litsea, Meliosma, Microtropis, Neolitsea, Nothapodytes, Psychotria, Rapanea, Rhododendron, Rhodomyrtus, Saprosma, Strobilanthes, Symplocos, and Syzygium.

The 20 intensively infested plots had a median of 473 Lantana stems per plot and a median of one tree per plot but no endemic tree species (Table 1).  The 26 moderately Lantana-infested plots had a median of 322.5 Lantana stems per plot, 5.5 trees but no endemic species per plot.  Similarly, the 11 plots with low Lantana infestation had a median of 119 Lantana stems per plot, 15 trees, and one endemic tree per plot.  Both the tree density and the density of endemic tree species was highest in the shola (control) plots with a median tree density of 99.5 trees per plot and a median of 25.5 endemic trees per plot (Table 1).

Endemic tree density decreased significantly and negatively with increase in Lantana density (Spearman rank correlation coefficient r_s=−0.72, p<0.0001).

 

 

Discussion

 

Our study shows that the regeneration of shola trees including endemic species decreases with increase in Lantana density.  Few shola trees survive under moderate Lantana cover and none under heavy infestation.  These results support the findings of Prasad (2012) who found a negative relationship between Lantana abundance and tree density.  We found species of Lasianthus, Litsea, Neolitsea, Symplocos, and Syzygium growing in plots with moderate and low infestation.

It has been found that a forest with a composition of about 75% of native species effectively prevents the establishment of Lantana (Stock 2004), however, as the Lantana cover increases and crosses 75% mark, the richness of native species decreases (Gooden et al. 2009).  This is because of the effects of Lantana on soil fertility (Bhatt et al. 1994) and soil seed banks (Fensham et al. 1994).  In the Himalayan foothills of India, Sharma & Raghubanshi (2007) found reduced native tree species richness and regeneration in Lantana dominated plots.  In another study, Sharma & Raghubanshi (2010) found that Lantana alters the tree composition and structure, due possibly to suppression of native tree regeneration.  Similarly, in the Nilgiri Biosphere Reserve, Lantana has been found to adversely affect the regeneration of native trees, and reduce plant diversity and alter species composition in the forest under-storey in Bandipur Tiger Reserve (Prasad 2010), and in Mudumalai Tiger Reserve (Ramaswami & Sukumar 2013).  Other researchers (Lamb 1991; Fensham et al. 1994; Sharma & Raghubanshi 2007) too have found a negative relationship between the regeneration of trees and Lantana density.

The regeneration of 52 shola species was studied by Madhu et al. (2017) in the Nilgiris.  They found the  highest survival rates for the two species of Syzygium (S. cumini and S. gardneri) at all elevations and aspects, with an average of 77% regeneration.  Syzygium spp. could be beneficial for the restoration of shola patches because of their highest chances of survival, but need protection at the initial stages as livestock and wild herbivores forage on their leaves due to their high nutritional value (Mohandass et al. 2016).  Moreover, Syzygium cumini can grow well in open conditions, whereas most shola species including other Syzygium spp. cannot, as they need shade to regenerate.  Therefore, planting Syzygium cumini will facilitate regeneration of shola trees.  Thus, growing a mix of species including both shade tolerant and light tolerant pioneer species as advocated by Sekar (2008) and Mohandass et al. (2016) could be a better strategy.  In addition to Syzygium cumini, Rhododendron nilagiricum, Syzygium calophyllifolium, and Viburnum hebanthum which are common can be planted (Murugan 2006; Mohandass et al. 2016).  Viburnum hebanthum has an added advantage that it tolerates poorly drained or water soaked soils.  Murugan (2006) found the seed viability of two species of Syzygium (S. tamilnadensis and S. calophyllifolium) to be 70–80% followed by Rhododendron nilagiricum (50–60%), and Viburnum hebanthum (50%). The species of Rhododendron, Syzygium, and Viburnum have long been used as enrichment plants to assist natural regeneration (Chandrasekhara & Muraleedharan 2001).  We also advise growing Rhodomyrtus tomentosa for it acts as a nurse plant for other shola species (Yang et al. 2010).  The nurse plants create favorable microhabitats for seed germination and seedling recruitment (Franco & Nobel 1989), however, the nursing effects depend on the shade tolerance of the species to be restored.  The species with greater shade tolerance help to accelerate the restoration process.

Once the Lantana is removed, planting of early successional species like Berberis tinctoria, Daphniphylum neilgherrense, Syzygium densiflorum (Mohandass et al. 2016), Rhododendron nilagiricum (Mohandass & Davidar 2010), and Rhodomyrtus tomentosa (Yang et al. 2010) could be helpful.  As pointed out by Mohandass & Davidar (2010) the frost resistant species of Rhododendron along with Rhodomyrtus sp. act as pioneers in the ecotones and grasslands and over time pave the way for more shade tolerant species.  Hence we suggest the planting of Rhododendron nilagiricum, Rhodomyrtus tomentosa, Syzygium calophyllifolium, Syzygium cumini, Syzygium tamilnadensis, and Viburnum hebanthum for the successful restoration of sholas in the Nilgiris post Lantana removal.

The cut root stock method as described by Love et al. (2009) could be used to remove Lantana as it has been found to be highly efficient to control its reinvasion.  Babu et al. (2009) in India (Corbett Tiger Reserve), Woodford (2000) and Somerville et al. (2011) in Australia have effectively managed Lantana and successfully regenerated native plants post Lantana removal.  What is common in these studies is that the Lantana was removed manually, a herbicide was sprayed over the area, or the removed Lantana was set on fire.  After this, seeds of native trees were planted and allowed to germinate with continuous monitoring and de-weeding until the trees were high enough to prevent the reinvasion by Lantana.  As Nilgiris South Division is one of the wettest areas of the reserve, the chances of shola restoration are high, as recovery of native species was higher in wetter areas (Prasad et al. 2018) in NBR.

 

Challenges to restoration

Climate change allows alien species to expand their ranges (Dukes & Mooney 1999; Simberloff 2000) particularly at higher altitudes due to the alleviation of cold limitation (Dukes et al. 2009) and makes the influence of invasions difficult to predict (Tylianakis et al. 2008).  In case of Lantana which has greater genetic variability (Day et al. 2003) some genes can adapt to the new climatic conditions and can help it to colonize new landscapes (Ledig et al. 1997). Climate change may also lead to extirpation of those species which are not genetically diverse because a narrower genotype range makes them least adaptable to environmental conditions (Rice & Emery 2003).  All this can severely impact the regeneration of shola trees and other native and endemic species in the upper Nilgiris. Another challenge is restoration of species with smaller population sizes like some endemic or rare species (Bell et al. 2003), where  a minimum viable population number is necessary for the establishment of these species (Falk et al. 2006).

 

 

Conclusion

 

The invasion by Lantana in the upper Nilgiris is disastrous to the biological wealth of this plateau and necessary steps for its removal need to be taken.  In the last few years, the forest department has taken measures to stop its spread by planting native plant species but with little success.  The removal of Lantana and Acacia has been  carried out in the reserve forests of the Nilgiris for many years, however, studies are necessary to assess its effectiveness.  The measures have to be taken persistently, and fast growing native plants have to be planted in the cleared plots with continuous monitoring for the first few years to restore the habitats.  Doing this would prevent the sites from functioning as a source for further invasion deep into the forests.  An adaptive management system needs to be developed in which Lantana removal could be used to enhance the local population livelihoods (Shaanker et al. 2010).  Although, there is no hard and fast solution to completely remove Lantana at this moment, we must continue working to develop innovative approaches.  The efforts of Woodford (2000), Babu et al. (2009), and Somerville et al. (2011) have shown us the way forward for the effective management of Lantana and successful regeneration of native plants post Lantana removal.  With some persistence and coordination between different stakeholders, similar plans could be worked out for Lantana in the Nilgiris.

 

 

Table 1. Median values (Range: minimum to maximum) of Lantana, tree and endemic tree densities in the plots with different levels of Lantana infestation.  Area sampled was 0.57ha in the experimental plots and 0.16ha in the control plots.

 

Category	Lantana infestation				Total
	Intensive (20 plots)	Moderate (26 plots)	Low (11 plots)	Control (shola, 4 plots)	61 plots
Lantana	473 (405–908)	322.5 (227–395)	119 (63–197)	0 (0)	330 (0–908)
All trees	1 (0–9)	5.5 (0–10)	15 (8–25)	99.5 (88–117)	6 (0–117)
Endemic species	0 (0)	0 (0–3)	1 (0–3)	25.5 (19–33)	0 (0–33)

 

 

For figure & image – click here

 

 

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