Consequences of Lantana Invasion


Invasion and plants
We assessed the consequence of invasion of lantana camara on the health of the ecosystem of the moist and dry deciduous forests at the Male Mahadeshwara Hills, Karnataka using plants as indicator taxa. The impact was studied at three levels of invasion of the weed on the structure and composition of the vegetation so as to assess if the lower and intermediate levels of invasion enhances the productivity and diversity of the ecosystem.

The impact of lantana on the diversity and species richness of herbs and shrubs was not very perceptible. The tree diversity was found to be high at the intermediate levels of invasion. In Dry Deciduous forests, there is a general decrease in the number of plant species that are dispersed passively and by animals though the number of individuals of all categories of trees decreased over the lantana gradient. However, there was an increase in the number of individuals of animal dispersed species at the medium levels of invasion. In Moist deciduous forests, there was no consistent pattern for species richness; but there was a general decline in wind and passive dispersed trees. We estimated the Importance Value Index values of all tree species along the lantana gradients. In Dry deciduous, trees such as Zizyphus oenoplia and Erythroxylon monogynum showed an increase in their IVI value with lantana density. However, other trees, including the important timber tree Hardwickia binata showed a decrease in their IVI value. In Moist deciduous sites, trees such as Canthium dicoccum showed a decrease whereas Phylllanthus emblica and Anogeissus latifolia showed an increase in their IVI values. Thus there is a marked difference in the way individual species respond to the presence of lantana invasion. As expected basal area summed over all trees decreased with increase in the lantana density in both Dry deciduous (r = -0.69, p<0.05) and Moist deciduous forests (r = -0.53, p<0.07). For regeneration, in Dry deciduous forests, there was a decrease in both species richness as well as abundance, but this decrease was not significant. However, this trend was not seen in Moist deciduous forest where species richness was highest in areas of high lantana intensity (r = 0.57, p<0.05).

Thus unlike generally believed, lantana does not always affect biodiversity negatively. and significantly. Most parameters of biodiversity did not show expected decrease with increase in the intensity of lantana. Nevertheless, lantana appears to reduce basal area and density, which is more of a structural consequence of increased lantana density in an area. In fact regeneration at seedling and sapling stage has been enhanced. Conservation of forest patches and limiting the human impact would go a long way in reducing the influence of lantana. Control of human activities might help in allowing for the re-growth of the forest and thereby reducing lantana spread. Due to the fact that lantana has a high rate of growth, the locals are also using it as a hedge plant. In MM Hills it is likely that lantana may be regulated by a proper management that involves encouraging its use that adds to the economy of the local populations.


Invasion and Birds
Using birds as an indicator taxon, we assessed the consequence of invasion of lantana camara on the health of the ecosystem of the moist and dry deciduous forests at the Male Madeshwara Hills, Karnataka. We studied the impact of lantana at three densities. Bird diversity was lower at high intensities of lantana in both the moist and dry deciduous forests but the species richness did not show a similar pattern. Various diversity parameters (such as species richness, Shannon diversity and abundance) were correlated with the average tree canopy cover and the average lantana cover. In the moist deciduous forest, bird species richness was positively correlated with average tree cover, but the Shannon index values were negatively correlated with the lantana cover. We stratified the birds into 4 guilds (Canopy, Understorey, Ground and Open Areas) based on their microhabitat preferences and analysed the impact of lantana on these guilds. There was a decrease in canopy specialists as the density of lantana increased in both vegetation types, whereas under-storey species were low at low levels of lantana. The other guilds did not display any patterns over the range of lantana sampled. We also stratified birds based on feeding habits and analysed their response to lantana. Insectivores and frugivores showed high species richness at moderate levels of lantana intensity in dry deciduous forests. Our results suggest that lantana does not affect the bird community as severely as it is believed to affect other components of the ecosystem.

Aravind N A