Recent surveies have documented alterations in flora due to invasive herbivores in the Andaman Islands. In this survey we demonstrate that the alteration is big plenty and rapid plenty to be detected by remotely sensed informations.
Using freely available Normalised Difference Vegetation Index ( NDVI ) imagination, we examined alterations in flora screen due to presence invasive herbivores in the Andaman Islands. Two clip periods were analysed utilizing different types of imaginations. Changes between 1985-95 and besides between 2001 and 2005 across four sites with different combinations of introduced chital cervid and elephants were examined. Consequences indicate that country with cervid have faster rates of debasement. The maximal rate of debasement occurred at sites with both elephants and cervid, and the lower limit where neither of the two carnal species occurred. There is a demand to extinguish invasive herbivores in the island.
KEYWORDS: invasives, remote feeling, debasement, alteration sensing
A recent publication pointed out that introduced herbivores in the Andaman Islands were doing vegetal alterations ( Ali, 2004 ) . These included a decrease in the figure of tree species every bit good as a decrease in radical country in countries where Chital or Spotted Deer ( Axis axis ) and Elephant ( Elephas maximus ) are found. . In this paper we set up that the alteration caused by these herbivores is big plenty and occurs over a clip frame that is short plenty to be detected by freely available satellite imagination. We besides discuss policy issues that need to be addressed desperately to undertake the jobs caused by animate beings that have become invasive.
The earlier survey had identified Interview Island as an uninhabited site which has both cervid and elephant. Small Andaman has neither, but has a late settled human population which has caused forest alterations, major in some parts, in the last two decennaries. The West side of Little Andaman is comparatively free of logging, invasion and other human force per unit areas, and has a little population of Onge tribals, This portion has been chosen for the analysis. The Mahatma Gandhi Marine National Park ( MGMNP ) has deer on its islands which are uninhabited, except for little colonies on Rutland island which have been eliminated from the analysis. Jarawa Reserve has a little population of Jarawa tribals, approximately 240 spread out over 700 sq kilometer ( UNESCO, 2010 ) . It besides has cervid and their densenesss are lower here than on Interview Island because of hunting by non-tribals on its fringe. The differences in these countries are summed up in Table 1.
Vegetationally, these countries were all wet evergreen wood, and are free of important human presence. However, big Numberss of deciduous species, particularly Lagerstromia hypoleuca, have started increasing in laterality in countries where chital are found, and this appears to be due to the fact that this species is non browsed by chital ( Ali, 2004 ) .
Numerous other surveies have besides shown debasement by invasives. Examples of these include debasement of flora by ferine caprine animals on Aldabra Atoll ( Rainbolt & A ; Coblenz, 1999 ) , the spread of alien works species by alien mammalian herbivores ( Davis et al. , 2009 )
To measure the alteration in flora screen across the four sites a comparing of Normalised Difference Vegetation Index ( NDVI ) trends over clip would bespeak the difference between the tendencies in flora screen. Areas near habitations and near the coastline have been eliminated from the analysis.
NDVI values are based on the rule that chlorophyll really strongly absorbs seeable visible radiation but reflects near-Infrared visible radiation. If there is more near-IR coefficient of reflection so the flora in that pel is likely to be dense.
NDVI analysis has been used for a figure of different sorts of analyses, including monitoring land debasement ( Tanser and Palmer, 1999 ) , calculate biomass and graze strength ( Kawamura et al. , 2003 ) estimation species profusion ( Katti et al. , 2002 ; Bawa et al. , 2002 ) , and to measure malaria hazard ( Dhiman, 2000 ) .
Satellite imagination has besides been progressively used in the sensing and direction of invasive species. Bonneau et Al. ( 1999 ) used imagination to place healthy bases of hemlock affected by insect plagues. Kimothi et Al. ( 2010 ) used imagination to map Lantana camara. Rouget et Al. ( 2003 ) used satellite imagination to map longterm landuse alterations partially caused by invasives. Bergstrom et Al. ( 2009 ) demonstrated that cat remotion resulted in an addition in rabbit Numberss doing environmental debasement at a World Heritage site. However, satellite imagination as non been used every bit much as its possible indicates: Mack ‘s ( 2000 ) statement that success with it still remains elusive, still appears to be valid. This is perchance the first case it has been used to supervise invasive herbivore impacts on flora.
In this analysis we use NDVI as a placeholder for flora screen or energy.
For 1986-1995, we used the graduated flora index ( CVI ) information compiled and mosaic by the National Institute of Environmental Studies, Japan. The informations were radiometrically and geometrically corrected prior to the computation of the normalized flora index. So this is no indistinguishable to the NDVI, in that it differs somewhat in the processing. The CVI was derived from the Advanced Very High Resolution Radiometer ( AVHRR ) orbiter platform bands 1 and 2.
One kilometer upper limit NDVI Composited Data Set for the period 2000 – 2005 was obtained via a Goddard Distributed Active Archive Centre ( DAAC ) Internet site. The merchandise is derived from the Moderate Resolution Imaging Spectroradiometer ( MODIS ) produced by choosing cloud-free values of NDVI from consecutive day-to-day acquisitions of informations and retaining the maximal value, which is assumed to be least affected by clouds, for each pel location. The compositing period by and large is limited to a 10-day or semi-monthly clip interval to minimise temporal fluctuations in the end point informations merchandise. Although ten-day NDVI images are available, we downloaded and analysed one-year maximal value complexs. Change in flora over clip was determined by suiting a regressional incline tendency line ( Pelkey et al. , 2002 ) . Positive inclines indicate addition in flora while negative inclines indicate lessening in flora energy. The figure of sample grids selected in each site is given in Table 1.
Pairwise comparings were so done utilizing box secret plans and additive maps. The additive map represents the a trial of the additive hypothesis the average A- Mean B = 0. The assurance interval represent Tukey ‘s accommodation for multiple comparings ( Chambers & A ; Hastie, 1992 ; Hothorn, Bretz & A ; Westfall, 2008 ) . This trial was performed utilizing Hothorn, Bretz & A ; Westfall ( 2009 ) .
Fig 2a and 2b show the alteration in the NDVI at the sampled sites for the two informations sets. It is evident that Little Andaman, with no herbivores, has suffered the least debasement ; in contrast, Interview Island, with two herbivores species, has suffered the maximal debasement. The other two, with lone chital, are in between.
This tendency has been repeated in all the wining analysis. The Box secret plans shown in Fig. 3a and 3b show same form.
Two statistical trials were used to prove this. The additive maps in Figs 4a and 4b reflect these tendencies for the two informations sets. The consequences utilizing the MODIS informations are more clearcut than the consequences utilizing the AVHRR information, since the within site fluctuation is much lower. Interview Island had a significantly higher rate of debasement than both Jarawa Reserve and Little Andaman.
Finally, Tables 5a and 5b give the consequences of a Kruskal-Wallis trial for the two informations sets. Small Andaman has a significantly lower rate of debasement than both Interview island and Jarawa Reserve for the 1985-1995 informations ; In the 2001-2005 information set, Interview Island degrades faster than the Jarawa-MGMNP bunch, which in bend degrades faster than Little Andaman. All but one of these is important.
The flora alterations in Little Andaman and Interview Island have already been documented ( Ali, 2004 ) . This survey further strengthens the findings of the old field studies. In this survey, the presence of autochthonal tribal populations is noted but is improbable to hold an consequence because both groups of tribals, being foragers, have really small impact on the wood. The Jarawa besides have ne’er been recorded as runing cervid, though poaching from the colonies outside the modesty may hold ironically slowed down forest debasement.
Interview Island has a high cervid population, every bit good as a ferine elephant population ( Ali, 2005 ) . The two deer-only topographic points ( We are including Jarawa Reserve among these since the Jarawa tribals, being foragers, do non run cervid, or cut down trees ) have a lower rate of debasement since tree harm by elephants does non happen.
There are legion beginnings of mistake that are possible. Areas near habitation have been avoided to extinguish mistakes due to logging and invasions. There are besides differences in orbiter detector alliance between different old ages. We have demonstrated that this does non do a difference, and the differences are great adequate to be picked up through distant feeling techniques. We avoided grids along the seashore to avoid the influence of alterations in coastline due to the detector alliance job. The lone beginning of difference that appears to stay is the presence or absence of invasive herbivores such as the chital and the elephant.
Plant transects on Interview Island suggest the causes of this debasement. The regeneration in logged countries here consists about wholly of Lagerstromia hypoleucos, one of two common species non browsed by chital ( the other being Pongamia pinnata, a coastal species on the island ) .
The reply seems to be the combination of chital and elephants. Elephants have damaged the flora severely in recent old ages, and have created a state of affairs where forest regeneration rates are higher than normal. The chital prevent regeneration by shoping on the seedlings.
The debasement observed over comparatively short clip spans is worrying, and indicates that the job of invasives here needs to be tackled on an pressing terms. Other invasives in the islands that have non been studied but need attending include ferine Canis familiariss and cats. Unfortunately, no other surveies on invasive herbivores have been done in this portion of the universe, and there is no baseline for comparing comparative debasement rates.
The internationally recognized scientific rule for covering with invasives is highly clear: in brief, if it is introduced and causes economic and environmental harm, take it. One does non necessitate nose count figures to formalize the determination to extinguish invasives. It is adequate to demo that debasement is go oning. We have shown a speedy method for set uping this.
We thank Srinivas Vaidyanathan for his remarks and inputs.