Upload
hoangcong
View
221
Download
0
Embed Size (px)
Citation preview
REVIEW OF LITERATURE
Success~on IS one of the most Important directional forces drlvlng vegetation (Horn
1974). Change In specles composition and processes, of communities over time is known
as ecolog~cal succession (Van der Maarel 1996; S~ngh el al. 2006). Most of the work on
successron concentrates on vegetat~onal development. There are three main types of
sucesslons dependrng on the h~story and lnrt~al cond~t~ons of the landscape. Succession
occurring on newly exposed substrate IS called pnmary successlon. as on volcanic
depos~ts. dune sand. and mud flats. Land that has been d~sturbed by eventirecumng
events l ~ k e fire, floods, humcanes, agnculture and pasture use, has topsoil, and exist~ng
sources for regeneration In the form of seed banks or tree stumps, and the vegetational
development on r t 1s called secondary successlon. Secular succession concerns long-term
vcgetat~onal changes to changes In cl~mate covering thousands of years. (Clernents 1916;
Van der Maarel 1996)
Success~on IS an old concept proposed nearly a century ago, but has seen lncreaslng
volumes of l~terature produced on the subject, attesting to 11s Importance in the current
scenano of land degradat~on. The subject has seen many theones, models and field
studres debat~ng d~fferent polnts of view, and therr ~mplicat~ons for central for restoration
ecology and b~od~vers~ty conservation.
It is now agreed that most of the succession seen 1s sequential, w~th one set of species
being replaced by that of another which is usually longer lived, with herbaceous species
being replaced by woody species (McCook 1994). This IS though by no means the only
pathway possible, with cyclic successlon and autosuccess~onidemographic being other
possibilit~es (Huston & Smlth 1987; Ylh et al. 1999; Platt & Connell 2003).
Clements (1916) was the first to suggest the concept of change in vegetation. According
to hlm the process of 'nudation' or formation of a bare area, was followed by 'migration
of specles', whlch lead to 'ecesls' or establ~shrnent of the spectes. The establ~shed species
produced a 'reaction' by altenng the habitat (eg casting shade, improving soil fertility) in
whlch they occurred, malung II more sultable for other life-forms, but detrimental to their
own existence as they could not compete w~th the new amvals. Th~s produced a
sequential replacement of specles, wlth the propagules of the later stages arriving at the
disturbed sue by 'relay flonstlcs'. He considered this pattern of succession more
appl~cable for pnmary successlon but not secondary successlon which could have a
exlstlng seed bank or root-stock for regeneration. The succession produced progressive
stab~l~zatlon leading to a slngle endpoint, a cllmax he defined by an assoclatlon of trees
that was slmllar to an 'super-orgasm'. An lmportant finding ln tus study that species
lnteractlon are facultative amel~oratlng so11 and mtcro-habltat and habitat conditions for
subsequent I~fe-forms was largely Ignored till the md-e~ghties when the role of posltive
interactions began regaining focus In ecological research (Bertness & Callaway 1994;
Bruno et al. 2003 ) as an Important process to be considered during succession and wlth
practical application In rcstoratlon of degraded landscapes (Castro 2002, 2004; Gomez et
el. 2004; Brooker et al. 2008).
Clements' concept of a 'super-organ~sm' was strongly refuted by Gleason (1926), who
considered that communit~es were ~ndiv~dualistic. This concept was camled further by
Egler's (1954) concept of 'Initial florist~c compostt~on' where the d~fferent growth rates
of species, that all occur from the lnlt~ation of success~on determines successlon, w~thout
leadlng to a slngle climax. Wllson eral. (1992) polnted out that there have been two
interpretat~ons of t h ~ s concept by researches through the years. In one Interpretation, that
they call 'complete lnltlal flonstlcs', propagules of all the specles needed for successlon
are w~despread and so available at every site In an area that experiences d~sturbance, as
ascnbed to by Connell & Slatyer (1977), Whittaker (1989). Whitmore (1989) and many
others. The other 1s called the 'pre-emptlve lnltlal floristics', where the specles that are
present ~ n ~ t ~ a l l y , dominate success~on and Influence ~ t s course by pre-ernptlng other
specles. According to thls lnterpretatlon, a d~fferent set of ~ m t ~ a l specles may be present
on other sltes. The two d~ffenng ~nterpretatlons have Important lmpl~cat~ons for land
management
Pickett et al. (2001) studylng successlon In the Buell successlon found that woody specles
appeared early In successlon. but were not able to establish successfully. Therefore
'volleys of ~nvaslon' by the same specles were necessary before the later successional
species could establ~sh In a site.
Besides the timrng of the propagules' arrival at the site, the I~fe-h~story traits of the
species were also wns~dered ~mportant to explain the sequence of species normally seen.
Different strategies, of life expectancy. slze, dispersal, growth and survival of specits
adapted to different polnts In succession were considered by Dmry & Nisbct (1973).
Gnme (1974) described three l ~ f e history strategies based on a comb~nat~on of two factors
stress and dlsturbance at different levels. Ruderals found in areas w~th low stress
(resource availab~l~ty) and htgh disturbance are usually herbs; stress tolerants occumng in
hlgh stress and low dlsturbance, are usually herbs, shrubs and trees; and competitors
found In places w~th low stress and low dlsturbance, are usually shrubs and trees.
Gleason (1926), Egler (1954), Dmry and Nlsbet (1973) did not consider interactions
between plants In thelr theories Tllman (1985) proposed the resource-ration hypothes~s
that cons~dered competltlon for resources and tradwffs in life-h~story traits in plants to
deal w~th resources. If these resources are inversely proportion as nltrogen availability
and light lntenslty are, then sequentlal replacement of species occurs. wthout sayng how
the resources change.
Huston & Sm~th (1987) too proposed a competltlon model for resources but based on
~nd~v~duals. They made no aprrorr assumption of correlation of I~fe-h~story strategies to
d~fferent polnts tn successlon, and took into account that many resources have been
proved to be ~nversely correlated In them ava~lab~lity. They stated that when plants are
adapted to explo~t one set of conditions (resource availability or environmental
conditions) and cannot compete In other cond~tions, plants have inversely correlated traits
and this produces sequentla1 replacement. Divergent, convergent, cycllc and suppressive
succession arc possible with different combination of life-history tram Their model
without explicitly stating it, considers that the change in conditions is brought about by
the plants themselves, thus explalnlng the change in envrronmental condltlons and
species sequence seen usually In successlon.
Horn (1974) described successlon as a plant- by-plant replacement process based on I~fe-
history traits of slze, age, growth rate of establishment and shade tolerance, without
considenng specles Interaction. Plcken (1976) expressed the same Idea genetically,
stating that ~t 1s lmportant to malntain the tram that allow ~t occupy a point In the
contlnnum of condlt~ons that charactenze succession but also have some vanabll~ty to
survlve In new condltlons
Connell and Slayer (1977) cons~dered the role of Interactions as central to the process of
successlon and proposed three different possibilities facilltat~on, Inhibition and tolerance
and their model has been the most lnfluentlal since Clements' concept (1916). Many
researchers now try to determlne the pathway that predominates a landscape before
recommending appropnate management practices for forestry or restoration (Kobayasht
2004). Walker and Chapln (1987) though conslder that forces cannot be segregated Into
three pans, and that more than one interaction maybe Important In any succession, with
facil~tat~on more Important In the lnltial phases and cornpetltlon more widespread later.
They considered blologlcal Interactions important to determlne not the outcome but the
rate of succession.
Rejmanek and Leps (1996) found that a particular assoclatlon could also change from
negative to neutral to negatlve again. Brooker and Kikividse (2008) stress the need to
differentlate between the lntenslty of competltlon, which 1s ~ t s absolute Impact, and
importance, whlch 11s vimpact relatrve to its environment. So even ~f competition or
negatlve lnteractlons are detected it is necessary to determine ~ t s Importance.
Greig-Sm~th (1952) Interpreted the 'super-organism' concept of Clements (1916) as
impllng "direct Interactions between Individuals both of the same species and d~fferent
spec~es" and studled palrwlse Interaction to deteremine ~f the Interactions were more in
the cl~max. He found that the secondary forest had more posltive lnteractlons w~th the
least In the prlmary forest. Focusing on species Interactlons, many stud~es have tned to
quant~fy the ~nteractlons, and study the trend in change of the typeislgn (pos~tive or
negat~ve) through succession.
Gre~g-Sm~th (1952) proposed the p~oneer-buildmg-mature phases for Interactlons.
According to t h ~ s hypothesis. dunng the pioneer stage there IS small scale heterogeneity
and the d~spers~on of spec~es IS random. In the burldlng phase, due to reproduct~on,
grouplng of plants occurs, so there are more number of Interactlons found. In tlme these
patches grow and coalesce, so the d~stnbut~on of indiv~duals IS random again. Grelg-
Srnlth (1952) formulated thls hypothes~s based on a study of chronosequence of tropical
forests. The recovering forest aged 15 years had the most number of interaction the
younger forests less, wlth the pristine forest having the least number of mteractlons- all of
which were positive.
Myster and Pickett (1992) formulated three hypotheses of which two are based on the
findlngs by Bauaz (1979) and Parish and Bazzaz (1982) of competltlon in early stages
of succession and the prevalence of broad n~ches for early successional species and
specialized ntches for the later successional specles. ( I ) There should be more
Interacttons and increase In intens~ty of lnteracttons with time and (2) there is more
competltlon among annuals and b l e ~ u a l s compared to perennials. (3) Abundant native
specles are ~nvolved In more Interactions compared to exotics, slnce abundant species
may be funct~onally domlnant and Interacting (Crawley 1986).
Testlng these hypotheses In the old field Buell success~on In USA, Myster and Plcken
(1992) found no proof for the first hypothesis, as the number of lnteractlons decreased
over 18 years. There was proof for the second hypothes~s, as there were more interactions
between annual and blemuals than among perenn~als and there were relatively more
poslt~ve lnteractlons than negative ~nteractions. It was the exotlcs that were more
abundant and lnvolved m more lnteractlons; In the later seres when the natlve species
~ncreased In abundance they were together m more Interacttons.
T~lman (1990) considered herblvory as an environmental factor on par with nutrient and
light availability, that determines trade-offs In competitive ability In plants that can
influence the course of succession. Interspec~fic assoclatlons withln plant communities
are a result of aggregated populat~ons, whlch result as a product of reproduction
(vegetatively), symbios~s/positive or m~cro-hab~tat heterogeneity like soil, topography,
light ctc. (Smith 1954). Comparing painvise interactions she found that the number of
interactions were decreased by grazing, as grazing pressures eliminate more favourable
mlcro-sltes and make the habitat more uniform, w~th a subsequent break down in
Interacttons.
S~milanly G~tay & Wilson (1995) found that grazing Increases heterogeneity at (0.1 m x
O.lm) scale, that is the average size of b~te of herbivores, but decreases heterogeneity at
larger scales. Studyng associations In landscapes - aged 1-28 years- protected from fire
and grazlng, they found that the lnteractlon panem followed the p~oneer-buildmg -mature
phases of Greig-Sm~th (1952). as a result affecting community structure.
Posit~ve lnteractlons In particular, as an Important ecolog~cal process in stable and
successional communltles are lncreas~ngly documented, in contrast to early ecological
schools of thought which concentrated on compehtlon and consumer processes to expla~n
the regulat~on of populations and communltles (Bemess & Leonard 1997; Stachowicz
2001; Brooker et al. 2008).
Posit~ve lnteractlons can create new habitats, In wh~ch many small scale positive or
negatrve tnteractions can occur (Jones 1997; Bruno et al. 2003), by ameliorat~on of stress.
Stress according to Stachow~cz (2001) is any exuinis~c condition that effects an
indiv~duals s u ~ ~ v a l or fitness, and can be physiological (example temperature, salinity,
drought conditions), phys~cal (e.g effects of wind, waves, currents) or biotic (competition,
predation, disease). Any organism that d~rectly or ~ndirectly Improves the environment
for individuals of its own species or other species is a habitat modifier. Jones (1997)
called the process ecosystem engineering and the species responsible for it as ecosystem
engineers. Many habitat modifiers whlch are the basis, on which entlre communit~es are
built, were called foundat~on species by Daylon (1975). Jones (1994, 1997) identified two
types of ecosystem engineers -autogenic and allogenic. He defined them as follows-
-autogenlc physlcal engineers directly transform the environment via endogenous
processes (e.g. tree growth, development) that alter the structwe of the engineer and the
engineer remains part of the engineered environment.
-allogen~c physlcal engineers change the envtronment by transfomlng hvlng or
nonllvlng materials from one phys~cal stage to another, and the engineer is not
necessarily part of the permanent physical ecosystem structure (eg. beavers).
The benefits accrulng from assoctatlon w~th habltat modlfiersl ecosystem engmeers can
vary. For intra-specific and inter-specific ~ndiv~duals thls may be defense agalnst
common predators or ameliorat~on of stress by virtue of their density or creation of
favourable m~cro-cllmates for ngeneratlon. The seedling and juvenlle stages are the most
vulnerable stages In a plant's life-hlstory, so favourable temperature, soil moishlre and
fertility conditions, protection against predators provided by adults can increase the rate
of survival and establishment of even conspec~fics, out welghing costs of even intense
competition (Bemess & Yeh 1994; Bruno 2000). Groups of indiv~duals could withstand
physiological stress better than sol~tary indiv~duals m conspeclfics of Iva ,frtescens, a
marsh elder. The scadlings of the elder were able to survive under adult can-specifics,
since the shade of the adult reduced evaporation and thus resultant soil salinity as
opposed to bare patches (Bertness & Yeh 1984). Positive interactions among con-
specifics have helped in maintainrng the upper inter-tidal limit of mussels (Bertness &
Leonard 1997).
The idea that facilitatron can benefit other species though promoted by the early
ecologists has been garnering ev~dence only recently and its implicat~ons for the
comrnunlty structure and functlonrng are greater than intra-speclfic facil~tations
Stachowicz (2001). There can be more than one inter-specific habitat modifer or
ecosystem engineer, whose effects may be small, and be practically indrscemrble or
slgnlficant enough to create new habitats (Jones et al. 1994; Jones et al. 1997). The
multiple eco-system engrneers sometimes interact together to enhance or degrade a
habitat (Brarser et al. 2008). S ~ m ~ l a r to rntra-spec~fic facilitation, inter-specific facllltation
too occurs by providing refuge from predators, nutrient transfer, trophic facilitation and
protection from competition.
Protectron from predation results. when plants in manne and terrestrial envimnrnents
suffer less herbrvory and Increase fitness by growing with species unpalatable to the
herbwore (Atsan & Dowd 1976). Insects l ~ v e on plants that have chemical defenses
(Bemays & Graham 1988). Troph~c facilitation can occur through many specific plant-
animal mutalisms like pollination and seed dispersal. When the plants are keystone
species like figs, a breakdown of the fig-figwasp mutualism can have Important
ecosystem level consequences (Hanison 2000). Nutrient acquisition in plants occurs in
stressful conditions by classic symbiotic associatrons like nitrogen-fixing bacteria in
nodules of legumes and due to the presence of endolecto myconhizal fungi (Stachowicz
2001). In fact some of these mycorrhizal fungi are the reason for the mono-dominance of
certain trees species, affecting the community structure of a forest.
Ants associated with Acacia spp, protects the trees from herbivory and other competing
plants and In return is provlded food and domictie by the plants (Janzen 1966). Posrtive
species-~nteractions have several Important consequences. They can Increase or decrease
species diversity in a place. Olne,ya lesora that acts as nurse plant has a greater number of
species growing In ~ t s shade than In bare areas of the Sonoran desert (Suzan et al. 1996).
On the other hand two ecosystem engineers, the white-tailed deer (Odocoileus
virginranus) and the lnvaslve plant Japanese stllt grass (Microstegium vimineum), Interact
to completely alter the structure and composltion of the subcanopy wlthln northern
dec~duous forests In USA, thereby decreas~ng the number of bird specles that were
dependant on the mid-canopy for nesting sites and food (Balser et al. 2008).
So though the effect of fac~lltatron on a local scale can either decrease or Increase
d~verslty, on a larger scale by increasing spatlal heterogene~ty, positive Interactions
Invariably Increase divers~ty at the landscape level and further at the ecosystem level tw
(Jones et al. 1997; Wright & Jones 2007). Since the effect that ecosystem engineers have
on the physical space in whlch other species live and these direct effects can last longer
than the llfetime of the organism - engineenng can in essence outlive the engineer
(Hastings et al. 2007). Thus ecosystem engneering/facilitation can enhance species
richness and composltion stability over time to change patterns of species dominance
(Badano a al. 2006).
There are variations In the strength of facilitation, which increases spatially, with thermal
stress, predator pressure and lower lat~tudes (Bertness & Leonard 1997; Stachowlzc
2000) and temporally, Increases In dner years (Gdmez-Apancro et al. 2004). When stress
decreases and benefits from posltlve Interactions decrease, competltlon becomes more
Important, so mutual~sm and competition are a continnum of interactions (Bronstein
1994; Stachowtzc 2001). However Mlchalet (2006), show that both negative and posltlve
interactions can occur at the same tlme, w~th the net effect being posltlve In tlmes of
stress. Vanous factors l~ke age of beneficiary or land facilitator and the presence of above
ground or below ground competltlon between the two can result in fitness loss for ecther
(M~chalet 2007).
The Importance of stress In determlnlng plant-plant relationsh~ps has been established
and evidence of fac~l~tat~ve effects between plants tended to come from severe
environments, such as deserts, arctlc or alplne tundra systems, or salt marshes. Increased
env~mnmental severity appeared to Increase either the potentla1 for, or strength of,
positive interactions, relative to negatlve interact~ons, thus shfting the observable net
interactions toward facil~tatton In extreme envlmnments (Callaway & Walker 1997;
Gdmez-Aparicio et al. 2004; Cav~eres et al. 2006).
The stress gradient hypothesis (SGH) based on the model of Bertness and Callaway
(1994) which includes both stress and consumer pressure as forces pmmotlng facilitation
exmints pancrns across gradients. Studies conducted along various stress gradients to
test thls model found confllctlng evldence for the SGH model. Choler et al. (2001) found
that increas~ng altitude was associated wlth lncreaslng frequency of facilitative
Interactions. They also found that facllitatlon depended on specres identity and facilitated
specles were common at the extreme ends of their env~ronmental tolerance and led to
range expanslon. Along the andity gradient (Gomn-Apanc~o et al. 2004, Agular & Sala
1999) found nurse plants ameliorated water stress, but Tielborger and Kadmon (2000)
found that wlth Increasing ramfall, the lnteractlons changed from negatlve to neutral, and
then to beneficlal In desert herbs facilitated by shrubs. However, Maestre et al. (2006)
found In a meta-analysis that there was no Increase in elther negatlve or posltlve
lnteractlons between plants in arid and semiarid environments.
The Importance of posltive lnteractlons has now been accepted and there- are many
attempts to Integrate ~t Into vanous general concepts to explaln population, community
and landscape level ecology. Bruno et al. (2003) have proposed a revlslon of the niche
theory. posltlve density dependence at high population densities, relatlonshlp between
specles dlverslty and community lnvlslbillty and role of competltlve dominants. The
expanslon of nlche is based on the model proposed by Hacker and Games (1997). where
the reallzed nlche is expanded by facllltat~on, which is itself a modification of the
intermediate d~stwbance hypothes~s (Sousa 1979). This model can in fact explain
Increase in diversity by facilitation wlth Increasing disturbance from medium to severe.
Michalet et al. (2006) further developed these ideas, suggeshng that facilitation promotes
diversity at medium to high environmental severity by expanding the range of stress-
intolerant competitive specles into harsh physical conditions.
Since facilitation has been recognized as an important stmcturing force In natural plant
commun~ties, 11 is be~ng recommended for developing vegetation restoratlon tools,
part~cularly in severe and h~ghly disturbed envmmments. Many ecosystem
engineersifac~litators have s~gn~ficant effects on Important ecosystem processes of
management concern-hydrology, nutrient cycling and retentlon, erosion and sed~ment
retention, for examplewh~le at the same time creatlng habitat for other specles that also
Influence b~ogeochem~cal processes vla nutrient uptake, conversion, and release (van
Breemen & Flnz~ 1998). 'F~nally, humans are often responsible for the loss or
~ntroduction of such englneenng specles, with the potentla1 for large secondary
consequences' (Coleman & W~lliams 2002). So there is cons~derable potential for
applyng the ecosystem englneenng concept in management. Ecosystem enpneers can be
Important tn controlling local m~croclimate and could therefore be ~nfluential In
maintatn~ng refuges for other species, even In the face of climate change (Cavieres et al.
2002). There are many studles reporting strong fac~l~tat~ve effects dunng restoratlon In
high mountaln environments (Aens et al. 2007). and M e d ~ t e m e a n regions (Gomez-
Apanc~o et al. 2004) and trop~cal ram-forests (Parrona et al. 1997).
Ident~fyng the facil~tator or ecosystem englneer that are of dtsproportionately important,
so that it can be managed to asslst in proactive management IS necessary (Hobbs et al.
2006). But predicting apnor wh~ch specles will be important as physical engineers is
difficult (Jones et al. 1997). Research and management should be gu~ded by strategically
identifying key knowledge gaps, and use precious and llnle available resources to
maintam single species that could ensure ecosystem conservation (Brooker et al. 2008).
Most of the studies regarding plant -plant positive mteractions, focus on 'nurse plant'
benefits found In condltlons of high stress. These nurse plants, create '~slands of fertility'
(Schleslnger & Pilmanls 1998; Agular & Sala 1999). found etther tn patches or bands
leading to so-called tlger or leopard vegetation (Aguiar & Sala 1999) reflectmg the
redistnbut~on of resources and progagules. These patches of vegetation have been the
focus of study for a long tlme (Kershaw & Looney 1985), including the role of nurse
plants (Shreve 193 1).
Nurse-plants are have recorded in deserts (Suzan et al. 1996), alptne regions (Cavieres
2006). salt marshes (Bertness & Yeh 1994). tnter-tidal regions (Bermess & Leonard
1997; Stachowlcz 2001; Bruno 2001), Medlterrenean regtons (Gomez-Aparicio et al.
2004) Many studles have found that the specles nchness under or around these nurse
plants 1s stgnlticantly h~gher than that found In bare areas. There are even reports of
them fac~lttating lnvaslves in Andes (Cavleres 2008).
Successful recruitment 1s crucial for the establishment and maintenance of population
levels of any species (Bertness & Yeh 1994), and nurse plants provtde optimum
conditions for germination, seedllng emergence and establishment by creating spatial
heterogeneity in an otherwise harsh environment. In any given case the collection of
factors or any slngle of these factors that make nurse plants, facilitators can differ
(Stachowicz 2000; Bruno 2001; Gomez-Apanc~o et al. 2005a, 2005b).
The shade of the nurse plants regulates the soil temperature and the ambient temperature
and by reducing evaporation of soil molsture makes more water available to young plants
(Shreve 1931; Holmgren 1997). In addlt~on the evapotransplratlon of the plant are less
under shade (Franco-Nobel 1989). Soil temperature is very important to determine the
health and growth of the newly germmated radlcle, whlch can dry fast. Holmgren (1997)
found that there 1s an tnteraction of micro-cl~matlc gradients and physiological tradeoffs,
so In mesrc condlt~ons where shade 1s the detnmental factor, as water is available
everywhere In the environment. But In xenc condtt~ons marked by extreme temperature
(htgh In case of and regions) and low molsture, life In the hgh light conditions is nearly
impossible, so the plants survtve better under shade
Many stud~es have found that the photosynthet~cally actlve radiatton IS better suited to
plant germinat~on under shade than In bare areas (Vallente et al. 1991; Casal et al. 2001).
The h~gher organlc matter content under the shade of nurse plants occurs due to abiotic
processes, mainly driven by wlnd and water, include redtstnbut~on of fine soil particles,
associated mineral nutnents and litter that 1s concentrated underneath vegetated patches.
Biotic processes results fmm the action of roots, whlch absorb nutnents from the soil
under the densely vegetated patches, as well as from the so11 of the bare-soil matrix
(Aguiar & Sala 1999). The vegetated patches also manage to accumulate more
progagules due abiotic factors like wind and rain and by biotically by attracting seed
dispersers like animals and birds by providing perches for them or because they bear
fruits. (Agu~ar & Sala 1999).
Besides interactrons, vegetation climax, is one of the most Important concepts in
succession. The existence of a slngle endpolnt the climax vegetatron by Clements
(1914), for a given set of cltmat~c characteristics of a site, has been recurrently
challenged, belng replaced by the acceptance of poly-cl~max based on differences In
hab~tats glving edaph~c, topograph~c, fire, and zootlc cl~max (Slngh et al. 2006). Absolute
climax has been cons~dered an abstract concept since communrtles are repeatedly subject
to drsturbances that prevent a communtty from belng at equiltbnum (Sheil 1999). Yet the
concept of a srngle cl~max has endured cnttcism, and 1s tacttly accepted in research
(Ptckett 1976). In fact, most studies evaluate the rate of successlon, based on the
companson of sltes w~th the 'cl~max pnmary forest' as the possible endpoint, either In
terms of spectes composition or structure of forests rn degraded tropical envuonments
(Corlen 1989; Myster & Walker 1997; Zhuang & Corlen 1997; Shell 1999; Rivera et al.
2000; Lu et al. 2003; Kobayashi 2004; Lebrlja-Trejos et al. 2008). Detenn~ning the
resilience of different forest types and the recovery ttme needed for any landscape to
resemble the poss~ble climax, is a domlnattng theme In recent successional studies.
Ewel (1980) found that w p ~ c a l dry forest (TDF) successton had few sera1 stages, so
predicted more resilience, compared to humid tropics. Though there is increasing
convergence through tlme, the rate of successlon decreases in time (Myster 1984; Myster
& Pickm 1990). Resilience is influenced by the hab~tat type and the initial conditions of
the site Including the type of d~sturbance (Keever 1983; Myster & Picken 1990, 1992).
Degraded lands need more time for recovery (Uhl et a1.1988; Lugo 2002). The resilience
rates recorded In TDF have been also Influenced by methodolog~cal constraints like the
cho~ce of reference sites, and sampllng criteria used (Kennard 2002; Pena-Claros 2003;
Lebrija-Trejos et al. 2008).
The TDF succession is charactensed by a short early phase dominated by herbs and
shrubs, followed by a ploneer tree phase to be replaced by pnmary forest specles
(Lebnja-Trejos et al. 2008). They also found that domtnant pioneer species were absent
from the natural regeneration dynam~cs of the mature forest, whlch is in contrast with
most secondary successions In TRF, where species that colonlze fallows are generally the
same ones lnvolved In the gap dynamics In mature forest .
Grasses and herbs domlnate for two years In Mexrco and for e~ght years In Bollvia
(Kennard 2002) There was a recovery of specles richness, w~th maximum reached at
rmd-success~onal stages, but not the or~ginal composition (Aide 1996; Colon & Lugo
2006; Lebrija-Trejos et al. 2008). A~de et al. (1996) found spec~es divers~ty low till 10
years, then began increasing from 10- 15 years to 40 years in Puerto Rico. In another also
In Puerto Rim in 45 years specles level were similar to than In the forest (Colon & Lugo
2006). In Bolivia. Pena-Claros (2003), and Toledo and Sal~ck (2006) found that the
species richness was higher In the under slorey, than tn the upper storey.
The convergence of vegetation stmcture was faster. Aide et al. (1996) found density,
basal area and height were s~mllar to the forest in 40 years. as did (Lebrija-Trejos et al.
2008) wh~le ~t reached 70 % In the a Boliv~an forest by 25 years and 50 years (Pena-
Claros 2003) and kept increasing with age In others (Toledo & Salick 2006). Dens~ty for
trees peaked after 25 years to 14,000 trees/ ha In Puerto Rico for trees t 1 cm dbh.
Density of trees exceeded and was twice as much as forest density In Bollvta (Kennard
2002)
Basal area Increased from 5m2 I ha in 9.5 years to 40m2/ha for trees ? I cm dbh In 60
years In Pueno Rlco (A~de et a1.1996); and from 12.3 m2/ha in the 2* year to 36.3m2/ha
for trees t 1 cm dbh In 40 years (Pena-Claros 2003) and 2.9 m2/ha In 5 years to 21.6
m'lha in Bollvia (Toledo & Sal~ck 2006). Basal area was the amibute that showed the
slowest ncovery in Mex~co (Lebrija-Trejos et al. 2008).
The distnbut~on of slze <lass of trees 2 10 cm. showed maximum dens~ty In lower slze
classes < 20 cm dbh (Kennard 2002) and Rulz et al. ( 2005) found that 61% of the trees
with dbh ( 2.5 to 5 cm) and 35 % wlth he~ght (>2.5-5 m). They found a reverse J-sahped
population structure as did Sabagol (1992) In Nicaragua with 87% of tress < 30 cm dbh
and average height of 15- 30 m. In Bollvla, Kennard (2002) found cover was l~m~ted to
10-20% in 1.2.3 years but Increased to 56% In 5 years.
Seed d~spersal is one of the ~mportant llmltlng factors In recruitment of species. In dry
forests wind is the most common mode of d~spersal (Bullock 1995). In the TDEF area.
where the study 'was conducted. endo-zoochory (69.2%) and anemochory 14% are the
most Important dispersal mode (Swampathan & Parthasarathy 2005). The mode of
dispersal can d~ffer w~th hab~tat type, with presence of perches or forest edges enhanc~ng
zoochory (Janzen 1988; Parrotta 1995) In Amazonia, autochory (60%) was the dominant
dispersal mode In open herbaceous areas w~th anemochory (40.2%) and endo-zoochory
(37.8%) being dom~nant in forest shmb vegetatlon (Arbelaez & Parrado-Rosselli 2005).
Bes~des pnmary d~spersal agents llke wmd, water, gravity and animals, secondary
dispersal by another agent from the first landing site of a dispened seed can occur. Ants
have been known to remove tlny seeds from animal dropp~ngs or from under the parent
tree to the~r nests (Turner 2001). Endochory can occur passively when the fruit is eaten as
part of a larger vegetatlon part by herb~vores (Elcott et al. 2007) or act~vely when animals
eat the fmlt for the reward offered by the plant. It 1s sometimes an expendable fleshy part,
In which case the seed IS dispersed after passlng through the gut or mouth of the anlmal
or the seed itself, where the seeds are hoarded and forgotten by animals (Turner 2001).
Though endochory is Important. the Importance of different herbivores is unclear. Elcoti
et al. (2007) found that endochory IS an Important agent of local and reg~onal populat~on
dispersal and support penlstence vla metapopulatlons. Since large herbivores can travel
far they can d~sperse seeds further than small mammals and are particularly important In
successional matnx havrng profound effect on commuruty development and structure.
(Elcott et al. 2007).
With the exception of a few pantropical weed trees, the woody success~onal flora of each
major tropical area- Afnca, Asia, and Amencas is restricted to that area, though there are
ecological equ~valcnts (Ewel 1980). Kellman (1980) pred~cted a homogenous herbaceous
weed flora and nucleated successron dominated by secondary trees specres In recovenng
forests. Most of the flora of earlier seres were reported from success~onal studies around
the world.
Gwen the sub-contrnent that Indla IS, Champron and Seth (1968) have lrsted 37 forest
types based on Thornthwalte's 1948 cllmat~c types, while they have themselves Identified
162 vegetation types based on a mrxture of factors like cl~mate, edaphr, other slte
factors, and biotic Influences These forests are inclusive of sub-groups based on
degradation due to human resource use and identifiable seral stages of the vegetation and
are l~sted below
Table 1: Forest types are groups and sub-groups classified under drfferent biomes In
India.
Biomes No of Forest types
Mo~st Trop~cal forests 62
Dry Trop~cal forests 39
Dry Montane Subtropical forests 17
Montane Temperate forests 3 1
Sub-Alpine forests 6
Alpine scrub 7
There have been relatively few studies on secondary succession, in India, compared to
the vast d~vers~ty of forest types seen. Most of these stud~es have focused on the molst
foresls prevaihng In Western Ghats (George et a1.1991; Pascal 1988) or northwestern
India (Rao & Ramakr~shnan. 1987) A prevlous study of succession In the trop~cal dry
evergreen forests (TDEF) In North Arcot and South Arcol areas recorded e~ght
success~onal stages leadlng from the Arr.\tidu spp. dom~nated grass stage to the cllmax
const~tuted by Alh~ztu urnurtr- Accrciu leucophloeu communltles (Dabholkar 1962)
Degraded lands In lnd~a are considered as being sera1 In nature, having orig~nated due to
abandoned cult~vat~on or degradation of forests, result~ng In grasslands and considered as
d~scl~maxes (Mlsra 1959). Though there are few stud~es to document the effect of grazing
on specles Interactions, there are many studies that have been conducted In grasslands to
evaluate the effect of grazlng on specles d~versity, b~omass productivity. A pattern of
Increase In specles d~vers~ty and net productivity of grasslands due to moderate levels of
grazing and loss of species under heavy grazlng reglmes is reported from H~machal
Pradesh, Varanasi and tropical savannahs In Ind~a (Singh & Mlshra 1969; Swartzan &
S~ngh 1974; Pandey & Singh 1992, Sabenval 1996), and from Serengeti in Africa (Mc
Naughton, 1979, 1993; Belsky 1992) to British l~mestone grasslands (Gibson & Brown
1992). However, cont~nued grazlng can increase not only recruitment but also extinction
(Gibson & Brown 1992).
Studies comparing grazed intensities, found that there was decrease in palatable species,
up to 30 % and increased the dom~nance of only a few species In Sahel, Africa
(Heirmaux 1998): Studying vegetational composition at increas~ng distance from a water
source Sasak~ et al. (2008) found that the influence of grazlng was more on volume than
on compos~tion.
Heavy grazlng selectively favours the establlshment of short turf and creeping perenn~al
such as Allopferrs cimicina, Brachariu distachya, Digitorio longflolru In S ~ I Lanka, and
thorny specles of Acuciu, Prosopis and Zizyphus in the V~ndhyas. Grasses like
Bothrrchlou perruso, Desmostochyu sp, Digituriu sp occur with legumrnous weeds like
Cu~sru Ioro As a result of protection from fire and grazlng, In 16 years there was an
increase in tree species richness from 4 to 16 and the tree denslty Increased from 14.6-
and 3.7- fold (Jose- F r a ~ n ~ a s 1983).
Somet~mes ~t IS the herbaceous flora of the early seres that is socially and economically
Important and ma~ntalned by grazing as in the famous Valley of flowers m Bhuyunder
valley In the Nanda D e v ~ Natlonal Park In H~malayas. An ever increas~ng list of
endangered species promoted the Lnd~an government to impose a total ban on grazing in
1982. A study conducted by Na~ than~ et al. (1992) showed that there IS subsequently less
m~neral~zatlon of so11 numents and the natural course of successlon has helped the
establ~shment of a few successional woody specles, which would eventually lead to the
eltminatlon of the herbaceous species.
Previous stud~es on the early to middle stages of successlon have shown that grazing can
reduce grass cover and favour establishment of woody plants, by reduc~ng competition
from grasses and risk of fires, and improv~ng dispersal of seeds of woody species by
grazing animals (Van Auken 2000; Rogues et al. 2001).
Spec~alization of tropical plants for hab~tat and m~cro-habitats, has been used to explain
the~r co-existence and the high species d~versity in trop~cal forests (Denslow 1987;
Gentry 1988; Clark et al. 1995) and savannahs (Barot at al 1999), w~th the species
regarded as being segregated along vanous environmental mches like I~ght, soil moisture
and nutrients (Silvertown 2004). Mass-effects, whereby the species establ~sh In sltes
through input of propagules from nearby favourable habitats in the absence of self-
sustalnlng populat~ons 1s also Important In explaining species richness (Shmida & Wilson
1988).
M~crohab~tat refers to environmental condlt~ons that vary at scales less than lo3 metres,
and hab~tats refer to strong environmental dlscont~nuity, usually at larger scales according
to Svemng (1999). Regeneration n~che IS regarded as the most important mche, as
plants' sens~ t~v~ty to factors changes with age and they are most vulnerable when they are
young (Collms & Good 1986; Svenn~ng & Balslev 1999). There have therefore being
many stud~es that study regeneration n~che's Importance to explain spatial patterns, and
thelr Influence on dens~ty and population structure.
Collins and Gwd (1986) compared the hab~tats of six tree species to cons~der their
effects on the regeneration of species and found factors like light, litter depth and nearest
neighbour occumnce as important. Various other factors have been known to ~nfluence
plants, including palms. The distribution of palms too, across tropics prov~de evidence of
the influence of heterogeneity at the level of habitats (Kahn & De Castro 1985; Peres
1994). and microhabitat as seen in the Amazonian palm community (Svenning 1999),
Costa Rican palms (Clark et al. 1995) and AFrican Borassus aethropum (Barot et al.
1999).
Clark et al. (1999) found that the distribution of palms at a scale of <I Ian' were
influenced by topography and edaph~c factors. Clark et al. (1995) found twlce the denslty
of palms on the steep slopes compared to gentle or lower slpoes, wlth spatial
heterogeneity at small to large scales (0.5 to 10 m2) affecting community structure.
Similarly Svenning (2001), found SIX species of palms in the Andean forests to be
correlated wlth altitude and aspect of mountains as well as edaphlc factors.
Schwaegerle & Bazzaz (1987) studing nine populatlons of Phlox in Texas, along
environmental gradients of several factors ltke light, nutrients, competition found that
populatlons of large plants were less sensitive to change avallablllty than smaller plants.
Different~at~on In populatlons occurred due to many processes, and populations in closed
habltats are genetically different from those In open hab~tats, allocating more resources to
persistence and competition and less to production of propagules for dispersal
(Schwaegerle & Bazzaz 1987).
There IS evidence that there is heterogeneity in microsites In homogeneous habitats
(Collins & Good 1986; Palm & Dixon 1990). Resource avallabllity Like soil, moisture,
light and nitrogen varied within patches of uniform vegetation and the range of resource
spatial difference was different among resources within a single community type. This
heterogeneity in resource dlstnbution 1s reflected in the distribution of plants (Colltns &
Good 1986; Dunslow 1987).
The difference in d~stribut~on beglns wltb amval of propagules. In heterogeneous
environments seeds settle in some sltes more readily than In other sites irrespective of
whether these sites are favourable for germinat~on, growth and establishment of the
specles (Bernard & Toft 2008). Ploneers were found to regenerate better In lighter
mlcrosltes and pnmary forest specles In darker mlcrosltes (Clark et al. 1993).
Besides regeneration, environmental factors Influence other stages of plant l~ fe too, like
growth and phenology. Llght was found to be an Important factor for growth and
reproduct~on, leadlng to population level consequences. (Oyama 1990; Svenn~ng 2002).In
1 1 populatrons of the dloeclous herb Jack-~n-the pulplt, Arrsaema rr~phyllum (Araceae),
studled for two years, Doust and Cavers (1982) found that the allocation of resources
differed among the genders depending on the type of habltats they were found in. Female
plants were found In mlcrosltes that had more Ilght, so11 pH and nutrients and male plants
were found In mlcrosltes that had less I~ght, so11 pH and nutrients. The size of plants also
d~ffered, females being 3.5 welgher than males, and allocating twice as much of dry
matter to flowers than males. More male flowersiplants in harsh habitats and more of
female flowers/plants In favorable environments have been reported In dioecious
Calophyllum brasiliense (Fischer & Dos Santos 2001) and in the Egyptian Thylmelueu
hirsum (Ramadan et al. 1994). Clark et al. (1987) found that in Zarnia skinnen, a long
lived dieocious cycad, that light and plant slze affected reproductive effort, with three
episodes of flowering In the secondary forest and only two in the darker pnmary forest in
a period of six years.
In dioeclous plants, various env~ronmental gradients like nutrients (Cox 1981),
temperature and soil rnolsture content (Freeman et at. 1980; Freeman & Vitale 1985), and
light (Onyekwelu & Harper, 1979). along which sexes segregate have been rdentified
producing deviations of sex ratio from 1:l (Meagher, 1980). A male-biased sex ratio is
usually more common In dioecious plants, as found in Chamaelirium luteum a lily
(Meagher. 1981), Borassus aethropum a savannah palm (Barot et al. 1999), double
coconut (Savage & Ashton 1983; Sllvertown 1987). and the cycad Zomia sk~nneri (Clark
& Clark 1987).
Among all factors light emerges as the singe most important factor that affects
distribution, density and population structure 'Tree species can In fact be arranged along
a continuum of adaptlve response to the avallab~l~ty and durat~on of incident radiation
(Denslow 1987). Light IS necessary for regeneration, establishment and growth of
seedlings (Denslow 1987; Clark et al. 1987, 1993; Svenning 2002), for growth of the
plant and reproductive activ~ty (Oyama 1990; Chazdon 1986; Svenning 2002).
The differential needs of resources and therefore choice of hab~tats and microhabitats by
plants is one of the major dnv~ng force that can explain the density, dispersion and
population structure of species (Alvarez-Buylla 1994; Barot et al. 1999). The reverse J
structure that populations usually show, though, is more a consequence of density
dependant mortality in the youngest ontogeny, than spatial heterogeneity (Van Valen
1975; Pinard 1993; Silva Matos et al. 1999; Souza & Martin 2002). In some palms the
seedlings were found w ~ t h adults as in friarleu deltoidae ( Svenning & Balslev 1999) but
many studies also report seedlings belng found away from the parents In palms such as
the Brazilian acaulescent palm AIruleu humifis (Souza & Martln 2002), and Eulerpe
edults (Silva Matos & Watklnson 1998) The Influence of spatial heterogeneity influences
all the ontogenlc stages, as demonstrated In Allalea hum11i.y (Souza & Martin 2002),
where fire was the lnfluenclng factor, whlle Barot et al (1999) found that the clumped
dlsperslon of all the ontogenlc stages In the Afncan Borossus uethiopurn was due to
nutnent nch patches In a savannah
There are however relatively few ecolog~cal stud~es of palms, w ~ t h most studies deallng
with taxonomic or econom~c botany of the family (Borchsenlus et al. 1998) even though
Arecaceae is one of the most useful group of plants dlsuibuted In the troplcs and parts of
subtroplcs, conslstlng of 201 genera and 2650 species (Mabberley 2000). Palms are
economically important as they Include major plantat~on specles like oil palm, coconut
and date palm. However, most palm products are non-commercial, being part and parcel
of dally llfe in ~ r a l areas worldwide, used predomtnantly for food, thatch, handicrafts,
construction and med~clne (Basu & Chakravany 1994; Borchsenius et al. 1998).
Most of the degraded lands or 'wastelands', as they are commonly called, serve as
common property resources (CPR) in Indio. owlng to then degradation. they do not offer
high returns to their usen. hence only the rural poor and lntermed~ary households use
them for fodder 'and fuel wood. Such 'wastelands' contribute to employment, asset
accumulat~on and to 14-23 per cent of the Income. especially for the rural poor (Jodha
1989). Patterns of use vary w~th gender, wlth the women belng recorded as the
predom~nant resource users in Himachal Pradesh (Berkes et al. 1998).
'Wastelands' In lndla are est~mated at 6385 million hectares, accounting for 20.17% of
the total land area (328.73 million hectares), according to the Natlonal Wastelands
Inventory Project, undertaken by Natlonal Remote Senslng Agency (2000). There are 13
categones of wastelands, of whlch degraded forests makeup 4.44% and grazlng lands
0.82% , degraded land under plantation0.18 %, land with or wlthout scrub 6.13%, gullled
and ravenous land 0.65% of the total Indian land mass. Of the total deslgned wastelands,
50% are non-forest areas.
The land ownership is private fallow land, v~llageiRevenue land or forests. The negatlve
Image of the 'wastelands' has ensured that it has long been a target for various
development schemes by the Central and State governments. The nation w d e Soclal
forestry programme Instead of supplying fodder and fuel for the local people was
diverted for commercial and lndustnal use (Slngh 1985). The Comprehensive Wasteland
Development Project In Tam11 Nadu initiated in 2002-2003 seeks to lease a hundred
thousand hectares of community lands to corporates, besides pnvate wastelands, without
llsting benefits for the local people (Sarvanan & Mahapatra 2003). Among the latest
threat to the local population's access to 'wastelands' for usufruct benefits is the proposal
to use I I million hectares of 'wastelands' (7 per cent of the cultivable area in the country)
for monocultures of Jatropha by 2012 to supply biofuels, to meet India's aim to achieve
20 per cent blend of bio-diesel by 2010 (Mishra & Awasthi 2006). The long-term
requirement to keep carbon in storage ln forestry projects requtred to be ma~nta~ned for
Clean Development Mechanism (CAD) under the Kyoto Protocol to mitigate cltmate
change, if implemented in Ind~a, can also conflict wtth the short-term needs of the poor, ~f
the energy and other biomass needs from the CPR are not addressed and the benefits of
carbon sequestration IS not channelled to the mral poor, lead~ng to tensions and eroston of
benefits (Gundimeda 2004). '
So t t IS necessary to tncorporate social sclence research wtth ecological research for
successful landscape restoratlon (Sabagol 1992, Sanchez- Azofe~fa et al. 2005) Parch et
al (2001) recommend uslng spontaneous successlon for ecolog~cal restoratron, a
relat~vely new field, keeping tn m~nd the alms of project restoratlon of cltmax vs
reclamat~on for soc~ally acceptable condtt~on or product~ve use, and evaluation of site
env~ronmental cond~ttons before dec~dlng whether spontaneous successton 1s an
appropnate way to ach~eve the alms. T h ~ s should be supported by pred~cttng successional
development, suggesting possible lnterventlon (cultural practices or species introduction)
at appropriate junctures of success~on and monitoring of results.
There are mtxed reports of the effect of dtfferent kinds of management. The choice of an
appropnate overstorey species in plantation is critical as the can 'catalyize' successlon by
influencing subsequent patterns of colonization. Nineteen specles of secondary tree
species were found established under Casuarina equiseirijoha, Eucalyptt~s robusfa and
Leucaena leucocephala, while there was no regeneration in bare unplanted areas (Parona
1998). George et al. (1991) too found that after 15 years the understorey in a Eucalyphcs
plantation in the Western Ghats, near wet evergreen forest had reached species richness
levels similar to the forest. However, exotics are generally cons~dered less su~table for
reforestation projects as they can turn mvaslve, so the search for su~table local species is
important (Blanc et al. 2002). Restorat~on projects that skip early successional species
and plant only late success~onal species have less understory richness (Arde et a1.1996).
The use of shrubs as nurse plants facilitating later success~onal specles has been
advocated for the Mediterrenean reglons (Castro et al. 2002; Gomez et al. 2004, 2005). A
recent study shows that rotating grazlng land to reduce grazing pressure in dry forest
pastures In N~caragua, recorded a total of 85 forest species found as adults In the pastures,
of wh~ch 60 and 30 specles were able to establ~sh as seedl~ngs and sapl~ngs (Esqu~vel et
al. 2008) So spontaneous succession, wlth a little intervention can help In conservation
of tree specles In the predom~nantly agricultural landscapes In trop~cs.
Rehab~litation of degraded trop~cal landscapes by Identifying stress-tolerant, natlve or
exotic species and appropnate management systems has made s~gn~ficant contributions.
S~nce wood and non-wood products are both Important 'the focus of "wastelands"
reforestat~on programmes for fuelwoodl timber should be broadened to rehabilltation
forestry' (Parona 1998).
I t IS possible to speed up design~ng appropriate resource management programs, by
incorporating trad~ttonal ecological knowledge (TEK), based on local people's
understand~ng of ecolog~cal processes (Berkes et al. 2000). There has been a growing
interest In TEK since 1980s to study specles Identification and classification eg.
enumeration of 48 species of mushrooms in Mex~co (Montaya et al. 2003), study and
proceeded to people understanding of the ecological processes (Alcorn 1989; Gadgil
1993; Huntington 2000).
Local commun~ties have been known to use thew TEK to manage ecosystems and
respond to changes showing a understanding of the complex processes at work in nature
(Berkes et al. 2000) TEK has been useful In savlng specles b~od~vers~ty (Gadgil 1993),
rare specles, recognlzlng and protecting keystone specles and to protect habitats
(Johames 1998; Berkes et al. 2000). In Ind~a, sacred grooves are an example of habitats
protected by cultural beliefs. (Gadgil 1993; Parthasarathy et al. 2008).
But while there are many promoters of TEK, there have been very few cases of synthesis
of TEK and sclence Many promoters have themselves caut~oned agalnst unquestioned
use of TEK (Huntlngton 2000), since it can be wrong as these are knowledge systems that
are usually shared and passed on orally. There IS also inertla to embrace this new
~nterdisc~pl~nary approach to research, but whlch, could be overcome by evidence from
studies documenting and incorporating TEK. Many are reluctant and unwilling, to use
TEK cons~dering It lack~ng In scientific v~gour; and to overcome the obstacle of using
social science methods to document TEK and the reluctance of the TEK holders to share
their knowledge (Huntington 2000, Berkes et al. 2000).
There have only a few instances when sclentlsts and TEK holders have worked together,
a whaling census being one (Huntlngton 2000). The Alaska Esklmo Whaling
Commission, fought against the ban on harvesting bowhead whales in 1977 by the
International whaling Commission. They were allowed a harvesting quota based on the
census of whales. The orignal census of 2000-3000 whales based on visual obsewatlon
was revised by considering visual and acoustic evidences from locations not considered
earher to Increase the census figures to 6000-8000, hased on information from Alaskan
Esktmos.
But there are successful cases of management practices that have been based on local
tradlttonal knowledge and cultural practices, including preservation of remanant forest
pathes of the TDEF In sacred groves (Parthasarathy et al. 2008). mum or shlftlng
cultlvatlon was judged to be harmful In a blodlverslty hotspot In northeastern areas of
Himalayan leading to a regulat~on of shifting cultivat~on in 1947 and promotion of agro-
forestry as the a more su~table and econom~cally susta~nable. But there 1s realization now
that jhum based on years of practlce and refinements, lnvolv~ng use of local cultivars in
fact IS better for conservation of blodlversity and soil and there are now efforts to
promote 11 agaln (Arunachalam et al. 2002)
Since the last twenty years many countnes have handed over management of natural
resources to the local communltles, which have to be monitored. When management
plans and monitonng systems are partlclpatory , incorporating TEK along with scientific
guidelines, they are more acceptable to local stakeholders and llkely to be effective even
afier the donor agencies q u ~ t s the project (Garcia & Lescuyer 2008).
The lrulas arr a hunter-gatherer tribe inhabltlng parts on the Commandel coast since pre-
Dravidian times, whose TEK has been tested and used several times in conservation of
biodiversity and restoration. The~r skills as hunters has been used in modem med~c~ne , to
collect venom of snakes used In producing antl-venom for bites of the four most
polsonous snakes in India and their knowledge of forest plants and their medic~nal value
has been documented and then herbal medicines are be~ng marketed (Methil 2008,
Madras Crocodile Bank 2008).