Modelo de Proceso de Direccionamiento Estratégico

A! transition! within! a! wetland! succession! occurs! when! a! boundary! separates! one! set! of! distinctive! ecological! or! environmental! records! from! another,! as! recorded! within! the! peat! record!at!the!site!(Elliott!et)al.,!2012).!The!Fen2Bog!Transition!(FBT)!is!a!term!used!by!Hughes! (1997)!to!describe!the!stage!during!raised!bog!development,!when!a!fen!develops!early!bog!or! pioneer!bog!characteristics.!During!the!transition!the!surface!peat!horizons!become!isolated! from! ground! and! surface! waters,! and! become! increasingly! reliant! upon! atmospheric! water! sources.! In! modern! mires! the! transition! is! largely! recognised! by! changes! in! vegetation! communities!(Zoltai!&!Vitt,!1995;!Elliott!et)al.,!2012),!in!addition!to!the!geochemical!changes! that! accompany! increasing! isolation! of! the! surface! peat! from! ground! and! surface! waters! (Kazda,!1995;!Hughes,!2000).!Decreased!nitrogen,!organic!carbon,!calcium,!magnesium!and!pH! have! been! observed,! with! an! increase! in! phosphorus! solubility! resulting! from! the! falling! pH! (Kazda!1995).!Transitions!in!UK!mires!have!occurred!via!a!“wet2pioneer”!route,!whereby!near! surface!water!tables!promote!the!development!of!sedge!fen!and!raised!mire!communities,!or! “dry2pioneer”! routes! associated! with! the! presence! of!Eriophorum) vaginatum! and! deeper,! fluctuating!water!tables!(Hughes,!2000;!Hughes!&!Dumayne2Peaty,!2002).!!

Knowledge! of! the! ombrophication! process! in! past! mire! successions! is! based! largely! on! mire! stratigraphies,! including! those! from! the! United! Kingdom! (Hughes! &! Dumayne2Peaty,! 2002;! Hughes!&!Barber,!2003;!2004;!Hughes!et)al.,!2000),!Minnesota!(Janssens,!1992),!and!Canadian! mires! (Lavoie! &! Richard,! 2000;! Muller!et) al.,! 2003).! Plant! macrofossils! may! be! an! effective! long2term! indicator! of! environmental! change,! however,! they! are! less! sensitive! to! minor! changes! in! mire! surface! wetness! (Hughes!et) al.,! 2006),! and! the! use! of! multiple! proxies! of! environmental! change! allow! better! characterisation! of! the! timing! and! nature! of! mire! transitions!(e.g.!testate!amoebae!communities,!Loisel!&!Garneau,!2010).!

While! the! FBT! has! not! been! specifically! addressed! during! New! Zealand! palaeoecological! studies,!there!is!evidence!that!Empodisma!species!are!present!from!early!in!bog!development! to!the!latter!stages!(Shearer,!1997;!Clarkson,!2002),!and!Empodisma!arrival!on!site!has!been! assumed! to! indicate! incipient! ombrotrophy! (Clarkson!et) al.,! 2004a).!Empodisma)species! occupy! a! wide! variety! of! mire! habitats,! including! both! fen! and! bog! (Johnson! &! Gerbeaux,! 2004),!and!so!the!presence!of!Empodisma)macrofossils!in!a!peat!stratigraphy!may!not!be!an! accurate! indicator! of! mire! nutrient! status.! Ombrophication! has! occurred! rapidly! in! mires! elsewhere,!within!a!period!of!decades!or!centuries!(Kuhry!et)al.,!1993;!Hughes!&!Barber,!2003;! Eckstein!et)al.,!2009;!Tahvanainen,!2011),!however,!there!may!be!a!lag,!or!biological!inertia!

(Tahvanainen,! 2011),! during! which! deep! rooted! fen! species! persist! in! the! newly! created! ombrotrophic! environment.! Thus! the! rapid! decline,! if! not! complete! absence! of! fen! species! (e.g.!Machaerina),!may!be!a!better!indicator!that!the!FBT!has!occurred!in!New!Zealand!mires,! rather!than!the!presence!of!Empodisma.!

There! has! been! a! lack! of! experimental! studies! exploring! the! mechanisms! and! rate! of! ombrophication!within!contemporary!mires!(sensu)Tahvanainen,!2011).!New!Zealand’s!current! mires! developed! after! the! termination! of! the! Last! Glacial! Maximum,! 18,! 000! cal! yrs! BP! (McGlone,! 2009),! and! the! literature! contains! few! references! to! contemporary! transitional! mires! within! which! the! FBT! might! be! studied.! Incipient! ombrotrophy! was! suggested! at! Swampy!Summit!in!Otago!(Walker!et)al.,!2001),!however,!McGlone!(2009)!argues!the!presence! of!the!mire!indicator!species!must!be!weighed!against!indicators!of!minerotrophic!inputs!to! the! mire.! Opuatia! fen! in! the! Hauraki! Plains! is! a! promising! site! for! further! research,! building! upon!the!work!of!Fritz!et)al.,!(2008)!which!proposed!a!mechanism!promoting!ombrophication! in! the! transitional! mire.) Empodisma) minus)arrival! in! the! recently! formed! west! Taupo! mires! was!noted!by!Clarkson!(1984),!allowing!future!observation!of!the!early!stages!of!the!FBT!in!a! montane!restiad!mire.!Overall,!however,!New!Zealand!mire!science!is!still!in!its!infancy,!with! mire! types! still! being! described! (e.g.! Rapson!et) al.,! 2006),! and! few! studies! examining! the! mechanisms!underlying!mire!development!(Clarkson!et)al.,!2005;!2009;!Fritz!et)al.,!2008).!

2.2.4 Allogenic!and!Autogenic!processes!during!mire!development!

An! important! issue! in! mire! development! is! whether! mire! species! determine! development! trajectories!by!modifying!their!environment,!or!whether!mire!development!occurs!in!response! to!the!external!environment!(Mitsch!&!Gosselink,!2000).!Raised!bog!development!is!unusual,! in!that!autogenic!processes!significantly!influence!the!process,!that!is,!processes!related!to!or! resulting!from!the!biotic!community!of!the!mire,!and!feedbacks!between!the!plant!biota!and! the!underlying!peat!substrate.!In!contrast,!allogenic!succession!is!vegetation!change!brought! about! by! abiotic! forces! external! to! the! community! (e.g.! fire,! volcanic! activity,! climate).! A! distinction!between!the!two!may!be!hard!to!make!(Hughes!&!Dumayne2Peaty,!2002),!as!both! autogenic! and! allogenic! forces! are! likely! to! play! a! part! in! any! succession,! the! relative! importance!of!each!type!depending!upon!the!environment,!and!vegetation!community.! Allogenic! factors! play! an! important! role! in! controlling! initiation! and! plant! succession! during! the!early!stages!of!mire!development,!with!the!autogenic!processes!gaining!importance!as!the! mire!develops!(Kratz!&!de!Witt,!1986).!While!some!may!suggest!it!is!wrong!to!label!individual! processes!as!auto!or!allogenic!in!origin!due!to!the!complex!nature!of!the!mire!development!

(Glenn2Lewin!&!van!der!Maarel!1992;!Hughes!&!Dumayne2Peaty,!2002),!the!identification!of! autogenic!processes!may!be!vital!to!the!restoration!of!ecosystem!function,!such!as!required! after! peatland! mining.! In! these! instances,! without! the! identification! of! those! species! or! processes! without! which! “normal”! successional! processes! will! not! occur,! divergence! from! previous! successional! pathways! may! occur,! resulting! in! a! new! vegetation! community! significantly!different!from!that!previously!found!at!the!site.!