Plant Ecology & Diversity Soil-induced impacts on forest structure drive coarse woody debris stocks across central Amazonia PLEASE SCROLL DOWN FOR ARTICLE

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Plant Ecology & Diversity Soil-induced impacts on forest structure drive coarse woody debris stocks across central Amazonia PLEASE SCROLL DOWN FOR ARTICLE
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  This article was downloaded by: [Ms José Pinto]On: 26 March 2014, At: 13:32Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: MortimerHouse, 37-41 Mortimer Street, London W1T 3JH, UK Plant Ecology & Diversity Publication details, including instructions for authors and subscription information: Soil-induced impacts on forest structure drive coarsewoody debris stocks across central Amazonia Demétrius L. Martins a , Juliana Schietti a , Ted R. Feldpausch b , Flávio J. Luizão c , Oliver L.Phillips d , Ana Andrade e , Carolina V. Castilho f , Susan G. Laurance g , Átila Oliveira h , Ieda L.Amaral h , José J. Toledo i , Laynara F. Lugli j , José Luiz Purri Veiga Pinto d , Erick M. OblitasMendoza j  & Carlos A. Quesada da  Programa de Pós-Graduação em Ecologia, Instituto Nacional de Pesquisas da Amazônia,Manaus, Brasil b  Geography, College of Life and Environmental Sciences, University of Exeter, Exeter, UK c  Coordenação de Pesquisa em Dinâmica Ambiental, Instituto Nacional de Pesquisas daAmazônia, Manaus, Brasil d  School of Geography, University of Leeds, Leeds, UK e  Biological Dynamics of Forest Fragments Project, National Institute for AmazonianResearch (INPA) and Smithsonian Tropical Research Institute, Manaus, Brazil f  Brazilian Agricultural Research Corporation – EMBRAPA, Centro de Pesquisa Agroflorestalde Roraima, Boa Vista, Brasil g  School of Marine and Tropical Biology, James Cook University, Cairns, Australia h  Tropical Ecology Assessment and Monitoring Network (TEAM), Campus de Rorainopolis,Rorainopolis, Brasil i  Universidade Estadual de Roraima, Campus de Rorainopolis, Rorainopolis, Brasil j  Programa de Pós Graduação em Ciências Florestais, Instituto Nacional de Pesquisas daAmazonia, Manaus, BrasilPublished online: 14 Mar 2014. To cite this article:  Demétrius L. Martins, Juliana Schietti, Ted R. Feldpausch, Flávio J. Luizão, Oliver L. Phillips, AnaAndrade, Carolina V. Castilho, Susan G. Laurance, Átila Oliveira, Ieda L. Amaral, José J. Toledo, Laynara F. Lugli, José LuizPurri Veiga Pinto, Erick M. Oblitas Mendoza & Carlos A. Quesada (2014): Soil-induced impacts on forest structure drivecoarse woody debris stocks across central Amazonia, Plant Ecology & Diversity, DOI: 10.1080/17550874.2013.879942 To link to this article: PLEASE SCROLL DOWN FOR ARTICLETaylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be reliedupon and should be independently verified with primary sources of information. Taylor and Francis shallnot be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and otherliabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to orarising out of the use of the Content.This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any  form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at    D  o  w  n   l  o  a   d  e   d   b  y   [   M  s   J  o  s   é   P   i  n   t  o   ]  a   t   1   3  :   3   2   2   6   M  a  r  c   h   2   0   1   4  Soil-induced impacts on forest structure drive coarse woody debris stocks across centralAmazonia Demétrius L. Martins a  *, Juliana Schietti a  , Ted R. Feldpausch  b , Flávio J. Luizão c , Oliver L. Phillips d , Ana Andrade e ,Carolina V. Castilho f  , Susan G. Laurance g , Átila Oliveir a h , Ieda L. Amaral h , José J. Toledo i , Laynara F. Lugli  j ,José Luiz Purri Veiga Pinto d , Erick M. Oblitas Mendoza  j and Carlos A. Quesada d a  Programa de Pós-Graduação em Ecologia, Instituto Nacional de Pesquisas da Amazônia, Manaus, Brasil;  b Geography, College of Lifeand Environmental Sciences, University of Exeter, Exeter, UK;  c Coordenação de Pesquisa em Dinâmica Ambiental, Instituto Nacional de Pesquisas da Amazônia, Manaus, Brasil;  d  School of Geography, University of Leeds, Leeds, UK;  e  Biological Dynamics of Forest  Fragments Project, National Institute for Amazonian Research (INPA) and Smithsonian Tropical Research Institute, Manaus, Brazil;   f    Brazilian Agricultural Research Corporation  –   EMBRAPA, Centro de Pesquisa Agro   󿬂  orestal de Roraima, Boa Vista, Brasil;  g  School of   Marine and Tropical Biology, James Cook University, Cairns, Australia;  h Tropical Ecology Assessment and Monitoring Network (TEAM), Campus de Rorainopolis, Rorainopolis, Brasil;  i Universidade Estadual de Roraima, Campus de Rorainopolis, Rorainopolis, Brasil;  j   Programa de Pós Graduação em Ciências Florestais, Instituto Nacional de Pesquisas da Amazonia, Manaus, Brasil  (  Received 20 December 2012;  󿬁 nal version received 20 December 2013 )  Background:  Coarse woody debris (CWD) is an essential component in tropical forest ecosystems and its quantity varieswidely with forest types.  Aims:  Relationships among CWD, soil, forest structure and other environmental factors were analysed to understand thedrivers of variation in CWD in forests on different soil types across central Amazonia.  Methods:  To estimate CWD stocks and density of dead wood debris, 75 permanent forest plots of 0.5 ha in size wereassessed along a transect that spanned ca. 700 km in undisturbed forests from north of the Rio Negro to south of the RioAmazonas. Soil physical properties were evaluated by digging 2-m-deep pits and by taking auger samples.  Results:  Soil physical properties were the best predictors of CWD stocks; 37% of its variation was explained by effectivesoil depth. CWD stocks had a two-fold variation across a gradient of physical soil constraints (i.e. effective soil depth,anoxia and soil structure). Average biomass per tree was related to physical soil constraints, which, in turn, had a strongrelationship with local CWD stocks. Conclusions:  Soil physical properties appear to control average biomass per tree (and through this affect forest structure anddynamics), which, in turn, is correlated with CWD production and stocks. Keywords:  anoxia; effective soil depth; carbon; forest dynamics; line intercept sampling; soil physical properties;topographic index; tropical forest; vegetation structure; necromass Introduction The interaction between different carbon stocks and  󿬂 owsconstitute the carbon cycle. Of the different stocks, above-ground biomass is most often assessed in tropical forests,however coarse woody debris (CWD) is also an essentialcomponent because of its role in biogeochemical cycles(Chambers et al. 2000; Clark et al. 2002; Wilcke et al. 2005; Palace et al. 2008). Within tropical forests, CWD accounts for 6  –  25% of total above-ground carbon stocks(Nascimento and Laurance 2002; Rice et al. 2004; Baker  et al. 2007; Palace et al. 2012), implying a total pan- Amazon CWD carbon stock of ca. 10 Pg (Chao et al.2009a). The variation in CWD stocks across the Amazon basin is thought to be modulated by environmental factors,such as hydrology and soils, and by forest biomass itself (Rice et al. 2004; Baker et al. 2007; Chao et al. 2009a). Amazonia holds a great diversity of tree species (ter Steege et al. 2000), and its forests vary substantially in bothvegetation dynamics (Phillips et al. 2004; Quesada et al.2012), and structure (Baker et al. 2004; Malhi et al. 2006;  Nogueira et al. 2008; Feldpausch et al. 2011). Our current  understanding suggests that CWD stocks generallydecrease from north-eastern to south-western Amazonia(Baker et al. 2007; Chao et al. 2009a). Spatial variation in CWD stocks across the landscape may respond both toshort-term climatic disturbances (e.g. Phillips et al. 2009; Negrón-Juárez et al. 2010) and to long-term differences inforest dynamics in response to environmental characteris-tics (Keller et al. 2004; Malhi et al. 2006; Chao et al. 2009a). Soils represent an important environmental gradi-ent in Amazonia, with a wide variety of soil types across the basin and with diverse chemical and physical conditions(Quesada et al. 2010, 2011). Variations in soil physical  properties across the basin have been related to a large proportion of the variation in tree turnover rates and meanforest wood density, with disturbance levels and vegetationstructure of Amazonian forests being related to different soil types (Quesada et al. 2012). *Corresponding author. Email:  Plant Ecology & Diversity , 2014 © 2014 Botanical Society of Scotland and Taylor & Francis    D  o  w  n   l  o  a   d  e   d   b  y   [   M  s   J  o  s   é   P   i  n   t  o   ]  a   t   1   3  :   3   2   2   6   M  a  r  c   h   2   0   1   4  Very few studies have tried to understand landscape-scale drivers of CWD stocks. Kissing and Powers (2010),working in secondary forests in Costa Rica, showed strong positive correlations between stand age and the amount of CWD. Chao et al. (2009a) working in mature forests inAmazonia showed that there was a relationship betweenforest structure and CWD, in particular with regard to biomass, wood density of living trees and mass of indivi-dual dead stems. Although these studies successfully asso-ciated CWD stocks with forest structure and dynamics, toour knowledge there has been no analysis of a potentialeffect of edaphic properties on CWD stocks. Since edaphicfactors, such as effective soil depth and structure, areimportant factors controlling forest structure and dynamics(Jirka et al. 2007; Quesada et al. 2012), they are likely to  be related to both the production and the stocks of CWD.We hypothesise that because poor soil physical conditionsimpose constraints on tree growth and survival, they result in increased stem turnover rates and, in turn, limit themaximum size that trees can attain. This way smaller trees yield smaller CWD stocks. Therefore, we may expect landscape-scale variation in soils to be linked to variationin CWD stocks. The forests south of the Rio Amazonasrepresent a vast, but poorly studied region in centralAmazonia, both in terms of vegetation and soil. Broadly,this region (Figure 1) is characterised by hydromophicsoils (RADAMBRASIL 1978; Sombroek 2000) of poor   physical structure (Quesada et al. 2011), in contrast to soilsnorth of Manaus, which are dominated by well-draineddeep soils. This region is also expected to have largevariation in above-ground biomass (AGB) (IBGE 1997).Central Amazonia, therefore, represents an ideal testingground for exploring edaphic and vegetation linkageswith CWD stocks.We examined stocks of CWD as a function of vari-ables related to biomass and stem density, and soil proper-ties across central Amazonia in order to understand thefactors that modulate the variation of these stocks.Speci 󿬁 cally, we tested the hypothesis that CWD stockswere larger in soils with no physical constraints and smal-ler in soils with increased physical constraints. Materials and methods Study sites Fieldwork was conducted across a ca. 700-km-long transect (Figure 1) in central Amazonia over a 1-year period (2010  –  2011). Data were collected in permanent plots of 0.5 ha,located north and south of the Rio Amazonas in the Stateof Amazonas, Brazil. There were two sites north of theAmazonas river, the Adolpho Ducke Forest Reserve (here-afterDuckeReserve  –  18plots)andtheBiologicalDynamicsof Forest Fragments Project site (BDFFP  –   12 plots). Thesouthern sites were located in the Purus  –   Madeira inter  󿬂 u-vial zone on a ca. 600 km transect established along theManaus  –  Porto Velho road (BR-319  –   45 plots).The Ducke Reserve has 10,000 ha of mature  terra   󿬁 rme  tropical moist forest and is situated at the peripheryof the city of Manaus (02° 95 ′  S, 59° 95 ′  W). The topo-graphy is undulating with alternating plateaux and rivulet valleys. The vegetation has a 30  –  37 m tall closed canopy,with emergent trees reaching 45 m (Ribeiro et al. 1999).Mean annual precipitation is 2524 mm (Coordenação de Figure 1. Spatial distribution of coarse woody debris (CWD) stocks and values of the topographyc index (TI). Size of red circles are proportional to variation in CWD stocks. High values of the topographic index (light grey to white) indicate poorly drained areas. 2  D.L. Martins  et al.    D  o  w  n   l  o  a   d  e   d   b  y   [   M  s   J  o  s   é   P   i  n   t  o   ]  a   t   1   3  :   3   2   2   6   M  a  r  c   h   2   0   1   4  Pesquisas em Clima e Recursos Hídricos, INPA, unpub-lished data). In general, soils are deep, well-drained andhave low bulk density. Ferralsols and acrisols are foundalong the slopes and plateaux, which are highly weatheredand have favourable physical conditions (i.e. stable aggre-gate structure, associated with good drainage) (Chauvelet al. 1987; Quesada et al. 2010). Near streams and valley  bottoms, wet and sandy soils (podzols) occur, but thesewere not included in this study. A total of 18 plots weresampled on acrisols and ferralsols for CWD and soils.Plots were at least 1 km apart and were 250 m long and20 m wide (0.5 ha), following the topographic contour (Magnusson et al. 2005).The BDFFP study site is located 80 km north of Manaus (2º 30 ′  S, 60º 00 ′  W). Data were collected inmature  terra  󿬁 rme  tropical moist forest, at least 1000 maway from fragment edges, in forest fragments >500 ha(Laurance et al. 1998). The forest canopy was 30  –  37 mtall, with emergent trees reaching up to 55 m. Annualmean precipitation ranged from 1900  –  3500 mm(Nascimento and Laurance 2002). CWD and soil weresampled in twelve 0.5 ha plots (positioned independentlyof topographic features (Laurance et al. 1998)) over fer-ralsols and acrisols.The plots located south of the Rio Amazonas werespaced along the BR-319 road on the inter  󿬂 uvial area between the Purus and Madeira rivers. Plots located closer to Manaus had closed lowland evergreen forest vegetation(IBGE 1997), while plots located closer to Porto Velhohad a more open-type lowland evergreen forest. Thisentire region is characterised by a  󿬂 at topography withelevations varying between 30  –  50 m (asl) over large dis-tances. Mean annual precipitation in this area varies from2155  –  2624 mm obtained from WorldClim global coverageat 2.5-min resolution (Hijmans et al. 2005). The soils are predominantly Plinthosols and Gleysols (Sombroek 2000),generally having varying degrees of soil water saturationand anoxic conditions. Soil physical structure is generallyrestrictive to root growth, with very high bulk density inthe subsoil, and thus these soils have varying degrees of hardness and effective soil depth. Subsoil layers that limit root penetration are frequent and vary from 30  –  100 cm indepth (RADAMBRASIL 1978; Sombroek 2000). In all sites, we sampled a total of 45 plots deployed in ninesite clusters, the clusters being at distances between 40and 60 km apart (Figure 1). Each site cluster was com- posed of a 5-km-long transect with  󿬁 ve plots of 250 × 20 m in size, at intervals of 1 km; following thetopographic contour. Coarse woody debris (CWD) stocks Field sampling of dead wood was made by (1) line intersect (van Wagner  1968) for fallen dead wood and (2) belt transects for standing dead trees (Palace et al. 2007; Chaoet al. 2008). For line intersect sampling, every piece of fallen dead woody material (trees, palms, lianas) with adiameter >10 cm that crossed the transect line wasmeasured and classi 󿬁 ed into one of three decay classes,following Chao et al. (2008): (1) recently fallen, solidwood, sometimes presenting minor degradation; (2) soundwood but already showing some sign of decay, such as theabsence of bark; (3) heavily decayed wood. In partly buriedmaterial, two perpendicular measures were taken and their mean was recorded as diameter. In plots that followed thetopographic contour, the central line of the 250-m long plot was used as the intersect line. In square plots, the intersect line was also 250 m length but followed the plot perimeter.Each 250-m transect was considered as an independent individual sample of CWD. To reduce biased estimationarising from multiple crossing of CWD pieces and endpoint  partial intersection (Af  󿬂 eck et al. 2005), we counted onceonly each piece of CWD (e.g. Gregoire and Valentine2003). Pieces at the endpoint of an intersect line wereincluded only if at least 50% of them was touched by thetransect line. As these plots along the contour did not run ina straight line and sometimes doubled up and ran at anacute angle, we took provisions to avoid multiple crossingsampling bias. We discounted areas where the same pieceof dead wood crossed the same transect line more thanonce. To compensate for lost plot area caused by multiplecrossing, an identical area was added to the plot to keep thetotal sampling area at 0.5 ha. As we assumed that theorientation of pieces of dead wood on the forest   󿬂 oor wasrandom we did not see advantage in using one line intersect design over another (see Bell et al. 1996).The belt transects for estimating standing dead treesand broken snags were 20 m wide along the 250 m trans-ect line. Standing dead stems with a diameter >10 cm weremeasured at 1.3 m height or at the lowest part of the snag,trying to avoid buttress roots where possible. If the snagwas shorter than 1.3 m, the measurement was taken at thehighest point possible. The height of snags taller than 2 mwas measured with a digital hypsometer (Vertex Laser VL400 Ultrasonic-Laser Hypsometer III, Haglöf Sweden)to the point where the diameter was 10 cm. The length anddiameter (>10 cm) of attached branches in standing deadtrees were visually estimated. To account for wood densityvariation following decay, standing dead trees and their occasional branches were also classi 󿬁 ed in the same wayas wood for the line intersects. CWD wood density Samples of dead wood ( n  = 726) that crossed the lineintersect in the plots were collected for measuring thedensity of CWD (dry weight per unit volume). A chainsawwas used to cut a disk sample from hard pieces. Softer wood pieces were sampled by using a bush knife. Thedisks were sub-sampled randomly. Void spaces were takeninto account for volume estimation by visually estimatingtheir proportion (Keller et al. 2004), but were not used for density correction, which may have caused an overestima-tion of up to 10% in some decay classes (Keller et al.2004; Chao et al. 2008). Soil drives coarse woody debris stocks in central Amazonia  3    D  o  w  n   l  o  a   d  e   d   b  y   [   M  s   J  o  s   é   P   i  n   t  o   ]  a   t   1   3  :   3   2   2   6   M  a  r  c   h   2   0   1   4
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