斑块分布机制

Ecological Engineering 36 (2010) 1719–1724 Contents lists available at ScienceDirect Ecological Engineering journa l homepage: www.e lsev ier .com Cross-s effe restora Yu Yoshi Un a Graduate Sch , Miya b Graduate Sch Japan c School of Agri n d Center for Eco a r t i c l Article history: Received 15 M Received in re Accepted 19 Ju Keywords: Facilitation–competition relationship Functional richness Mongolian desert steppe Multiple spati Species richne Vegetation rec actio getati ales o at a image, we established five 2500m2 plots in each of three shrub density classes (low, moderate, high) in a desert steppe in Mongolia. To evaluate the facilitative functions of shrubs at multiple spatial scales, we recorded the total number of plant species at three nested spatial scales in each plot: 25, 400, and 2500m2. The facilitative effect of shrubs on plant species richness was more pronounced at larger scales. Denser shrub communities increased plant species diversity at a larger scale. However, the increased taxonomic 1. Introdu Degrada ity of local and ecologi also has ser activities in provided b of food, fol necessary t ecosystems ples can co balance bet tion. Facilitat plant–plant as a tool to ∗ Correspon E-mail add (Y. Yoshihara) 0925-8574/$ – doi:10.1016/j. al scales ss overy diversity was not clearly related to increased functional diversity in this system. This scale dependency in species diversity can be explained by the degree to which spatial heterogeneity of habitats within the plots increased as plot size increased. These results support the hypothesis of scale-dependent changes in the balance between facilitation and competition. Therefore, transplanting shrub saplings at high-density and a larger scale could potentially improve the success of vegetation restoration in arid regions. © 2010 Elsevier B.V. All rights reserved. ction tion in arid–semiarid ecosystems is impairing the abil- peoples to effectively use the biological, physiological, cal resources of this land (Wezel and Rath, 2002), but ious consequences like poverty at a global scale. Human arid areas depend strongly on the ecosystem services y arid–semiarid ecosystems, including the provision iage resources, and soil stabilization. It is therefore o restore the ecosystem functions provided by these and ensure sustainable management so that local peo- ntinue to enjoy ecosystem services while striking a ween sustainable production and preventing degrada- ion, an ecological term that describes positive interactions, has received considerable attention accelerate vegetation restoration processes, particu- ding author. Tel.: +81 229 84 7380; fax: +81 229 84 7380. resses: yoshiyu@bios.tohoku.ac.jp, marmota.sibirica@gmail.com . larly in arid areas (Flores and Jurado, 2003; Padilla and Pugnaire, 2006; Brooker et al., 2008). Planting of trees or shrubs in sandy land to control desertification and provide a more favorable envi- ronment for other species is an example of this approach (Zhang et al., 2004). Shrub establishment increases the content of fine soil particles, soil moisture, and seed density in the soil. Furthermore, it enhances the accumulation of organic C and increases total N, and decreases pH in proximity to the shrubs (Facelli and Temby, 2002; Su and Zhao, 2003; Zhao et al., 2007). This soil amelioration results in greater diversity, density, height, cover, and above- ground and belowground biomass of herbaceous species (Facelli and Temby, 2002; Su and Zhao, 2003; Zhang et al., 2004; Zhao et al., 2007). In addition, grazing-sensitive plants growing close to shrubs can be protected from herbivory, particularly if the shrub species have spines, toxic fruits or leaves (Rebollo et al., 2002). Consequently, the species richness of understory plants is related to the size of the individual shrubs according to a simple power relationship for a wide array of species (Maestre and Cortina, 2005). The facilitative effects of planted shrubs generally increase as the shrubs develop, but after a certain point of development the effectiveness eventually diminishes due to competition for light and other resources (Reisman-Berman, 2007). To fully benefit see front matter © 2010 Elsevier B.V. All rights reserved. ecoleng.2010.07.018 patial-scale patterns in the facilitative tion of desert steppe haraa,∗, Takehiro Sasakib, Toshiya Okuroc, Jamsran ool of Agricultural Science, Tohoku University, 232-3, Yomogita, Naruko-Onsen, Ohsaki ool of Life Sciences, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai 980-8578, culture and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, Japa system Study, Mongolian State University of Agriculture, Mongolia e i n f o arch 2010 vised form 23 June 2010 ly 2010 a b s t r a c t Facilitation (positive plant–plant inter in arid areas. Shrubs can accelerate ve not been evaluated at large spatial sc of shrub change across spatial scales / locate /eco leng ct of shrubs and potential for darmaad, Kazuhiko Takeuchic gi 989-6711, Japan ns) is a potential means to accelerate vegetation restoration on recovery by means of soil amelioration, but this effect has r across scales. Here, we examined the facilitative function desert steppe in Mongolia. Using a high-resolution satellite 1720 Y. Yoshihara et al. / Ecological Engineering 36 (2010) 1719–1724 Fig. 1. Overvie in the Mongol from the fa avoid comp such as wat The rela ical process 1997; Gasc magnitude Asia, indivi develop ben all surface r sand transp These envir larger spati those that less, most s at a single shrubs and 2001). Stud scales or ac study, we e changed acr cations for e hypothesis larger scale Species d function an and its hea ing). Howev strongly co gate for fun 2005). The d correlated 2002). In M generally e is, two or m compared n 2. Materia 2.1. Site des Our stu 106◦16′E) in steppe ecol average aro ages around is received d is characterized by a mixture of patchily distributed shrubs and herbs. The shrubspecies foundmost frequently in the studyareaare na spp. (Fabaceae, Caragana microphylla, C. leucophloea, and aea inate i et a ing b s of tellit desig at a ale a nd it o sol spat umm on w sing were of se te et trut man on o ents. d a t ode ablis rrela , but eld su id-A the 1 re, w view view rub. each each -air o e fac 007) lives n the ubs plan wof the study area, inset: location of the Saintsagaan soum (country) ia. cilitative action of shrubs, tall plants must be able to etition with the shrubs for light and other resources er (Pihlgren and Lennartsson, 2008). tive importance of the parameters that control ecolog- es appears to vary with the spatial scale (Bissonette, oigne et al., 2005), and this can alter the nature or of the facilitative effect. In sandy grasslands in eastern dual shrubs trap wind-blown sands, and soil mounds eath the shrub canopy. As the mounds grow, the over- oughness of a site increases, and the wind velocity and ort rate both decrease (Li et al., 2002; He et al., 2008). onmental changes can promote vegetation recovery at al scales through ecological processes that differ from function at the scale of individual shrubs. Neverthe- tudies of shrub facilitation effects have been conducted small scale, as in studies of the relationship between their neighbors (Zhao et al., 2007; Tewksbury and Lloyd, ies that have evaluated the function of shrubs at large ross spatial scales remain scant. Thus, in the present xamined whether the facilitative function of shrubs oss spatial scales, andwhether such changes had impli- nhancing sustainableuseofMongolian rangelands.Our was that the facilitation effect would be enhanced at s. iversity is commonly used as an indicator of ecosystem d therefore of the services provided by an ecosystem lth (including the recovery processes it is undergo- er, unless the taxonomic and functional diversity are rrelated, taxonomic diversity cannot serve as a surro- ctional diversity (Naeem, 2002; Micheli and Halpern, egree to which taxonomic and functional diversity are has not been reported for most ecosystems (Naeem, Caraga C. pygm is dom (Sasak of graz pattern 2.2. Sa We density that sc we fou field. T with a in the s sificati area, u Pixels series Laliber ground density sificati surem selecte (low, m we est autoco 1000m 2.3. Fi Inm within structu shrub shrub eachsh within ple on forced Becaus et al., 2 sity of dung o the shr ber of ongolian rangeland ecosystems, plant communities xhibit functional redundancy (Sasaki et al., 2009); that ore species often serve similar functions. We therefore ot only species richness but also functional richness. ls and methods cription dy area was situated near Mandalgobi (45◦46′N, Mongolia, which is in the country’s steppe and desert ogical zones (Fig. 1). Summer and winter temperatures und 19 and −14 ◦C, respectively. Annual rainfall aver- 170mm (coefficient of variance =28%), most of which uring the summer. Vegetation on sandy soil in the area 25m2 (5× (50×50m To inves samples (10 mound sam the mound inter-moun particle siz clay conten ISSS (1994) 2.4. Data an Because lated the ca ), and it is assumed that the region’s sandy soil, which d by large particles, is suitable for their establishment l., 2008). The study area has a long history (centuries) y domestic livestock under nomadic or semi-nomadic land use. e image and ground truthing ned the present study to test the hypothesis that shrub large spatial scale would affect ecological processes at nd would thereby affect vegetation recovery. However, difficult to estimate shrub density at a large scale in the ve this problem, we obtained a panchromatic imagery ial resolution of 0.7m captured by a QuickBird satellite er (July 14th) of 2008 (Fig. 2). An object-oriented clas- as performed on the imagery that covers 64km2 study eCognition professional 4.0 (Definiens Imaging GmbH). identified as shrubs or non-shrub cover through a gmentation and classification after the workflow of al. (2004). We also randomly located fifteen 400m2 hing plots in the study area, measured shrub areas and ually, andcomparedshrubcover/density fromtheclas- f the QuickBird image with those ground-based mea- After confirming that the positions were correct, we otal of 15 areas, with 5 areas at each of the three levels rate, high) of shrub density. At the center of each area, hed a 2500-m2 (50×50m) plot (Fig. 2). To avoid spatial tion between plots, the plots were separated by at least remained within the same general landscape position. rvey ugust 2008,we counted thenumber ofCaragana shrubs 5 plots. To formulate a description of shrub andmound e measured the major axis (the longest diameter of ed from above), minor axis (the shortest diameter of ed from above), shrub height, and mound height for Wealso systematically established ten1×1mquadrats plot and collected the aboveground vegetation sam- quadrat. These vegetation samples were dried in a ven at 70 ◦C for 48h to determine the plant biomass. ilitative effects can be altered by grazing intensity (Smit , we estimated the grazing intensity based on the den- tock dung. We counted the number of sheep and goat ten quadrats. To evaluate the facilitative functions of at multiple spatial scales, we recorded the total num- t species at three nested spatial scales in each plot: 5m extent), 400m2 (20×20m extent), and 2500m2 extent). tigate the soil texture, we extracted five paired core -cm diameter×15-cm depth) from mounds and inter- ple points in each plot. For each plot, we homogenized samples into one bulk sample, and did the same for the d samples. In the laboratory, we determined the soil e distribution (coarse sand, fine sand, and the silt and ts) of each homogenized sample using the criteria of . alysis the shrubs were either round or elongated, we calcu- nopy size of each shrub based on the assumption that Y. Yoshihara et al. / Ecological Engineering 36 (2010) 1719–1724 1721 Fig. 2. QuickB the locations o truthing, the d Boxes represe the canopy minor axes shrub area shrubs, and (Table 1). Table 1 Structural cha Shrub densit Low Moderate High ird panchromatic images (0.7-m resolution) showing (a–c) enlarged images of the stud f individual plots indicated. (a) Plot L3 (low-density shrubs), (b) plot M4 (moderate-den ark dots in (a) and (b) were confirmed to be mostly shrubs, and the undulating surfaces nt the 2500-m2 study plots where the field survey was conducted. could be modeled as an ellipse, and used the major and to calculate the area. We further calculated the total within a plot as the mean canopy size× the number of the shrub cover as the total shrub area×100/plot area We selec ered key to al., 2009), f (Table 2). W Mongolian racteristics of the shrubs and soil mounds in each density level. y Number of shrubs Shrub size Major axis (cm) Minor axis (cm) Canopy size (cm Mean 60.4 53.7 37.4 1596 SD (within plots) – 31.1 15.8 1876 SD (between plots) 61.2 16.8 16.2 1535 Mean 157.2 63.0 48.4 3550 SD (within plots) – 42.7 32.3 5278 SD (between plots) 65.1 15.7 13.7 1977 Mean 461.2 92.2 70.4 7866 SD (within plots) – 70.1 52.6 12,884 SD (between plots) 75.9 7.5 6.4 1513 y plots and (d) the overall study site in western Mandalgobi, with sity shrubs), and (c) plot H1 (high-density shrubs). Based on ground and dark areas in (c) are mostly shrub mounds and their shadows. ted several functional traits of species that are consid- determining their role within an ecosystem (Sasaki et or a total of 33 categories of 8 plant functional traits e compiled this trait data from an existing reference on flora (Grubov, 1982), supplemented with information 2) Shrub area (m2/plot) Cover (% of plot area) Shrub height (cm) Mound height (cm) 8.0 0.3 14.0 5.5 – 5.9 5.2 7.9 0.3 8.0 3.6 55.5 2.2 18.2 6.5 – – 7.2 6.8 32.0 1.3 1.9 2.1 361.4 14.5 21.1 17.1 – – 9.6 14.6 79.6 3.2 2.0 3.4 1722 Y. Yoshihara et al. / Ecological Engineering 36 (2010) 1719–1724 Table 2 Plant functional traits and the related categories used in our analyses. “Multiple membership” defines whether a species can belong to more than one category for a trait. Plant functional trait Trait categories 1 ody a 2 erenn 3 ed; p 4 5 6 ate or 7 ate; m 8 fascic provided by data with fi We ana among the the assump richness w interaction comparison performed shrub densi (PCA) on th between sh PC-ORD sof used LSD te fine particle at three shr the Statistic 3. Results We foun across all th atively low between th richness sh P=0.044, d density× sc richness di 5×5m sca was signific scale (P=0. tional richn (P=0.433), There w tional trait densities, b Stipa increa in 2 of 5 p density, an differ signifi although bi mean± SD) about 2 an (9.4±3.4 g/ The soil p shrub dens the mounds of coarse sa shrub dens tent (Fig. 5) shrub dens indicating t greater wit he (a) species richness and (b) functional richness of plant species as a of spatial scale at each shrub density. (Values represent means± SD.) The onnect the mean values at the three spatial scales. cussion major finding was that the facilitative effect of shrubs nt species richness depended on the spatial scale, and the as most pronounced at the largest scale. The extent of the tion by shrubs, which we represented by the species rich- us showed a drastic change at a certain shrub density; the Growth form Grass; forb; sub-shrub (only wo Life history Annual; biennial; herbaceous p Lateral spread Erect (solitary); tussock; branch Phylogenetic group Monocotyledon; dicotyledon Leaf margin Entire; toothy; revolute; thorny Leaf shape Linear; lanceolate; elliptical; ov Leaf form Entire; lobed; pinnatisect; pinn Leaf attachment Opposite; alternate; decussate; Jigjidsuren and Johnson (2003), and validated these eld observations. lyzed differences in dung density and plant biomass treatments using univariate ANOVA after confirming tion of homogeneity of variance. Species and functional ere analyzed using two-way ANOVA to examine the terms between shrub density and spatial scale. Post hoc s using the least-significant-difference (LSD) test were to test for statistically significant differences between ty levels. We conducted principal components analysis e correlation matrix at the plot level to find relationship rub density and soil particle size distribution, using the tware (version 4.0; McCune and Mefford, 1999). We st to compare statistically the contents of coarse and s in soil samples among the mounds and inter-mound ub density levels. These analyses were performed using a 6.0J software (Systat Inc.). d a mean of 6.66 (SD=4.17) pieces of dung per m2 e study plots, indicating that grazing intensity was rel- . There were no significant differences in dung density e shrubdensity levels (F=2.13, P=0.160, d.f. = 2) Species owed a significant density× scale interaction (F=2.73, .f. = 4, Fig. 3). However, functional richness showed no ale interaction (F=1.85,P=0.138, d.f. = 4, Fig. 3). Species d not differ significantly among shrub densities at a le (P=0.236) or at a 20×20m scale (P=0.950), but antly higher in the high-density plots at the 50×50m 040). Shrub density had no significant effect on func- ess at the 5×5m scale (P=0.057), the 20×20m scale or the 50×50m scale (P=0.338). as no obvious difference in the composition of func- s (based on the functions in Table 2) among shrub ut the abundance of late-successional species such as sed as shrubdensity increased; this specieswas present lots at low shrub density, 3 of 5 plots at moderate d 5 of 5 plots at high density. Plant biomass did not cantly among density levels (F=2.62, P=0.114, d.f. = 2), omass in the moderate-density plots (16.3±6.1 g/plot, and the high-density plots (13.2±4.3 g/plot) were d 1.5 times the biomass in the low-density plots plot). Fig. 3. T function curves c 4. Dis One on pla effect w facilita ness, th article sizedistribution alsodifferedbetween the three ities and between positions (Fig. 4). Soil collected from beneath shrubs showed a significantly greater content nd than soil from the samples between mounds in each ity, but showed no significant difference in clay con- . The difference increased in magnitude with increasing ity, and the difference was significant for coarse sand, hat the spatial heterogeneity of soil particle size was hin the high-density plots. dense shru ever, this in with a com although fu difference a (2009) dem plant comm our study. P danceof shr Multiple membership t the base); shrub No ial; woody perennial Yes rostrate Yes No Yes obovate; oblong; round Yes ultipinnate Yes ulate Yes bs increased species diversity at a larger scale. How- crease in taxonomicdiversitywasnot clearly associated parable increase in functional diversity in this system; nctional diversity increased with increasing scale, the mong shrub densities was not significant. Sasaki et al. onstrated the existence of functional redundancy in unities in Mongolian rangelands similar to the one in lant biomass was positively correlated with the abun- ubs, butdidnot respond to the shrubdensity in a simple Y. Yoshihara et al. / Ecological Engineering 36 (2010) 1719–1724 1723 Fig. 4. Principal components analysis (PCA) of the soil particle size taken between the mounds that collected below shrubs (inter-mound) and samples collected from these mounds (on-mound) at each shrub density level. manner. However, given that the proportion of late-successional plants was the highest in the dense shrub communities, the net effect of shrubs on Mongolian rangeland ecosystems appears to be positive. There is growing evidence that both positive (i.e., facilitation) and negative (i.e., competition) interactions occur simultaneously between interacting plants (Brooker et al., 2008). Clarifying the mechanisms responsible for the balance betweenpositive andneg- ative interactions in plant communities is a central topic in ecology, Fig. 5. Propor mounds and o class labeled w