Vegetational sampling of avian habitats stresses the use of methods primarily designed for forest birds. This paper describes a technique for sampling vegetational structure in uneven patchy habitats such as shrublands. Using the method, avian habitats in old field shrublands of northwestern Arkansas were analyzed

James, Douglas A.

UARK (University of Arkansas )

Journal of the Arkansas Academy of Science Volume 46 Article 4 1992 Measuring Shrubland Vegetational Structure Using Avian Habitats as an Example Douglas A. James University of Arkansas, Fayetteville Follow this and additional works at: https://scholarworks.uark.edu/jaas  Part of the Plant Biology Commons, and the Terrestrial and Aquatic Ecology Commons Recommended Citation James, Douglas A. (1992) "Measuring Shrubland Vegetational Structure Using Avian Habitats as an Example," Journal of the Arkansas Academy of Science: Vol. 46 , Article 4. Available at: https://scholarworks.uark.edu/jaas/vol46/iss1/4 This article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able to read, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking prior permission from the publisher or the author. This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu. 46 Proceedings Arkansas Academy of Science, Vol.46, 1992IYIHaVoLJJ\JliN vj)3JlTXxLJ13J_4r\J.NIU Viiivjl_jA/\.A lv>/r\l.r\_LioJLrvLJv^l LJrvt-jDOUGLAS A.JAMESDepartment of Biological SciencesUniversity ofArkansasFayetteville, AR 72701ABSTRACTVegetational sampling of avian habitats stresses the use of methods primarilydesigned for forest birds. This paper describes a technique for sampling vegetationalstructure in uneven patchy habitats such as shrublands. Using the method, avianhabitats in oldfield shrublands of northwestern Arkansas were analyzed.INTRODUCTIONThe sampling ofvegetational structure in avian ecological studies hasstressed forest habitats and forest birds (James and Shugart, 1970) orignored fine details emphasizing instead overall characteristics ofvegetation (MacArthur and Mac Arthur, 1961). Because of the unevencharacter of shrubland vegetation produced by the mosaic pattern ofalternating patches of grasses, shrubs and small trees, the task ofmeasuring vegetational structure in this habitat is especially challenging.Early successional old fields and various scrub and shrubland asso-ciations are examples of this type of environment. Ihave been studyingavian microhabitats in these environments on four continents and foundit necessary to adopt a method for sampling vegetational structure thatwas suited to this unique situation. This study describes the samplingtechnique Ideveloped and used. Itis designed to determine the finestructure of old field shrubland vegetation and also depict overallconfigurations. The example ofits use that is presented is the analysis ofavian habitats in old fields ofnorthwestern Arkansas.MATERIALS ANDMETHODSPositions of birds encountered in the field were marked and thesepoints became centers of circular plots measuring 14.6 m in radius, thusequaling 669.7 square meters. Within these plots 1 1vegetational factorswere measured. The height of the tallest tree or bush in the plot wasrecorded. Also, an estimate of the average vegetation height wasobtained from several measurements throughout the plot using acalibrated pole. The calibrated metal pole was 3.0 m long and 10 mm indiameter, and was marked off into 0.6 m intervals. The 0.6-m intervalswere accentuated using different colored paints. The pole was positionedvertically from the ground at random points in the plot and the totalnumbers of leaves touching it in each of the 0.6-ft intervals wererecorded in the followingeight sections: 0.0-0.6 m, 0.6-1.2 m, 1.2-1.8 m,1.8-2.4 m, 2.4-3.0 m, 3.0-3.7 m, 3.7-4.3 m, and over 4.3 m. Thisconstituted 8 vegetational factors. For making leaf counts above the 3-mheight of the pole, the pole was lifted overhead to appropriate heights.For the unusual very high trees leaves were counted using an overheadrange finder.There were a total of 40 random pole positions used in countingleaves. These were distributed in four orthogonal line transectsoriginating at the center point of the plot, the first transect being definedby following the direction indicated by a random twirlof a compass dial.Ten random pole positions were located in each of the four transects. Thetotal leaf counts for the plot in each of the 0.6-m intervals was obtainedby summing across all forty pole positions for each interval. The 11thand final factor measured was the count of all live woody stems,regardless of size, encountered along each of the four line transects andsummed togive a total for the plot. The stem count was made in a 0.3 -mwide band along the transects at aheight of 1.2m.From the vegetational factors measured in the field five additionalfactors were calculated. These added ones pertained to vegetationalpatterns. Four of the added factors indicated degree of evenness in thevegetation. These all were based on the commonly used measure J' forexpressing evenness in ecological communities (Piclou, 1975),r=u'/H'maxwhere H'max is the log of the number of categories under considerationand 11'is the Shannon index fordiversity,H^-Epjlogpjin which in this case pjis the proportion ofthe total vegetation existing ineach category. Evenness has been used in studies of vegetational pattern(Pielou, 1966), high values of J' indicating an even distribution ofvegetation, low values being associated with uneven or patchy mosaicpatterns.Foliage vertical evenness was a pattern factor that summed the totalleaves in each 0.6-m level across all 40 sample points. The parameter p,then became the proportion of the grand total number of leaves (N) thatoccurred ineach of the levels (p;= n/N, where n is the number of leavesin the ith level). High diversity and evenness existed when the leaveswere uniformly distributed through all strata, low values were associatedwith uneven distributions between vertical strata. Foliage coarse grainedhorizontal evenness was calculated using total leaves in each of the fourtransects summed across all strata, p; representing the proportion of theoverall total number of leaves that occurred in each transect. Thisproduced a measure relating to the distribution of vegetation from sectorto sector over the circular sample plot, a low evenness value showing avery patchy distribution of vegetation between sectors, a high valueindicating an uniform density in vegetation from place to place in theplot. Foliage fine grained evenness used the total number of leavestouching the pole at each of the 40 random pole-sample positions. Theparameter p; was the proportion of leaves found at the ith randomposition compared to the total number of leaves counted over the wholeplot. In this case a low evenness value was associated with a highlyirregular pattern of vegetation density from place to place within sectorsof the plot as wellas between sectors. High values ofevenness indicateda uniform rather than patchy pattern of vegetation on a fine scale fromplace to place in the plot.Stem evenness represents the pattern of shrubbiness in the sample plotwhere p;is the proportion of total stems occurring in each of the 4transects. High values show an even distribution of low woodyvegetation throughout the plot, low values indicate a irregular patchypattern of shrubs. The measure of stem variability was calculated bysumming the absolute values of the differences in number of stemsbetween successive transects in the plot. This was not adjusted forrelative number of stems in the sample plot so the calculation of H' and J'was not performed in this case. Starting with a transect, the number ofstems in that transect was subtracted from the number in the adjacenttransect in the circle. The absolute value of that difference was thensummed with the absolute value of the difference between the secondtransect and its adjacent one in the circle, and so forth until four suchvalues were totaled from the four transect comparisons. Ifthis index ofstem variability was high itshowed that there was considerable variation46Journal of the Arkansas Academy of Science, Vol. 46 [1992], Art. 4Published by Arkansas Academy of Science, 1992Proceedings Arkansas Academy of Science, Vol.46, 199247in shrubbiness between sectors in the plot circle, a low value indicatedthe existence ofa rather uniform shrubbiness throughout the plot.In addition to the plots around bird locations a series ofsamples wereobtained the centers of which were randomly determined. This provided acharacterization of the overall habitat in which the birds occurred, andserved for comparison to the microhabitats occupied by the bird species.Because this technique has been employed by me on severalcontinents and itwas never possible to find poles of the same diametersin these diverse places, each pole used was standardized to a string linevertically suspended by a light plumb through the vegetation. Thisessentially represented a dimensionless point piercing the vegetationalstructure. To perform the standardization the measuring pole waspositioned and the leaves counted in each 0.6-m interval. Then a longerpole was anchored in the ground at a slant with a string line and plumbattached to its tip. This pole was carefully positioned so that the stringline dropped right next to the measuring pole. Next the measuring polewas moved to the side so that the string line took up its position. Theleaves touching the string line were counted in the 0.6-m intervals usingthe nearby pole as a measuring guide. Of course the string line touchedfewer leaves than the wide diametered pole. The conversion needed wascalculated by dividing the total number ofleaves touching the string bythe total touching the pole. This was repeated for a number of polepositions to obtain an average of the conversion ratio. When compilingthe data obtained using this pole the leaf count totals per stratum weremultiplied by the conversion factor to produce a standardized valueconverted to string line measurements. In the case of the study in oldfields of northwestern Arkansas reported here the conversion factor was0.6. Thus the pole leaf counts were multiplied by this value to standardizethem.RESULTS ANDDISCUSSIONThis method of vegetational sampling has been used inmy studies ofavian community ecology in shrubland habitats on a global scale inGhana in West Africa (1970-1971), Nepal in South Asia (1981-1982),Belize in Central America in (1988-1989), and North America innorthwestern Arkansas in 1972 (Posey, 1974) plus northern Michiganbeginning in 1987 and still in progress. An example of the kinds ofresults that are obtained are presented here (Table 1) portraying theTable 1. Mean values for vegetational factors measured in shrubby oldfield habitats innorthwestern Arkansas, comparing random samples withthe habitats occupied by three bird species.Mean values of factorsVegetational nandom Meadow- Indigo Wht-eyedfactor Snnple lark Bunting VireoAvg. vegetational height (m) 1.0 0.9 1.1 2.2Height tallest tree (m) 4.4 3.9 8.5 9.6•total steins at 1.2 mheight 21.9 12.5 26.8 91.9¦natal leaves 0-0.6 mhigh 88.1 85.4 89.3 Bi.nTotal leaves 0.6-1.2 m high 17.3 15.0 13.3 27.0Total leaves 1.2-1.8 m high 3.6 3.0 7.0 19.5Total leaves 1.8-2.4 m high 2.8 1.9 5.3 17.5Total leaves 2.4-3.0 m high 2.4 2.1 4.4 10.4Total leaves 3.0-3.7 mhigh 2.1 1.7 3.7 10.8Total leaves 3.7-4.3 m high 1.8 1.5 2.9 7.2Total leaves above 4.3 m high 3.9 2.5 6.1 19.9Foliage vertical evenness 0.43 0.44 0.46 0.74Foliage coarse grained 0.98 0.98 0.99 0.97horizontal evennessFoliage fine grained 0.95 0.94 0.93 0.94horizontal evennessStem evenness 0.31 0.33 0.73 0.93Stem variability 17.8 13.5 23.8 46.2Arkansas situation (Posey, 1974). In Table 1 the first column of figuresare the mean values for each vegetational factor obtained from therandom vegetational samples, thus representing an evaluation of thevegetational structure that existed in the study area. Compare these withthe next three columns, which are the mean values for the same factorsbut in the microhabitats occupied by 3 bird species in the study area. TheEastern Meadowlark (Sturnella magna) occurs in the more open parts ofthe shrubland habitat, the White-eyed Vireo Q/ireo griseus) occupies themost dense shrubby thickets, and the Indigo Bunting {Passerina cyanea)is between these extremes.The three species shown in Table 1 are representative of a total of 17species sampled in the Arkansas study (Posey, 1974). As an example ofthe kinds of analyses that can be made using this information, ordinaryprincipal components ordination (Cooley and Lohnes, 1971) of thespecies in habitat space can be performed using the combined set ofvegetational factors (Fig. 1). The firstprincipal component (abscissa) wasFigure 1. Habitat ordination of shrubby old field birds innorthwesternArkansas based on the first twoprincipal components of habitat factors.associated with degree of foliage density in the vegetational factors, opencountry to the left, dense shrubland to the right. Notice the positions ofthe 3 species mentioned above; the Eastern Meadowlark at the opengrassland edge on the left of the ordination, the White-eyed Vireo far tothe right in the thick shrubby environs, and the Indigo Bunting inbetween. The second principal component (ordinate) was heavilyweighted on factors relating to horizontal evenness in foliage density, aneven distribution of vegetation from place to place occurring at the top ofthe ordinate in Figure 1, an uneven vegetational mosaic patternpositioned at the bottom. Note that although both species occupied ahabitat of medium vegetational density on the shrubbiness axis (Figure1), the Bobwhite (Colinus virginianus) selected environs having auniformly dense vegetation while the Brown Thrasher (Joxostoma rufum)occurred inhabitats characterized by having scattered bare areas.When conducting the study in the shrublands of Nepal nearKathmandu, the four field personnel involved in taking the samplesperformed an exercise designed to test an aspect of the reliability of themethod. Each of the four investigators sampled the same plot foreach oftwo plots, one plot in open country, the other indense shrubland. Fromthe four samples on a given plot, and comparing two of the samples at atime, coefficients of community similarity (Cox, 198S) were calculatedfor that plot using the respective values obtained for the 11 vegetationalfactors measured in the field. Allpermutations of the four samples on aplot produced six community similarity coefficients, or a total of12 suchcoefficients from the two plots. The average of these 12 coefficients was85%, which is far short of the perfect similarity value of 100%theoretically expected from replicate samples on the same plot However,Cox (1985) points out that replicate samples of the same communitycommonly show similarity coefficients ofaround only 85%. Therefore, inthis regard the method described here is comparable in reliability to othercommunity sampling methods.47Journal of the Arkansas Academy of Science, Vol. 46 [1992], Art. 4https://scholarworks.uark.edu/jaas/vol46/iss1/448 Proceedings Arkansas Academy of Science, Vol. 46, 1992Itshould be noted that this method was developed in the late 1960sbefore the metric system of measurements was universally adopted inscientific publications. Therefore, English system units were used, andhave continued tobe used through the years for the sake ofuniformity indata collection. Expressing the design of the method in metric unitsmakes itlook odd. To clarify things Inow give the original English unitsused, which willassist those who want to perform vegetational analysesforcomparison tomy results. The radius of the plot was 48 ft.Therefore,the four transects were each 48 ftlong. The pole used in counting leaveswas 10 ft tall divided into 2-ft intervals; 0-2 ft, 2-4 ft, 4-6 ft,6-8 ft, 8-10ft,and was raised to count leaves at heights of10-12 ft, 12-14 ft,and over14 ft. The four narrow transects in which woody stems were countedwere each 48 ftlong and 1ft wide.LITERATURE CITEDCOOLEY, W.C. and P.R. LOHNES. 1971. Multivariate data analysis.John Wiley Sons, New York,364 p.COX, G.W. 1985. Laboratory manual of general ecology, 5th ed. WilliamC. Brown, Dubuque, Iowa, 248 p.JAMES, F.C. and H.H. SHUGART, JR. 1970. A quantitative method ofhabitat description. Audubon Field Notes 24:727-736.MACARTHUR,R.H. and J. W. MACARTHUR. 1961. On bird speciesdiversity. Ecology 42:594-598.PIELOU, E.C. 1966. Species diversity and pattern diversity in the studyofecological succession. J. Theoret. Biol. 10:370-383.PIELOU, E.C. 1975. Ecological diversity. John Wiley & Sons, NewYork,165 p.POSEY, A.F. 1974. Vegetational habitats of breeding birds in Ozarkshrubby old fields. Unpubl. Doctoral Disser., Univ. Arkansas, 42 p.48Journal of the Arkansas Academy of Science, Vol. 46 [1992], Art. 4Published by Arkansas Academy of Science, 1992

English

Measuring Shrubland Vegetational Structure Using Avian Habitats as an Example

ScholarWorks@UARK

Journal of the Arkansas Academy of ScienceVolume 46 Article 41992Measuring Shrubland Vegetational Structure UsingAvian Habitats as an ExampleDouglas A. JamesUniversity of Arkansas, FayettevilleFollow this and additional works at: http://scholarworks.uark.edu/jaasPart of the Plant Biology Commons, and the Terrestrial and Aquatic Ecology CommonsThis article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able toread, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking priorpermission from the publisher or the author.This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academyof Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu.Recommended CitationJames, Douglas A. (1992) "Measuring Shrubland Vegetational Structure Using Avian Habitats as an Example," Journal of the ArkansasAcademy of Science: Vol. 46 , Article 4.Available at: http://scholarworks.uark.edu/jaas/vol46/iss1/446 Proceedings Arkansas Academy of Science, Vol.46, 1992IYIHaVoLJJ\JliN vj)3JlTXxLJ13J_4r\J.NIU Viiivjl_jA/\.A lv>/r\l.r\_LioJLrvLJv^l LJrvt-jDOUGLAS A.JAMESDepartment of Biological SciencesUniversity ofArkansasFayetteville, AR 72701ABSTRACTVegetational sampling of avian habitats stresses the use of methods primarilydesigned for forest birds. This paper describes a technique for sampling vegetationalstructure in uneven patchy habitats such as shrublands. Using the method, avianhabitats in oldfield shrublands of northwestern Arkansas were analyzed.INTRODUCTIONThe sampling ofvegetational structure in avian ecological studies hasstressed forest habitats and forest birds (James and Shugart, 1970) orignored fine details emphasizing instead overall characteristics ofvegetation (MacArthur and Mac Arthur, 1961). Because of the unevencharacter of shrubland vegetation produced by the mosaic pattern ofalternating patches of grasses, shrubs and small trees, the task ofmeasuring vegetational structure in this habitat is especially challenging.Early successional old fields and various scrub and shrubland asso-ciations are examples of this type of environment. Ihave been studyingavian microhabitats in these environments on four continents and foundit necessary to adopt a method for sampling vegetational structure thatwas suited to this unique situation. This study describes the samplingtechnique Ideveloped and used. Itis designed to determine the finestructure of old field shrubland vegetation and also depict overallconfigurations. The example ofits use that is presented is the analysis ofavian habitats in old fields ofnorthwestern Arkansas.MATERIALS ANDMETHODSPositions of birds encountered in the field were marked and thesepoints became centers of circular plots measuring 14.6 m in radius, thusequaling 669.7 square meters. Within these plots 1 1vegetational factorswere measured. The height of the tallest tree or bush in the plot wasrecorded. Also, an estimate of the average vegetation height wasobtained from several measurements throughout the plot using acalibrated pole. The calibrated metal pole was 3.0 m long and 10 mm indiameter, and was marked off into 0.6 m intervals. The 0.6-m intervalswere accentuated using different colored paints. The pole was positionedvertically from the ground at random points in the plot and the totalnumbers of leaves touching it in each of the 0.6-ft intervals wererecorded in the followingeight sections: 0.0-0.6 m, 0.6-1.2 m, 1.2-1.8 m,1.8-2.4 m, 2.4-3.0 m, 3.0-3.7 m, 3.7-4.3 m, and over 4.3 m. Thisconstituted 8 vegetational factors. For making leaf counts above the 3-mheight of the pole, the pole was lifted overhead to appropriate heights.For the unusual very high trees leaves were counted using an overheadrange finder.There were a total of 40 random pole positions used in countingleaves. These were distributed in four orthogonal line transectsoriginating at the center point of the plot, the first transect being definedby following the direction indicated by a random twirlof a compass dial.Ten random pole positions were located in each of the four transects. Thetotal leaf counts for the plot in each of the 0.6-m intervals was obtainedby summing across all forty pole positions for each interval. The 11thand final factor measured was the count of all live woody stems,regardless of size, encountered along each of the four line transects andsummed togive a total for the plot. The stem count was made in a 0.3 -mwide band along the transects at aheight of 1.2m.From the vegetational factors measured in the field five additionalfactors were calculated. These added ones pertained to vegetationalpatterns. Four of the added factors indicated degree of evenness in thevegetation. These all were based on the commonly used measure J' forexpressing evenness in ecological communities (Piclou, 1975),r=u'/H'maxwhere H'max is the log of the number of categories under considerationand 11'is the Shannon index fordiversity,H^-Epjlogpjin which in this case pjis the proportion ofthe total vegetation existing ineach category. Evenness has been used in studies of vegetational pattern(Pielou, 1966), high values of J' indicating an even distribution ofvegetation, low values being associated with uneven or patchy mosaicpatterns.Foliage vertical evenness was a pattern factor that summed the totalleaves in each 0.6-m level across all 40 sample points. The parameter p,then became the proportion of the grand total number of leaves (N) thatoccurred ineach of the levels (p;= n/N, where n is the number of leavesin the ith level). High diversity and evenness existed when the leaveswere uniformly distributed through all strata, low values were associatedwith uneven distributions between vertical strata. Foliage coarse grainedhorizontal evenness was calculated using total leaves in each of the fourtransects summed across all strata, p; representing the proportion of theoverall total number of leaves that occurred in each transect. Thisproduced a measure relating to the distribution of vegetation from sectorto sector over the circular sample plot, a low evenness value showing avery patchy distribution of vegetation between sectors, a high valueindicating an uniform density in vegetation from place to place in theplot. Foliage fine grained evenness used the total number of leavestouching the pole at each of the 40 random pole-sample positions. Theparameter p; was the proportion of leaves found at the ith randomposition compared to the total number of leaves counted over the wholeplot. In this case a low evenness value was associated with a highlyirregular pattern of vegetation density from place to place within sectorsof the plot as wellas between sectors. High values ofevenness indicateda uniform rather than patchy pattern of vegetation on a fine scale fromplace to place in the plot.Stem evenness represents the pattern of shrubbiness in the sample plotwhere p;is the proportion of total stems occurring in each of the 4transects. High values show an even distribution of low woodyvegetation throughout the plot, low values indicate a irregular patchypattern of shrubs. The measure of stem variability was calculated bysumming the absolute values of the differences in number of stemsbetween successive transects in the plot. This was not adjusted forrelative number of stems in the sample plot so the calculation of H' and J'was not performed in this case. Starting with a transect, the number ofstems in that transect was subtracted from the number in the adjacenttransect in the circle. The absolute value of that difference was thensummed with the absolute value of the difference between the secondtransect and its adjacent one in the circle, and so forth until four suchvalues were totaled from the four transect comparisons. Ifthis index ofstem variability was high itshowed that there was considerable variation46Journal of the Arkansas Academy of Science, Vol. 46 [1992], Art. 4Published by Arkansas Academy of Science, 1992Proceedings Arkansas Academy of Science, Vol.46, 1992 47in shrubbiness between sectors in the plot circle, a low value indicatedthe existence ofa rather uniform shrubbiness throughout the plot.In addition to the plots around bird locations a series ofsamples wereobtained the centers of which were randomly determined. This provided acharacterization of the overall habitat in which the birds occurred, andserved for comparison to the microhabitats occupied by the bird species.Because this technique has been employed by me on severalcontinents and itwas never possible to find poles of the same diametersin these diverse places, each pole used was standardized to a string linevertically suspended by a light plumb through the vegetation. Thisessentially represented a dimensionless point piercing the vegetationalstructure. To perform the standardization the measuring pole waspositioned and the leaves counted in each 0.6-m interval. Then a longerpole was anchored in the ground at a slant with a string line and plumbattached to its tip. This pole was carefully positioned so that the stringline dropped right next to the measuring pole. Next the measuring polewas moved to the side so that the string line took up its position. Theleaves touching the string line were counted in the 0.6-m intervals usingthe nearby pole as a measuring guide. Of course the string line touchedfewer leaves than the wide diametered pole. The conversion needed wascalculated by dividing the total number ofleaves touching the string bythe total touching the pole. This was repeated for a number of polepositions to obtain an average of the conversion ratio. When compilingthe data obtained using this pole the leaf count totals per stratum weremultiplied by the conversion factor to produce a standardized valueconverted to string line measurements. In the case of the study in oldfields of northwestern Arkansas reported here the conversion factor was0.6. Thus the pole leaf counts were multiplied by this value to standardizethem.RESULTS ANDDISCUSSIONThis method of vegetational sampling has been used inmy studies ofavian community ecology in shrubland habitats on a global scale inGhana in West Africa (1970-1971), Nepal in South Asia (1981-1982),Belize in Central America in (1988-1989), and North America innorthwestern Arkansas in 1972 (Posey, 1974) plus northern Michiganbeginning in 1987 and still in progress. An example of the kinds ofresults that are obtained are presented here (Table 1) portraying theTable 1. Mean values for vegetational factors measured in shrubby oldfield habitats innorthwestern Arkansas, comparing random samples withthe habitats occupied by three bird species.Mean values of factorsVegetational nandom Meadow- Indigo Wht-eyedfactor Snnple lark Bunting VireoAvg. vegetational height (m) 1.0 0.9 1.1 2.2Height tallest tree (m) 4.4 3.9 8.5 9.6•total steins at 1.2 mheight 21.9 12.5 26.8 91.9¦natal leaves 0-0.6 mhigh 88.1 85.4 89.3 Bi.nTotal leaves 0.6-1.2 m high 17.3 15.0 13.3 27.0Total leaves 1.2-1.8 m high 3.6 3.0 7.0 19.5Total leaves 1.8-2.4 m high 2.8 1.9 5.3 17.5Total leaves 2.4-3.0 m high 2.4 2.1 4.4 10.4Total leaves 3.0-3.7 mhigh 2.1 1.7 3.7 10.8Total leaves 3.7-4.3 m high 1.8 1.5 2.9 7.2Total leaves above 4.3 m high 3.9 2.5 6.1 19.9Foliage vertical evenness 0.43 0.44 0.46 0.74Foliage coarse grained 0.98 0.98 0.99 0.97horizontal evennessFoliage fine grained 0.95 0.94 0.93 0.94horizontal evennessStem evenness 0.31 0.33 0.73 0.93Stem variability 17.8 13.5 23.8 46.2Arkansas situation (Posey, 1974). In Table 1 the first column of figuresare the mean values for each vegetational factor obtained from therandom vegetational samples, thus representing an evaluation of thevegetational structure that existed in the study area. Compare these withthe next three columns, which are the mean values for the same factorsbut in the microhabitats occupied by 3 bird species in the study area. TheEastern Meadowlark (Sturnella magna) occurs in the more open parts ofthe shrubland habitat, the White-eyed Vireo Q/ireo griseus) occupies themost dense shrubby thickets, and the Indigo Bunting {Passerina cyanea)is between these extremes.The three species shown in Table 1 are representative of a total of 17species sampled in the Arkansas study (Posey, 1974). As an example ofthe kinds of analyses that can be made using this information, ordinaryprincipal components ordination (Cooley and Lohnes, 1971) of thespecies in habitat space can be performed using the combined set ofvegetational factors (Fig. 1). The firstprincipal component (abscissa) wasFigure 1. Habitat ordination of shrubby old field birds innorthwesternArkansas based on the first twoprincipal components of habitat factors.associated with degree of foliage density in the vegetational factors, opencountry to the left, dense shrubland to the right. Notice the positions ofthe 3 species mentioned above; the Eastern Meadowlark at the opengrassland edge on the left of the ordination, the White-eyed Vireo far tothe right in the thick shrubby environs, and the Indigo Bunting inbetween. The second principal component (ordinate) was heavilyweighted on factors relating to horizontal evenness in foliage density, aneven distribution of vegetation from place to place occurring at the top ofthe ordinate in Figure 1, an uneven vegetational mosaic patternpositioned at the bottom. Note that although both species occupied ahabitat of medium vegetational density on the shrubbiness axis (Figure1), the Bobwhite (Colinus virginianus) selected environs having auniformly dense vegetation while the Brown Thrasher (Joxostoma rufum)occurred inhabitats characterized by having scattered bare areas.When conducting the study in the shrublands of Nepal nearKathmandu, the four field personnel involved in taking the samplesperformed an exercise designed to test an aspect of the reliability of themethod. Each of the four investigators sampled the same plot foreach oftwo plots, one plot in open country, the other indense shrubland. Fromthe four samples on a given plot, and comparing two of the samples at atime, coefficients of community similarity (Cox, 198S) were calculatedfor that plot using the respective values obtained for the 11 vegetationalfactors measured in the field. Allpermutations of the four samples on aplot produced six community similarity coefficients, or a total of12 suchcoefficients from the two plots. The average of these 12 coefficients was85%, which is far short of the perfect similarity value of 100%theoretically expected from replicate samples on the same plot However,Cox (1985) points out that replicate samples of the same communitycommonly show similarity coefficients ofaround only 85%. Therefore, inthis regard the method described here is comparable in reliability to othercommunity sampling methods.47Journal of the Arkansas Academy of Science, Vol. 46 [1992], Art. 4http://scholarworks.uark.edu/jaas/vol46/iss1/448 Proceedings Arkansas Academy of Science, Vol. 46, 1992Itshould be noted that this method was developed in the late 1960sbefore the metric system of measurements was universally adopted inscientific publications. Therefore, English system units were used, andhave continued tobe used through the years for the sake ofuniformity indata collection. Expressing the design of the method in metric unitsmakes itlook odd. To clarify things Inow give the original English unitsused, which willassist those who want to perform vegetational analysesforcomparison tomy results. The radius of the plot was 48 ft.Therefore,the four transects were each 48 ftlong. The pole used in counting leaveswas 10 ft tall divided into 2-ft intervals; 0-2 ft, 2-4 ft, 4-6 ft,6-8 ft, 8-10ft,and was raised to count leaves at heights of10-12 ft, 12-14 ft,and over14 ft. The four narrow transects in which woody stems were countedwere each 48 ftlong and 1ft wide.LITERATURE CITEDCOOLEY, W.C. and P.R. LOHNES. 1971. Multivariate data analysis.John Wiley Sons, New York,364 p.COX, G.W. 1985. Laboratory manual of general ecology, 5th ed. WilliamC. Brown, Dubuque, Iowa, 248 p.JAMES, F.C. and H.H. SHUGART, JR. 1970. A quantitative method ofhabitat description. Audubon Field Notes 24:727-736.MACARTHUR,R.H. and J. W. MACARTHUR. 1961. On bird speciesdiversity. Ecology 42:594-598.PIELOU, E.C. 1966. Species diversity and pattern diversity in the studyofecological succession. J. Theoret. Biol. 10:370-383.PIELOU, E.C. 1975. Ecological diversity. John Wiley & Sons, NewYork,165 p.POSEY, A.F. 1974. Vegetational habitats of breeding birds in Ozarkshrubby old fields. Unpubl. Doctoral Disser., Univ. Arkansas, 42 p.48Journal of the Arkansas Academy of Science, Vol. 46 [1992], Art. 4Published by Arkansas Academy of Science, 1992

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Measuring Shrubland Vegetational Structure Using Avian Habitats as an Example

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