Proceedings of the Third International Conference on Invasive ...

<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive SpartinaChapter 2: Spartina Distribution and SpreadTable 2. Change in area covered by non-native Spartina species between2001 and 2003 averaged over all sites surveyed, comparing aerial photointerpretation measurements (APIM) with field measurements and fieldestimates.SpeciesS. AlternifloraHybridsAverage Site Change in Area from 2001-2003Field Measurement +Field Estimates(N=28)**APIM(N=5)*317.00% 213.05%S. densiflora 52.83% n/aS. patens -84.2% n/aAll Species 244.41% 213.1%* Five <strong>of</strong> <strong>the</strong> 28 sites had only aerial photo interpretation measurementsfor 2001. For <strong>the</strong>se five sites, a 2001 field estimate was calculated using aregression curve based on a correlation between <strong>the</strong> existing 2001 and2003 field measurements. This 2001 field estimate was used in <strong>the</strong> place<strong>of</strong> <strong>the</strong> 2001 field survey data to calculate <strong>the</strong> change in area from 2001-2003.** For five sites <strong>of</strong> <strong>the</strong> 28 sites, 2001 aerial photo interpretation measurementwas used in <strong>the</strong> place <strong>of</strong> <strong>the</strong> 2001 field survey data to calculate<strong>the</strong> change in area from 2001-2003.Data AnalysesData were subjected to a variety <strong>of</strong> quality assurancemethods (Zaremba et al. 2004). Cross-tabulation <strong>of</strong>categorical names was done to check for typographicalerrors and duplications. Summary statistics were <strong>the</strong>ncalculated for quantitative variables to check forunreasonable ranges and outliers. Descriptive statistics werecalculated and raw data transformed as needed to meetrequirements <strong>of</strong> parametric statistical tests.We tested <strong>the</strong> hypo<strong>the</strong>sis that <strong>the</strong>re was an increase inarea covered by non-native Spartina using a t-test betweenarea covered in 2001 and 2003. The hypo<strong>the</strong>sis that aparticular species, site type or bay region (latitude) had aninfluence on <strong>the</strong> change in area covered between 2001 and2003 was tested with an Analysis <strong>of</strong> Variance (ANOVA).We tested <strong>the</strong> hypo<strong>the</strong>sis that site latitude had a significanteffect on change in area covered between 2001 and 2003 byusing an Analysis <strong>of</strong> Covariance (ANCOVA). The accuracy<strong>of</strong> field identification <strong>of</strong> S. alterniflora, S. foliosa and <strong>the</strong>irhybrids was tested statistically with a Chi-square test <strong>of</strong>frequencies <strong>of</strong> correct field identification <strong>of</strong> S. alterniflora,S. alterniflora hybrids, and S. foliosa. This test used <strong>the</strong>genetic analysis as <strong>the</strong> true (or <strong>the</strong>oretically expected)frequencies and <strong>the</strong> field observations as <strong>the</strong> observedfrequencies.Based on data averaged over all species and all sitessampled, <strong>the</strong> non-native species and hybrids <strong>of</strong> Spartinaincreased 244% in area covered (paired sample t-test, p =0.003) between 2001 and 2003 (Table 2). Field surveys(field measurement plus estimates) showed an increase <strong>of</strong>non-native Spartina <strong>of</strong> 15% in <strong>the</strong> North Bay, 292% in <strong>the</strong>Central Bay and 177% in <strong>the</strong> South Bay from 2001 to 2003.These measurements showed that non-native Spartina (allspecies) increased from 2001-2003 by 172% at Type I sites(tidal, micro-tidal, and formerly diked bayland, and backbarrier marsh), by 504% at Type II sites (fringing tidalmarsh, mud flats and estuarine beaches), by 108% at TypeIII sites (major tidal sloughs, creeks or flood controlchannels), and by 169% at Type IV sites (urbanized rock,riprap, dock, ramp, marina).S. patens occurred at only one site in <strong>the</strong> North Bay, aSite Type I. It decreased in area covered by 84%.S. densiflora decreased in nearly as many sites (3) as itincreased (4). Statistical tests were precluded for S.densiflora because <strong>of</strong> low sample sizes but <strong>the</strong> averagepercent change in area covered was 53% with a range from-94% to +219%. Spartina densiflora was mapped at onlyone sample location in <strong>the</strong> North Bay (Pt. Pinole), where itincreased by 114%. Spartina densiflora increased by 43% in<strong>the</strong> Central Bay. Spartina densiflora increased in Type I andType III sites but apparently decreased slightly at Type IIsites. No S. densiflora were noted at Type IV sites.Hybrids make up most <strong>of</strong> <strong>the</strong> non-native coverage and<strong>the</strong>ir proportion among <strong>the</strong> non-natives increased in 2003compared to 2001 accounting for 83% <strong>of</strong> <strong>the</strong> non-nativecoverage in 2001 and increasing to 90% <strong>of</strong> non-nativecordgrasses in 2003. Hybrids increased in cover three-foldbetween 2001 and 2003 (paired sample t-test, p < 0.001)with a range from -90% to +2175% depending on site.Hybrids increased in area covered in 19 <strong>of</strong> 23 marshessampled, a statistically significant proportion <strong>of</strong> <strong>the</strong> sites(non-parametric sign test, p = 0.003).Hybrids in <strong>the</strong> South Bay were responsible for <strong>the</strong> 177%increase in non-native invasive Spartina between 2001-2003. Hybrids increased by 403% in <strong>the</strong> Central Bay.Hybrids were not found in any sample sites <strong>of</strong> <strong>the</strong> NorthBay. Hybrids had higher mean and total area covered in <strong>the</strong>Central Bay than in <strong>the</strong> South Bay in both 2001 and 2003.The slight trend <strong>of</strong> percent change in hybrid area coveredwith latitude (south-to-north trend) was not statisticallysignificant (p = 0.18).While hybrid acreage increased greatly from 2001 to2003 across all site types, site types I and II had higherpercent increases, on average, than site types III and IV(non-parametric sign test; p = 0.254). Analysis <strong>of</strong> <strong>the</strong> areacovered by hybrids (log-transformed square meters) in 2003found no statistical difference among site types (ANOVA,p = 0.377).Aerial Photos versus Field MeasurementsThe estimates <strong>of</strong> <strong>the</strong> area covered by non-nativeSpartina hybrids differed between <strong>the</strong> aerial photo-77-