Post-industrial brownfields with spontaneous vegetation often remain in early successional stages for decades longer than non-contaminated sites. Previous work comparing abandoned industrial and agricultural lands in New Jersey found no difference in species richness or diversity between brownfields and old fields, but did find old fields had higher cover of native forbs while brownfields had higher percent cover of native grasses. Differences between old-field and brownfield plant communities may be due to environmental filtering in brownfields for stress-tolerant adaptations specific to certain phylogenetic groups, resulting in lower phylogenetic diversity in brownfields. To investigate this possibility, we made phylogenetic trees for six brownfields and seven old fields using the R package brranching and calculated the phylogenetic diversity metrics for each community using the R package picante. We calculated two-way analyses of variance (ANOVA) to compare the main effects of site type and season and the interaction effect between site type and season on each phylogenetic diversity metric. We conducted a cluster analysis to determine which sites group together based on phylogenetic similarity. We additionally examined relationships between phylogenetic diversity metrics and time since site abandonment.
Results/Conclusions
Analyses found no evidence for lower phylogenetic diversity overall in brownfields but suggested that younger brownfields have lower phylogenetic diversity, possibly due to environmental filtering. A two-way ANOVA of Faith’s Phylogenetic Diversity (Faith’s PD) found season to be significant (p<0.001) but not site type or the interaction effect. Faith’s PD was highest for old fields in spring, while brownfields had high Faith’s PD values in both spring and summer. Abundance-weighted mean pairwise phylogenetic difference (MPD) and standardized effect size of MPD (SESMPD) varied less than Faith’s PD between site types and across seasons. None of the main effects were found to be significant in either ANOVA of MPD or SESMPD. Cluster analysis of phylogenetic distance matrices did not group brownfield and old-field communities separately. In old fields, all measures of phylogenetic diversity had either no trend or a negative correlation with site age, while all measures of phylogenetic diversity were positively correlated with site age in brownfields. Recently abandoned brownfields have the highest levels of stress from contamination and poor soil quality. Older brownfields may be able to support higher phylogenetic diversity due to diminishing stress over time through build up of organic matter.