Estimates of biodiversity are sensitive to different sampling methods. Much research has tested how different ecological plot designs affect patterns of plant richness. However, no published comparison of methods used by botanical collectors and ecologists exists. Botanical collectors employ a random walk approach to generate exhaustive species lists of plants occurring in an area. Ecologists often test hypotheses by subsampling the “universe” of plant species in relationship to an environmental gradient. Ecologists also estimate species abundances, generating information about ecosystem integrity that critically complements richness. Richness documents variation in species identity, while abundance reveals which species drive ecosystem processes. We expect that botanical surveys capture more species than ecological transects, although the magnitude of potential differences is unknown. It also remains uncertain whether divergent richness estimates differentially shape interpretation about ecological conditions. Further, because botanical surveys are not paired with ecological transects, exhaustive documentation of species richness is rarely contextualized by which species are most abundant. To address these gaps, we sampled plant richness (botanical random walk and ecological transects) and abundance (transects only) along a 66-mile recreational greenway in Colorado, USA. We compared richness estimates of the two approaches and evaluated whether differences in richness led to different ecological interpretations. We further evaluated species abundance to better contextualize findings associated with richness.
Results/Conclusions
The botanical survey captured 433 species, while the ecological transects captured 116. This discrepancy reflects that the botanical survey captured both abundant and uncommon species, while the transects captured predominantly abundant species. Across the entire greenway, the botanical (53%) and ecological (43%) approaches estimated similar proportions of native species, providing a comparable ecological interpretation. When partitioning richness across habitat types, the richness estimates more strongly diverged. Ecological transects more severely underestimated species richness, and overestimated the proportion of introduced species, in habitat types of smaller areal extent (i.e., with less replication). However, abundance estimates provided critical context to patterns of richness, revealing that three species of introduced grasses comprised ~50% of the plant cover. Thus, while the botanical approach best captured the full range of species present, the ecological approach highlighted which species are likely to drive ecosystem processes associated with biological invasions. These findings highlight the complementary nature of the two approaches for describing different dimensions of ecosystem integrity.