Documenting effects of urbanization on flora using herbarium records

Abstract

Summary 1.As human populations increasingly live in cities, urban floras and the ecosystem services they provide are under increasing threat. Understanding the effects of urbanization on plants can help to predict future changes and identify ways to preserve biological diversity. Relatively few studies document changes through time in the flora of a focal region and those that do primarily address European floras. They often rely on contemporary spatial gradient studies as surrogates for changes with time. 2. We compare historical species records (prior to 1940) with the current flora for Marion County, Indiana, USA, home to Indianapolis, the 13th largest city in the United States. Specimens from the Friesner Herbarium of Butler University and other vouchered records for the county provided the basis for historical records. Current records are derived from inventories of 16 sites conducted by Herbarium staff and other botanists over the past 15 years. 3. Physiognomic group, wetland classification and nativity (native vs. non-native) were determined for each species. Fidelity to high-quality habitat was quantified using coefficients of conservatism (C-values). 4. The last 70 years have seen a significant turnover in species presence, most notably a decrease in native plant species number (2.4 per year) and quality, with an accompanying increase in non-native plants of 1.4 per year. Loss of species has been non-random, with a disproportionate number of high-quality wetland plants lost. The signature of past land use can be seen in physiognomic changes in the composition of the flora that reflect the shift from agriculture to urban ⁄ suburban land use. 5. Many invasive non-native shrubs now present have escaped from cultivation, highlighting the combined threats of habitat conversion and human plant preference to native flora in cities. These invasives likely present the greatest threat to remaining biodiversity. 6. Synthesis. This study demonstrates the value well-documented historical records, such as those housed in herbaria, can have in addressing current ecological issues.

Living More Than Just Enough for the City: Persistence of High-Quality Vegetation in Natural Areas in an Urban Setting

“…This is the case for each of the three sites in our study where these species were found. In contrast, previous studies have documented the disproportionate extirpation of high-quality species from wetlands over the last 70 years in Marion County due to land conversion [39].…”

“…The most commonly encountered, Asian honeysuckle species in the genus Lonicera, are the subject of costly eradication efforts. They, and several other of the woody invasive species identified in our studies, were intentionally planted by the Indianapolis Parks Department in the early part of the twentieth century along boulevards throughout the city [39]. Asian bush honeysuckles are found primarily along the margins of woods in the Midwestern United States, but can spread into deeper cover.…”

Decline in lichen biodiversity on oak trunks due to urbanization

“…Numerous studies have investigated how a spatial gradient from rural, suburban to urban areas affects the diversity and abundance of organisms. Most studies have concluded that the number of species and their abundance generally decreases with increasing urbanization (Mercado Cárdenas and Buddle ), but there are exceptions particularly when invasive species (Dolan et al ) and generalist species (Magura et al , Tóthmérész et al ) are involved. The same reduction in species and their abundance toward the city centre can also be observed in temporal studies.…”

Community Involvement to Address a Long-standing Invasive Species Problem: Aspects of Civic Ecology in Practice

“…Amur bush honeysuckles and other shrubs escaped from the ornamental horticultural trade are the largest physiognomic group among invasive non-native plants appearing in the flora growing outside of cultivation in Indianapolis over the last 70 years (Dolan et al 2011). This phenomenon is likely occurring in many cities and is underappreciated.…”