Conservation Investment for Rare Plants in Urban Environments

Abstract

Budgets for species conservation limit actions. Expending resources in areas of high human density is costly and generally considered less likely to succeed. Yet, coastal California contains both a large fraction of narrowly endemic at-risk plant species as well as the state's three largest metropolitan regions. Hence understanding the capacity to protect species along the highly urbanized coast is a conservation priority. We examine at-risk plant populations along California's coastline from San Diego to north of San Francisco to better understand whether there is a relationship between human population density and: i) performance of at-risk plant populations; and ii) conservation spending. Answering these questions can help focus appropriate strategic conservation investment. Rare plant performance was measured using the annualized growth rate estimate between census periods using the California Natural Diversity Database. Human density was estimated using Census Bureau statistics from the year 2000. We found strong evidence for a lack of a relationship between human population density and plant population performance in California's coastal counties. Analyzing US Endangered Species expenditure reports, we found large differences in expenditures among counties, with plants in San Diego County receiving much higher expenditures than other locations. We found a slight positive relationship between expenditures on behalf of endangered species and human density. Together these data support the argument that conservation efforts by protecting habitats within urban environments are not less likely to be successful than in rural areas. Expenditures on behalf of federally listed endangered and threatened plants do not appear to be related to proximity to human populations. Given the evidence of sufficient performance in urban environments, along with a high potential to leverage public support for nature in urban environments, expenditures in these areas appear to be an appropriate use of conservation funds.

Plant population success across urban ecosystems: A framework to inform biodiversity conservation in cities

“…This confirms previous studies (e.g. Aronson et al., ; Ramalho & Hobbs, ; Schwartz et al., ) and takes two steps forward by quantifying the relative importance of natural remnants in comparison to other types of urban ecosystems and by considering the population status of all plant species that occur at a given time across different ecosystem types.…”

“…Indeed, many urban studies: measure species numbers without considering differences or changes in plant species’ population status (i.e. established vs. casual populations; Shwartz et al., ), employ biodiversity measures related to all plant species in total (or to all native species) without accounting specifically for rare or threatened species (Shwartz et al., ), analyse biodiversity patterns at larger spatial scales without untangling the specific contribution of different urban ecosystems within land use mosaics (Schwartz, Smith, & Steel, ), or do not consider urban land use history as an important predictor of biodiversity (Ramalho & Hobbs, ). …”

“…While there is broad evidence that various groups of species can colonise urban ecosystems by dispersal, the ability to cross the next barrier, the reproduction threshold, has not been quantified systematically for larger sets of plant species (Shwartz et al., ; but see Lawson, Lamar, & Schwartz, ; Schwartz et al., )—although this barrier is crucial for biodiversity conservation. The dispersal and reproduction barriers that species have to negotiate are relevant for all anthropogenic ecosystems.…”

“…(or to all native species) without accounting specifically for rare or threatened species (Shwartz et al, 2014), 3. analyse biodiversity patterns at larger spatial scales without untangling the specific contribution of different urban ecosystems within land use mosaics (Schwartz, Smith, & Steel, 2013), or 4. do not consider urban land use history as an important predictor of biodiversity (Ramalho & Hobbs, 2012).…”

“…The reproduction barrier is key for long-term population establishment in all ecosystem types. Some species, having overcome the survival but not the reproduction barriers, occur with casual populations both in natural remnants and in anthropogenic ecosystems [Colour figure can be viewed at wileyonlinelibrary.com] systematically for larger sets of plant species (Shwartz et al, 2014; but see Lawson, Lamar, & Schwartz, 2008;Schwartz et al, 2013)although this barrier is crucial for biodiversity conservation. The dispersal and reproduction barriers that species have to negotiate are relevant for all anthropogenic ecosystems.…”