Comparing convenience and probability sampling for urban ecology applications

Abstract

Urban forest ecosystems confer multiple ecosystem services. There is therefore a need to quantify ecological characteristics in terms of community structure and composition so that benefits can be better understood in ecosystem service models. Efficient sampling and monitoring methods are crucial in this process. Full tree inventories are scarce due to time and financial constraints, thus a variety of sampling methods exist. Modern vegetation surveys increasingly use a stratified‐random plot‐based sampling to reduce the bias associated with convenience sampling, even though the latter can save time and increase species richness scores. The urban landscape, with a high degree of conspecific clustering and high species diversity, provides a unique biogeographical case for comparing these two methodological approaches. We use two spatially extensive convenience samples of the urban forest of Meran (Italy), and compare the community structure, tree characteristics and ecosystem service provision with 200 random circular plots. The convenience sampling resulted in a higher species diversity, incorporating more rare species. This is a result of covering more area per unit sampling time. Pseudorandom subplots were compared to the random plots revealing similar Shannon diversity and sampling comparability indices. Measured tree variables (diameter at breast height, height, tree‐crown width, height to crown base) were similar between the two methods, as were ecosystem service model outputs. Synthesis and applications. Our results suggest that convenience sampling may be a time and money saving alternative to random sampling as long as stratification by land‐use type is incorporated into the design. The higher species richness can potentially improve the accuracy of urban ecological models, which rely on species‐specific functional traits.

Assessing methods for comparing species diversity from disparate data sources: the case of urban and peri‐urban forests

“…Plot-based sampling requires different methods from those of individual-based protocols (sensu Gotelli and Colwell 2001), as plots involve samples of multiple, grouped individuals as replicates, rather than single individuals (Speak et al 2018). Plot-based sampling requires different methods from those of individual-based protocols (sensu Gotelli and Colwell 2001), as plots involve samples of multiple, grouped individuals as replicates, rather than single individuals (Speak et al 2018).…”

“…(Further information about the study sites can be found in Table 1 of Blood et al 2016. This field plot measurement and sampling protocol is increasingly being used in cities outside the United States as model input models to estimate urban forest structure and ecosystem services (Yang et al 2017, Speak et al 2018). Other measurements included height, land use, crown width, crown light exposure, and tree location within plot.…”

“…Similarly, over the last decade, local-level data are being increasingly collected in urban forests across the world using standardized protocols, allowing researchers to address regional-, national-, and continental-level applied urban ecology questions, such as those comparing species diversity and distributions (Kendal et al 2014, Staudhammer et al 2015, Jenerette et al 2016, Yang et al 2017, Speak et al 2018). Similarly, over the last decade, local-level data are being increasingly collected in urban forests across the world using standardized protocols, allowing researchers to address regional-, national-, and continental-level applied urban ecology questions, such as those comparing species diversity and distributions (Kendal et al 2014, Staudhammer et al 2015, Jenerette et al 2016, Yang et al 2017, Speak et al 2018).…”

“…We can test hypotheses about the homogenization of species composition (Pearse et al 2018) or the abundance and occurrence of invasive species across urban-to-rural gradients (Staudhammer et al 2015). This type of data is key in estimating and modeling the supply of ecosystem services from urban and peri-urban forests (PF; Nowak et al 2008, Speak et al 2018. This type of data is key in estimating and modeling the supply of ecosystem services from urban and peri-urban forests (PF; Nowak et al 2008, Speak et al 2018.…”

“…Still, questions remain about how forest dynamics in rural contexts compare to those of urban environments (Blood et al 2016). Also, further information is needed on how the increasing use of available plot-level data in both rural and urban forests can be used to address questions regarding ecological disturbance, functionality, and homogenization (Staudhammer et al 2015, Speak et al 2018. Such studies of tree and plant diversity among and within forested ecosystems can help characterize differences and similarities in communities across different disturbance regimes and scales (Yang et al 2017).…”