title: An Evaluation of Plotless Sampling Using Vegetation Simulations and Field Data from a Mangrove Forest.
abstract: In vegetation science and forest management, tree density is often used as a variable. To determine the value of this variable, reliable field methods are necessary. When vegetation is sparse or not easily accessible, the use of sample plots is not feasible in the field. Therefore, plotless methods, like the Point Centred Quarter Method, are often used as an alternative. In this study we investigate the accuracy of different plotless sampling methods. To this end, tree densities of a mangrove forest were determined and compared with estimates provided by several plotless methods. None of these methods proved accurate across all field sites with mean underestimations up to 97% and mean overestimations up to 53% in the field. Applying the methods to different vegetation patterns shows that when random spatial distributions were used the true density was included within the 95% confidence limits of all the plotless methods tested. It was also found that, besides aggregation and regularity, density trends often found in mangroves contribute to the unreliability. This outcome raises questions about the use of plotless sampling in forest monitoring and management, as well as for estimates of density-based carbon sequestration. We give recommendations to minimize errors in vegetation surveys and recommendations for further in-depth research.
authors.affiliation: Laboratory of Plant Biology and Nature Management, Vrije Universiteit Brussel, Brussels, Belgium ; Plant Production Systems, Wageningen University and Research Centre, Wageningen, The Netherlands.
authors.forename: Renske
authors.initials: R
authors.lastname: Hijbeek
authors.forename: Nico
authors.initials: N
authors.lastname: Koedam
authors.forename: Md Nabiul Islam
authors.initials: MN
authors.lastname: Khan
authors.forename: James Gitundu
authors.initials: JG
authors.lastname: Kairo
authors.forename: Johan
authors.initials: J
authors.lastname: Schoukens
authors.forename: Farid
authors.initials: F
authors.lastname: Dahdouh-Guebas
mesh_terms: D018533:Biomass; D003198:Computer Simulation; D004784:Environmental Monitoring / Q000379:methods*; D065928:Forests; D007630:Kenya; D012984:Software; D014197:Trees; D053833:Wetlands