Nested versus non-nested characterization of vegetation
composition and species richness at multiple spatial scales
Wentworth, T.R., White, P.S., Wheeler, B.E., Taverna, K., Kuppinger,D.,
Jacobs, L.A., Fridley, J.D., Amanda Senft and Peet, R.K.
1. Introduction
1. The importance of characterizing species richness and composition of
vegetation at multiple spatial scales is increasingly recognized by
ecologists, but there is no consensus as to whether variation with scale is
best characterized by subplots arranged in a design that is nested or nonnested. Many crucial aspects of biodiversity management and research
may depend on this design choice.
2. Description of the Stholgren and PEL methods?
3. We compared nested and non-nested designs for characterizing species
richness (as species-area and species-accumulation curves) of vascular
plants using data collected by the Carolina Vegetation Survey in 0.04 ha
2. Theory & Background

What are the major goals of applying methods that capture multi-scale
composition? Community characterization? Richness? Species area?

Do we wish to address pragmatic issues such as efficiency of collecting
the data?

Description of the Stholgren and PEL methods?

The fundamental difference between these designs is in how they are
influenced by spatial autocorrelation structure and in how well they allow
characterization of change in vegetation structure with change in grain of
observation.

The critique that nested designs are statistically inappropriate is bogus
and stems Misunderstand of which values are compared.

Question of replication and the confounding of grain and extent? With
Stohlgren the replication is not meaningful because it draws on the same
dataset.
Methods.

The Wentworth dataset which allows a comparison of the two methods.
Hypotheses, Analyses & Results
1. Species-accumulation curves will differ between the two strategies. The
difference in area between the two curves might provide an interesting
metric of spatial autocorrelation structure. BROOKE WILL ATTACK.
2. Accumulating species with area is the same as a SPARC for nested data,
but is quite different than a SPARC for non-nested data.
3. "Waviness" in the SPARC will exist for the non-nested curve. Occasionally,
a non-nested SPARC will have segments with negative slope because it's
possible to go from a very rich, small-scale plot in a particular module to a
species-poor, larger-scale plot in another module. TOM CONSULTS
4. Only with the species accumulation curve does a non-nested approach
make sense, because it can almost certainly better predict 400m2 and
1000m2 richness. Perhaps we should examine how much better an
accumulation curve predicts 400m2 and 1000m2 richness? We also
explore the complex question of which strategy allows more effective
extrapolation of richness to larger spatial extent. MEETING SCHEDULED.
5. For a given species the probability of encountering in the sample
increases with size, number, and dispersion of the subplots, and with the
density and dispersion of the plants.
Discussion

If the goal is to provide a strategy to inventory all species in a large plot,
neither method presents a clear advantage.

Although either method can be used to examine species-area
relationships, the nested design constrains the result to the desired
monotonic response for each replicate.

Non-nested designs are superior when the goal is to find as many species
as possible within a specific subsample of a larger target area.

Only nested subplots are appropriate if the goal is to assess changes in
species composition with changing grain size of observation, because
non-nested plots confound the influence of grain with that of extent.
(Stohlgren-like methods inflate the middle values). Nested designs offer a
means to interpret underlying spatial patterns of richness that non-nested
designs do not.
Conclusions
We conclude that nested designs are equivalent or superior for most applications
and should be the standard method for multi-scale inventories.
Literature cited
Barnett, D.T. & T.J. Stohlgren. 2003. A nested-intensity design for surveying
plant diversity. Biodiversity and Conservation 12:255-278.
Palmer, M. & White, P.S. 1994.
Peet, R.K., Wentworth, T.R. & White, P.S. 1998. A flexible, multipurpose method
for recording vegetation composition and structure. Castanea 63:262-274.
Rosenzweig
Stohlgren, T.J., Falkner, M.B., & Schell, L.D. 1995. A modified-Whittaker mested
vegetation sampling method. Vegetatio 117:113-121.