View source for Special topics

Vegetation and Soils Methods

Vegetation controls for and influences elevation and is one of the main structural components of vertebrate habitat. The composition and condition of the vegetative community influences the spatial distribution and use by wildlife.  Colonization and establishment of marsh vegetation are reliant on the underlying sediment characteristics, elevation, and water quality (e.g. salinity) of the site.  Estimating the salinity regime can be as critical as elevation in predicting the colonization of tidal marsh species after restoration.  Common vegetation monitoring parameters include relative dominance and percent cover, frequency estimates of species, delineation by aerial sampling, inundation regimes, salinity profiles and primary productivity.  Most of these parameters relate to species richness and diversity as well as structural aspects of vegetation (cover, heterogeneity, etc).  Only productivity addresses the functional ability of vegetation to support faunal trophic levels including the vertebrates that make up the conservation target of river delta restoration (Birds, Salmon) and the species they prey on (macroinvertebrates).  Primary productivity may involve destructive and/or non-destructive sampling and the merits of these approaches warrants further study.    
Relative Dominance Estimate (Ocular)
A range of factors strongly affects the effective measurement of relative dominance.  Reliance on ocular cover estimates can be inaccurate compared to frequency measurement, yet allow for very rapid description of a large number of species.  The size, shape, and stratification of sampling quadrats in relation to vegetation patchiness very strongly affects the between sample variation, and thus the statistical error when you attempt to compare means.  As there is known variation across elevation, failure to stratify by elevation introduces unnecessary error into means.  Estimates need not be made for all species depending on the hypothesis being tested.
Relative dominance estimates should reference the following decisions:
Stratify by standard inundation regime zones
Define quadrat shape and size in response to observed patchiness, and species area curves
Justify the level taxa groupings appropriate for the study

Frequency Estimate
Switching from ocular cover estimates to frequency can increase accuracy and  precision where target species are not too rare.  
Vegetation delineation (remote sensing)
Physiognomic patches can be detected using high resolution aerial photography.
Use a maximum pixel dimension of ## when delineating.
Patches of discrete vegetation can be delineated using aerial photography 

Inundation regime estimation 
Typically elevation is used as a surrogate for inundation regime in its effect tidal marsh ecosystems, however tidal range and mean high water varies among sites.  An objective measure of inundation regime is necessary for comparison among sites.  While field measurement can use absolute measures, a site specific conversion process must be developed to translate elevation into comparable units among sites.  Typically a percent of time inundated curve is used.  However plant physiological response is to redox levels and oxygen deficit, and sensitivity to inundation varies over time.  We propose a maximum inundation duration during spring as the best available surrogate for inundation effect on plants. 
Soil condition (i.e., soil texture, organic matter content, biochemistry and nutrient availability) are also key determinants of vegetative growth and habitat quality.  How long marsh soils take to recharge after agricultural use has ceased is a key question regarding the success of vegetation colonization in addition to looking at salinity and elevation.  Soil particle size is a key variable in sediment transport.  Techniques include measuring the rate and character of soil development using cores, pore-water salinity and texture analysis.  Cores involve lab analysis which focus on percent sand, silt, and clay or particle size fractionations, soil organic matter content, and nutrient availability.