PROPOSAL

COMMUNITY CHARACTERIZATION AND DISTURBANCE EFFECTS
ON
WETLAND COMMUNITIES IN
EVERGLADES NATIONAL PARK;
UNDERSTANDING DISTURBANCE
AND WETLANDS RESTORATION
IN THE HOLE-IN-THE-DONUT

WILLIAM J. PLATT

LOUISIANA STATE UNIVERSITY

February 1996

INTRODUCTION

The current pineland studies involve primarily demographics of pine trees and larger shrubs in the understory. Little research has been focused on the herbaceous understory and the associated communities within the pineland proper and the adjacent prairies. This is a critical community, especially since Hurricane Andrew virtually eliminated all pinelands outside Everglades National Park. Understanding the ecology and importance of the understory and how the communities change in relation to natural and anthropogenic disturbance is key to ensure the survival of the pineland communities as a whole. Therefore, the pineland research program is being modified to cover the herbaceous understory elements in addition to the pines and shrubs. This modification is a logical extension and continuation of the existing research. This work is being conducted in conjunction with the need to understand restoration success and potential for the communities in and around Long Pine Key area in relation to the restoration project now underway in the Hole-in-the-Donut (HID). An understanding of the communities and their ecological interactions with one another and abiotic factors influencing them is key to understanding management of the pine-wetland habitats, and successful restoration of the HID which is surrounded by and was formerly pine-wetland habitat.

The only portion of the Miami Rock Ridge that survives as an intact landscape is that portion located inside Everglades National Park (ENP). Nonetheless, that part of the Miami Rock Ridge inside ENP has been subjected to a variety of disturbances both anthropogenic and natural. Most anthropogenic alterations have occurred during the first part o f the twentieth century. Changes in hydroperiods and fire regimes, as well as logging and mechanized agriculture, and exotic pest plants, all have resulted in a landscape very different from that present prior to 1900.

These anthropogenic actions differ in their impacts on the natural communities of the Miami Rock Ridge area and interact with natural disturbances in a mostly unknown way. Natural and most human disturbances constitute relatively minor disruptions. Alterations of hydroperiods and fire regimes produced changes in vegetation; logging removed slash pines, but reseeding occurred. Because the indigenous species are still present and the physical environment was not disrupted, restoration of more natural conditions (e.g. hydroperiods, fire regimes) are likely to induce responses resulting in shifts towards states closer to those that occurred during presettlement times.

Mechanized agriculture (in the region of the Hole-in-the-Donut, hereafter HID), has produced much more pronounced environmental changes. Almost all traces of original habitats have been removed. Pine savanna and short-hydroperiod prairie vegetation were almost completely removed. Natural features of the substrate (rock ridge limestone and its topographic gradient) were removed by rock plowing and a much more level deep fine rubble was created. Nutrients were added by fertilization. Following cessation of agriculture, no changes were made in the substrate; exotics invaded and now are a major threat to surrounding natural communities. Small-scale environmental changes have not changed exotic-dominated communities. Larger-scale manipulations appear to be required to change ecological systems in the HID.

Proposed manipulations of the HID need to be based in some sort of theoretical framework for prediction (and testing) the consequences of manipulations. In many cases where human manipulations have resulted in complete removal of all vegetation and major changes in the environment and/or substrate, primary succession has been used as a theoretical framework to predict the outcome of restoration. Succession theory is based on two important concepts. Disturbance drives the system away from equilibrium (climax states), but there always is a tendency for the system to return toward some equilibrium. Interactions among species are postulated to be the primary driving force inducing changes in the various stages and resulting in shifts toward climax equilibrium conditions.

In autogenic succession models seral pathways are proposed in which successive stages of development are influenced by processes (primarily interactions among species) that lead to changes from pioneer toward climax conditions. Initially, there is an unmanipulated site that has been transformed by anthropogenic disruption. This site is manipulated in some way (presumably to create a substrate suitable for primary succession). The manipulated site is characterized by certain initial conditions (including both the environment and any remaining biota). Recovery of remnant biota and immigration of other biota (both native and exotic species) into the manipulated site occur over time following the manipulations. Initial assemblages of pioneer species form, affected by the filters of the manipulations and post-manipulation environmental conditions. Following colonization, populations are affected by stochastic events and variability in the physical environment as they increase in size on the site. Pioneer communities and ecosystems form with development of trophic webs and energy flow and nutrient cycling. Local allogenically-driven variation in communities and ecosystems may develop as a result of temporal and spatial heterogeneity combined with the prior processes. Interactions occur among species in relation to environmental conditions and may require long periods of time for complete expression (i.e., to reach a "climax " stage). Changes may also occur within the different communities/ecosystems on sites as a function of "natural" processes such as recurrent natural disturbances and environmental changes.

Succession models have not proven very effective in guiding restoration. Starting with de nova conditions most commonly results in a long period of single-species dominance (often by non- indigenous species). The suggestion is that environmental conditions are created that favor certain species, and these species are not readily replaced (Connell & Slayter's inhibition model of succession). Certain species also may change the environment in ways not favoring indigenous species (e.g., nitrogen-fixing species in habitats with low N content of soils).

An alternative model for restoration is based on evolutionary adaptation of species for certain ranges of environmental conditions. The effectiveness of restoration is postulated to depend on the ability to create conditions for which indigenous species are adapted (and thus favored over nonadapted species). Severely altered habitats are predicted to have to be manipulated in ways that result in environmental characteristics similar to those in unaltered habitats containing the indigenous species. What are those environmental conditions of importance of the indigenous species? non-indigenous species? How critical are those local environmental conditions (how broad are the ranges of environmental variation tolerated by the desired and non-desired species)? Given that basic environmental conditions are suitable, indigenous species are predicted to colonize a site, become established, and persist over time even if non- indigenous species also invade the site. Will changes over time in populations and communities resemble those predicted to occur as a result of natural processes and disturbances? Will species interact in ways that resemble those interactions occurring in natural communities? Manipulations needed to effect restoration become definable once characteristics of natural systems important to indigenous species are known.


Proposed Research

A general research strategy for a five year period involves two complementary components:

  1. quantitative descriptions of the relationships between environmental characteristics and vegetation; and

  2. experimental manipulations of disturbances within ranges of environmental characteristics delineated from field study to explore responses of indigenous species.

Quantitative data are needed to relate patterns of species distributions to environmental variation. The first goal for the next few years is to characterize the among and within site variations for the Miami Rock Ridge region of ENP. There are many different sites within ENP that can serve as models - each is unique physiographically. Measurement of the landscape-level variation among sites will provide one crucial component of the range of environmental characteristics. Within sites, ranges of environmental conditions should be described to provide the additional crucial local components of environmental variation. The second goal for the next five years is to characterize patterns of distribution of species relative to ranges of environmental variation among and within sites in the Miami Rock Ridge region of ENP.. Are species associated with site-level characteristics? or with within-site level characteristics? or both? How broadly/narrowly distributed are species relative to the total range of environmental characteristics among and within sites?

Analytical techniques involved are descriptive in nature. The data collected can be used to develop quantitative descriptions of environmental level characteristics. Species area curves can be used to describe scale of biodiversity. Dominance-diversity curves can be used to describe relationships between numbers of species and their relative abundances. Vertical structure can be described through delineation of strata within sites. These (and other) measurements can be compared within and among sites via multivariate/ANOVA designs and parametric/nonparametric analyses. Quantitative association of site characteristics with species distributions also can be obtained using multivariate (ordination and PCA) techniques.

Experimental manipulations of disturbances within ranges of environmental characteristics delineated from field study are needed to explore responses of indigenous species to environmental changes. The effects of natural disturbances (flooding, drought, fires, etc.) on vegetation need to be studied within the context of environmental variation. How do natural disturbances alter species composition,structure, and dynamics? Is there differential mortality? What are patterns of change after disturbances have occurred? Is there differential growth? reproduction? Do communities tend to return to the pre-disturbance state over time or are effects of disturbances to shift systems toward different states? Creation of experimental disturbances that mimic natural disturbances can be used to explore those characteristics of disturbances and of environments that are important in determining vegetation patterns in the landscape. Fundamental characteristics of disturbances and/or sites can be manipulated. Responses of species to different experimental disturbances can provide insights into those characteristics of disturbances and of sites important for the indigenous species.

Those specific research projects planned as part of a five year program are focused on understanding vegetation patterns and dynamics in the natural savanna communities in the Miami Rock Ridge region of ENP.

The first project is a characterization of savanna habitats in the Miami Rock Ridge region of ENP. A minimum of 24 study sites will be selected to encompass the range of geographic variation from the easternmost Pine Island area around the entrance station) to the westernmost Mahogany Hammock region. The range of sites selected will enable among area variation to be characterized. Four sites will be in the Pine Island region. Twelve sites will be in the Long Pine Key region. Four sites will be in the Pines West region. Four sites will be in the Mahogany Hammock region.

For each study site, within site variation will be characterized. Three primary characteristics of environmental variation will be examined for each study area. Elevation & topographic changes will be characterized and related to hydrology, perhaps in conjunction with someone interested in surficial flow and hydrology. Characteristics of the limestone substrate will be delineated, hopefully in collaboration with a geologist/soil scientist. The characteristics of soils (location, depth, characteristics) will be explored also, again hopefully in conjunction with a soils scientist and someone interested in soil nutrients. Other characteristics of the environment may emerge over time as the studies progress.

The ground cover vegetation will be described in large plots (20 x 50m) located at different elevations along transects within each study area. The species composition and species-area relationships will be compiled using nested plots within the large tenth-hectare plots. The vertical structure of the vegetation will be described using randomly located small plots (inside the large plot) within which vegetation heights are measured periodically. The spatial heterogeneity of vegetation will be described by relating small- scale variations in elevations and soil characteristics to vegetation patterns with the large tenth-hectare plots. Community characteristics (dominance-diversity relationships) will be described using frequencies of occurrence within nested plots within the large plots. The dynamics of dominant species will be described, hopefully in conjunction with a population biologist.

The second project is examining the responses of vegetation to disturbances. The effects of large-scale disturbances, in the form of fires, will be studied using twelve LPK plots. The plots will encompass a range from pine savannas to short-hydroperiod prairies in fire blocks that experience different fire regimes. Half the plots are burned during wet years and half are burned during dry years. Half of the plots are burned early in the wet season and half are burned later in the wet season.

Measurements of vegetation will be made in study areas experiencing different fire regimes. Ground cover vegetation will be characterized periodically to asses any changes resulting from fires. Dominant species will be studied. The dynamics of slash pines will be studied using large 4 ha plots in which all trees are marked and mapped. Growth, mortality and recruitment will be studied as a function of the fire regime. The dynamics of the dominant species in the ground cover, especially grasses and shrubs, also will be studied as a function of the dire regimes (again, hopefully in conjunction with a population biologist).

The community dynamics following creation of localized disturbances in the ground cover also will be studied within the context of the fire regimes already established on LPK. Study areas within each of the fire blocks will be selected that encompass a range from pine savannas to short-hydroperiod prairies. Half the plots are burned during wet years and half are burned during dry years. Half of the plots are burned early in the wet season and half are burned later in wet season. Within small plots (1m2 and 4m2) vegetation will be characterized and then subjected to experimental treatments: control - no manipulation, hot fires, soil removal, hot fires + soil removal. These plots will be followed over time to describe the colonization process, the origin of colonists, and the dynamics of reformation of the ground cover.

All of the results of these quantitative descriptive studies and of the field experiments will hopefully be used to develop conceptual and predictive models, hopefully in conjunction with others working on soils, nutrient relationships, population biology, etc.


Relationships between environmental characteristics and vegetation of the Miami Rock Ridge region of Everglades National Park

The patterns of distribution of species in nature are related to characteristics of the environment. The goal of our study is to characterize the relationships between the among and within site variation in environmental characteristics and vegetation that occurs in the Miami Rock Ridge region of ENP. There are many different rock ridge sites within ENP; each is somewhat unique physiographically and may have some distinct elements of vegetation. Measurement of the landscape-level variation among sites will provide one crucial component useful in relating environmental characteristics to vegetation. Within sites, local patterns also will provide components useful in relating environmental characteristic to vegetation.

We will be collecting data that will be used to describe quantitatively relationships between environmental characteristics and vegetation. Most of these data will be independent of specific species. For example, species area curves will be used to describe the scale of biodiversity; is most diversity local or regional? Dominance-diversity curves will be used to describe relationships between numbers of species and their relative abundances. Do only a few species dominate a particular community? Or are there several species that share dominance? How many rare species are there? Do the numbers of rare species vary among and within community types? Vertical structure can be described through delineation of strata within sites. What is the diversity of heights of vegetation?

These (and other) measurements can be compared within and among sites using fairly complicated statistical analyses. Quantitative association of site characteristics with species distributions also can be obtained using multivariate (ordination and PCA) techniques. For the purposes of our study, it is important that the quantitative data be collected carefully.

A minimum of 24 study sites will be selected to encompass the range of geographic variation from the easternmost Pine Island area (around the entrance station) to the westernmost Mahogany Hammock region. The range of sites selected will enable among area variation to be characterized. Four sites will be in the Pine Island region. Twelve sites (one in each fire block) will be int he Long Pine Key region. Four sites each will be in the Pines West and Mahogany Hammock regions.

Within each site, one transect will be established in the field. Along this transect, at different elevations, large plots (20 x 50m) will be established. Three primary characteristics of environmental variation will be examined for each study area using these plots. Elevation & topographic changes will be characterized (as among plot variable) and related to hydrology. Characteristics of the limestone substrate and soils (location, depth, characteristics) will be explored (as among plot variables) also. Other characteristics of the environment may emerge over time as the studies progress.

The ground cover vegetation will be described in the large plots. The species composition and species- area relationships will be compiled using nested plots within the large tenth-hectare plots. The vertical structure of the vegetation will be described using randomly located small plots (inside the large plot) within which vegetation heights are measured periodically. The spatial heterogeneity of vegetation will be described by relating small-scale variations in elevation, substrate, and soil characteristics to vegetation patterns with the large tenth-hectare plots. Community characteristics (dominance-diversity relationships) will be described using frequencies of occurrence within nested plots within the large plots.


PLOT ESTABLISHMENT

Transects have already been established using the theodolite in three locations: Blocks D, I, and H-J. These transects run form glades into adjacent pinelands. Each transect was established to run somewhat perpendicular to the glades, and thus maximal changes in elevation occur along the transect. These transects run between 400 and 600 m in length. There will be a number of plots along each transect. The locations of plots will be determined by changes in elevation and the need for replicated plots within ranges of elevation. Each plot will have a unique code, which will consist of the Block number and the order of that plot relative to the plot in the center of the glades (which will be assigned number 1). Thus, in I, there will be plots I1-1, I1-2, ...

The theodolite will be used to re-establish the transect line. There are already permanent pieces of rebar marking the transect (every 100-200m). The theodolite will be set up over one of the pieces of rebar, and the prisms will be placed at the next closest rebar to sigh the line. Then, points along the line will be chose to be corner of plots.

Each plot will be 20 x 50m. In all our samples, the 20m side will run a long the transect, so that the long axis of the plot will be perpendicular to the transect. Thus the plot will tend to be oriented so that elevation differences are minimal. The location of the plot relative to the transect will be constrained by the need to have general elevations within plots as similar as possible. Therefore, it one side of the transect is more level than the other, use that side. If the two sides are simil;ar in general elevation, then the side is to be chose randomly.

The plot is subdivided into ten 10 x 10m, modules. Four of the ten modules in the plot will be used for what is called intensive measurement. These four modules forma block in the center of the plot (i.e., they can not be ont he ends the plot). The other six modules will be used for what is called releve measurements.

Corners of modules within plots will be marked in the field with 18 pieces of 3/8 inch rebar and plastic PVC pipe to cover the rebar. A piece of rebar is anchored in the ground at a designated location along the transect. We will (hopefully) use a portable drill to open the limestone for each piece of rebar. All holes need to be drilled as vertically as possible, so that the rebar and plastic pipe are vertical. If a tree is located exactly at the corner of a module, place the rebar and pole as close as possible to the correct point.

The points surveyed along the transects will become the " occupied points ", whose X nd Y coordinates are entered as a set number (either 0,0 or 20,0). These points become corners of the plot. initially the three module corners along the transect line will be established (o,o; 10,0; 20,0). All other corners within plots will then be mapped relative to the occupied points. All corners (except the occupied point) are located by "shooting the prisms" until the exact location is obtained (i.e. from 0,0 we would should 0,10; 0,20; 0,30;...20,50). It is important to have the corners placed as precisely as possible, so that modules are exactly 10.00 x 10.00 m. When shooting the module corners for final positions, z coordinates should be obtained relative to the occupied point (which is set at z = 0). When all 18 points are located, do not shut down the theodolite. it will be used to measure submodules also.

Each plot will have the same map coordinates and mudle names. These are designed to make filed orientation to the plot as easy as possible. For convention, we will always designate X as the direction along the transect and Y will be the direction perpendicular to the transect. The values of X will increase in the upslope direction (away from the center of glades) and the values of Y will increase away from the transect. Thus, a given coordinate can be easily located in the field. The coordinates of the poles will be written on them in black magic marker so that it is easy to locate plots. Modules are to be referred to by the smallest values of X and Y on the corners of the modules. Thus modules are 0,0; 0,10;0,20;0,30;0,40;10,0;10,10; 10,20; 10,30; 10,40. (Note that the plot coordinates and module numbers are the same in each plot. Therefore, it will be important that all data sheets used have the unique plot number entered.)

The 0,0 location of each plot will eventually be referenced using GPS and also for absolute elevation. it is important to measure the elevations of each 0,0 point relative to the 0,0 points in adjacent plots. Thus, relative elevations will be known and this will minimize later work of referencing plots.


SUBPLOTS WITHIN THE FOUR INTENSIVE MODULES

The four subplots that will be used for intensive measurements have to be selected as one of two combinations. They will be either 0,10; 0,20; 10,10; 10,20; or 0,20; 0,30; 10,20; 10,30. These will be selected randomly. Within each of the four intensive modules, submodules will be established. Two corners are randomly selected from each of the four modules. Using the theodolite, two points are measured that are 3.16m from each corner along the module borders, and a third is measured as 3.16m from both borders. The direction of measurement will depend on which module is involved. A piece of rebar is inserted at each point. In the example below, the module is 0,10. The three points surveyed from that corner are 0,13.16; 3.16.10; and 3.16,13.16. A second submodule will be established within the first, starting at the same corner. It will be 1.00 x 1.00 m. In the example used above (module 0,10), the coordinates would be 0,11; 1,10; and 1,11.

It is important to minimize stepping on the vegetation in the submodules. Please work outside these as much as possible. Under no circumstances should 1 x 1 m submodules be entered while establishing the plot. if the vegetation is too trampled in the submodules, they will have to be redone.

The smaller submodules, 0.32 x 0.32 m and 0.10 x 0.10 m will hot have rebar marking the corners. We will sample those subplots using a frame that is placed over the rebar at the corners of the 1 x 1 m submodule.

Note that within each plot there will be eight submodules of 3.16 x 3.16m, and eight submodules of 1.00 x 1.00 m. Each of these submodules will require three pieces of rebar, for a total of 48 pieces of rebar (in addition to the 18 required to set up the plot). This means that a total of 66 pieces of rebar will be in place for each plot. Only the corners of modules need to have permanent plastic PVC pipe, however. When sampling, PVC can be used to cover the corners of the 3.16 x 3.16 m submodule to keep track of location and removed when sampling is completed.


This document was provided by Dr. William J. Platt, and was prepared for the Everglades Digital Library by:
Project Director
Everglades Information Network & Digital Library
Florida International University Libraries