**Ecological Land Units: Supplementary metadata for ELU30 raster data**

**Background**

Conservation planning at any scale---regional, landscape level, or
local---requires an understanding of patterns of environmental variation
and biological diversity. This dataset was developed as a tool for
assessing the biophysical character of landscapes, and for mapping the
distribution and composition of community assemblages across those
landscapes. Informed decisions on where to focus conservation efforts
require such tools.

Data on biological distributions are very often inadequate to a
large-scale analysis of biodiversity. The close relationship of the
physical environment to ecological process and biotic distributions
underpins the ecological sciences, and in the absence of suitable
biological datasets, conservation science has recognized that physical
diversity could be an acceptable surrogate for biological diversity.
Research has repeatedly demonstrated especially strong links between
ecosystem pattern and process and climate, bedrock, soils, and
topography. This recognition led to the development of the ecological
land unit, or ELU.

The ELU is a composite of several layers of abiotic information:
elevation, bedrock geology, distribution of deep glacial sediments that
mask bedrock's geochemical effects, moisture availability, and landform.
An ELU grid of 30 meter cells was developed for the Lower New
England-Northern Piedmont (LNE) and North Atlantic Coast (NAC)
ecoregions. The ELU dataset describes the "ecological potential" of the
landscape, but carries no information about actual landuse or landcover
in a region where human alterations to the landscape have everywhere
affected the natural vegetation. The current dataset informs ELUs with
landcover data, bringing them to earth by telling us what is actually on
the ground. We may use this dataset to map ecological systems, which are
dynamic assemblages of communities that occur in a mosaic on the
landscape, and that are linked by shared ecological processes and
environmental gradients. A brief discussion of each of the layers of
information built into the current dataset follows.

**Dataset content and development**

[Elevation classes]{.underline}

Elevation has been shown to be a powerful predictor of the distribution
of forest communities in the Northeast. Temperature, precipitation, and
exposure commonly vary with changing altitude. We broke continuous
elevation data for the LNE and NAC ecoregions (from the National
Elevation Dataset of the USGS) into discrete elevation classes with
relevance to the distribution of forest types region-wide. Meaningful
biotic zones would be defined with quite different elevation cut-offs in
the northern and southern parts of the region, so class ranges
necessarily approximate critical ecological values.

Table 1. Ranges for elevation classes.

  ------------ --------------------- -----------------------------------------
  *Elevzone*   *M (ft)*              *Characteristic forest type*

  1000/2000    0-6 & 6-234 (0-20 &   Oak, pine-oak, pine-hemlock, maritime
               20-800)               spruce, floodplain forest

  3000         234-533 (800-1700)    Hemlock-N. hardwoods, N. hardwoods,
                                     lowland spruce-fir

  4000         533-762 (1700-2500)   Northern hardwoods, spruce-hardwoods

  5000         762-1158 (2500-4000)  Krummholz, montane spruce-fir, alpine
                                     communities
  ------------ --------------------- -----------------------------------------

[Bedrock geology and deep sediments]{.underline}

Bedrock geology strongly influences area soil and water chemistry. Even
in glaciated landscapes, studies suggest that soil parent material is
commonly of local origin, rarely being ice-transported more that a few
miles from its source. Bedrock types also differ in how they weather and
in the physical characteristics of the residual soil type. Because of
this, local lithology is usually the principle determinant of soil
chemistry, texture, and nutrient availability. Many ecological community
types are closely related to the chemistry and drainage of the soils or
are associated with particular bedrock exposures.

We grouped bedrock units on the bedrock geology maps of ME, NH, VT, MA,
CT, RI, NY, PA, NJ, and MD into seven general classes (Table 2). We
based our scheme on broad classification schemes developed by other
investigators which emphasize chemistry and texture, and on bedrock
settings that are important to many ecological communities, particularly
to herbaceous associations. Please refer to another file accompanying
this metadata, bedgeo_src.doc, for information on bedrock geology source
materials.

In some settings deep sediments of glacial origin mantle the bedrock.
The consolidated bedrock of valleys of pro-glacial lakes, for example,
may lie under many meters of fine lacustrine sediments, and deep coarse
deltaic or outwash deposits often overlay the bedrock in pine barrens
and sand plains in the northeast. In these settings it is the nature of
the sediments---their texture, compactness, and moisture-holding
capacity, their nutrient availability, their ability to anchor overstory
trees in a wind disturbance\--that is ecologically relevant, and not the
nature of the underlying bedrock. We used a USGS dataset of sediments of
the glaciated northeast to identify such places. The USGS map was
compiled at a coarse scale (1:1,000,000), but we made the data a little
"smarter" by informing it with our landform map (please see the document
on landforms that accompanies this metadata). Our landform layer was
compiled at a much finer scale (the scale of the digital elevation
models from which they were shaped, 1:24,000), and we allowed the deep
coarse or fine sediments of the USGS dataset to be mapped only on those
landforms on which they would naturally be expected to occur. In the
case of sandy, coarse sediments, this would be in broad basin and
valley/toe slope settings; in the case of fine clayey lacustrine or
marine sediments, in these same settings, plus low hills and lower
sideslopes. The

seven bedrock classes were numbered 100 through 700 (Table 2), and the
coarse and fine sediments classes were numbered 800 and 900,
respectively.

Table 2. Bedrock geology classes.

+---------------+------------+---------+----------------+------------+
| *Geology      | *L         | *Met    | *Comments*     | *Some      |
| class*        | ithotypes* | a-equiv |                | char       |
|               |            | alents* |                | acteristic |
|               |            |         |                | co         |
|               |            |         |                | mmunities* |
+---------------+------------+---------+----------------+------------+
| 100: ACIDIC   | Mudstone,  | (Low    | Low to         | Many: low- |
| SEDIMENTARY / | claystone, | grade:) | moderately     | and        |
| MET           | siltstone, | slates, | resistant      | mid        |
| ASEDIMENTARY: | n          | phy     | rocks typical  | -elevation |
| fine- to      | on-fissile | llites, | of valleys and | matrix     |
| co            | shale,     | p       | lowlands with  | forests,   |
| arse-grained, | sandstone, | elites; | subdued        | fl         |
| acidic        | con        | (Mod    | topography;    | oodplains, |
| sed/metased   | glomerate, | grade:) | pure sandstone | oak-pine   |
| rock          | breccia,   | s       | and            | forest,    |
|               | greywacke, | chists, | meta-sediments | deciduous  |
|               | arenites   | pelitic | are more       | swamps and |
|               |            | s       | resistant and  | marshes    |
|               |            | chists, | may form low   |            |
|               |            | gr      | to moderate    |            |
|               |            | anofels | hills or       |            |
|               |            |         | ridges         |            |
+---------------+------------+---------+----------------+------------+
| 200: ACIDIC   | Fissile    |         | Low            | Shale      |
| SHALE:        | shales     |         | resistance;    | cliff and  |
| Fine-grained  |            |         | produces       | talus,     |
| acidic        |            |         | unstable       | shale      |
| sedimentary   |            |         | slopes of fine | barrens    |
| rock with     |            |         | talus          |            |
| fissile       |            |         |                |            |
| texture       |            |         |                |            |
+---------------+------------+---------+----------------+------------+
|               |            |         |                |            |
+---------------+------------+---------+----------------+------------+
| 300:          | Limestone, | Marble  | Lowlands and   | Rich fens  |
| CALCAREOUS    | dolomite,  |         | depressions,   | and        |
| SEDIMENTARY / | dolostone, |         | stream/river   | wetlands,  |
| META          | other      |         | channels,      | rich       |
| -SEDIMENTARY: | carb       |         | ponds/lakes,   | woodlands, |
| ba            | onate-rich |         | groundwater    | rich cove  |
| sic/alkaline, | clastic    |         | discharge      | forests,   |
| soft          | rocks      |         | areas; soils   | cedar      |
| sed/metased   |            |         | are thin       | swamps,    |
| rock with     |            |         | alkaline       | alkaline   |
| high calcium  |            |         | clays, high    | cliffs     |
| content       |            |         | calcium, low   |            |
|               |            |         | potassium;     |            |
|               |            |         | rock is very   |            |
|               |            |         | susceptible to |            |
|               |            |         | chemical       |            |
|               |            |         | weathering;    |            |
|               |            |         | often          |            |
|               |            |         | underlies      |            |
|               |            |         | prime          |            |
|               |            |         | agricultural   |            |
|               |            |         | areas          |            |
+---------------+------------+---------+----------------+------------+
|               |            |         |                |            |
+---------------+------------+---------+----------------+------------+
| 400:          | Calc       | Lightly | Variable group | Rich       |
| MODERATELY    | shales,    | to mod. | depending on   | coves,     |
| CALCAREOUS    | calc       | metamo  | lithology but  | in         |
| SEDIMENTARY / | pelites    | rphosed | generally      | termediate |
| METASED:      | and        |         | susceptible to | fens       |
| Neutral to    | s          | calc    | chemical       |            |
| basic,        | iltstones, | pelites | weathering;    |            |
| moderately    | calc       | and     | soft shales    |            |
| soft          | sandstones | quar    | often underlie |            |
| sed/metased   |            | tzites, | agricultural   |            |
| rock with     |            | calc    | areas          |            |
| some calcium  |            | schists |                |            |
| but less so   |            | and     |                |            |
| than above    |            | phy     |                |            |
|               |            | llites, |                |            |
|               |            | calc-s  |                |            |
|               |            | ilicate |                |            |
|               |            | gr      |                |            |
|               |            | anofels |                |            |
+---------------+------------+---------+----------------+------------+
|               |            |         |                |            |
+---------------+------------+---------+----------------+------------+
| 500: ACIDIC   | Granite,   | G       | Resistant,     | Many:      |
| GRANITIC:     | gra        | ranitic | quartz-rich    | matrix     |
| Quartz-rich,  | nodiorite, | gneiss, | rock,          | forest,    |
| resistant     | rhyolite,  | charno  | underlies mts  | high       |
| acidic        | felsite,   | ckites, | and poorly     | elevation  |
| igneous and   | pegmatite  | migm    | drained        | types,     |
| high grade    |            | atites, | depressions;   | bogs and   |
| met           |            | qu      | uplands &      | peatlands  |
| a-sedimentary |            | artzose | highlands may  |            |
| rock;         |            | gneiss, | have little    |            |
| weathers to   |            | qua     | internal       |            |
| thin coarse   |            | rtzite, | relief and     |            |
| soils         |            | quartz  | steep slopes   |            |
|               |            | gr      | along borders; |            |
|               |            | anofels | generally      |            |
|               |            |         | sandy          |            |
|               |            |         | nutrient-poor  |            |
|               |            |         | soils          |            |
+---------------+------------+---------+----------------+------------+
|               |            |         |                |            |
+---------------+------------+---------+----------------+------------+
| 600: MAFIC /  | (Ul        | Gree    | Moderately     | Traprock   |
| INTERMEDIATE  | trabasic:) | nstone, | resistant;     | ridges,    |
| GRANITIC:     | a          | amphib  | thin, rocky,   | greenstone |
| quartz-poor   | northosite | olites, | clay soils, sl | glades,    |
| alkaline to   | (Basic:)   | epid    | acidic to sl   | alpine     |
| slightly      | gabbro,    | iorite, | basic, high in | areas in   |
| acidic rock,  | diabase,   | gra     | magnesium, low | A          |
| weathers to   | basalt     | nulite, | in potassium;  | dirondacks |
| clays         | (Int       | bos     | moderate hills |            |
|               | ermediate, | tonite, | or rolling     |            |
|               | qua        | e       | topography,    |            |
|               | rtz-poor:) | ssexite | uplands and    |            |
|               | diorite/   |         | lowlands,      |            |
|               | andesite,  |         | depending on   |            |
|               | syenite/   |         | adjacent       |            |
|               | trachyte   |         | lithologies;   |            |
|               |            |         | quartz- poor   |            |
|               |            |         | plutonic rocks |            |
|               |            |         | weather to     |            |
|               |            |         | thin clay      |            |
|               |            |         | soils with     |            |
|               |            |         | topographic    |            |
|               |            |         | expressions    |            |
|               |            |         | more like      |            |
|               |            |         | granite        |            |
+---------------+------------+---------+----------------+------------+
|               |            |         |                |            |
+---------------+------------+---------+----------------+------------+
| 700:          | S          |         | Thin rocky     | Serpentine |
| ULTRAMAFIC:   | erpentine, |         | iron-rich      | barrens    |
| m             | soapstone, |         | soils may be   |            |
| agnesium-rich | py         |         | toxic to many  |            |
| alkaline rock | roxenites, |         | species, high  |            |
|               | dunites,   |         | magnesium to   |            |
|               | pe         |         | calcium ratios |            |
|               | ridotites, |         | often contain  |            |
|               | talc       |         | endemic flora  |            |
|               | schists    |         | favoring high  |            |
|               |            |         | magnesium, low |            |
|               |            |         | potassium,     |            |
|               |            |         | alkaline       |            |
|               |            |         | soils; upland  |            |
|               |            |         | hills, knobs   |            |
|               |            |         | or ridges      |            |
+---------------+------------+---------+----------------+------------+

[Landforms: Please see accompanying document]{.underline} IN PREPARATION

[The ELU grid]{.underline}

With the elevation, substrate, and landform layers, all the elements for
assembling ecological land units, or ELUs, are in place. ELU code values
for each cell in the region-wide grid are simply the summed class values
for elevation zone, substrate, and landform for that cell. For example,
a cell in a wet flat (landform 31) at 1400 feet (elevation class 2000)
on granitic bedrock (substrate class 500) would be coded 2531.

**ELU_code = Elev class (ft) + Substrate class + Landform**

1000 (0-800) 100 Acidic sed/metased 4 Steep slope

2000 (800-1700) 200 Acidic shale 5 Cliff

3000 (1700-2500) 300 Calc sed/metased 11 Flat summit/ridgetop

4000 (2500-4000) 400 Mod. calc sed/metased 13 Slope crest

500 Acidic granitic 21 Hilltop (flat)

600 Mafic/intermed granitic 22 Hill (gentle slope)

700 Ultramafic 23 N-facing sideslope

800 Coarse sediments 24 S-facing sideslope

900 Fine sediments 30 Dry flat

31 Wet flat

32 Valley/toe slope

41 Flat at bottom of steep slope

43 N-facing cove/draw

44 S-facing cove/draw

51 River

52 Lake/pond/reservoir

Waterbodies from the National Hydrography Dataset (NHD), which was
compiled at a scale of 1:100,000 and is available for the whole region,
were incorporated into the landform layer (landform codes 51 and 52).
Single-line stream and river arcs from the NHD were not burned into the
landforms\-- only those river reaches that are mapped as polygons.

The ELU grid for the Lower New England/Northern Piedmont and North
Atlantic Coast Ecoregions comprises 503 unique combinations of elevation
zone, substrate type, and landform. We added an "ELU_color" item to the
attribute table, and used it to construct a coding scheme that assigns
ELU values to groups of a particular ecological character. Symbolizing
on the ELU_color item creates a simplified display of the complex ELU
dataset (see "Displaying the data" below). A fragment of the attribute
table for the two-ecoregion ELU grid is reproduced in Table 3.

Table 3. Sample set of three ecological land unit codes ("value" item)
from the ELU value

attribute table for the LNE and NAC ecoregions.

**Displaying the data**

Several Arcview legends are included with the dataset. They may be used
to symbolize separate components of ELUs: elevation zone (elevzone.avl),
substrate (substrate.avl), landform (landform30.avl), and ELUs
(elu30.avl). It should be noted that, because of the complexity of the
ELU dataset (503 unique values), elu30.avl groups ELUs and simplifies
their display. Bedrock classes are not broken out for display on the
steeper and "small patch" landforms, but are in the broader areas of
flats and low hills. The color tones in these broad areas correspond to
bedrock types and can be read as a backdrop, a visual context for
smaller ELU occurrences associated with more dramatic topography. ELU
map reading takes practice.