## Supplementary metadata for the ELU30 raster dataset

**Background**

An understanding of patterns of environmental variation and biological
diversity is fundamental to conservation planning at any
scale---regional, landscape level, or local. 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. A second dataset (a "systems" grid) was developed that
informs ELUs with landcover data, bringing them to earth by telling us
what is actually on the ground in a region where human alterations to
the landscape have everywhere affected the natural vegetation. The ELU
dataset itself carries no information about actual landuse or landcover,
however. A brief discussion of each of the layers of information built
into the ELUs 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 NAP ecoregion (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         0 - 234 (0-800)  Oak, pine-oak, pine-hemlock, maritime spruce,
                                floodplain forest

  2000         234 - 533        Hemlock-northern hardwoods, N. hardwoods,
               (800-1700)       lowland spruce-fir

  3000         533 - 762        Northern hardwoods, spruce-hardwoods
               (1700-2500)      

  4000         762 - 1158       Spruce-fir, spruce-hardwoods
               (2500-4000)      

  5000         \> 1158 (\>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 soil or
are associated with particular bedrock exposures.

We grouped bedrock units on the bedrock geology maps of NY, VT, NH, and
ME 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 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 \[incomplete\]]{.underline}

[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

4000 (\> 4000) 500 acidic granitic 21 Hilltop (flat)

600 mafic/intermed granitic 22 Hill (gentle slope)

700 ultramafic 23 NW-facing sideslope

800 coarse sediments 24 SE-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

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 Northern Appalachians and Boreal Forest Ecoregion
comprises 497 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.

**Data structure: the attribute table**

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

attribute table for the NAP ecoregion.

**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 (497 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.