A Conservation Vision for Maine Using Ecological Land Units
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The pace and scale of Maine's land conservation projects have grown dramatically in recent years, with more than 1.5 million acres protected in the last decade. While conservation strategies have been guided by the current condition of forests and wetlands, less attention has been directed to protecting the "enduring features" of landform, geology, and elevation. By incorporating patterns of these enduring features, depicted as Ecological Land Units (ELUs), into conservation planning, we can more fully account for the variability inherent in the underlying landscape and the biodiversity it supports.
This project explores the relationship between Maine's biotic landscape, in the form of natural communities, and the physical landscape, in form of ELUs. It also examines how well natural communities and ELUs are represented in Maine's current conservation lands. Specifically, this project has three objectives:
- Assess the current representation of Ecological Land Units (abiotic factors) and natural communities (biotic factors) on conserved land in Maine, including Maine's Ecological Reserves.
- Identify landscape features (both biotic and abiotic) in Maine that are under-represented on Maine's protected lands.
- Investigate relationships between ELUs and natural communities, and test the utility of ELUs for identifying and predicting natural communities.
While 15% of Maine's lands are in some form of conservation (ownership or easement), only 3% are restricted from timber harvesting. Our results indicate that viable examples of 79 of the state's 98 natural community types (81%) are represented on conserved lands that have been set aside from timber harvesting. Of the nineteen types not represented, twelve are rare (i.e., ranked S1, S2, or S3), and only two are forested (Balsam Poplar Floodplain Forest and Hardwood Seepage Forest).
Natural community representation is poorer when geographic representation is considered. Dividing the state into seven geographic "sections," only 31% of the natural community types are represented on lands restricted from timber harvesting. Not surprisingly, portions of the state with the largest amount of conservation land, such as northwest Maine, have the best representation of natural communities. Conversely, regions with comparatively less conservation land, such as the Aroostook Hills and Lowlands, Eastern Lowlands, and South Coastal and Southern Interior sections, have poorer protection of natural communities.
Representation of ELUs may be assessed through individual ELUs or ELU groups (ELUs clustered into more broadly defined units). Representation of ELUs and ELU groups is higher statewide than representation of natural communities. Of the 368 ELUs found across Maine, 336 (91%) are represented on conservation land as a whole, and 294 (80%) are represented on the subset of conserved land that is restricted from timber harvesting. Within each of Maine's seven geographic sections, an average of 41% of the ELU types are captured within the subset of conservation lands restricted from timber harvesting.
Each of Maine's 25 ELU groups are represented on conservation lands statewide, and conservation lands within each of the state's seven geographic sections contain an average of 78% of the ELU groups known to occur in those respective regions. Most ELU groups that are inadequately represented on conservation lands are rare in each geographic section and account for less than 1% of each section's landscape.
In comparison to natural communities, the higher representation of ELUs and ELU groups on conservation land may be explained by at least two factors. First, natural community representation is limited by the incompleteness of our inventory efforts; ELU data, in contrast, is available as a "wall to wall" coverage of the state. Moreover, our analysis of ELU representation considers only presence/absence and relative proportions, while natural community representation includes considerations of minimum size and condition (i.e., viability or ecological integrity).
The ELU components of geology, slope, and landform may be highly effective at predicting natural community occurrence on the landscape. Using over 1,000 mapped natural communities, ELU components predicted the correct natural communities more than 80% of the time. The success of ELU groups at predicting natural communities varied by group. In a case study of the Bigelow Reserve, the "Alpine" ELU group was mapped with the appropriate natural communities 96% of the time, but the correlation between other ELU groups and natural communities at Bigelow was not as strong, in part due to issues of scale. Most of the "Acidic Cliff/Outcrop/Talus" ELU group, for example, is mapped as Fir - Heartleaf Birch Sub-alpine Forest, likely because the acidic cliffs portrayed by ELU groups occur at too fine a scale to be depicted on natural community maps derived from air photos.
The results of this study indicate that ELUs may serve several important roles in conservation planning:
- Identifying specific areas of the state that could fill ecological gaps in the state's portfolio of conservation lands, such as the Aroostook Hills and Lowlands, Eastern Lowlands, and South Coastal Plain.
- Serving as an effective surrogate for approximating natural community diversity in cases where natural community information is lacking; and
- Incorporating a representative diversity of enduring features and conserving their associated biodiversity over the long term.
The creation and application of ELUs are relatively recent additions to the state's conservation toolbox. Additional work would be useful at improving the utility of ELUs for the purposes noted above. Some of these "next steps" are noted below:
- Natural community representation on conservation lands is limited by the incompleteness of natural community data. MNAP efforts to complete an initial broad-brush inventory of the state are currently scheduled to finish within the next five years, but this effort is contingent on funding.
- This type of analysis points to the need for a complete, unified, accessible database of conservation lands in the state. Currently this information is held by numerous parties with no protocol for acquiring or sharing data.
- Minimum area thresholds are needed to approximate the size required for an ELU or ELU group to support viable natural communities. This minimum area would relate to the natural patch size (small patch, large patch, matrix) of the ELUs or ELU groups and associated natural communities.
- Further work is needed to describe, quantify, and map larger landscape units (i.e. at the scale of township or larger) that capture specific repeated patterns and orientations of ELUs and ELU groups.