Northeast Regional Blanding’s Turtle Conservation Plan
PART II. SITE DELINEATION AND RANKING
Updated May 28, 2014
______________________________________________________________________________
Summary. This document provides an overview of the preliminary site delineation and site ranking criteria for Blanding’s
turtle populations in the Northeastern United States.
______________________________________________________________________________
Site Delineation
This document outlines the NEBTWG approach for delineating Blanding’s turtle sites as well as ranking and
prioritizing them across the region in the context of the Northeast Blanding’s Turtle Conservation Planning
process. The sites described in this document are meant to represent a relatively closed population, and
correspond to an element occurrence (EO) as defined by NatureServe. While animals may leave the “site”
during their lifetimes, most animals will remain within the site boundaries throughout an entire year.
NatureServe (2006) uses the following description:
“Generally, a principal EO corresponds to a population or metapopulation. Principal EOs are typically
separated from each other by barriers to movement or dispersal, or by specific distances defined for each
Element across either unsuitable habitat, or suitable but apparently unoccupied habitat.”
To delineate sites, we mapped in accordance with criteria outlined by NatureServe, and in a manner
compatible with mapping already in use by the five states in the region. Where states differ, we used the most
commonly used criteria. Here we outline mapping specifications.
Separation Distance
NatureServe suggests that separation distance should be specified in the following way:
“In addition to barriers that totally, or almost completely, prevent movement and/or dispersal distances
of intervening area that restrict movement may also separate EOs. These distances are used to delineate
the population units between which gene flow is significantly reduced. For comparison, IUCN (1996)
characterizes reduced gene flow between units as “typically one successful migrant individual or gamete
per year or less”. For most species, data from gene flow studies does not exist; thus, decisions on
separation distances should be made on the basis of best information available. Also, consideration of
gene flow is not applicable to Elements that disperse widely (e.g., birds, wind-dispersed plants or insects),
Elements having very long generation times (e.g., giant tortoises, plants characterized by long-term seed
banking or dormancy, persisting clones), or Elements that are dependent on rare but recurrent
phenomena for dispersal (e.g., floods, major storms).”
For Blanding’s turtle, NatureServe suggests the following distances:
“Continuous riverine-riparian corridors, 10 km; mosaics of aquatic-wetland and undeveloped upland
habitat, 10 km; continuous, undeveloped upland habitat lacking aquatic or wetland habitat, 5 km; upland
habitat with significant but not intense development (e.g., scattered buildings in otherwise “natural”
habitat), 2 km. Other separation distances may be used when adequate site-specific data indicate that
these separation distances are inappropriate for a particular population. Any such deviations should be
explained in the element occurrence record.”
We used a ‘buffer’ distance around each observation of 1300 m, a distance currently in use by Massachusetts
and New Hampshire. This distance was based on observed movement distances by Blanding’s turtle in the
Northeast. This distance may also be increased based on local habitat characteristics (e.g., wetland availability
outside the buffer distances). The 1300 m buffer distance represents a separation distance of 2600 m, a
distance between the 2 km distance suggested by NatureServe when mapping “upland habitat with significant
but not intense development (e.g., scattered buildings in otherwise ‘natural’ habitat)”, which best describes
most sites within the Northeast region, and the 5 km distance to use when mapping “continuous,
undeveloped upland habitat lacking aquatic or wetland habitat”.
We propose prioritizing sites for 2013 sampling where the selected buffer distance (of 1300 m or more) does
not adequately encompass habitat, so that we can better delineate the extent of these populations. We will reevaluate these separation distances after 2013 sampling is complete.
Barriers
Regarding barriers to movements, NatureServe suggests that:
“For species, barriers are those that almost completely prevent movement or dispersal of the Element,
thereby obstructing or severely limiting gene flow. These barriers are usually abrupt, and may be relatively
narrow. Typical instances of barriers for a given species should be specified in the EO specifications for
that Element (e.g., four-lane divided highways may limit bog turtle movement; dams exceeding 3½
meters [approximately 20 feet] in height may restrict movement of salmon; large rivers may limit small
mammal movement; deserts may curtail movement of montane insects; tidal inlets greater than a certain
width may be a barrier for beach plants).”
For Blanding’s turtle, NatureServe defines a barrier as:
“A busy highway or highway with obstructions such that turtles rarely if ever cross successfully;
untraversable topography (e.g., cliff); densely urbanized area lacking aquatic or wetland habitat.”
We propose splitting sites by high intensity development as defined by the 2006 NLCD and major and
secondary roads, defined in the TIGER roads database. Secondary roads in the Tiger database are numbered
U.S. and state highways, which typically have >1000 cars per day in our region. These are the same classes
currently used by New Hampshire to separate EOs, and Massachusetts uses similar classification in their
state-wide roads database. These road types were scored 4.5 and 3.65 (out of 5) as barriers to movement in
the 12/2011 EMBL expert poll. Many respondents noted that these should be seen as filters rather than
barriers since animals are able to cross, allowing genetic connectivity between sites separated by them, but
mortality is high enough that the sites on opposite sides of such roads should be generally regarded
separately. This characterization is consistent with NatureServe guidelines. Macro-sites that will be treated as
single management units will be used to connect sites on opposite sides of such large roads. Many expert poll
respondents also noted that local roads and development act as less severe filters (i.e., causing mortality, but
not acting as a barrier). In the poll, they were scored as less of a barrier (local road: 2.35; development: 2.6-3.5
out of 5), and therefore local roads and low to moderate intensity development are allowed within the site
boundaries.
Process
The delineation process is as follows:
1. All EO source points and polygons (including historical data) are combined with the new data
points from 2012 sampling.
2. Each observation is then buffered by 1300m, and overlapping polygons are merged together.
3. The resulting polygons are cut by primary and secondary roads from 2011 Tiger Roads data and
high intensity development as defined by the 2006 NLCD.
4. Medium, and low density development from the 2006 NLCD are removed from the site area
calculations, but these cover classes do not divide a site.
Quality Ranks
NatureServe uses the following criteria to assign Quality Ranks to Element Occurrences:
EO Rank Description:
A=
excellent estimated viability
B=
good estimated viability
C=
fair estimated viability
D=
poor estimated viability
E=
verified extant (viability not assessed)
H=
historical
F=
failed to find
X=
extirpated
Massachusetts has adopted these criteria, with more specific criteria for Blanding’s turtle:
A=
Excellent estimated viability. Known or suspected to have relatively large populations and known
nesting activity. Excellent wetland quality and upland habitat with light impact by humans (i.e.,
development, roads, and fragmentation)
B=
Good estimated viability. Known populations that may not be likely to persist over the long-term,
but are still a potentially viable population. An intermediate to moderate level of human impact.
C=
Fair estimated viability. Only single individuals observed (adults or juveniles); unknown breeding
activity at site, possibly not a viable population over the long-term. A moderate to heavy level of
human impact.
D=
Poor estimated viability. Population has high potential for extinction due to heavy human impacts.
Like Massachusetts, we propose to use NatureServe methodology (i.e., size, condition, and landscape context)
to rank populations throughout the Northeast. To do this, we will continue to modify and utilize the Generic
Guidelines for the Application of Occurrence Ranks and the Key for Ranking Species Element Occurrences Using the Generic
Approach developed by NatureServe (2008):
http://www.natureserve.org/explorer/eorankguide.htm#Generic ,
http://www.natureserve.org/explorer/keyforgenericeoranking.pdf
Identifying Conservation Priorities
We propose using a hierarchical metric structure to rank sites as conservation priorities across the Northeast.
We propose 8 broad classes of metrics that will each be ranked relative to one another by an expert survey
conducted in November 2012. Each of the 8 metrics are made up of a combination of sub-metrics (many of
which are correlated, but measure slightly different site characteristics) that were ranked relative to the other
sub-metrics in that same class. In this way, correlated metrics do not have undue influence on the final
ranking metric.
The following metrics were used, in the following classes:
Class I. Site size:
- Total undeveloped area within the site boundaries (using NLCD 2006)
Class II. Within site fragmentation:
% of total site area that is medium or low intensity development (2006 NLCD. Note, the high
intensity development was already removed from the site area).
% of impervious surface cover (calculated as the sum of the NLCD impervious surface cover cells
within the site, divided by the total site area).
Road density within site (calculated as the linear distance of primary, secondary, and local roads
within the site divided by total site area).
Class III. Habitat abundance and quality within site:
Wetland area within the site (calculated as the total area sum of “Palustrine Emergent”, “Palustrine
Scrub Shrub” and “Palustrine Unconsolidated Bottom” wetland types from NWI within the site).
Wetland diversity (Simpson’s diversity index applied to the 3 NWI wetland types described above,
note that wetland classification using NWI has relatively low accuracy). [12/2012 Note: the NWI
does not accurately distinguish among types throughout the region, so this metric was dropped from
the analysis. We are investigating the use of TNC’s Ecological Systems Map for this purpose instead.]
- Sum of HRC values (habitat suitability values) of all cells within the site from B. Compton’s 2007
Blanding’s turtle habitat model (Note: where not available, this sub-metric will be excluded from the
analysis).
Class IV. Surrounding landscape context:
Distance to next nearest site
Fragmentation of surrounding landscape (5km buffer around site, not including the site area itself):
% of 5 km landscape that is developed (2006 NLCD)
% impervious surface cover within 5km surrounding landscape
Road density within 5km (calculated as the linear distance of primary, secondary, and local roads
within the site divided by buffer area).
Traffic volume in the surrounding landscape (If available at the regional scale – possibly from LCC
data) [12/2012 Note: these data are not yet available regionally and won’t be until 2014.]
Class V. Blanding’s turtle population Size:
Relative abundance based on 2012 sampling (Note: for sites that do not have this information
available, this will be excluded from analysis)
Age structure (if available) (% of the total animals caught on site that are young adults)
Class VI: Conservation measures already underway
Total protected acres within the % of the site that is permanently protected (from TNC data-layer)
Total protected acres within the % of the site that is protected in any way (from TNC data-layer)
Demonstrable commitment to site by local NGO/agency/community (rated 0 or 1)
Ongoing EMBL-specific management on site (rated 0 or 1)
Class VII: Nesting habitat availability
-
-
Availability of nesting habitat within the site (as determined through aerial photos). This is,
unfortunately, a difficult characteristic to determine remotely (as it must be to be applied across the
region). Sites will be scored based on the acreage of nesting habitat available within the site using a
pattern-matching technique with known nest sites and aerial photographs. (As with all metrics, this
will be rescaled 0 to 1)
Known excellent (managed or monitored) nesting habitat on site (scored 0 or 1, in this way a site
with a known nest site is offered ‘bonus points’)
Class VIII: Potential change in habitat suitability
Estimated % increase in development within the site by 2080 (using NALCC output)
Estimated % increase in development within a 5km buffer around the site by 2080 (using NALCC
output)
Estimated change in temperature (degrees C) by 2080 (using NALCC output)
Estimated change in precipitation (mm/year) by 2080 (using NALCC output)
The metrics above were scored by experts in the December 2012 EMBL poll (Table 2). The hierarchical
ranking procedure was used so that broad classes of metrics will be on equal footing. For metrics not
currently available, or available for only some sites, (e.g., HRC scores) those metrics will be dropped from the
analysis for those sites for which they are unavailable.
Table B1. Results of 2012 expert poll that ranked site delineation criteria.
CV
Class Metrics
Average
%
relative
to
other
classes
Class I. Site Size (area)
3.73
0.27
0.15
Class II. Within site fragmentation
3.45
0.30
0.14
Class III. Habitat abundance and quality
3.91
0.27
0.16
Class IV. Surrounding landscape context
3.27
0.31
0.13
Class V. Known Blanding's turtle population
3.36
0.33
0.14
Class VI. Conservation measures currently underway
2.64
0.35
0.11
Class VII. Estimated nesting habitat*
Class VIII. Potential change in habitat suitability in the
future
2.18
0.54
0.09
2.27
0.49
0.09
% of
the
class'
weight
Sub-metrics Broken out by class
Class I. Site area
% relative
to all other
subclasses
1.00
0.15
Class II. % of total site area that is medium or low
intensity development
2.82
0.35
0.26
0.04
Class II. % of impervious surface cover.
3.55
0.26
0.32
0.04
Class II. Road density within site.
4.64
0.15
0.42
0.06
Class III. Wetland area within the site
3.55
0.34
0.40
0.06
Class III. Wetland diversity
2.36
0.47
0.27
0.04
Class III. Sum of HRC values (habitat suitability index)
2.90
0.34
0.33
0.05
Class IV. Distance to next nearest site
Class IV. % of the surrounding landscape that is
developed
3.18
0.34
0.20
0.03
3.00
0.39
0.19
0.02
3.00
0.30
0.19
0.02
Class IV. % impervious surface cover within the
surrounding landscape
Class IV. Road density within 5km
3.36
0.31
0.21
0.03
Class IV. Traffic volume in the surrounding 5km buffer
3.36
0.33
0.21
0.03
Class V. Relative abundance based on 2012 sampling
3.64
0.33
0.29
0.04
Class V. Age structure if available
2.55
0.37
0.20
0.03
Class V. Total animals seen on site from EO data
3.64
0.19
0.29
0.04
Class V. Known reproduction on site
2.64
0.42
0.21
0.03
Class VI: % of the site that is permanently protected
3.73
0.34
0.32
0.03
Class VI: % of the site from TNC data-layer that is listed
as protected (whether permanent or not)
3.00
0.30
0.26
0.03
Class VI: Demonstrable commitment to site by local
community
2.55
0.41
0.22
0.02
Class VI: Ongoing EMBL-specific management on site
2.36
0.43
0.20
0.02
Class VII: Availability of nesting habitat within the site
2.64
0.35
0.47
0.04
Class VII: Known excellent (i.e., monitored or managed)
nesting habitat
3.00
0.39
0.53
0.05
Class VIII: Estimated % increase in development within
the site over the next 80 years (from LCC output)
3.00
0.42
0.31
0.03
Class VIII: Estimated % increase in development within a
5km buffer around the site over the next 80 years (from
LCC output)
2.55
0.44
0.26
0.02
Class VIII: Estimated change in temperature over the next
80 years (from LCC output)
2.00
0.45
0.21
0.02
Class VIII: Estimated change in precipitation mm/year
(from LCC output)
2.18
0.57
0.22
0.02
After each sub-metric is calculated for each site, and the metrics are ranked by experts, each sub-metric is
rescaled to 1 by dividing by the largest value. “Negative” metrics (those that reduce site quality) will be
subtracted from 1. Each sub-metric is then weighted according to the responses from the 2012 expert poll.
For each class, sub-metrics are summed and divided by the number of metrics included in that class to
produce a single metric (scaled 0 to 1) for that class. Class metrics are then weighted according to the 2012
poll results and combined to create a final regional ranking metric.
An additional empirically derived ranking will be conducted using the results from the 2012 sampling. These
ranking schemes, as well as those used in Massachusetts and New Hampshire will be compared.