PLN Mapping Project Data: Quality of Information
This citizen mapping is based on best-available government data, which is not always complete or up to date. The BC government’s 2003 Forest Range and Practices Act (FRPA) gave the Forest Industry responsibility for maintaining some forest data, which then became proprietary and unavailable to citizens. The PLN doesn’t identify everything that ought to be protected and site-specific decisions need to be field-verified. While these community maps are substantially true, the scale of the mapping also doesn’t include some important details, and local knowledge needs to be added!
PLN Design Method
It was most important that the Protected Landscape Network (PLN) included and connected the most environmentally sensitive and rare habitats on Read Island. These areas includes steep slopes, dry bluff tops, streams, lakes and wetlands (refer to Map 2). Old forest (forest 140 years or older) are also considered sensitive and important ecosystems on Read Island as many species specifically require old forests for habitat and these areas are increasingly rare and fragmented. The PLN, which was to be designed around these “habitat nodes”, needed to include representations of the naturally rare (not necessarily considered environmentally sensitive) ecosystems as well as the dominant “backbone” ecosystems of Read Island (refer to Map 4). The ArcGIS extension, Land Facet Mapper was used to compute the most efficient route between wetland and old forest “habitat nodes” such that the route than joined the nodes was most similar habitat-wise to the habitat nodes. For example, random points were generated at the locations of all the wetlands on Read Island and statistics about the topographic characteristics of these areas were generated. These statistics were used to analyze the rest of the island and find the shortest path that connected the wetlands such that the route was most similar topographically to wetlands. Steep slopes and cutblocks 10 years old or less were used as impediments to the selected route so the program planned the route around them. The resulting route also had to be at least 200m wide. According to literature on wildlife coordior analysis, the cooridor must be a mininum of 200m wide for wildlife to use it.
Routes were generated this way for wetlands, old forest on poor site index, old forest on medium site index, and old forest on rich site index. For the old forest, the program generated routes that connected the remaining old forest on Read Island while favouring the oldest forest stands and and similar site productivity.
Maps were made of these four routes and Herb Hammond analyzed how well they protected Read Island’s naturally rare and dominant ecosystems by looking at the combinations of leading tree species, site index and stand age, and site series that the routes contained. After many iterations of this process we were able to produce the core of the Protected Landscape Network to which we added buffered streams, dry bluff areas and steep slopes.
Data Sets Used for the PLN
Vegetation Resource Inventory (VRI) – This data is produced by the Province of B.C. using aerial photo interpretation and ground sampling. It uses polygons to represent forest cover. Limitations of this data are that it does not include information for private forest lands, in these areas there is no tree species or stand age information. Also, the stand age information is often not up-to-date because the Province must receive harvesting and fire/catastrophic event information from licensees, and then these updates are rolled into annual releases of the dataset.
Discovery Islands Sensitive Ecosystems Inventory – This data was produced by the Discovery Islands Ecosystem Mapping (DIEM) Project in 2014. It is based on Terrestrial Ecosystem Mapping (TEM) produced by the Province of BC in the 1990s, and was ground truthed in 2014. This data is mapped at 1:20,000 scale which means that one unit of measurement on the map equals 20,000 of the same units on the ground; i.e., 1 cm on the map = 20,000 cm (200 metres) on the ground. This limits the detail that the map can represent to an ecosystem that is 200m2 in area. The spatial detail of this information is worsened because of its “component based” mapping method inherent in the TEM dataset. The method delineates a larger encompassing ecosystem and lists up to three other ecosystems within it. For example a Woodland ecosystem that has a 20% Herbaceous ecosystem component; we know that there is a Herbaceous ecosystem within the Woodland but we don’t know exactly where.
Canadian Digital Elevation Data (CDED) – This data is 1:20,000 elevation data produced using photogrammetry. It is in a raster format rather than contours, which is good for topographic analysis but imposes “rasterized” representation of features.
Fresh Water Atlas (FWA) Streams Lakes and Wetlands – Fresh water features mapped at a 1:20,000 scale by the Province of BC. The 1:20,000 scale imposes a limit of detail that does not capture lakes and wetlands less than 200m2 in area and creeks less than 200m long. Also, because the stream network was generated by modelling, the linework is generalized and can be imprecise or even inaccurate.
Terrestrial Ecosystems Mapping (TEM) – This data was produced by the Province of BC in the 1990s. It uses polygons to map different ecosystems based on the dominant vegetation at climax succession. It is mapped at a 1:20,000 scale which means one unit of measurement on the map equals 20,000 of the same units on the ground. This limits the detail that the map can represent to an ecosystem that is 200m2 in area. The spatial detail of this information is worsened because of its “component based” mapping method. This method delineates a larger encompassing ecosystem and lists up to three other ecosystems within it. For example a moderately dry/rich ecosystem might have a 20% dry/poor ecosystem component; we know that there is a dry ecosystem within the moderately dry/rich one but we don’t know exactly where.
RESULTS Openings – This dataset is produced by the Province of B.C. and contains polygons representing harvested cutblocks or natural disturbances where silviculture activities are planned. A limitation of this dataset is that it is often not up-to-date while waiting for licensees to submit their harvesting/natural disturbance information. Also, this dataset only shows cutblocks on Crown forest licenses and does not contain information for private forest lands.
Google Earth – These orthophotos captured and hosted by Google were used to find cutblock openings that were not in the RESULTS – Openings dataset.
WL0046 Woodlot Plan – The map of planned cutblocks shown in the WL0046 Woodlot Plan was used to create a dataset of planned harvesting polygons. This dataset only shows planned harvesting activity on WL0046 and on WL2062 but not on any private managed or industrial forest lands.
Forest Service Roads – This dataset is produced by the Province of B.C. A limitation of this dataset is that the road linework can be shifted or generalized as it is mapped at a 1:20,000 scale.
Digital Road Atlas (DRA) – This dataset is produced by the Province of B.C. A limitation of this dataset is that the road linework can be shifted or generalized as it is mapped at a 1:20,000 scale.
Forest Tenure Managed Licenses – Polygons designating forest managed license areas by Woodlot number. This dataset is produced by the Province of B.C.
Zoning – This dataset is a cadastral map from the Strathcona Regional District with land zoning designations.
Percent Slope – This data was computed from the Canadian Digital Elevation Data and represents percent slope of the landscape. It has a spatial resolution of 25m which means there is one slope reading for every 25x25m grid cell.
Wetness Index – This data was computed from the Canadian Digital Elevation Data and represents the capacity of the landscape to collect and hold water. It has a spatial resolution of 25m which means there is one wetness reading for every 25x25m grid cell.
Topographic Position Index – This data was computed from the Canadian Digital Elevation Data and represents the concavity and convexity of the landscape. It has a spatial resolution of 25m which means there is one elevation reading for every 25x25m grid cell.