All the data in this article was sourced from this research paper by SPU’s professor Eric Long: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0298231
Logging, a pivotal industry in Blakely Island’s history, dominated the landscape from the mid-1800s (when European settlers arrived) to the closure of Spencer Mill in 1946. The practice of patch-cut logging, also known as clear-cutting, created open spaces where underbrush could thrive without the hindrance of canopy cover. This ecological shift played a significant role in the sustained high deer population on the island.
Despite the closure of the once-thriving lumber mill in Thatcher Bay, patch-cut logging made a resurgence in the 1990s and persisted until 2005. This period coincided with a remarkable surge in the island’s deer population, reaching its peak in 2008, marking the highest recorded numbers.
Timber volume, a measure of the number of trees in a given area, plays a crucial role in shaping habitat quality and food availability, indirectly influencing the deer population. As timber volume increases, the deer population may decline due to the loss of suitable forage and habitat in the closed canopy forest. The y-axis represents the timber volume in cubic meters per square kilometer (m³/km²), indicating timber density within a specific area.
Canopy coverage refers to the percentage of land covered overhead by forest canopy. This is measured using satellite imagery. Timber volume and canopy coverage are related. Canopy coverage is affected by tree numbers, limb length, and foliage density. In 2006, canopy coverage was recorded, covering 90.74% of the island. A net gain of 0.40 km² of forest coverage was calculated after canopy coverage rose to 93.21% in 2020.
Shrub/scrub habitat refers to grassland or land with shrubbery. “HA” refers to hectares (about 2.5 acres). In 2001, there were about 65 hectares of total early seral (shrub/scrub) habitat. By 2010, that number dropped to about 52. This is a relatively significant 20.2% loss of shrub/scrub habitat. As timber volume and canopy coverage increased, less light reached the forest floor, causing decreased shrub/scrub habitat.
Blakely’s deer are an isolated community constrained to about six-and-a-half square miles of mountainous terrain bordered by rocky cliffs. They are notably smaller in stature and brain size than their mainland counterparts. While you might assume this would be the cause of their falling numbers, it’s quite the opposite.
Deer rely on forest floor brush as a majority food source. They spend their days grazing on shrubs, young trees, etc. In times of forest aggregation (increased tree numbers and growth of the tree canopy), these shrubs are covered in shade. With less light on the forest floor, shrub numbers decrease, and the deer’s food diminishes. As Professor Eric Long writes, this is one cause of the decline of the deer population.
Despite changes in the forest, the number of deer on this predator-free island is still higher than on the mainland.