Cull

History of deer colonization - Response of vegetation to deer - Response of animals to deer and squirrel - Deer biology

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Effect of browsing history on the vegetation - Role of chemical defences on deer browsing - Effects of reduced plant abundance on pollination - Effect of hunting on tree regeneration - Effect of prolonged deer population reduction on the vegetation

Effect of prolonged deer population reduction on the vegetation

Exclosures experiments - Deer cull experiments

Deer cull experiments

Aim & scope - Where & when - How - Main results - Conclusion - Scientific Publications

Aim and scope

Deer culls were conducted to assess the potential and trajectory of recovery of vegetation that had been exposed to over 50 year of deer browsing, and the potential changes in songbirds populations.

Our comparative study suggested that vegetation and songbird population had been severely affected on these islands (see Different browsing histories and Response of birds to deer browsing).

On the right: forest interior on Reef Island before the cull.

Severe culls (over 80% of deer population) were completed on two medium sized islands in order to monitor the ensuing changes in their vegetation and avifauna and to compare them with those documented on control sites.

To verify the potential of the vegetation to respond to an absence of deer in the control sites, three 20x20 meter exclosures were installed on each of them.

Baseline data on the vegetation and songbirds had been collected in each site before the culls.

Culls were repeated periodically to maintain the remaining deer population at a low level. Vegetation and songbirds were monitored regularly.

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Where and when

Deer cull experiments occurred in two sites:

North:

Reef Island (cull)
Kunga island (control and 3 exclosures)
East Limestone (control and 3 exclosures).

South:

SGang Gwaay (cull)
Louscoone Point (control and 3 exclosures)

Vegetation and songbirds were monitored first in 1995 and 1997, before the culls.
Vegetation was then monitored in 1998, 1999, 2000, 2001, 2002, 2005 and 2007.
Songbird populations were monitored in 1999, 2001, 2005 and 2007.

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How

We monitored the two main habitats found on these islands: the forest interior and the forest edge (shoreline).

Vegetation was monitored within these two habitats.

Forest interior plots were based on pre-existing, evenly spaced, points used for songbird counts. Shoreline plots were selected to represent different shoreline types, exposures and aspects, more or less evenly spaced around the islands.

Measurements were taken at two different scales:

Forest interior and exclosure sites were sampled within 25m radius circle plots and 3,6m radius circle plots

Shoreline sites were sampled within 10m radius circle plots and 3,6m radius circle plots.

Main topographic, botanic and geographic features were also recorded.

Pictures of each plot were taken regularly in order to visualize the changes in the vegetation.

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Main Results

Changes in the vegetation

A glance on the pictures showing the evolution of the different plots since the cull gives us a good idea of the changes that occurred.

On control islands, vegetation remained sparse and heavily browsed.
Below, the same plot on Kunga island in 1997, 2001 and 2007 (from left to right).

However, vegetation has a potential for recovery, as proven by the changes of the vegetation within the exclosures.
Below, an exclosure on Kunga in 2007.

On the islands were deer population was dramatically reduced, vegetation has recovered since 1997.
Below, evolution of vegetation in different plots on Reef Island.

Before the cull

4 years later

8 years later

10 years later

Before the cull

4 years later

8 years later

Before the cull

2 years later

8 years later

10 years later

Changes in bird populations

The bird species which are the most dependant on understorey were rare on islands with a long history of deer browsing and common on islands without deer (see Response of songbirds to deer browsing).

These species make a remarkable come back on Reef Island.

These charts give the average number of individuals recorded per point count station (for the method, see Response of songbirds to deer browsing) on Reef Island in 1995 (before the cull) and in 2007 (10 years after the cull).

While there is no clear trend in the number of individuals that do not depend on the understorey (above), the number of individuals of all species that depend on the understorey increased between 1995 and 2007 (below).

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Conclusion

Research in still ongoing and data are still being analysed. However, at first glance, both vegetation and songbirds depending on this vegetation seem to have a potential to recover if given time.

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Scientific Publications

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