|Forest Investment Account (FIA) - Forest Science Program|
|FIA Project Y102041|
|Early-seral forest stands and their relationship to wildlife populations and ecosystem stability.|
|Project lead: Karl Larsen (Thompson Rivers University)|
|Contributing Authors: Stromgren, Eric J.; Larsen, Karl W.|
|Subject: Forest Investment Account (FIA), British Columbia|
|Series: Forest Investment Account (FIA) - Forest Science Program|
|Biodiversity across landscapes is more than simply a species count; it also includes the range of habitats and ecological processes (‘diversity’) present. If these processes are interrupted, an integral component of the ecosystem is lost, leading to more visible consequences such as species declines or extirpations. We are entering (or already in) a bottleneck, with regards to the ecological processes across much of our ‘working forest’. Once beetle-salvage operations taper off, sources of wood will become even more constrained, leading to increasing pressure on the stands of mature forest remaining on a landscape dominated by younger stands. |
Effective planning for biodiversity on these landscapes requires understanding how stands of different age-classes contribute to the ‘functioning’ of the forest ecosystem, and when mature stands can be harvested as younger stands start to support ‘mature forest’ species. However, far more work has been done on the opposite end of the spectrum, namely understanding the importance of ‘old growth’ forest stands. Important questions that now need addressing are: What are the implications of dwindling stands of mature forest, in terms of ecological processes and wildlife resilience? When do younger stands begin to play a ‘mature role’, and can we understand the features that contribute to this change? Science-based planning (or ‘ecosystem-based management’) for the harvest of mature timber will need to consider the impact of an increasing dominance of younger stands on the landscape. The overarching goal of the proposed study is to facilitate this planning process, by providing greater insight into how the young-to-mature stand representation influences the wildlife component of ecosystems. The study will occur in the Interior Douglas-fir (IDF) ecosystem of BC. Extensive harvesting has occurred in the IDF in the past. But, with a declining timber supply from lower-elevation sites, wood flow from the IDF will become increasingly critical in sustaining the forest industry.
We will focus on how the representation of younger forest stands (and their habitat attributes) influence an important component of the wildlife community. We will collect detailed information on two ‘keystone’ prey species strongly tied to mature and young forest habitats, respectively, and this in turn will reveal the links between their predators to the habitat types. We will use red squirrels (Tamiasciurus hudsonicus) and yellow-pine chipmunks (Tamias amoenus) as focal prey species, for several reasons. One, both animals are important in the diet of forest predators . In particular, the goshawk (Accipiter gentilis) predates heavily on squirrels [2,3]. A recent American study showed squirrel abundance was the best variable for explaining reproductive output by these birds , and Harrower  has routinely observed squirrels being delivered to goshawk nests in the BC interior. Squirrels also figure in the diet of marten and other smaller mustelids such as ermine [6,7], and it has been argued that we need to re-examine the widely-held notion that these predators are primarily dependent on voles and mice, as larger prey such as squirrels provide higher caloric intake . Mustelids, and to a lesser extent raptors, also prey heavily on chipmunks [6,9]. Overall, these two prey species represent integral parts of the vertebrate food web within the forests of BC. Other reasons for using these animals are (a) they are tractable and conducive to study  and (b) they represent contrasting associations: squirrels tend to be found in more mature stands of forest , whereas chipmunks are tied to well-developed understories in younger, open forests [11,12]. The transition of young stands into ‘mature forest’ therefore reflects mirror-image changes in habitat suitability to these two animals, and consequently, in prey availability for their predators. It is this ‘transition’ and its implications to the wildlife community that we are seeking to understand.
A critical yet often ignored concept in wildlife management is that presence of animals, and even their densities, do NOT necessarily reflect habitat suitability [13,14]. To predict population/community resiliency, we need to understand how and when individuals colonize different stand types (e.g. leaving a mature stand, and settling in a younger stand) and begin contributing to the maintenance of the population (and the ecosystem). This concept is linked to habitat ‘source’ and ‘sink’ theory, i.e. how different habitats act as net importers or exporters of animals, and contribute differently to population and community stability . We will consider but not rely solely on abundance as a measure of habitat suitability. Instead, we will include measurements of reproductive success and the dispersal process in our investigation of how habitat conditions and animal occupancy ‘shifts’ along the early seral:mature forest transition.
As mentioned, the mature-to-old-growth forest transition (not young-to-mature) has been a major focus of forest ecosystem work, but there is research on younger forests that we will build upon. For example, Sullivan and colleagues have done detailed study on the relationship of wildlife to various types of stands and silviculture treatments. Much of their work has focused on smaller rodents, such as voles [17,18,19,etc.]. But, in work on squirrels, young stands of pine were found to have low survival and high recruitment, suggesting they could indeed act as ‘sinks’ , whereas in coastal forests, squirrel populations did not respond to commercial thinning . Within the BC interior, red squirrels densities and other measurements appeared to be similar in thinned and old-growth stands of pine . More recently, Haughland & Larsen  found red squirrel dispersers in thinned ‘poor’ IDF habitat were unable to successfully move into mature forest, and in a pilot project to the one proposed here , dispersing squirrels appeared to respond to age-related changes in young forests when seeking out new habitat.
Where our work will build upon these previous studies is that (1) we will include a range of forest stands in our project, not focusing on one pair-wise comparison, and (2) we will collect detailed information on the dispersal process (origin, investigation, settlement, survival) using tools such as telmetry. This in turn provides data on sources and timing of mortality, in relation to the predator community. Our study will allow for better-informed planning and decisions, in terms of how wildlife communities will be impacted by rates and amounts of wood removal in forests where stand ages are becoming skewed towards younger classes.
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|Related projects:  FSP_Y091041,  FSP_Y113041|
Executive Summary (0.6Mb)
Presentation to ICAS (11.5Mb)
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Updated September 19, 2011
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