Background
Forest management has undergone a paradigm shift in recent decades. It was initially focused on heavily managing forests to focus on clearcut extraction and monocultural tree planting, a forest management style analogous to agriculture. Forests are more than a source of timber: They provide us goods and services such as habitat for plants, animals and fungi. They purify water and retain soil; they cycle nitrogen and carbon (Mace et al., 2012; Weber & Van Cleve, 1981). Links have been made between biodiversity and the amount and quality of ecosystem goods and services: Forests that are more heavily managed for timber are less productive and diverse (Mace et al., 2012; Gamfeldt et al., 2016; van der Plas et al., 2016). Subsequently, the ability of these forests to provide all those services is compromised under heavily managed regimes. In the 1980s, an alternate management scheme emerged: Ecosystem-Based Management (EBM) (Lindenmayer et al., 2012). A critical element of EBM is the emulation of natural disturbances. The boreal forest of Northern Alberta has evolved for thousands of years alongside regular wildfires, leading to plant assemblages that have acquired some resilience to disturbance. In theory, if forest managers can harvest a forest in a manner that emulates a wildfire, the ecosystem will be resilient to the disturbance and will regenerate efficiently and without loss of biodiversity or function (Franklin, 1989; Lindenmayer & Franklin, 2002) . While a harvest will never be able to completely mimic the physical effects of fire, it can mimic the post-fire landscape, which includes a multitude of unburned forest remnants, also called islands (Figure 1). In order to emulate a post fire landscape, harvesters place retention patches within their clearcuts (Figure 2).
Rmenants are thought to be useful for a few different reasons. First, they provide a source of heterogenous forest structure on a post disturbance landscape. Structural heterogeneity is hypothesized to improve forest biodiversity and function compared to forests with a homogenous age-class canopy. Second, forest remnants provide a microclimate buffer to the surrounding disturbed area through shading, potentially helping the recover of species that depend on a forest microclimate. Finally, forest remnants provide a habitat for forest dependent understory species, allowing them to continue to exist on a post-disturbance landscape forest (Andison, 2003; Baker et al., 2016; Moussaoui et al., 2016b).
The understory is a particularly important part of the forest, as it contains most of the plant diversity and animal food sources. If more diverse forests result in more ecosystem goods and services, then the conservation of understory biodiversity is especially important to maintain a functional forest (Roberts, 2004).
Rmenants are thought to be useful for a few different reasons. First, they provide a source of heterogenous forest structure on a post disturbance landscape. Structural heterogeneity is hypothesized to improve forest biodiversity and function compared to forests with a homogenous age-class canopy. Second, forest remnants provide a microclimate buffer to the surrounding disturbed area through shading, potentially helping the recover of species that depend on a forest microclimate. Finally, forest remnants provide a habitat for forest dependent understory species, allowing them to continue to exist on a post-disturbance landscape forest (Andison, 2003; Baker et al., 2016; Moussaoui et al., 2016b).
The understory is a particularly important part of the forest, as it contains most of the plant diversity and animal food sources. If more diverse forests result in more ecosystem goods and services, then the conservation of understory biodiversity is especially important to maintain a functional forest (Roberts, 2004).
Edge Effects
When a continuous forest is disturbed, the edge of the forest bordering the new disturbance will undergo changes in structure over the years due to edge effects. The removal of adjacent trees increases the light exposure that reaches the forest floor, resulting in increased productivity and growth in the understory layer. Additionally, trees on the edge are no longer buffered by adjacent forest, making them more susceptible to death by windthrow (Mascarua-Lopez et al., 2009). Edges created by clearcut and edges created by fire are known to be different. The edge of a clearcut is distinct and abrupt: on one side you have forest, and on the other all trees are removed, and the vegetation is trampled (Figure 4). The edges following a fire are more complex. A fire will leave more of a “gradient” edge, where the landscape directly adjacent to unburned forest will experience a low severity burn as the fire loses momentum and burns out (Harper 2004; Harper 2015). This means fire remnants are likely surrounded by a partially burned strip of forest that will help buffer the unburned section of forest from edge effects (Figure 3) (Moussaoui 2016a; Harper 2004). Excessive edge effects are detrimental to the function of island remnants, as they change the microclimatic conditions to become inhospitable to some forest-adapted plants. Additionally, excessive tree mortality can eliminate the heterogenous forest structure offered by the remnants, and prevent them from buffering the microclimate of adjacent disturbed areas (Moussaoui 2016a).
Research Objectives
My two main research goals are to compare fire and harvest references and examine whether they are effective at maintaining forest dependant understory species on the post disturbance landscape and determine if harvest remnants are effective analogues to fire remnants. This research aims to assess the viability of harvest retention as a forest management practice.
1. My first broad research objective is to examine the understory plant communities of the different treatment types to assess if they are significantly different from each other. Specifically, I want to test the following:
2. My second broad research objective is to examine the role of forest structure on understory community assemblages and microclimatic conditions. Specifically, I want to test the following:
1. My first broad research objective is to examine the understory plant communities of the different treatment types to assess if they are significantly different from each other. Specifically, I want to test the following:
- Are the compositions of harvest remnants different from the compositions of fire remnants?
- Are the compositions of remnants different from the compositions of undisturbed reference forest (within fire/harvest treatments)?
- Are the compositions of edge plots different from those of interior plots (within fire/harvest treatments)?
2. My second broad research objective is to examine the role of forest structure on understory community assemblages and microclimatic conditions. Specifically, I want to test the following:
- Does decreased canopy cover and/or increased tree mortality lead to higher soil and microclimate temperatures?
- Is high tree cover associated with late-successional understory species?
- Are high volumes of recent deadwood associated with early-successional understory species?
Expected Results
I expect to find that islands and references have similar plant communities. I also expect to see differences between the understory composition of fires and harvest, specifically in how they differ in edge effects. I would predict fire edges be more similar to fire interiors, while harvest edges will be different from harvest interiors. I expect to see a positive corelation between low canopy covers, recent deadwood, and high microclimate temperatures. Finally, I expect plots with high tree covers will contain late successional species, and plots with lots of deadwood to contain more early successional species.