Background & Rationale
Ecosystem Based Management
Forested ecosystems provide many services to humans (Perera & Buse 2014), including goods and products created from harvesting trees. However, the extraction of forest products during harvest may result in changes to forest canopies and overall structure over time and a loss of habitat from simplification of internal structure, which decreases the complex heterogeneous forest structures that promote biodiversity (Moussaoui et al. 2016). The simplification of forest structure as a result of traditional forest management practices (i.e. clearcutting) results in a loss of forest complexity, which can be detrimental to forest recovery (Gustafsson et al. 2012). The practice of retention forestry is a concept developed in harvest settings to leave behind intact forest for the purposes of maintaining supply of ecosystem services and provisioning biodiversity, increase public perception of harvesting and enrich the structure and composition of postharvest forest, among other benefits (Gustaffson et al. 2012).
In order to preserve forest structure, minimize incidental tree mortality and promote biodiversity (Moussaoui et al. 2016), harvesting practices have shifted to Ecosystem Based Management-- which mimics the mosaic of forested landscape left behind following a wildfire through creation of island remnants (Gustaffson et al. 2012). Though previous studies have compared the efficacy of retention harvest and created remnants in moderating tree survival to reference forest or clearcuts (EMEND Experiment, Spence et al. 1999), they haven't compared tree mortality retention islands directly to island remnants created by wildfires, the disturbance of interest (Ghandi et al. 2004, Moussaoui et al. 2016).
The boreal forests of Canada often experience large scale tree mortality events due to wildfires as the predominant disturbance (Aakala et al. 2009, Dragotescu & Kneeshaw 2012). However, as wildfires burn across a landscape they leave behind unburned and intact patches of forest, called island remnants (Perera & Buse 2014). These remnants are thought to be ecologically significant through the preservation of forest structure, habitat and as a source of seeds for regeneration (Moussaoui et al. 2016, Perera & Buse 2014, Dragotescu & Kneeshaw 2012). In fact, forest remnants are thought to be key components of forest recovery following wildfire (Moussaoui et al. 2016). Ecosystem Based Forest Management mimics large-scale natural disturbance in a harvest setting.
Of specific concern in evaluating the efficacy of island remnants is the success of tree survival. The creation of harsh edges following disturbances (Harper et al. 2015) can result in heightened rates of tree mortality, of which large scale mortality events can have detrimental effects on many facets of forested ecosystems (Ecke, Löfgren & Sörlin 2002; Murcia 1995; Harper et al. 2005) and bring to light the effectiveness of leaving behind these intact patches of forests in the first place.
Tree mortality commonly occurs as a natural process in forests (Franklin et al. 1987), and tree deaths can be both beneficial and detrimental. Overall, they influence stand structure, species composition and diversity (Thorpe et al. 2008). Tree deaths can create habitat, through the creation of standing snags and coarse woody debris (Jönsson & Jonsson 2007). They allow an opening in the forest canopy which can facilitate regeneration through the increase in sunlight and exposed mineral soil (Harper et al. 2015), and some species specialize in survival in created edges (Schlossberg & King 2008). Dead trees also provide downed wood for decomposition and nutrient cycling processes.
However, tree mortality has negative consequences as well, and these become especially concerning when tree mortality rates increase above background rates. After trees die, they switch from being a carbon sink to a carbon source (Hogg & Michaelian 2015), which is an important aspect to consider with respect to climate change. Tree death may remove habitat for species that depend on full living canopies and products from living trees (Ecke, Löfgren & Sörlin 2002). There is also a risk that with widespread tree mortality, forest species may be at risk of takeover by invasive species or an ecosystem shift. Previous studies have found that forest species’ declines are commonly linked to the removal of forest canopy and related edge effects (Murcia 1995; Harper et al. 2005). In fact, in many forest types edge creation and canopy dieback is associated with invasive species takeovers or ecosystem shifts from forests to grasslands (which has been predicted to occur in the boreal forests of AB following wildfire) (Stralberg et al. 2018). In this project, I aim to understand mortality rates in island remnants to determine how effective tree survival is in island remnants following disturbances. If tree mortality is occurring at high rates in these residual patches of forest relative to reference stands, this can negate the benefits provided by leaving behind patches of live intact forest.
Overall, understanding the dynamics of tree mortality in island remnants created by both natural (wildfire) and anthropogenic (harvest) disturbances can help track forest recovery following major forest disturbances. If a large difference in tree mortality is observed between treatment types, this may inform management decisions for future ecosystem-based management objectives. Because of the continued demand for boreal forest resources, understanding residual tree mortality in created island remnants will be an important consideration of the effectiveness of this form of retention forestry. If certain factors can predict increased mortality rates, prioritizing areas to control for heightened tree mortality risk will effectively address ecosystem based management objectives, through the creation of island remnants to preserve forest structure and live canopy trees.
In order to preserve forest structure, minimize incidental tree mortality and promote biodiversity (Moussaoui et al. 2016), harvesting practices have shifted to Ecosystem Based Management-- which mimics the mosaic of forested landscape left behind following a wildfire through creation of island remnants (Gustaffson et al. 2012). Though previous studies have compared the efficacy of retention harvest and created remnants in moderating tree survival to reference forest or clearcuts (EMEND Experiment, Spence et al. 1999), they haven't compared tree mortality retention islands directly to island remnants created by wildfires, the disturbance of interest (Ghandi et al. 2004, Moussaoui et al. 2016).
The boreal forests of Canada often experience large scale tree mortality events due to wildfires as the predominant disturbance (Aakala et al. 2009, Dragotescu & Kneeshaw 2012). However, as wildfires burn across a landscape they leave behind unburned and intact patches of forest, called island remnants (Perera & Buse 2014). These remnants are thought to be ecologically significant through the preservation of forest structure, habitat and as a source of seeds for regeneration (Moussaoui et al. 2016, Perera & Buse 2014, Dragotescu & Kneeshaw 2012). In fact, forest remnants are thought to be key components of forest recovery following wildfire (Moussaoui et al. 2016). Ecosystem Based Forest Management mimics large-scale natural disturbance in a harvest setting.
Of specific concern in evaluating the efficacy of island remnants is the success of tree survival. The creation of harsh edges following disturbances (Harper et al. 2015) can result in heightened rates of tree mortality, of which large scale mortality events can have detrimental effects on many facets of forested ecosystems (Ecke, Löfgren & Sörlin 2002; Murcia 1995; Harper et al. 2005) and bring to light the effectiveness of leaving behind these intact patches of forests in the first place.
Tree mortality commonly occurs as a natural process in forests (Franklin et al. 1987), and tree deaths can be both beneficial and detrimental. Overall, they influence stand structure, species composition and diversity (Thorpe et al. 2008). Tree deaths can create habitat, through the creation of standing snags and coarse woody debris (Jönsson & Jonsson 2007). They allow an opening in the forest canopy which can facilitate regeneration through the increase in sunlight and exposed mineral soil (Harper et al. 2015), and some species specialize in survival in created edges (Schlossberg & King 2008). Dead trees also provide downed wood for decomposition and nutrient cycling processes.
However, tree mortality has negative consequences as well, and these become especially concerning when tree mortality rates increase above background rates. After trees die, they switch from being a carbon sink to a carbon source (Hogg & Michaelian 2015), which is an important aspect to consider with respect to climate change. Tree death may remove habitat for species that depend on full living canopies and products from living trees (Ecke, Löfgren & Sörlin 2002). There is also a risk that with widespread tree mortality, forest species may be at risk of takeover by invasive species or an ecosystem shift. Previous studies have found that forest species’ declines are commonly linked to the removal of forest canopy and related edge effects (Murcia 1995; Harper et al. 2005). In fact, in many forest types edge creation and canopy dieback is associated with invasive species takeovers or ecosystem shifts from forests to grasslands (which has been predicted to occur in the boreal forests of AB following wildfire) (Stralberg et al. 2018). In this project, I aim to understand mortality rates in island remnants to determine how effective tree survival is in island remnants following disturbances. If tree mortality is occurring at high rates in these residual patches of forest relative to reference stands, this can negate the benefits provided by leaving behind patches of live intact forest.
Overall, understanding the dynamics of tree mortality in island remnants created by both natural (wildfire) and anthropogenic (harvest) disturbances can help track forest recovery following major forest disturbances. If a large difference in tree mortality is observed between treatment types, this may inform management decisions for future ecosystem-based management objectives. Because of the continued demand for boreal forest resources, understanding residual tree mortality in created island remnants will be an important consideration of the effectiveness of this form of retention forestry. If certain factors can predict increased mortality rates, prioritizing areas to control for heightened tree mortality risk will effectively address ecosystem based management objectives, through the creation of island remnants to preserve forest structure and live canopy trees.
Questions & Objectives
The main objective of my study is to determine the survival or mortality of trees in retention patches (specifically island remnants) after a disturbance (either fire or harvest) has occurred. This can be used to measure the efficacy of implementing Ecosystem Based Management in harvesting protocols, and inform forest management practices going forward, with respect to the creation of island remnants. If tree mortality amounts differ vastly between fire and harvest created island remnants, the efficacy of these remnants will be questioned. Specifically, if tree mortality is occurring at high rates in harvest island remnants, then these patches of forest preserved initially for their living trees will cease to function as habitat for wildlife and to promote regeneration. Heightened tree mortality may increase the risk of invasive species takeovers, ecosystem shifts and impede a full living canopy for wildlife protection and resources. The practice of leaving intact forest through island remnant creation during a harvest to promote forest recovery and support remaining species can be hindered if enough remaining trees die shortly after the harvest.
Because previous studies have only compared harvest island remnants to clearcuts or reference forests, this research adds fire-created island remnants as a comparison. Are there differences in tree mortality in post-harvest remnants compared to post fire remnants? And what do these differences look like compared to a reference forest? Do we see the influence of edge effects on tree mortality rates, compared to more interior parts of remnants or reference forests? Are certain tree species affected differently with respect to mortality rates? And finally, does the size of the island remnant predict amounts of tree mortality seen?
Because previous studies have only compared harvest island remnants to clearcuts or reference forests, this research adds fire-created island remnants as a comparison. Are there differences in tree mortality in post-harvest remnants compared to post fire remnants? And what do these differences look like compared to a reference forest? Do we see the influence of edge effects on tree mortality rates, compared to more interior parts of remnants or reference forests? Are certain tree species affected differently with respect to mortality rates? And finally, does the size of the island remnant predict amounts of tree mortality seen?
Expected Results
I anticipate seeing a difference in tree mortality between location type--reference forest and island remnants, regardless of disturbance type. Island remnants are completely surrounded by disturbances, and living trees in these remnants likely experience more stress from wind, light exposure and edge effects. I expect that fire islands will have less mortality than harvest islands, because harvesting equipment often damages trees on edges, resulting in higher mortality, and there are biological and physiological aspects of wildfires that will be missing from harvest-created island remnants that could mitigate post-disturbance tree mortality. Further, smaller islands will have higher mortality amounts due to a higher edge to interior forest ratio and increased edge effects over the island as a whole. I predict that edge plots will have higher mortality than interior plots due to the influence of edge effects, and that in conjunction with this certain tree species may have higher mortality rates because different species occupy certain niches and a disruption to these environments could cause high rates of stress and therefore higher mortality rates.
References
Aakala, Tuomas, et al. "Contrasting patterns of tree mortality in late‐successional Picea abies stands in two areas in northern Fennoscandia." Journal of Vegetation Science 20.6 (2009): 1016-1026.
Angers, Virginie A. “Snag dynamics in boreal mixedwood and coniferous forests.” PhD dissertation. University of Quebec Montreal. (2011)
Dragotescu, Iulian, and Daniel D. Kneeshaw. "A comparison of residual forest following fires and harvesting in boreal forests in Quebec, Canada." Silva Fennica 46.3 (2012): 365-376.
Ecke, Frauke, Ola Löfgren, and Dieke Sörlin. "Population dynamics of small mammals in relation to forest age and structural habitat factors in northern Sweden." Journal of Applied Ecology 39.5 (2002): 781-792.
Franklin, Jerry F., Herman H. Shugart, and Mark E. Harmon. "Tree death as an ecological process." BioScience 37.8 (1987): 550-556.
Gandhi, Kamal JK, et al. "Harvest retention patches are insufficient as stand analogues of fire residuals for litter-dwelling beetles in northern coniferous forests." Canadian Journal of Forest Research 34.6 (2004): 1319-1331.
Gustafsson, Lena, et al. "Retention forestry to maintain multifunctional forests: a world perspective." BioScience 62.7 (2012): 633-645.
Harper, Karen A., et al. "Edge influence on forest structure and composition in fragmented landscapes." Conservation biology 19.3 (2005): 768-782.
Harper, Karen A., et al. "Edge influence on vegetation at natural and anthropogenic edges of boreal forests in Canada and Fennoscandia." Journal of Ecology 103.3 (2015): 550-562.
Hogg, Edward H., and Michael Michaelian. "Factors affecting fall down rates of dead aspen (Populus tremuloides) biomass following severe drought in west‐central Canada." Global change biology 21.5 (2015): 1968-1979.
Jönsson, Mari T., and Bengt Gunnar Jonsson. “Assessing Coarse Woody Debris in Swedish Woodland Key Habitats: Implications for Conservation and Management.” Forest Ecology and Management 242, no. 2 (April 30, 2007): 363–73. https://doi.org/10.1016/j.foreco.2007.01.054.
Moussaoui, Louiza, et al. "Can retention harvest maintain natural structural complexity? A comparison of post-harvest and post-fire residual patches in boreal forest." Forests 7.10 (2016): 243.
Murcia, Carolina. "Edge effects in fragmented forests: implications for conservation." Trends in ecology & evolution 10.2 (1995): 58-62.
Perera, Ajith, and Lisa Buse. "Ecology of wildfire residuals in boreal forests." (2014).
Thorpe, H. C., S. C. Thomas, and J. P. Caspersen. "Tree mortality following partial harvests is determined by skidding proximity." Ecological Applications 18.7 (2008): 1652-1663.
Schlossberg, Scott, and David I. King. "Are shrubland birds edge specialists." Ecological applications 18.6 (2008): 1325-1330.
Spence, J. R., W. J. A. Volney, M. G. Weber, V. J. Lieffers, S. A. Luchkow, and T. W. Vinge. “The Alberta EMEND Project : Recipe and Cooks` Argument,” May 1, 1999. https://www.osti.gov/etdeweb/biblio/336573.
Stralberg, Diana, Xianli Wang, Marc-André Parisien, François-Nicolas Robinne, Péter Sólymos, C. Lisa Mahon, Scott E. Nielsen, and Erin M. Bayne. “Wildfire-Mediated Vegetation Change in Boreal Forests of Alberta, Canada.” Ecosphere 9, no. 3 (2018): e02156. https://doi.org/10.1002/ecs2.2156.
Aakala, Tuomas, et al. "Contrasting patterns of tree mortality in late‐successional Picea abies stands in two areas in northern Fennoscandia." Journal of Vegetation Science 20.6 (2009): 1016-1026.
Angers, Virginie A. “Snag dynamics in boreal mixedwood and coniferous forests.” PhD dissertation. University of Quebec Montreal. (2011)
Dragotescu, Iulian, and Daniel D. Kneeshaw. "A comparison of residual forest following fires and harvesting in boreal forests in Quebec, Canada." Silva Fennica 46.3 (2012): 365-376.
Ecke, Frauke, Ola Löfgren, and Dieke Sörlin. "Population dynamics of small mammals in relation to forest age and structural habitat factors in northern Sweden." Journal of Applied Ecology 39.5 (2002): 781-792.
Franklin, Jerry F., Herman H. Shugart, and Mark E. Harmon. "Tree death as an ecological process." BioScience 37.8 (1987): 550-556.
Gandhi, Kamal JK, et al. "Harvest retention patches are insufficient as stand analogues of fire residuals for litter-dwelling beetles in northern coniferous forests." Canadian Journal of Forest Research 34.6 (2004): 1319-1331.
Gustafsson, Lena, et al. "Retention forestry to maintain multifunctional forests: a world perspective." BioScience 62.7 (2012): 633-645.
Harper, Karen A., et al. "Edge influence on forest structure and composition in fragmented landscapes." Conservation biology 19.3 (2005): 768-782.
Harper, Karen A., et al. "Edge influence on vegetation at natural and anthropogenic edges of boreal forests in Canada and Fennoscandia." Journal of Ecology 103.3 (2015): 550-562.
Hogg, Edward H., and Michael Michaelian. "Factors affecting fall down rates of dead aspen (Populus tremuloides) biomass following severe drought in west‐central Canada." Global change biology 21.5 (2015): 1968-1979.
Jönsson, Mari T., and Bengt Gunnar Jonsson. “Assessing Coarse Woody Debris in Swedish Woodland Key Habitats: Implications for Conservation and Management.” Forest Ecology and Management 242, no. 2 (April 30, 2007): 363–73. https://doi.org/10.1016/j.foreco.2007.01.054.
Moussaoui, Louiza, et al. "Can retention harvest maintain natural structural complexity? A comparison of post-harvest and post-fire residual patches in boreal forest." Forests 7.10 (2016): 243.
Murcia, Carolina. "Edge effects in fragmented forests: implications for conservation." Trends in ecology & evolution 10.2 (1995): 58-62.
Perera, Ajith, and Lisa Buse. "Ecology of wildfire residuals in boreal forests." (2014).
Thorpe, H. C., S. C. Thomas, and J. P. Caspersen. "Tree mortality following partial harvests is determined by skidding proximity." Ecological Applications 18.7 (2008): 1652-1663.
Schlossberg, Scott, and David I. King. "Are shrubland birds edge specialists." Ecological applications 18.6 (2008): 1325-1330.
Spence, J. R., W. J. A. Volney, M. G. Weber, V. J. Lieffers, S. A. Luchkow, and T. W. Vinge. “The Alberta EMEND Project : Recipe and Cooks` Argument,” May 1, 1999. https://www.osti.gov/etdeweb/biblio/336573.
Stralberg, Diana, Xianli Wang, Marc-André Parisien, François-Nicolas Robinne, Péter Sólymos, C. Lisa Mahon, Scott E. Nielsen, and Erin M. Bayne. “Wildfire-Mediated Vegetation Change in Boreal Forests of Alberta, Canada.” Ecosphere 9, no. 3 (2018): e02156. https://doi.org/10.1002/ecs2.2156.