Forest structures and resource availability
Even-aged, monospecific stands that are favoured after clearcutting
often have a homogeneous three-dimensional canopy structure which might,
therefore, reduce the heterogeneity in resource availability for plants
(Fedrowitz et
al.
2014). In Central Europe, management has shifted to single tree
harvesting since the 90’s to obtain more continuous cover forests
(Gustafsson
et
al. 2019). This management regime affects light quantity (Forrester
et
al. 2018) and heterogeneity and, consequently, understory plant
composition and density (Bengtsson et al. 2000, Getzin et al. 2012,
Duguid and
Ashton
2013). In addition, different tree species produce different crown
structures (Ampoorter et al.
2015,
2016) and react differently to disturbances such as wind and snow
damage, or pest outbreaks (Burton et al. 2014, Hilmers et al. 2018).
More recently retention forestry has been promoted to enhance structural
complexity in rather homogeneous, even-aged stands to favour forest
biodiversity (Gustafsson et al.
2012,
2019). Understory plant species
composition, species richness, and functional diversity have been shown
to be affected by retention measures (Halpern et al. 2012, Lindenmayer
et al. 2012). Retention forestry alters microclimate and resource
availability across spatial and temporal scales, potentially affecting
understory plant composition and density (Aubry et al. 2009, Kriebitzsch
et
al.
2013). Introducing structural diversity by creating gaps, or by leaving
habitat trees, will affect light quality and quantity, wind speed and
air humidity, soil temperature and moisture, litter input, and hence
nutrient availability at the forest floor (Abd Latif and
Blackburn
2010). In addition, these abiotic conditions will also vary across
several temporal scales (daily fluctuations, seasonal changes,
year-to-year variation, Leuschner et
al.
2017). In particular, the spatio-temporal variability of light quantity
at the forest floor is usually greater in structurally more complex
forest stands (Liira et
al.
2007). Thus the complex interplay of these changes results in an altered
resource availability for plants (light, nutrients, water), and hence
provides competitive advantages to certain species over others.
Understory plant species
composition, species richness, and functional diversity have been shown
to be affected by retention measures (Halpern et al. 2012, Lindenmayer
et
al.
2012).