Influences of evergreen gymnosperm and deciduous angiosperm tree species on the functioning of temperate and boreal forests

Abstract

It has been recognized for a long time that the overstorey composition of a forest partly determines its biological and physical-chemical functioning. Here, we review evidence of the influence of evergreen gymnosperm (EG) tree species and deciduous angiosperm (DA) tree species on the water balance, physical-chemical soil properties and biogeochemical cycling of carbon and nutrients. We used scientific publications based on experimental designs where all species grew on the same parent material and initial soil, and were similar in stage of stand development, former land use and current management. We present the current state of the art, define knowledge gaps, and briefly discuss how selection of tree species can be used to mitigate pollution or enhance accumulation of stable organic carbon in the soil. The presence of EGs generally induces a lower rate of precipitation input into the soil than DAs, resulting in drier soil conditions and lower water discharge. Soil temperature is generally not different, or slightly lower, under an EG canopy compared to a DA canopy. Chemical properties, such as soil pH, can also be significantly modified by taxonomic groups of tree species. Biomass production is usually similar or lower in DA stands than in stands of EGs. Aboveground production of dead organic matter appears to be of the same order of magnitude between tree species groups growing on the same site. Some DAs induce more rapid decomposition of litter than EGs because of the chemical properties of their tissues, higher soil moisture and favourable conditions for earthworms. Forest floors consequently tend to be thicker in EG forests compared to DA forests. Many factors, such as litter lignin content, influence litter decomposition and it is difficult to identify specific litter-quality parameters that distinguish litter decomposition rates of EGs from DAs. Although it has been suggested that DAs can result in higher accumulation of soil carbon stocks, evidence from field studies does not show any obvious trend. Further research is required to clarify if accumulation of carbon in soils (i.e. forest floor + mineral soil) is different between the two types of trees. Production of belowground dead organic matter appears to be of similar magnitude in DA and EG forests, and root decomposition rate lower under EGs than DAs. However there are some discrepancies and still are insufficient data about belowground pools and processes that require further research. Relatively larger amounts of nutrients enter the soil-plant biogeochemical cycle under the influence of EGs than DAs, but recycling of nutrients appears to be slightly enhanced by DAs. Understanding the mechanisms underlying forest ecosystem functioning is essential to predicting the consequences of the expected tree species migration under global change. This knowledge can also be used as a mitigation tool regarding carbon sequestration or management of surface waters because the type of tree species affects forest growth, carbon, water and nutrient cycling.

Tree species identity mediates mechanisms of top soil carbon sequestration in a Norway spruce and European beech mixed forest

“…We found a greater C accumulation in forest floor layers under Norway spruce than under European beech which is consistent with other observations in which conifers species stored greater amounts of SOC in the forest floor than deciduous species did (Augusto et al 2015;Vesterdal et al 2013). However, the lack of significant differences in litterfall inputs between plots seems to indicate that output processes are more important factors affecting forest floor C accumulation than the amount of litterfall per se.…”

“…These evidences are the basis for the establishment of mixed forest to promote soil C sequestration as compared to monospecific stands. For instance, conifers species generally accumulate greater SOC stock in the forest floor layers than do deciduous species (Augusto et al 2015). On the other hand, the greater root biomass found in deciduous forests (Finér et al 2007) together with the importance of root litter as C input to the mineral soil might induce a greater C accumulation in the mineral soil under broadleaf species.…”

“…Different tree species can have differential effect on the mechanisms that mediate the C cycle (Augusto et al 2015). Thus, their intermingling can have a profound effect on C accumulation rates and SOC distribution within the soil profile (Chapin 2003).…”

“…Causal influences among these variables can be partitioned using structural equation models (SEM; Grace 2006). SEM has been shown to be a powerful tool to study multiple processes operating in complex system and may allow us to interpret tree species effects on SOC stock and distribution (Augusto et al 2015;Vesterdal et al 2013) and, thus, to better understand the consequences of human interventions that aim at enhancing C sequestration.…”

A Review of Processes Behind Diversity—Productivity Relationships in Forests

“…[92,94,95] Transpiration and wateruse efficiency P Cr Inter-specific differences in water-use efficiency or transpiration rate (per unit crown projection area or sapwood area) will influence whether water availability (and uptake) is higher or lower for a given species in mixture compared with its monoculture; e.g., if a species A is mixed with another species B that has a high demand for water, species A may experience more intense competition for water in mixture, while species B experiences less intense competition. [20,96] Litter layer as a sponge or barrier P F or Cr [92,97] …”