Interactions with successional stage and nutrient status determines the life‐form‐specific effects of increased soil temperature on boreal forest floor vegetation

Abstract

The boreal forest is one of the largest terrestrial biomes and plays a key role for the global carbon balance and climate. The forest floor vegetation has a strong influence on the carbon and nitrogen cycles of the forests and is sensitive to changes in temperature conditions and nutrient availability. Additionally, the effects of climate warming on forest floor vegetation have been suggested to be moderated by the tree layer. Data on the effects of soil warming on forest floor vegetation from the boreal forest are, however, very scarce. We studied the effects on the forest floor vegetation in a long-term (18 years) soil warming and fertilization experiment in a Norway spruce stand in northern Sweden. During the first 9 years, warming favored early successional species such as grasses and forbs at the expense of dwarf shrubs and bryophytes in unfertilized stands, while the effects were smaller after fertilization. Hence, warming led to significant changes in species composition and an increase in species richness in the open canopy nutrient limited forest. After another 9 years of warming and increasing tree canopy closure, most of the initial effects had ceased, indicating an interaction between forest succession and warming. The only remaining effect of warming was on the abundance of bryophytes, which contrary to the initial phase was strongly favored by warming. We propose that the suggested moderating effects of the tree layer are specific to plant life-form and conclude that the successional phase of the forest may have a considerable impact on the effects of climate change on forest floor vegetation and its feedback effects on the carbon and nitrogen cycles, and thus on the climate.

Half a century of multiple anthropogenic stressors has altered northern forest understory plant communities

“…The response of the vegetation to a warmer climate will largely resemble that due to nitrogen deposition (i.e., eutrophication effects; cf. Walker et al 2006, Hedwall et al 2015, and we cannot exclude the possibility that some of the effects we attribute to eutrophication are due to climate change. As most evidence of climate driven eutrophication effects originates from northern ecosystems with low nitrogen deposition, it is, however, largely uncertain how these drivers may interact.…”

Stand type affects fluxes of volatile organic compounds from the forest floor in hemiboreal and boreal climates

“…According to long-term remote sensing data, warming-induced changes in vegetation productivity and growing season length are already visible in the Northern Hemisphere (Park et al 2016). Ground vegetation is affected when temperatures increase and nutrient levels change due to warming (Hedwall et al 2015). Vegetation BVOC emissions from the subarctic heath were found to increase by warming induced vegetation change together with litter addition (Valolahti et al 2015).…”

Bryophytes in fir waves: Forest canopy indicator species and functional diversity decline in canopy gaps

“…In contrast to undisturbed forests, bryophyte community metrics such as total cover or species richness tend to decline in managed (e.g., Quinby, ; Dovčiak, Halpern, Saracco, Evans, & Liguori, ; Gallo & Lencinas, ), fertilized (cf. Hedwall, Skoglund, & Linder, ), polluted (Zvereva & Kozlov, ), and fragmented (Baldwin & Bradfield, ) forest ecosystems. In addition to these community metrics, the abundance or presence of individual bryophyte species can often indicate specific environmental conditions (e.g., canopy gaps, Promis, Gärtner, Reif, & Cruz, ; Stehn et al., ), or disturbance (e.g., fire, Macdonald, ; forest pests, Stehn et al., ).…”