Stand-Level Variation Drives Canopy Water Storage by Non-vascular Epiphytes Across a Temperate-Boreal Ecotone

Abstract

Epiphytes, including bryophytes and lichens, can significantly change the water interception and storage capacities of forest canopies. However, despite some understanding of this role, empirical evaluations of canopy and bole community water storage capacity by epiphytes are still quite limited. Epiphyte communities are shaped by both microclimate and host plant identity, and so the canopy and bole community storage capacity might also be expected to vary across similar spatial scales. We estimated canopy and bole community cover and biomass of bryophytes and lichens from ground-based surveys across a temperate-boreal ecotone in continental North America (Minnesota). Multiple forest types were studied at each site, to separate stand level and latitudinal effects. Biomass was converted into potential canopy and bole community storage on the basis of water-holding capacity measurements of dominant taxa. Bole biomass and potential water storage was a much larger contributor than outer canopy. Biomass and water storage capacity varied greatly, ranging from 9 to >900kg ha–1 and 0.003 to 0.38 mm, respectively. These values are lower than most reported results for temperate forests, which have emphasized coastal and old-growth forests. Variation was greatest within sites and appeared to reflect the strong effects of host tree identity on epiphyte communities, with conifer-dominated plots hosting more lichen-dominated epiphyte communities with lower potential water storage capacity. These results point to the challenges of estimating and incorporating epiphyte contributions to canopy hydrology from stand metrics. Further work is also needed to improve estimates of canopy epiphytes, including crustose lichens.

Climate warming causes photobiont degradation and carbon starvation in a boreal climate sentinel lichen

“…These persistent effects could lead to gradual impoverishment of the ecosystem impacts of epiphyte communities, such as modulation of canopy hydrology. Epiphytic lichens can significantly impact canopy and bole water retention and flow, and this property is directly related to their WHC (Van Stan and Pypker, 2015; Hembre et al, 2021).…”

“…For example, epiphytic lichens are increasingly recognized as sensitive climate indicators because they are largely decoupled from soil conditions, making them particularly responsive to atmospheric moisture and temperature (Ellis, 2019;Smith et al, 2020). Epiphytic lichens have significant impacts on ecosystem nutrient and water budgets in forests, while providing food and shelter for diverse animals (Asplund and Wardle, 2016;Porada et al, 2014Porada et al, , 2018Hembre et al, 2021). Therefore, characterizing the climate responses of lichens is not only valuable for monitoring atmospheric changes, but it can also help predict how loss of function in lichens could have broader consequences for forest ecosystems.…”

Impact of changing climate on bryophyte contributions to terrestrial water, carbon, and nitrogen cycles

“…In turn, the ground bryophyte layer and biocrust bryophytes mediate water movement from the atmosphere to the soil (Xiao et al, 2015;Gall et al, 2022). Studies indicate that forest type and age can greatly impact potential epiphyte bryophyte interception (and short-term storage), which can vary from < 1 mm of incoming precipitation in continental temperate (Hembre et al, 2021) and tropical secondary forest to nearly 5 mm in an old-growth tropical cloud forest (K€ ohler et al, 2007). Consequently, it is not surprising that in a global modeling effort, Porada et al (2018) estimated that epiphytic bryophytes in forests may increase rainfall interception by more than 60%, but with great spatial heterogeneity.…”

“…3m–r; Elumeeva et al ., 2011; Grau‐Andrés et al ., 2021). Variation in water storage capacity is also species‐specific (Davey, 1997; Michel et al ., 2013) and can be related to bryophyte functional groups (Lett et al ., 2021), providing evidence that not all bryophytes should be categorized as one functional group and that community composition drives bryophyte impacts on the water cycle (Hembre et al ., 2021). An example of this is that deeper bryophyte layers (a functional trait) have a greater capacity for water storage, which results in colder soils and better temperature insulation compared to thinner bryophyte layers that hold less water.…”