Too much, too soon? Two Swedish case studies of short-term deadwood recruitment in riparian buffers

Abstract

Forested riparian buffers are retained along streams during forest harvest to maintain a number of ecological functions. In this paper, we examine how recently established riparian buffers along northern Swedish streams provide deadwood, a key objective for riparian buffer management in Sweden. We used observational and experimental data to show that the investigated buffers provided large volumes of deadwood to streams and riparian zones shortly after their establishment, likely jeopardizing continued recruitment over the long term. Deadwood volume decreased with increasing buffer width, and the narrowest buffers tended to blow down completely. Wider buffers (~ 15 m) provided similar volumes of deadwood as narrow buffers due to blowdowns but were, overall, more resistant to wind-felling. It is clear from our study, that wider buffers are currently a safer strategy for riparian management that aims to sustain provision of deadwood and other ecological objectives continuously on the long term.

Protecting our streams by defining measurable targets for riparian management in a forestry context

“…Large wood serves multiple functions in riparian‐stream ecosystems: wood (i) reduces water flow and diverts part of it into the riparian forest, (ii) retains sediments, nutrients and organic matter, (iii) diversifies habitats and (iv) enhances biodiversity on land and water (Martens et al., 2020). In managed forests, most LW enters the streams soon after harvest, with less recruitment during the rest of the rotation (Kuglerová et al., 2023). Thus, LW may limit stream fish biomass and biodiversity in streams, as well as riparian organisms that utilize wood as substrate in second‐growth forests, for more than 200 years (Hylander et al., 2005; Johnson & Almlöf, 2016; Martens et al., 2020).…”

“…Similarly stringent post‐harvest targets could be imposed also for stream and riparian ecosystems, aiming at, for example, an average volume or pieces of LW per stream length and/or riparian area (Figure 2). Forest managers then could make a local assessment whether the target is possible to achieve through natural LW recruitment from riparian buffers (Kuglerová et al., 2023, Table 1) or whether harvesting and adding logs is necessary, a practice that is being tested in Washington State (Martens et al., 2021). Such evaluations should also target long‐term consequences, that is, how persistent and functional such structures will be decades after the initial placement (Marttila et al., 2016).…”

Experimental riparian forest gaps and increased sediment loads modify stream metabolic patterns and biofilm composition

“…Small canopy gaps with lower (but not 0) shading within riparian buffers can locally promote primary production in streams (Bechtold et al, 2017) without the negative effects of increased temperatures. Further, such a management strategy would better balance environmental and economic goals because trees harvested from canopy gaps can compensate for the necessary increase in buffer width along streams in clear-cuts (Davies & Nelson, 1994;Kuglerov a et al, 2020Kuglerov a et al, , 2023.…”

“…Furthermore, increases in fine-grained substrates are common after forest harvest, site preparation, and ditching, and we show that if protective measures fail to reduce sediment transport, the benefits of increased light for aquatic primary consumers might disappear. For example, the current management of riparian buffers in Sweden leads to enormous blow-downs of trees and root wads right at the stream edges (Kuglerov a et al, 2023), leading to increased light, but also to increased sediment loading from the damaged stream banks. From our study, we can conclude that the combination of the two does not have a positive effect on the primary production of forest streams.…”