Long-Term Impacts of Forest Ditching on Non-Aquatic Biodiversity: Conservation Perspectives for a Novel Ecosystem

Abstract

Artificial drainage (ditching) is widely used to increase timber yield in northern forests. When the drainage systems are maintained, their environmental impacts are likely to accumulate over time and along accompanying management, notably after logging when new forest develops on decayed peat. Our study provides the first comprehensive documentation of long-term ditching impacts on terrestrial and arboreal biodiversity by comparing natural alder swamps and second-generation drained forests that have evolved from such swamps in Estonia. We explored species composition of four potentially drainage-sensitive taxonomic groups (vascular plants, bryophytes, lichens, and snails), abundance of species of conservation concern, and their relationships with stand structure in two-ha plots representing four management types (ranging from old growth to clearcut). We found that drainage affected plot-scale species richness only weakly but it profoundly changed assemblage composition. Bryophytes and lichens were the taxonomic groups that were most sensitive both to drainage and timber-harvesting; in closed stands they responded to changed microhabitat structure, notably impoverished tree diversity and dead-wood supply. As a result, natural old-growth plots were the most species-rich and hosted several specific species of conservation concern. Because the most influential structural changes are slow, drainage impacts may be long hidden. The results also indicated that even very old drained stands do not provide quality habitats for old-growth species of drier forest types. However, drained forests hosted many threatened species that were less site type specific, including early-successional vascular plants and snails on clearcuts and retention cuts, and bryophytes and lichens of successional and old forests. We conclude that three types of specific science-based management tools are needed to mitigate ditching effects on forest biodiversity: (i) silvicultural techniques to maintain stand structural complexity; (ii) context-dependent spatial analysis and planning of drained landscapes; and (iii) lists of focal species to monitor and guide ditching practices.

The Potential of Production Forests for Sustaining Lichen Diversity: A Perspective on Sustainable Forest Management

“…Two stands were old eutrophic boreo-nemoral stands and nine stands were post-wildfire stands in Scots pine-dominated dry boreal or paludified (Polytrichum and Vaccinium) sites (documented by [23,59], respectively). In six wildfire stands (three naturally regenerating and three salvage logged Our study system included 127 forest stands distributed among the following five common forest site-type groups (sensu [57]): (1) 35 dry boreal forests (mostly Vaccinium vitis-idaea type) on higher fluvioglacial landforms and till mounds with podzols (pH KCl 3.5 to 5.0) where the top layer is periodically dry and ground water deeper than 2 m; (2) 24 meso-eutrophic forests (mostly Oxalis type) on till mounds or rolling plains with podzols or stagnic Luvisols (pH KCl 3.2 to 4.2) where ground water is usually deeper than 2 m; (3) 26 eutrophic boreo-nemoral forests (mostly Aegopodium type) predominantly on undulating sandy till plains with favorably moist (in springtime anaerobic) Gleyic Cambisols or Luvisols (pH KCl 4.7 to 6.5) almost lacking organic horizon; (4) 20 mobile-water swamp forests on thin seasonally flooded Eutric histosols and Fluvisols with a peat layer >30 cm (pH KCl 5.0 to 6.5) in lowlands and valleys along rivers or around bogs; (5) 24 artificially drained swamp forests (Oxalis type, originating from type 4, see [16]) on well decomposed peat soils (pH KCl 4.0 to 6.5). The dry boreal stands were dominated by Scots pine (Pinus sylvestris) (Figure 2a-c); the other sites hosted conifer/deciduous mixtures with Norway spruce (Picea abies) ( Figure 2d-e) or, in some Oxalis type stands, with Scots pine.…”

“…Lobaria pulmonaria (epiphytic macrolichen) Dispersal/establishment Spatio-temporal connectivity of nemoral broad-leaved trees and aspen in reserves [42,77,96,[105][106][107][108] Menegazzia terebrata (epiphytic macrolichen) Air moisture and quality Hydrologically intact semi-open moist and wet forests [16,105,109,110] Chaenotheca gracilenta (epixylic microlichen) Microhabitat Supply of shady moist microhabitats on dying and uprooted old trees in reserves [15,43,50,105] Xylopsora friesii (epiphytic/epixylic microlichen) Disturbance regime Conifer forests with continuity of small-scale disturbances and slow-grown old trees [46,111] Species sensitive to reduced rotations and functioning of mature production stands…”

“…Microhabitat and -climate Mature species-rich moist and wet forests [16,42,46,81,105] Chaenotheca brachypoda (epiphytic/epixylic microlichen) Microhabitat Supply of senescent trees with bark and wood crevices in close-canopy stands [15,43,50,105] Chaenothecopsis haematopus (saproxylic calicioid fungus) Fungal tree pathogens Soft exposed wood on deciduous trees that die standing [15,43,112] Calicium parvum (epiphytic microlichen) Pine management Landscape-scale continuity of mature pine stands [15,88,105] Multiclavula mucida (epixylic basidiolichen) Full decay cycles of fallen trees Supply of well decayed large trunks in close-canopy stands [105]…”

“…The uncertainties related to such gaps of knowledge remain greatest for the most species-rich and poorly detectable taxon groups.In this paper, our main aim is to characterize, in operational terms for SFM, the ecological composition of lichens (lichenized fungi) in forest landscapes. We build on nearly 20 years of research on biodiversity in Estonian forests where we have used standard sampling designs to test the responses of species and assemblages to various influences of even-aged forestry (e.g., [15][16][17][18]). The Estonian context is suitable for general insight because it has, until recently, adopted a "semi-natural forestry" approach, which mitigates environmental impacts of even-aged forestry and forestry drainage by frequently using natural regeneration, tree retention, and low intensity of thinnings [19,20].…”

Dynamics of tree layer composition, tree age and large diameter trees in Habitats Directive Annex I forest habitats in Estonia on the basis of monitoring data collected from 2010–2012

“…The protection of late-succession habitats and continuous forest areas (including areas with natural disturbances) is the primary goal in Estonian forest nature conserva-tion (Nature Conservation Act). Longtime human influence on forests and especially rapid intensification of forest clear-cutting and ditching during the last centuries have resulted in low continuity of forest landscapes (Laasimer, 1965;Lõhmus et al, 2004;Etverk & Meikar, 2008;Lõhmus & Kraut, 2010;Remm et al, 2013). Most especially valuable habitats in Estonia are now maintained within nature conservation areas or special strict protection zones in national parks and landscape protection areas.…”