From tree-related microhabitats to ecosystem management: A tree-scale investigation in productive forests in Estonia.

A diversity of microhabitats has been suggested to play a key role in mediating the co-occurrence of trees with specific tree-inhabiting biodiversity, which may further influence ecosystem functioning. However, this triple relationship between tree characteristics, tree-related microhabitats (TreMs), and biodiversity has not been described explicitly enough to set quantitative targets of ecosystem management. The two major approaches directly targeting TreMs in ecosystem management are tree-scale field assessment of TreMs and precautionary management, which both require insights into the predictability and magnitude of specific biodiversity-TreM relationships. To obtain such insights, we analysed tree-scale relationships between the diversity of TreM development processes (four classes: peculiarity; pathology; injury; emergent epiphyte cover) and selected biodiversity variables based on 241 live trees (age range 20-188 years) of two species (Picea abies, Populus tremula) in hemiboreal forests in Estonia. We addressed the diversity and abundance of epiphytes, arthropods, and gastropods; their specific response to TreMs was disentangled from tree age and tree size effects. We found that a relatively small improvement in the biodiversity responses studied was attributable solely to TreMs, and that such contribution was more frequently observed in young trees. Unexpectedly, several age- or size-independent effects of TreMs were negative, suggesting trade-offs with other factors of biodiversity relevance (such as tree foliage suppression due to injuries that created TreMs). We conclude that tree-scale microhabitat inventories have only limited potential to resolve the general problem of providing diverse habitats for biodiversity in managed forests. The basic sources of uncertainty are that microhabitat management is mostly indirect (managing TreM-bearing trees and stands rather than TreMs themselves) and that snapshot surveys cannot address various time perspectives. We outline a set of basic principles and constraints for spatially heterogeneous and precautionary forest management that includes TreM diversity considerations. These principles can be further elaborated through multi-scale research on functional biodiversity links of TreMs.

Regionally Varying Habitat Relationships in Lichens: The Concept and Evidence with an Emphasis on North-Temperate Ecosystems.

Habitat ecology of lichens (lichen-forming fungi) involves diverse adaptations to stressful environments where lichens use specific habitat conditions. Field observations confirm that such habitat 'preferences' can vary significantly across species' distribution ranges, sometimes revealing abrupt changes over short distances. We critically review and generalize such empirical evidence as broad ecological patterns, link these with the likely physiological mechanisms and evolutionary processes involved, and outline the implications for lichen conservation. Non-replicated correlative studies remain only suggestive because the data are frequently compromised by sampling bias and pervasive random errors; further noise is related to unrecognized cryptic species. Replicated evidence exists for three macroecological patterns: (a) regional limiting factors excluding a species from a part of its microhabitat range in suboptimal areas; (b) microhabitat shifts to buffer regionally adverse macroclimates; (c) substrate suitability changed by the chemical environment, notably air pollution. All these appear to be primarily buffering physiological challenges of the adverse conditions at the macrohabitat scale or, in favorable environments, coping with competition or predation. The roles of plasticity, adaptation, dispersal, and population-level stochasticity remain to be studied. Although lichens can inhabit various novel microhabitats, there is no evidence for a related adaptive change. A precautionary approach to lichen conservation is to maintain long-term structural heterogeneity in lichen habitats, and consider lichen ecotypes as potential evolutionarily significant units and a bet-hedging strategy for addressing the climate change-related challenges to biodiversity.

Restoration dilemmas between future ecosystem and current species values: The concept and a practical approach in Estonian mires.

Ecosystem restoration is gaining political and economic support worldwide, but its exact targets and costs often remain unclear. A key issue, both for predicting restoration success and assessing the costs, is the uncertainty of post-restoration development of the ecosystem. A specific combination of uncertainties emerges when ecosystem restoration would negatively affect pre-restoration species conservation values. Such dilemma appears to be common, but largely ignored in restoration planning; for example, in historically degraded forests, wetlands and grasslands that provide novel habitats for some threatened species. We present a framework of linked options for resolving the dilemma, and exemplify its application in extensive mire restoration in Estonia. The broad options include: redistributing the risks by timing; relocating restoration sites; modifying restoration techniques; and managing for future habitats of the species involved. In Estonia, we assessed these options based on spatially explicit mapping of expected future states of the ecosystem, their uncertainty, and the distribution of species at risk. Such planning documentation, combined with follow-up monitoring and experimentation, can be used for adaptive management, by funding organizations and for academic research.

A simple survey protocol for assessing terrestrial biodiversity in a broad range of ecosystems.

Finding standard cost-effective methods for monitoring biodiversity is challenging due to trade-offs between survey costs (including expertise), specificity, and range of applicability. These trade-offs cause a lack of comparability among datasets collected by ecologists and conservationists, which is most regrettable in taxonomically demanding work on megadiverse inconspicuous taxon groups. We have developed a site-scale survey method for diverse sessile land organisms, which can be analyzed over multiple scales and linked with ecological insights and management. The core idea is that field experts can effectively allocate observation effort when the time, area, and priority sequence of tasks are fixed. We present the protocol, explain its specifications (taxon group; expert qualification; plot size; effort) and applications based on >800 original surveys of four taxon groups; and we analyze its effectiveness using data on polypores in hemiboreal and tropical forests. We demonstrate consistent effort-species richness curves and among-survey variation in contrasting ecosystems, and high effectiveness compared with casual observations both at local and regional scales. Bias related to observer experience appeared negligible compared with typical assemblage variation. Being flexible in terms of sampling design, the method has enabled us to compile data from various projects to assess conservation status and habitat requirements of most species (specifically rarities and including discovery of new species); also, when linked with site descriptions, to complete environmental assessments and select indicator species for management. We conclude that simple rules can significantly improve expert-based biodiversity surveys. Ideally, define (i) a common plot size that addresses multiple taxon groups and management goals; (ii) taxon groups based on field expertise and feasible number of species; (iii) sufficient and practical search time; (iv) a procedure for recording within-plot heterogeneity. Such a framework, combined with freedom to allocate effort on-site, helps utilizing full expertise of observers without losing technical rigor.

Long-term impacts of forest ditching on non-aquatic biodiversity: conservation perspectives for a novel ecosystem.

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.