Abstract. The condition of forest ecosystems depends on the temporal and spatial pattern of management interventions and natural disturbances. Remnants of previous conditions persisting after disturbances, or ecosystem legacies, collectively comprise ecosystem memory. Ecosystem memory in turn contributes to resilience and possibilities of ecosystem reorganization following further disturbance. Understanding the role of disturbance and legacies is a prerequisite for maintaining resilience in the face of global change. Several legacy concepts discussed in the peer-reviewed literature, including disturbance, biological, soil, land-use, and silvicultural legacies, overlap in complex ways. Here, we review these established legacy concepts and propose that the new terms "material legacy" (individuals or matter, e.g., survivors, coarse woody debris, nutrients left after disturbance) and "information legacy" (adaptations to historical disturbance regimes) cut across these previous concepts and lead to a new classification of legacies. This includes six categories: material legacies with above-and belowground, and biotic and abiotic categories, and information legacies with above-and belowground categories. These six legacies are influenced by differential patterns of editing and conditioning by "legacy syndromes" that result from natural or human-manipulated disturbance regimes that can be arranged along a gradient of naturalness. This scheme is applied to a case study of hemiboreal forests in the Baltic States of Estonia, Latvia, and Lithuania, where natural disturbance, traditional clearcut silviculture, and afforestation of abandoned agricultural lands constitute the three main legacy syndromes. These legacy syndromes in turn influence forest response to management actions and constrain resilience, leading to a mosaic of natural, manipulated, and artificial (novel) ecosystems across the landscape, depending on how the legacies in each syndrome affect ecological memory.
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Root and butt rot is the most destructive disease of conifers in the Northern Hemisphere, but little is known about the dynamics of yield loss in stands of different ages, site types, and species composition. This study aimed to estimate butt rot incidence, causal fungi, and related wood yield loss in Picea abies (L.) H. Karst. stands in Latvia. A total of 24 745 stumps were examined on 318 forest sites, and 21.8% of them contained rot. There was a positive correlation between stand age and butt rot frequency. Proportion of other tree species in a stand had no influence on incidence of the rot, but significant differences were observed among different forest site types. The length of decay columns in 114 stems analysed was 6.6 ± 2.6 m on average. Based on the observed butt rot frequencies in Latvian P. abies stands of different age classes, volumes of decay-degraded wood in a fully stocked stand would comprise about 19.7 m3·ha–1 at the age of 40 years, 57.4 m3·ha–1 at 60 years, 54.9 m3·ha–1 at 80 years, 63.1 m3·ha–1 at 100 years, and 91.8 m3·ha–1 at 120 years, corresponding to 6%–16% of a total standing volume.
& Key message Volume predictions of sample trees are basic inputs for essential National Forest Inventory (NFI) estimates. The predicted volumes are rarely comparable among European NFIs because of country-specific dbh-thresholds and differences regarding the inclusion of the tree parts stump, stem top, and branches. Twenty-one European NFIs implemented harmonisation measures to provide consistent stem volume predictions for comparable forest resource estimates. & Context The harmonisation of forest information has become increasingly important. International programs and interest groups from the wood industry, energy, and environmental sectors require comparable information. European NFIs as primary source of forest information are well-placed to support policies and decision-making processes with harmonised estimates. & Aims The main objectives were to present the implementation of stem volume harmonisation by European NFIs, to obtain comparable growing stocks according to five reference definitions, and to compare the different results. & Methods The applied harmonisation approach identifies the deviations between country-level and common reference definitions. The deviations are minimised through country-specific bridging functions. Growing stocks were calculated from the unharmonised, and harmonised stem volume estimates and comparisons were made. This article is part of the topical collection on Forest information for bioeconomy outlooks at European level
Highlights• Climate effects and human influence on forest fire activity in Latvia was assessed using time-series analysis.• Drought conditions during summer season had the strongest effect on fire activity of tested climatic variables.• Negative trends and spatial distribution pattern of fire activity suggests of prevailing human influence on forest fire regime over the 20th century. AbstractFire as disturbance of forests has an important ecological and economical role in boreal and hemiboreal forests. The occurrence of forest fires is both climatically and anthropogenically determined and shifts in fire regimes are expected due to climate change. Although fire histories have been well documented in boreal regions, there is still insufficient information about fire occurrence in the Baltic States. In this study, spatio-temporal patterns and climatic drivers of forest fires were assessed by means of spatial and time-series analysis. The efficiency of Canadian Fire Weather (FWI) indices as indicators for fire activity was tested. The study was based on data from the literature, archives, and the Latvian State Forest service database. During the period 1922-2014, the occurrence and area affected by forest fires has decreased although the total area of forest land has nearly doubled, suggesting improvement of the fire suppression system as well as changes in socioeconomic situation. The geographical distribution of forest fires revealed two pronounced clusters near the largest cities of Riga and Daugavpils, suggesting dominance of human causes of ignitions. The occurrence of fires was mainly influenced by drought. FWI appeared to be efficient in predicting the fire occurrence: 23-34% of fires occurred on days with a high or extremely high fire danger class, which overall had a relative occurrence of only 4.3-4.6%. During the 20th century, the peak of fire activity shifted from May to April, probably due to global warming and socioeconomic reasons. The results of this study are relevant for forest hazard mitigation and development of fire activity prediction system in Latvia.
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