Reconstruction of a 253-year long mast record of European beech reveals its association with large scale temperature variability and no long-term trend in mast frequencies

Synchronous production of large seed crops, or mast years (MYs), is a common feature of many Fagus species, which is closely linked to the dynamics of forest ecosystems, including regeneration of canopy trees and changes in animal population densities. To better understand its climatic controls and check for the presence of long-term temporal trends in MY frequencies, we reconstructed MY record of the European beech (Fagus sylvatica L.) for the southern Swedish province of Halland over 1753-2006. We used superimposed epoch analysis (SEA) to relate MY (a) to summer temperature fields over the European subcontinent and (b) to the patterns of 500 mb geopotential heights over the 35-75 degrees N. For the MY reconstruction, we used newly developed regional beech ring-width chronology (1753-2006), an available summer temperature reconstruction, and a discontinuous historical MY record. A Monte Carlo experiment allowed identification of the thresholds in both growth and summer temperature anomalies, indicative of historical MYs, which were verified by dividing data into temporally independent calibration and verification sub-periods.MYs were strongly associated with both the 500 mb height anomalies and average summer temperatures during two years preceding a MY: a mast year (t) followed a cold summer two years (t-2) prior to the mast year and a warm summer one year prior (t-1) to the mast year. During t-2 years, the geographical pattern of 500 mb height anomalies exhibited a strong height depression in the region centered in the Northern Sea and extending toward eastern North America and statistically significant (p<0.05) temperature anomalies covering predominantly southern Scandinavia (area below 60 N) and British Isles. A year immediately preceding a mast year (t-1) was characterized by a strong regional high pressure anomaly centered in southern Scandinavia with significant temperature anomalies extended mostly over southern Scandinavia and Germany.The long-term mean MY return interval was 6.3 years, with 50 and 90% probabilities of MY occurrence corresponding to 6 and 15 years, respectively. Periods with intervals significantly shorter than the long-term mean were observed around 1820-1860 and 1990-2006 (means 3.9 and 3.2 years, respectively). However, the difference in return intervals between two sub-periods themselves was not significant.Geographically large and temporally rapid changes in atmospheric circulation among years, responsible for summer temperature conditions in the Northern Europe, are likely primary environmental drivers of masting phenomenon. However, decadal and centurial variability in MY intervals is difficult to relate directly to temperature variability, suggesting the presence of conditions "canceling" would-be MYs. Long-term MY reconstruction demonstrates high variability of reproductive behavior in European beech and indicates that a period with shorter MY intervals at the end of 20th may be not unique in a multi-century perspective

Temperate forest development during secondary succession: effects of soil, dominant species and management

With the increase in abandoned agricultural lands in Western Europe, knowledge on the successional pathways of newly developing forests becomes urgent. We evaluated the effect of time, soil type and dominant species type (shade tolerant or intolerant) on the development during succession of three stand attributes: above-ground biomass, stand height (HT) and stem density (SD). Additionally, we compared above-ground biomass (AGB) in natural and planted forests, using ten chronosequences (8 from the literature and 2 from this study). Both AGB and HT increased over time, whereas SD decreased. HT, SD and AGB differed among species types. For example, birch had greater HT than alder, willow and ash at a similar age and had higher SD than pine and oak at a similar age. However, birch showed lower AGB than pine. HT and AGB differed among soil types. They were higher in rich soil than in poor soils. Comparative analysis between chronosequences showed an effect of the regeneration method (natural regeneration vs plantation) on above-ground biomass. Planted sites had higher AGB than natural regeneration. Time, soil type, species and regeneration method influenced the mechanism of stand responses during secondary succession. These characteristics could be used to clarify the heterogeneity and potential productivity of such spontaneously growing temperate forest ecosystems

Landscape effects on anuran pond occupancy in an agricultural countryside: barrier-based buffers predict distributions better than circular buffers

Species movement and occupancy of habitat patches are dependent on landscape permeability. Some land-use types (e.g., roads) may be barriers to animal movement. Analyses of the effect of landscape structure on patch occupancy usually use circular buffers around focal patches. The main assumption of this methodological approach is that species are affected by a particular landscape element equally in every direction from a given patch. This assumption is likely not to hold if animal movement is restricted by barriers because barriers reduce movement patterns and reshape the ideal circular buffer into a noncircular buffer. We developed a method to determine the effect of landscape variables on the distribution of two amphibian species that explicitly takes dispersal barriers into account. We extracted landscape variables within (i) circular buffers (CB) and (ii) barrier-based buffers (BBB). BBB were produced by reducing the boundaries of CB according to major impassable barriers. The BBB approach almost doubled the explained deviance of multiple regression models in comparison with the CB approach. Moreover, CB and BBB models included different predictor variables. We suggest that the BBB approach is more useful than the traditional CB analyses of species–habitat relationships because ecological barriers are explicitly taken into account

Imperfect detection and its consequences for monitoring for conservation

Biodiversity monitoring is important to identify conservation needs and test the efficacy of management actions. Variants of “abundance” (N) are among the most widely monitored quantities, e.g., (true) abundance, number of occupied sites (distribution, occupancy) or species richness.We propose a sampling-based view of monitoring that clearly acknowledges two sampling processes involved when monitoring N. First, measurements from the surveyed sample area are generalized to a larger area, hence the importance of a probability sample. Second, even within sampled areas only a sample of units (individuals, occupied sites, species) is counted owing to imperfect detectability p. If p < 1, counts are random variables and their expectation E(n) is related to N via the relationship E(n) ÿ*p. Whenever p < 1, counts vary even under identical conditions and underestimate N, and patterns in counts confound patterns in N with those in p. In addition, part of the population N may be unavailable for detection, e.g., temporarily outside the sampled quadrat, underground or for another reason not exposed to sampling; hence a more general way of describing a count is E(n) ÿ*a*p, where a is availability probability and p detection, given availability. We give two examples of monitoring schemes that highlight the importance of explicitly accounting for availability and detectability. In the Swiss reptile Red List update, the widespread and abundant slow worm (Anguis fragilis) was recorded in only 22.1% of all sampled quadrats. Only an analysis that accounted for both availability and detectability gave realistic estimates of the species’ distribution. Among 128 bird species monitored in the Swiss breeding bird survey, de tection in occupied 1 km quadrats averaged only 64% and varied tremendously by species (3–99 %); hence observed distributions greatly underestimated range sizes and should not be compared among species.We believe that monitoring design and analyses should properly account for these two sampling processes to enable valid inferences about biodiversity. We argue for a more rigorous approach to both monitoring design and analysis to obtain the best possible information about the state of nature. An explicit recognition of, and proper accounting for, the two sampling processes involved in most monitoring programs will go a long way towards this goa