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In this study we draw attention to the inherent variability in the results of trial trenching, when taking into account the countless variations in orientation and positioning of trenches. Grids of trial trenches were simulated time and again on the excavation plans of 16 archaeological sites from Flanders, Belgium. Orientation and positioning of the grid layout was shifted randomly, whilst the area coverage varied from 2.5% to 80%. The intersection rates of the archaeological features allow to gain more insight in trends and variability that are inherent to the chosen design of trial trenches. It is assessed how robust a chosen grid layout performs on (multi-period) archaeological sites and how variable these results might be. The most effective layout appears to be a grid with short, parallel and discontinuous trenches or a standard grid, closely followed by 2 m wide continuous trenches. Implementing 4 m wide trenches reduces the effectiveness of the latter method substantially. When the area coverage of the trenches is below 10%, the results of the archaeological prospection become unreliable and can potentially lead to a substantial over-or underestimation of the actual feature density on the site. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Models project that climate warming will cause the tree line to move to higher elevations in alpine areas and more northerly latitudes in Arctic environments. We aimed to document changes or stability of the tree line in a sub-Arctic model area at different temporal and spatial scales, and particularly to clarify the ambiguity that currently exists about tree line dynamics and their causes. The study was conducted in the Torneträsk area in northern Sweden where climate warmed by 2.5 °C between 1913 and 2006. Mountain birch ( Betula pubescens ssp. czerepanovii) sets the alpine tree line. We used repeat photography, dendrochronological analysis, field observations along elevational transects and historical documents to study tree line dynamics. Since 1912, only four out of eight tree line sites had advanced: on average the tree line had shifted 24 m upslope (+0.2 m year assuming linear shifts). Maximum tree line advance was +145 m (+1.5 m year in elevation and +2.7 m year in actual distance), whereas maximum retreat was 120 m downslope. Counter-intuitively, tree line advance was most pronounced during the cooler late 1960s and 1970s. Tree establishment and tree line advance were significantly correlated with periods of low reindeer ( Rangifer tarandus) population numbers. A decreased anthropozoogenic impact since the early 20th century was found to be the main factor shaping the current tree line ecotone and its dynamics. In addition, episodic disturbances by moth outbreaks and geomorphological processes resulted in descent and long-term stability of the tree line position, respectively. In contrast to what is generally stated in the literature, this study shows that in a period of climate warming, disturbance may not only determine when tree line advance will occur but if tree line advance will occur at all. In the case of non-climatic climax tree lines, such as those in our study area, both climate-driven model projections of future tree line positions and the use of the tree line position for bioclimatic monitoring should be used with caution. [ABSTRACT FROM AUTHOR]

Question: What are the age structure and growth trends in a 160-year old not-managed Pinus sylvestris plantation with spontaneous development of Quercus robur and can recruitment of Q. robur be related to the radial growth pattern of the P. sylvestris overstorey? Location: Mattemburgh forest reserve, The Netherlands. Methods: Throughout the forest, we sampled 103 oaks and 102 pines with an increment corer. Tree ring widths were measured and cross-dated to produce mean ring width series. With these data we determined tree ages, investigated growth trends and identified growth releases and suppressions. Results: Q. robur is uneven-aged: some individuals recruited around 1925, but most reached coring height in the 1940s. The latter recruitment period related to a transition from stressed to released growth of the overstorey pines, growth releases of the oldest Q. robur and occurrence of P. sylvestris regeneration. No further recruitment has taken place since 1950. Conclusions: This study demonstrates that an old pine plantation can develop spontaneously into well-structured pine forest with an understorey of oak and pine. However, understorey recruitment in these forest types is not a continuous process and in this case a single allogenic canopy disturbance triggered its establishment. [ABSTRACT FROM AUTHOR]