Large-scale historical afforestation failure with Pinus cembra in the Swiss Prealps

Between the nineteenth and early twentieth centuries, large-scale afforestation projects were undertaken in the Swiss Prealps. The Swiss stone pine (Pinus cembra L.), an emblematic alpine tree with important economic potential, conservation value and ecological relevance, was one of the species used in these afforestation efforts. We investigated the distribution and site characteristics of all known natural populations and planted stands in the canton of Fribourg (Switzerland). Between 1885 and 1952, artificial afforestation was carried out in the mountainous regions of the canton of Fribourg. Nearly 450,000 seedlings of P. cembra were planted. One century later, only approximately 650 trees survived (0.15% of all planted trees). Moreover, no natural regeneration can be observed in the afforested stands. Since no known harvest activities were undertaken in these planted stands, the whole afforestation campaign of P. cembra in the canton of Fribourg can be described as a failure. Possible causes are investigated and discussed. In this region, P. cembra occurs naturally only in particular microrefugia with markedly rough topography. We argue that the lack of knowledge or consideration of the ecology of the species at a local scale can be an important factor leading to this failure. In the actual context of large-scale afforestation projects anticipating and mitigating the negative effects of global warming, our study highlights the importance of a precise understanding of species ecology and regional conditions.

Pinus cembra L. tree-ring data as a proxy for summer mass-balance variability of the Careser Glacier (Italian Rhaetian Alps)

Glacial extent and mass balance are sensitive climate proxies providing solid information on past climatic conditions. However, series of annual mass-balance measurements of more than 60 years are scarce. To our knowledge, this is the first time the latewood density data (MXD) of the Swiss stone pine (Pinus cembra L.) have been used to reconstruct the summer mass balance (Bs) of an Alpine glacier. The MXD-based Bs well correlates with a Bs reconstruction based on the May to September temperature. Winter precipitation has been used as an independent proxy to infer the winter mass balance and to obtain an annual mass-balance (Bn) estimate dating back to the glaciological year 1811/12. The reconstructed MXD/precipitation-based Bn well correlates with the data both of the Careser and of other Alpine glaciers measured by the glaciological method. A number of critical issues should be considered in both proxies, including non-linear response of glacial mass balance to temperature, bedrock topography, ice thinning and fragmentation, MXD acquisition and standardization methods, and finally the ‘divergence problem’ responsible for the recently reduced sensitivity of the dendrochronological data. Nevertheless, our results highlight the possibility of performing MXD-based dendroglaciological reconstructions using this stable and reliable proxy.

The influence of carbon-containing greenhouse gases on the dynamics of radial increment of Pinus cembra and Picea abies in the conditions of the Gorgany Nature Reserve

Based on the tree-ring chronology, we studied the radial increment of Swiss stone pine (Pinus cembra L.) and common spruce, or Norway spruce (Picea abies L.) as indicators of dendrochronological studies and, based on tree-ring chronology, reconstructed the annual changes of stem biomass and the amount of carbon accumulated in it by P. cembra and P. abies in the Gorgany Nature Reserve. Swiss stone pine stands are of great zoological importance as biotopes of nutcracker (Nucifraga caryocatactes L.), crossbill (Loxia curvirostra L.), capercaillie (Tetrao urogallus L.) and other representatives of rare boreal fauna. Samples were taken from trees of the Playa forest district of the Brusturyan Forest Hunting Range State Enterprise of the Transcarpathian Regional Forestry Administration (P. cembra and P. abies) from trees that did not have visual signs of damage in the Gorgany Nature Reserve. By cross-dating the radial increments of two radii for each tree, individual chronological series were drawn up. Carbon sequestration in P. cembra and P. abies stem wood was evaluated on the basis of dendrochronological analysis of radial increment. The accuracy of cross-dating of dendrochronological series of individual trees, individual chronological series, and representativeness of the generalized series were verified by conventional methods. It was found that the average annual radial increment of the trees under study is 11.48 mm in P. cembra and 14.39 in P. abies, and varies in the range of 1.86–5.49 mm. The data obtained indicate an increase in the ability of P. cembra and P. abies to accumulate carbon with increasing age. The study of carbon sequestration in the stem wood of P. cembra and P. abies, based on dendrochronological analysis, made it possible to reconstruct the annual variation in stem biomass increment and accumulated carbon. The analysis of interdependence of the radial increment of P. cembra and P. abies in the Gorgany Nature Reserve and the value of carbon-containing greenhouse gases in the atmosphere, carried out by the augmented data sample, made it possible to specify the periods most significant for the formation of annual rings. The reaction in radial increment is most pronounced from June to September, with the annual values of carbon-containing greenhouse gases being maximally reflected in radial increment for the period from October to April.

Climate warming does not adequately translate to increased radial stem growth of coniferous species along the Alpine treeline ecotone

<p>It is well established, that tree growth at high elevations is mainly limited by low temperature during the growing season and climate warming was frequently found to lead to more growth and expansion of trees into alpine tundra. However, dendroclimatological studies revealed contradictory growth response to recent climate warming at the upper elevational limit of tree growth, and transplant experiments unveiled that high elevation tree provenances are not adequately benefiting from higher temperatures when planted at lower elevation. We therefore re-evaluated growth response of trees to recent climate warming by developing tree ring series of co-occurring conifers (Swiss stone pine (<em>Pinus cembra</em>), European larch (<em>Larix decidua</em>), and Norway spruce (<em>Picea abies</em>)) along several altitudinal transects stretching from the subalpine zone to the krummholz-limit (1630–2290 m asl; n=503 trees) in the Central European Alps (CEA). We evaluated whether trends in basal area increment (BAI) are in line with two phases of climate warming which occurred from 1915–1953 and from mid-1970s until 2015. We expected that BAI of all species shows an increasing trend consistent with distinct climate warming during the study period (1915–2015) amounting to >2 °C. Although enhanced tree growth was detected in all species in response to climate warming, results revealed that at subalpine sites (<em>i</em>) intensified climate warming since mid-1970s did not lead to corresponding increase in BAI, and (<em>ii</em>) increase in summer temperature primarily favored growth of Norway spruce, although Swiss stone pine dominates at high altitude in the CEA and therefore was expected to mainly benefit from climate warming. At treeline BAI increase was above the determined age trend in all species, whereas at the krummholz-limit only deciduous larch showed minor growth increase. We explain missing adequate growth response to recent climate warming (<em>i</em>) by strengthened competition for resources (primarily nutrients and light) in increasingly denser stands at subalpine sites leading to changes in carbon allocation among tree organs, and (<em>ii</em>) by frost desiccation injuries of evergreen tree species at the krummholz-limit. Our findings indicate that tree growth response to climate warming at high elevation is possibly nonlinear, and that increasing competition for resources and the influence of climate factors beyond the growing season impair stem growth. </p>

Growth Trends of Coniferous Species along Elevational Transects in the Central European Alps Indicate Decreasing Sensitivity to Climate Warming

Tree growth at high elevation in the Central European Alps (CEA) is strongly limited by low temperature during the growing season. We developed a tree ring series of co-occurring conifers (Swiss stone pine, Norway spruce, European larch) along elevational transects stretching from the subalpine zone to the krummholz limit (1630–2290 m asl; n = 503 trees) and evaluated whether trends in basal area increment (BAI) are in line with two phases of climate warming, which occurred from 1915–1953 and from 1975–2015. Unexpectedly, results revealed that at subalpine sites (i) intensified climate warming in recent decades did not lead to a corresponding increase in BAI and (ii) increase in summer temperature since 1915 primarily favored growth of larch and spruce, although Swiss stone pine dominates at high elevations in the Eastern CEA, and therefore was expected to mainly benefit from climate warming. At treeline, BAI increases in all species were above the level expected based on determined age trend, whereas at the krummholz limit only deciduous larch showed a minor growth increase. We explain missing adequate growth response to recent climate warming by strengthened competition for resources (nutrients, light, water) in increasingly denser stands at subalpine sites, and by frost desiccation injuries of evergreen tree species at the krummholz limit. To conclude, accurate forecasts of tree growth response to climate warming at high elevation must consider changes in stand density as well as species-specific sensitivity to climate variables beyond the growing season.

Ecological and genetic aspects of distribution of the marginal populations of Swiss stone pine (Pinus cembra L.) in Ukrainian Carpathians

Current distributions of Swiss stone pine mostly cover the mountain regions of Europe (Alps and Carpathians). Easternmost distribution of this species is located in western Ukraine. Due to environmental fragmentation in Eastern Carpathians and competition with Norway spruce and other species, marginal populations of Swiss stone pine create isolated island, where other species are not able to cope with harsh conditions. Still, Pinus cembra L. play an important role for soil-formation and soil-protection in high elevations. The evidence of recent reduction in the area of Swiss stone pine raises the question whether the introduction of this species at lower altitudes can be successful? According to the studies conducted on reciprocal transplant experiments, Swiss stone pine population from higher elevation are able to profit in low elevation sites. Thus, parallelly with gene conservation activity, the possibilities of assisted migration should be recognized for this species.