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•Scots pine and European beech maximum densities vary along a climate gradient.•The Reineke’s boundary line can be restated in terms of the Martonne aridity index.•The maximum density ...line pattern of variation with climate is species-specific.•The competition equivalence between species depends on climate and mean tree size.
The maximum size-density relationship (MSDR) reflects the boundary site occupancy and the self-thinning line for a given species, being a useful tool in forestry. Studies focusing on the MSDR often do not cover the whole distribution of the studied species, which results in different boundaries for a given species in different regions. A common MSDR is lacking for the increasingly demanded large-scale studies. However, this information is important where silvicultural responses must be prioritized among monospecific stands or where comparisons among maximum and relative stand densities between and within species are required.
For the purposes of this study, we used data from 9911 sample plots located in Scots pine and European beech monospecific stands. Both of these species are of considerable importance and widely distributed throughout Europe. The data came from National or Regional Forest Inventories of five European countries (Austria, Germany, France, Spain and Poland) and therefore were distributed across a wide range of climatic conditions.
The main aim of this study was to determine whether the MSDR of these species depends on environmental variables and to develop a MSDR model for each species that explain this variability along a climate gradient.
The resulting models showed that both parameters of species boundary lines were climate-dependent, but that the pattern of variation differed between species. Hence, the higher the humidity, the steeper the MSDR (more negative exponent) and the higher the intercept for beech, while in the case of pine, the higher the humidity, the straighter the MSDR and the lower the intercept. According to these models, the stand density indices, for a reference diameter of 25cm, varied with the humidity in a different way for each species. Consequently, the ratio between the two species increases with humidity, although it also depends on stand diameter.
These results are in accordance with the yield level theory and could contribute to the development of more precise silvicultural guidelines and growth models based on the self-thinning line. Moreover, they are of particular importance in the discussion of growth and the effects of mixing on mixed species stands.
•Forest management in the Mediterranean basin is challenging in a warming world.•Scientific studies provide evidence on the short-term benefits of management.•The implications of management for ...long-term resilience have been seldom assessed.•Management for short-term benefits frequently has unintended effects.•An explicit consideration of trade-offs and long-term effects of management is needed.
As global climate becomes warmer, the maintenance of the structure and function of Mediterranean forests constitutes a key challenge to forest managers. Despite the need for forest adaptation, an overall evaluation of the efficacy of current management strategies is lacking. Here we describe a theoretical framework for classifying management strategies, explicitly recognizing trade-offs with other, untargeted ecosystem components. We then use this framework to provide a quantitative synthesis of the efficacy of management strategies in the Mediterranean basin. Our review shows that research has focused on strategies aimed at decreasing risk and promoting resistance in the short-term, rather than enhancing long-term resilience. In addition, management strategies aiming at short-term benefits frequently have unintended consequences on other adaptation objectives and untargeted ecosystem components. Novel empirical studies and experiments focusing both on adaptation objectives and multiple responses and processes at the ecosystem level are needed. Such progress is essential to improve the scientific basis of forest management strategies and support forest adaptation in the Mediterranean basin.
To assess the spatial patterns of forest expansion (encroachment and densification) for mountain pine (Pinus uncinata Ram.) during the last 50 years at a whole mountain range scale by the study of ...different topographic and socio-economic potential drivers in the current context of global change. The study area includes the whole distributional area of mountain pine in the Catalan Pyrenees (north-east Spain). This represents more than 80 municipalities, covering a total area of 6018 km². Forest cover was obtained by image reclassification of more than 200 pairs of aerial photographs taken in 1956 and 2006. Encroachment and densification were determined according to changes in forest cover, and were expressed as binary variables on a 150 x 150 m cell-size grid. We then used logistic regression to analyse the effects of several topographic and socio-economic variables on forest expansion. In the period analysed, mountain pine increased its surface coverage by 8898 ha (an increase of more than 16%). Mean canopy cover rose from 31.0% in 1956 to 55.6% in 2006. Most of the expansion was found on north-facing slopes and at low altitudes. Socio-economic factors arose as major factors in mountain pine expansion, as encroachment rates were higher in municipalities with greater population losses or weaker primary sector development. The spatial patterns of mountain pine expansion showed a good match with the main patterns of land-use change in the Pyrenees, suggesting that land-use changes have played a more important role than climate in driving forest dynamics at a landscape scale over the period studied. Further studies on forest expansion at a regional scale should incorporate patterns of land-use changes to correctly interpret drivers of forest encroachment and densification.
El gestor forestal se enfrenta al desafío de tener que adaptar sus prácticas a un contexto de creciente incertidumbre ambiental, motivado por el cambio climático y las alteraciones en los regímenes ...de perturbaciones. El artículo repasa brevemente el concepto de gestión forestal adaptativa y las fases que componen este tipo de procesos. A continuación, identifica algunas líneas estratégicas de actuación a las que puede acogerse el gestor forestal para promover la progresiva adaptación de las masas al cambio climático y reforzar su resiliencia. Finalmente, remarca la importancia de monitorear adecuadamente la respuesta de las masas a los tratamientos ejecutados para poder evaluar, en base a ello, su pertinencia para la consecución de los objetivos perseguidos. Además, aboga por continuar estableciendo nuevas parcelas de seguimiento y ensayos y exprimir el potencial de las nuevas tecnologías y de los avances existentes en materia de análisis de datos y modelización para el ajuste y mejora de la práctica selvícola y de la planificación forestal.
AIM: To assess the effects of climate change, past land uses and physiography on the current position of the tree line in the Catalan Pyrenees and its dynamics between 1956 and 2006. LOCATION: More ...than 1000 linear kilometres of sub‐alpine tree line in the Catalan Pyrenees (north‐east Spain) METHODS: Using aerial photographs and supervised classification, we reclassified the images into a binary raster with ‘tree’ and ‘non‐tree’ values, and determined canopy cover in 1956 and 2006. We then determined the change in position of the tree line between 1956 and 2006 based on changes in forest cover. We used the distance from the position of the tree line in 1956 to the theoretical potential tree line – determined from interpretation of aerial photographs, identifying the highest old remnants of forest for homogeneous areas of the landscape in terms of bioclimatic conditions, bedrock, landform and exposure – as a surrogate of intensity of past land uses. RESULTS: Our analyses showed that the Pyrenean tree line has moved upwards on average almost 40 m (mean advance ± SE: 35.3 ± 0.5 m, P < 0.001), although in most cases it has remained unchanged (61.8%) or advanced moderately, i.e. between 25 and 100 m (23.7%); only 9.2% of the locations have advanced more than 100 m. Upward shifts of the tree line were significantly larger in locations heavily modified in the past by anthropogenic disturbance (mean advance 50.8 ± 1.1 m) compared with near natural tree line locations (19.7 ± 0.8 m, P < 0.001), where the mean displacement was much lower than expected and was not related to changes in temperature along the study period. MAIN CONCLUSIONS: Our results stress the impact of the cessation of human activity in driving forest dynamics at the tree line in the Catalan Pyrenees, and reveal a very low or even negligible signal of climate change in the study area.
A positive relationship between tree diversity and forest productivity is reported for many forested biomes of the world. However, whether tree diversity is able to increase the stability of forest ...growth to changes in climate is still an open question. We addressed this question using 36,378 permanent forest plots from National Forest Inventories of Spain and Québec (Eastern Canada), covering five of the most important climate types where forests grow on Earth and a large temperature and precipitation gradient. The plots were used to compute forest productivity (aboveground woody biomass increment) and functional diversity (based on the functional traits of species). Divergence from normal levels of precipitation (dryer or wetter than 30-year means) and temperature (warmer or colder) were computed for each plot from monthly temperature and precipitation means. Other expected drivers of forest growth were also included. Our results show a significant impact of climate divergences on forest, but not always in the expected direction. Furthermore, although functional trait diversity had a general positive impact on forest productivity under normal conditions, this effect was not maintained in stands having suffered from temperature divergence (i.e., warmer conditions). Contrary to our expectations, we found that tree diversity did not result in more stable forest’s growth conditions during changes in climate. These results could have important implications for the future dynamics and management of mixed forests worldwide under climate change.
•Browsing can reduce or prevent tree seedling regeneration in forests.•We assessed the impact of grazing conditions in the Pyrenees on forest regeneration.•Mortality for conifers was much lower ...(<15%) than for B. pendula (>40%).•Browsing depended on distance to shrubs, site and the type of forest cover.•Both meso- and micro-habitat affect the patterns of plant damage by herbivores.
Browsing damage is among the most determinant factors that limit the establishment of tree seedlings in forests. In some areas, this process leads to massive mortalities that can reduce or even completely prevent the regeneration of some tree species. Mediterranean mountain forests have undergone during the last decades important changes in land-uses that have significantly altered the type and abundance of herbivore populations. In this study we assessed the impact of current grazing conditions in forest regeneration using a set of experimental plantations established in the Eastern Pyrenees in areas visited by domestic livestock (cattle and horses) and wild ungulates (mainly roe deer and chamois). We analyzed during 4years the role of seedling species and size, mesohabitat (elevation and type of forest cover) and microhabitat (herbaceous cover, distance to shrub, and light availability) on the browsing-induced mortality of more than 500 seedlings of Pinus sylvestris, Pinus uncinata, Betula pendula and Abies alba, the most common tree species in the study area. Browsing-induced mortality for the three conifer species was much lower (<15%) than the one observed for B. pendula (>40%) and depended on both microhabitat – mainly on the distance to protective elements such as shrubs; and mesohabitat, with an interaction between the elevational belt (site) and the type of forest cover (gaps vs. understory). In the subalpine belt, browsing on A. alba and P. uncinata was higher during summer at plots located in the forest understory whereas, during winter, it was higher at plots located in gaps. The study shows that both mesohabitat and microhabitat can exert an effect on the patterns of plant damage by herbivores, providing useful information to adapt forest management in areas particularly exposed to them.
•Forest management will determine future service provision by Mediterranean forests.•Ecosystem services trade-offs and synergies are determined by site productivity.•No forest management policy is ...able to maximize provision of all services.•Climate change influenced service provision less than forest management.
Mediterranean forests play a key role in providing services and goods to society, and are currently threatened by global change. We assessed the future provision of ecosystem services by Mediterranean pine forests under a set of management and climate change scenarios, built by combining different regional policies and climate change assumptions. We used the process-based model SORTIE-ND to simulate forest dynamics under each scenario. We coupled the outputs of SORTIE-ND with empirical and process-based models to estimate changes in harvested timber, carbon storage, mushroom yield, water provision, soil erosion mitigation and habitat for biodiversity by 2100, and assessed the trade-offs and synergies between services. Our results suggest that future provision of ecosystem services by Mediterranean forests will be more strongly determined by management policies than by climate. However, no management policy maximized the provision of all services. The continuation of the business-as-usual management would benefit some services to the detriment of water provision, but leads to higher vulnerability to extreme drought-events or wildfires. Managing for reducing forest vulnerability will balance the provision of services while reducing the risk of damage to forest functioning. We also found multiple spatial synergies between ecosystem services provision, likely driven by differences in site productivity.
•P. nigra forests showed important post-fire vegetation shifts to other woody types.•Post-fire transitions to grassland were restricted to very specific site conditions.•Pre-fire tree cover and land ...use critically affected tree-species regeneration.•Post-fire pine regeneration was restricted to sites close to unburned patches.•Site quality and burn severity critically determined post-fire hardwood cover.
In the Mediterranean, non-serotinous pinewoods are suffering an increasing occurrence of high-severity crown fires that usually drive vegetation shifts to fire-adapted communities and a decrease in pine-dominated area. Here we used a case-study approach on a large area dominated by Pinus nigra Arn. ssp. salzmannii burned in 1998 to gain further understanding of the relative importance of different factors related to local topography (elevation, aspect, slope, curvature), pre-fire vegetation (land-use history, canopy cover) and fire behavior (burn severity, presence of unburned patches) as drivers of post-fire regeneration dynamics. The results find that pine shows locally resilient responses driven mainly by factors related to fire effects (presence of unburned patches) and the characteristics of the pre-fire vegetation (i.e. stable forest areas). When fire-induced changes from pine dominance to other types of vegetation occurred, landscape 15years post-fire was dominated by woody vegetation, with some rare grassland communities emerging under very specific conditions (mountain ridges, hilltops and rocky sites). Conversion from forest to shrubland occurred mainly in the most xeric sites (south-facing areas, in some cases with steep slopes) and areas dominated by young pine stands prior to the fire. We found manageable factors such as the pre-fire structure and composition of the vegetation strongly determine the occurrence of post-fire regeneration trajectories dominated by tree species regeneration. This knowledge can be used to define preventive management strategies oriented to direct regeneration dynamics in anticipation of fire occurrence. At landscape level, managing forest fuels to favor the occurrence of unburned patches and modify their spatial distribution along the burned landscape will favor a more resilient pine response. At stand level, adjusting silvicultural interventions to favor the natural establishment of late-successional tree species will favor post-fire oak regeneration.
Key message
Elevation markedly modified the species-specific phenotypic responses of trees to light. The effects from elevation mostly occurred at organ level (SLA) for the montane species, but at ...whole-plant level (allocation traits) for the subalpine ones. The subalpine species allocate more carbon to roots under closed canopies at low elevation. Contrary to expectations, most species displayed smaller specific leaf area at high elevation. The most drought-intolerant species was more severely affected by drought under shade than in open microsites.
Context
Understanding the phenotypic responses of mountain tree species to different levels of local irradiance can be of critical importance for elucidating their capacity to relocate above their current distributional limit in response to environmental changes.
Aims
To evaluate whether the response of different co-occurring forest tree species to local irradiance varies when they are growing at various elevations or beyond their current distributional limit.
Methods
Seedlings of four tree species (
Betula pendula
Roth.,
Pinus sylvestris
L.,
Abies alba
Mill., and
Pinus uncinata
Ram. ex DC.) were planted under different irradiance levels (forest understory vs natural gaps) and at various elevation (montane–subalpine ecotone and subalpine belt). After four growing seasons, 48 plants per species were excavated to assess allocational (biomass distribution) and morphological (specific leaf area) traits. Midday leaf water potential was recorded during a period of intense drought.
Results
The subalpine species (
A. alba
and
P. uncinata
) increased their allocation to the root system at low elevation and under dense canopy. We observed constant or higher SLA in all species when they develop in the subalpine belt.
B. pendula
was affected more severely by drought at low elevations and under shade than in open microsites.
Conclusion
We found marked species-specific phenotypic variability of tree seedlings to increasing irradiance, with these responses modulated by the elevation at which the trees were growing.
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