Tree Age Distributions Research Articles

Regimes of global and national oil palm cultivations from 2001 to 2018

Oil palm is the dominant global oil crop due to its high productivity and diversified usage in many sectors. Since the late 20th century, oil palm cultivations proliferated in Southeast Asia, West Africa, and Latin America. However, global market factors, different national and regional policies, and smallholder versus commercial planting regimes in different areas lead to significant differences in economic benefits and environmental problems from deforestation and loss of biodiversity. We investigated changes in global and national distributions against suitability and indices of tree age distribution change for industrial oil palm (IOP) and smallholder oil palm (SOP). Spatial and temporal change analyses show that: i) For most tree ages, the proportion of global oil palm planting in suitable areas was less than 50%, but the impact of temporal regimes, from possible market factors and local policies, on planting structure should not be neglected; ii) Central America, South America, and West Africa were less suitable for oil palm cultivation compared to Southeast Asia. While, as two dominant oil palm planting countries, Indonesia and Malaysia had relatively low planting suitability, with 39.23% of Indonesia’s IOP, 44.85% of Indonesia’s SOP, 30.90% of Malaysia’s IOP and 18.77% of Malaysia’s SOP in highly and most suitable intervals; iii) There exist clear differences between IOP and SOP in terms of suitability, planting structure and spatial expansion patterns; iv) Hysteresis effect exists between latecomers (countries in West Africa and Latin America) and forerunner (Indonesia and Malaysia) in terms of spatial expansion; v) The spatial expansion patterns of oil palm planting centers have obvious scale effects for both IOP and SOP, with clear inter-country and intra-country differences. This paper reinterprets the global distribution of tree age and spatial expansion pattern and recommends scientific strategies to guide site selection and planting structure that enable oil palm cultivation for sustainable development.

Probability Distribution of Tree Age for the Simple Birth-Death Process, with Applications to Distributions of Number of Ancestral Lineages and Divergence Times for Pairs of Taxa in a Yule Tree.

In this contribution, a general expression is derived for the probability density of the time to the most recent common ancestor (TMRCA) of a simple birth-death tree, a widely used stochastic null-model of biological speciation and extinction, conditioned on the constant birth and death rates and number of extant lineages. This density is contrasted with a previous result which was obtained using a uniform prior for the time of origin. The new distribution is applied to two problems of phylogenetic interest. First, that of the probability of the number of taxa existing at any time in the past in a tree of a known number of extant species, and given birth and death rates, and second, that of determining the TMRCA of two randomly selected taxa in an unobserved tree that is produced by a simple birth-only, or Yule, process. In the latter case, it is assumed that only the rate of bifurcation (speciation) and the size, or number of tips, are known. This is shown to lead to a closed-form analytical expression for the probability distribution of this parameter, which is arrived at based on the known mathematical form of the age distribution of Yule trees of a given size and branching rate, which is derived here de novo, and a similar distribution which additionally is conditioned on tree age. The new distribution is the exact Yule prior for divergence times of pairs of taxa under the stated conditions and is potentially useful in statistical (Bayesian) inference studies of phylogenies.

Effect of land-use legacy on the future carbon sink for the conterminous US

Abstract. Modeling the effects of the terrestrial carbon sink in the future depends upon not just current-day land use and land cover (LULC) but also the legacy of past LULC change (LULCC), which is often not considered. The age distribution of trees in the forest depends upon the history of past disturbances, while the nutrients in the soil depend upon past LULC. Thus, establishing the correct initial state of the vegetation and soil is crucial to model accurately the effect of biogeochemical cycling with environmental change in the future. This study models the effects of LULCC from 1750 to 2014 using the land-use harmonization dataset (LUH2) of land-use transitions with the terrestrial ecosystems model (TEM) for the conterminous US. Modeled LULC include plant functional types (PFTs) of potential vegetation, as well as managed cropland, pastureland, and urban areas. LULCC is treated using a cohort approach, in which a separate cohort occurs every year there is a land-use transition, thereby ensuring proper age structure of forests and regrowth with the correct soil nutrients. From 2000–2014 the modeled net ecosystem productivity (NEP) is 989 TgC yr−1 for the conterminous US but only −15 TgC yr−1 if accounting for carbon lost from land-use transitions and management. The hypothesis is that the initial state of the vegetation and soils significantly affects the future state of the terrestrial carbon sink. In this study, LULC remains constant in the future, with the NCAR CCSM4 RCP8.5 climate used to force the TEM-Hydro model. The following experiments are run from 2015 to 2100, including (a) restarting from existing cohorts in 2014 (RESTART), (b) reinitializing in 2015 based on condensing the cohorts for each PFT into a single cohort (CONDENSED), and (c) restarting from average cohort conditions for each PFT (AVERAGE). The NEP is too low when using condensed cohorts without reinitializing due to a larger increase in heterotrophic respiration (Rh) resulting from the assumption of mature forests. The carbon stocks are larger than using all the cohorts if condensed cohorts are reinitialized due to the assumption of mature, equilibrated forests. Where nitrogen-limited, forest regrowth is enhanced if regrowth starts from more nutrient-rich conditions. Water fluxes are dominated by environmental factors but can be slightly dependent upon the underlying carbon dynamics. It is therefore necessary to account for past disturbances when modeling future changes in carbon dynamics.

Predicting the Future Age Distribution of Conifer and Broad-Leaved Trees Based on Survival Analysis: A Case Study on Natural Forests in Northern Japan

Predicting future stand conditions based on tree age is crucial for natural forest management. The objective of this study was to model and predict the future age distribution of Picea jezoensis, Abies sachalinensis, and broad-leaved trees by assessing the past and current survival trends of preserved stands located at the University of Tokyo Hokkaido Forests (UTHF), Furano, Japan. This study analyzed forest census data of four plots (927 trees) in a preserved permanent area over 30 years (1989–2019). Individual tree-ring data were identified using a resistograph to determine the current tree age of the targeted trees. The predicted age distributions nearly converged to the shape of the survival probability curve. Among the scenario predictions, the multimodal age class distribution of P. jezoensis was predominant among all prediction scenarios. In contrast, the exponential shape of A sachalinensis and the age distribution of broad-leaved trees in the 100% scenario gradually shifted to the multimodal shape at the 50% scenario prediction. The species composition of conifer and broad-leaved trees and their age distribution would reach stable states in the long run by reaching a climax state. Therefore, it is theoretically possible to maintain stands under the pre-climax stage by allowing high growth rates at the stand level. The suggested age class-prediction of living and dead trees can improve the natural forest management of UTHF.

Large old trees increase growth under shifting climatic constraints: Aligning tree longevity and individual growth dynamics in primary mountain spruce forests.

In a world of accelerating changes in environmental conditions driving tree growth, tradeoffs between tree growth rate and longevity could curtail the abundance of large old trees (LOTs), with potentially dire consequences for biodiversity and carbon storage. However, the influence of tree-level tradeoffs on forest structure at landscape scales will also depend on disturbances, which shape tree size and age distribution, and on whether LOTs can benefit from improved growing conditions due to climate warming. We analyzed temporal and spatial variation in radial growth patterns from ~5000 Norway spruce (Picea abies [L.] H. Karst) live and dead trees from the Western Carpathian primary spruce forest stands. We applied mixed-linear modeling to quantify the importance of LOT growth histories and stand dynamics (i.e., competition and disturbance factors) on lifespan. Finally, we assessed regional synchronization in radial growth variability over the 20th century, and modeled the effects of stand dynamics and climate on LOTs recent growth trends. Tree age varied considerably among forest stands, implying an important role of disturbance as an age constraint. Slow juvenile growth and longer period of suppressed growth prolonged tree lifespan, while increasing disturbance severity and shorter time since last disturbance decreased it. The highest age was not achieved only by trees with continuous slow growth, but those with slow juvenile growth followed by subsequent growth releases. Growth trend analysis demonstrated an increase in absolute growth rates in response to climate warming, with late summer temperatures driving the recent growth trend. Contrary to our expectation that LOTs would eventually exhibit declining growth rates, the oldest LOTs (>400 years) continuously increase growth throughout their lives, indicating a high phenotypic plasticity of LOTs for increasing biomass, and a strong carbon sink role of primary spruce forests under rising temperatures, intensifying droughts, and increasing bark beetle outbreaks.

Ecological Dynamics and Regeneration Expansion of Treeline Ecotones in Response to Climate Change in Northern Bhutan Himalayas

The alpine treeline ecotones are an early indicator of vegetation’s response to changes in climate, and the advancement of diffuse treeline ecotones has been associated with mean annual warming temperatures. However, the knowledge of how tree demographic size, age and population distribution, and regeneration decrease with increasing elevation and mean annual temperature remain fragmentary in Bhutan. There was no explanation of how treelines migrate in response to the climate. Therefore, the objectives of this study were to investigate tree demographic size and age and population distribution, as well as the regeneration expansion of treeline ecotones of Abies densa trees in response to climate change. Demographic data from thirty transect bands from treeline ecotones and reconstructed mean annual temperatures from tree-rings were used. Regression analysis was used to establish a relationship between elevation/temperature and demographic tree size and age, as well as to determine recruitment frequency distributions and whether these could be driven by climate change. The tree demography indicated that the treeline ecotone in our sampling site is temperature limited. Hence, cooler temperatures at higher elevations should drive decreases in basal diameter, age and recruitment frequencies. From the dendroecological analysis, the diffuse treeline ecotones appear to be climbing on average 1.00 m per year in Northern Bhutan. We also found that the recruitment frequency has increased over recent years (1850–2017), as temperatures continue to rise. The thermal treeline ecotones will be likely to serve as a line of bioclimatic reference against which other zones of bioclimate can be defined. With documented responses of treeline ecotones toward mean annual temperatures, the expectation is that additional warming will continue to influence regeneration expansion in the future. This dynamic response of treeline ecotones towards the climate acts as an indicator of climate change. Information about climbing treelines and altered ecotones should be a vital part of the material for decision makers to consider, to assess impacts and threats to Himalayan alpine biota.

Age and spatial distribution of the world's oldest trees.

Extremely old trees have important roles in providing insights about historical climatic events and supporting cultural values. Yet there has been limited work on the global distribution and conservation of these trees. We extracted information on 197,855 tree cores at 4,854 sites, and combined it with other tree age data from a further 156 sites, to determine the age of the world's oldest trees and quantify the factors influencing their global distribution. We found that extremely old trees >1,000 years are rare. Among 30 individual trees that exceeded 2,000 years old, 27 occurred in high mountains. Our model suggests that many of the existing oldest trees occur in high-elevation, cold and arid mountains with limited human disturbance. This pattern is markedly different from that of the tallest trees, which are more likely to occur in more mesic and productive locations. Global warming and expansion of human activities may induce rapid population declines of extremely old trees. New strategies, including targeted establishment of conservation reserves in remote regions, especially those in western Table 1 parts of China and USA, are required to protect these trees. This article is protected by copyright. All rights reserved.

Drainage ditches enhance forest succession in a raised bog but do not affect the spatial pattern of tree encroachment.

The study was conducted in the raised bog Kusowo (Baltic region, West Pomerania, Poland). Along a transect line crossing two open mires affected by forest succession we analysed tree age distribution. One of those mires had been drained in the past years and still retained some open ditches, while the other one was located far from the ditches. Every 10 meters along the transect line one tree was drilled at the root collar in order to determine its age. We also conducted phytosociological analyses and short-term water level measurements in the sample plots. We expected faster tree encroachment in the undisturbed part of the open mire. The results showed, that there were no significant differences in water table level and in soil moisture indicator values between the formerly drained and undisturbed open mire. There were also no statistically significant differences in tree encroachment between the disturbed and undisturbed mires. Location and the age distribution of the trees suggest that changes in the tree growth conditions cannot be directly explained by the general decreasing of water level in the bog, although periods following drainage works were associated with more numerous establishment of young trees, in the drained part of the bog as well as in the part not directly affected by drainage ditches.

Causes and consequences of reduced human intervention in formerly managed forests in Japan and other countries

In Japan, abandonment of forest management and underuse of forest resources are substantial challenges to environmental protection and sustainable wood production, while in many other countries, leaving a forest untouched may be perceived as positive for conserving the forest. This study thus analyses the scientific knowledge landscape on the causes and consequences of reduced human intervention in formerly managed forests and compares differences between Japan and other countries. Advanced search rules in the bibliographic databases returned 188 publications [35 for Japan and 153 for other countries] related to reduced human intervention in formerly managed forests. Reduced human intervention in formerly managed forests occurred in developed countries in the mid-twentieth century because of socio-economic changes and was primarily directed by small-scale private landowners, causing structural homogenisation, stand ageing, and canopy closure, often followed by the consequences of decreasing biodiversity and ecosystem services in Japan and other countries. In Japan, heavy dependency on wood imports at the expense of biodiversity and ecosystem services and the impending need for harvesting abundant mature forests due to the unbalanced tree age distribution possibly enhanced the recognition and urgency of underuse as a threat to biodiversity and wood security, while in other countries, multiple management objectives of diverse landowners probably dispersed the recognition of underuse. Although less recognised in other countries, the absence of forest management can pose a risk to biodiversity and ecosystem services. Hence, reactivating forest management in underused private forests can be a cost-effective precautionary approach against possible damage from underuse-induced ecosystem disservices. Policy implications for sustainable forest management in underused private forests are discussed from a perspective beyond conventional private ownership.

Factors Associated with Establishment and Growth of Pinus coulteri and Pinus sabiniana in California’s Central Coast Bioregion

Abstract Forest inventory indicated recent decline in a P. coulteri population at its northern extent but live stems in sympatric P. sabiniana increased. Patterns of cone production, localized factors associated with regeneration, relations between wildfire and tree age distributions, and correlations between climate, seedling establishment, and tree growth were analyzed as potential mechanisms underlying unequal demographics between the two species. Four findings emerged: (1) P. sabiniana had a higher frequency of open cones at the time of observation, but cone production was size-biased, and cone production rates were similar for both species; (2) P. sabiniana seedlings were associated with a higher proportion of bare ground cover and westerly aspects, whereas establishment of P. coulteri seedlings was correlated with warm growing seasons and high vapor-pressure deficits, and seedlings occurred on northernly aspects; (3) age distributions of stands inside and outside a wildfire perimeter did not differ for either species, but annual growth increments of P. coulteri were greater within the fire perimeter; and (4) P. coulteri was even-aged, establishment was episodic, and occurred approximately 10 years post-wildfire. In contrast, the age distribution of P. sabiniana was highly variable, consistent with continuous recruitment, and establishment was not correlated with a climate signal.

Tree diversity patterns along the latitudinal gradient in the northwestern Russia

BackgroundOne of the key forest characteristics is the biodiversity, particularly the diversity of trees which are forest ecosystem engineers. Nowadays the most worldwide common approach for assessment of forest conditions and dynamics is based on the systematic monitoring, performed at a set of regularly structured plots. To fulfill the existing gap in this sort of knowledge on the Russian forests, an extensive study of tree species diversity on a regular network was conducted in north-west of Russia.MethodsThe study used the ICP Forests monitoring network that spans over 1700 km along the western Russian border from forest-tundra in the north to broadleaved-coniferous forests in the south. Tree data were collected at 710 sites that were assigned along a regular grid. We performed series of statistical analyses of the tree species distribution and diversity in relation to environmental and anthropogenic factors.ResultsAccording to the Maxent species distribution modelling results only Pinus sylvestris, Betula sp. and Picea abies have the potential to grow throughout the study area. The locally maximum tree species diversity varies along the latitudinal gradient from 1 to 3 species in the north to 5–7 species in the south. Monocultural stands are relatively abundant across the study area, being especially common in the south taiga. The prevailing part of the monocultural stands is represented by Scots pine (72%). The age distribution of dominant trees has a clear connection with the intensity of forest use. We found that recent wildfire events had only little effect on tree diversity in the study area.ConclusionsWe demonstrated that ICP Forests monitoring network enables to successfully establish the main qualitative and quantitative relations of the spatial variation of tree species diversity to climatic, landscape, soil and anthropogenic factors. Analysis of the influence of these factors on tree species distribution allowed us to conclude that with the continuing trend of reducing the frequency and intensity of fires, Norway spruce will further replace Scots pine and Betula sp. in the north-western Russia. Extending the monitoring network, especially adding the time-series context, could provide novel appealing opportunities for forest dynamics projection and sustainable management.

The impact of three periods of housing development upon the urban forest of Shrewsbury, England

A significant body of recent research has identified that trees in the urban environment provide considerable benefits to society, both providing desirable places to live and helping to reduce the impact of the urban population on the wider environment. If we are to continue to benefit from the urban forest in the future, a knowledge of the existing resource, its condition and future viability is a fundamental requirement. The design and creation of newly built development present one of the biggest threats to and greatest opportunities for urban forests but have not been analysed in depth. An assessment using i-tree ECO recorded the extent, nature and quality of the urban forest resource in residential areas of the town of Shrewsbury. Comparisons were then made between three separate study areas within the town based upon the period in which they were primarily constructed. The pre-1950 residential housing areas had significantly greater canopy cover (17.8%) when compared with 1951–1985 housing (13.1%) and post-1985 housing areas (9.9%). Analysis of tree age, size and ownership distributions identified that larger growing garden trees in the earlier housing schemes were the major contributor to this difference in canopy cover between areas. For this case study, we can conclude there is a negative trend in urban canopy cover that relates to the size of garden space allocated to more modern residential properties, which is not sufficiently compensated for by tree planting in adjacent public areas.

Hierarchical classification approach for mapping rubber tree growth using per-pixel and object-oriented classifiers with SPOT-5 imagery

There has been growing interest in Malaysia to increase the productivity of latex. This made accurate knowledge of rubber tree growth and age distribution a helpful decision making tool for the government, rubber plantation managers, and harvesters. Gathering this information using conventional methods is difficult, time consuming, and limited in spatial coverage. This paper presents hierarchical classification approach to obtain accurate map of rubber tree growth age distribution using SPOT-5 satellite imagery. The objective of the study is to evaluate the performance of pixel-based and object-oriented classifiers for rubber growth classification. At the first level, the general land cover was classified into eight land cover classes (soil, water body, rubber, mature oil palm, young oil palm, forest, urban area, and other vegetation) using Mahalanobis distance (MD), k-nearest neighbor (k-NN), and Support Vector Machine (SVM) classifiers. Thereafter, the best classification map, k-NN output, was used to select only pixels that belong to the rubber class from the SPOT-5 image. The extracted pixels served as input into the next classification hierarchy where four classifiers, MD, k-NN, SVM, and decision tree (DT), were implemented to map rubber trees into three intra-classes (mature, middle-aged, and young rubbers). The result produced overall accuracy of 97.48%, 96.90%, 96.25%, and 80.80% for k-NN, SVM, MD, and DT respectively. The result indicates that object-oriented classifiers are better than pixel-based methods mapping rubber tree growth.

Tree Age Distributions Reveal Large-Scale Disturbance-Recovery Cycles in Three Tropical Forests.

Over the past few decades there has been a growing realization that a large share of apparently ‘virgin’ or ‘old-growth’ tropical forests carries a legacy of past natural or anthropogenic disturbances that have a substantial effect on present-day forest composition, structure and dynamics. Yet, direct evidence of such disturbances is scarce and comparisons of disturbance dynamics across regions even more so. Here we present a tree-ring based reconstruction of disturbance histories from three tropical forest sites in Bolivia, Cameroon, and Thailand. We studied temporal patterns in tree regeneration of shade-intolerant tree species, because establishment of these trees is indicative for canopy disturbance. In three large areas (140–300 ha), stem disks and increment cores were collected for a total of 1154 trees (>5 cm diameter) from 12 tree species to estimate the age of every tree. Using these age estimates we produced population age distributions, which were analyzed for evidence of past disturbance. Our approach allowed us to reconstruct patterns of tree establishment over a period of around 250 years. In Bolivia, we found continuous regeneration rates of three species and a peaked age distribution of a long-lived pioneer species. In both Cameroon and Thailand we found irregular age distributions, indicating strongly reduced regeneration rates over a period of 10–60 years. Past fires, windthrow events or anthropogenic disturbances all provide plausible explanations for the reported variation in tree age across the three sites. Our results support the recent idea that the long-term dynamics of tropical forests are impacted by large-scale disturbance-recovery cycles, similar to those driving temperate forest dynamics.

Understanding recruitment failure in tropical tree species: Insights from a tree-ring study

Many tropical tree species have population structures that exhibit strong recruitment failure. While the presence of adult trees indicates that appropriate regeneration conditions occurred in the past, it is often unclear why small individuals are absent. Knowing how, when and where these tree species regenerate provides insights into their life history characteristics. Based on tree age distributions inferences can be made on past forest dynamics and information is obtained that is important for forest management. We used tree-ring analyses to obtain tree ages and reconstruct >200years of estimated establishment rates in a sparsely regenerating population of Afzelia xylocarpa (Fabaceae), a light-demanding and long-lived canopy tree species. We sampled all 85 Afzelia trees >5cm diameter at breast height (dbh) in a 297-ha plot in a seasonal tropical forest in the Huai Kha Khaeng (HKK) Wildlife Sanctuary, western Thailand. The age distribution of the sampled Afzelia trees revealed two distinct recruitment peaks centred around 1850 and 1950. The presence of distinct age cohorts provides a strong indication of disturbance-mediated recruitment. Additionally we found three lines of evidence supporting this interpretation. (1) Similarly aged trees were spatially aggregated up to ∼500m, a scale larger than single tree-fall gaps. (2) High juvenile growth rates (5–10mmdbhyear−1) of extant small and large trees indicate that recruitment took place under open conditions. (3) A significant positive correlation between tree age and local canopy height indicates that trees recruited in low-canopy forest patches. Likely causes of these severe canopy disturbances include windstorms and ground fires, which are common in the region. In addition, successful establishment seems to be favoured by wetter climate conditions, as the estimated establishment rate was correlated to the Palmer Drought Severity Index (PDSI). Thus, the co-occurrence of canopy disturbance and favourable climatic conditions may provide a window of opportunity for Afzelia establishment. Our results indicate that forest patches with occurrence of large Afzelia trees have undergone high-severity canopy disturbance prior to establishment, suggesting that these disturbances have shaped forests at HKK. Tree-ring analyses provide a powerful tool to understanding tropical tree establishment patterns. Rare, high-severity canopy disturbances may play a key role in the regeneration of long-lived tropical canopy tree species with recruitment failure, potentially in interaction with climate variability to determine variation in establishment success over decades or centuries.

Optimal control for forest management and conservation analysis in dehesa ecosystems

This paper presents a deterministic finite time horizon dynamic optimisation model aimed to determine optimal paths for artificial plantations and natural regeneration of two main tree species in dehesa multiple use ecosystems, holm oak (Quercus ilex L.) and cork oak (Q. suber L.). Whilst dehesa forest sustainability problems associated to exhaustive use of grazing resources have been indirectly approached by European Union authorities, providing support for artificial plantations over treeless land, no mention is made to natural regeneration techniques. In this sense, the formulated model allows for natural regeneration of already established ageing stands as a complement or even a substitute of actual reforestation practices. The proposed methodology is neither designed to determine optimal rotation of tree species nor optimal decorticating or pruning cycles of cork oaks and holm oaks, respectively. Instead, this information enters the model exogenously through knowledge of region specific silvicultural cycles for those commercially relevant tree species, and the optimisation program acts as an optimal land use allocator and thus a practical tool for policy analysis purposes. In addition to existing cost benefit analysis applications in dehesa ecosystems, the presented model allows in one side efficient evaluation of long term management dynamics —thus oak woodlands sustainability can be tested for sufficiently large time horizons—, and in the other, management decisions, instead of being forced through predefined scenarios, correspond to the optimal actions a decision agent would take from the complete set of feasible possibilities given actual land use and tree age distributions.

How organisms reach and colonize bromeliads: a field experimental test of two of Picado’s hypotheses, and the effect of tree age and cardinal distribution on bromeliads in Cartago, Costa Rica

Existen numerosos estudios sobre la biodiversidad dentro de los tanquesde agua de las bromelias. Sin embargo, poco se sabe sobre cómo lleganlos organismos hasta los tanques de agua ubicados en las partes altasdel bosque. El efecto de la edad de los árboles y la distribución cardinalde las bromelias en el dosel son aspectos mejor conocidos, pero casi nohay datos para las especies centroamericanas, por lo tanto, estudiamosla ecología de las bromelias en Pejibaye de Jiménez, Costa Rica. Parano destruir bromelias naturales, fabricamos 150 bromelias artificialescon vasos de plástico para poner a prueba las hipótesis de Picadosobre la colonización de los tanques bromelícolas mediante lluvia yresiduos que caen de las ramas. Colocamos las bromelias artificiales enel bosque en febrero 2012 y siete semanas después recolectamos losmacroinvertebrados que las habitaban. También medimos bromeliasy diámetros de los árboles en 100 individuos de Gliricidia sepium ycontamos las bromelias en los cuatro puntos cardinales del dosel en60 árboles. En concordancia con las hipótesis de Picado, las bromeliasque no recibieron lluvia tuvieron 2,9 veces menos invertebrados queel tratamiento control, y las bromelias que no recibieron residuosregistraron 3,4 veces menos invertebrados que el control. Los árboles másgrandes tienen más bromelias y éstas son más grandes, posiblementedebido a que son árboles más viejos, con mayor complejidad estructural.El número medio de bromelias fue menor en el lado oeste de las copas,justo la parte que recibe menos luz solar. Estos resultados no sóloevalúan las hipótesis de Picado en el centenario de su publicación, sinoque también son potencialmente útiles para la conservación de lasbromelias y de los complejos microecosistemas que hospedan.ABSTRACTNumerous studies have been conducted on the biodiversity of organismsthat inhabit bromeliad water tanks. However, little is known about howorganisms reach these tanks (also called “phytotelmata”). Two otheraspects of bromeliad ecology, the effect of tree age and the cardinaldistribution of bromeliads in canopies are slightly better known, butstill little research has been done on these subjects for Central Americanbromeliads. To improve understanding of these subjects, we studiedbromeliad ecology in Pejibaye de Jiménez, Cartago, Costa Rica. To avoiddestroying natural phytotelmata, we built 150 artificial bromeliadswith plastic cups to test Picado’s hypotheses that phytotelmata arecolonized via rain and debris. We set them in the field in February 2012and collected macroinvertebrates from them after seven weeks. We alsomeasured bromeliad leaf length and trunk diameters in 100 Gliricidiasepium trees and counted bromeliads in the four cardinal directionsof 60 trees. In agreement with Picado’s hypotheses, the bromeliadsthat did not receive rainwater had 2,9 times less invertebrates thanthe control, and the bromeliads that did not receive debris had 3,4times less invertebrates than the control. Larger trees had more andlarger bromeliads growing on them, possibly because they were olderand had more structural complexity. Mean number of bromeliads waslower in the west side of canopies, the side that receives less sunlight.These findings not only address Picado’s hypotheses in the centenaryof their publication, but also are potentially useful for conservation ofbromeliads and the complex microecosystems that they house.

Past surface instability of Miage debris-covered glacier tongue (Mont Blanc Massif, Italy): a decadal-scale tree-ring-based reconstruction

Debris-covered glaciers may host several biological forms that colonize the debris cover, especially if the glacier tongue reaches sufficiently low altitudes (down to about 1700 m a.s.l. at Miage Glacier, Western Italian Alps) thus allowing also tree growth. Supraglacial trees colonizing the debris-covered tongue are strongly influenced in growth and distribution by substrate characteristics and instability. The tree age distribution at Miage Glacier presents a positive gradient towards the glacier terminus, which was found to be related to the decreasing glacier surface velocity. By analysing tree-ring growth anomalies on the glacier and at a control site at the tree line over the 20-year period 1987–2006, it was found that trees growing on the glacier presented the highest percentages of abrupt growth changes (AGCs)>+70% with respect to the four previous years. Considering tree displacement on the glacier surface over the same 20-year period and the recorded AGCs, it was found that the central-lower portion of the southern lobe towards the margins was the most unstable. The temporal analysis of AGC>+40% confirmed a period of higher glacier surface instability, reaching a maximum in the years 1988 (on lobe S) and 1989 (on lobe N), probably related to the passage of a kinematic wave in the glacier tongue. Our analysis suggests that supraglacial trees hold useful information on the glacier tongue dynamics and that both AGC>+70% and AGC>+40% may be used as a proxy for substrate instability in spatio-temporal reconstructions in the Alpine environment.

Differentiating between climate effects and forest growth dynamics effects on decreasing groundwater recharge in a lowland region in Northeast Germany

Summary Declining groundwater levels in some forested regions in Northeast Germany indicate a reduction in groundwater recharge. Various interlinked aspects, such as changes in climate conditions and changes in forest structure, have been considered as the main factors affecting the regional level of groundwater recharge. For this study, the water balance model WaSiM-ETH was used to calculate groundwater recharge in a 104 km 2 area between 1958 and 2007. Climate impact analysis was driven by observed data from neighbouring meteorological stations. Changes in forest stands were reconstructed from the current status and literature studies. The model-based analysis showed that the average groundwater recharge under forest areas decreased from 1958 to 2007, with a trend of 2.3 mm/yr 2 . The most important effect was changing climatic boundary conditions, which made up 53% of the decrease. Declining precipitation is identified as the main factor. Changes in tree age distribution caused 18% of the decrease, and the change of ground vegetation under pines (Pinus sylvestris) accounts for 29%. In respect of the complexity and the interconnectivity of the processes of groundwater recharge, the necessity of using process-oriented distributed models such as WaSiM-ETH is discussed. We conclude that changes in forest stands affecting groundwater recharge could play a significant role in the water balance, especially in regions with a priori low total runoff, this has up to now often remained unquantified.

The influence of glacier surface processes on the short-term evolution of supraglacial tree vegetation: The case study of the Miage Glacier, Italian Alps

Supraglacial debris cover allows vegetation to colonize glacier surface, and whenever it is enough stable and thick, also shrubs and trees can germinate and grow. Supraglacial tree growth and distribution patterns on the glacier are closely connected with the debris-covered glacier dynamics and evolution. The aim of the research reported here was to evaluate the tree age and tree distribution patterns on the glacier tongue and the influence of ice-cliff backwasting, close to glacier terminus, on tree loss. We analysed the fragile and fast-changing environment that is present on the lower ablation sector of the Miage Glacier (Mont Blanc Massif, Italian Alps) where some ice cliffs are present and backwasting and downwasting phenomena occur. Tree features and short-term evolution were analysed with respect to glacier variations (mainly surface displacements and ice ablation) and geometry changes of the two most representative ice cliffs. The supraglacial trees’ life time resulted to be mainly controlled by glacier surface displacements and by the occurrence of backwasting and downwasting processes, whereas tree germination was associated with fine debris presence. These factors, controlling plants’ life and growth on the glacier, are an actual limit when supraglacial trees are analysed to reconstruct past environmental changes occurred on the glacier tongue. Moreover, we found that a large number of trees die under conditions of dominating backwasting inducing the loss of debris substrate (condition met especially on the northern glacier lobe). Instead, in the case of prevalence of downwasting (condition mainly observed on the southern glacier lobe), trees more easily survive and flow downvalley transported by the glacier flux.