Late Holocene vegetation dynamics and deforestation in Rano Aroi: Implications for Easter Island's ecological and cultural history

Rull V., Canellas-Bolta N., Margalef O., Saez A., Pla-Rabes S., Giralt S. (2015) Late Holocene vegetation dynamics and deforestation in Rano Aroi: Implications for Easter Island's ecological and cultural history. Quaternary Science Reviews. 126: 219-226.
Link
Doi: 10.1016/j.quascirev.2015.09.008

Abstract:

Easter Island (Rapa Nui) has been considered an example of how societies can cause their own destruction through the overexploitation of natural resources. The flagship of this ecocidal paradigm is the supposed abrupt, island-wide deforestation that occurred about one millennium ago, a few centuries after the arrival of Polynesian settlers to the island. Other hypotheses attribute the forest demise to different causes such as fruit consumption by rats or aridity but the occurrence of an abrupt, island-wide deforestation during the last millennium has become paradigmatic in Rapa Nui. We argue that such a view can be questioned, as it is based on the palynological study of incomplete records, owing to the existence of major sedimentary gaps. Here, we present a multiproxy (pollen, charcoal and geochemistry) study of the Aroi core, the first gap-free sedimentary sequence of the last millennia obtained to date in the island. Our results show changing vegetation patterns under the action of either climatic or anthropogenic drivers, or both, depending on the time interval considered. Palm forests were present in Aroi until the 16th century, when deforestation started, coinciding with fire exacerbation -likely of human origin- and a dry climate. This is the latest deforestation event recorded so far in the island and took place roughly a century before European contact. In comparison to other Easter Island records, this record shows that deforestation was neither simultaneous nor proceeded at the same pace over the whole island. These findings suggest that Easter Island's deforestation was a heterogeneous process in space and time, and highlights the relevance of local catchment traits in the island's environmental and land management history. © 2015 Elsevier Ltd.

Read more

Leaf and stem economics spectra drive diversity of functional plant traits in a dynamic global vegetation model

Sakschewski B., von Bloh W., Boit A., Rammig A., Kattge J., Poorter L., Penuelas J., Thonicke K. (2015) Leaf and stem economics spectra drive diversity of functional plant traits in a dynamic global vegetation model. Global Change Biology. : 0-0.
Link
Doi: 10.1111/gcb.12870

Abstract:

Functional diversity is critical for ecosystem dynamics, stability and productivity. However, dynamic global vegetation models (DGVMs) which are increasingly used to simulate ecosystem functions under global change, condense functional diversity to plant functional types (PFTs) with constant parameters. Here, we develop an individual- and trait-based version of the DGVM LPJmL (Lund-Potsdam-Jena managed Land) called LPJmL- flexible individual traits (LPJmL-FIT) with flexible individual traits) which we apply to generate plant trait maps for the Amazon basin. LPJmL-FIT incorporates empirical ranges of five traits of tropical trees extracted from the TRY global plant trait database, namely specific leaf area (SLA), leaf longevity (LL), leaf nitrogen content (Narea), the maximum carboxylation rate of Rubisco per leaf area (vcmaxarea), and wood density (WD). To scale the individual growth performance of trees, the leaf traits are linked by trade-offs based on the leaf economics spectrum, whereas wood density is linked to tree mortality. No preselection of growth strategies is taking place, because individuals with unique trait combinations are uniformly distributed at tree establishment. We validate the modeled trait distributions by empirical trait data and the modeled biomass by a remote sensing product along a climatic gradient. Including trait variability and trade-offs successfully predicts natural trait distributions and achieves a more realistic representation of functional diversity at the local to regional scale. As sites of high climatic variability, the fringes of the Amazon promote trait divergence and the coexistence of multiple tree growth strategies, while lower plant trait diversity is found in the species-rich center of the region with relatively low climatic variability. LPJmL-FIT enables to test hypotheses on the effects of functional biodiversity on ecosystem functioning and to apply the DGVM to current challenges in ecosystem management from local to global scales, that is, deforestation and climate change effects. © 2015 John Wiley & Sons Ltd.

Read more

Balancing the risks of hydraulic failure and carbon starvation: A twig scale analysis in declining Scots pine

Salmon Y., Torres-Ruiz J.M., Poyatos R., Martinez-Vilalta J., Meir P., Cochard H., Mencuccini M. (2015) Balancing the risks of hydraulic failure and carbon starvation: A twig scale analysis in declining Scots pine. Plant, Cell and Environment. : 0-0.
Link
Doi: 10.1111/pce.12572

Abstract:

Understanding physiological processes involved in drought-induced mortality is important for predicting the future of forests and for modelling the carbon and water cycles. Recent research has highlighted the variable risks of carbon starvation and hydraulic failure in drought-exposed trees. However, little is known about the specific responses of leaves and supporting twigs, despite their critical role in balancing carbon acquisition and water loss. Comparing healthy (non-defoliated) and unhealthy (defoliated) Scots pine at the same site, we measured the physiological variables involved in regulating carbon and water resources. Defoliated trees showed different responses to summer drought compared with non-defoliated trees. Defoliated trees maintained gas exchange while non-defoliated trees reduced photosynthesis and transpiration during the drought period. At the branch scale, very few differences were observed in non-structural carbohydrate concentrations between health classes. However, defoliated trees tended to have lower water potentials and smaller hydraulic safety margins. While non-defoliated trees showed a typical response to drought for an isohydric species, the physiology appears to be driven in defoliated trees by the need to maintain carbon resources in twigs. These responses put defoliated trees at higher risk of branch hydraulic failure and help explain the interaction between carbon starvation and hydraulic failure in dying trees. Understanding the physiological responses of leaves to drought is crucial since they are the site of both photosynthesis and transpiration, and hence play key roles in balancing the risks of carbon starvation and hydraulic failure. Co-occurring healthy and unhealthy Scots pines showed different responses to summer drought: while healthy trees showed a typical response to drought for an isohydric species, atypical physiology in unhealthy trees appears to be driven by the need to maintain carbohydrate availability in needles and twigs. These responses put unhealthy trees at higher risk of branch hydraulic failure and help to explain the interaction between carbon-starvation and hydraulic failure in dying trees. © 2015 John Wiley & Sons Ltd.

Read more

The effects of the NAO on the ice phenology of Spanish alpine lakes

Sanchez-Lopez G., Hernandez A., Pla-Rabes S., Toro M., Granados I., Sigro J., Trigo R.M., Rubio-Ingles M.J., Camarero L., Valero-Garces B., Giralt S. (2015) The effects of the NAO on the ice phenology of Spanish alpine lakes. Climatic Change. : 0-0.
Link
Doi: 10.1007/s10584-015-1353-y

Abstract:

Three Spanish alpine lakes located in the Central Range (Peñalara Lake and Cimera Lake) and the Pyrenees (Redon Lake) are selected to understand the effects of the North Atlantic Oscillation (NAO) on ice phenology. A conceptual lake model is formulated based on Pearson’s correlation coefficients obtained between season-scale time series of the NAO index, climatic data (i.e., precipitation, air temperature and snow data) and limnological variables (ice phenology records). The results suggest that the effects of the NAO are only reflected in the thawing process via the air temperature and the insulating effect of snow accumulation on the ice cover. An altitude component is evident in our survey because the effects of the NAO on Peñalara Lake (the lowest altitude studied lake) are restricted to winter, whereas for Redon Lake (the highest altitude studied lake), the effects extend into spring. A latitudinal component is also clear when comparing our data with northern European lakes. Snow accumulation primarily depends on the air temperature at high latitudes, and both precipitation and the air temperature control snow accumulation at lower latitudes. Consequently, in northern Europe, the NAO signal is primarily reflected in lake ice phenology via the air temperature, whereas our results confirm that in southern Europe, the strong dependence of precipitation on the NAO determines the importance of the NAO for lake ice cover. © 2015 Springer Science+Business Media Dordrecht

Read more

Foliar and soil concentrations and stoichiometry of nitrogen and phosphorous across European Pinus sylvestris forests: Relationships with climate, N deposition and tree growth

Sardans J., Alonso R., Janssens I.A., Carnicer J., Vereseglou S., Rillig M.C., Fernández-Martínez M., Sanders T.G.M., Peñuelas J. (2015) Foliar and soil concentrations and stoichiometry of nitrogen and phosphorous across European Pinus sylvestris forests: Relationships with climate, N deposition and tree growth. Functional Ecology. : 0-0.
Link
Doi: 10.1111/1365-2435.12541

Abstract:

This study investigated the factors underlying the variability of needle and soil elemental composition and stoichiometry and their relationships with growth in Pinus sylvestris forests throughout the species' distribution in Europe by analysing data from 2245 forest stands. Needle N concentrations and N:P ratios were positively correlated with total atmospheric N deposition, whereas needle P concentrations were negatively correlated. These relationships were especially pronounced at sites where high levels of N deposition coincided with both higher mean annual temperature and higher mean annual precipitation. Trends towards foliar P deficiency were thus more marked when high N deposition coincided with climatic conditions favourable to plant production. Atmospheric N deposition was positively correlated with soil solution NO3- , SO42- , K+, P and Ca2+ concentrations, the soil solution NO3-:P ratio, total soil N and the total soil N:Olsen P ratio and was negatively correlated with soil Olsen P concentration. Despite these nutrient imbalances, during the period studied (1990-2006), N deposition was positively related with Pinus sylvestris absolute basal diameter (BD) growth, although only accounting for the 10% of the total variance. However, neither N deposition nor needle N concentration was related with relative annual BD growth. In contrast, needle P concentration was positively related with both absolute and relative annual BD growth. These results thus indicate a tendency of European P. sylvestris forests to store N in trees and soil in response to N deposition and unveil a trend towards increased nutrient losses in run-off as a consequence of higher soil solution N concentrations. Overall, the data show increasing ecosystem nutrient imbalances with increasingly limiting roles of P and other nutrients such as K in European P. sylvestris forests, especially in the centre of their distribution where higher levels of N deposition are observed. Thus, although the data show that N deposition has had an overall positive effect on P. sylvestris growth, the effect of continuous N deposition, associated with decreasing P and K and increasing N:P in leaves and in soil, may in the future become detrimental for the growth and competitive ability of P. sylvestris trees. © 2015 British Ecological Society.

Read more

Foliar elemental composition of European forest tree species associated with evolutionary traits and present environmental and competitive conditions

Sardans J., Janssens I.A., Alonso R., Veresoglou S.D., Rillig M.C., Sanders T.G.M., Carnicer J., Filella I., Farre-Armengol G., Penuelas J. (2015) Foliar elemental composition of European forest tree species associated with evolutionary traits and present environmental and competitive conditions. Global Ecology and Biogeography. 24: 240-255.
Link
Doi: 10.1111/geb.12253

Abstract:

Aim: Plant elemental composition and stoichiometry are crucial for plant structure and function. We studied to what extent elemental stoichiometry in plants might be strongly related to environmental drivers and competition from coexisting species. Location: Europe. Methods: We analysed foliar N, P, K, Ca and Mg concentrations and their ratios among 50 species of European forest trees sampled in 5284 plots across Europe and their relationships with phylogeny, forest type, current climate and N deposition. Results: Phylogeny is strongly related to overall foliar elemental composition in European tree species. Species identity explained 56.7% of the overall foliar elemental composition and stoichiometry. Forest type and current climatic conditions also partially explained the differences in foliar elemental composition among species. In the same genus co-occurring species had overall higher differences in foliar elemental composition and stoichiometry than the non-co-occurring species. Main conclusions: The different foliar elemental compositions among species are related to phylogenetic distances, but they are also related to current climatic conditions, forest types, drivers of global change such as atmospheric N deposition, and to differences among co-occurring species as a probable consequence of niche specialization to reduce direct competition for the same resources. Different species have their own 'fixed' foliar elemental compositions but retain some degree of plasticity to the current climatic and competitive conditions. A wider set of elements beyond N and P better represent the biogeochemical niche and are highly sensitive to plant function. Foliar elemental composition can thus be useful for representing important aspects of plant species niches. © 2014 John Wiley & Sons Ltd.

Read more

Potassium: A neglected nutrient in global change

Sardans J., Penuelas J. (2015) Potassium: A neglected nutrient in global change. Global Ecology and Biogeography. 24: 261-275.
Link
Doi: 10.1111/geb.12259

Abstract:

Aim: Potassium (K) is the second most abundant nutrient in plant photosynthetic tissues after nitrogen (N). Thousands of physiological and metabolic studies in recent decades have established the fundamental role of K in plant function, especially in water-use efficiency and economy, and yet macroecological studies have mostly overlooked this nutrient. Methods: We have reviewed available studies on the content, stoichiometry and roles of K in the soil-plant system and in terrestrial ecosystems. We have also reviewed the impacts of global change drivers on K content, stoichiometry and roles. Conclusions: The current literature indicates that K, at a global level, is as limiting as N and phosphorus (P) for plant productivity in terrestrial ecosystems. Some degree of K limitation has been seen in up to 70% of all studied terrestrial ecosystems. However, in some areas atmospheric K deposition from human activities is greater than that from natural sources. We are far from understanding the K fluxes between the atmosphere and land, and the role of anthropogenic activities in these fluxes. The increasing aridity expected in wide areas of the world makes K more critical through its role in water-use efficiency. N deposition exerts a strong impact on the ecosystem K cycle, decreasing K availability and increasing K limitation. Plant invasive success is enhanced by higher soil K availability, especially in environments without strong abiotic stresses. The impacts of other drivers of global change, such as increasing atmospheric CO2 or changes in land use, remain to be elucidated. Current models of the responses of ecosystems and carbon storage to projected global climatic and atmospheric changes are now starting to consider N and P, but they should also consider K, mostly in arid and semi-arid ecosystems. © 2015 John Wiley & Sons Ltd.

Read more

Trees increase their P: N ratio with size

Sardans J., Penuelas J. (2015) Trees increase their P: N ratio with size. Global Ecology and Biogeography. 24: 147-156.
Link
Doi: 10.1111/geb.12231

Abstract:

Aim: Phosphorus (P) tends to become limiting in ageing terrestrial ecosystems, and its resorption efficiency is higher than for other elements such as nitrogen (N). We thus hypothesized that trees should store more P than those other elements such as N when tree size increases and that this process should be enhanced in slow-growing late-successional trees. Location: Catalan forests. Methods: We used data from the Catalan Forest Inventory that contains field data on the P and N contents of total aboveground, foliar and woody biomasses of the diverse mediterranean, temperate and alpine forests of Catalonia (1018 sites). We used correlation and general linear models to analyse the allometric relationships between the nutrient contents of different aboveground biomass fractions (foliar, branches and stems) and total aboveground biomass. Results: Aboveground forest P content increases proportionally more than aboveground forest N content with increasing aboveground biomass. Two mechanisms underlie this. First, woody biomass increases proportionally more than foliar biomass, with woody biomass having a higher P:N ratio than foliar biomass. Second, the P:N ratio of wood increases with tree size. These results are consistent with the generally higher foliar resorption of P than of N. Slow-growing species accumulate more total P aboveground with size than fast-growing species, mainly as a result of their large capacity to store P in wood. Main conclusions: Trees may have developed long-term adaptive mechanisms to store P in biomass, mainly in wood, thereby slowing the loss of P from ecosystems, reducing its availability for competitors and implying an increase in the P:N ratio in forest biomass with ageing. This trend to accumulate more P than N with size is more accentuated in slow-growing, large, long-lived species of late successional stages. In this way they partly counterbalance the gradual decrease of P in the soil. © 2014 John Wiley & Sons Ltd.

Read more

Allocation, stress tolerance and carbon transport in plants: How does phloem physiology affect plant ecology?

Savage J.A., Clearwater M.J., Haines D.F., Klein T., Mencuccini M., Sevanto S., Turgeon R., Zhang C. (2015) Allocation, stress tolerance and carbon transport in plants: How does phloem physiology affect plant ecology?. Plant, Cell and Environment. : 0-0.
Link
Doi: 10.1111/pce.12602

Abstract:

Despite the crucial role of carbon transport in whole plant physiology and its impact on plant-environment interactions and ecosystem function, relatively little research has tried to examine how phloem physiology impacts plant ecology. In this review, we highlight several areas of active research where inquiry into phloem physiology has increased our understanding of whole plant function and ecological processes. We consider how xylem-phloem interactions impact plant drought tolerance and reproduction, how phloem transport influences carbon allocation in trees and carbon cycling in ecosystems and how phloem function mediates plant relations with insects, pests, microbes and symbiotes. We argue that in spite of challenges that exist in studying phloem physiology, it is critical that we consider the role of this dynamic vascular system when examining the relationship between plants and their biotic and abiotic environment. © 2015 John Wiley & Sons Ltd.

Read more

Population Dynamics of Aphthona whitfieldi (Coleoptera: Chrysomelidae), Pest of Jatropha curcas, and Environmental Factors Favoring Its Abundance in Burkina Faso

Sawadogo, A., Nagalo, E., Nacro, S., Rouamba, M., Kenis, M. (2015) Population Dynamics of Aphthona whitfieldi (Coleoptera: Chrysomelidae), Pest of Jatropha curcas, and Environmental Factors Favoring Its Abundance in Burkina Faso. Journal of insect science (Online). 15: 0-0.
Link
Doi: 10.1093/jisesa/iev084

Abstract:

Pages