Forecasted increase drought frequency and severity may drive worldwide declines in forest productivity. Species-level responses to a drier world are likely to be influenced by their functional traits. Here, we analyse forest resilience to drought using an extensive network of tree-ring width data and satellite imagery. We compiled proxies of forest growth and productivity (TRWi, absolutely dated ring-width indices; NDVI, Normalized Difference Vegetation Index) for 11 tree species and 502 forests in Spain corresponding to Mediterranean, temperate, and continental biomes. Four different components of forest resilience to drought were calculated based on TRWi and NDVI data before, during, and after four major droughts (1986, 1994-1995, 1999, and 2005), and pointed out that TRWi data were more sensitive metrics of forest resilience to drought than NDVI data. Resilience was related to both drought severity and forest composition. Evergreen gymnosperms dominating semi-arid Mediterranean forests showed the lowest resistance to drought, but higher recovery than deciduous angiosperms dominating humid temperate forests. Moreover, semi-arid gymnosperm forests presented a negative temporal trend in the resistance to drought, but this pattern was absent in continental and temperate forests. Although gymnosperms in dry Mediterranean forests showed a faster recovery after drought, their recovery potential could be constrained if droughts become more frequent. Conversely, angiosperms and gymnosperms inhabiting temperate and continental sites might have problems to recover after more intense droughts since they resist drought but are less able to recover afterwards.

Nitrogen uptake, nitrogen demand and internal nitrogen cycling were studied to address the question of the importance of nutrient storage in Quercus species with contrasting leaf longevities. We carried out this study at the whole-plant level with young trees (2-4 years old) of three Mediterranean Quercus species: the evergreen Q. ilex, the marcescent/evergreen Q. faginea, and the deciduous Q. pyrenaica. Seasonal dynamics of nitrogen in all compartments of the plant were followed for 3 years. Nitrogen losses were measured through litter production, herbivory and fine root shedding. Nitrogen uptake was estimated using increments of nitrogen plant content plus accumulative nitrogen losses. Nitrogen uptake was limited to a few months during late winter and spring. Before budbreak, acquired nitrogen was stored in old-leaf cohorts of evergreen and woody compartments. After budbreak, Quercus species relied first on soil uptake and second on nitrogen retranslocation to supply new growth requirements. However, in most cases we found a high asynchrony between nitrogen demand by growing tissues and soil supply, which determined a strong nitrogen retranslocation up to 88.4% of the nitrogen demand throughout leaf expansion. Except for the first year after planting, the above- and underground woody fractions provided more nitrogen to the new tissues than the old leaf cohorts. Differences in the benefit of nitrogen withdrawn from senescent and old leaves were not found between species. We conclude that sink/source interaction strength was determined by differences between nitrogen demand and uptake, regulating internal nutrient cycling at the whole plant level.

Summary1. Nitrogen-use efficiency (NUE N ) is often decomposed into the product of N productivity ( A N ) and the mean residence time of N (MRT N ). Theory suggests a trade-off between both components, but direct experimental evidence is still scarce. A field study with young trees of the evergreen Quercus ilex and the marcescent-evergreen Quercus faginea was carried out to test this trade-off through analysis of plant traits at organ, whole-plant and population levels. 2. Specific leaf area (SLA) was the main trait positively related to A N in Q. faginea . By contrast, greater litter production and consumption by caterpillars resulted in larger N losses and shorter MRT N in Q. faginea . Early leaf senescence in Q. faginea produced leaf litter with high N concentration that contributed significantly to N loss. Moreover, Q. ilex had higher plant survivorship. The inverse relationship between leaf longevity and SLA is probably a key component of the trade-off between N losses and plant N productivity. 3. Quercus faginea had greater N uptake from soil, linked to its longer specific root length of fine roots and greater biomass allocation to underground tissues. Smaller N losses in Q. ilex compensated for its smaller N uptake and allowed a similar N balance at whole-plant level. 4. Our results support the hypothesis of a trade-off between A N and MRT N . Quercus ilex had a long MRT N , while Q. faginea has a high A N , and vice versa . The long MRT N in Q. ilex involves not only reduced N loss through long intrinsic leaf life span, but also resistance to harsh environmental factors and defence against herbivores. This suggests that a long MRT N is a potentially successful strategy in nutrient-poor environments.

tropical rainforests harbor exceptionally high biodiversity and store large amounts of carbon in vegetation biomass. However, regional variation in plant species richness and vegetation carbon stock can be substantial, and may be related to the heterogeneity of topoedaphic properties. therefore, aboveground vegetation carbon storage typically differs between geographic forest regions inassociation with the locally dominant plant functional group. A better understanding of the underlying factors controlling tropical forest diversity and vegetation carbon storage could be critical for predicting tropical carbon sink strength in response to projected climate change. Based on regionally replicated 1-ha forest inventory plots established in a region of high geomorphological heterogeneity we investigated how climatic and edaphic factors affect tropical forest diversity and vegetation carbon storage. plant species richness (of all living stems >10 cm in diameter) ranged from 69 to 127 ha −1 and vegetation carbon storage ranged from 114 to 200 t ha −1 . While plant species richness was controlled by climate and soil water availability, vegetation carbon storage was strongly related to wood density and soil phosphorus availability. Results suggest that local heterogeneity in resource availability and plant functional composition should be considered to improve projections of tropical forest ecosystem functioning under future scenarios.Tropical forests host two thirds of terrestrial biota 1 and comprise one fourth of the planet's terrestrial carbon (C) stored in aboveground vegetation biomass (AGB) 2 . It has been proposed that biodiversity positively affects carbon storage in hyper-diverse tropical forests 3 , but this finding has been repeatedly challenged by studies showing that relationships between species diversity and ecosystem functioning are dependent on the scale of observation 4,5 , and usually saturate at high levels of species richness, such as in tropical forests 6,7 . As a consequence, relationships between biodiversity and C storage remain poorly resolved for tropical forests [6][7][8] . It is inherently difficult to disentangle factors determining tropical ecosystem functioning and isolating possible effects of species diversity,

1. The negative impacts of drought on forest growth and productivity last for several years generating legacies, although the factors that determine why such legacies vary across sites and tree species remain unclear. 2. We used an extensive network of tree-ring width (RWI, ring-width index) records of 16 tree species from 567 forests, and high-resolution climate and normalized difference vegetation index (NDVI) datasets across Spain during the common period 1982-2008 to test the hypothesis that climate conditions and growth features modulate legacy effects of drought on forests. Legacy effects of drought were calculated as the differences between detrended-only RWI and NDVI series (i.e. after removing long-term growth trends) and pre-whitened RWI and NDVI series predicted by a model including drought intensity. Superposed Epoch Analysis (SEA) was used to estimate whether legacy effects differed from random. Finally, legacy effects were related to water balance, growth persistence and variability, and tree species identity. 3. We found a widespread occurrence of drought legacy effects on both RWI and NDVI, but they were seldom significant. According to SEA, first-year drought legacies were negative and different from random in 9% and 5% of the RWI and

No abstract

The N economy of saplings of the Mediterranean Quercus pyrenaica Willd. species was analysed at wholeplant level. The amount and timing of N cycling were determined by strong seasonality in N productivity, which peaked in late spring. Most leaf N was allocated to a main first flush of leaves in early spring, and a minor second flush during early summer or autumn. After peak of N productivity, the allocation of biomass production and N resources was mainly switched to lignotuber and coarse roots. Q. pyrenaica displayed a non-conservative pattern of N use as compared with other co-occurring Quercus species. Potential leaf N-resorption efficiency was moderate, but N proficiency was low, which contributed to high losses of N throughout leaf litter and to short mean residence times of N (MRT N ). Additionally, summer water stress reduced foliar area, producing leaf litter with a high N concentration due to almost negligible resorption efficiency, and in some cases, the loss of the whole above-ground fraction. A large investment of plant resources to the root system appeared as a key trait in the N economy and plant fitness of young Q. pyrenaica saplings, allowing them: (1) to counteract N losses and to maintain a positive N balance, (2) to access deep soil resources (water and nutrients), and (3) to 'safe'-store N for coupling supply and demand processes during spring growth or sprouting after a strong summer drought.

No abstract