Root traits explain different foraging strategies between resprouting life histories

11 páginas, 5 figuras, 2 tablas.Drought and fire are prevalent disturbances in Mediterranean ecosystems. Plant species able to regrow after severe disturbances (i. e. resprouter life history) have higher allocation to roots and higher water potential during the dry season than coexisting non-resprouting species. However, seedlings of non-resprouters have a higher survival rate after summer drought. We predict that, to counteract their shallow-rooting systems and to maximize seedling survival, non-resprouters have root traits that confer higher efficiency in soil resource acquisition than resprouters. We tested this prediction in seedlings of less than 1.5 months old. We select 13 coexisting woody species (including both resprouters and non-resprouters), grew them in a common garden and measured the following root traits: length, surface, average diameter, root tissue density (RTD), specific root length (SRL), surface:volume ratio (SVR), specific tip density (STD), tip distribution in depth, internal links ratio (ILR), and degree of branching. These root traits were compared between the two resprouting life histories using both standard cross-species and phylogenetic-informed analysis. Non-resprouters showed higher SRL and longer, thinner and more branched laterals, especially in the upper soil layers. The external links (i. e. the most absorptive root region) were also more abundant, longer, thinner and with higher SVR for non-resprouters. The results were supported by the phylogenetic-informed analysis for the root traits most strongly related to soil resource acquisition (SRL, SVR and branching pattern). The seedling root structure of non-resprouters species allows them to more efficiently explore the upper soil layer, whereas seedling roots of resprouters will permit both carbon storage and deep soil penetration.We thank all the volunteers for their help in the common garden and laboratory tasks, especially H. Simo˜es, J. Bandeira, C. Pérez-Cervelló, S. Ribeiro and B. Moreira. The Banc de Llavors Forestals of Generalitat Valenciana provided the installations for the common garden experiment. This work has been financed by the Spanish projects SINREG (REN2003-07198-C02-02/GLO), PERSIST (CGL2006-07126/BOS), and GRACCIE (CONSOLIDER– Ingenio 2010 program; CSD200-00067). CEAM is supported by the Generalitat Valencia and Bancaixa; CIDE is supported by the Generalitat Valencia and the University of Valencia.Peer reviewe

Towards understanding resprouting at the global scale

Understanding and predicting plant response to disturbance is of paramount importance in our changing world. Resprouting ability is often considered a simple qualitative trait and used in many ecological studies. Our aim is to show some of the complexities of resprouting while highlighting cautions that need be taken in using resprouting ability to predict vegetation responses across disturbance types and biomes. There are marked differences in resprouting depending on the disturbance type, and fire is often the most severe disturbance because it includes both defoliation and lethal temperatures. In the Mediterranean biome, there are differences in functional strategies to cope with water deficit between resprouters (dehydration avoiders) and nonresprouters (dehydration tolerators); however, there is little research to unambiguously extrapolate these results to other biomes. Furthermore, predictions of vegetation responses to changes in disturbance regimes require consideration not only of resprouting, but also other relevant traits (e.g. seeding, bark thickness) and the different correlations among traits observed in different biomes; models lacking these details would behave poorly at the global scale. Overall, the lessons learned from a given disturbance regime and biome (e.g. crown-fire Mediterranean ecosystems) can guide research in other ecosystems but should not be extrapolated at the global scale.This work was performed under the framework of the TREVOL projects (CGL2012-39938-C02-01 to J.G.P.) from the Spanish Government. A.L.J., R.B.P., A.V. and S.P. were supported by the following grants: IOS-1252232 (NSF), IOS-0845125 (NSF), CGL-2011-30531-CO2-02 (SURVIVE Project, Spain), ID-1120458 (Fondo Nacional de Desarrollo Científico y Tecnológico, FONDECYT, Chile), respectively

Effects of a fire response trait on diversification in replicated radiations.

Fire has been proposed as a factor explaining the exceptional plant species richness found in Mediterranean regions. A fire response trait that allows plants to cope with frequent fire by either reseeding or resprouting could differentially affect rates of species diversification. However, little is known about the generality of the effects of differing fire response on species evolution. We study this question in the Restionaceae, a family that radiated in Southern Africa and Australia. These radiations occurred independently and represent evolutionary replicates. We apply Bayesian approaches to estimate trait-specific diversification rates and patterns of climatic niche evolution. We also compare the climatic heterogeneity of South Africa and Australia. Reseeders diversify faster than resprouters in South Africa, but not in Australia. We show that climatic preferences evolve more rapidly in reseeder lineages than in resprouters and that the optima of these climatic preferences differ between the two strategies. We find that South Africa is more climatically heterogeneous than Australia, independent of the spatial scale we consider. We propose that rapid shifts between states of the fire response trait promote speciation by separating species ecologically, but this only happens when the landscape is sufficiently heterogeneous

Waratah theft in Brisbane Water National Park - an analysis of the blue paint poaching reduction program

The flowers of Waratahs, Telopea speciosissima (family Proteaceae) are regularly harvested illegally from natural bushland, particularly close to urban areas such as the New South Wales Central Coast. The removal of Waratah blooms from the wild may have implications for the long-term survival of local populations because of the interaction between wildfire events, subsequent flowering and limited seedling recruitment opportunities. To reduce the incidence of theft, blue acrylic paint was applied to blooms to reduce their commercial value. The painting of blooms in 2004 did not significantly reduce the incidence of wildflower theft when compared to unpainted blooms, but overall losses were lower (27%) than in 2003 (33%). However, painting of blooms had a deleterious affect on fruit production on plants with multiple heads with painted blooms having significantly reduced fruit set compared to unpainted blooms. Painting of blooms had no significant effect on seed quality (seed production per fruit, seed germination or seedling vigour) when compared to unpainted blooms. The painting of Waratah blooms to reduce theft was relatively ineffective and decreased fruit production. Alternative strategies should be considered to reduce wildflower theft in the area

Physiological drought responses improve predictions of live fuel moisture dynamics in a Mediterranean forest.

The moisture content of live fuels is an important determinant of forest flammability. Current approaches for modelling live fuel moisture content typically focus on the use of drought indices. However, these have mixed success partly because of species-specific differences in drought responses. Here we seek to understand the physiological mechanisms driving changes in live fuel moisture content, and to investigate the potential for incorporating plant physiological traits into live fuel moisture models. We measured the dynamics of leaf moisture content, access to water resources (through stable isotope analyses) and physiological traits (including leaf water potential, stomatal conductance, and cellular osmotic and elastic adjustments) across a fire season in a Mediterranean mixed forest in Catalonia, NE Spain. We found that differences in both seasonal variation and minimum values of live fuel moisture content were a function of access to water resources and plant physiological traits. Specifically, those species with the lowest minimum moisture content and largest seasonal variation in moisture (Cistus albidus: 49–137% and Rosmarinus officinalis: 47–144%) were most reliant on shallow soil water and had the lowest values of predawn leaf water potential. Species with the smallest variation in live fuel moisture content (Pinus nigra: 96–116% and Quercus ilex: 56–91%) exhibited isohydric behaviour (little variation in midday leaf water potential, and relatively tight regulation of stomata in response to soil drying). Of the traits measured, predawn leaf water potential provided the strongest predictor of live fuel moisture content (R2 = 0.63, AIC = 249), outperforming two commonly used drought indices (both with R2 = 0.49, AIC = 258). This is the first study to explicitly link fuel moisture with plant physiology and our findings demonstrate the potential and importance of incorporating ecophysiological plant traits to investigating seasonal changes in fuel moisture and, more broadly, forest flammability.This study was made possible thanks to the collaboration of and the staff from the Natural Park of Poblet, P Sopeña, and the technical staff from MedForLab. This study was funded by the Spanish Government (RYC-2012-10970, AGL2015-69151-R). R. H. Nolan was supported with funding from the New South Wales Office of Environment and Heritage, via the Bushfire Risk Management Research Hub. We benefitted from critical comments from J Voltas, JM Moreno and L Serrano and instrument loans from R Savín

History matters: previous land use changes determine post-fire vegetation recovery in forested Mediterranean landscapes

Land use changes and shifts in disturbance regimes (e.g. wildfires) are recognized worldwide as two of the major drivers of the current global change in terrestrial ecosystems. We expect that, in areas with large-scale land use changes, legacies from previous land uses persist and affect current ecosystem responses to climate-associated disturbances like fire. This study analyses whether post-fire vegetation dynamics may differ according to specific historical land use histories in a Mediterranean forest landscape of about 60,000 ha that was burnt by extensive fires. For that, we assessed land use history of the whole area through the second half of the XXth century, and evaluated the post-fire regeneration success in terms of: (i) forest cover and (ii) tree species composition (biotic-dispersed, resprouter species, Quercus spp. vs. wind-dispersed species with or without fire-resistant seed bank, Pinus spp.). Results showed that stable forest areas exhibited a higher post-fire recovery than younger forests. Furthermore, the longer since crop abandonment translates into a faster post-fire recovery. Results highlight that to anticipate the impacts of disturbances on ecosystems, historical land trajectories should be taken into account.Collaborative work was facilitated by the Consolider-Ingenio Montes CSD2008-00040 project by Spanish Ministry of Science and Innovation. Postdoctoral and predoctoral fellowships to CPP (EX2009-0703) and BSH (FPU) were provides by Spanish Ministry of Education

Projected changes in Australian fire regimes during the 21st century and consequences for ecosystems

Climate projections show Australia becoming significantly warmer during the 21st century, while precipitation decreases over much of the continent. Such changes are generally considered to increase wildfire risk. Nevertheless, using a process-based model of vegetation dynamics and vegetation–fire interactions, we show that while burnt area increases in southern and central Australia, it decreases in northern Australia. Overall the projected increase in fire by the end of the 21st century is small (0.7–1.3% of land area equivalent to 12–24% of current burnt area, depending on the climate scenario). The direct effects of increasing CO2 on vegetation productivity and water-use efficiency influence simulated fire regimes: CO2 effects tend to increase burnt area in arid regions, but increase vegetation density and reduce burnt area in forested regions. Increases in fire promotes a shift to more fire-adapted trees in wooded areas and their encroachment into grasslands, with an overall increase in forested area of 3.9–11.9% of land area by the end of the century. The decrease in fire in northern Australia leads to an increase in tree cover (ca 20%) and an expansion of tropical forest. Thus, although the overall change in burnt area is small it has noticeable consequences for vegetation patterns across the continent

Bird pollinators, seed storage and cockatoo granivores explain large woody fruits as best seed defense in Hakea

Nutrient-impoverished soils with severe summer drought and frequent fire typify many Mediterranean-type regions of the world. Such conditions limit seed production and restrict opportunities for seedling recruitment making protection from granivores paramount. Our focus was on Hakea, a genus of shrubs widespread in southwestern Australia, whose nutritious seeds are targeted by strong-billed cockatoos. We assessed 56 Hakea species for cockatoo damage in 150 populations spread over 900 km in relation to traits expected to deter avian granivory: dense spiny foliage; large, woody fruits; fruit crypsis via leaf mimicry and shielding; low seed stores; and fruit clustering. We tested hypothesises centred on optimal seed defenses in relation to (a) pollination syndrome (bird vs insect), (b) fire regeneration strategy (killed vs resprouting) and (c) on-plant seed storage (transient vs prolonged).Twenty species in 50 populations showed substantial seed loss from cockatoo granivory. No subregional trends in granivore damage or protective traits were detected, though species in drier, hotter areas were spinier. Species lacking spiny foliage around the fruits (usually bird-pollinated) had much larger (4–5 times) fruits than those with spiny leaves and cryptic fruits (insect-pollinated). Species with woody fruits weighing >1 g were rarely attacked, unlike those with spiny foliage and small cryptic fruits. Fire-killed species were just as resistant to granivores as resprouters but with much greater seed stores. Strongly serotinous species with prolonged seed storage were rarely attacked, with an order of magnitude larger fruits but no difference in seed store compared with weakly/non-serotinous species. Overall, the five traits examined could be ranked in success at preventing seed loss from large woody fruits (most effective), fruit clustering, low seed stores, spinescence, to crypsis (least effective). We conclude that the evolution of large woody fruits is contingent on pollinator type (dictates flower/fruit location, thus apparency to granivores), level of serotiny (response to poor soils and fire that requires prolonged seed defense) and presence of a formidable granivore (that promotes strong defense)