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Ratio of post-coppicing to pre-coppicing aboveground volume (recovered size) by harvest group for each species. The ratio of post-: pre-coppicing volume recovery did not vary among species at 9 (white) or 19 (gray) months after coppicing (Kruskal–Wallis; χ2 = 3.57, P = 0.468; χ2 = 4.30, P = 0.368, respectively). For the box plots, boxes indicate the inner quartile range, the solid line denotes the median, dots are outliers, and asterisks denote the mean. A single outlier for L. tulipifera for the 19-month harvest group is not shown (value = 3.37). Species are ordered (left to right) by their position along the savanna-to-wetland gradient (Schafer and Just 2014)
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Key message: Along a fire frequency gradient, we found a savanna tree species had the greatest below ground decay compartmentalization after coppicing as compared to other resprouting species located at mesic gradient positions.
Abstract:
In pyrophilic ecosystems, woody plants are repeatedly injured or topkilled (i.e. aboveground tissue is killed...
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Research has shown that warming and drought change plant phenolics. However, much of this work has centered on the effects of individual abiotic stressors on single plant species rather than the concurrent effects of multiple stressors at the plant community level. To address this gap, we manipulated rainfall and air temperature to test for their i...
Citations
... It is therefore considered a key functional trait in many ecosystems worldwide (Clarke et al., 2013;Pausas and Keeley, 2014;Pausas et al., 2016Pausas et al., , 2018Ottaviani et al., 2017). In fire-prone environments, the capacity and strength of post-fire resprouting depends mainly on carbohydrates stored belowground and on dormant buds and meristems that are protected from the heat of fire by soil, bark, or other specialized structures (Knox and Clarke, 2005;Moreira et al. 2012;Clarke et al., 2013;Paula et al., 2016;Pausas et al., 2018), although other mechanisms may also be important (e.g., Just et al. 2017). ...
Premise:
Resource availability affects biomass allocation in ways that could influence plant responses to disturbance such as fire. This is important because fire also varies across landscapes in ways that are correlated to resource availability. We hypothesized that plants growing in landscape microsites with a shortage of nutrients and water allocate more biomass and resources to belowground structures (and thus promote traits that enhance post-fire resprouting ability) than plants in more mesic sites.
Methods:
We selected sites in three contrasting topographies (3 gullies, 3 midslopes, and 3 ridges) that supported different vegetation types and fire regimes, in Jalisco, Mexico. At each site, we measured soil nutrient and water content and light availability. Then we sampled biomass and root starch allocation in three post-fire resprouting shrubs that grow across a wide range of microenvironmental conditions.
Results:
The ridges showed the highest values of solar radiation and the lowest of soil N and water content. Overall, we found a significant tendency for higher root-to-shoot (R/S) ratios, greater fine root biomass, and higher root starch content, in individuals growing in ridges or midslopes compared to the values of the plants living in gullies.
Conclusions:
Plants located in open canopy sites, characterized by a shortage of nutrients and water, tend to allocate more biomass belowground than plants in wet and fertile sites. Thus, plants in wet and fertile forests should be more vulnerable to increased disturbance such as wildfires.
... Recommendations 1 and 2 seem particularly important to implement in A. rubrum, A. saccharinum and B. papyrifera as L W was more influential than L L . Additionally, these species have the lowest wood density (Table 1) and are likely to develop extensive wood decay if large branches are removed due to a lower compartmentalization capacity (Just et al., 2017). Recommendations 3 and 4 should be encouraged in A. platanoides, F. pennsylvanica and Q. rubra as L L was more influential than L W . Recommendation 5 seems particularly important to implement in Q. rubra as it was the only species within which CS T was influential. ...
The reiteration process involves the replication of large and complex modules of a tree structure. Reiteration may occur in sequential (i.e. normal) tree development but may also appear on old structures in response to a traumatic event (delayed traumatic reiterations, DTR), stress or internal constraints. This process is of prime interest in the context of managing trees located under electrical networks as DTR are the tree parts that will repeatedly be trimmed because of their interaction with electric wires.
However, the determinants of DTR growth are still largely unknown. In order to identify the most important DTR growth determinants and their scale of action, we measured 1061 DTR in 285 trees of six species located in 11 cities in the province of Quebec, Canada, along a large climatic gradient. Nine explicative variables, four at the local scale (dealing with within crown light and water supply), three at the tree scale (ontogeny, urban surrounding environment and crown shape), and two at the geographic scale (regional temperature and precipitation), were used to explain DTR growth. Boosted regression trees were used to fit the complex response of DTR length to each individual variable and to quantify the influence of each variable and the influence of the three scales.
Results enabled us to link the response of DTR growth to physiological processes and provide evidence of a mostly local control of DTR growth potentially influenced by a combination of water supply, light availability, and C reserves. Tree size had a relatively strong influence, while the urban environment and maintenance conditions had only a weak effect. Although the regional climatic conditions were found to affect DTR growth, their effects varied greatly among species. Based on our results, we provide some recommendations for the management and modeling of urban trees, and draw insight for future research.
... Longleaf pine savanna requires frequent burning to maintain an open canopy and grassy ground cover (Heyward 1939). On Fort Bragg, prescribed fire is typically applied on a three-year rotation (Just et al. 2017), which approximates the estimated historical fire return interval for longleaf pine savannas (Frost 2006, Stambaugh et al. 2011. These prescribed burns are typically applied using lowintensity backing fires early in the growing season, which matches the historical fire season (Fill et al. ...
Fire controls tree cover in many savannas by suppressing saplings through repeated topkill and resprouting, causing a demographic bottleneck. Tree cover can increase dramatically if even a small fraction of saplings escape this fire trap, so modelling and management of savanna vegetation should account for occasional individuals that escape the fire trap because they are “better” (i.e. they grow faster than average) or because they are “lucky” (they experience an occasional longer‐than‐average interval without fire or a below‐average fire severity). We quantified variation in growth rates and topkill probability in Quercus laevis (turkey oak) in longleaf pine savanna to estimate the percentage of stems expected to escape the fire trap due to variability in 1) growth rate, 2) fire severity, and 3) fire interval. For trees growing at the mean rate and exposed to the mean fire severity and the mean fire interval, no saplings are expected to become adults under typical fire frequencies. Introducing variability in any of these factors, however, allows some individuals to escape the fire trap. A variable fire interval had the greatest influence, allowing 8% of stems to become adults within a century. In contrast, introducing variation in fire severity and growth rate should allow 2.8% and 0.3% of stems to become adults, respectively. Thus, most trees that escape the fire trap do so because of luck. By chance, they experience long fire‐free intervals and/or a low‐severity fire when they are not yet large enough to resist an average fire. Fewer stems escape the fire trap by being unusually fast‐growing individuals. It is important to quantify these sources of variation and their consequences to improve understanding, prediction, and management of vegetation dynamics of fire‐maintained savannas. Here we also present a new approach to quantifying variation in fire severity utilizing a latent‐variable model of logistic regression.
... Another possible explanation is the difference in chemical composition of stems among species. Species having high resprouting potential, such as D. beccariana, is known to have several strategies to protect their stems against decomposers (Just et al., 2017;Poorter et al., 2010). Especially, stems of D. beccariana might contain high lignin or secondary metabolites such as phenols, which possibly hamper termite feeding (Freschet et al., 2012;Guérard et al., 2007;Just et al., 2017). ...
... Species having high resprouting potential, such as D. beccariana, is known to have several strategies to protect their stems against decomposers (Just et al., 2017;Poorter et al., 2010). Especially, stems of D. beccariana might contain high lignin or secondary metabolites such as phenols, which possibly hamper termite feeding (Freschet et al., 2012;Guérard et al., 2007;Just et al., 2017). The termites might feed more on D. beccariana after these metabolites were sufficiently degraded by fungi (Ulyshen, 2016). ...
This study investigated the contribution of termites to mass loss of dead wood (Macaranga bancana, Elateriospermum tapos, and Dillenia beccariana) in a lowland tropical rainforest, Brunei Darussalam. Mesh bag method was used to exclude termites, and the mass remaining was monitored after 3, 7, 13, and 23 months. C/N ratio of the samples was analyzed after 13 and 23 months. Initial wood density was 0.63, 0.92, and 1.02 g/cm3 for M. bancana, E. tapos, and D. beccariana, respectively, and the termite contribution to mass loss was an average (range) of 13.05±5.68 (4.17-29.59%), 3.48±1.13 (2.20-6.49), and 3.40±1.92% (0.74-10.78), respectively. Until 7 months, termites contributed highly to mass loss, given the low initial wood density, and interaction effect of species and treatment was significant. After 7 months, the contribution decreased in M. bancana and E. tapos, whereas it increased consistently in D. beccariana. The interaction effect was not significant, whereas differences in C/N ratio among the species were significant, with a lower C/N ratio in M. bancana and E. tapos than in D. beccariana. After 23 months, the differences in C/N ratio were not significant, and ants were present at 40% of control samples in M. bancana and E. tapos. Our results suggest that the contribution of termites to mass loss varies by dead wood species and is temporally variable. Initial wood traits could affect the termite feeding in the beginning, however, termites thereafter could forage in response to the varying C/N ratio among species and predators.
... For example, both seed dispersal ( Denham, 2008;Parr et al., 2007) and predation have been shown to be influenced by fire ( Zwolak et al., 2010). Additionally, wood decay compartmentalization may influence species persistence in pyrophilic systems ( Just et al., 2017;Romero et al., 2009). Unfortunately, little information on how these and other processes may influence invasive species dynamics is typically available and identifying their relative influence on seedling establishment is challenging (e.g., Clark et al., 1999). ...
Fire-promoting, open-canopy ecosystems are under threat of conversion to a fire-deterring, closed-canopy condition due to woody encroachment. This conversion of vegetation structure has been fostered by introduced woody plant species. We performed a field experiment to quantify growth, survival, and establishment success of six invasive, woody species along a managed longleaf pine savanna–wetland gradient in the Sandhills of North Carolina, USA. We investigated the effects of prescribed fire, fire history, dispersal, and abiotic conditions on the invasibility of sites along the gradient. Across 18 study sites, seeds of the six woody species were sown using three sowing methods that mimicked primary and secondary dispersal; each site contained paired plots located in savanna and savanna-wetland ecotone vegetation communities. We identified sowing treatment, abiotic conditions, seedling size, and prescribed fire as important factors for controlling woody invasion, as they prevented 5 of 6 study species from establishing in the landscape. However, the landscape was not immune to invasion. At the end of the 42-month study period, three species had established in unburned sites. In sites burned after seedling emergence, only one species, Pyrus calleryana, survived and established. We found P. calleryana survival and establishment to be a function of seedling size, soil humic matter content, and sowing treatment. Successful invasion and establishment of woody individuals in open-canopied systems increases the likelihood of fire-deterrence and further woody encroachment, threatening ecosystem integrity.
