Question: How do forest microhabitats impact seasonal microclimate conditions and phenological seedling strategies in two co-occurring Mediterranean Quercus species with different leaf habits?Location: Pinus halepensis woodlands, Provence, SE France.Methods: Ninety sets of three acorns of Quercus ilex (evergreen) or Quercus pubescens (winter-deciduous) were sown under various P. halepensis canopy cover conditions. Canopy cover and litter depth were measured at each sowing point, and soil moisture and temperature were measured twice monthly. Seedling phenology and aerial development were monitored during the second growing season under different microhabitats.Results: During rainy periods, soil moisture was higher under open canopy and thinner litter layers, whereas during summer drought soil moisture was higher under dense canopy and thicker litter layers. Quercus pubescens seedlings had higher growth activity than Q. ilex before summer drought, whereas the pattern reversed during autumnal growth. Dense canopy cover strongly delayed budburst and decreased foliar development in Q. pubescens, which was more affected than Q. ilex. Depending on species phenology, litter thickness can influence height growth of flushes during early summer.Conclusions: Quercus pubescens has a phenological strategy to allow development of maximal foliar area before summer drought, a typical growth strategy of Mediterranean winter-deciduous species. In contrast, later phenological activity of evergreen Q. ilex enables it to cope with the dry period and capitalize on autumnal precipitation events. Dense cover acts as shelter in the dry season but can reduce soil moisture during wetter seasons. In contrast to Q. ilex, Q. pubescens appeared strongly dependent on canopy cover, suggesting that Q. ilex has a larger regeneration niche in Aleppo pine woodlands. In the context of global change, this 'microhabitat effect' on species-specific phenological strategy underlines the need to consider effects of local environmental conditions on regenerating species.
Mixed plantations have been receiving increasing attention for their documented or supposed potential benefits over monospecific plantations. In particular, the use of neighbouring (or nurse) vegetation around target plants can enhance their performance through limitation of the competing herb layer, and can also improve their morphology.Here we examine the benefits and drawbacks of using neighbour treatments on the response of target trees in open plantations. We set up an experimental plantation in southern France, in which two co-occurring target oak species (the evergreen Quercus ilex and the deciduous Quercus pubescens) were introduced in different neighbour treatments using a tree (Pinus halepensis) and a shrub species (the nitrogen-fixing Coronilla glauca). Oaks were planted with pine neighbours at two densities, with shrub neighbours, in a mixture of pines and shrubs or without neighbours. The ground vegetation was either regularly weeded or left to grow in order to detect any indirect facilitation interactions. Target oak responses (survival, growth, and morphology) were monitored over 7 years. Soil water content and light availability were also measured throughout the experiment.We found competition to be the dominant process driving interactions between neighbours and target tree species. Growth was reduced for both species, but more in weeded than in unweeded treatments, showing an alleviation of competitive interactions by neighbours through limitation of herb layer development. However, in both ground vegetation treatments, growth was severely reduced with Coronilla shrubs. Survival was only significantly impaired for the less shade-tolerant Q. pubescens oak used in combination with shrubs. The negative influence of the neighbour treatments was mainly attributable to light interception, which was particularly high by shrub canopy. Soil moisture was also slightly reduced by shrub neighbours, but it remained high with pines in the unweeded treatment owing to a limited abundance of herbs. However, stem form was improved by the neighbour treatments: oaks developed narrower crowns and greater slenderness with neighbours, whereas oaks in the open showed a bushy morphology. These findings emphasize the need to clearly identify key objectives before implementing mixed plantations (e.g. maximising growth, survival, improving morphology, etc.) and to use active management to control potential undesirable effects of the neighbouring vegetation on target plants.
Indirect methods to estimate parental status, such as the observation of parental provisioning, have been problematic due to potential biases associated with imperfect detection. We developed a method to evaluate parental status based on a novel combination of parental provisioning observations and hierarchical modeling. In the summers of 2009 to 2011, we surveyed 393 sites, each on three to four consecutive days at Forêt Montmorency, Québec, Canada. We assessed parental status of 2331 adult songbirds based on parental food provisioning. To account for imperfect detection of parental status, we applied MacKenzie et al.'s (2002) two-state hierarchical model to obtain unbiased estimates of the proportion of sites with successfully nesting birds, and the proportion of adults with offspring. To obtain an independent evaluation of detection probability, we monitored 16 active nests in 2010 and conducted parental provisioning observations away from them. The probability of detecting food provisioning was 0.31 when using nest monitoring, a value within the 0.11 to 0.38 range that was estimated by two-state models. The proportion of adults or sites with broods approached 0.90 and varied depending on date during the sampling season and year, exemplifying the role of eastern boreal forests as highly productive nesting grounds for songbirds. This study offers a simple and effective sampling design for studying avian reproductive performance that could be implemented in national surveys such as breeding bird atlases.
Synovigenic insects resorb oocytes when food is scarce and mature oocytes when food is plentiful. These two antagonistic processes allow an optimal allocation of resources to reproduction and somatic functions. Unlike hymenopteran parasitoids, ladybirds cannot resorb mature oocytes present in the oviducts. Is the energy contained in these oocytes lost or is there a mechanism for recovering it when needed? Females of two species of ladybird beetles Adalia bipunctata (L.) and Adalia decempunctata (L.) that are starved for >24 h lay single infertile eggs, which they immediately eat, and these eggs comprise the mature oocytes in the oviducts at the onset of starvation. This behaviour has some similarities to egg dumping reported in herbivorous insects and is part, in ladybird beetles, of a process to retrieve energy invested in reproduction. Such behaviour may exist in other predatory synovigenic insects species that do not invest in maternal care.
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