Forest microhabitats differentially influence seedling phenology of two co‐existing Mediterranean oak species

Abstract

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.

Divergent growth trends and climatic response of Picea obovata along elevational gradient in Western Sayan mountains, Siberia

“…Low inter-serial correlation coefficients indicate that, apart from the general climatic influence, there are other factors within the site which make a significant contribution to the variability of growth on the scale of individual trees. Other observation of individual-scale factors" input in spruce growth patterns was made in Canada (Montoro Girona et al2016Girona et al , 2017 It is logical to assume that at the study area this role is played by micro-conditions (Barber et al 2000;Kulagin et al 2006;Monnier et al 2012;Lange et al 2016), which are characterized by high diversity and mosaic structure in mountain ecosystems due to high terrain heterogeneity. This is confirmed by analysis of local sub-sets based on inter-serial correlation coefficients.…”

Do litter-mediated plant-soil feedbacks influence Mediterranean oak regeneration? A two-year pot experiment

“…To our knowledge, there is no recognized litter trait influencing litter effects on soil humidity, but this would deserve further attention. Interestingly, litters with low decomposition rates could improve soil humidity in dry periods by maintaining a thick layer of litter over time, thereby reducing soil evaporation (Monnier et al 2012), which may result beneficial for seedlings. Traits such as ratio of thickness per mass may also influence litter ability to retain soil water (Donath and Eckstein 2008).…”

Microclimate in forests with varying leaf area index and soil moisture: potential implications for seedling establishment in a changing climate

“…Finally, besides T and VPD, overstorey tree species composition usually also influences abiotic (soil pH, texture, nutrient levels, litter amounts, etc.) and biotic (cover and composition of herbaceous vegetation) conditions in the forest floor (Gilliam & Roberts 2003;George & Bazzaz 2003;Monnier et al 2012), which all affect the survivability of seedlings in the understorey.…”