Plant community response to drought-induced canopy defoliation in a Mediterranean Quercus ilex forest

Saura-Mas S., Bonas A., Lloret F. (2014) Plant community response to drought-induced canopy defoliation in a Mediterranean Quercus ilex forest. European Journal of Forest Research. : 0-0.
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Doi: 10.1007/s10342-014-0848-9

Resum:

Climate change has increased drought-induced tree die-off in many parts of the world, and future climate models expect a higher recurrence of these perturbations. However, few studies have addressed plant community recovery after drought events, particularly in Mediterranean forests. This study evaluates the consequences of drought-induced die-off of the dominant holm-oak (Quercus ilex) trees on composition, structure and recruitment of the plant community, 6 years after a severe drought episode in Montserrat mountain (Catalonia, NE Spain). We evaluated the relationship of the vegetation response variables to two parameters related to the die-off consequences: canopy openness, as a measure of radiation arriving to ground, and canopy defoliation weighed by plant size, as a measure of drought impact on dominant neighbor plants. We also included in our analyses topographic situation to account for the proximity to ridge summits. Six years after the drought episode, the main findings were as follows: (1) There was a general loss of canopy cover, but Q. ilex still remained as dominant; nevertheless, the small tree Phyllirea latifolia and the shrub Buxus sempervirens tended to increase its relative abundance in the upper vegetation canopy; (2) overall, in open canopy conditions, species richness was higher mostly due to the presence of shade-intolerant herbaceous plants and early successional shrubs, such as Cistus albidus; (3) die-off did not result in increasing recruitment of the dominant species but preexisting Q. ilex sprouts were taller in sites with more open canopy; (4) there was a negative relationship between weighed defoliation and understory height, including Q. ilex sprouts, that can be attributed to large drought impact to both understory and canopy holm-oaks in some microhabitats, such as sites with abundant outcrops. This study highlights the ways in which Q. ilex Mediterranean forests regenerate after drought-induced events of canopy die-off. This regeneration involves changes in community structure and composition involving the increase in species, mostly small shrubs and herbaceous plants, which are able to grow in habitats created by canopy openness, likely becoming dominant in the landscape, as well as the arrival of non-dominant shrubs and short trees to the canopy. Potential shift in vegetation may be facilitated by the lack of increasing recruitment of Q. ilex, but this may be counterbalanced by the ability of holm-oak canopy to resprout and because pre-established saplings grown more with canopy openness. Thus, if tree canopies do not recover in a certain amount of time after the drought episode, then defoliation could lead to permanent changes in diversity and composition of the community.

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Adult root structure of mediterranean shrubs: Relationship with post-fire regenerative syndrome

Saura-Mas S., Lloret F. (2014) Adult root structure of mediterranean shrubs: Relationship with post-fire regenerative syndrome. Plant Biology. 16: 147-154.
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Doi: 10.1111/plb.12043

Resum:

Life-history attributes can impose differences on root system structures and properties related to nutrient and water uptake. Here, we assess whether plants with different post-fire regenerative strategies (resprouters, seeders and seeder-resprouters) differ in the topological and morphological properties of their root systems (external path, altitude, magnitude, topological index, specific root length, root length, root-to-shoot biomass ratio, length of the main axis of the root system and link length). To achieve these objectives, we sampled individuals from eight woody species in a shrubland located in the western Mediterranean Basin. We sampled the adult root systems using manual field excavation with the aid of an air compressor. The results indicate that resprouters have a higher root-to-shoot ratio, confirming their higher ability to store water, starch and nutrients and to invest in the belowground biomass. Moreover, this pattern would allow them to explore deeper parts of the soil layers. Seeder species would benefit from a higher specific root length, pointing to increased relative root growth and water uptake rates. This study confirms that seeders and resprouters may differ in nutrient and water uptake ability according to the characteristics of their root system. Species that can both resprout and establish seedlings after fire had different patterns of root system structure; in particular, root:shoot ratio was more similar to resprouters and specific root length was closer to seeders, supporting the distinct functional performance of this type of species. © 2013 German Botanical Society and The Royal Botanical Society of the Netherlands.

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