Some ecological impacts of Quercus rotundifolia trees on the understorey environment in the "montado" agrosilvopastoral system, southern Portugal.

Abstract

The influence of Quercus rotundifolia trees on precipitation chemistry, soil physical and chemical characteristics, light, nutrient and water availability and biomass production of the understorey was studied in a "montado" at Évora (southern Portugal). Ca and K were added to the soil by throughfall (21.05 and 38.49 kg/ha, respectively) and gross rainfall (3.49 and 3.98 kg/ha). Thickness of the soil organic layer and nutrient availability decreased with the distance from the tree trunk and were higher in ungrazed areas. Soil temperature was higher in areas without canopy, especially in winter. Soil moisture tended to decrease and refill faster in areas without canopy influence. PAR (photosynthetic active radiation) was intercepted around 75 to 90% by the canopy depending on the time of the year, and showed significant diurnal differences between inside and outside the canopy. Biomass production of the herbaceous layer responded more to water and fertilizer in the areas outside the tree canopy and without artificial shading than under the canopy. However, when the rate between the distinct biomass and the control was calculated, the response to water was more efficient under the canopy for the three treatments in the second year.

Effets de chênes verts isolés sur les variations spatiales et temporelles de l’humidité du sol dans les dehesas du centre-ouest de l’Espagne

“…In our study, water interception and transpiration should overweigh the positive effects of trees on water-holding capacity, as observed in North American savannas [27]. A similar pattern has been reported by Nunes et al [30], for Portuguese dehesas with an annual rainfall of 666 mm. In more humid dehesas (annual rainfall above 700 mm) soil water content was always higher beneath than beyond the tree canopy [20].…”

Ability of Cistus L. shrubs to promote soil rehabilitation in extensive oak woodlands of Mediterranean areas

“…The study shrubs may have a positive role on SOC (10.3-11.4 g kg −1 in the 0-5 cm top soil layer), as reported for other Mediterranean shrubs (Moro et al 1996;Monokrousos et al 2004) and shrubs in a subtropical savanna (Hibbard et al 2001), following the pattern observed for trees in oak woodlands of Mediterranean areas (Dahlgren et al 1997;Nunes 2004;Moreno and Obrador 2007). However, relative to barren areas (8.1 g kg −1 ), the increment of SOC was low, which is in line with average values reported by Moreno and Obrador (2007) for dehesas encroached after 10-15 years.…”

“…Those values are within the range reported by Escudero et al (1985) for litter amount beneath Q. rotundifolia (1.7-4.6 Mg DM ha −1 ). Also, amounts of necromass under shrub canopies fall within the range observed by Nunes (2004) for Q. rotundifolia (1.3-3.0 Mg DM ha −1 ), in the neighbourhood of the study area. Similar necromass observed for CL and Q. rotundifolia is in agreement with litterfall amounts of the same magnitude, and also with the similar decomposition rate exhibited by the leaf litter of CL (−0.44 year −1 ) as compared to that for Q. rotundifolia (−0.48 year −1 ) (Sá et al 2005).…”

“…They predominantly show a sandy texture, loam sandy to sandy loam, low contents of organic C (6-10 g kg −1 ); pH (H 2 O) values range from 4.9 to 5.3 and contents of extractable Ca, Mg, K and Na range, respectively, 1.2-1.9, 0.5-0.8, 0.05-0.15 and 0.14-0.20 cmol c kg −1 . Extractable P is very low, ranging from 1 to 9 mg kg −1 (Nunes 2004).…”

“…Cistus salviifolius L. and C. ladanifer L. are undoubtedly the most representative species in oak woodland areas degraded by previous cereal crops and livestock overgrazing (Martín Bolaños and Guinea López 1949). Several studies developed at tree level in Mediterranean oak woodlands, including Portugal (Nunes 2004), have shown that trees provide carbon sequestration and enhance SOM and nutrient pools beneath the canopies, preventing thus soil erosion and land degradation. However, few studies have focused so far the potential role of encroachment on the recovery of soil physical and chemical quality, and on tree natural regeneration and system sustainability.…”