Can native shrubs facilitate the early establishment of contrasted co‐occurring oaks in Mediterranean grazed areas?

Abstract

Questions: Can shrubs (Cytisus multiflorus) and large herbivore exclusion (fence) facilitate seedling survival and growth of marcescent and sclerophyllous oaks (Quercus pyrenaica vs Q. ilex subsp. ballota) under a bioclimatic limit in Mediterranean grazed areas?Location: Open oak woodlands, central-western Spain. Methods:A 2-yr field experiment was conducted by planting 200 seedlings of each Quercus species under four different treatments combining the influence of nurse shrubs and fencing on Quercus seedling survival and growth.Results: Cytisus multiflorus enhanced poor Quercus seedling survival found in the study area, at least during the first 2 yr after planting and particularly during the first dry season. The improvement in soil organic matter under the shrub canopy may have contributed to this positive effect, which was more pronounced on Q. pyrenaica seedlings. Seedling herbivory did not seem to be a limitation to survival. Increased seedling growth in both species was also very low, and no growth was recorded 2 yr after planting without shrubs. The positive shrub effect on seedling growth, especially marked in fenced areas, was more important in Q. pyrenaica in the first growing period and in Q. ilex in the second; 2 yr after planting no difference in shrub effect on growth was found in either Quercus species. Seedling herbivory was a limitation to seedling growth in areas without shrubs, mainly in the case of Q. pyrenaica. Conclusions:In Mediterranean grazed areas with important summer drought and very sandy soil, shrubby C. multiflorus plants have a clear facilitative effect on seedlings of ecologically contrasted Quercus species. The facilitative effect was found in both marcescent and sclerophyllous oak seedlings, but to a different degree depending on the species considered and the variable measured (survival or growth). In terms of survival, the marcescent species was more favoured by shrub cover than the sclerophyllous one, and this effect was accentuated through time. However, in terms of growth, although Q. pyrenaica was initially more favoured by shrubs, differences between the two species were attenuated after 2 yr. Therefore, C. multiflorus can have a key role in restoration of these oak degraded environments.

Ecological Restoration of Abies religiosa Forests Using Nurse Plants and Assisted Migration in the Monarch Butterfly Biosphere Reserve, Mexico

“…Thus, the use of nurse plants in the early stages of a reforestation program with A. religiosa is highly recommended, as was found with planted Lupinus elegans serving as nurse plants in a previous study (Blanco-García et al, 2011) and, in our case, with the existing nurse plants (mostly the shrub Baccaris conferta). Our results are very similar to the patterns of survival found when Quercus petraea, Q. pyrenaica, and Q. ilex were grown under the shade of native shrubs (Genista florida, Cytisus scoparius, and C. multiflorus), and without the nurse effect, in studies conducted in harsh environments (Torroba-Balmori et al, 2015;Alday et al, 2016;Costa et al, 2017). In recent decades, the determinant role of facilitation has been recognized as a positive interaction among species that directly affects their performance, distribution and metabolism (Bruno et al, 2003;Brooker et al, 2008).…”

“…In recent decades, the determinant role of facilitation has been recognized as a positive interaction among species that directly affects their performance, distribution and metabolism (Bruno et al, 2003;Brooker et al, 2008). The role of shade as a modifier of microclimatic conditions is important because this mechanism of improving microclimatic conditions is one of the most recognized forms of facilitation (Callaway et al, 2002;Callaway, 2007;Walker et al, 2007;Torroba-Balmori et al, 2015;Alday et al, 2016;Costa et al, 2017). The effects of nurse plants are of particular importance to plants growing under severe climatic conditions, as predicted by the stress gradient hypothesis (Bertness and Callaway, 1994;Callaway et al, 2002).…”

“…provenances (see Table 1) were planted in 50 blocks with nurse plants and in 20 main plots without nurse plants (in open field treatment). With the experience gained in the Las Palomas site 2 years previously, the blocks in the Los Ailes site were composed of one seedling from each of the six populations, randomly selected and planted in a circle around the stem of the nurse plants, similar to the methodology used by Costa et al (2017) (Figure 3B), and around an imaginary point for the blocks without nurse plants (open field; Figure 3C). This unorthodox arrangement of seedlings in the blocks helped ensure that all the seedlings under the nurse plant treatment received approximately equal levels of shade.…”

Dinámica de la flora arvense en forestaciones de terrenos agrícolas

“…Algunos trabajos han puesto de manifiesto desde hace tiempo el efecto facilitador de los matorrales en la restauración de zonas degradadas del bosque mediterráneo (Villa et al, 2012;Costa et al, 2017). Dichos autores obtuvieron mejores resultados en una plantación de encina y rebollo bajo Cytisus multiflorus (L´Hér.)…”

Increasing aridity threatens the sexual regeneration of Quercus ilex(holm oak) in Mediterranean ecosystems

“…In Q. ilex, recruitment occurs in full sun only when annual precipitation is 700 mm or more [10], but as precipitation decreases, seedlings need shade to compensate for evapotranspiration, until reaching a lower limit of annual precipitation, around 250 mm, when the water deficit can no longer be compensated by the shade [10,12]. In the wild, nurse plants facilitate the establishment of seedlings in many Quercus species under Mediterranean climate conditions because they improve soil conditions, reduce predation on seeds and seedlings, and provide shade that favors a positive water balance of seeds and young plants [8,[13][14][15][16][17][18]. However, Quercus seedlings need light to grow, so the intense shade that favors recruitment under high evaporative demand makes their subsequent development to seedlings and juveniles difficult or even impossible [19,20].…”