Managing cattle grazing and overstorey cover for the conversion of pine monocultures into mixedMediterranean woodlands

Abstract

Question: A large proportion (70%) of coniferous forest area in Israel is used for livestock grazing. Recently, the possibility of managing these monospecific plantations to form mixed conifer-broad-leaved woodlands via natural regeneration processes has been considered. In light of this we pose the question, how does the interaction of cattle grazing and overstorey thinning (hereafter, thinning) affect natural regeneration in east Mediterranean pine plantations?Location: Menashe region, Mediterranean Israel (rainfall = 600 mmÁyr À1 ). Methods:The experiment was carried out in a mature (50 yr) Pinus brutia plantation. Ten plots (0.25 ha) were selected, representing thinned (five plots, %100 treesÁha À1 , leaf area index, LAI%3) and non-thinned (five plots, %230 treesÁha À1 , LAI%6) forest patches. Paired 100-m 2 subplots were positioned within each plot, one of which was fenced to exclude cattle grazing while the other remained available for grazing. Recruitment, growth and shoot water potential of pines and broad-leaved tree species were measured after 10 yr of grazing exclusion.Results: The density of newly emerged (up to 3-mo-old) pine seedlings was decreased by thinning but not affected by grazing. However, pine sapling (established seedlings) density and height were increased by thinning and decreased by grazing. Sapling density of the dominant native oak Quercus ithaburensis was reduced by both thinning and grazing. Thinning enhanced the growth of Q. ithaburensis saplings while grazing restricted their height. Grazing and thinning had no significant effect on the total sapling density of broad-leaved tree species, but grazing restricted their height and reduced species richness. Grazing reduced topsoil water content in non-thinned plots but had no effect in the thinned plots. Grazing increased the water potential of pine seedlings while thinning reduced it. Both grazing and thinning had no effect on the water potential of mature Pistacia lentiscus shrubs.Conclusions: Natural regeneration within east Mediterranean pine plantations is limited by both dense overstorey cover and cattle grazing. While grazing exclusion is necessary for the establishment and early growth of recruits, reintroduction of grazing at later phases may facilitate the development of young forests by controlling competition.

Forests growing under dry conditions have higher hydrological resilience to drought than do more humid forests

“…grazing being more frequent in the northern forests and mixed sheep and goat grazing more typical of the southern ones. Forests located in the central part of Israel were usually less intensively grazed (Osem et al, 2015). In this study, we assume that grazing had relatively comparable effect on forest structure and thus on catchment water budget in the forested catchments of our study region.…”

Manipulating ungulate herbivory in temperate and boreal forests: effects on vegetation and invertebrates. A systematic review

“…In parallel with broad-scale changes in herbivore populations, local effects can cascade to regional trends in biodiversity [18] and include development of new, relatively stable alternative states of some ecosystems [5,19,20]. Thus, herbivory is highly important for the maintenance of forest habitat values, including structural and compositional heterogeneity, as well as biodiversity [12,[21][22][23].…”

Understory structure and function following release from cattle grazing and overstory thinning in Mediterranean conifer plantations

“…In a previous study within the same system, we found the effect of overstory thinning and grazing on tree recruitment in the forest understory to depend on sapling size. While smaller saplings (<20 cm in height) were generally more abundant in grazed non-thinned areas, larger saplings were more abundant in the ungrazed-thinned areas (Osem et al 2015). Higher frequency of tree and shrub species in the understory of non-thinned plots may be related to better seedling establishment of large seeded woody species such as Q. calliprinos, S. officinalis, and Phillyrea latifolia resulting from facilitative effects of the overstory (Alon and Kadmon 1996) and related ground litter layer (Sayer 2006).…”

“…Previous studies looking at the understory in East Mediterranean pine plantations have focused primarily on natural regeneration of tree species (Osem et al 2009(Osem et al , 2013(Osem et al , 2015. In this study we pursued a more comprehensive understanding of the ways by which understory structure and function is driven by management factors.…”