Increasing Drought Sensitivity and Decline of Atlas Cedar (Cedrus atlantica) in the Moroccan Middle Atlas Forests

Abstract

An understanding of the interactions between climate change and forest structure on tree growth are needed for decision making in forest conservation and management. In this paper, we investigated the relative contribution of tree features and stand structure on Atlas cedar (Cedrus atlantica) radial growth in forests that have experienced heavy grazing and logging in the past. Dendrochronological methods were applied to quantify patterns in basal-area increment and drought sensitivity of Atlas cedar in the Middle Atlas, northern Morocco. We estimated the tree-to-tree competition intensity and quantified the structure in Atlas cedar stands with contrasting tree density, age, and decline symptoms. The relative contribution of tree age and size and stand structure to Atlas cedar growth decline was estimated by variance partitioning using partial-redundancy analyses. Recurrent drought events and temperature increases have been identified from local climate records since the 1970s. We detected consistent growth declines and increased drought sensitivity in Atlas cedar across all sites since the early 1980s. Specifically, we determined that previous growth rates and tree age were the strongest tree features, while Quercus rotundifolia basal area was the strongest stand structure measure related to Atlas cedar decline. As a result, we suggest that Atlas cedar forests that have experienced severe drought in combination with grazing and logging may OPEN ACCESSForests 2011, 2 778 be in the process of shifting dominance toward more drought-tolerant species such as Q. rotundifolia.

Ecological response of Cedrus atlantica to climate variability in the Massif of Guetiane (Algeria)

“…The National Park of Belezma recorded the highest level of tree mortality: in Djebel Tuggurt, wide areas showed forest decline and mortality and were invaded by Fraxinus xanthoxyloïdes, whereas in Djebel Boumerzoug C. atlantica almost disappeared and the space has been invaded by another drought-tolerant species, Quercus ilex. In Morocco, Mokrim (2009) and Linares et al (2011) reported similar results. Linares et al (2011) noticed that C. atlantica forests that have experienced severe drought in combination with grazing and logging may be in the process of shifting dominance toward more drought-tolerant species such as Q. rotundifolia.…”

“…The current climate change is significantly affecting Mediterranean forests (Resco de Dios et al, 2007). Recent studies in northwestern Africa reported recurrent drought events over the last few decades (Touchan et al, 2008a(Touchan et al, , 2010Linares et al, 2011;Kherchouche et al, 2012Kherchouche et al, , 2013, suggesting climate conditions more limiting to tree growth and drought-sensitive species geographical distribution, especially for those at the edge of their range (Fritts, 1976). Atlas cedar, Cedrus atlantica (Manneti), is a drought-sensitive tree that could be affected by recent climate variability.…”

“…Atlas cedar, Cedrus atlantica (Manneti), is a drought-sensitive tree that could be affected by recent climate variability. During recent decades, high rates of mortality have been reported in Algeria (Alileche, 2012;Megdoud, 2012;Kherchouche et al, 2013) and Morocco (El Abidine, 2003;Linares et al, 2011). In Algeria, Allen et al (2010) reported that the recent C. atlantica mortality began as small patches on drier aspects in the arid near-Sahara mountains, eventually coalescing into large patches affecting all ages on all exposures.…”

Environmental Drivers of Holocene Forest Development in the Middle Atlas, Morocco

“…These different strategies leave Cedrus more vulnerable to extended temperature-driven summer drought and low soil moisture. This phenomenon is implicated in current dieback of Cedrus in NW Africa (Linares et al, 2011;Rhanem, 2011) and encroachment of Quercus rotundifolia into cedar forest areas (Figure 4). Field observations highlight the current decline at the lower limits of the species' elevation range and a healthy state toward the upper limits, further supporting temperature-driven abiotic stress as a key driver of ongoing dieback (Rhanem, 2011).…”

The effects of thinning intensity and tree size on the growth response to annual climate in Cedrus atlantica: a linear mixed modeling approach

“…More than 20,000 ha are predominantly planted with C. atlantica in France (Courbet et al 2007). In the context of climate change, a larger introduction of C. atlantica is now recommended by the French national guidelines (Roman-Amat 2007) but decline and mortality events have been recently reported in its native area (Allen et al 2010;Linares et al 2011), urging for deeper insight in Atlas cedar drought tolerance. We therefore aimed to answer the following questions: (1) Does a reduction in stand competition induced by thinning affect the climategrowth relationship of Atlas cedar?…”