Climate effects on stem radial growth ofQuercus suberL.: does tree size matter?

Abstract

The cork oak (Quercus suber L.) is periodically harvested for bark (cork) throughout its lifetime. Trees undergo physiological changes as they age which affect stem diameter growth and their sensitivity to climate. However, little is known about trees age-or size-related growth changes and it remains unclear if trees of different ages (sizes) have similar climate-growth relationships. In this study, we examined the increment in stem basal area of 47 randomly selected (large and small) cork oaks over a 12-year period to assess divergent climate-growth relationships. Our approach, using a machine learning algorithm on unlabelled data sets of basal area increments, successfully filtered out tree-clusters that suggested a size (age)-dependent growth response to climate. On average, the basal area increment was more than three times larger in larger-trees clusters compared with smaller-trees clusters. A large tree (diameter >75 cm) on average added 105 cm 2 y −1 to its basal area against 25 cm 2 y −1 in a small tree (diameter <35 cm). Additionally, in smaller-trees, cork harvesting intensified the negative impact of drought on tree growth, and worsened post-drought recovery. These findings highlight the need to consider biological growth trends for accurate predictions of trees responses to drought.

Is Cork Growth a Reliable Proxy for Stem Diameter Growth in Cork Oak (Quercus suber L.)? Implications for Forest Management under Climate Change in Mediterranean Regions

“…Section 2.1), which probably had a negative impact on cambium activity, much more influenced by the climatic factors prevailing in the current growth season (Figure 3). Trees might use (less) current photosynthates to support this cambial activity [27] because the "non-cork" (wood) growth probably competes with other carbon sinks namely with reproduction efforts [7,11,28,29].…”

“…The widely held assumption of these studies is that cork-ring width (or cork growth) at breast height is a reliable predictor of tree stem diameter (and basal area) growth, since cork represents a large part of cork oak's radial increment [8], and the contribution of a "non-cork" (wood) growth to that increment is ignored. On one hand, such a consensus derives from the difficulty and scarcity of measurements of wood growth, which is slow and results in narrow and undefined tree rings [9], while cork growth shows wide and clearly defined rings; on the other hand, few studies have addressed stem radial growth sensitivity to climate [8,10,11].…”

“…Moreover, climatic influence on corkring width is relatively poorly expressed [5][6][7]-only strongly linked to the previous autumn-winter rainfall. Thus, cork growth variations may be insufficient for an adequate interpretation of climate change effects on stem diameter growth, considering that the activity of the phellogen is less sensitive to climatic influences than that of the cambium [8] and particularly unsuitable because cork-ring area growth responses are possibly biased by the size-related stem radial growth dynamics [11].…”

Cork Oak Forests Soil Bacteria: Potential for Sustainable Agroforest Production

“…These woodlands are well adapted to the Mediterranean climate, where summers are warm and dry, and winters mild and wet. Over recent decades, a severe reduction in cork oak forests areas has been occurring, which is mainly due to the increasing of temperatures and long drought seasons [ 4 ], but also to changes in land use and new pathogen emergence [ 1 ]. Indeed, disease incidence and drought play the most significant role in trees health and forest ecosystem sustainability, where the consequences of water deficits further enhance fungal diseases [ 5 ].…”

“…With the upcoming increase in frequency and severity of drought events, new strategies for mitigating both abiotic and biotic stress effects on forests became crucial [ 4 ]. Beneficial microorganisms have been used as important partners for helping host plants to better tolerate these factors [ 8 ].…”