Responses of Chinese fir and Schima superba seedlings to light gradients: Implications for the restoration of mixed broadleaf-conifer forests from Chinese fir monocultures

Abstract

Although Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantations are widely grown for timber production in southern China, they have low biodiversity and provide limited ecosystem services. To address this problem, C. lanceolata are increasingly mixed with broadleaf Schima superba Gardn. & Champ. (Theaceae). The success of these mixed plantations relies on introducing each species in the appropriate sequence, which requires understanding how tree species respond to light variations. We therefore compared S. superba and C. lanceolata seedling light tolerance in shaded houses under five light gradients (5%, 15%, 40%, 60%, and 100% sunlight). Our findings showed that S. superba seedlings exhibited greater net height increment (ΔHt), net diameter growth (ΔDia), leaf area, root mass, stem mass, leaf mass, and total mass under low light conditions (15% sunlight). However, as sunlight increased, these growth variables became higher in C. lanceolata seedlings. With more sunlight, both species experienced a drop in height to diameter ratio (HDR), and specific leaf area (SLA), but an elevated root to shoot ratio. Additionally, under the same light levels, S. superba seedlings exhibited greater leaf area and root to shoot ratio than C. lanceolata seedlings. Our results suggested that S. superba might be more suitable for underplanting beneath a heavy canopy due to its shade-tolerant traits. In contrast, C. lanceolata was less shade-tolerant, having an optimum seedling growth under full sunlight. These findings suggest that underplanting S. superba seedlings in C. lanceolata monoculture plantation (i.e., underplanting regeneration approach) could be a better silvicultural alternative than simultaneously planting both seedlings.

Effects of light intensity on non-structural carbohydrate contents and C:N:P stoichiometry in Cunninghamia lanceolata and Schima superba

“…As S. superba is better adapted to low light intensity (shade tolerant), it would be advisable to plant S. superba later once the canopy of C. lanceolata is well developed but allowing enough sunlight (up to15%-60%). Conversely, in dense stands of C. lanceolata, thinning to allow sufficient light to reach the understory would be recommended to expedite the natural regeneration and subsequent growth of S. superba as we observed better growth of S. superba under low light intensity [31].…”

“…This morphology allows heat dissipation, avoiding damage from overheating and high transpiration rates [2,34]. Conversely, shaded conditions result in increasing area and decreasing thickness of leaves [22,31], with low leaf mass per unit area [12]. Increasing leaf area allows plants to acquire more light for photosynthesis [5,35] and is thus an adaptation to lowlight environments [34].…”

“…Five light intensity levels (100%, 60%, 40%, 15%, and 5% of full sunlight) were created using shade houses covered with black nylon shade cloth of differing mesh size [31]. The relative irradiance was estimated with a light meter on a clear day in summer and summarized in Table 1.…”

“…& Champ -the two most important forest species in subtropical China, which are intended for establishment of mixed species forest. It has been shown that S. superba seedlings under low light exhibited greater net height increment, net diameter growth and total biomass than C. lanceolata [31]. However, we still know little about the effect of varying light intensities on leaf morphological and functional responses in these two species.…”

Responses of leaf morphology, NSCs contents and C:N:P stoichiometry of Cunninghamia lanceolata and Schima superba to shading

“…Like other monocultures, the sustainability of C. lanceolata plantations is threatened by soil degradation, production loss, biodiversity reduction, and a lack of selfregeneration [26][27][28][29][30]. In order to solve this problem, S. superba, a broadleaf tree, is increasingly mixed with C. lanceolata stands [26,27,31,32]. Previous studies showed that C. lanceolate is shade-intolerant tree, in contrast, S. superba is shade-tolerant tree [26].…”