Abstract
Enrichment planting in naturally recovering secondary forests or in tree plantations is increasingly being used as strategy to restore later-successional, large-seeded tropical forest trees. We seeded two tree species (Otoba novogranatensis and Ruagea glabra) in three agricultural sites in Southern Costa Rica: abandoned pastures, eight to ten year old secondary forests and three year old tree plantations (containing two N-fixing of four total tree species). We measured micrometeorological conditions, soil water content, plant water potential, leaf area, foliar C and N, and photosynthesis to better understand mechanistic responses of seedlings to conditions in the different successional habitats. Micrometeorological conditions, soil water content, and plant water potential were generally similar across habitats. Certain aspects of leaves (such as Specific Leaf Area and foliar N content), and photosynthesis (e.g. quantum yield and electron transport rate) were highest in the plantations, intermediate in the secondary forests, and lowest in abandoned pastures. Enhanced rates of photosynthetic biochemistry (such as Vxmax and Jmax) and Photosystem II efficiency (e.g. thermal energy dissipation) occurred in leaves from the plantations compared to the abandoned pastures, which may be related to higher leaf %N content. Results suggest that foliar N may be of greater importance than soil water content and micrometeorological factors in driving differences in photosynthetic processes across planting habitats. Planting seeds of these two species in plantations containing three year old trees (including two N-fixing species) enhances certain aspects of their photosynthesis and growth, compared to seedlings in abandoned pastures with non-native grasses, and thus can help increase forest recovery on abandoned agricultural lands.
Highlights
Efforts to restore tropical forests have increased substantially over the past decade
Grass cover was highest in pastures, intermediate in secondary forests, and lowest in plantations with the reverse pattern for bare ground; herbaceous cover was similar across habitats (Table 1)
Prior research at our study sites showed that seedlings were taller, had lower root:shoot ratios, and higher leaf N content when they were planted in tree plantations, compared to secondary forests or abandoned pastures (Cole et al 2011)
Summary
Efforts to restore tropical forests have increased substantially over the past decade. Foliar P concentration was somewhat higher in the plantations and did not differ between abandoned pastures and secondary forests (Cole et al 2011); surprisingly, litterfall P and C:P did not differ across the three habitats (Celentano et al 2011) These results, as well as other studies (Cusack & Montagnini 2004, Siddique et al 2008), suggest that the initial species can strongly influence nutrient dynamics and growth, and in turn, the successional trajectory in a site. The goal of this study was to better understand the physiological mechanisms underlying differences in growth for seedlings direct-seeded in abandoned pastures, secondary forests, and plantations that contain two N-fixing trees to restore premontane tropical forest in Southern Costa Rica. We tested whether PSII efficiency, photosynthetic capacity, and biochemistry differed within the tree plantations, abandoned pasture, and secondary forest habitats
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