Dominance of legume trees alters nutrient relations in mixed species forest restoration plantings within seven years

Abstract

Failures in reforestation are often attributed to nutrient limitation for tree growth. We compared tree performance and nitrogen and phosphorus relations in adjacent mixed-species plantings of contrasting composition, established for forest restoration on Ultisol soil, originally covered by tropical semi-deciduous Atlantic Forest in Southeast Brazil. Nutrient relations of four tree species occurring in both planting mixtures were compared between a legume-dominated, speciespoor direct seeding mixture of early-successional species (''legume mixture''), and a species-diverse, legume-poor mixture of all successional groups (''diverse mixture''). After 7 years, the legume mixture had 6-fold higher abundance of N 2 -fixing trees, 177% higher total tree basal area, 22% lower litter C/N, sixfold higher in situ soil resin-nitrate, and 40% lower in situ soil resin-P, compared to the diverse mixture. In the legume mixture, non-N 2 -fixing legume Schizolobium parahyba (Fabaceae-Caesalpinioideae) had significantly lower proportional N resorption, and both naturally regenerating non-legume trees had significantly higher leaf N concentrations, and higher proportional P resorption, than in the diverse mixture. This demonstrate forms of plastic adjustment in all three non-N 2 -fixing species to diverged nutrient relations between mixtures. By contrast, leaf nutrient relations in N 2 -fixing Enterolobium contortisiliquum (FabaceaeMimosoideae) did not respond to planting mixtures. Rapid N accumulation in the legume mixture caused excess soil nitrification over nitrate immobilization and tighter P recycling compared with the diverse mixture. The legume mixture succeeded in accelerating tree growth and canopy closure, but may imply periods of N losses and possibly P limitation. Incorporation of species with efficient nitrate uptake and P mobilization from resistant soil pools offers potential to optimize these tradeoffs.

Soil dynamics and carbon stocks 10 years after restoration of degraded land using Atlantic Forest tree species

“…In both restoration models and in the Control, the reduction of bulk density and consequent increase in porosity (Table 2) may have been caused by the growth of the planted trees and natural regeneration (Engel and Parrotta, 2001;Siddique et al, 2008). After the protection and reforestation of the study site, the increase of organic matter content (Table 4), through litterfall and root growth, may have been the main agent of this change.…”

“…The variation in soil nutrient contents and quality of accumulated litter (Table 4 and 6) support the findings of their study that restoration models may contribute differently to changes of soil chemical properties. However, changes in soils occurred earlier in the Low Diversity treatment than in other treatments (Table 4), which may indicate higher rates of nutrient cycling promoted by species composition (Siddique et al, 2008) and by more rapid establishment of forest structure (Engel and Parrotta, 2001). Another factor that may have contributed to the differences between restoration models is the soil preparation methods used, i.e., the minimal cultivation employed in the Low Diversity treatment and the conventional tillage employed in the High Diversity treatment.…”

“…For both restoration models in relation to the Control, the lower C:N ratio in accumulated litter indicated the pronounced effect of the models in terms of biological nitrogen fixation, especially in the Low Diversity treatment, which has a higher density of N 2 -fixing leguminous trees (Siddique et al, 2008). These authors studied the dominance of leguminous trees and relationships among nutrients seven years after the plantations were established, comparing the Low Diversity and High Diversity treatments.…”

Ecofunctional Traits and Biomass Production in Leguminous Tree Species under Fertilization Treatments during Forest Restoration in Amazonia

“…Several studies have suggested the use of leguminous tree species in forest plantations to reclaim soil fertility [14][15][16][17][18]. These species have been used for fallow enrichment and green fertilization for both restorative and commercial purposes in forest plantations [19][20][21].…”

Testing heterogeneity–diversity relationships in tropical forest restoration

“…Canopy cover influences woody recruitment through a number of mechanisms including: enhancing bird activity and thereby dispersal of zoochorous seeds (Howe 1990;Jones et al 2004;Fink et al 2009); reducing cover of light-demanding pasture grasses (Holl 2002a;Hooper et al 2002); providing intermediate light conditions favorable for tree growth (Loik and Holl 2001); and enhancing nutrient availability (Siddique et al 2008;Celentano et al 2011). These mechanisms are all likely operating at our sites, but it is impossible to evaluate their relative importance without manipulating them independently.…”