Effects of grasses on sapling establishment and the role of transplanted saplings on the light environment of pastures: implications for tropical forest restoration

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Abstract

Question

Does the presence of grasses affect the establishment (survival and growth) of tree saplings in an abandoned tropical pasture, and what is the potential of established saplings to modify pasture microenvironmental conditions, particularly light incidence?

Location

Abandoned cattle pasture, in the humid tropics of SE Mexico (18°25′–18°45′ N, 95°00′–95°18′ W).

Methods

The establishment of four native fast-growing tree species in a tropical abandoned pasture was evaluated. Saplings of Cecropia obtusifolia, Hampea nutricia, Omphalea oleifera and Erythrina folkersii were transplanted using a split-plot design. Plant survival and growth were evaluated over 12 mo under two experimental treatments: presence and absence of grasses. Light incidence at ground level was used to evaluate microclimate conditions under the grass matrix, compared to light incidence under saplings established in the pasture.

Results

Saplings had high survival (49–88%) regardless of the presence of grasses. In the presence of grasses, growth of surviving saplings either increased or was not impacted, and in only one out of eight comparisons did grasses negatively affect growth. The impact of saplings on light incidence in abandoned pastures depended on sapling species architecture: species with large total leaf area and canopy area ( H. nutricia and E. folkersii) significantly reduced light incidence (12–29% of total incidence), while narrow-canopy species ( C. obtusifolia and O. oleifera) generated less intense shade (37–89% of total incidence).

Conclusions

Grasses did not seem to represent a crucial limiting factor in sapling establishment of fast-growing native species in the short term. In addition, shading by recruited saplings of some native species could be important to out-compete grasses in the future, as well as for ‘facilitating’ regeneration of more shade-tolerant species. Transplantation of fast-growing native saplings into abandoned pastures, even without manipulation of the grasses, could be a useful practice for landscape-scale restoration programmes in tropical areas. Evaluation of the longer-term consequences (beyond the 1-yr span of this study) warrants further research.

We evaluated the effects of grasses on the establishment of four fast-growth tree saplings in a Neotropical abandoned pasture, and the potential of saplings to modify light incidence. Grasses did not seem to represent a limiting factor in sapling establishment in the short term. Shading by recruited saplings could be important to outcompete grasses and therefore ‘facilitate’ more shade-tolerant species.

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