doi:10.1016/j.foreco.2008.12.004
Copyright © 2008 Elsevier B.V. All rights reserved.
Edge effects on soil seed banks and understory vegetation in subtropical and tropical forests in Yunnan, SW China
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Luxiang Lina and Min Cao
, a,
, 
aXishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, 88 Xuefu Road, Kunming 650223, PR China
Received 7 July 2008;
revised 28 November 2008;
accepted 1 December 2008.
Available online 8 January 2009.
Abstract
Human-induced forest edges are common in many forest landscapes throughout the world. Forest management requires an understanding of their ecological consequences. This study addressed the responses of three ecological groups (non-forest species, secondary forest species and primary forest species) in edge soil seed banks and edge understory vegetation, and explored the relationship between the invasion of non-forest species in edge understory vegetation and the accumulation of their seeds in edge soil seed banks. The soil seed banks and understory vegetation were sampled along transects established at the edges of a continuous subtropical evergreen broad-leaved forest tract (Lithocarpus xylocarpus forest) bordering anthropogenic grasslands and three tropical seasonal rain forest fragments (Shorea wantianshuea forest) bordering fallows. Species composition in both soil seed banks and understory vegetation showed great difference among edge sites. In soil seed banks, the dominance (relative abundance and relative richness) of each ecological group did not change significantly along the edge to interior gradient. In understory vegetation, the invasion of non-forest species concentrated on the first several meters along the edge to interior gradient. The dominance of secondary forest species decreased with distance from the edge, while the dominance of primary forest species increased with distance from the edge. In forest edge zones, the invasion of a majority of non-forest species in understory vegetation lags behind the accumulation of their seeds in soil seed banks. Forest edges do not act as a good barrier for the penetration of non-forest species seeds. The lack of non-forest species in understory vegetation must then be due to conditions that are not appropriate for their establishment. Therefore, to prevent germination and survival of non-forest species further into the forest, management should focus on maintaining interior forest conditions.
Keywords: Ecological group; Invasion; Non-forest species; Primary forest species; Secondary forest species
Fig. 1. Geographical locations of the two study areas in Yunnan Province, SW China.
Fig. 2. DCA ordination diagrams for plots of understory vegetation, samples of soil seed banks in late rainy season and late dry season at the edges of Lithocarpus xylocarpus forest. The numbers near the symbols indicate the distance from the edge. For understory vegetation, 1: 0–5 m; 2: 5–10 m; 3: 10–15 m, 4: 15–20 m, 5: 20–25 m, 6: 25–30 m, 7: 30–35 m, 8: 35–40 m, 9: 40–45 m, 10: 45–50 m, 11: 50–55 m, 12: 55–60 m. For soil seed banks, 1: −10 m, 2: 0 m, 3: 5 m, 4: 10 m, 5: 20 m, 6: 50 m.
Fig. 3. DCA ordination diagrams for plots of understory vegetation, samples of soil seed banks in late rainy season and late dry season at the edges of Shorea wantianshuea forest. The numbers near the symbols indicate the distance from the edge (see Fig. 2).
Fig. 4. The relative richness (Mean ± SE, n = 3) and relative abundance (Mean ± SE, n = 3) of each ecological groups in understory vegetation and soil seed banks in late rainy season and late dry season at the edges of Lithocarpus xylocarpus forest. Distances with negative signs were outside from the forest edge into the grassland.
Fig. 5. The relative richness (Mean ± SE, n = 3) and relative abundance (Mean ± SE, n = 3) of each ecological groups in understory vegetation and soil seed banks in late rainy season and late dry season at the edges of Shorea wantianshuea forest. Distances with negative signs were outside from the forest edge into the fallow.
Fig. 6. The abundance of Eupatorium adenophorum in understory vegetation and soil seed banks along the edge to interior gradient in Lithocarpus xylocarpus forest.
Table 1.
The characteristics of forest edge sites.

Table 2.
The number of species in each ecological group in both edge soil seed banks and edge understory vegetation for the two forest types.

Table 3.
F value and significance of response variables in GLM ANOVA models.

NS: not significant.
a Response = intercept + edge site + distance + edge site × distance.
b There are three edge sites both for
Lithocarpus xylocarpus forest and for
Shorea wantianshuea forest (see
Table 1).
c There are twelve distances at
Lithocarpus xylocarpus forest edges and ten distances at
Shorea wantianshuea forest edges for DCA plot scores. There are five distances for DCA soil sample scores.
* 0.01 ≤
P < 0.05.
** 0.001 ≤
P < 0.01.
*** P < 0.001
Table 4.
The inward limits of non-forest species in understory vegetation estimated by negative exponential models.
a The data from three edge sites (Nanshahe, Huiduhe, Canopy walkway) were pooled to fitted the model because the effect of edge site is not significant (two way ANOVA,
F = 0.560,
P ≥ 0.05).
*** P < 0.001.

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