Nonconstituent species in soil seed banks as indicators of anthropogenic disturbance in forest fragments

Abstract

Forest fragmentation is prevalent in regions with high human population density, but also with high biological diversity, such as southwestern China. Predicting potential changes in species composition in native forest ecosystems resulting from forest fragmentation is an important approach in assessing forest ecosystems and sustainable management of forests. The term nonconstituent species is proposed for plant species that occur in a natural landscape but are not native to it. We hypothesized that fragmentation of continuous forests significantly increases both the richness and the size of soil seed banks of nonconstituent species. To test our hypothesis we compared soil seed banks in three small fragments and one large tract of subtropical evergreen broad-leaved forest in Yunnan Province, southwestern China. In total, 249 species were identified in all soil samples from the four sites. Nonconstituent species represented 36.4%-61.5% of the total taxa and 33.8%-59.6% of total germinants from soil samples in the three forest fragments, but only 3.7%-7.9% of total taxa and 7.5%-9.4% of total germinants from soil samples in the continuous forest tract. Both richness and size of soil seed banks of nonconstituent species were greater under forest fragments than under continuous forest. A majority of nonconstituent species were native weeds and annual herbs with wind-dispersed seeds; most were present in soil seed banks but not in aboveground vegetation. We suggest that nonconstituent species in soil seed banks could be used as an indicator species group for assessing human disturbance. If so, the richness and size of soil seed banks of nonconstituent species could play an important role in quantifying disturbance in forests.Résumé : La fragmentation de la forêt est courante dans les régions à forte densité de population humaine, telles que le sud-ouest de la Chine où il y a une grande diversité biologique. Dans l'évaluation des écosystèmes forestiers et dans le contexte de l'aménagement durable des forêts, il est important d'anticiper les changements que la fragmentation de la forêt pourrait entraîner dans la composition en espèces des écosystèmes forestiers indigènes. L'expression « espèce non constituante » est proposée pour désigner les espèces de plantes qui se retrouvent dans un paysage naturel mais qui ne sont pas originaires de cet endroit. Nous avons fait l'hypothèse que la fragmentation des forêts continues devrait significativement augmenter tant la richesse que la taille des banques de graines des espèces non constituantes présen-tes dans le sol. Pour tester notre hypothèse, nous avons comparé les banques de graines de trois petits fragments et d'une grande étendue de forêt subtropicale de feuillus à feuillage persistant dans la Province de Yunnan, dans le sudouest de la Chine. Au total, 249 espèces ont été identifiées dans les échantillons de sol provenant de quatre stations. Les espèces non constituantes représentaient 36,4 % à 61,5 % de tous les taxons et 33,8 % à 59,6 % de toutes les graines ...

Edge effects on soil seed banks and understory vegetation in subtropical and tropical forests in Yunnan, SW China

“…The significant changes of plant composition in understory vegetation at forest edges could occur over a few years to decades after edge creation (Matlack, 1994;Meiners and Pickett, 1999;Harper and Macdonald, 2002), which might be attributed to the long-term accumulation of external seeds at forest edges. We have found that the invasion of non-forest species in understory vegetation lags behind that in soil seed banks in the forest interior (>200 m into the forest from the edge) (Lin et al, 2006). However, for the forest edge, we still do not know the contrasting response of non-forest species in soil seed banks and understory vegetation.…”

“…Non-forest species are species growing in habitats different from closed forests or their successional communities and usually include native and non-native weeds and plants that have escaped from cultivation (Lin et al, 2006). In this study, we used this categorization to explore the general pattern of plant species responses to the forest edge.…”

Impact of Cardamom Cultivation on the Composition and Dynamics of Soil Seed Banks in a Conservation Forest in Sri Lanka: Implications for Conservation

“…are an important component of the soil seed banks of Asian tropical and subtropical forests (Chandrashekara & Ramakrishanan, 1993;Lin et al, 2006;Metcalfe & Turner, 1998), we predict that seeds of M. indica will be present in the soils that we sampled, but at much higher densities in the soils of abandoned cardamom plantations than adjacent natural forests.…”

“…The greater abundance of the Elettaria presumably reflects increasing propagule pressure arising from reproduction of the residual cardamom plants, (Dalling & Denslow, 1998;Lin et al, 2006;Tang et al, 2006). Taken together, the higher abundance of herbs, light-demanding trees and non-native species in the seed banks of CP than NF explains their separation into distinct clusters in ordination space, and suggests that they represent distinct floristic communities.…”

“…Thirdly, it has been documented that when a landscape undergoes extensive change as a result of human activities, plant communities become more susceptible to invasion by non-native plant species (Hansen & Clevenger, 2005 (Conn et al, 1984;Lin et al, 2006;Moffatt et al, 2004;Peterson & Carson, 1996). Hence, we test the prediction that forests disturbed by cardamom cultivation manifest a greater abundance and species richness of non-native species in the soil seed bank than in adjacent undisturbed natural forests.…”