Forest seedling community response to understorey filtering by tree ferns

James M. R. Brock, George L. W. Perry, Tynan Burkhardt & Bruce R. Burns

James Brock, surrounded by silver fern Cyathea dealbata – the symbol of New Zealand national sports teams, recording the seedling community in experimental tree fern plot no. 115 at Huapai, in west Auckland, New Zealand. Photo credit: Edin Whitehead.

Tree ferns can be a common component of the understorey of tropical and southern temperate forests. In New Zealand’s broad-leaved podocarp forests they are frequently abundant in the understorey, forming near-continuous sub-canopies representing up to 50% of the stems and 21% of biomass. Tree ferns form deep, slow to decompose leaf (frond) litter, intercept high proportions (up to 50%) of sub-canopy light, and indiscriminately destroy seedlings and saplings when up to 3 m long dead fronds disconnect from the trunk and fall to the forest floor. Despite many hypotheses considering the likely effect of these processes (e.g. strong negative effects on establishment of shade-intolerant conifers), there have been no attempts to experimentally test the response of the seedling community to these potential effects.

Our research was conducted in the forests of northern New Zealand which comprise mixed broad-leaf canopies at 10–20 m with emergent conifers supporting 27 species across 13 families. Average rainfall at the sites is 1,280 mm per year, and the soils comprise volcanic sandy loams and granular clays. In our study, we first undertook a field survey to describe where seedlings are growing in the landscape and consider what might influence where they are growing including shading, depth of leaf litter, how close nearby trees and tree ferns are, and soil moisture. We then experimentally manipulated 160 tree ferns above seedling plots, to examine how tree fern litter and shading contribute to the patterns observed in the field survey.

The field survey showed that landscape-level seedling density is affected by the presence of tree ferns. Seedling densities of both angiosperms and conifers are up to 50% lower within the drip-line of a tree fern (i.e. within the area covered by the fronds projecting from the top of the tree fern); this reduction is associated with a doubling of leaf litter depth. Our field manipulation of tree ferns removed either litter and/or fronds from within and above seedlings plots. In the litter and frond removal treatment, we found that seedlings of two species of podocarp (Podocarpus totara and Phyllocladus trichomanoides) were consistently turning up, as well as there being increased seedlings densities and species richness. Our study suggests that through macro-litter and shading, tree ferns influence seedling community composition by reducing the density of canopy angiosperm and conifer species that can establish, particularly suppressing conifers in seedling communities within their drip-lines.

This is a plain language summary for the paper of Brock et al. published in the Journal of Vegetation Science.

Slow recovery of arbuscular mycorrhizal fungi and plant community after fungicide application: An eight-year experiment

Hana Pánková, Tomáš Dostálek, Kristýna Vazačová & Zuzana Münzbergová

Study site – dry grassland in the central part of the Czech Republic. Photo credit: Hana Pánková.

Dry grasslands represent one of the most species-rich communities in Europe with a high occurrence of rare species. Some of the grasslands were changed to agricultural fields with intensive application of fertilizers or pesticides. After their abandonment, the former fields may be recolonized by dry grassland species. However, the recovery is a slow process, and many rare plant species, typical for dry grassland habitats, are absent in the formerly abandoned fields even after several decades. One of the reasons for their absence should be changes in the soil biota caused by previous intensive agriculture. The key component of soil biota for the growth of rare grassland plant species are arbuscular mycorrhizal fungi. Arbuscular mycorrhizal fungi are microscopic soil organisms, which establish a reciprocal beneficial association with plants. They help to transport nutrients and water to the plant roots and protect them against pathogens by the production of special chemicals. These fungi may be suppressed by different agricultural practices including fungicide application. Many of rare grassland species are dependent on association with these fungi, and therefore they are not able to grow on former fields, where these fungi are missing. Additionally, such changes in soil biota improve growth of large grasses, which further suppress the performance of rare plant species.

In our study, we evaluated the recovery of plant communities and arbuscular mycorrhizal fungi in dry grasslands after fungicide application. Further, the grazing was implemented on the part of the area to simulate traditional management intervention used for support of plant biodiversity. We evaluated the occurrence of particular plant species and functionality of fungi every year.

Parts of study sites were fenced to prevent grazing. Photo credit: Hana Pánková.

The results showed that the effect of fungicide application on the functionality of fungi persisted five years after the last fungicide application on ungrazed parts of the area, and even the recovery of fungi after introducing the grazing management was not sufficient for recovery of the rare plants. Grazing led to the suppression of grasses, but forbs were still largely absent with only a few exceptions of good colonizers of open habitats. This suggests that the absence of rare species could be caused by changes in the composition of the fungal community or low availability of their seeds. Direct addition of seeds of the forbs and/or adding suitable arbuscular mycorrhizal fungi may thus be tested as possible methods to support the recovery of the dry grassland community.

This is a plain language summary for the paper of Pánková et al. published in the Journal of Vegetation Science.

The assembly of a plant network in alpine vegetation

Gianalberto Losapio, Marcelino de la Cruz, Adrián Escudero, Bernhard Schmid & Christian Schöb

The study site in the Swiss Alps (Lämmerenboden, 2300 m a.s.l.). Photo credit:
Gianalberto Losapio.

Plant ecology has always focused on interactions among species within communities. Ecological research has targeted the importance of negative interactions such as competition among plants for resources. But in the last years, there is increasing interest in understanding how plants can cooperate with each other. This is particularly the case in harsh ecosystems like the alpine where some stress-tolerant plants contribute to ameliorating growing conditions for their neighbours. In our study, we analysed the spatial distribution of plants and modelled their associations to test how plant networks are formed and maintained in alpine vegetation. We collected data about the spatial location and the phenotype of thousands of individual plants and analysed them with the state-of-the-art computational model. We found that plant species were highly connected through many positive interactions. Dominant, stress-tolerant species were the most important plants for supporting the plant community network. The plant community network was more cohesive than expected by chance. This study reveals a new class of mechanisms underlying the formation of plant communities and has important implications for understanding the biodiversity of alpine vegetation.

This is a plain language summary for the paper of Losapio et al. published in the Journal of Vegetation Science.