Gap Microsites Research Articles

Effects of gap size on natural regeneration and micro-environmental soil conditions in European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst) dominated mixed forest

The study focused on the effects of gap size on natural regeneration of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies L.) and micro-environmental soil conditions in gaps of different sizes under temperate mixed forest in the Czech Republic. Six gaps comprising two for small (≥ 200 m<sup>2</sup>), medium (≥ 500 m<sup>2</sup>) and big (≥ 900 m<sup>2</sup>) each were selected. Ten circular 1 m<sup>2</sup> subsampling plots were established at 2 m intervals along individual North-South-East-West transects, including one at the gap centre. Regeneration was monitored in 2014 and repeatedly in 2019. Soil conditions were only measured in 2019. Gap size was found to be a significant parameter for European beech natural regeneration in 2014. Besides, the quick occupation of European beech in gaps at natural beech zone provoked its prolific regeneration compared to Norway spruce in 2014. However, in 2019 the recent threat of weather variabilities was responsible for the general abysmal growth performance of natural regeneration. Division of gap microsites into different within-gap positions based on prevailing light or shade conditions was helpful in assessing the significant variations of soil conditions within-gap positions and among gap sizes. Soil temperature and moisture significantly influenced the regeneration of European beech and Norway spruce, respectively.

Impact of environmental change on a rare high-mountain tall-herb species: a case study on Achillea lingulata in the Ukrainian Carpathians

ABSTRACT Spatio-temporal trends in distribution and population size of Achillea lingulata (Asteraceae), a high-mountain tall-herb species, are analyzed in the Ukrainian Carpathians. These shifts have been revealed due to comparison of the historical literature and herbarium records with the current species distribution, as well as by the long-term monitoring of its populations under different conditions. The species demonstrates opposite dynamic patterns in different types of habitats: negative in abandoned meadows and positive in rock-associated tall-grass communities. That results in the shrinkage of the species distribution at the expense of its secondary grassland habitats, but the increase in size of the saxicolous populations. These trends are associated with the vegetation succession caused by the main drivers of environmental change in the mountains: the abandonment of traditional land use (mainly grazing) and global warming. Biological and habitat characteristics of A. lingulata are described. It has rather narrow habitat requirements and needs gap microsites for the seed recruitment, therefore their availability determines the species distribution and abundance. The post-grazing restoration succession results in denser vegetation cover and replacement of A. lingulata in the meadows. However, vegetation-free microhabitats persist around the rocky outcrops in the high-mountain zone which are most favorable habitats for the species. The evident decline of its lowermost populations implies the effect of climate change which also enhances successional changes. The Ukrainian localities of that rare Carpathian-Balkan species are confined to the northern limit of its geographical range.

Light response of Fagus sylvatica L. and Abies alba Mill. in different categories of forest edge – Vertical abundance in two silvicultural systems

In managed Dinaric montane fir (Abies alba Mill.) and European beech (Fagus sylvatica L.) forests, the light response of young beech and fir in gap microsites was studied during three consecutive growing periods (2009, 2010, and 2011) under controlled environmental conditions in stands of single-tree and irregular shelterwood silvicultural system. According to maximal quantum yield, the different response between species in microsite light categories was evidenced for silver fir on microsites with predominating diffuse light and for beech on microsites with predominating direct light, respectively.Abundance and change of share in microsite light categories was compared over different elevation belts on comparable sites between two silvicultural systems. The share of forest edge area was bigger in the irregular shelterwood system. Change in width of forest edge (20, 30 and 40m) did not affect the proportion and share of the microsite in both regions of different silvicultural system. Separation of microsite areas between both silvicultural systems, evident in lower elevation belts was not evident in the most conflict and highest elevation zone, while the absolute values of all categories above 700m in both systems were almost identical, indicating the same, small-scale irregular shelterwood system, known also as the freestyle silvicultural approach.

Effects of gap microsites and bamboo on Abies faxoniana regeneration in a subalpine forest, China

To clarify the effects of gap size and age, as well as microsites on Abies faxoniana recruitment in gaps with or without dwarf bamboo, the occurrences of A. faxoniana seedlings and saplings on four microsites were examined in a subalpine forest in Wanglang Natural Reserve, southwestern China. Results showed that: (1) while increased gap size had little effect on the seedling densities, it significantly reduced the sapling densities on moss-cover ground in A gaps (without bamboos) and those on moss-cover ground and decaying logs in AF gaps (with bamboos; P < 0.05). (2) Increased gap age also exerted little effect on the seedling densities while significantly reduced the sapling densities on decaying logs in AF gaps (P < 0.05). (3) Most of A. faxoniana seedlings and saplings occurred on decaying logs in AF gaps, but in A gaps A. faxoniana regeneration had no preference on microsites. Compared to gap characteristics, microsites are more important for A. faxoniana regeneration.

Gap size and position influence variable response of Fagus sylvatica L. and Abies alba Mill.

Montane forests of silver fir (Abies alba Mill.) and European beech (Fagus sylvatica L.) in the Dinaric region are the largest continuous forest area in Central Europe, where silver fir’s regression is one of the region’s major concerns. Designing appropriate sized canopy gap spatio-temporal dynamics is the main silvicultural tool for indirect promotion of silver fir. Within gap microsites, categories based on shares of direct and diffuse radiation proved to be an interesting conceptual model for explaining microsite variation and seedling success induced by light and general climate variability.In order to evaluate the response of beech and fir in different gap microsites, different light regimes were evaluated based on the proportion between direct and diffuse radiation in three different sizes of forest gap in managed forests. The photosynthesis response to different light conditions (max. photosynthetic rate – Amax and quantum yield – Φ) in beech and silver fir was compared on all microsites during three consecutive g periods (2009, 2010, and 2011) under controlled environmental conditions.A different response between species in microsite light categories was shown between different gap sizes. In all microsite categories of both species, quantum yield appeared at lower light intensities with increasing gap size, with the exception of beech with a predominant direct light component, in which yield significantly increased. In order to favour fir, gaps with low direct light levels should be created, while existing gaps should be extended towards the southern gap edge. Our conclusions emphasize the importance of gaps, relatively smaller in size (0.03–0.11ha) but significant in contributing to increasing the competitive advantage of fir in mountainous, mixed-species Dinaric forests.

Early competition between the exotic herb Rumex acetosella and two native tussock grasses with different palatability and water stress tolerance

Semiarid grasslands in NW Patagonia (Argentina) are dominated by Festuca pallescens and Pappostipa speciosa, two native tussock grasses that differ in water stress tolerance and in palatability to livestock. Both species regenerate in gap microsites invaded by the exotic herb Rumex acetosella. We performed a greenhouse experiment to study the effect of Rumex competition on early growth of the dominant tussock-grasses. In February 2008 we used about 4-month-old seedlings to establish competition treatments that simulated a dry or wet summer. Competition among grasses was also quantified to relativize the effect of Rumex competition on each grass species. Rumex seedlings had a negative impact on grass seedlings, but it was not greater than that produced by any co-dominant grass. Grass species did not differ in their sensitivity to competition by Rumex or to water stress. In dry conditions, there was an intense underground competition between grass species, but there was no evidence of underground competition from Rumex. The low competitive ability of Rumex under water stress may indicate that its invasive potential from a seedling stage would be limited by the aridity of the environment. Moreover, the high bud production of Rumex seedlings suggests an early contribution to the soil bud bank, a key eco-biologic trait of this invasive species. Therefore, the estimation of the bud bank abundance and the study of how vegetative regeneration may be interfering grass recruitment should be considered in future research.

Tree regeneration in the threatened forest of Robinson Crusoe Island, Chile: The role of small-scale disturbances on microsite conditions and invasive species

Biological invasions are a major driver of biodiversity loss on islands. After disturbances, invasive plant species can establish affecting forest regeneration microsites. On Robinson Crusoe Island (33°S, Juan Fernández Archipelago, Chile) small-scale treefall canopy gap microsites are most frequently used by “endemic montane forest” species for regeneration. Regeneration can be hampered when invasive species establish and alter gap conditions. We evaluated the role of small-scale disturbances on regeneration and identified tree regeneration microsites in gaps, gap borders, and closed forest. We collected information on the effects caused by invasive species by sampling 30 gaps with a range of invasive species cover, including gaps where invasive species were removed. We analyzed the impact of native ferns and invasive species, regeneration substrates and light availability on native tree species regeneration and juvenile tree performance traits. Our aim was to analyze small-scale disturbances and identify threshold values for the variables related with tree regeneration presence–absence, density and performance, particularly considering invasive species competition. We used classification and regression trees to identify variables and their threshold values influencing native tree species regeneration. Gap borders and small gaps (<200m2) were preferred microsites for regeneration. Native tree species seemed able to compete as long as invasive species cover did not exceed 10%. Fern cover >10% facilitated tree regeneration and performance. Competition from invasive species for space, water and nutrients was likely more important than for light. Restoration should attempt to recreate intermediate disturbance conditions considering the threshold values identified. Thresholds for variables important for restoration processes can help in the control of invasive species.

Post‐fire shrub recruitment in a semi‐arid grassland: the role of microsites

AbstractQuestion: (1) Which factors regulate post‐fire recruitment and spread of the shrub Senecio bracteolatus in Patagonian grasslands? (2) What is the role of the grass Stipa speciosa on S. bracteolatus establishment in the post‐fire succession?Location: Northwest Patagonia, Argentina.Methods: We studied the effect of fire on S. bracteolatus recruitment and density by comparing these variables between burned and unburned grasslands. In burned areas, we compared abiotic characteristics and seedling establishment under the canopy of grasses (S. speciosa) and in gaps (inter‐tussock areas). Post‐fire interactions between S. bracteolatus seedlings and S. speciosa were studied using field and greenhouse experiments.Results: Density of S. bracteolatus was higher in burned than in unburned areas. In burned sites, seedlings were more abundant under tussock grasses, whereas juveniles were more abundant in gaps. Tussocks generated more attenuated micro‐environmental conditions than gaps during stressful summers. Gaps were more abundant in burned sites, while “under tussock” microsites were more frequent in unburned sites. In burned areas, tussocks allowed higher establishment of seedlings (facilitation), but gaps allowed more seedling growth and higher persistence of juveniles.Conclusions: Fire promoted S. bracteolatus recruitment in Patagonian grasslands by increasing the availability of favourable gap microsites. Grass protection for shrub seedlings became negative with time, probably due to competition with grasses. Gaps led to better performance and persistence of shrub plants. Six years after fire, higher shrub recruitment and adult density (observed as a trend) in burned grassland provides an opportunity for potential S. bracteolatus invasion.

Seed size, growth rate and gap microsite conditions as determinants of recruitment success for pioneer species

Summary 1 We examined how seed size and seedling growth rate influence recruitment success of neotropical pioneer species. We investigated the soil seed bank, and followed seedlings from emergence and establishment to the sapling stage in artificially created gaps in secondary forest on the Barro Colorado Nature Monument, Panama. 2 To simulate microsite variation within gaps, litter addition/removal and soil disturbance treatments were applied to seedling plots in a factorial design. 3 Seedling emergence was almost three-fold higher in litter-free plots than in control plots. 4 We found a negative relationship between seed mass and seed abundance in the soil, seed mass was positively correlated with seedling emergence success from the seed bank and with seedling survival through to the end of the first dry season. 5 In the 18 months following the first dry season we observed an uncoupling of seed mass from seedling performance. Seedling mortality was now a function of maximum relative growth rate, with higher mortality of fast-growing species attributable to herbivory, notably by shoot-borers. 6 We propose that a seed size-dependent trade-off between dispersal success (selecting for large seed number), and emergence‐establishment success (selecting for large seed size) can explain the maintenance of wide variation in seed size among pioneer species. Secondarily, a trade-off between growth rate and susceptibility to herbivores acting at the post-establishment phase may contribute to observed differences in light requirements among pioneer species.

A test of the hypothesis of ecological equivalence in an Australian subtropical rain forest

We tested the hypothesis that tree species in a subtropical rain forest in south-east Queensland are ecologically equivalent and therefore have identical environmental requirements for their regeneration. We assessed the evidence that juveniles of species differed in their distributions in treefall gap microsites and along gradients of light availability, soil pH, soil PO4-P availability and soil NO3-N availability. Pairwise comparisons were made on a subset of the common species selected on the basis that they showed a relatively high level of positive association, and would therefore, a priori, be expected to have similar regeneration requirements. Detailed comparisons between the species failed to demonstrate evidence for species differentiation with respect to their tolerance of the disturbance associated with gap microsites or to the gradient of NO3-N availability. However, species differed markedly in their distributions along the soil pH gradient and along the gradients of light availability and soil PO4-P availability. The overall level of ecological differentiation between the species is high: seven out of the 10 possible species pairings showed evidence for ecological differentiation. Such niche differentiation amongst the juveniles of tree species may play an important role in maintaining the species richness of rain-forest communities.

Secondary Succession, Gap Dynamics, and Community Structure in a Southern Appalachian Cove Forest

Forest succesion was studied in a species—rich cove forest of the Great Smoky Mountains, Tennessee. Long—term compositional and structural changes in secondary stands, 15—63 yr after agricultural abandonment circa 1920, were compared to an adjacent old—growth stand. Later successional trends were projected by computer simulation. The colonizing stand (15 yr) was dominated by Liriodendron tulipifera and Robinia pseudoacacia. Common old—growth species absent at this early stage included Aesculus octandra, Fagus grandifolia, and Tsuga Canadensis. By year 40, Liriodendron dominated the overstory and all old—growth dominants were represented in the understory. After 60 yr, Acer saccharum was clearly the most abundant understory species; gap model projections indicated that after 200 yr it will dominate the forest. The actual old—growth stand was dominated by Acer saccharum. Species richness peaked at mid—succession (°50 yr), while diversity (H') and evenness (J') of species biomass were highest at the old—growth stage. Richness peaked with the coexistence of shade—intolerant colonizers in the overstory and shade—tolerants in the understory. Canopy—gap processes of the secondary and old—growth stands differed sharply. The old—growth canopy was composed of large, spreading, and overlapping crowns, while the second—growth stand was composed of narrow, nonoverlapping crowns. Gaps in the secondary stand tended to be small (&lt;100 m2) but numerous. The regeneration of intolerants was low and individual gap microsites were not markedly different from the understory as a whole. Old—growth gaps were often larger, higher light microsites which contrasted sharply with the shaded forest floor. The wider range of gap sizes in old forests accommodates a variety of species, including intolerants, contributing to the high canopy species diversity of old—growth cove forests.