Closed-canopy Patches Research Articles

Microbiotope selection in saproxylic bees and wasps (Hymenoptera, Aculeata): cavity-nesting communities in forests and wooded pastures are affected by variation in openness but not deadwood

Saproxylic insects are an important component of forest biodiversity; however, their ecological requirements are mostly studied on beetles, while other groups are less considered. Aculeate Hymenoptera provide valuable ecosystem services, and some rely on deadwood cavities. We studied cavity-nesting aculeate Hymenoptera using wooden trap-nests set in a heterogeneous partially rewilded woodland area in Central Bohemia, Czech Republic, and tested their nesting preferences in association with canopy openness, amount of deadwood, and the diversity of surrounding vegetation types. We used 100 trap-nests in five microbiotopes—forest edge, shady closed-canopy forest, open patches in closed-canopy forest, open-grown trees in wooded pasture, and shady groves in wooded pasture, over 2 years. We reared 824 specimens belonging to 26 species of saproxylic hymenopterans. We found no effect of microbiotope on total species richness and richness of nest parasites, but richness of nest builders was highest in forest edge and lowest in open-grown trees in wooded pasture. Species composition of hymenopterans was driven by a wider habitat context: despite the proximity of the habitats, the forest, especially closed-canopy patches, hosted a different community, dominated by wasps, than open wooded pasture. Moreover, open patches in forest differed in composition from the closed-canopy patches, suggesting that in production forests, the diversity of saproxylic hymenopterans may be limited by the overall low share of open canopy stages. Deadwood (amount and diversity) did not affect the saproxylic bees and wasps in any way.Implications for insect conservationOur results support conservation measures leading to diversification of the forest canopy and vegetation structure in order to support rich communities of saproxylic Hymenoptera, especially in protected areas.

Effects of habitat heterogeneity on bird communities in the forests of northeastern Germany

Habitat heterogeneity is a key factor for regulating biodiversity in temperate lowland forests. Specifically, stands associated with late forest development phases provide important habitat structures for many rare and threatened forest bird species. However, how forest stands that differ in their structural complexity, canopy conditions and tree species composition affect forest bird assemblages both at the local and landscape scale remains largely unclear. In a young moraine lake landscape of northeastern Germany, we assessed correlations of bird diversity and bird composition with stand properties. We used data from 48 transects (400 m) established in (1) unmanaged, closed-canopy, mature stands that were dominated by Fagus sylvatica (UDS), and (2) diverse managed, mixed coniferous stands with a mosaic of open and closed canopy patches (MCS). We found that bird communities of the UDS strongly differed from those in the MCS, with open habitat species being more frequent in the MCS. By contrast, differences in diversity measures were less distinct. Moreover, we identified nine indicator species for the UDS (Columba oenas, Cyanistes caeruleus, Muscicapa striata, Leiopicus medius, Certhia brachydactyla, Ficedula parva, Dryobates minor, Sturnus vulgaris, Ficedula hypoleuca) and seven indicator species for the MCS (Periparus ater, Pyrrhula pyrrhula, Regulus regulus, Prunella modularis, Lophophanus cristatus, Emberiza citronella, Anthus trivialis). Several famous ancient beech forest patches in Müritz National Park and the UNESCO Biosphere Reserve “Schorfheide-Chorin” were found to harbour the set of the UDS indicator species. The UDS support of bird coenosis is typical for old mature broadleaved forests and can be considered as an effective tool for bird conservation. Our results further indicate that the combination of unmanaged and managed stands associated with different habitat complexities would benefit forest bird assemblages at the landscape scale. Key words: forest specialist birds, bird conservation, non-managed forests, old-growth patches, Ficedula parva, Leiopicus medius, coniferous forest

Pans as possible pedological hotspots in an arid African savanna

Vegetation dynamics in savannas are largely determined by water availability as well as soil nutrient dynamics. Species composition differs significantly from nutrient-rich soils to nutrient-poor soils, where the former is dominated by fine-leafed palatable woody species and the latter by broad-leafed and less palatable ones. Whilst this typically occurs at a landscape or catena scale, it is also interestingly observed at a localised and micro scale in areas such as wetlands and termite mounds. Wetlands are important edaphic contrasts in savannas and are paradoxically prevalent in the semi-arid to arid regions. In Southern Africa endorheic (inward draining) wetlands, known as pans, are particularly ubiquitous in arid regions but are not well studied compared to other wetland types. These wetlands were the focus of this study, which took place in the semi-arid savanna of the Limpopo plains, South Africa. The key research aims of this study were to determine how the pans differed from the surrounding terrestrial savanna landscape with respect to soil texture and chemistry, woody plant density and vegetation species composition. Top and sub soil samples were analysed to a depth of 30 and 60 cm and vegetation transects were carried out across three identified ‘hydro-ecological’ zones, i.e. the pan centre, the wooded wetland zone around the pan and representative terrestrial savanna habitat. In addition, drone aerial imagery was utilised to accurately determine woody species density and visually understand habitat changes. As hypothesised, the physiochemical properties of the soils differed along the study gradient from terrestrial to wetland, where in general the soil fertility, clay content and water holding capacity increased. The high clay content of the pans facilitates the surface pooling of rainwater and the possible maintenance of wetland conditions in these depressions which were found to be localised soil nutrient hotspots. The wooded wetland and terrestrial areas differed from each other in woody species composition where the terrestrial areas were largely dominated by broad leafed tree and shrub species and the wooded wetland areas had few to no broad-leafed species present but rather a dominance of fine-leafed Senegalia/Vachelia species. In addition, the Senegalia/Vachelia dominated habitat had a higher tree density than the surrounding bushveld, forming closed canopy patches in some areas. This change in vegetation and soil dynamics are important in savanna ecology as these habitats function quite differently from each other with respect to nutrient cycling, herbivore behaviour and biodiversity. It was concluded that these pans are nutrient-rich hotspots, likely playing an important ecological role in the savanna landscape. Furthermore, as they are likely to be key water sources and preferential forage sites, they could be the first to show signs of degradation and be useful indicators for land managers. These pans should be highlighted as sensitive habitats with regional conservation significance, which are deserving of adequate protection from surrounding threats such as mining.

Increasing woody cover facilitates competitive exclusion of a savanna specialist

Anthropogenically modified systems tend to have homogenous wildlife communities. While this process is well documented, the mechanisms driving the convergence of species in human-modified systems are unclear. There are at least two compelling ecological explanations for the loss of specialized species in these settings; changes to the distribution and quality of resources (i.e. environmental conditions) and changes to competitive interactions. Without a better understanding of the mechanisms behind biotic homogenization, it is difficult to take appropriate conservation and management actions to maintain diverse communities.We investigated the roles of environmental conditions and competition in driving biotic homogenization in one of the world's most imperiled ecosystems; the longleaf pine (Pinus palustris) savanna of the American Southeast. Specifically, we investigated how generalist gray squirrels (Sciurus carolinensis) are replacing the more specialized fox squirrels (S. niger) in shrub and hardwood encroached Southeastern savannas. To test how changes to habitat and competition affect the specialist fox squirrel, we undertook a landscape scale manipulation. We experimentally manipulated competition by removing gray squirrels from closed-canopy patches embedded in longleaf pine savanna.Fox squirrels showed a strong response to gray squirrel removal, increasing their activity by 300% in the interior of closed-canopy patches. Fox squirrels in control patches did not use the interior of closed-canopy patches.Our experimental results support the hypothesis that biotic homogenization occurs when human-induced changes to the environment alter competitive interactions.

Regeneration Dynamics Following the Formation of Understory Gaps in a Slovakian Beech Virgin Forest

The frequency and size of canopy gaps largely determine light transmission to lower canopy strata, controlling structuring processes in the understory. However, quantitative data from temperate virgin forests on the structure of regeneration in gaps and its dynamics over time are scarce. We studied the structure and height growth of tree regeneration by means of sapling density, shoot length growth and cumulative biomass in 17 understory gaps (29 to 931 m2 in size) in a Slovakian beech (Fagus sylvatica L.) virgin forest, and compared the gaps with the regeneration under closed-canopy conditions. Spatial differences in regeneration structure and growth rate within a gap and in the gap periphery were analyzed for their dependence on the relative intensities of direct and diffuse radiation (high vs. low). We tested the hypotheses that (i) the density and cumulative biomass of saplings are higher in gaps than in closed-canopy patches, (ii) the position in a gap influences the density and height growth of saplings, and (iii) height growth of saplings increases with gap size. Sapling density and biomass were significantly higher in understory gaps than under closed canopy. Density of saplings was positively affected by comparatively high direct, but low diffuse radiation, resulting in pronounced spatial differences. In contrast, sapling shoot length growth was positively affected by higher levels of diffuse radiation and also depended on sapling size, while direct radiation intensity was not influential. Conclusively, in this forest, regeneration likely becomes suppressed after a short period by lateral canopy expansion in small gaps (<100 m2), resulting in a heterogeneous understory structure. In larger gaps (≥100 m2) saplings may be capable even at low plant densities to fill the gap, often forming a cohort-like regeneration layer. Thus, gaps of different sizes imprint on the resulting canopy structure in different ways, enhancing spatial heterogeneity.

Do composition and richness of woody plants vary between gaps and closed canopy patches in subtropical forests?

AbstractQuestionsDo composition and richness of woody plants differ between gaps and closed canopy in subtropical forests, and does this difference vary across life stages of tree species? Is tree species richness in gaps a function of regeneration density?LocationSubtropical Shorea robusta Gaertn (Sal) forest, central Nepal.MethodsWe collected vegetation data from two old‐growth S. robusta forest stands. We sampled 128 plots of 100 m2 equally spread between the two habitats: gap and closed canopy. In each plot, we recorded the total number of woody species, number of individuals of seedlings and saplings of tree species and measured the DBH of all saplings. We compared species richness and composition of total woody species, seedlings and saplings between the two habitats. We used ordination to analyse species composition, and an individual‐based species accumulation curves to illustrate the effect of density on species richness.ResultsThe species composition of total woody species and seedlings was similar in both habitats, but species composition of saplings differed between habitats. Total woody and seedling richness were similar between habitats at one site, but were richer under closed canopy at the other site. Sapling richness was higher in gaps at both sites and was a function of stem density at one site, but not at the other site.ConclusionsGaps are not always areas of higher woody species richness and therefore may be less important than expected for the overall species richness of woody plants. Instead, they are potentially important for enhancing local tree richness by increasing sapling richness. Gap disturbance is the primary driver of structural heterogeneity in forests where topographic and edaphic gradients are negligible.

Butterfly behavioural responses to natural Bornean tropical rain-forest canopy gaps

Abstract:Natural tree canopy gaps allow sunlight to penetrate to the forest floor, a major environmental component and resource for many tropical rain-forest species. We compare here how butterflies use sunny areas created by the natural gaps in canopies in comparison with adjacent closed-canopy areas. We chose butterflies as our focal organisms as they are taxonomically tractable and mobile, yet habitat sensitive. Previous studies have shown that butterfly diversity in tropical forests responds to varying degrees of canopy openness. Here we assess butterfly behavioural responses to gaps and equivalent sized closed-canopy patches. Butterfly occupancy time and behaviour were simultaneously observed 61 times in gaps and 61 times in equivalent sized closed-canopy patches across four sites in a tropical rain forest in northern Borneo. Out of the 20 most frequently recorded species, 12 were more frequently recorded or spent more time in gaps, four occurred more frequently in closed-canopy areas, and four showed no significant differences. Overall agonistic, basking, patrolling and resting were more common in gaps compared with the closed canopy. Many butterfly species have complex behavioural requirements for both gaps and closed canopies, with some species using these different areas for different behaviours. Each butterfly species had particular habitat requirements, and needed both canopy gaps and closed canopy areas for ecological and behavioural reasons, emphasizing the need for natural light heterogeneity within these systems.

Re-envisioning the structure of last glacial vegetation in New Zealand using beetle fossils

A series of 18 fossil beetle assemblages are used to reconstruct the paleoenvironment of the northwest West Coast, New Zealand, over the period of the last interstadial–stadial transition (ca. 37,000–21,300 cal yr BP). The samples were recovered from an in-filled hollow within a dune field ca. 9 km south west of Westport (41°47′S, 171°30′E). This fossil beetle reconstruction is compared to an existing palynological reconstruction from the same site. The beetle assemblages indicate an environment of marshy shrubland interspersed with closed canopy coastal vegetation prior to glacial onset, and a mosaic of closed canopy patches and open tussock grassland during full glacial conditions. These interpretations, contrast with the palynologically based interpretation which indicates subalpine shrubland prior to glacial onset and widespread grassland with little woody vegetation during the period of maximum glacial cooling. This study is consistent with other non-pollen studies in New Zealand and indicates that the palynological interpretation of the paleoenvironment of the Westport region downplays the importance of closed canopy vegetation in the area during the transition from interstadial to full glacial (stadial) conditions. It challenges the interpretation of open vegetation at low elevations during glacial periods from pollen studies.

Soil respiration response to experimental disturbances over 3 years

Soil respiration is a major pathway for carbon cycling in terrestrial ecosystems yet little is known about its response to natural and anthropogenic disturbances. This study examined soil respiration response to prescribed burning and thinning treatments in an old-growth, mixed-conifer forest on the western slope of the Sierra Nevada Mountains. Experimental treatments were applied in 2001 using a full factorial design consisting of two levels of burning and three levels of thinning, and included: unburned–unthinned (UN), unburned–overstory thinned (US), unburned–understory thinned (UC), burned–unthinned (BN), burned–understory thinned (BC), and burned–overstory thinned (BS). We measured soil respiration rate (SRR), soil moisture ( M S), soil temperature ( T S), and litter depth (LD) for three replicates of each of three dominant patch types (closed canopy, open canopy, and ceanothus shrub) within each of the six treatments ( n = 54). The same sampling points were measured from May to August in 2000 (pre-treatment) and in 2002, 2003, and 2004 (post-treatment). Within our sampling period there was as much as 37% variation ( p = 0.0005) between years in the undisturbed patches, which appeared to be driven by changes in precipitation. SRR also varied by year in all treated plots (US: p = 0.0516; UC: p = 0.0006; BN: p = 0.0158; and BC: p = 0.0040), with the exception of BS ( p = 0.3344). SRR response to disturbance varied with patch type, year, and treatment type. In most cases, burning and the combination of burning and thinning had less of an effect on mean SRR than thinning alone. Ceanothus patches appear to have recovered fastest, while treatment effects remained 3 years after thinning in closed canopy ( p = 0.0483 and 0.0333 in UC and US, respectively) and open canopy patches ( p = 0.0191 in US). Open canopy patches showed no response to any treatment aside from US. Both UC and US increased SRR in closed canopy and ceanothus patches, and US decreased SRR in open canopy patches. BS increased SRR in 2004 in closed canopy patches ( p = 0.0108), but no significant changes occurred in any patch type in response to BN or BC treatments. Across all treatments, the relationship of SRR with temperature, moisture, and litter depth changed in post-disturbance years. The results of this study can be used to help understand how management of Sierran mixed-conifer forests affects soil carbon sequestration.

Effects of Vegetation Patches on Soil Nutrient Pools and Fluxes within a Mixed-Conifer Forest

Abstract At a spatially heterogeneous mixed-conifer forest in the central California Sierras, we quantified total carbon (C) and nitrogen (N), inorganic N, and net N mineralization in organic (O) and surface (0–15 cm) mineral soils, and in situ fluxes of inorganic N and ortho-phosphate using resin lysimeters under three patch types: closed canopy conifer, sparsely vegetated open canopy, and Ceanothuscordulatus thickets. In O horizons, total N and C pools ranked: closed canopy > Ceanothus > open canopy. In mineral soils, total N pools under Ceanothus exceeded those under closed canopy patches by about 30%. For 2 years, nitrate concentrations and rates of net N mineralization in O horizons were 4× greater under Ceanothus than under the other patch types. Similarly, ammonium concentrations and net N mineralization in mineral horizons were more than 80 and 200% greater, respectively, under Ceanothus than under the other patch types. In situ fluxes of nitrate were 4× greater beneath Ceanothus for 1 year, and no differences were found among the patch types for another year. Despite the interannual variability, our data suggest that Ceanothus contributes to a greater proportion of total N mineralized than based on cover alone, and may be important for forest nutrition under current conditions and after forest burning. FOR. SCI. 51(3):211–220.

Fifty Years of Landscape Transformation in Managed Forests of Southern Finland

Intensive forest management has changed both local and regional characteristics of Fennoscandian forest. However, quantitative documentation of landscape transformations is rare. In this study, five forest landscapes were examined in order to define and quantify forest landscape transformation in southern Finland from the 1940s to the 1970s and 1990s. These areas of 140-200 km2 contained both private and state-owned forests. Digital aerial photographs of each area were classified into no-canopy forest (clear-cut and seedling stands, open mires) and closed-canopy forest (young and mature stands). Patch density, mean patch size, largest patch index and edge density calculated for closed-canopy patches indicated fragmentation from the 1940s to the 1970s and recovery from the 1970s to the 1990s. Trends were very similar in both ownership groups. Thus, fragmentation of closed-canopy forests has not progressed continuously in southern Finland, but shows different patterns depending on the period. However, the recovery observed between the 1970s and 1990s does not necessarily mean an increased abundance of the natural old-growth areas that are needed to host many of the currently threatened species.

HURRICANE DISTURBANCE AND THE POPULATION DYNAMICS OF A TROPICAL UNDERSTORY SHRUB: MEGAMATRIX ELASTICITY ANALYSIS

The role of environmental variation in the population dynamics of the tropical understory shrub Ardisia escallonioides was explored using single-environment matrix analysis and dynamic-environment megamatrix analysis. We investigated how variation in forest-canopy openness caused by hurricanes affected population dynamics. A 7 × 7 patch-transition matrix was created to model forest dynamics based on the historical frequency and strength of hurricanes in south Florida. Seven 8 × 8 stage-classified matrices for plant population dynamics were derived from four field populations and two posthurricane years. These populations spanned a strong gradient of forest-canopy openness resulting from hurricane disturbance caused by Hurricane Andrew (24 August 1992). The patch-transition matrix was analyzed for its stable patch distribution. The seven single-environment matrices were each analyzed for population growth rates and elasticity of stage classes. The 56 × 56 megamatrix was analyzed for population growth rate, reproductive value, stable patch-stage distribution, and elasticity of both patches and stages. Population growth rate of the single-environment matrix models (8 × 8) was lowest for the shadiest environment (λ = 1.0), intermediate but variable for intermediate environments, and highest for the most open environment (λ = 1.96). The population growth rate (λ) of the megamatrix model was 1.71. The stable patch-stage distribution was characterized by a high proportion of seeds in open patches. Reproductive value was highest for very large adults in open patches. Megamatrix elasticity analysis revealed several components of the demography that were not apparent from examination of the single-environment matrices. Although closed-canopy patches were the most common type of environment, elasticity analysis of the megamatrix showed that the highest patch elasticity was for the most open environment. We found contrasting predictions for the relative importance of life history stages to population growth rate from single-environment analysis vs. the megamatrix analysis. In the most common single-environment patch, very large adults had the highest elasticity. In the megamatrix, small juveniles contributed the most elasticity and all stages contributed some elasticity. For plant species inhabiting temporally varying environments, megamatrix analysis offers new insight into the importance of both patches and stage classes.

An Integrated Model of Demography, Patch Dynamics and Seed Dispersal in a Woodland Herb, Primula vulgaris

Primula vulgaris is a woodland herb often associated with canopy gaps. The canopy regeneration cycle results in a permanently changing environment which confers a dynamic character to the overall system of P. vulgaris populations inhabiting a forest. In order to describe the dynamics of this spatially structured population, we built a matrix model that incorporates both the spatio-temporal variation in its population dynamics and the dynamics of the forest habitat given by the opening and closure of canopy gaps. To build the model, we combined empirical data on 1) the demography of populations in various forest patches and 2) canopy closure rate. We then used the model to test the effect of disturbance rate and long-distance (i.e., off-patch) seed dispersal on overall population dynamics. Simulation results suggest that overall population growth rate of P. vulgaris would be enhanced by high gap opening rates, as this would increase the relative frequency of clearings, where population growth rate is maximal. Our analysis also predicts a negative effect of long-distance seed dispersal on overall population dynamics, since seeds dispersing out of occupied patches would have a high probability of landing in closed canopy patches. These results are an example of the costs of long-distance seed dispersal on overall population dynamics. Finally, the potential role of long-distance seed dispersal in the colonization of newly opened gaps is discussed.

Broad Landscape Relations of the Moss Flora from Inland Dry Rainforest in North Queensland, Australia

The moss flora of dry rainforest in north Queensland was surveyed in conjunction with a vascular plant survey. Moss species richness was strongly correlated with patch area mean annual rainfall, and vascular plant species richness. Moss species richness rises where volcanic craters within the study area increase moisture status. Geological substrate had a stronger relationship with associations within the mass flora as defined by the TWINSPAN classificatory procedure and with individual moss species than either landform category or classificatory groups of vascular plants. The association of four species with large closed canopy patches may reflect a humid microclimate and suggests that all else being equal large patches will preserve more species than many small areas of rainforest. However, a high proportion of rare species were associated with the soil surface and there was no obvious way of predicting their locality.

EFFECT OF SUCCESSIONAL STAGES ON THE ESTABLISHMENT OF QUERCUS CALLIPRINOS IN AN EAST MEDITERRANEAN MAQUIS

A sowing experiment was conducted to investigate whether and how secondary succession affects the establishment success of Quercus calliprinos, a leading species of East Mediterranean maquis. Acorns of Q. calliprinos were sown at equivalent densities in experimental plots representing three different stages of the succession: open patches (gaps) dominated by annual plants, patches of low woody vegetation dominated by the early-successional dwarf shrub Sarcopoterium spinosum, and patches of mature Q. calliprinos trees. These patch types represent early, middle, and late stages of the succession. Seedlings that emerged in the experimental plots were monitored for survival and growth during two successive years. Seedling emergence was lowest beneath the canopy of Q. calliprinos trees (2%), intermediate in patches of S. spinosum (54%), and highest in gaps (85%). Seedling survivorship exhibited an opposite pattern: 67% beneath the canopy of Q. calliprinos trees. 43% in patches of S. spinosum, and only 4% in gaps. The combined probability of pre-emergence and post-emergence survival was 23% in patches of S. spinosum, 3% in closed-canopy patches, and 1% in gaps. These results indicate that (I) secondary succession may have considerable effects on the establishment success of Q. calliprinos in Mediterranean maquis, and (2) post-emergence death of Q. calliprinos seedlings may modify patterns of establishment generated by earlier germination and emergence responses. The significance of these results for the natural dynamics and management of maquis dominated by Q. calliprinos is discussed with respect to the concepts of “regeneration niche” and “succession models”.