Young Forests Research Articles

Attenuated asymmetry of above- versus belowground stoichiometry to a decadal nitrogen addition during stand development.

Deciphering the linkage between ecological stoichiometry and ecosystem functioning under anthropogenic nitrogen (N) deposition is critical for understanding the impact of afforestation on terrestrial carbon (C) sequestration. However, the specific changes in above- versus belowground stoichiometric asymmetry with stand age in response to long-term N addition remain poorly understood. In this study, we investigated changes in stoichiometry following a decadal addition of three levels of N (control, no N addition; low N addition, 20 kg N ha-1 year-1; high N addition, 50 kg N ha-1 year-1) in young, intermediate, and mature stands in three temperate larch plantations (Larix principis-rupprechtii) in North China. We found that low N addition had no impact on both above- (leaf and litter) and belowground (soil and microbe) stoichiometry. In contrast, high N addition resulted in significant asymmetry in above- versus belowground stoichiometry, which then diminished during stand development. Following 10 years of N inputs, the young and intermediate plantations transitioned from a state of relative N limitation to co-limitation by both N and phosphorus (P), whereas the mature plantation continued to experience relative N limitation. Conversely, soil microorganisms exhibited relative P limitation in all three plantations. Broader niche differentiation (N limitation for trees, but P limitation for microorganisms) under long-term N input may have been responsible for the faster attainment of stoichiometric homeostasis in mature plantations than in young plantations. Our findings provide stoichiometric-based insight into the operating mechanisms of large C sinks in young forests, particularly above- versus belowground C stock asymmetry, and highlight the need to consider the role of flexible stoichiometry when forecasting future forest C sinks.

Ground beetle trophic interactions alter available nitrogen in forest soil

It is generally held that microbes exert primary control over nitrogen availability in temperate forests. Yet the role of soil and litter‐dwelling invertebrates to provide additional control via the breakdown of organic matter is an area of current exploration. Through trophic interactions within soil food webs, predators may indirectly affect prey with cascading effects on litter breakdown and nitrogen availability. The importance of these interactions, however, may be context‐dependent, varying with the stage of forest development and associated decomposer species composition given that young and old forests have vast differences in nitrogen availability, vegetation litter, soil properties and invertebrate functional groups. We examined ground beetle control over soil nitrogen and soil properties using a 68‐day mesocosm experiment that manipulated trophic structure (omnivore + predator beetles, predator beetles, and no beetles) in a young and old forest stand in the northeastern United States. In the young forest, net nitrogen mineralization decreased under predator + omnivore and the bulk soil C:N ratio in the old forest. However, we found no response in either forest context to the predator only treatment. Our study demonstrates the potential for ground beetles to strongly impact nitrogen availability and soil properties in forest ecosystems. Therefore, animal trophic interactions and their contexts must be included in our paradigm of nutrient cycles in temperate forests.

Carnivore exclosures to protect sheep affect the distribution of a wild cervid

With the recent recovery of large carnivores in Europe, preventive measures to protect livestock are on the rise. Fences that exclude carnivores from grazing areas have been proven as effective, but they can be costly as well as posing a barrier for wildlife. We studied the effect of exclosures of > 10 km2 to protect sheep Ovis aries on the distribution and density of moose Alces alces using fecal pellet group counts in two study areas in southeastern Norway. During the summer grazing season, the fences were powered. Outside of the grazing season, one exclosure remained fenced while the other fence was demounted. This quasi‐experimental setting allowed us to investigate whether fences had a barrier effect for moose, and/or whether moose density was affected by interactions with sheep (competition or facilitation) or large carnivores (refuge hypothesis). During winter, moose pellet group density was about equal inside and outside of the exclosure with demounted wire strands, but less than half inside the permanently fenced exclosure compared to outside, indicating a potential fragmentation effect of the fence. During the grazing season, when wire strands were powered, moose pellet group density was equal or doubled inside as compared to outside both exclosures. Moose may have sought refuge from large carnivores inside the fences. Fecal pellet group densities of moose and sheep inside the fence were neither positively (facilitation) nor negatively (competition) correlated. However, moose used young forest, the most used habitat type by sheep, to a lesser extent inside than outside of the exclosures, maybe due to interference competition. Our study demonstrates that livestock protection fences can have an impact on more than the targeted wildlife species. To understand the mechanisms behind direct and indirect effects of fences, monitoring the movement and survival of individuals by means of GPS and camera traps would be needed.

Nitrogen and phosphorus additions affect fruiting of ectomycorrhizal fungi in a temperate hardwood forest

The functioning of mycorrhizal symbioses is tied to soil nutrient status, suggesting that nutrient availability should influence the reproduction of mycorrhizal fungi. To quantify the effects of nitrogen (N) and phosphorus (P) availability on ectomycorrhizal fungal fruiting, we collected >4000 epigeous sporocarps representing 19 families during the course of a season in a full factorial NxP addition experiment in six replicate forest stands. Nutrient effects on fruiting shifted as the season progressed, with early fruiting species responding more to P and late-fruiting species responding more to N. The composition of species fruiting in young successional forests differed more with nutrient addition than in mature forests. Sporocarp abundance and species richness were suppressed by N addition. This work shows that N and P availability affect ectomycorrhizal fungal fruiting, with these effects taking place within a context defined by stand age and the progression of fruiting across the season.

Species mixtures enhance fine root biomass but inhibit root decay under throughfall manipulation in young natural boreal forests

Fine roots play crucial roles in terrestrial biogeochemical cycles. Although biodiversity loss and changes in precipitation are two major drivers of global change, our understanding of their effects on fine root biomass (FRB), root functional traits, and fine root decay (FRD) remains incomplete. We manipulated precipitation in young boreal forests dominated by Populus tremuloides, Pinus banksiana, and their relatively even mixtures using 25 % addition, ambient, and 25 % reduction in throughfall during the growing season. We collected root samples using soil core and trunk-traced methods to quantify FRB and root traits, and we simulated fine root decay using an in-situ experiment over 531 days. We found that compared to the average of single-species-dominated stands, species mixtures increased FRB by 41 % under ambient throughfall, by 89 % under throughfall reduction and by 71 % under throughfall addition. Root surface area, fine root volume, and root length density responded to species mixtures similarly to FRB. Meanwhile, species mixtures reduced FRD across all water treatments. There was a positive relationship between the effect of species mixtures on the FRD of absorptive roots and those on the FRB. Our results highlight that species mixtures could modify carbon cycling by enhancing fine root biomass accumulation and reducing its decomposition of young boreal forests under changing precipitation.

Historical pyrodiversity in Douglas-fir forests of the southern Cascades of Oregon, USA

Our understanding of forest dynamics and successional pathways in coastal Douglas-fir (Pseudotsuga menziesii var menziesii) forests with relatively frequent mixed-severity fires is limited by a lack of annually precise dendroecological reconstructions that combine records of historical fires and tree establishment. The processes by which old-forest heterogeneity developed under historical fire regimes with recurrent low- and moderate-severity fires has not been well studied at fine temporal scales and across spatial scales. We developed crossdated multi-century records of fire and tree establishment histories in old forests (170 – 550 years) at 34 plots distributed across six sites. Study sites include warm-dry to cool-moist Douglas-fir forest types found in the southern west Cascades of Oregon, USA. Spatial variability in historical fire frequency and fire effects resulted in tremendous diversity in forest developmental histories, age structure, and forest conditions. Most historical fire intervals were very frequent (<10 years) to frequent (<25 years) in dry Douglas-fir forests. Exceptionally high fire frequency and an abrupt decrease in fire frequency after European colonization in dry Douglas-fir forests adds to growing evidence and recognition of Indigenous fire stewardship in montane Douglas-fir forests. In moist forests where Douglas-fir is seral to western hemlock, fire intervals were frequent to moderately frequent (<50 years), but intervals varied substantially over time. Relatively young moist forests burned frequently while mature moist forests had long fire intervals (50–160 years). Nearly all tree establishment cohorts were preceded by either stand-replacing (28 %) or non-stand-replacing fires (64 %). However, tree cohorts only provided evidence of 16 % of historical fire events that we reconstructed from cambial fire scars. This study demonstrates that frequent fire can be an important driver of forest development and in some contexts shapes the structure of coastal old-growth Douglas-fir forests, which are often characterized as developing from endogenous disturbances during long fire-free periods. The high level of pyrodiversity we observed was associated with variation in and interactions of micro-climate, topography, fuels, and Indigenous fire stewardship. We recommend rigorous dendroecological reconstructions across the coastal Douglas-fir region to refine our understanding of the geography of fire-mediated forest developmental dynamics in this important forest type, to inform forest management, conservation, and ecocultural restoration.

Enhancing ecohydrological simulation with improved dynamic vegetation growth module in SWAT

The Soil and Water Assessment Tool (SWAT) model has been widely used for simulating ecohydrological processes such as streamflow and evapotranspiration (ET) under different land use and climate conditions. The growth of vegetation is a crucial link in the ecohydrological process. However, the model uses a simplified Environmental Policy Impact Climate (EPIC) model, which has limitations in simulation of dynamic vegetation growth. Therefore, this study aims to enhance SWAT by incorporating the forest aging data and optimizing the dormancy and forest vegetation growth modules. The application of this modified model with a case study shows that the accuracy of leaf area index (LAI) simulation has significantly improved (coefficient of determination (R2) increased by 0.16, the Nash-Sutcliffe efficiency (NSE) increased from −0.18 to 0.87, and the absolute value of percent bias (PBIAS) decreased by 50.99%), and with moderate improvement in streamflow simulation (NSE increased by 0.03, PBIAS decreased by 4.60%). Furthermore, optimizing the dynamic growth model of vegetation led to significant increases in LAI (151.58%) and ET (5.25%) values in the forest area, while streamflow and water yield decreased by 4.28% and 4.16%, respectively, across the watershed. The results indicate that dynamic vegetation growth led to increased ET, resulting in a decrease in streamflow and water yield. Overall, our results suggest that the modified SWAT model effectively simulated the process of forest growth from young forest to mature stages, significantly improving the accuracy of simulated hydrological processes. This methodology can be applied to other watersheds to simulate ecohydrological processes and can be valuable in management of ecosystems and water resources at watershed scale.

Exploring the diversity of non-industrial private forest properties in Southern Sweden

ABSTRACT Diverse forest landscapes contribute to reaching various forest policy goals. Understanding how the diversity of forests in a landscape is distributed among forest properties and how it is related to biogeographical and ownership factors can be helpful for effective policy implementation. We created a forest characteristics-based typology of non-industrial private forest properties aiming to capture the between-property forest diversity in a municipality in southern Sweden, and studied how it was related to owner age and gender, landscape position, and storm damage. Using public data of forests and latent profile analysis, we detected five clusters of properties. Four clusters differed mainly by age structure and species composition. One of them was clearly marked by a high proportion of young mixed forest following severe storm damage >15 years prior. The fifth cluster was marked by a greater occurrence of nature conservation agreements and conservation value forests. Conifer-dominated properties were larger than broadleaf-dominated properties. Owner age only slightly differed between clusters, being higher for properties characterized by a prevalence of older coniferous or by noble broadleaved forests and nature conservation. Properties in the latter cluster were more often owned by women and located close to lakes.

UAV or satellites? How to find the balance between efficiency and accuracy in above ground biomass estimation of artificial young coniferous forest?

The accurate estimation of Above Ground Biomass (AGB) is the basis for plantation forest carbon trading. This study focused on Picea crassifolia artificial plantations, extracting individual tree crown diameters and heights using Unmanned Aerial Vehicles (UAV) data and calculating the individual tree biomass using allometric growth equations. These results were then used to train a satellite image AGB prediction model. In additional, satellite images were resampled to different resolutions to assess the impact of satellite image resolution on model the accuracy. Finally, the model with the highest accuracy among the deep learning algorithms was selected to predicts the AGB within the P. crassifolia plantation forest. The results indicated that the accuracy of single tree crown diameters extracted from P. crassifolia point clouds significantly surpassed those extracted from general point clouds and Crown Height Model (CHM), while the accuracy of the heights extracted from all three sources was similar; RepLKNet outperformed GoogLeNet and ResNet in identifying plantation forest; random forest slightly outperformed XGBoost in the capability of AGB prediction, while the accuracy of the AGB prediction models initially increasd and then decreasd with satellite image resolution, reaching the highest accuracy at a resolution of 50 m. This indicates that the optimal satellite image resolution for estimating the AGB in the study area was affected by scale effects of 50 m. Compared with the combination of satellite data and manual field measurements, the concurrent use of UAVs and satellites offers significant advantages in terms of efficiency and accuracy. UAVs can replace manual sampling for carbon sequestration transactions for plantations.

Integrating Active and Passive Remote Sensing Data for Forest Age Estimation in Shangri-La City, China

The accurate mapping of age structure and access to spatially explicit information are essential to optimal planning and policy-making for forest ecosystems, including forest management and sustainable economic development. Specifically, surveying and mapping the age structure of forests is crucial for calculating the carbon sequestration capacity of forest ecosystems. However, spatial heterogeneity and limited accessibility make forest age mapping in mountainous areas challenging. Here, we present a new workflow using ICESat-2 LiDAR data integrated with multisource remote sensing imagery to estimate forest age in Shangri-La, China. Two methods—a climate-driven exponential model and a random forest algorithm—are compared to infer the age structure of the five dominant species in Shangri-La. The climate-driven model, with an R2 of 0.67 and an RMSE of 12.79 years, outperforms the random forest model. The derived wall-to-wall forest age map at 30 m resolution reveals that nearly all forests in Shangri-La are mature or overmature, especially among the high-elevation species Abies fabri (Mast.) Craib and Picea asperata Mast., compared with Pinus yunnanensis Franch., Quercus aquifolioides Rehd. and E.H. Wils. and Pinus densata Mast., where the age structure is more evenly distributed across different elevation ranges. Younger forests are frequently found around human settlements and along the Jinsha River valley, whereas older forests are located in remote and high-elevation areas that are less disturbed. The combined use of active and passive remote sensing data has resulted in substantial improvements in the spatial detail and accuracy of wall-to-wall age mapping, which is expected to be a cost-effective approach for supporting forest management and carbon accounting in this important ecological region. The method developed here can be scaled to other mountain areas both to understand the age patterns and structure of mountain forests and to provide critical information for forestation, reforestation and carbon accounting in surface-to-high mountain areas, which are increasingly crucial for climate mitigation.

Does afforestation increase soil water buffering? A demonstrator study on soil moisture variability in the Alpine Geroldsbach catchment, Austria

This study employed an operational monitoring network to measure soil moisture and runoff behaviour continuously in the Alpine catchment Geroldsbach-Götzens, Austria. We hypothesize that afforestation can have a positive impact on soil water buffering. To analyse the impact of soil properties and vegetation cover changes on soil water dynamics, four experimental plots were established on grassland and monitoring stations were installed in the forest. The rainfall test site is equipped with an automatic weather station to obtain meteorological observations, and weirs to measure surface runoff of natural occurring precipitation events and artificial rainfall simulations. In the plots, 200 soil moisture sensors were installed at five different depths, aimed to track and visualize infiltration and subsurface flow processes. Another twenty sensors monitored soil moisture at different afforestation stages in the forested part of the catchment. The measurements show that soils covered with young and old-growth forest have a higher and more stable soil moisture content than grassland and soils with a lack of vegetation throughout the seasons. We observed large spatial differences at plot scale, where the spatial variability of soil moisture increases with depth and is highest during convective precipitation. The initial conditions and rainfall characteristics play an important role in infiltration processes and soil water storage. Our rainfall test site demonstrated the challenges of innovative monitoring techniques and that it offers opportunities for more experiments to gather evidence-based data as input for flood models. Overall findings confirm the sponge effect of forest soils and indicate that afforestation as Nature-Based Solution reduces the temporal soil moisture variability, buffering soil water during precipitation events, which can be beneficial for runoff reduction in Alpine catchments.

Effect of nitrogen and phosphorus fertilization on the temporal dynamics of soil microbial community and multifunctionality in young and mature subtropical forests

Effect of nitrogen and phosphorus fertilization on the temporal dynamics of soil microbial community and multifunctionality in young and mature subtropical forests

Asymmetrical predation intensity produces divergent antipredator behaviours in primary and secondary prey.

It is widely recognized that predators can influence prey through both direct consumption and by inducing costly antipredator behaviours, the latter of which can produce nonconsumptive effects that cascade through trophic systems. Yet, determining how particular prey manage risk in natural settings remains challenging as empirical studies disproportionately focus on single predator-prey dyads. Here, we contrast foraging strategies within the context of a primary and secondary prey to explore how antipredator behaviours emerge as a product of predation intensity as well as the setting in which an encounter takes place. We studied the effects of spotted owls (Strix occidentalis) on two species experiencing asymmetrical risk: dusky-footed woodrats (Neotoma fuscipes; primary prey) and deer mice (Peromyscus spp.; alternative prey). Woodrats are most abundant within young forests, but predominantly captured by owls foraging within mature forests; in contrast, deer mice occur in high densities across forest types and seral stages and are consumed at lower per-capita rates overall. We deployed experimental foraging patches within areas of high and low spotted owl activity, created artificial risky and safe refuge treatments, and monitored behaviour throughout the entirety of prey foraging bouts. Woodrats were more vigilant and foraged less within mature forests and at riskier patches, although the effect of refuge treatment was contingent upon forest type. In contrast, deer mice only demonstrated consistent behavioural responses to riskier refuge treatments; forest type had little effect on perceived risk or the relative importance of refuge treatment. Thus, habitat can interact with predator activity to structure antipredator responses differently for primary versus secondary prey. Our findings show that asymmetrical predation can modulate both the magnitude of perceived risk and the strategies used to manage it, thus highlighting an important and understudied contingency in risk effects research. Evaluating the direct and indirect effects of predation through the paradigm of primary and secondary prey may improve our understanding of how nonconsumptive effects can extend to population- and community-level responses.

Tree richness increased biomass carbon sequestration and ecosystem stability of temperate forests in China: Interacted factors and implications

Biodiversity loss and forest degradation have received increasing attention worldwide, and their effects on forest biomass carbon storage and stability have not yet been well defined. This study examined 1275 tree plots using the field survey method to quantify the effects of tree diversity, tree sizes, and mycorrhizal symbiont abundance on biomass carbon storages (Cs) and NDVI (Normalized Difference Vegetation Index)-based ecosystem stability (standard deviation/mean NDVI = NDVI_S) during the field survey period from 2008 to 2018. Our data showed Cs and NDVI_S averaged at 31–108 t ha−1 and 32.04–49.28, respectively, and positive relations between Cs and NDVI_S were observed (p < 0.05). Large forest-type and regional variations were found in these two parameters. Broadleaf forests had 74% of Cs (p < 0.05) of the conifer forests, but no differences were in NDVI_S. Cold regions at high latitudes had 71% of NDVI_S in the warm regions at low latitudes, while no differences were in Cs. Moist regions at high longitudes had 2.04 and 1.28-fold higher Cs and NDVI_S (p < 0.05). The >700 m a.s.l. regions had 1.24-fold higher Cs (p < 0.01) than the <700 m a.s.l. regions, but similar NDVI_S (p > 0.05). Nature Reserves had 1.94-fold higher Cs but 30% lower NDVI_S than outside Reserves (p < 0.001). > 40-year-old forests had 1.3- and 2-fold higher Cs and NDVI_S than the young forests. Structural equation modeling and hierarchical partitioning revealed the driving paths responsible for these variations. Tree richness was positively associated with Cs and ecosystem stability, contributing 21.6%–30.6% to the total effects on them; tree sizes significantly promoted the Cs, but had negligible impacts on NDVI_S. MAT's total effects on NDVI_S of conifer forests were 40% higher than that of broadleaf forests, MAP's total effects on Cs varied with forest types; arbuscular mycorrhizal tree dominance exhibited a smaller positive impact on Cs and ecosystem stability in comparison to other factors. Our findings underscore that the significance of climatic-adapted forest management, diversity conservation, and big-sized tree protections can support the achievement of carbon neutrality in China from biomass carbon sequestration and ecosystem stability.

Leaf trait networks shift toward high modularity during the succession of a subtropical forest, in southwest China

During the process of forest succession, coexisting plant species fulfill diverse functions by modifying the interrelationships among functional traits. Examining the interrelationships of functional traits across multiple dimensions would enable a comprehensive understanding of the plants’ adaptive strategies during forest succession. Plant trait networks (PTNs) comprehensively capture and visualize these intricate relationships among functional traits. Nonetheless, the changes in PTNs during forest secondary succession remain unclear. In this study, we measured 24 functional traits related to leaf resource acquisition, photosynthesis, hydraulics, and physical defense across tree species at three successional stages: young forest (YF), intermediate forest (IF), and old-growth forest (OF) in the Ailao Mountains, Southwest China. We established leaf trait networks (LTNs) to investigate the interrelationships among functional traits during forest succession. Our results revealed a decrease in the Edge Density decreased and an increase in the Modularity as succession advanced. In the YF stage, leaf nitrogen, photosynthetic rate, and force to punch were the hub traits; whereas, canopy exposure and leaf dry mass were highly connected traits in the IF and OF stages, respectively. The connectivity of highly connected traits was related to the plant’s life-history strategies and environmental adaptations at different successional stages. In terms of the importance of the four trait dimensions, resource acquisition and photosynthetic traits consistently demonstrated strong connectivity within LTNs throughout the succession. We concluded that co-occurring tree species adapted to the changing environmental conditions by adjusting trait modules through alternative strategies during secondary succession. Specifically, resource acquisition and trait coordination were more advantageous in the YF stage, while higher modularity offered greater opportunities for niche differentiation in the OF stage. This study provides new insights into exploring the mechanisms of forest succession through the analysis of trait correlation networks.

Veteranising Scots pine trees by initiating tree hollowing: Inoculation with the fungal keystone species Porodaedalia pini

Hollow trees are crucial for forest biodiversity but are becoming increasingly rare in many ecosystems, including the Scots pine forests of northern Europe. Here, we inoculated heartwood of live Scots pine trees with the fungal keystone species Porodaedalia pini to initiate tree hollowing. The fungus was inoculated in 50-, 110- and 170-year old stands, using wood dowels containing mycelia. Three different strains were used to test for intraspecific variation. Molecular analysis of samples from inoculated trees seven years after treatment showed that 67% were successfully colonised, with no differences between stands. Fungal strain had no effect on colonisation success. Our findings suggest that inoculation with P. pini has the potential to be an efficient method to restore a key ecological process, tree hollowing, in degraded Scots pine forests. The possibility of initiating the process even in young trees may be a way to accelerate the formation of hollow pines in younger forests.

Plants, fungi, and carabid beetles in temperate forests: both observed and dark diversity depend on habitat availability in space and time

ContextThe loss of ancient forests threatens many species. Effective nature conservation needs information on how forest availability in the surrounding landscape in space and time determines the diversity of multiple taxa.ObjectivesWe explored the relationship between forest availability at different spatiotemporal scales and the diversity of various groups: vascular plants (woody species, ground layer), epiphytes (bryophytes and lichens), fungi (ectomycorrhizal, arbuscular mycorrhizal, pathogenic, saprotrophic), and carabid beetles. Besides the observed diversity, we also estimated dark diversity, i.e. suitable but absent species. Dark diversity is theoretically a sensitive metric in detecting ecosystem conditions as it is typically relatively large and contains susceptible species.MethodsWe recorded the observed diversity by field sampling and soil DNA in 100 temperate ancient old-growth forest sites in southern Estonia; dark diversity was estimated for the same sites using species co-occurrence data. Forest availability estimates were obtained from four topographic maps (1900s-2010s) at the 0.5–5 km radius.ResultsThe biodiversity of forest specialists was higher at larger historical forest availability at the spatial scale of 2–5 km radius. The diversity of light-demanding forest ecotone taxa mainly had negative relationships with young forests on previous agricultural lands (at 0.5–2 km radius). Dark diversity models were often more strongly associated with forest availability than observed diversity models.ConclusionsDark diversity enhances our understanding of how current and historical forest availability affects local biodiversity. As young forests cannot provide suitable habitats for many forest-dwelling species, stable forest habitats must be preserved as source areas to enhance biodiversity.

Mature oak forests retain the capacity of young forests to respond to elevated CO2

Mature oak forests retain the capacity of young forests to respond to elevated CO2

Diversity and Distribution of Monocot Understory Herbs during Tropical Forest Succession in Northeastern Costa Rica

Broad-leaved monocot herbs form one of the most common and diverse growth forms of Neotropical plants. Their significance and frequency of occurrence is particularly notable in the understories of tropical rainforests, where they form a dominant element. We assessed and quantified changes in the cover and diversity of understory herb communities in a chronosequence of 1 ha permanent plots established as part of a multidisciplinary study on tropical forest regeneration in the Atlantic lowlands of northeastern Costa Rica. Sampled were two young stands cleared 12 years ago, two secondary forests with 21 and 39 of years of recovery since clearance, and two stands in old-growth primary forest. Changes in species composition during succession were assessed using Chao’s Jaccard similarity index. Observed species richness ranged from 15 to 26 species in individual plots, with the greatest number of species in the 21-year intermediate-age and fewest in the young 12-year plots. Herb species sampled represented 6 families, 15 genera, and 39 species, with the Araceae contributing the largest number of species. Ten species were sampled in all six stands, while fourteen species were found exclusively in one plot. Herb density (ramets m−2) showed a hump-shade trend, with peak density in the intermediate stands and a lower level in mature and young secondary forests. Mean herb cover in 25 m2 quadrats ranged from 2.0% (young stand) to 22.7% (intermediate-age stand) and differed significantly both among stand types and among sites. Both observed and estimated species richness increased along the chronosequence as a whole, with the highest number of species in primary forest, although only slightly higher than in intermediate-age stands. Over half of the species exhibited some degree of clonal growth, with the extent of clonal spread varying among species and forest stands. Although we did not find a clear pattern between clonality and forest age, we observed a greater number of clonal patches in secondary over primary forest stands.

Seasonal movements of small-island birds along habitat and elevation gradients highlights the conservation value of small-scale agroforests

Knowledge on species distributions and seasonal movement patterns within landscapes is important for understanding their ecology and roles in agroecosystems, and is critical for enabling their effective conservation and monitoring, particularly in small-island states where conservation resources are limited. We undertook bird surveys to examine species distributions across a range of agricultural land-use intensities and elevations on the Caribbean island of Grenada by collecting data over 6 repeated monthly surveys (3 wet season, 3 dry season) at sites located in a variety of habitats spread over 6–300 m elevation. We observed a gradual upslope increase in bird species diversity and abundance from the mid-wet season to the late-dry season, as well as a movement from reduced-canopy habitats to closed-canopy habitats in the dry season. The mid-elevation hillsides of Grenada consist of a diverse mosaic of closed canopy secondary forest patches, interspersed among more open agroforests and small-scale cropping and grazed areas. These agroecosystems appear to provide important habitats to birds throughout the year, especially open canopy agroforests in the wet season. We also found that open mixed agroforests contained a greater diversity of fruit, flower, and seed resources than closed canopy habitats such as secondary forest, cacao agroforests, young secondary forests, or dry forest scrub; and that plant food diversity was highest in the wet season. However, bird abundance significantly increased in closed canopy forest habitats during the dry season, suggesting that intact canopy forests provide important dry season habitat for many Grenadian birds, which may be particularly important for species in drier lowland areas experiencing more intensive agricultural land use and urban and resort development. Overall, this research demonstrates the importance of maintaining the functional connectivity of treed habitats at local and landscape scales for species conservation, as well as the contribution of diverse, small-scale agriculture to maintaining small-island bird communities.