Causes of spatial patterns of dead trees in forest fragments in Illinois

Natural disturbances introduce spatial heterogeneity into forests by causing non-random mortality of trees. We examined whether wind was the primary cause of spatial patterns of dead trees at fragment- and individual tree-levels in three fragments of temperate deciduous forests in Illinois, USA. Dead trees and wind-caused types of mortality were expected to be higher at forest edges, on windward aspects, in poorly-drained soils, and adjacent to existing canopy gaps. The extent of wind-related mortality was determined by comparing spatial and temporal patterns of dead trees, as well as characteristics of trees downed by single windstorms versus all dead trees. At the fragment-level, we used randomly located quadrats of 25×25 m to sample edge and interior areas of Trelease Woods, Brownfield Woods, and Hart Woods in 1995-1996 and again in 1999-2000. We noted type of mortality (standing dead, snapped-off, or uprooted trees), and measured DBH ( 10 cm) and direction of fall of each dead tree. The same measures were made for trees felled by two single storms in 1994. At the individual tree-level, domino effects were evaluated by comparing openness surrounding target treefalls vs. an equal sample size of living trees. The study provided limited evidence that wind caused spatial patterns of dead trees. Instead, spatial patterns of dead trees in the fragments accumulated from domino effects at the individual tree-level in two of the three fragments. Dead trees were more associated with preexisting gaps. Contrary to our predictions at the fragment-level, the frequency of dead trees was not greater at edges, on windward aspects, or in poorly drained soils. This study demonstrated the complexity of spatial patterns of dead trees in forest fragments. The significant domino effects indicated that the occurrence of dead trees was not random, but determined by previous disturbances.     

Age-related Decline in Forest Ecosystem Growth: An Individual-Tree, Stand-Structure Hypothesis

Forest growth is important both economically (yielding billions of dollars of annual revenues) and ecologically (with respect to ecosystem health and global carbon budgets). The growth of all forests follows a predictable general trend with age. In young forests, it accelerates as canopies develop; it then declines substantially soon after full canopy leaf area is reached. The classic explanation for the decline in growth invoked the increasing respiration costs required to sustain the larger masses of wood characteristic of older forests. Direct measurements of respiration have largely refuted this hypothesis, and recent work has focused on stand-level rates of resource supply, resource use, and growth. We developed and tested a hypothesis at the scale of individual trees (in relation to stand structure) to explain this declining stand-level rate of stem growth. According to our hypothesis, changes in stand structure allow dominant trees to sustain high rates of growth by increasing their acquisition of resources and using these resources efficiently (defined as stem growth per unit of resource used); smaller, nondominant trees grow more slowly as a result of their more limited acquisition of resources and a reduced rate of growth per unit of resource acquired. In combination, these two trends reduce overall stand growth. We tested this hypothesis by comparing growth, growth per unit of leaf area, and variation among trees within plots in two series of plantations of Eucalyptus in Brazil and by estimating individual-tree rates of growth and use of light, water, and nutrients in a plantation of Eucalyptus saligna in Hawaii. Our results supported the individual-tree hypothesis. We conclude that part of the universal age-related decline in forest growth derives from competition-related changes in stand structure and the resource-use efficiencies of individual trees. Received 19 February 2001; accepted 19 June 2001.     

Big eucalypts grow more slowly in a warm climate: evidence of an interaction between tree size and temperature

Large trees are critical components of forest ecosystems, but are declining in many forests worldwide. We predicted that growth of large trees is more vulnerable than that of small trees to high temperatures, because respiration and tissue maintenance costs increase with temperature more rapidly than does photosynthesis and these costs may be disproportionately greater in large trees. Using 5 00 000 measurements of eucalypt growth across temperate Australia, we found that high temperatures do appear to impose a larger growth penalty on large trees than on small ones. Average stem diameter growth rates at 21 °C compared with 11 °C mean annual temperature were 57% lower for large trees (58 cm stem diameter), but only 29% lower for small trees (18 cm diameter). While our results are consistent with an impaired carbon budget for large trees at warmer sites, we cannot discount causes such as hydraulic stress. We conclude that slower growth rates will impede recovery from extreme events, exacerbating the effects of higher temperatures, increased drought stress and more frequent fire on the tall eucalypt forests of southern Australia.     

Drivers of aboveground wood production in a lowland tropical forest of West Africa: teasing apart the roles of tree density,tree diversity,soil phosphorus,and historical logging

Tropical forests currently play a key role in regulating the terrestrial carbon cycle and abating climate change by storing carbon in wood. However, there remains considerable uncertainty as to whether tropical forests will continue to act as carbon sinks in the face of increased pressure from expanding human activities. Consequently, understanding what drives productivity in tropical forests is critical. We used permanent forest plot data from the Gola Rainforest National Park (Sierra Leone) – one of the largest tracts of intact tropical moist forest in West Africa – to explore how (1) stand basal area and tree diversity, (2) past disturbance associated with past logging, and (3) underlying soil nutrient gradients interact to determine rates of aboveground wood production (AWP). We started by statistically modeling the diameter growth of individual trees and used these models to estimate AWP for 142 permanent forest plots. We then used structural equation modeling to explore the direct and indirect pathways which shape rates of AWP. Across the plot network, stand basal area emerged as the strongest determinant of AWP, with densely packed stands exhibiting the fastest rates of AWP. In addition to stand packing density, both tree diversity and soil phosphorus content were also positively related to productivity. By contrast, historical logging activities negatively impacted AWP through the removal of large trees, which contributed disproportionately to productivity. Understanding what determines variation in wood production across tropical forest landscapes requires accounting for multiple interacting drivers – with stand structure, tree diversity, and soil nutrients all playing a key role. Importantly, our results also indicate that logging activities can have a long‐lasting impact on a forest's ability to sequester and store carbon, emphasizing the importance of safeguarding old‐growth tropical forests.     

Age structure and climate sensitivity of a high Andean relict forest of Polylepis rodolfo-vasquezii in central Peru

For a better understanding of forest ecology, tree-ring studies can provide information on climate sensitivity, tree growth patterns and population age structure that can inform about stand dynamics such as recruitment of new individuals, and other interspecific interactions related to competition and facilitation. Little is known about the ecology of the recently identified high Andean tree species Polylepis rodolfo-vasquezii. Here, we analyzed the relationship between tree size and age of two P. rodolfo-vasquezii forest stands located in the central Peruvian Andes at 11°S in latitude, and compared their growth patterns and climate sensitivity. We measured the height and diameter of each individual tree and collected tree core samples of living trees and cross sections of dead standing trees to generate two centennial tree-ring chronology at Toldopampa (1825–2015 CE) and at Pomamanta (1824–2014 CE) sites. The dendrochronological dates were evaluated by ¹⁴C analysis using the bomb-pulse methods analyzing a total of 9 calendar years that confirm the annual periodicity of this tree species. At the Toldopampa stand most trees ranged from 70 to 80 years old, with a 190-year old individual, being an older and better preserve forest than Pomamanta, with younger trees, probably because more human disturbances due to closer village proximity. No significant relationships were found between tree age and size in the oldest stand alerting that tree diameter should not be used as a metric for estimating tree ages as a general rule. The distinct growth patterns and the size-age relationship observed at the two forests may reflect distinct histories regarding human activities such as fire and logging. Nevertheless, both the Toldopampa and the Pomamanta tree-ring width chronologies exhibited common growth patterns and shared a similar positive response to temperature of the current growing season. Overall, our study confirmed the annual radial growth periodicity in P. rodofolfo-vasquezii trees using an independent method such as ¹⁴C analyses and a strong climate sensitivity of this tree species. These findings encourage the development of an extensive P. rodolfo-vasquezii tree-ring network for ecological and paleoclimate studies in the tropical Andes in South America.     

Growth variation in Abies georgei var. smithii along altitudinal gradients in the Sygera Mountains, southeastern Tibetan Plateau

A network of nine Smith fir (Abies georgei var. smithii) ring-width chronologies was constructed from sites ranging in elevation from 3,550 to 4,390 m above sea level (a.s.l.) in the Sygera Mountains, southeastern Tibetan Plateau. High-elevation trees had lower growth rates than did low-elevation trees. The mean tree-ring series intercorrelation (RBAR) increased with elevation. Principal component analysis identified three elevation zones (around 3,600, 3,800, and >4,200 m a.s.l.) with distinctive tree-ring growth patterns. Five chronologies with elevation >4,200 m a.s.l. were highly correlated. Overall, the initiation of tree-ring growth in Smith fir is controlled by common climatic signals, such as July minimum temperature, across a broad altitudinal range. Precipitation was not a growth-limiting factor across stands. Regardless of differences in stand elevation, topographical aspect, and tree age, the radial growth of Smith fir trees was markedly similar in response to common climatic signals, perhaps as a result of the relatively high-elevation of these forests (above 3,550 m a.s.l.) and the abundant summer monsoon rainfall. In addition, radial tree growth along the altitudinal gradients was indicative of a recent warming trend on the southeastern Tibetan Plateau.     

Forest response to increasing typhoon activity on the Korean peninsula: evidence from oak tree‐rings

The globally observed trend of changing intensity of tropical cyclones over the past few decades emphasizes the need for a better understanding of the effects of such disturbance events in natural and inhabited areas. On the Korean Peninsula, typhoon intensity has increased over the past 100 years as evidenced by instrumental data recorded from 1904 until present. We examined how the increase in three weather characteristics (maximum hourly and daily precipitation, and maximum wind speed) during the typhoon activity affected old‐growth oak forests. Quercus mongolica is a dominant species in the Korean mountains and the growth releases from 220 individuals from three sites along a latitudinal gradient (33–38°N) of decreasing typhoon activity were studied. Growth releases indicate tree‐stand disturbance and improved light conditions for surviving trees. The trends in release events corresponded to spatiotemporal gradients in maximum wind speed and precipitation. A high positive correlation was found between the maximum values of typhoon characteristics and the proportion of trees showing release. A higher proportion of disturbed trees was found in the middle and southern parts of the Korean peninsula where typhoons are most intense. This shows that the releases are associated with typhoons and also indicates the differential impact of typhoons on the forests. Finally, we present a record of the changing proportion of trees showing release based on tree‐rings for the period 1770–1979. The reconstruction revealed no trend during the period 1770–1879, while the rate of forest disturbances increased rapidly from 1880 to 1979. Our results suggest that if typhoon intensity rises, as is projected by some climatic models, the number of forest disturbance events will increase thus altering the disturbance regime and ecosystem processes.     

Changing growth response to wildfire in old‐growth ponderosa pine trees in montane forests of north central Idaho

North American fire‐adapted forests are experiencing changes in fire frequency and climate. These novel conditions may alter postwildfire responses of fire‐adapted trees that survive fires, a topic that has received little attention. Historical, frequent, low‐intensity wildfire in many fire‐adapted forests is generally thought to have a positive effect on the growth and vigor of trees that survive fires. Whether such positive effects can persist under current and future climate conditions is not known. Here, we evaluate long‐term responses to recurrent 20th‐century fires in ponderosa pine, a fire‐adapted tree species, in unlogged forests in north central Idaho. We also examine short‐term responses to individual 20th‐century fires and evaluate whether these responses have changed over time and whether potential variability relates to climate variables and time since last fire. Growth responses were assessed by comparing tree‐ring measurements from trees in stands burned repeatedly during the 20th century at roughly the historical fire frequency with trees in paired control stands that had not burned for at least 70 years. Contrary to expectations, only one site showed significant increases in long‐term growth responses in burned stands compared with control stands. Short‐term responses showed a trend of increasing negative effects of wildfire (reduced diameter growth in the burned stand compared with the control stand) in recent years that had drier winters and springs. There was no effect of time since the previous fire on growth responses to fire. The possible relationships of novel climate conditions with negative tree growth responses in trees that survive fire are discussed. A trend of negative growth responses to wildfire in old‐growth forests could have important ramifications for forest productivity and carbon balance under future climate scenarios.     

Posthurricane Seedling Structure in a Multi‐aged Tropical Dry Forest: Implications for Community Succession

Hurricane‐caused tree mortality in tropical dry forests occurs predominantly in early successional species. Consequently, hurricanes may accelerate succession in these forests. Forest regeneration, however, must be measured over an extended posthurricane time period to demonstrate this pattern. In this study, we recorded tree seedlings in 19 Florida Keys forests during May–August 1995, 3 years after Hurricane Andrew. For these forests—spanning a chronosequence from 14 to over 100 years since the most recent clearing—we used weighted averaging regression on relative abundances of pre‐hurricane trees to calculate a successional age optimum for each species; and used weighted averaging calibration to calculate inferred successional ages for stands based on pre‐hurricane trees and on posthurricane seedlings. To test the hypothesis that successional stage of seedlings exceeded successional stage of pre‐hurricane trees, we compared inferred stand ages based on posthurricane seedlings with those based on pre‐hurricane trees. Across the study area, inferred stand ages based on posthurricane seedlings were greater than those based on pre‐hurricane trees (P < 0.005); however, more seedlings in the youngest stands were early successional than in older stands. Of 29 species present both as pre‐hurricane trees and posthurricane seedlings, 23 had animal‐dispersed seeds. These results provide evidence that: (1) hurricanes do not ‘reset’ succession, and may accelerate succession; and (2) a strong legacy of stand successional age influences seedling assemblages in these forests.     

Characterizing growth rings in the trees of Perú: A wood anatomical overview for potential applications in dendroecological-related fields

Sustainable forestry requires accurate ecological information such as species composition, growth rates and recruitment dynamics. Tree growth rates are usually obtained through long-term periodic re-measurements of individual trees or through the analysis of tree growth rings in stem cross sections. However, tree growth ring analysis was traditionally thought to be only possible in biomes with strong seasonality such as those found in high latitude temperate regions. A lack of data on the occurrence and characteristics of tree rings in tropical trees may be due to a lack of investigations. Here we characterise the growth rings of 183 tree species from seven forest types across an altitudinal gradient in northern and central Perú at macro- and microscopic levels. A correspondence analysis showed an association between phylogenetic relatedness and the level of distinctiveness in the growth rings. Deciduous species of seasonally dry tropical forests were associated with distinct growth rings and mainly delimited by marginal parenchyma, while indistinct growth rings were associated with evergreen trees from lowland Amazonian and pre-montane wet forests. Additionally, for the first time the presence of growth ring boundaries defined by marginal phloem is reported in two tropical tree species, Gallesia integrifolia (Spreng.) Harms and Vochysia mapirensis Rusby. This contribution represents the most exhaustive record to date of the occurrence and anatomy of growth rings in trees of the Peruvian tropics, which can be used to inform future dendrochronological studies.     

Development processes and growth pattern of Pinus densiflora stands in central eastern Korea

Stand growth and developmental processes were investigated in Pinus densiflora Siebold et Zucc. stands of different ages in the central eastern region of Korea. Stands were inventoried and five trees per stand were sampled for stem analysis, age estimation, and growth analysis. More than 80% of sampled trees in a stand were established within 3–5 years, and most stands had a single cohort structure. The initial growth of pine seedlings was slow, but the height growth accelerated beyond 2–3 m height, 5–10 years after establishment. Linear growth was maintained until 10–12 m height, at which suppressed trees fell behind and might die out. The young stand was composed of pure pines, while few pine seedlings and saplings were found in the understory of older stands. The peak of diameter growth rate occurred around 5–15 years after tree establishment, implying that competition begins during that period. The pine stand development follows four stages: (1) the young stage when the growth rate increases and peaks; (2) the height competition stage when trees focus on height growth for light while maintaining a narrow DBH and height distribution; (3) the differentiation stage when suppressed trees die out, and the DBH distribution becomes wider; and (4) the mature stage when stands have a multi-canopy structure with a wide DBH and height distribution, while the understory is dominated by other tree species. The changes in growth rates and stand structure through forest development would be implemented to predict alterations of above-ground carbon sequestration rates.     

A comparison of structural characteristics between old-growth and postfire second-growth hemlock–hardwood forests in Adirondack Park, New York, U. S. A.

1 This study compares the structural characteristics of 12 old‐growth and six postfire second‐growth hemlock–northern hardwood stands in north central Adirondack Park, New York, in order to test the null hypothesis that there are no differences in species composition, size structure, age structure and attributes such as dead wood and canopy gaps between old‐growth stands and this type of second‐growth forest. 2 The second‐growth forests of this study regenerated following widespread logging‐related fires in either 1903 or 1908; the old growth and second growth have similar environmental settings. 3 Estimates of stand ages, derived from an increment core of the oldest tree in each stand, range from 88 to 390 years. 4 Structural attributes are related to stand age (i.e. stage of development). In comparison with the second‐growth forests of this study, older stands are characterized as (a) a larger average diameter of canopy trees; (b) a greater basal area of trees; (c) a lower density of canopy trees and of all trees ≥ 10 cm d.b.h.; (d) a higher density of eastern hemlock (Tsuga canadensis (L.) Carrière) trees; (e) a higher density of large trees (≥ 50 cm d.b.h.); (f) larger canopy gaps; and (g) a greater volume of coarse woody debris (both logs ≥ 20 cm d.b.h. and snags ≥ 10 cm d.b.h.). 5 Despite differences between old growth and second growth, especially in species composition, it appears from observations of the 18 stands that second‐growth forests are developing some structural characteristics of old growth. 6 Structural attributes of the old‐growth forests are similar to characteristics of the same forest type in geographically distant areas in eastern USA.     

Forest recovery after swidden cultivation across a 40-year chronosequence in the Atlantic forest of southern Bahia, Brazil

Tree species composition and structure of a 40-year chronosequence of secondary forests was compared with old-growth forests in southern Bahia, Brazil. Twelve stands were randomly selected that represented three age classes: 10, 25, and 40 year old with four replications in each class. All stands selected had been established after abandonment from swidden cultivation and were surrounded by old-growth forests. In every stand, ten 0.01-ha transects were established and all stems (≥5 cm diameter at breast height) were measured and identified. Results were compared with the dataset of two neighboring old-growth sites. Mean diameter, total height, and stand basal area increased with age. Number of trees/ha peaked in 40 year old stands. The results showed that secondary forests in this region take much more than 40 years to recover the structure of old-growth forests. In contrast, species richness recovery was rapid with a continuous accumulation of species with age in secondary forests. Species richness and diversity increased with age as did similarity between secondary stands and old-growth stands. More than half of the species found in the 40 year old stands were shared with the neighboring old-growth forests. However, species richness and diversity were higher in old growth sites.     

Functional traits determine tree growth and ecosystem productivity of a tropical montane forest: Insights from a long‐term nutrient manipulation experiment

Trait‐response effects are critical to forecast community structure and biomass production in highly diverse tropical forests. Ecological theory and few observation studies indicate that trees with acquisitive functional traits would respond more strongly to higher resource availability than those with conservative traits. We assessed how long‐term tree growth in experimental nutrient addition plots (N, P, and N + P) varied as a function of morphological traits, tree size, and species identity. We also evaluated how trait‐based responses affected stand scale biomass production considering the community structure. We found that tree growth depended on interactions between functional traits and the type or combination of nutrients added. Common species with acquisitive functional traits responded more strongly to nutrient addition, mainly to N + P. Phosphorous enhanced the growth rates of species with acquisitive and conservative traits, had mostly positive effects on common species and neutral or negative effects in rare species. Moreover, trees receiving N + P grew faster irrespective of their initial size relative to trees in control or to trees in other treatment plots. Finally, species responses were highly idiosyncratic suggesting that community processes including competition and niche dimensionality may be altered under increased resource availability. We found no statistically significant effects of nutrient additions on aboveground biomass productivity because acquisitive species had a limited potential to increase their biomass, possibly due to their generally lower wood density. In contrast, P addition increased the growth rates of species characterized by more conservative resource strategies (with higher wood density) that were poorly represented in the plant community. We provide the first long‐term experimental evidence that trait‐based responses, community structure, and community processes modulate the effects of increased nutrient availability on biomass productivity in a tropical forest.     

Effect of temperature and precipitation on the annual diameter growth of Scots pine on drained peatlands and adjacent mineral soil sites in Finland

The climate conditions of the current and previous growing seasons have been shown to influence growth of coniferous trees in mineral soils sites. These dependencies may be different in peatlands where growth is generally more dependent on variations in soil water conditions. In the Nordic and Baltic countries, millions of hectares of peatlands and wetlands have been drained in order to enhance forest production. These drainage networks do not guarantee stable soil water conditions for the whole stand rotation. It is thus likely that precipitation in particular may have a different influence on annual growth in peatland to that in mineral soil sites. We studied the effect of precipitation and temperature on the inter-annual diameter growth of Scots pine (Pinus sylvestris L.) in Finland in drained peatland forests. The diameter growth data were limited to periods when growth response to drainage had levelled out. For comparison, growth data were also collected from adjacent mineral soil trees. The climate variables were monthly mean temperature and precipitation in a given location estimated from observations at the nearest weather stations by means of spatial smoothing. We used mixed linear models in describing the annual diameter growth of individual trees as a function of tree size and stand properties and expressed the residual variation as a function of climate parameters. The peatland and mineral soil growth variations showed different dependence on climate parameters. Peatland trees within 5 m of a ditch showed different climate responses compared to those located further away. Precipitation in July was negatively correlated with the diameter growth of peatland trees but there was no correlation with temperature. Growth of trees in mineral soils was positively correlated with March and April mean temperatures and May and June mean precipitation. The residual growth indices showed largely similar patterns in peatlands and mineral soil sites.     

Divergent growth responses of healthy and declining spruce trees to climatic stress: A case study from the Western Carpathians

Long-lived tree species optimize resource allocation processes, and there are likely trade-offs between the growth and response to environmental stressful conditions. The study aims to investigate the growth of healthy and declining Norway spruce trees using dendrochronological analysis. We have selected a natural high mountain spruce population and established 27 sampling plots in Poľana Mts. We measured 270 trees, from which we visually evaluated 133 individuals. Moreover, 51 trees were sampled for increment cores. Our study reveals thatspecific extreme combination of winter, spring and summer temperatures and precipitation sums within the particular year 1974 induced long-term growth divergence of neighboring spruce trees of comparable age and size and differentiated between healthy and declining (highly defoliated) trees. This period accounts for a decrease in size of relativized increments by 30.2% in declining trees compared to visually healthy individuals. Trees with a low ability to recover from climatic stress compensate the response to environmental conditions by lower growth rates. In high mountain temperate forests, the long-term growth decline of spruce trees last about 40 years. The single-tree selection silvicultural system should be preferred in high mountain conditions, where frequent small-scale, low-intensity disturbances drive stand dynamics. Trees showing low growth resilience to revealed combination of weather conditions should be preferentially removed from stands , especially within the transformation of even-aged spruce monocultures using selective cuttings.     

Drought and cold spells trigger dieback of temperate oak and beech forests in northern Spain

Dieback in temperate forests is understudied, despite this biome is predicted to be increasingly affected by more extreme climate events in a warmer world. To evaluate the potential drivers of dieback we reconstructed changes in radial growth and intrinsic water-use efficiency (iWUE) from stable isotopes in tree rings. Particularly, we compared tree size, radial-growth trends, growth responses to climate (temperature, precipitation, cloudiness, number of foggy days) and drought, and changes in iWUE of declining and non-declining trees showing contrasting canopy dieback and defoliation. This comparison was done in six temperate forests located in northern Spain and based on three broadleaved tree species (Quercus robur, Quercus humilis, Fagus sylvatica). Declining trees presented lower radial-growth rates than their non-declining counterparts and tended to show lower growth variability, but not in all sites. The growth divergence between declining and non-declining trees was significant and lasted more in Q. robur (15–30 years) than in F. sylvatica (5–10 years) sites. Dieback was linked to summer drought and associated atmospheric patterns, but in the wettest Q. robur sites cold spells contributed to the growth decline. In contrast, F. sylvatica was the species most responsive to summer drought in terms of growth reduction followed by Q. humilis which showed coupled changes in growth and iWUE as a function of tree vigour. Low growth rates and higher iWUE characterized declining Q. robur and F. sylvatica trees. However, declining F. sylvatica trees became less water-use efficient close to the dieback onset, which could indicate impending tree death. In temperate forests, dieback and growth decline can be triggered by climate extremes such as dry and cold spells, and amplified by climate warming and rising drought stress.     

Wind damage and response in New Zealand forests: a review

The literature on wind damage in New Zealand forests is reviewed to investigate how abiotic and biotic factors influence damage severity, damage type, and forest recovery. Winds that damage forests tend to result from extra-tropical depressions or from topographically enhanced westerly air flows. Severe wind damage can occur when wind speeds exceed c. 0 km/hr, although investigating the relationship between damage and wind speeds is difficult, as gusts, for which speed is usually unrecorded, are important. Damage is often quantified by estimates of area affected, with some authors detailing the size and species of damaged trees within a given area. Key abiotic factors that influence damage patterns are topographical position, edaphic conditions, and disturbance history. Important biotic factors are tree height, tree health, position of the tree within the stand, and species. Damage type (uprooting or breakage) is primarily controlled by canopy position and rooting depth. Forest responses to wind damage include sprouting, recruitment, release, and suppression, with the dominant mode of forest recovery being strongly influenced by the severity of damage, and the species composition of the stand. As noted in international literature on wind damage, a lack of consistent methods, combined with poor species and spatial coverage, makes identifying general trends difficult. Investigating the role of wind damage in New Zealand forests has focused to date on Nothofagus forests and plantations of exotic trees and few studies have investigated long term dynamics following wind disturbance events.     

Host preference and growth patterns of ivy (Hedera helix L.) in a temperate alluvial forest

Recent studies have highlighted the role of lianas in shaping stand dynamics both in tropical and temperate forests. However, English ivy (Hedera helix L.), one of the most widespread lianas in Europe, has received little attention. We conducted a study in the Siro Negri alluvial forest (NW Italy) to determine what factors most affected ivy distribution and investigate its interactions with the trees in the stand. We evaluated the influence of tree size, age, species, and neighborhood crowding on ivy occurrence. In addition, growth ring widths were used to explore the development pattern of climbing stems. Fifty-two percent of trees in our study plots carried ivy, a value comparable to liana incidence found in mature tropical forests. Tree characteristics and their spatial pattern significantly influenced ivy distribution. Preferred hosts were large, isolated trees, while the effect of tree age and species on ivy occurrence was marginal. Growth pattern analysis revealed that radial growth was positively related to the available space on the tree trunk for each ivy stem. We conclude that neighborhood crowding around trees and competition among climbing stems relying on the same trunk may reduce the colonization rate of ivy.     

The direct regeneration hypothesis in northern forests

Question: Can the direct regeneration hypothesis (DRH) be used to predict post‐disturbance regeneration after fire, wind disturbance, and clearcutting in northern forests? Do life‐history traits such as regeneration strategy and shade tolerance influence post‐disturbance regeneration success of tree species? Location: Northern forests in North America. Methods: A meta‐analysis was conducted by collecting published data on pre‐ and post‐disturbance stand compositional characteristics in the northern forests. For each tree species, compositional difference (CD) was calculated as the difference between basal area proportions of the post‐ and pre‐disturbance stands, but for post‐disturbance stands <25 years of age, post‐disturbance proportions were calculated based on relative stem density. Results: Species response to disturbances was best explained by regeneration strategy, while disturbance type had no effect on CD. The proportion of broadleaf trees with either strong or weak vegetative reproduction ability increased after all disturbances. Serotinous species had CD values not significantly different from zero after fire, while CD for semi‐serotinous species was negative. The post‐disturbance proportions of non‐serotinous conifers decreased after all forms of disturbance. Conclusions: All disturbances promote broadleaf trees, regardless of regeneration strategy (suckering, sprouting, or seeding). The DRH is supported for conifers with serotinous cones after fire. Fire causes local extinction of non‐serotinous conifers, while wind and clearcutting only decrease the proportion of non‐serotinous conifers because of partial survival of seed sources and advanced regeneration. This study suggests that increasing stand‐replacing disturbances associated with global climate change will promote broadleaf trees in northern forests.