Dung beetle communities as biological indicators of riparian forest widths in southern Brazil

Riparian forests provide important habitat for many wildlife species and are sensitive to landscape change. Among terrestrial invertebrates, dung beetles have been used to investigate the effects of environmental disturbances on forest structure and diversity. Since many studies demonstrated a negative response of dung beetle communities to increasing forest fragmentation, and that most dung beetle species had a more pronounced occurrence during warmest seasons, three hypotheses were tested: (1) Scarabaeinae richness, abundance, diversity and evenness are lower in thinner riparian zone widths than in wider widths during the warmest seasons; (2) Scarabaeinae richness and abundance are positively influenced by leaf litter coverage and height and canopy cover; and (3) Scarabaeinae composition varies with the reduction in riparian vegetation and among annual seasons. We selected four fragments with different riparian zone widths in three secondary streams in southern Brazil. In each fragment, four sampling periods were carried out seasonally between spring 2010 and winter 2011. We collected dung beetles using pitfall traps with two types of bait. We collected 1289 specimens distributed among 29 species. In spring and summer, dung beetle richness was higher in fragments with the widest riparian zone than in those with a thinner riparian zone, and it did not vary between fragments in fall and winter seasons. Dung beetle abundance did not differ among fragments with different riparian zone widths, but it was higher in spring and summer than fall and winter. Richness and abundance were positively influenced by leaf litter. While dung beetle diversity was higher in fragments with wider riparian zone widths than in those with thinner widths, the evenness was similar among fragments. Dung beetle composition differed between the fragments with the widest and thinnest riparian zones, and it also varied among the seasons. Our results suggest that decreased riparian zones affect negatively to dung beetle community structure in southern Brazil. Fragments with thinner riparian zones had lower beetle richness in warmest seasons and an altered community composition. In this sense, the dung beetles are potentially good indicators of riparian forest fragmentation since some species were indicators of a particular riparian zone width. From a conservation perspective, our results demonstrate that the new Brazilian Forest Code will greatly jeopardize not only the terrestrial and aquatic biodiversity of these ecosystems, but also countless other ecological functions.     

Tree Species Composition and Diversity at Different Levels of Disturbance in Popa Mountain Park,Myanmar

Tropical forests are highly threatened by human activities, even within the protected areas that have been established to conserve biodiversity. Human activities may have different degrees of impact on vegetation structure, composition and diversity. Some studies have measured direct evidence of human activities in forming disturbance gradients, while others have quantified canopy cover as a proxy for disturbance. When measurement is confined to human activities, disturbance may be underestimated in areas of poor canopy cover where forest degrading activities have ceased. Where measurements are restricted to canopy cover, disturbance may be underestimated in areas of extensive canopy cover that may have been subject to past disturbances, and overestimated for areas where canopy cover is naturally sparse. Combining indicators of past and present disturbances is therefore necessary to examine the full spectrum of human disturbances. Forest vegetation in Popa Mountain Park, Myanmar was surveyed and classified into three levels of disturbance—undisturbed, medium disturbed and highly disturbed—derived from evidence of cutting and canopy cover. The forests are second or third growth after clearing for agriculture in the early 20th century. All trees with ≥10 cm diameter at breast height in 168 sample plots (10 m × 10 m) were identified and measured. Density, basal area and diversity decreased and dominance rose when disturbance increased. Canonical correspondence analysis (CCA) clearly discriminated three forest stands and CCA axes were significantly correlated to soil moisture, soil nitrogen, elevation, slope, aspect, distance from park boundary and distance from villages. Abstract in Myanmar is available at http://www.blackwell‐synergy.com/loi/btp .     

Effects of fire and spruce beetle outbreak legacies on the disturbance regime of a subalpine forest in Colorado

Aim There is increasing research attention being given to the role of interactions among natural disturbances in ecosystem processes. We studied the interactions between fire and spruce beetle (Dendroctonus rufipennis Kirkby) disturbances in a Colorado subalpine forest. The central questions of this research were: (1) How does fire history influence stand susceptibility to beetle outbreak? And conversely, (2) How does prior occurrence of a beetle outbreak influence stand susceptibility to subsequent fire? Methods We reconstructed the spatial disturbance history in a c. 4600 ha area by first identifying distinct patches in the landscape on aerial photographs. Then, in the field we determined the disturbance history of each patch by dating stand origin, fire scars, dates of mortality of dead trees, and releases on remnant trees. A geographical information system (GIS) was used to overlay disturbance by fire and spruce beetle. Results and main conclusions The majority of stands in the study area arose following large, infrequent, severe fires occurring in c. 1700, 1796 and 1880. The study area was also affected by a severe spruce beetle outbreak in the 1940s and a subsequent low‐severity fire. Stands that originated following stand‐replacing fire in the late nineteenth century were less affected by the beetle outbreak than older stands. Following the beetle outbreak, stands less affected by the outbreak were more affected by low‐severity fire than stands more severely affected by the outbreak. The reduced susceptibility to low‐severity fire possibly resulted from increased moisture on the forest floor following beetle outbreak. The landscape mosaic of this subalpine forest was strongly influenced by the interactions between fire and insect disturbances.     

Stand‐replacing fires reduce susceptibility of lodgepole pine to mountain pine beetle outbreaks in Colorado

Aim As climate change is increasing the frequency, severity and extent of wildfire and bark beetle outbreaks, it is important to understand how these disturbances interact to affect ecological patterns and processes, including susceptibility to subsequent disturbances. Stand‐replacing fires and outbreaks of mountain pine beetle (MPB), Dendroctonus ponderosae, are both important disturbances in the lodgepole pine, Pinus contorta, forests of the Rocky Mountains. In the current study we investigated how time since the last stand‐replacing fire affects the susceptibility of the stand to MPB outbreaks in these forests. We hypothesized that at a stand‐scale, young post‐fire stands (< c. 100–150 years old) are less susceptible to past and current MPB outbreaks than are older stands. Location Colorado, USA. Methods We used dendroecological methods to reconstruct stand‐origin dates and the history of outbreaks in 23 lodgepole pine stands. Results The relatively narrow range of establishment dates among the oldest trees in most sampled stands suggested that these stands originated after stand‐replacing or partially stand‐replacing fires over the past three centuries. Stands were affected by MPB outbreaks in the 1940s/1950s, 1980s and 2000s/2010s. Susceptibility to outbreaks generally increased with stand age (i.e. time since the last stand‐replacing fire). However, this reduced susceptibility of younger post‐fire stands was most pronounced for the 1940s/1950s outbreak, less so for the 1980s outbreak, and did not hold true for the 2000s/2010s outbreak. Main conclusions Younger stands may not have been less susceptible to the most recent outbreak because: (1) after stands reach a threshold age of > 100–150 years, stand age does not affect susceptibility to outbreaks, or (2) the high intensity of the most recent outbreak reduces the importance of pre‐disturbance conditions for susceptibility to disturbance. If the warm and dry conditions that contribute to MPB outbreaks concurrently increase the frequency and/or extent of severe fires, they may thereby mitigate the otherwise increased landscape‐scale susceptibility to outbreaks. Potential increases in severe fires driven by warm and dry climatic trends may lead to a negative feedback by making lodgepole pine stands less susceptible to future MPB outbreaks.     

What is the role of local landscape structure in the vegetation composition of field boundaries?

Question: How distinct is the flora of field boundaries? How does the structure of field boundaries determine the composition of vegetation? Location: Estonia, six 4 km × 4 km agricultural areas. Methods: We studied the vegetation of fields and field boundaries using 2 m × 2 m sample plots. We estimated the frequency of species in both habitat types, applied an MRPP test to analyse the vegetation composition of field boundaries with various combinations of landscape features (ditches, roads, tree and bush layers) illustrating this by DCA ordination, and used indicator species analysis to determine the characteristic species of each boundary type. Results: Ca. 45% of the flora of field boundaries comprised species found on agricultural land. Most typical species in fields — agrotolerants — were also the most common in field boundaries. The vegetation of road verges and grassy boundaries consisted mainly of disturbance‐tolerant species. Woody boundaries were characterised by shade‐tolerant and nitrophilous species. Ditch banks included species typical of moist habitats and semi‐natural grasslands. Few threatened or protected species were observed. Conclusion: The vegetation composition of field boundaries varied due to the complex effects of landscape structure around and in these boundaries. Plant species in agricultural landscapes can be classified into two broad emergent groups on the basis of their different responses to agricultural disturbances — agrotolerant species and nature‐value species. Agrotolerant species are promoted by agriculture, nature‐value species include rare weeds and habitat specialists. We suggest that high‐nature‐value species should prevail in monitoring the effects of land‐use intensification on biodiversity rather than total species richness.     

Wide corridors with much environmental heterogeneity best conserve high dung beetle and ant diversity

Landscape ecological networks (ENs) consist of landscape-scale conservation corridors that connect areas of high natural value within a production mosaic with protected areas (PAs). In South Africa, ENs have been implemented on a large spatial scale to offset the negative impacts of plantation forestry on indigenous grasslands. We focus on corridor width as a factor for conserving dung beetle and ant diversity within an EN. We also investigate the importance of natural environmental heterogeneity (elevation, vegetation type) and habitat quality (soil hardness, invasive alien plant density). We sampled dung beetles and ants in 30 corridors of different sizes, and at ten sites in a nearby PA. In addition, we also analysed dung beetles according to their feeding guild. Tunnelling dung beetle species richness increased with corridor width. Rolling dung beetle species richness was higher in the PA than in the corridors of the EN. The dung beetle assemblage within the EN differed from that within the PA. Corridors of various widths differed in ant composition but not in species richness. Furthermore, the PA and the EN differed in environmental variables, which contributed to differences in dung beetle species richness and assemblage composition. Within the EN, environmental heterogeneity across the landscape was more important than corridor width for driving species diversity of both dung beetles and ants. When planning future ENs, wide corridors (>280 m) that encompass as much natural heterogeneity across the landscape as possible will best conserve the range of local insect species.     

Effects of riparian vegetation width and substrate type on riffle beetle community structure

Riffle beetle community structure is influenced by the preservation condition of stream riparian vegetation. Though, the width of riparian vegetation required to ensure conservation of stream insect communities is still controversial. Effects of alterations in riparian vegetation widths on stream insect community structure can be overcame by other environmental variables, like substrate type, hindering accurate assessments. We tested the effects of different riparian vegetation widths (>40, 30–15, 15–5 and <5 m) along with different substrate types (inorganic and organic) on riffle beetle community structure in southern Brazilian 4th‐ to 5th‐order streams. Riparian buffer widths and substrate types influenced riffle beetle community structure, but no interaction between them was observed. Reduced riparian vegetation widths downstream were associated with changes in riffle beetle dominant genera (Macrelmis predominated only in streams with narrowest riparian widths). Additionally, communities in organic substrates had lower equitability and different dominant genera (Hexacylloepus and Heterelmis) than inorganic ones. Our results showed that reductions in riparian vegetation were associated with water pollution and changes in riffle beetle community structure, suggesting that buffer strips narrower than 5 m are not adequate to maintain environmental integrity of southern Brazilian streams. These results have special importance for the conservation of stream insects in Brazil, as reductions up to less than 5 m in stream banks of small properties are allowed by the new Brazilian Forest Code, independently of stream order.     

自然火干扰对新疆喀纳斯旅游区森林景观树种结构的影响

 自然火干扰是森林生态系统的正常行为, 是决定森林物种构成、群落结构和生物多样性的主要因素。该研究将新疆喀纳斯旅游区作为研究对象, 把自然火干扰和树种结构作为不可分割的整体, 就喀纳斯旅游区树种结构对自然火干扰的响应进行了分析。结果表明, 受自然火干扰林分和长期未受干扰林分的树种结构之间存在明显的差异, 自然火干扰对阔叶针叶树种比、树种丰富度(Ma)和Shannon-Wiener多样性指数(H′)存在极显著的影响, 受自然火干扰后, 三者均表现出增大的特征。此外, 所调查范围内曾发生8次自然火干扰事件, 并且不同时期发生的自然火干扰对以阔叶针叶树种比为特质的季相结构和树种丰富度存在极显著的影响。自然火干扰是影响新疆喀纳斯旅游区季相结构和组成结构的主要因素之一。     

Prolonged tropical forest degradation due to compounding disturbances: Implications for CO2 and H2O fluxes

Drought, fire, and windstorms can interact to degrade tropical forests and the ecosystem services they provide, but how these forests recover after catastrophic disturbance events remains relatively unknown. Here, we analyze multi‐year measurements of vegetation dynamics and function (fluxes of CO₂ and H₂O) in forests recovering from 7 years of controlled burns, followed by wind disturbance. Located in southeast Amazonia, the experimental forest consists of three 50‐ha plots burned annually, triennially, or not at all from 2004 to 2010. During the subsequent 6‐year recovery period, postfire tree survivorship and biomass sharply declined, with aboveground C stocks decreasing by 70%–94% along forest edges (0–200 m into the forest) and 36%–40% in the forest interior. Vegetation regrowth in the forest understory triggered partial canopy closure (70%–80%) from 2010 to 2015. The composition and spatial distribution of grasses invading degraded forest evolved rapidly, likely because of the delayed mortality. Four years after the experimental fires ended (2014), the burned plots assimilated 36% less carbon than the Control, but net CO₂ exchange and evapotranspiration (ET) had fully recovered 7 years after the experimental fires ended (2017). Carbon uptake recovery occurred largely in response to increased light‐use efficiency and reduced postfire respiration, whereas increased water use associated with postfire growth of new recruits and remaining trees explained the recovery in ET. Although the effects of interacting disturbances (e.g., fires, forest fragmentation, and blowdown events) on mortality and biomass persist over many years, the rapid recovery of carbon and water fluxes can help stabilize local climate.     

Effects of biotic disturbances on forest carbon cycling in the United States and Canada

Forest insects and pathogens are major disturbance agents that have affected millions of hectares in North America in recent decades, implying significant impacts to the carbon (C) cycle. Here, we review and synthesize published studies of the effects of biotic disturbances on forest C cycling in the United States and Canada. Primary productivity in stands was reduced, sometimes considerably, immediately following insect or pathogen attack. After repeated growth reductions caused by some insects or pathogens or a single infestation by some bark beetle species, tree mortality occurred, altering productivity and decomposition. In the years following disturbance, primary productivity in some cases increased rapidly as a result of enhanced growth by surviving vegetation, and in other cases increased slowly because of lower forest regrowth. In the decades following tree mortality, decomposition increased as a result of the large amount of dead organic matter. Net ecosystem productivity decreased immediately following attack, with some studies reporting a switch to a C source to the atmosphere, and increased afterward as the forest regrew and dead organic matter decomposed. Large variability in C cycle responses arose from several factors, including type of insect or pathogen, time since disturbance, number of trees affected, and capacity of remaining vegetation to increase growth rates following outbreak. We identified significant knowledge gaps, including limited understanding of carbon cycle impacts among different biotic disturbance types (particularly pathogens), their impacts at landscape and regional scales, and limited capacity to predict disturbance events and their consequences for carbon cycling. We conclude that biotic disturbances can have major impacts on forest C stocks and fluxes and can be large enough to affect regional C cycling. However, additional research is needed to reduce the uncertainties associated with quantifying biotic disturbance effects on the North American C budget.     

When the forest dies: the response of forest soil fungi to a bark beetle-induced tree dieback

Coniferous forests cover extensive areas of the boreal and temperate zones. Owing to their primary production and C storage, they have an important role in the global carbon balance. Forest disturbances such as forest fires, windthrows or insect pest outbreaks have a substantial effect on the functioning of these ecosystems. Recent decades have seen an increase in the areas affected by disturbances in both North America and Europe, with indications that this increase is due to both local human activity and global climate change. Here we examine the structural and functional response of the litter and soil microbial community in a Picea abies forest to tree dieback following an invasion of the bark beetle Ips typographus, with a specific focus on the fungal community. The insect-induced disturbance rapidly and profoundly changed vegetation and nutrient availability by killing spruce trees so that the readily available root exudates were replaced by more recalcitrant, polymeric plant biomass components. Owing to the dramatic decrease in photosynthesis, the rate of decomposition processes in the ecosystem decreased as soon as the one-time litter input had been processed. The fungal community showed profound changes, including a decrease in biomass (2.5-fold in the litter and 12-fold in the soil) together with the disappearance of fungi symbiotic with tree roots and a relative increase in saprotrophic taxa. Within the latter group, successive changes reflected the changing availability of needle litter and woody debris. Bacterial biomass appeared to be either unaffected or increased after the disturbance, resulting in a substantial increase in the bacterial/fungal biomass ratio.     

Structural dynamics of a natural mixed deciduous forest in western Thailand

Abstract. Structural dynamics of a natural tropical seasonal – mixed deciduous – forest were studied over a 4-yr period at Mae Klong Watershed Research Station, Kanchanaburi Province, western Thailand, with particular reference to the role of forest fires and undergrowth bamboos. All trees > 5 cm DBH in a permanent plot of 200 m × 200 m were censused every two years from 1992 to 1996. The forest was characterized by a low stem density and basal area and relatively high species diversity. Both the bamboo undergrowth and frequent forest fires could be dominant factors that prevent continuous regeneration. Recruitment, mortality, gain (growth of survival tree plus ingrowth) and loss in basal area (by tree death) during the four years were 6.70%/yr, 2.91%/yr, 1.22%/yr and 1.34%/yr, respectively. Mortality was size dependent; middle size trees (30–50 cm) had the lowest mortality, while the smallest (5–10 cm) had the highest mortality. Tree recruitment was observed particularly in the first two years, mostly in the area where die-back of undergrowth bamboo occurred. The bias of the spatial distribution of recruitment to the area of bamboo die-back was significant and stronger than that to the forest canopy gaps. Successful regeneration of trees which survive competition with other herbs and trees after dieback of bamboo could occur when repeated forest fires did not occur in subsequent years. It is suggested that both the fire disturbance regime and bamboo life-cycle greatly influence the structure and dynamics of this seasonal tropical forest.     

Changes in woody vegetation abundance and diversity after natural disturbances causing different levels of mortality

Questions: How does woody vegetation abundance and diversity differ after natural disturbances causing different levels of mortality? Location: Abies balsamea–Betula papyrifera boreal mixed‐wood stands of southeast Quebec, Canada. Methods: Woody vegetation abundance and diversity were quantified and compared among three disturbance‐caused mortality classes, canopy gap, moderate‐severity disturbances, and catastrophic fire, using redundancy analysis, a constrained linear ordination technique, and diversity indices. Results: Substantial changes in canopy tree species abundance and diversity only occurred after catastrophic fire. Shade‐tolerant, late‐successional conifer species remained dominant after canopy gap and moderate‐severity disturbances, whereas shade‐intolerant, early‐successional colonizers dominated canopy tree regeneration after catastrophic fire. Density and diversity of mid‐tolerant and shade‐intolerant understory tree and shrub species increased as the impact of disturbance increased. Highest species richness estimates were observed after catastrophic fire, with several species establishing exclusively under these conditions. Relative abundance of canopy tree regeneration was most similar after canopy gap and moderate‐severity disturbances. For the sub‐canopy tree and shrub community, relative species abundances were most similar after moderate‐severity disturbances and catastrophic fire. Vegetation responses to moderate‐severity disturbances thus had commonalities with both extremes of the disturbance‐caused mortality gradient, but for different regeneration layers. Conclusions: Current spatio‐temporal parameters of natural disturbances causing varying degrees of mortality promote the development of a complex, multi‐cohort forest condition throughout the landscape. The projected increase in time intervals between catastrophic fires may lead to reduced diversity within the system.     

The Impact of Fine-Scale Disturbances on the Predictability of Vegetation Dynamics and Carbon Flux

Predictions from forest ecosystem models are limited in part by large uncertainties in the current state of the land surface, as previous disturbances have important and lasting influences on ecosystem structure and fluxes that can be difficult to detect. Likewise, future disturbances also present a challenge to prediction as their dynamics are episodic and complex and occur across a range of spatial and temporal scales. While large extreme events such as tropical cyclones, fires, or pest outbreaks can produce dramatic consequences, small fine-scale disturbance events are typically much more common and may be as or even more important. This study focuses on the impacts of these smaller disturbance events on the predictability of vegetation dynamics and carbon flux. Using data on vegetation structure collected for the same domain at two different times, i.e. “repeat lidar data”, we test high-resolution model predictions of vegetation dynamics and carbon flux across a range of spatial scales at an important tropical forest site at La Selva Biological Station, Costa Rica. We found that predicted height change from a height-structured ecosystem model compared well to lidar measured height change at the domain scale (~150 ha), but that the model-data mismatch increased exponentially as the spatial scale of evaluation decreased below 20 ha. We demonstrate that such scale-dependent errors can be attributed to errors predicting the pattern of fine-scale forest disturbances. The results of this study illustrate the strong impact fine-scale forest disturbances have on forest dynamics, ultimately limiting the spatial resolution of accurate model predictions.     

Species richness and resilience of forest communities: combined effects of short-term disturbance and long-term pollution

Recovery of the species richness of plant communities after experimental disturbances of various severities were studied in spruce forests polluted by atmospheric entry of SO₂ and heavy metals from a copper smelter. In the three toxic load zones (impact, buffer, and background), 60 experimental “pit-and-mound” complexes (sized 1 m × 2 m, 20 complexes in each zone) were created. Colonization of disturbed areas by vascular plants was observed during a 6-year period after the disturbance. The results showed that the recovery processes were affected by disturbance severity and that the recovery differed significantly among the communities. In all of the zones, species richness increased rapidly after mild disturbance. In degraded communities, levelling of differences in the rate of colonization after mild and severe disturbances was observed. The highest colonization rate was found in the communities of background zone, while the lowest was found in the heavily degraded communities of impact zone. The disturbances significantly increased the species diversity of communities in all zones and caused a certain reversion of degraded communities to previous stage of anthropogenic succession. Mild disturbance promoted the greatest increase in the diversity indices. The study results indicate that recovery rate of species richness of plant communities is determined by the duration of negative effect of disturbances. Recovery also depends significantly on the magnitude and endurance of positive effect of disturbances. The studied communities differed significantly in these parameters. The study results also suggest that short-term disturbances can significantly modify the process of transformation of plant communities by atmospheric pollution. On the other hand, long-term pollution can considerably modify the response of forest communities to disturbances. The results also conclude that the resilience of communities does not exclusively depend on their species richness.     

Disturbance dynamics and history of an old-growth subalpine fir (Abies fargesii) forest in central China

Disturbance history of an old-growth subalpine fir (Abies fargesii) forest in the Shennongjia Mountains of central China was reconstructed using dendroecological methods. Increment cores were extracted from 468 trees within six 100 m × 50 m permanent transects distributed across the old-growth subalpine fir forest of 300 ha. Growth patterns of 299 fir cores were examined for abrupt increases in radial growth to indicate formation of past canopy gaps and for rapid early radial growth to indicate establishment in past canopy gaps. The results showed that 70.8 % of the canopy fir trees experienced an average of 0.78 (ranging from 0 to 2) major release event for an average of 15.8 (ranging from 10 to 24) years, and an average of 1.94 (ranging from 0 to 3) moderate release events for an average of 25.6 (ranging from 10 to 36) years before they reached canopy. Recruitment pulse of trees coincided temporally with the peak of disturbance rate from the 1900s to the 1910s, suggesting occurrence of intense disturbance events during the time period. Radial growth analyses indicated that a history with small-scale disturbance events has resulted in the formation of the old-growth subalpine fir forest, and stand-replacing disturbances might not be necessary for the development of the forest. This study provides strong evidence that there are substantial variations in the disturbance severity and frequency over time. Most disturbance events might rather cause treefall gaps than clear large areas of forest at once. Thus, the old-growth subalpine fir forest experienced frequent gap-scale disturbances and few large-scale disturbances in its development history.     

基于景观可达性的广州市林地边界动态分析

林地边界是景观边界中一种特殊类型,受综合因素的影响而呈现动态变化,其发生位移的位置和方向能清晰地反映出该地段的土地利用过程和强度。通过对广州市1985年、1995年和2007年的土地利用数据进行分析,基于市内主要公路的分布进行景观可达性分区,提取林地边界并根据边界性质进行分类分析,着重研究了林地边界的动态变化特征。结果表明,研究时段内广州市林地面积相对稳定,而林地斑块数量和林地边界总长度持续增加,林地呈现出边界复杂化和景观破碎化的趋势。广州市林地的邻接景观以耕地为绝对优势的局面因建设用地和水域的增加而打破,表现为林地与耕地邻接边界长度迅速减少,而林地与水域、林地与建设用地邻接边界显著增加。从1985年到2007年,林地与耕地邻接边界的减少速度随着与主要公路距离的增加而变缓;林地与建设用地邻接边界增速最快的区域逐渐远离主要公路;林地与水域邻接边界更多分布于主要公路1km以外的区域,且随着时间推移逐渐靠近主干道路。     

Factors influencing bark beetle outbreaks after forest fires on the Iberian Peninsula

Fires are among the most globally important disturbances in forest ecosystems. Forest fires can be followed by bark beetle outbreaks. Therefore, the dynamic interactions between bark beetle outbreaks and fire appear to be of general importance in coniferous forests throughout the world. We tested three hypotheses of how forest fires in pine ecosystems (Pinus pinaster Alton and P. radiata D. Don) in Spain could alter the population dynamics of bark beetles and influence the probability of further disturbance from beetle outbreaks: fire could affect the antiherbivore resin defenses of trees, change their nutritional suitability, or affect top-down controls on herbivore populations. P. radiata defenses decreased immediately after fire, but trees with little crown damage soon recovered with defenses higher than before. Fire either reduced or did not affect nutritional quality of phloem and either reduced or had no effect on the abundance, diversity, and relative biomass of natural enemies. After fire, bark beetle abundance increased via rapid aggregation of reproductive adults on scorched trees. However, our results indicate that for populations to increase to an outbreak situation, colonizing beetles must initiate attacks before tree resin defenses recover, host trees must retain enough undamaged phloem to facilitate larval development, and natural enemies should be sufficiently rare to permit high beetle recruitment into the next generation. Coincidence of these circumstances may promote the possibility of beetle populations escaping to outbreak levels.