Radial patterns of xylem sap flow in non-, diffuse- and ring-porous tree species

We investigated radial patterns of sap flux density and wood properties in the sapwood of young loblolly pine (Finns taeda L.), mature white oak (Quercus alba L.) and sweetgum (Liquidambar styraciflua L.), which represent three major classes of wood anatomy: non-porous (coniferous), ring-porous and diffuse-porous. Radial measurements of xylem sap flux density were made in sections of xylem extending to 20 mm and 20–40 mm from the cambium. These measurements were compared with measurements of the relative water content (R_s) and sapwood specific gravity (ρ_r) of corresponding radial sections. In both hardwood species, sap flow differences were rarely significant between the two depth intervals. In pine, a 59% reduction in daily sap flux density from outer to inner sapwood was found. This could not be accounted for by a 3% drop in R_s; rather, an accompanying 9% reduction in ρ_r indicated a transition between the depth intervals from mature to juvenile sapwood, and is the probable cause of the lower flux rate in the inner xylem of pine.     

热消散探针在粉单竹液流研究中的应用

通过对计算树干液流密度的Granier经验公式进行试验验证和校正,比较不同长度的热消散探针(TDP)测量粉单竹液流的结果,探讨TDP在粉单竹液流研究中的适用性,并与邻近生长的常见树种荷木的液流日变化进行比较分析.结果表明:由于粉单竹的竹壁较薄、解剖结构异质性较高,10 mm探针可能低估粉单竹的液流密度,8和5 mm探针监测的液流密度值较准确.粉单竹液流密度平均值和日变化格局的偏度均大于荷木,而夜间荷木的液流活动比粉单竹活跃,说明粉单竹的夜间补水不如荷木.以TDP探针研究竹子的液流是可行的,但应用于不同竹种之前,必须对Granier经验公式进行有效的验证和校正.     

Sap flow of the southern conifer, <Emphasis Type="Italic">Agathis australis</Emphasis> during wet and dry summers

Key message

Analysis of sap flux density during drought suggests that the large sapwood and rooting volumes of larger trees provide a buffer against drying soil.

Abstract

The southern conifer Agathis australis is amongst the largest and longest-lived trees in the world. We measured sap flux densities (F _d) in kauri trees with a DBH range of 20–176 cm to explore differences in responses of trees of different sizes to seasonal conditions and summer drought. F _d was consistently higher in larger trees than smaller trees. Peak F _d was 20 and 8 g m^?2 s^?1 for trees of diameters of 176 and 20 cm, respectively, during the wet summer. Multiple regression analysis revealed photosynthetically active radiation (PAR) and vapour pressure deficit (D) were the main drivers of F _d. During drought, larger trees were more responsive to D whilst smaller trees were more responsive to soil drying. Our largest tree had a sapwood area of 3,600 cm². Preliminary analysis suggests stem water storage provides a buffer against drying soil in larger trees. Furthermore, F _d of smaller trees had higher R ² values for soil moisture at 30 and 60 cm depth than soil moisture at 10 cm depth (R ² = 0.68–0.97 and 0.55–0.67, respectively) suggesting that deeper soil moisture is more important for these trees. Larger trees did not show a relationship between F _d and soil moisture, suggesting they were accessing soil water deeper than 60 cm. These results suggest that larger trees may be better prepared for increasing frequency and intensity of summer droughts due to deeper roots and/or larger stem water storage capacity.

     

Changes in stem water content influence sap flux density measurements with thermal dissipation probes

Key message

Stem WC may decline during the day. Zero-flow dT _m increases when WC decreases. Use of nighttime dT _m in the calculation of sap flux density during the day might introduce errors.

Abstract

There is increasing evidence of diel variation in water content of stems of living trees as a result of changes in internal water reserves. The interplay between dynamic water storage and sap flow is of current interest, but the accuracy of measurement of both variables has come into question. Fluctuations in stem water content may induce inaccuracy in thermal-based measurements of sap flux density because wood thermal properties are dependent on water content. The most widely used thermal method for measuring sap flux density is the thermal dissipation probe (TDP) with continuous heating, which measures the influence of moving sap on the temperature difference between a heated needle and a reference needle vertically separated in the flow stream. The objective of our study was to investigate how diel fluctuations in water content could influence TDP measurements of sap flux density. We analysed the influence of water content on the zero-flow maximum temperature difference, dT _m, which is used as the reference for calculating sap flux density, and present results of a dehydration experiment on cut branch segments of American sycamore (Platanus occidentalis L.). We demonstrate both theoretically and experimentally that dT _m increases when stem water content declines. Because dT _m is measured at night when water content is high, this phenomenon could result in underestimations of sap flux density during the day when water content is lower. We conclude that diel dynamics in water content should be considered when TDP is used to measure sap flow.     

基于整树称重法的Granier经验公式对毛白杨树干液流测定的适用性

为了评估Granier经验公式在树干液流测定中的适用性,以毛白杨为对象,利用热扩散式探针法(TDP)测定树木的液流速率,以整树称重法进行同步测定,对比分析Granier经验公式在毛白杨树干液流测定中是否存在误差,并对整树称重法测定的蒸腾速率与热扩散法测定的温差系数K进行幂指数回归拟合,建立校正的Granier公式。结果表明:与整树称重法测定的蒸腾速率相比,通过Granier经验公式计算的液流速率低估了67.7%;建立了毛白杨的Granier校正公式F_d=0.0135K^0.6952(R²=0.77),校正后Granier公式的计算结果与整树称重法测定的蒸腾速率相比仅降低了3.4%,具有较好的一致性。因此,采用Granier经验公式计算毛白杨树干液流速率需进行校正。     

Interactive effects of wood decomposer fungal activities and bryophytes on spruce seedling regeneration on coarse woody debris

Decaying logs are important seedbeds in boreal and subalpine forests. However, biotic and abiotic factors and their interactions related to seedling colonization patterns on logs remain unclear. In the present study, we evaluated the influence of bryophyte communities, wood decay type (white-, brown-, and soft-rot) owing to decomposer fungal activities, and environmental abiotic factors on seedling establishment in an old-growth subalpine coniferous forest in Japan. Among the tree species recorded on the conifer logs, Picea jezoensis var. hondoensis was the most dominant. Log surfaces were covered with distinctive patches of liverwort Scapania bolanderi and moss Pleurozium schreberi (approximately 33% cover for each). Redundancy analysis showed that brown-rot in sapwood significantly affects the bryophyte and seedling community on the logs. Generalized linear models suggested that the total bryophyte cover, Scapania cover, and white-rot in heartwood positively associate with Picea seedling density, whereas Pleurozium cover and basal area of adjacent Picea adults negatively associate with Picea seedling density. Results of structural equation modeling suggested that the brown-rot of sapwood positively associates with Scapania cover that has a positive effect on Picea seedling density. Furthermore, brown-rot of sapwood inhibited the Pleurozium cover, thus contributing to the Scapania dominance on the logs. These results suggest that fungal wood decomposer activities affect colonization of Picea seedlings in an indirect way via structuring bryophyte community on the logs.     

Higher phenotypic plasticity does not confer higher salt resistance to <Emphasis Type="Italic">Robinia pseudoacacia</Emphasis> than <Emphasis Type="Italic">Amorpha fruticosa</Emphasis>

A greenhouse experiment was conducted in which two leguminous species commonly used in the Yellow River Delta for vegetation restoration, Robinia pseudoacacia and Amorpha fruticosa, were subjected to five salt treatments: 0, 50, 100, 150, and 200 mmol L^?1. We aimed to determine which of the two species would be better suited for growth in a saline environment, and whether the acclimation capacity to salinity resulted from an inherently higher phenotypic plasticity. The results showed that salinity affected most growth and biomass parameters but had no effects on most leaf traits and physiological parameters of the two species. Height, relative growth rate of crown area, root biomass, and leaf mass ratio of R. pseudoacacia were reduced by higher salinity, while A. fruticosa was not affected. Chlorophyll a-to-chlorophyll b ratio and total antioxidative capacity of A. fruticosa increased with higher salinity, whereas those of R. pseudoacacia remained unchanged. Root mass ratio and vitamin C concentration of both species were not affected by salinity, whereas vitamin C concentration of A. fruticosa was higher than that of R. pseudoacacia. The root-to-shoot ratio of A. fruticosa was higher than that of R. pseudoacacia in most salt treatments. Of all leaf traits, only leaf area differed between treatments. R. pseudoacacia generally exhibited a greater plasticity than A. fruticosa in response to salinity, but A. fruticosa was more resistant to the higher salinities than R. pseudoacacia, and was thus a better candidate for vegetation restoration in saline areas.     

华南地区常见树种导管特征与树干液流的关系

为探讨树木结构与功能的关系,对华南地区常见8种树木边材的导管特征进行观察,并利用Granier热扩散探针法测量干、湿季树干的液流密度,分析导管特征与树干液流的关系。结果表明,除红锥(Castanopsis hystrix)有两种导管外,大叶相思(Acacia auriculaeformis)、荷木(Schima superba)、火力楠(Michelia macclurei)、藜蒴(C.fissa)、马占相思(A.mangium)、柠檬桉(Eucalyptus citriodora)、尾巨桉(E.urophylla×E.grandis)的导管类型单一。导管特征在种间存在明显差异,且导管长度、密度和孔径之间存在明显相关性,它们与标准化的边材面积呈现显著相关。湿季液流最大值与导管特征无明显相关性,但整树最大蒸腾速率与导管特征呈显著相关;树木的日蒸腾量与导管特征也有明显相关性。因此,树木的液流速率并不受树干的导管影响;而树干的导管孔径与边材面积间的负相关权衡机制,可以降低树种间由于导管孔径差异引起的树干的水分输送速率的差异性。     

Sapflow+: a four-needle heat-pulse sap flow sensor enabling nonempirical sap flux density and water content measurements

? To our knowledge, to date, no nonempirical method exists to measure reverse, low or high sap flux density. Moreover, existing sap flow methods require destructive wood core measurements to determine sapwood water content, necessary to convert heat velocity to sap flux density, not only damaging the tree, but also neglecting seasonal variability in sapwood water content. ? Here, we present a nonempirical heat-pulse-based method and coupled sensor which measure temperature changes around a linear heater in both axial and tangential directions after application of a heat pulse. By fitting the correct heat conduction-convection equation to the measured temperature profiles, the heat velocity and water content of the sapwood can be determined. ? An identifiability analysis and validation tests on artificial and real stem segments of European beech (Fagus sylvatica L.) confirm the applicability of the method, leading to accurate determinations of heat velocity, water content and hence sap flux density. ? The proposed method enables sap flux density measurements to be made across the entire natural occurring sap flux density range of woody plants. Moreover, the water content during low flows can be determined accurately, enabling a correct conversion from heat velocity to sap flux density without destructive core measurements.     

Sap flux of five co-occurring tree species in a temperate broad-leaved forest during seasonal soil drought

In an old-growth forest in Central Germany, sap flux was studied in five broad-leaved tree species that were assumed to differ in drought sensitivity. Under moist soil conditions, average daily sap flux density (J _s) in the outermost xylem varied by a factor of 2.3 among the species (67–152 g cm⁻² per day, n=5 trees per species), and declined in the sequence Fagus sylvatica > Acer pseudoplatanus > Tilia cordata > Carpinus betulus > Fraxinus excelsior. Decreasing soil moisture content (Θ) resulted in linearly reduced J _s in four of the species. During a dry period, J _s was reduced by 44% in T. cordata, 39% in F. sylvatica, 37% in A. pseudoplatanus and 31% in C. betulus compared to sap flux at equal vapour pressure deficit (D) in the wet period. F. excelsior, the only ring-porous species studied, lacked a significant response in J _s to D and Θ. The relative reduction in water use during the dry period was not related to the assumed drought sensitivity of the species as inferred from their abundance in natural woodlands. J _s was positively correlated with tree diameter at breast height (DBH) in three species but decreased with DBH in two species. Dyeing experiments revealed that DBH accounted for 94% of the variation in sapwood area found in a bulk sample of all diffuse-porous trees. This suggests that DBH is a reliable estimator of sapwood area of temperate diffuse-porous species irrespective of species identity. In contrast, sap flux density was found to be greatly dependent on tree species. The estimated whole-plant water use for diffuse-porous trees of a given diameter (49 cm) ranged between 74 and 168 kg per day per species under moist soil conditions. Thus, in temperate mixed forests, species-specific differences in water use can result in a considerable spatial heterogeneity of canopy transpiration.     

Crown conductance in dwarf, medium, and tall pitch pines in the Long Island Pine Plains

The New York Pine Plains are a unique ecosystem with normal statured and a dwarfed variety of pitch pines (Pinus rigida Mill.). Growing interspersed with the dwarf pines are trees of intermediate height and features. Several hypotheses have been put forward as to why some of the trees are dwarfed, but none have been substantiated. In this study, we tested whether dwarf or medium trees are hydraulically limited compared to normally growing trees. Granier style sap flux sensors were installed in three to six trees of each tree type and sap flux was measured in early August 2004. Sap flux measurements were scaled to crown stomatal conductance using leaf area to sapwood area ratios for each tree. Contrary to expectation, dwarf and medium stature trees had very low leaf area to sapwood area ratios, but high crown stomatal conductances compared to normal trees. Analyses of leaf area, ring widths, and crown stomatal conductance indicate that differences between normal, and dwarf and medium pines are not due to hydraulic limitation, but that stunted growth may be due to other causes.     

Sap flow measurements in grapevines (Vitis vinifera L.) 2. Granier measurements

The Granier-system, a relatively simple and continuous method for measuring sap flux density, has been adapted and evaluated for its use in older, mature grapevines. The original calibration of Granier (1985, Annales Sciences Forestieres, 42, 193-200) could be extended to a sap flux density of up to 400 10^-6 m³ m^-2 s^-1 with only little error at high flux densities. A time lag of around 20 min was apparent between transpiration and calculated sap flow which was attributed to the thermal mass of the sensors themselves. The time lag and the consequently dampened response of the system caused a very low accuracy over short time periods thus reducing the value for detailed plant physiological investigations. However, when integrating over longer time intervals, much of the error cancelled out. For daily values the maximum error was within ±10% and after a period of 89 days only 1.5% error remained. This method is thus best suited for long term measurements of total water use. This revised version was published online in June 2006 with corrections to the Cover Date.     

Pine stumps act as hotspots for seedling regeneration after pine dieback in a mixed natural forest dominated by <Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis>

Over the past few decades, rural forest ecosystems in Japan have experienced dynamic vegetation changes due to forest dieback and changes in land use, leading to the loss of local species populations and biodiversity. The aim of this study was to evaluate the importance of pine (Pinus densiflora) stumps and logs for tree seedling regeneration in a mixed natural forest in Kyoto Prefecture, Japan, that had previously experienced severe pine dieback, and to determine which factors most greatly affect seedling establishment. Seedlings of 17 tree species were recorded on pine stumps and logs in later stages of decay, among which Chamaecyparis obtusa and Rhododendron reticulatum were most dominant. Both of these species had a greater density on pine stumps than on logs or soil, despite stumps covering less than 0.5% of the study area. In addition, the seedling densities of both species were positively associated with moss cover on coarse woody debris, but negatively associated with wood pH. Brown rot in the sapwood and heartwood, which occurred more frequently in stumps than in logs, also positively associated with the seedling densities of both species. Predictive modelling showed that C. obtusa seedlings exhibited a stronger response to pH in stumps than in logs. Therefore, since brown-rotted wood is acidic due to fungal decay activities, brown-rotted pine stumps may present hotspots of C. obtusa seedling regeneration at the study site.     

北京绿化树种油松、雪松和刺槐树干液流的空间变异特征

城市绿化树木具有多重生态效应, 其耗水量不容忽视。在不了解树干液流空间变异的前提下, 将点的测定值推广到整树或者林段尺度会产生很大的误差。为准确地确定整树耗水, 采用热消散探针法研究了夏秋季北京成年常绿树种油松(Pinus tabulaeformis)、雪松(Cedrus deodara)和刺槐(Robinia pseudoacacia)树干液流的空间变异特征及产生原因。各树种树干液流存在方位变异, 受树干靠南的方向受光较多、木材解剖特征和枝下高高度的影响, 油松和雪松液流密度与方位之间的关系较为固定, 而刺槐液流密度与方位之间的关系表现出随机性。不同方位每小时液流密度之间高度相关(p < 0.000 1)。因此, 可以基于这种关系准确地计算其他方位的液流(R² > 0.91, p < 0.000 1)。油松和雪松树干液流的径向变异显著, 较深处和较浅处树干液流的日变化格局相似, 但是较深处的液流明显滞后于较浅处的树干液流, 且较浅处树干液流对环境因子的响应远高于深处的液流。不同深度树干液流之间密切相关, 因此可以利用较浅处的液流外推其他深度的液流(R² > 0.89, p < 0.000 1)。然而, 同一棵树不同方位径向剖面特征不同, 雪松南向较深处的液流明显高于其他方位, 且滞后不显著, 这与树冠南向受光较多有关。结合误差分析, 采取北向15 mm和75 mm深处的液流密度均值来估算整树耗水较为准确。     

The effect of fertilization on sap flux and canopy conductance in a Eucalyptus saligna experimental forest

Land devoted to plantation forestry (50 million ha) has been increasing worldwide and the genus Eucalyptus is a popular plantation species (14 million ha) for its rapid growth and ability to grow well on a wide range of sites. Fertilization is a common silvicultural tool to improve tree growth with potential effects on stand water use, but the relationship between wood growth and water use in response to fertilization remains poorly quantified. Our objectives in this study were to determine the extent, timing and longevity of fertilization effects on water use and wood growth in a non‐water limited Eucalyptus saligna experimental forest near Hilo, HI. We evaluated the short‐ and long‐term effects of fertilization on water use by measuring sap flux per unit sapwood area, canopy conductance, transpiration per unit leaf area and water‐use efficiency in control and fertilized stands. Short‐term effects were assessed by comparing sap flux before and after fertilizer application. Long‐term effects were assessed by comparing control plots and plots that had received nutrient additions for 5 years. For the short‐term response, total water use in fertilized plots increased from 265 to 487 mm yr^?1 during the 5 months following fertilization. The increase was driven by an increase in stand leaf area accompanied by an increase in sap flux per unit sapwood area. Sap flux per unit leaf area and canopy conductance did not differ during the 5 months following fertilizer additions. For the last 2 months of our short‐term measurements, fertilized trees used less water per unit carbon gain (361 compared with 751 kg H₂O kg C^?1 in control stands). Trees with 5 years of fertilization also used significantly more water than controls (401 vs. 302 mm yr^?1) because of greater leaf area in the fertilized stands. Sap flux per unit sapwood area, sap flux per unit leaf area, and canopy conductance did not differ between control and fertilized trees in the long‐term plots. In contrast to the short‐term response, the long‐term response of water use per unit wood growth was not significant. Overall, fertilization of E. saligna at our site increased stand water use by increasing leaf area. Fertilized trees grew more wood and used more water, but fertilization did not change wood growth per unit water use.     

疏伐对黄土丘陵区刺槐林蒸腾的影响

黄土高原地区植被建设已达到土壤水分承载力的阈值,需要对现有林分进行结构优化并提升其生态功能。不合理的林分密度是导致黄土丘陵区刺槐林土壤干化、生长衰退的主要原因之一。疏伐可以优化林分结构,并能够通过控制蒸腾耗水来调控土壤水分,是促进刺槐林可持续生长的有效手段。疏伐对黄土丘陵区刺槐林蒸腾有何影响,目前并不清楚。研究基于树干液流法估算了4个不同疏伐强度（样地1：52%、样地2：48%、样地3：35%、样地4：未疏伐）下刺槐单株尺度的液流速率与林分尺度的日平均蒸腾量,并分析了不同时间尺度下液流速率与环境因子的关系,以阐明疏伐对黄土丘陵区刺槐林蒸腾的影响。结果表明：（1） 单株尺度刺槐蒸腾速率（即液流速率）随疏伐强度减小（林分密度增大）呈现下降趋势（样地1：0.53 kg cm^-2 d^-1、样地2：0.41 kg cm^-2 d^-1、样地3：0.31 kg cm^-2 d^-1、样地4：0.33 kg cm^-2 d^-1）;（2） 观测期林分尺度日平均蒸腾量随疏伐强度减小呈现上升趋势（样地1：0.90 mm/d、样地2：1.18 mm/d、样地3：1.04 mm/d、样地4：1.44 mm/d）;（3） 在半小时尺度与日尺度上,各样地液流速率与环境因子的关系没有显著差异,半小时尺度单株液流速率均与太阳辐射相关性最高（相关系数0.883-0.908）,液流速率日变化过程与环境因子日变化过程存在时滞现象;日尺度单株液流速率与饱和水汽压亏缺相关性最高（相关系数0.843-0.913）,样地间日尺度单株液流速率的差异性随着饱和水汽压亏缺增大而增大。研究结果初步反映了疏伐导致的林分密度变化对刺槐蒸腾的影响,将为黄土丘陵区刺槐林的结构改造、功能提升和土壤水分调控提供理论支持。     

Seasonal variations in moisture use in a piñon–juniper woodland

In water-limited environments of the intermountain region of North America, summer precipitation may play a role in the structure and function of aridland communities and ecosystems. This study examined the potential reliance on summer precipitation of two widespread, coexisting woody species in the southwestern United States, Pinus edulis Englmn. (Colorado piñon) and Juniperus osteosperma (Torr) Little (Utah juniper). The current distributions of P. edulis and J. osteosperma are highly suggestive of different dependencies on summer rainfall. We hypothesized that P. edulis was dependent on summer precipitation, utilizing summer precipitation even during extremely dry summers, whereas J. osteosperma was not dependent, using summer precipitation only when amounts were above some minimum threshold. Using sap flux and stable isotopic methods to assess seasonal water sources and water use efficiency, we examined the response of these two species to seasonal variations in moisture at a site located near the northern limits of the North American monsoon. Both sap flux and isotopic results indicated that P. edulis was responsive to summer rain, while J. osteosperma was not. Following summer rain events, sap flux density increased in P. edulis for several days, but not in J. osteosperma. Isotopic evidence indicated that P. edulis took up summer-derived moisture to a greater extent than J. osteosperma. Values of the natural abundance stable isotope ratio of carbon of leaf soluble carbohydrates increased over the summer for P. edulis, indicative of assimilation at higher water use efficiency, but were invariant for J. osteosperma. Our results supported the hypothesis that P. edulis and J. osteosperma are differentially sensitive to summer precipitation and are discussed in the light of potential changes in the seasonality of precipitation associated with climate change.     

Fossil wood of <Emphasis Type="Italic">Betula erkovetskiensis</Emphasis> sp. nov. (Betulaceae) from the Miocene of the Erkovetskii Brown Coal Field,Amur Region,Russia

A new species, Betula erkovetskiensis Blokhina et O.V. Bondarenko (Betulaceae), from the deposits of the Sazanka Formation (upper Middle?Upper Miocene) of the Erkovetskii Brown Coal Field (Amur Region, Russia) is described based on anatomical features of fossil wood. The new species shows some wood anatomical characters of the extant birch subgenus Betula, B. davurica, B. nigra (section Dahuricae), and B. papyrifera (section Betula). Fossil wood of Betula is found in the Amur Region for the first time.     

Fossil wood of <Emphasis Type="Italic">Pinus priamurensis</Emphasis> sp. nov. (Pinaceae) from the Miocene deposits of the Erkovetskii Brown Coal Field,Amur Region

New species of the pine fossil wood, Pinus priamurensis sp. nov. (Pinaceae) from the Sazanka Formation (upper Middle Miocene–Upper Miocene) of the Erkovetskii Brown Coal Field (Amur Region) is described. The new species shares some wood anatomical features with modern species of the subsection Pinus (section Pinus, subgenus Pinus). This is the first record of fossil wood of Pinus in the Amur Region.     

Effect of host species,host nest density and nest size on the occurrence of the shining guest ant <Emphasis Type="Italic">Formicoxenus nitidulus</Emphasis> (Hymenoptera: Formicidae)

Understanding habitat requirements of species is important in conservation. As an obligate ant nest associate, the survival of the globally vulnerable shining guest ant, Formicoxenus nitidulus, is strictly tied to that of its hosts (mound building Formica ants). We investigated how host species, nest density, inter-nest distance and nest mound size relate to the occurrence of F. nitidulus. In total, 166 red wood ant nests were surveyed in SW Finland (120 Formica polyctena, 25 F. rufa, 14 F. aquilonia, 5 F. pratensis, and 2 F. lugubris). Overall, F. nitidulus was found in 60% of the nests. For the actual analysis, only F. polyctena and F. rufa nests were included due to the small number of other nests. F. nitidulus was more likely to be found among F. polyctena than F. rufa. Also, while inter-nest distance was not important, a high nest density, commonly found in polydomous (multi-nest) wood ant colonies, was beneficial for F. nitidulus. The guest ant was also more likely to be found in large host nests than small nests. Thus, our results show that the best habitat for the guest ant is a dense population of host nest mounds with a high proportion of large mounds. Conservation efforts should be directed at keeping the quality of the red wood ant habitats high to preserve their current populations and to increase colonization. This will not only benefit the guest ant, but also a plethora of other species, and help in maintaining the biodiversity of forests.