The factors determining species commonness and rarity are poorly understood, particularly in highly diverse communities. Theory predicts that interactions with neighbors of the same (conspecific) and ...other (heterospecific) species can influence a species' relative abundance, but empirical tests are lacking. By using a hierarchical model of survival for more than 30,000 seedlings of 180 tropical tree species on Barro Colorado Island, Panama, we tested whether species' sensitivity to neighboring individuals relates to their relative abundance in the community. We found wide variation among species in the effect of conspecific, but not heterospecific, neighbors on survival, and we found a significant relationship between the strength of conspecific neighbor effects and species abundance. Specifically, rare species suffered more from the presence of conspecific neighbors than common species did, suggesting that conspecific density dependence shapes species abundances in diverse communities.
Summary
Deep‐water access is arguably the most effective, but under‐studied, mechanism that plants employ to survive during drought. Vulnerability to embolism and hydraulic safety margins can predict ...mortality risk at given levels of dehydration, but deep‐water access may delay plant dehydration. Here, we tested the role of deep‐water access in enabling survival within a diverse tropical forest community in Panama using a novel data‐model approach.
We inversely estimated the effective rooting depth (ERD, as the average depth of water extraction), for 29 canopy species by linking diameter growth dynamics (1990–2015) to vapor pressure deficit, water potentials in the whole‐soil column, and leaf hydraulic vulnerability curves. We validated ERD estimates against existing isotopic data of potential water‐access depths.
Across species, deeper ERD was associated with higher maximum stem hydraulic conductivity, greater vulnerability to xylem embolism, narrower safety margins, and lower mortality rates during extreme droughts over 35 years (1981–2015) among evergreen species. Species exposure to water stress declined with deeper ERD indicating that trees compensate for water stress‐related mortality risk through deep‐water access.
The role of deep‐water access in mitigating mortality of hydraulically‐vulnerable trees has important implications for our predictive understanding of forest dynamics under current and future climates.
Tropical forests are well known for their high woody plant diversity. Processes occurring at early life stages are thought to play a critical role in maintaining this high diversity and shaping the ...composition of tropical tree communities. To evaluate hypothesized mechanisms promoting tropical tree species coexistence and influencing composition, we initiated a census of woody seedlings and small saplings in the permanent 50 ha Forest Dynamics Plot (FDP) on Barro Colorado Island (BCI), Panama. Situated in old‐growth, lowland tropical moist forest, the BCI FDP was originally established in 1980 to monitor trees and shrubs ≥1 cm diameter at 1.3 m above ground (dbh) at ca. 5‐year intervals. However, critical data on the dynamics occurring at earlier life stages were initially lacking. Therefore, in 2001 we established a 1‐m2 seedling plot in the center of every 5 × 5 m section of the BCI FDP. All freestanding woody individuals ≥20 cm tall and <1 cm dbh (hereafter referred to as seedlings) were tagged, mapped, measured, and identified to species in 19,313 1‐m2 seedling plots. Because seedling dynamics are rapid, we censused these seedling plots every 1–2 years. Here, we present data from the 14 censuses of these seedling plots conducted between the initial census in 2001 to the most recent census, in 2018. This data set includes nearly 1 M observations of ~185,000 individuals of >400 tree, shrub, and liana species. These data will permit spatially‐explicit analyses of seedling distributions, recruitment, growth, and survival for hundreds of woody plant species. In addition, the data presented here can be linked to openly‐available, long‐term data on the dynamics of trees and shrubs ≥1 cm dbh in the BCI FDP, as well as existing data sets from the site on climate, canopy structure, phylogenetic relatedness, functional traits, soil nutrients, and topography. This data set can be freely used for non‐commercial purposes; we request that users of these data cite this data paper in all publications resulting from the use of this data set.
In this paper, we present a method to adjust a stochastic logistic differential equation (SLDE) to a set of highly sparse real data. We assume that the SLDE have two unknown parameters to be ...estimated. We calculate the Maximum Likelihood Estimator (MLE) to estimate the intrinsic growth rate. We prove that the MLE is strongly consistent and asymptotically normal. For estimating the diffusion parameter, the quadratic variation of the data is used. We validate our method with several types of simulated data. For more realistic cases in which we observe discretizations of the solution, we use diffusion bridges and the stochastic expectation-maximization algorithm to estimate the parameters. Furthermore, when we observe only one point for each path for a given number of trajectories we were still able to estimate the parameters of the SLDE. As far as we know, this is the first attempt to fit stochastic differential equations (SDEs) to these types of data. Finally, we apply our method to real data coming from fishery. The proposed adjustment method can be applied to other examples of SDEs and is highly applicable in several areas of science, especially in situations of sparse data.
Background： The first three censuses of the 50-ha plot at Barro Colorado Island spanned an unusually harsh dry season during the 1983 El Nitro. By the early 1990s, we had documented increases in tree ...mortality, tree growth, and large population fluctuations of many species during the 1982-1985 census interval. At the time, we asserted that increasing drought frequency would greatly affect the forest. With the benefit of five more censuses at Barro Colorado from 1995-2015, we can now put the 1980 conditions in a longer perspective and test the hypothesis that increasing droughtiness has continued to change the forest. Methods： A 50-ha forest plot on Barro Colorado Island was censused eight times, in 1982 and every five years since 1985. All free-standing woody stems were measured, mapped, and identified in each census. Results： 1） The period 1982-1992 included several extreme dry seasons, not just 1983, but since then there have been few such droughts. 2） Dbh growth declined from a peak in the early 1980s to its lowest in the early 1990s. From 1995-2015 it increased slightly, but not returning to the initial peak. Nearly every species and all dbh categories followed the same pattern. 3） The elevated stand-wide mortality rate of large trees during the 1982-1985 drought has not returned, and most individual species showed the same pattern of elevated mortality in the 1980s followed by low and fairly stable mortality after 1990. 4） Sapling mortality declined after 198,5, but rose again in the late-90s, so the 1980s drought period no longer looks unusual. Mortality of individual species＇ saplings fluctuated erratically, including cases where mortality during the drought was lower than after. 5） Population sizes of individual species fluctuated in all possible directions. Some species declined precipitously during the drought, then recovered, but others did not recover. Other species increased in abundance during the drought. Conclusions＂ Droughts of the 1980s elevated tree growth and mortality at Barro Colorado, but since 1990, demographic rates have remained lower, paralleling a moderate climate with few severe droughts after 1990. Moisture-demanding species suffered during the drought, but many have since recovered. We do not know how often such drought periods recur. Moreover, many species＇ abundances fluctuated over 35 years with no known cause.
Beta-Diversity in Tropical Forest Trees Condit, Richard; Pitman, Nigel; Leigh, Egbert G. ...
Science (American Association for the Advancement of Science),
01/2002, Volume:
295, Issue:
5555
Journal Article
Peer reviewed
The high alpha-diversity of tropical forests has been amply documented, but beta-diversity-how species composition changes with distance-has seldom been studied. We present quantitative estimates of ...beta-diversity for tropical trees by comparing species composition of plots in lowland terra firme forest in Panama, Ecuador, and Peru. We compare observations with predictions derived from a neutral model in which habitat is uniform and only dispersal and speciation influence species turnover. We find that beta-diversity is higher in Panama than in western Amazonia and that patterns in both areas are inconsistent with the neutral model. In Panama, habitat variation appears to increase species turnover relative to Amazonia, where unexpectedly low turnover over great distances suggests that population densities of some species are bounded by as yet unidentified processes. At intermediate scales in both regions, observations can be matched by theory, suggesting that dispersal limitation, with speciation, influences species turnover.
Background
Central America is one of the most diverse floristic provinces in the world, but comprehensive plant lists for the region are incomplete and need frequent updating. Full geographic ranges ...of individual species are seldom known. Our detailed forest inventory plots of Panama thus lack a global geographic perspective. In order to provide one, we assembled a thoroughly vetted checklist of all tree species of Panama, along with an estimate of each one’s range size based on published specimen records.
Results
1) Panama has 3043 tree species in 141 families and 752 genera; 57.6% were ≥ 10 m tall and 16.9% were 3-5 m tall.2) The widest ranges were >1.5×10
7
km
2
, covering the entire neotropics and reaching >30
∘
latitude; 12.4% of the species had ranges exceeding 10
7
km
2
. The median range was 6.9×10
5
km
2
.3) At the other extreme, 16.2% of the species had a range <20,000 km
2
, a criterion suggesting endangered status.4) Range size increased with a tree species’ height and varied significantly among families.5) Tree census plots, where we mapped and measured all individuals, captured 27.5% of the tree species, but a biased selection relative to range size; only 4.5% of the species in plots had ranges <20,000 km
2
.
Conclusions
Our checklist of the trees of Panama, based on rigorous criteria aimed at matching plot censuses, is 20% larger than previous. By recording species’ maximum heights, we allow comparisons with other regions based on matching definitions, and the range sizes provide a quantitative basis for assessing extinction risk. Our next goal is to merge population density from plot censuses to add rigor to predictions of extinction risk of poorly-studied tropical tree species.
Summary
The relative importance of tree mortality risk factors remains unknown, especially in diverse tropical forests where species may vary widely in their responses to particular conditions.
We ...present a new framework for quantifying the importance of mortality risk factors and apply it to compare 19 risks on 31 203 trees (1977 species) in 14 one‐year periods in six tropical forests. We defined a condition as a risk factor for a species if it was associated with at least a doubling of mortality rate in univariate analyses. For each risk, we estimated prevalence (frequency), lethality (difference in mortality between trees with and without the risk) and impact (‘excess mortality’ associated with the risk, relative to stand‐level mortality).
The most impactful risk factors were light limitation and crown/trunk loss; the most prevalent were light limitation and small size; the most lethal were leaf damage and wounds. Modes of death (standing, broken and uprooted) had limited links with previous conditions and mortality risk factors.
We provide the first ranking of importance of tree‐level mortality risk factors in tropical forests. Future research should focus on the links between these risks, their climatic drivers and the physiological processes to enable mechanistic predictions of future tree mortality.
Accurate estimates of forest biomass stocks and fluxes are needed to quantify global carbon budgets and assess the response of forests to climate change. However, most forest inventories consider ...tree mortality as the only aboveground biomass (AGB) loss without accounting for losses via damage to living trees: branchfall, trunk breakage, and wood decay. Here, we use ~151,000 annual records of tree survival and structural completeness to compare AGB loss via damage to living trees to total AGB loss (mortality + damage) in seven tropical forests widely distributed across environmental conditions. We find that 42% (3.62 Mg ha−1 year−1; 95% confidence interval CI 2.36–5.25) of total AGB loss (8.72 Mg ha−1 year−1; CI 5.57–12.86) is due to damage to living trees. Total AGB loss was highly variable among forests, but these differences were mainly caused by site variability in damage‐related AGB losses rather than by mortality‐related AGB losses. We show that conventional forest inventories overestimate stand‐level AGB stocks by 4% (1%–17% range across forests) because assume structurally complete trees, underestimate total AGB loss by 29% (6%–57% range across forests) due to overlooked damage‐related AGB losses, and overestimate AGB loss via mortality by 22% (7%–80% range across forests) because of the assumption that trees are undamaged before dying. Our results indicate that forest carbon fluxes are higher than previously thought. Damage on living trees is an underappreciated component of the forest carbon cycle that is likely to become even more important as the frequency and severity of forest disturbances increase.
Tree mortality is typically considered the only source of biomass loss in forest systems. A pervasive but commonly neglected biomass loss is the damage to living trees (i.e., branchfall, trunk breakage, wood decay). We show that 42% of total aboveground biomass loss is due to damage to living trees across seven tropical forests. Our results contrast with the typically low forest biomass losses estimated only from tree mortality and suggest that forest carbon turnover may be higher than previously thought. Since forest disturbance rates are expected to increase under climate change, biomass loss to damage is likely to become more important
Supplemental protocol for liana censuses Schnitzer, Stefan A.; Rutishauser, Suzanne; Aguilar, Salomón
Forest ecology and management,
03/2008, Volume:
255, Issue:
3
Journal Article
Peer reviewed
Open access
Lianas affect many aspects of tropical forest dynamics and thus the study of their ecology is critical for a comprehensive understanding of tropical forest ecology. Recently, we initiated a complete ...census of all lianas ≥1
cm diameter in the 50
ha forest dynamics plot on Barro Colorado Island, Panama using the census protocol developed by Gerwing et al. Gerwing, J.J., Schnitzer, S.A., Burnham, R.J., Bongers, F., Chave, J., DeWalt, S.J., Ewango, C.E.N., Foster, R., Kenfack, D., Martinez-Ramos, M., Parren, M., Parthasarathy, N., Perez-Salicrup, D.R., Putz, F.E., Thomas, D.W., 2006. A standard protocol for liana censuses. Biotropica 38, 256–261. This protocol marked an important advance in the study of lianas by providing a standard methodology that can be used for liana censuses worldwide, thereby making accurate comparisons among studies possible. During the course of our census, however, we encountered a number of recurring situations that were critical for accurate and repeatable liana censuses, but were not covered in the protocol of Gerwing and colleagues. In this paper, we present a supplemental protocol that covers these additional situations. Our supplement, combined with the protocol developed by Gerwing et al., provides a more complete set of methods with provisions for situations commonly encountered in liana censuses.
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