| Literature DB >> 24844297 |
Lydia E S Cole1, Shonil A Bhagwat2, Katherine J Willis3.
Abstract
The time taken for forested tropical ecosystems to re-establish post-disturbance is of widespread interest. Yet to date there has been no comparative study across tropical biomes to determine rates of forest re-growth, and how they vary through space and time. Here we present results from a meta-analysis of palaeoecological records that use fossil pollen as a proxy for vegetation change over the past 20,000 years. A total of 283 forest disturbance and recovery events, reported in 71 studies, are identified across four tropical regions. Results indicate that forests in Central America and Africa generally recover faster from past disturbances than those in South America and Asia, as do forests exposed to natural large infrequent disturbances compared with post-climatic and human impacts. Results also demonstrate that increasing frequency of disturbance events at a site through time elevates recovery rates, indicating a degree of resilience in forests exposed to recurrent past disturbance.Entities:
Mesh:
Year: 2014 PMID: 24844297 PMCID: PMC4354292 DOI: 10.1038/ncomms4906
Source DB: PubMed Journal: Nat Commun ISSN: 2041-1723 Impact factor: 14.919
Main features and variables extracted from published pollen diagrams for recovery rate calculations.
| Disturbance type | Factor causing impact on forest vegetation, shown on pollen diagram or referred to in the text | See |
| Geographical attributes | Potential influencers of forest ecology/disturbance response | Location, altitude, latitude, longitude |
| Standardized rate of disturbance events (SRD) | Average number of disturbance events in a site per 1,000 years | SRD=( |
| Recovery Rate (RR) | Rate of increase in forest abundance relative to degree of disturbance-induced change, that is, % increase in forest pollen abundance per year in relation to pre-disturbance level | RR=(((Fmax–Fmin)/(Fpre–Fmin))*100)/Trec |
| Forest abundance maximum pre-disturbance (%) | Percentage of forest pollen at maximum point pre-decline (that is, baseline forest pollen percentage) | Fpre |
| Forest abundance minimum at disturbance (%) | Percentage of forest pollen at minimum point during disturbance event | Fmin |
| Forest abundance at maximum recovery (%) | Percentage of forest pollen at point of maximum recovery (before a stabilizing point or further decline) | Fmax |
| Time period of recovery (years) | Time period from maximum reduction to maximum recovery | Trec |
| Forest abundance decline (%) | Percentage decline in forest pollen from Fpre | FD=((Fpre–Fmin)*100)/Fpre |
RR=recovery rate; SRD=standardized rate of disturbance.
Forest recovery is described as the maximum increase in percentage of forest pollen after a decline, before a stabilizing point or further decline. (Forest abundance is used as a crude descriptor of past vegetation extent reconstructed from fossil pollen, but is not representative of a quantifiable forest area.) (n=number of disturbance events).
Disturbance types and indicators (proxies) extracted from published palaeoecological studies.
| Natural | Climate (C)Precipitation (CP)Sea-level rise (CS) | Oxygen isotopes, fire (low levels, not linked to human presence), magnetic susceptibility, lithologyRainfall, monsoon strength variation, climate drying (CD)Sea level |
| Large infrequent (LI) | Hurricane (LI-H), landslide (LI-L), fire (LI-F), volcano (volcanic ash) (LI-V) | |
| Human (FC) | Burning (B) | Microfossil & macrofossil charcoal |
| Forest clearing (FC) | Temporary, predominantly resulting from shifting cultivation (SC), or more permanent, generally selective clearing, or not described (FC) signified by for example, fruit trees, | |
| Agriculture (Ag) | Agricultural indicators, for example, fruit trees— | |
| Unclear | (U) | Disturbance indicators present but specific type not clarified |
Disturbance types and proxies (used to identify the former) were extracted either from published pollen diagrams or from the associated text. Abbreviations for the different disturbance types are given in parentheses. Smaller natural perturbations such as tree falls, though not explicitly defined due to the difficulty of identification through fossil pollen analysis, may also contribute to large infrequent (LI) disturbance events. (See Supplementary Data 1 for the full record of disturbance types referred to here.)
Figure 1Number of disturbance events versus years to 95.5% forest recovery.
The relationship between recorded disturbance events and numbers of years for 95.5% recovery to pre-disturbance forest abundance baseline at each event (n=283) is shown. Recovery rates were used to calculate the time taken to a projected 95.5% recovery, that is, the median extent of recovery for the data set.
Results of multiple regression analysis using Model I.
| Intercept | −1.597 | 0.252 | 0.000 |
| Latitude | −0.020 | 0.012 | 0.111 |
| Location—Africa | 0.856 | 0.315 | 0.009 |
| Location—Central America | 0.794 | 0.351 | 0.027 |
| Location—South America | 0.252 | 0.223 | 0.264 |
| Disturbance category—FC | 0.296 | 0.187 | 0.115 |
| Disturbance category—LI | 0.764 | 0.423 | 0.072 |
| Disturbance category—U | 0.936 | 0.346 | 0.007 |
| Log(SRD) | 0.914 | 0.082 | 0.000 |
Output for Model I: log(RR)~Latitude+Location+Disturbance Category+log(SRD), n=283. Location—Asia and Disturbance Category—Climate were set as the reference groups for the initial model output.
*Subgroups within categorical variables that are significantly different from the reference set.
†SRD is a highly statistically significant independent predictor of RR.
Figure 2Composite figure showing recovery rates (RRs) of different covariates.
Panels display the relationship between RR and (a) disturbance categories, (b) geographical locations and (c) against the standardized rate of disturbance (SRD). (a) Box plot of RR for grouped disturbance categories. C, climate-related factors (n=87); FC, anthropogenic forest clearance, grouping FC, SC, B, Ag and combinations of these (n=166); LI, natural large infrequent events (n=13); U, cause of disturbance unclear (n=17). (b) Box plot of RR for different location groups. S, South America (n=85); C, Central America (n=111); Af, Africa (n=29); A, Asia (n=85). (c) Scatter plot illustrating the relationship between the RR and SRD. Throughout, RR and SRD are plotted on logarithmic axes to accommodate the variability in these data sets. The vertical line in a and b represents the median RR for the entire data set, that is, 0.455% relative recovery per year. Shaded areas on a and b represent the interquartile range and the whisker lines the 95% confidence intervals for each category.
Figure 3Map highlighting the World’s tropical forest ecosystems and the location of all studies included in this meta-analysis.
For each of the four regions, the number of disturbance events (n) and median time to 95.5% recovery of pre-disturbance baseline (median RR) are shown. (The WWF Biome of tropical and subtropical moist broadleaf forests is shown in green40.)
Figure 4Composite figure showing the standardized rate of disturbance (SRD) of different disturbance categories and locations.
Box plots displaying the relationship between the SRD and (a) different grouped disturbance categories and (b) geographical location groups. (See Fig. 2 legend for details on notation and sample sizes). The SRD is plotted on a logarithmic scale to accommodate the variability in the data set. The vertical line in a and b represents the median SRD for the entire data set, that is, 1.072 disturbance events per 1,000 years. Shaded areas on a and b represent the interquartile range and the whisker lines the 95% confidence intervals for each category.
Results of multiple regression analysis using Model II.
| Intercept | 0.213 | 0.200 | 0.291 |
| Location—Asia | −0.308 | 0.307 | 0.320 |
| Location—Central America | 0.296 | 0.283 | 0.298 |
| Location—Africa | 0.229 | 0.414 | 0.519 |
| Disturbance category—LI | 0.021 | 0.084 | 0.804 |
| Disturbance category—C | −0.103 | 0.032 | 0.002 |
| Disturbance category—U | −0.075 | 0.046 | 0.106 |
Output for Model II: log(SRD)~Location+Disturbance Category, n=283. Location—Africa and Disturbance Category—Forest Clearance were set as the reference groups for the initial model output.
*The SRD caused by climatic impacts (C) is significantly different from that caused by forest clearance (FC).