Impacts of invasive browsers on demographic rates and forest structure in New Zealand

Background/Question/Methods

Assessing the large scale impact of deer populations on forest structure and composition is important because of their increasing abundance in many temperate forests. Deer are invasive animals and sometimes thought to be responsible for immense damage to New Zealand’s forests. We report demographic changes taking place among 40 widespread indigenous tree species over 20 years, following a period of record deer numbers in the 1950s and a period of extensive hunting and depletion of deer populations during the 1960s and 1970s.

Results/Conclusions

Across a network of 578 plots there was an overall 13% reduction in sapling density of our study species with most remaining constant and a few declining dramatically. The effect of suppressed recruitment when deer populations were high was evident in the small tree size class (30 – 80 mm dbh). Stem density decreased by 15% and species with the greatest annual decreases in small tree density were those which have the highest rates of sapling recovery in exclosures indicating that deer were responsible. Densities of large canopy trees have remained relatively stable. There were imbalances between mortality and recruitment rates for 23 of the 40 species, 7 increasing and 16 in decline. These changes were again linked with sapling recovery in exclosures; species which recovered most rapidly following deer exclusion had the greatest net recruitment deficit across the wider landscape, indicating recruitment suppression by deer as opposed to mortality induced by disturbance and other herbivores. Species are not declining uniformly across all populations and no species are in decline across their entire range. Therefore we predict that with continued deer presence some forests will undergo compositional changes but that none of the species tested will become nationally extinct.

Impacts of invasive browsers on demographic rates and forest structure in New Zealand. Available from: http://www.researchgate.net/publication/267285500_Impacts_of_invasive_browsers_on_demographic_rates_and_forest_structure_in_New_Zealand [accessed Oct 9, 2015].

Chloroplast microsatellites: new tools for studies in plant ecology and systematics

The nonrecombinant, uniparentally inherited nature of organelle genomes
makes them useful tools for evolutionary studies. However, in plants, detecting
useful polymorphism at the population level is often difficult because of the
low level of substitutions in the chloroplast genome, and because of the slow
substitution rates and intramolecular recombination of mtDNA. Chloroplast
microsatellites represent potentially useful markers to circumvent this problem
and, to date, studies have demonstrated high levels of intraspecific variability.
Here,we discuss the use of these markers in ecological and evolutionary
studies of plants, as well as highlighting some of the potential problems
associated with such use.

Calibration of the Radiocarbon Time Scale for the Southern Hemisphere: AD 1850-950

We have conducted a series of radiocarbon measurements on decadal samples of dendrochronologically dated wood from both hemispheres, spanning 1000 years (McCormac et al. 1998; Hogg et al. this issue). Using the data presented in Hogg et al., we show that during the period AD 950-1850 the 14C offset between the hemispheres is not constant, but varies periodically (~130 yr periodicity) with amplitudes varying between 1 and 10‰ (i.e. 8-80 yr), with a consequent effect on the 14C calibration of material from the Southern Hemisphere. A large increase in the offset occurs between AD 1245 and 1355. In this paper, we present a Southern Hemisphere high-precision calibration data set (SHCal02) that comprises measurements from New Zealand, Chile, and South Africa. This data, and a new value of 41 ± 14 yr for correction of the IntCal98 data for the period outside the range given here, is proposed for use in calibrating Southern Hemisphere 14C dates.

Analysis of Extended Partial Least Squares for Monitoring Large-Scale Processes

This paper theoretically analysis the recently proposed "Extended Partial Least Squares" (EPLS) algorithm. After pointing out some conceptual deficiencies, a revised algorithm is introduced that covers the middle ground between Partial Least Squares and Principal Component Analysis. It maximises a covariance criterion between a cause and an effect variable set (partial least squares) and allows a complete reconstruction of the recorded data (principal component analysis). The new and conceptually simpler EPLS algorithm has successfully been applied in detecting and diagnosing various fault conditions, where the original EPLS algorithm did only offer fault detection.