Good day,
I need to design a sampling method to quantify the regeneration of the selected species at different altitudes/canopy closures in a national park. The park is about 9000 ha and ranges in altitude from sea level to about 600 m (tropical rain-forest conditions).
I am dealing with 6 tree species, 3 of which are relatively rear and found only at the peaks. I was thinking about going along with transects and using these to determine DBH (diameter at breast height) size class distribution of the species, but I was informed this may not be the best approach. Any Suggestions?
The problem with transects is that you may not encounter the tree species at your different altitudes even though they might be there! A better strategy is to create plots at different altitudes, which have a greater probability of containing your species. You can then determine DBH and sizes classes. You can also use tree-ring-derived age distributions and/or remote-sensing, but you should also do seedling counts to determine if regeneration is taking place. Three plots every 100 m across 3 different widely spaced areas should do it. But you can actually place the plots along transects or even do strip transects. Don't use random plots imo – what if no trees occur in your 'randomly' placed plot, even though there are trees right next to it? If there is no tree in a plot, you can't measure it lol. The design is up to you – there is no right or wrong way in ecological experiments. But the interpretation is critical :)
Have you considered the Nearest Neighbour Method of assessing trees. This method was developed as an assessment protocol for assessing wildlife damage to trees, but may be used to visit and assess any aspect of trees that can be observed and/or measured. One advantage of this method is that the accuracy of the assessment can be set before field work commences and it is repeatable.
Ref: Pepper H W (1998) Nearest Neighbour Method for quantifying wildlife damage to woodands. Forestry Commission, Edinburgh, UK
On examples of plots/transects for tree/forest sampling see the attached
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DBH method is good enough but few other methods are also need to be used to determine the Regeneration process and as well as to compare between other studied plant species such as counting the total individuals of germinating plant species and age class, litter depth in each sampling zone and various other environmental gradients related to the regeneration process. I hope this will give tremendous opportunity to interpret the data during discussion.
First, decide on the gradient along which the regeneration is to be measured, Second, decide on plot size and whether placement will be random or not. 1-ha plot size within which complete enumeration of all erect woody species is done is sufficient. Number of the plots will depend on sampling intensity, desired level of accuracy and cost and time implications. Then have a technical definitions of seedling, sapling, medium-sized trees and large trees. Collect the data and segregate it according to size classes and habitat gradient (altitude?), You can the compare composition similarity by Spearman's rank correlation coefficient or any other appropriate statistic. You will document all species in each plot, and determine the proportional composition of the species of interest therein. Good luck.
Thanks everyone, I have a good idea where to start.
Joshua A. Spiers.
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