We describe a wireless sensor network designed for the long-term study of rare and endangered species of plants. We wish to monitor plants and their environment via high-resolution cameras and temperature, humidity, rainfall, wind, and solar radiation sensors. Our units must be “invisible” (camouflaged), very low energy, and must allow distributed local computation. Data rates are 1 to 100 bytes/second per node, but networks can be large — an early prototype had 60 nodes. Failures are expensive and we must exploit redundancy whenever possible. Nodes are stationary but for energy reasons may decline to participate in transmissions. We have designed two wireless routing protocols that satisfy these constraints. Multipath On-demand Routing (MOR) computes multiple optimal routes to avoid depleting the energy at any given node. Geometric Routing scales to large networks, relying on Geographic Routing when possible and on selected global information otherwise. We have simulated and are implementing both protocols.
Large numbers of Metrosideros polymorpha trees have died in the montane rain forest on the Island of Hawai'i, but previous research has failed to identify a principal cause. This paper describes an experiment that tests the hypothesis that nutrient deficiency is the principal cause of tree death and stand—level dieback. Treatments were fertilizing, stand thinning, and a combination of the two. No significant change in the mortality rate was caused by the treatments; however, stem diameter growth of surviving trees was found to be nutrient limited at all sites. We conclude that nutrient deficiency is not the principal cause of most Metrosideros dieback, but it may be a contributing factor.
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